diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8f7320a..3769d89 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -55,7 +55,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   survives only as the fallback on anchor-less charts). At most **two wires are ever lit at
   once**: when overlapping decay tails (fast passages) would light a run of wires, the
   flash collapses to the outermost pair of the lit span — one bracket, never a picket
-  fence. With no scorer attached, nothing changes.
+  fence. The gem's rim joins in: on a confirmed hit the outline flashes in the
+  string's own colour with the same intensity treatment as the wires, fading with the
+  scorer's alpha. With no scorer attached, nothing changes.
 
 ### Changed
 - **`GET /api/song/{f}?stems=1`** (new, opt-in) — returns the pack's playable stem
diff --git a/plugins/highway_3d/screen.js b/plugins/highway_3d/screen.js
index ecba3fb..390785e 100644
--- a/plugins/highway_3d/screen.js
+++ b/plugins/highway_3d/screen.js
@@ -1,16075 +1,16109 @@
-// 3D Highway visualization plugin — Three.js note highway.
-// Visual layer from joel's prototype (vibrant palette, glowing strings,
-// fret heat, dynamic lane, chord frame-boxes, per-note connector labels,
-// board projection, outline+core note meshes) adapted into the
-// feedBackViz setRenderer contract (feedBack#36) so it works in the
-// main player and per-panel in splitscreen without any architectural
-// changes.
-
-(function () {
-    'use strict';
-
-    /* ======================================================================
-     *  Constants
-     * ====================================================================== */
-
-    // Three.js is vendored under static/vendor/three/ in core (pinned r170 —
-    // see static/vendor/three/VERSION). The bundled plugin loads from the
-    // same origin to avoid the first-launch CDN round-trip and to pin the
-    // version against breakages from upstream Three.js drift.
-    const THREE_URL = '/static/vendor/three/three.module.min.js';
-    const THREE_CDN = 'https://cdn.jsdelivr.net/npm/three@0.170.0/build/three.module.min.js';
-
-    /* ── Butterchurn audio-reactive background ──────────────────────────
-     * Mounts a Butterchurn (WebGL MilkDrop) canvas BEHIND the transparent
-     * 3D highway. On desktop it's driven by the guitar/mic input (the song
-     * audio lives in JUCE, not the webview <audio>); in a browser it taps
-     * the song <audio> directly.
-     * ──────────────────────────────────────────────────────────────────── */
-    const BC_VENDOR = '/api/plugins/highway_3d/assets/vendor/';
-    const BC_FRAME = 1024;
-    const BC_WORKLET = '/api/plugins/highway_3d/assets/viz-worklet.js';
-    const _bcMeters = { gtr: 0, song: 0 }; // live levels shown in the panel readout
-    const BC_BTN = 'background:rgba(255,255,255,.09);color:#cfe3ff;border:1px solid rgba(255,255,255,.16);border-radius:5px;padding:3px 8px;cursor:pointer;font:12px system-ui';
-    let _bcLoading = null;
-    function _bcLoadLib() {
-        if (_bcLoading) return _bcLoading;
-        _bcLoading = new Promise((resolve, reject) => {
-            const add = (url, next) => {
-                const s = document.createElement('script');
-                s.src = url; s.async = true;
-                s.onload = next; s.onerror = () => reject(new Error('load ' + url));
-                document.head.appendChild(s);
-            };
-            add(BC_VENDOR + 'butterchurn.min.js', () =>
-                add(BC_VENDOR + 'butterchurnPresets.min.js', resolve));
-        });
-        // Don't cache a rejected promise: a transient load failure (network
-        // hiccup, blocked request) must not permanently disable the feature for
-        // the session. Clearing _bcLoading lets the next mount retry the load.
-        _bcLoading.catch(() => { _bcLoading = null; });
-        return _bcLoading;
-    }
-    function _bcResolve() { let b = window.butterchurn; if (b && b.default) b = b.default; return b; }
-    function _bcPresets() { let p = window.butterchurnPresets; if (p && p.default) p = p.default; return p; }
-    function _bcIsDesktop() {
-        const d = window.feedBackDesktop || window.slopsmithDesktop;
-        return !!(d && d.isDesktop && d.audio && typeof d.audio.getRawAudioFrame === 'function');
-    }
-    // Fast-forward an index to the first entry after time `ct` (used on seek/loop).
-    // Position at the first entry whose time is >= ct (strict <), so an event
-    // landing exactly on the seek/loop target time is still fired by the update
-    // walkers (which consume `<= ct`) instead of being skipped past here.
-    function _bcFfIdx(arr, ct, key) { if (!arr) return 0; let i = 0; while (i < arr.length && (arr[i][key] || 0) < ct) i++; return i; }
-    // Force-free a canvas's WebGL context so the GPU resources are released
-    // immediately instead of lingering until GC — repeated Butterchurn
-    // mount/unmount cycles otherwise pile up live contexts toward the browser cap.
-    function _bcReleaseCanvasGL(canvas) {
-        if (!canvas || typeof canvas.getContext !== 'function') return;
-        let gl = null;
-        try { gl = canvas.getContext('webgl2') || canvas.getContext('webgl'); } catch (e) { gl = null; }
-        if (!gl || typeof gl.getExtension !== 'function') return;
-        try { const lose = gl.getExtension('WEBGL_lose_context'); if (lose) lose.loseContext(); } catch (e) {}
-    }
-
-    // Desktop: bridge GUITAR input PCM + SONG output level into a Web Audio node
-    // Butterchurn can tap. Guitar gives spectral texture from your playing; the
-    // song's output meter (getLevels) injects an energy pulse so the visuals also
-    // react to the backing track (JUCE plays it — there's no song PCM to FFT).
-    function _bcGuitarFeed(actx, onReady) {
-        const latest = new Float32Array(BC_FRAME);
-        let polling = true, songLevel = 0, chartLevel = 0;
-        let node = null, sp = null, silent = null;
-        const api = (window.feedBackDesktop || window.slopsmithDesktop).audio;
-        const gainNow = () => (_bcLoadSettings().guitarGain) || 6;
-
-        // Keep the source node processing (silently — JUCE already monitors the
-        // guitar), and hand it to Butterchurn via the onReady callback.
-        function attach(srcNode) {
-            silent = actx.createGain(); silent.gain.value = 0;
-            srcNode.connect(silent); silent.connect(actx.destination);
-            try { if (onReady) onReady(srcNode); } catch (e) {}
-        }
-        // Fallback for contexts without AudioWorklet support.
-        function useScriptProcessor() {
-            let phase = 0, phase2 = 0;
-            const TWO_PI = Math.PI * 2;
-            const oscStep = TWO_PI * (90 / actx.sampleRate);
-            const oscStep2 = TWO_PI * (520 / actx.sampleRate);
-            sp = actx.createScriptProcessor(BC_FRAME, 1, 1);
-            sp.onaudioprocess = (e) => {
-                const out = e.outputBuffer.getChannelData(0);
-                const n = Math.min(out.length, latest.length);
-                const lvl = songLevel, clvl = chartLevel, gg = gainNow();
-                for (let i = 0; i < out.length; i++) {
-                    const g = (i < n ? latest[i] : 0) * gg;
-                    const song = lvl * (0.7 * Math.sin(phase) + 0.3 * (Math.random() * 2 - 1)) * 1.4;
-                    const chart = clvl * (0.5 * Math.sin(phase2) + 0.5 * (Math.random() * 2 - 1)) * 1.5;
-                    phase += oscStep; if (phase > TWO_PI) phase -= TWO_PI;
-                    phase2 += oscStep2; if (phase2 > TWO_PI) phase2 -= TWO_PI;
-                    const v = g + song + chart;
-                    out[i] = v > 1 ? 1 : (v < -1 ? -1 : v);
-                }
-            };
-            attach(sp);
-            console.log('[viz3d] audio feed: ScriptProcessor (fallback)');
-        }
-
-        // Preferred path: AudioWorklet (runs off the main thread).
-        if (actx.audioWorklet && typeof actx.audioWorklet.addModule === 'function' && typeof AudioWorkletNode === 'function') {
-            actx.audioWorklet.addModule(BC_WORKLET).then(() => {
-                if (!polling || sp) return;
-                node = new AudioWorkletNode(actx, 'viz-feed', { numberOfInputs: 0, numberOfOutputs: 1, outputChannelCount: [1] });
-                attach(node);
-                console.log('[viz3d] audio feed: AudioWorklet');
-            }).catch((e) => {
-                console.warn('[viz3d] AudioWorklet unavailable, using ScriptProcessor:', e && e.message);
-                if (polling && !sp && !node) useScriptProcessor();
-            });
-        } else {
-            useScriptProcessor();
-        }
-
-        // Guitar PCM poll → waveform + level meter (+ pushed to the worklet).
-        (function pcmLoop() {
-            if (!polling) return;
-            Promise.resolve(api.getRawAudioFrame(BC_FRAME)).then((f) => {
-                if (f && f.length) {
-                    if (f.length >= BC_FRAME) latest.set(f.subarray(0, BC_FRAME));
-                    else { latest.fill(0); latest.set(f); }
-                    let s = 0; for (let i = 0; i < BC_FRAME; i++) s += latest[i] * latest[i];
-                    _bcMeters.gtr = Math.sqrt(s / BC_FRAME) * gainNow();
-                    if (node) node.port.postMessage({ frame: latest.slice(0), song: songLevel, chart: chartLevel, gain: gainNow() });
-                }
-            }).catch(() => {}).then(() => { if (polling) setTimeout(pcmLoop, 16); });
-        })();
-        // Song output meter poll → music energy pulse.
-        (function levelLoop() {
-            if (!polling) return;
-            Promise.resolve(api.getLevels && api.getLevels()).then((L) => {
-                if (L && typeof L.outputLevel === 'number') {
-                    songLevel = Math.min(1, L.outputLevel * ((_bcLoadSettings().songGain) || 1.8));
-                    _bcMeters.song = songLevel;
-                    if (node) node.port.postMessage({ song: songLevel, chart: chartLevel, gain: gainNow() });
-                }
-            }).catch(() => {}).then(() => { if (polling) setTimeout(levelLoop, 40); });
-        })();
-
-        return {
-            setChart(v) { chartLevel = v; },
-            stop() {
-                polling = false;
-                try { if (sp) { sp.disconnect(); sp.onaudioprocess = null; } } catch (e) {}
-                try { if (node) node.disconnect(); } catch (e) {}
-                try { if (silent) silent.disconnect(); } catch (e) {}
-            }
-        };
-    }
-    // Browser audio is sourced by REUSING the highway's own shared analyser
-    // (the same #audio / stems side-chain tap the fog scenery uses), passed in
-    // as `audioProvider` to _bcCreateController. We deliberately do NOT open a
-    // second createMediaElementSource on #audio here: it can only be called
-    // once per element (a second tap throws InvalidStateError and permanently
-    // disables the other consumer), it would route the song through a fresh,
-    // possibly-suspended context and mute playback, and it would miss the stems
-    // side-chain that sloppaks expose at window.feedBack.stems.getAnalyser().
-    /* ── Controls + readability (localStorage-backed, global config) ───── */
-    const BC_LS = 'viz3d_settings';
-    const BC_DEFAULTS = { enabled: true, opacity: 1.0, laneDim: true, laneDimStrength: 0.45, chartAccents: true, colorTint: true, chartStrength: 1.0, tintStrength: 0.65, guitarGain: 6, songGain: 1.8, cyclePool: 'all', hold: false };
-    let _bcSettings = null;
-    function _bcLoadSettings() {
-        if (_bcSettings) return _bcSettings;
-        let saved = {};
-        try { saved = JSON.parse(localStorage.getItem(BC_LS) || '{}'); } catch (e) {}
-        _bcSettings = Object.assign({}, BC_DEFAULTS, saved);
-        return _bcSettings;
-    }
-    function _bcSaveSettings() { try { localStorage.setItem(BC_LS, JSON.stringify(_bcSettings)); } catch (e) {} }
-    const _bcControllers = new Set();
-    function _bcApplyAll() { _bcControllers.forEach((c) => { try { c.applySettings(); } catch (e) {} }); }
-    // Live-apply hook for the plugin's settings.html. The visualizer's on/off +
-    // slider controls now live in the standard settings panel (settings.html),
-    // which persists them into the BC_LS blob and then calls this so a mounted
-    // highway re-reads and applies them immediately. Defined on window at module
-    // scope so it's available regardless of whether a highway is mounted yet;
-    // settings.html guards the call with `?.` for the not-yet-loaded case.
-    window.h3dBcApplySettings = function () {
-        _bcSettings = null;        // drop the cache so the next read reloads from localStorage
-        _bcLoadSettings();
-        _bcApplyAll();
-        try { _bcUpdatePanelPreset(); } catch (e) {}
-    };
-
-    // Preset curation: favorites / bans (persisted globally) + the "primary"
-    // controller the panel's preset buttons drive.
-    // Seeded once on first run (reputation-based starter set; user can edit freely).
-    const BC_DEFAULT_FAVORITES = [
-        'Flexi, martin + geiss - dedicated to the sherwin maxawow',
-        'Geiss - Reaction Diffusion 2',
-        'Geiss - Spiral Artifact',
-        'Flexi + Martin - cascading decay swing',
-        'Flexi - mindblob [shiny mix]',
-        'Geiss - Cauldron - painterly 2 (saturation remix)',
-        'Zylot - Paint Spill (Music Reactive Paint Mix)',
-        'Flexi - predator-prey-spirals',
-        'Rovastar + Loadus + Geiss - FractalDrop (Triple Mix)',
-        'Flexi, fishbrain, Geiss + Martin - tokamak witchery',
-    ];
-    const BC_DEFAULT_BANS = [
-        'martin - mucus cervix',
-        'Goody - The Wild Vort',
-        'martin - extreme heat',
-        'Unchained - Rewop',
-        'high-altitude basket unraveling - singh grooves nitrogen argon nz+',
-        '$$$ Royal - Mashup (197)',
-        '$$$ Royal - Mashup (431)',
-        'suksma - uninitialized variabowl (hydroponic chronic)',
-        'shifter - dark tides bdrv mix 2',
-        '_Mig_049',
-    ];
-    const _bcFavorites = new Set();
-    const _bcBanned = new Set();
-    let _bcListsLoaded = false;
-    function _bcLoadLists() {
-        if (_bcListsLoaded) return; _bcListsLoaded = true;
-        try { (JSON.parse(localStorage.getItem('viz3d_favorites') || '[]') || []).forEach((n) => _bcFavorites.add(n)); } catch (e) {}
-        try { (JSON.parse(localStorage.getItem('viz3d_banned') || '[]') || []).forEach((n) => _bcBanned.add(n)); } catch (e) {}
-        let seeded = false;
-        try { seeded = !!localStorage.getItem('viz3d_seeded'); } catch (e) {}
-        if (!seeded) {
-            BC_DEFAULT_FAVORITES.forEach((n) => _bcFavorites.add(n));
-            BC_DEFAULT_BANS.forEach((n) => _bcBanned.add(n));
-            try { localStorage.setItem('viz3d_seeded', '1'); } catch (e) {}
-            _bcSaveLists();
-        }
-    }
-    function _bcSaveLists() {
-        try { localStorage.setItem('viz3d_favorites', JSON.stringify([..._bcFavorites])); } catch (e) {}
-        try { localStorage.setItem('viz3d_banned', JSON.stringify([..._bcBanned])); } catch (e) {}
-    }
-    // Re-add the bundled defaults anytime (merges; a default-fav un-bans, a default-ban un-favs).
-    function _bcRestoreDefaults() {
-        BC_DEFAULT_FAVORITES.forEach((n) => { _bcBanned.delete(n); _bcFavorites.add(n); });
-        BC_DEFAULT_BANS.forEach((n) => { _bcFavorites.delete(n); _bcBanned.add(n); });
-        try { localStorage.setItem('viz3d_seeded', '1'); } catch (e) {}
-        _bcSaveLists(); _bcUpdatePanelPreset(); _bcRenderList();
-    }
-    let _bcPrimary = null;
-    let _bcPane = null, _bcListEl = null, _bcFilterEl = null, _bcPaneOpen = false, _bcCollapsed = false;
-
-    function _bcStatusMark(name) {
-        return _bcFavorites.has(name) ? '★ ' : (_bcBanned.has(name) ? '🚫 ' : '');
-    }
-    function _bcSetHold(v) {
-        const s = _bcLoadSettings();
-        s.hold = !!v; _bcSaveSettings();
-        const b = _bcPanel && _bcPanel.querySelector('#vz-hold');
-        if (b) b.textContent = s.hold ? '▶ Resume' : '⏸ Hold';
-    }
-    // Drives both panels off the right edge. Order when both open (L→R):
-    //   visualizer panel → preset pane → window edge. Pane lives off-screen by
-    //   default; opening it shoves the panel LEFT to make room.
-    function _bcLayout() {
-        if (_bcPanel) {
-            let tx = 0;
-            if (_bcCollapsed) tx = 210;        // tuck the whole panel off the right edge
-            else if (_bcPaneOpen) tx = -248;   // slide panel LEFT to make room for the pane
-            _bcPanel.style.transform = 'translateX(' + tx + 'px) translateY(-50%)';
-        }
-        if (_bcPane) {
-            _bcPane.style.transform = (_bcPaneOpen && !_bcCollapsed) ? 'translateX(0) translateY(-50%)' : 'translateX(calc(100% + 16px)) translateY(-50%)';
-        }
-    }
-    function _bcSetPane(open) {
-        _bcPaneOpen = !!open && !_bcCollapsed;
-        const b = _bcPanel && _bcPanel.querySelector('#vz-listbtn');
-        if (b) b.textContent = _bcPaneOpen ? '>>' : '<<';
-        if (_bcPaneOpen) _bcRenderList();
-        _bcLayout();
-    }
-    function _bcRenderList() {
-        if (!_bcListEl) return;
-        const ctrl = _bcPrimary;
-        const keys = (ctrl && ctrl.keys) ? ctrl.keys : [];
-        const filt = ((_bcFilterEl && _bcFilterEl.value) || '').toLowerCase();
-        const cur = ctrl && ctrl.curName;
-        const frag = document.createDocumentFragment();
-        for (let i = 0; i < keys.length; i++) {
-            const name = keys[i];
-            if (filt && name.toLowerCase().indexOf(filt) === -1) continue;
-            const row = document.createElement('div');
-            row.textContent = _bcStatusMark(name) + name;
-            row.title = name;
-            row.style.cssText = 'padding:3px 7px;border-radius:4px;cursor:pointer;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;font-size:11px;' +
-                (name === cur ? 'background:rgba(110,160,255,.28);' : '') + (_bcBanned.has(name) ? 'opacity:.55;' : '');
-            row.addEventListener('click', () => {
-                if (!_bcPrimary) return;
-                _bcPrimary.loadByName(name, 1.0);
-                _bcSetHold(true); // picked from the list → sit on it
-            });
-            frag.appendChild(row);
-        }
-        _bcListEl.innerHTML = '';
-        _bcListEl.appendChild(frag);
-    }
-    function _bcUpdatePanelPreset() {
-        if (!_bcPanel) return;
-        const name = _bcPrimary ? (_bcPrimary.curName || null) : null;
-        const nameEl = _bcPanel.querySelector('#vz-pname');
-        const favBtn = _bcPanel.querySelector('#vz-fav');
-        const banBtn = _bcPanel.querySelector('#vz-ban');
-        const cntEl = _bcPanel.querySelector('#vz-pcount');
-        if (nameEl) { nameEl.textContent = (name ? _bcStatusMark(name) : '') + (name || '—'); nameEl.title = name ? (name + ' — click for full list') : ''; }
-        if (favBtn) favBtn.textContent = (name && _bcFavorites.has(name)) ? '★ Favorited' : '☆ Favorite';
-        if (banBtn) banBtn.textContent = (name && _bcBanned.has(name)) ? '🚫 Banned' : '🚫 Ban';
-        if (cntEl) cntEl.textContent = '★ ' + _bcFavorites.size + '   🚫 ' + _bcBanned.size;
-        if (_bcPaneOpen) _bcRenderList();
-    }
-
-    let _bcPanel = null, _bcPanelKeyBound = false;
-    function _bcEnsurePanel(host) {
-        if (_bcPanel && _bcPanel.isConnected) {
-            // Singleton panel: follow the active highway. If it's still parented
-            // to a different wrap (e.g. another mounted highway instance such as
-            // Virtuoso's embedded one), move it — and the pane — to this wrap so
-            // it appears on whichever highway is currently on-screen.
-            if (host && _bcPanel.parentNode !== host) {
-                host.appendChild(_bcPanel);
-                if (_bcPane) host.appendChild(_bcPane);
-            }
-            return _bcPanel;
-        }
-        const s = _bcLoadSettings();
-        const p = document.createElement('div');
-        p.id = 'viz3d-panel';
-        p.style.cssText = 'position:absolute;top:50%;right:10px;z-index:100000;pointer-events:auto;font:12px/1.45 system-ui,sans-serif;' +
-            'color:#cfe3ff;background:rgba(8,10,20,0.82);padding:9px 11px;border-radius:8px;width:186px;' +
-            'box-shadow:0 2px 12px rgba(0,0,0,0.5);user-select:none;transition:transform 0.28s ease;';
-        p.innerHTML =
-            '<div style="display:flex;align-items:center;justify-content:space-between;margin-bottom:7px"><span style="font-weight:600">🌀 Visualizer</span><button id="vz-listbtn" title="Show / hide full preset list" style="' + BC_BTN + ';padding:1px 7px">&lt;&lt;</button></div>' +
-            // On/off + opacity/dim/chart/tint/gain controls now live in the
-            // plugin's Settings panel (settings.html). This in-canvas panel is
-            // only the LIVE preset browser (pick / favorite / ban / cycle).
-            '<div style="opacity:.55;font-size:11px;margin:2px 0 6px">Background &amp; reactivity options are in Settings ▸ 3D Highway.</div>' +
-            '<div style="display:flex;align-items:center;gap:6px;margin:4px 0">' +
-              '<button id="vz-prev" style="' + BC_BTN + '">◀</button>' +
-              '<div id="vz-pname" style="flex:1;text-align:center;font-size:11px;opacity:.9;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;cursor:pointer" title="">—</div>' +
-              '<button id="vz-next" style="' + BC_BTN + '">▶</button>' +
-            '</div>' +
-            '<div style="display:flex;gap:6px;margin:4px 0">' +
-              '<button id="vz-fav" style="' + BC_BTN + ';flex:1">♡ Favorite</button>' +
-              '<button id="vz-ban" style="' + BC_BTN + ';flex:1">🚫 Ban</button>' +
-            '</div>' +
-            '<div style="display:flex;gap:6px;align-items:flex-end;margin:6px 0">' +
-              '<label style="flex:1">Cycle <select id="vz-cyc" style="width:100%;background:#11141f;color:#cfe3ff;border:1px solid rgba(255,255,255,.15);border-radius:5px;padding:3px"><option value="all">All</option><option value="favorites">Favorites</option><option value="bans">Bans</option></select></label>' +
-              '<button id="vz-hold" style="' + BC_BTN + '">⏸ Hold</button>' +
-            '</div>' +
-            '<div style="margin:5px 0 4px;font-size:11px;opacity:.75"><span id="vz-pcount">★ 0   🚫 0</span></div>' +
-            '<div id="vz-meter" style="opacity:.65;margin-top:6px;font:11px/1.3 monospace">gtr —  ·  song —</div>' +
-            '<div style="opacity:.45;margin-top:4px;font-size:11px">` or ‹‹ to hide</div>';
-        (host || document.body).appendChild(p);
-
-        // Slide handle (<< / >>) so the panel can tuck off the right edge and stop
-        // covering the Now / Up-Next labels.
-        const tab = document.createElement('button');
-        tab.textContent = '>>';
-        tab.title = 'Hide / show controls';
-        tab.style.cssText = 'position:absolute;top:6px;left:-23px;width:23px;height:28px;border:none;cursor:pointer;' +
-            'background:rgba(8,10,20,0.82);color:#cfe3ff;border-radius:7px 0 0 7px;font:12px/1 monospace;padding:0;';
-        p.appendChild(tab);
-        tab.addEventListener('click', () => {
-            _bcCollapsed = !_bcCollapsed;
-            if (_bcCollapsed) _bcPaneOpen = false; // collapsing the panel hides the pane too
-            tab.textContent = _bcCollapsed ? '<<' : '>>';
-            const lb = p.querySelector('#vz-listbtn'); if (lb) lb.textContent = _bcPaneOpen ? '>>' : '<<';
-            _bcLayout();
-        });
-
-        // Sliding preset-list pane (sits to the LEFT of the control panel)
-        const pane = document.createElement('div');
-        pane.id = 'viz3d-listpane';
-        pane.style.cssText = 'position:absolute;top:50%;right:10px;z-index:99999;pointer-events:auto;width:236px;max-height:74vh;display:flex;flex-direction:column;' +
-            'background:rgba(8,10,20,0.93);border-radius:8px;box-shadow:0 2px 14px rgba(0,0,0,0.55);color:#cfe3ff;' +
-            'font:12px system-ui,sans-serif;overflow:hidden;transform:translateX(calc(100% + 16px)) translateY(-50%);transition:transform 0.28s ease;';
-        pane.innerHTML =
-            '<div style="display:flex;align-items:center;justify-content:space-between;padding:7px 9px 7px 10px;font-weight:600;border-bottom:1px solid rgba(255,255,255,.1)"><span>Presets</span><button id="vz-defaults" title="Restore the bundled default favorites + bans" style="' + BC_BTN + ';font-weight:400">↺ defaults</button></div>' +
-            '<input id="vz-filter" placeholder="filter…" spellcheck="false" style="margin:8px 9px 6px;padding:4px 7px;background:#11141f;color:#cfe3ff;border:1px solid rgba(255,255,255,.15);border-radius:5px;outline:none">' +
-            '<div id="vz-list" style="overflow-y:auto;padding:0 4px 8px"></div>';
-        (host || document.body).appendChild(pane);
-        _bcPane = pane;
-        _bcListEl = pane.querySelector('#vz-list');
-        _bcFilterEl = pane.querySelector('#vz-filter');
-        _bcFilterEl.addEventListener('input', _bcRenderList);
-        pane.querySelector('#vz-defaults').addEventListener('click', _bcRestoreDefaults);
-
-        const q = (id) => p.querySelector(id);
-        _bcPanel = p;
-
-        // Preset curation wiring (favorites / bans / cycle / reset)
-        _bcLoadLists();
-        const cyc = q('#vz-cyc');
-        cyc.value = s.cyclePool || 'all';
-        // Read fresh: settings.html writes can replace _bcSettings, so the `s`
-        // captured at panel creation may be stale by the time this fires.
-        cyc.addEventListener('change', () => { _bcLoadSettings().cyclePool = cyc.value; _bcSaveSettings(); });
-        _bcSetHold(!!s.hold); // sync the Hold button label to the saved state
-        q('#vz-hold').addEventListener('click', () => _bcSetHold(!_bcLoadSettings().hold));
-        q('#vz-listbtn').addEventListener('click', () => _bcSetPane(!_bcPaneOpen));
-        q('#vz-pname').addEventListener('click', () => _bcSetPane(!_bcPaneOpen));
-        q('#vz-prev').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.step(-1); });
-        q('#vz-next').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.step(1); });
-        q('#vz-fav').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.toggleFav(); });
-        q('#vz-ban').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.banCur(); });
-        _bcSetPane(false); // start collapsed; sets the list-button label
-        _bcUpdatePanelPreset();
-
-        // Live level readout — proves the song (not just guitar) is driving things.
-        // Self-stops when the panel is removed (_bcPanel !== p).
-        (function meterLoop() {
-            if (_bcPanel !== p) return;
-            const m = p.querySelector('#vz-meter');
-            if (m) m.textContent = 'gtr ' + _bcMeters.gtr.toFixed(2) + '  ·  song ' + _bcMeters.song.toFixed(2);
-            setTimeout(meterLoop, 150);
-        })();
-
-        if (!_bcPanelKeyBound) {
-            _bcPanelKeyBound = true;
-            window.addEventListener('keydown', (e) => {
-                if (e.key !== '`' || e.metaKey || e.ctrlKey || !_bcPanel) return;
-                const tag = (e.target && e.target.tagName) || '';
-                if (tag === 'INPUT' || tag === 'TEXTAREA') return;
-                const reveal = _bcPanel.style.display === 'none';
-                _bcPanel.style.display = reveal ? '' : 'none';
-                if (_bcPane) _bcPane.style.display = reveal ? '' : 'none';
-            });
-        }
-        return _bcPanel;
-    }
-
-    // Create a Butterchurn background controller bound to a wrap element.
-    function _bcCreateController(wrap, sizeProvider, audioProvider) {
-        const ctrl = { viz: null, actx: null, guitar: null, map: null, keys: [], cycle: 0, dead: false, lastW: -1, lastH: -1, canvas: null, backdrop: null, scrim: null, tint: null, wrap: wrap };
-        // Layered DOM in the wrap, all BEHIND the transparent 3D highway:
-        //   backdrop(z-4 dark) → bc canvas(z-3) → tint(z-2 instrument color) → scrim(z-1 lane dim)
-        const mkLayer = (cls, css) => { const d = document.createElement('div'); d.className = cls; d.style.cssText = css; wrap.appendChild(d); return d; };
-        const backdrop = mkLayer('viz3d-backdrop', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-4;background:#070710;pointer-events:none;');
-        const canvas = document.createElement('canvas');
-        canvas.className = 'viz3d-bc';
-        canvas.style.cssText = 'position:absolute;top:0;left:0;z-index:-3;pointer-events:none;';
-        wrap.appendChild(canvas);
-        const tint = mkLayer('viz3d-tint', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-2;pointer-events:none;mix-blend-mode:overlay;background:transparent;');
-        const scrim = mkLayer('viz3d-scrim', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-1;pointer-events:none;');
-        ctrl.canvas = canvas; ctrl.backdrop = backdrop; ctrl.scrim = scrim; ctrl.tint = tint;
-
-        ctrl.applySettings = function () {
-            const s = _bcLoadSettings();
-            canvas.style.display = s.enabled ? '' : 'none';
-            canvas.style.opacity = String(s.enabled ? s.opacity : 0);
-            if (s.laneDim) {
-                const a = Math.max(0, Math.min(1, s.laneDimStrength)).toFixed(3);
-                scrim.style.display = '';
-                scrim.style.background = 'linear-gradient(to right, rgba(0,0,0,0) 0%, rgba(0,0,0,' + a +
-                    ') 30%, rgba(0,0,0,' + a + ') 70%, rgba(0,0,0,0) 100%)';
-            } else {
-                scrim.style.display = 'none';
-            }
-        };
-
-        // ── Preset curation (favorites / bans / cycle mode) ──
-        ctrl.curName = null; ctrl.lastManual = 0;
-        ctrl.allList = () => (ctrl.keys || []).filter((k) => !_bcBanned.has(k));
-        ctrl.pool = () => {
-            const mode = _bcLoadSettings().cyclePool || 'all';
-            if (mode === 'bans') return (ctrl.keys || []).filter((k) => _bcBanned.has(k));
-            if (mode === 'favorites') {
-                const f = (ctrl.keys || []).filter((k) => _bcFavorites.has(k) && !_bcBanned.has(k));
-                if (f.length) return f;
-            }
-            return ctrl.allList();
-        };
-        ctrl.browseArr = () => ctrl.keys || []; // ◀▶ and the list pane walk the full preset list
-        ctrl.loadByName = (name, blend) => {
-            if (!ctrl.viz || !name || !ctrl.map || !ctrl.map[name]) return;
-            try { ctrl.viz.loadPreset(ctrl.map[name], blend || 0); ctrl.curName = name; } catch (e) {}
-            _bcUpdatePanelPreset();
-        };
-        ctrl.autoTick = () => {
-            if (ctrl.dead || _bcLoadSettings().hold) return;
-            if (performance.now() - ctrl.lastManual < 8000) return;
-            const pool = ctrl.pool();
-            if (!pool.length) return;
-            let name = pool[(Math.random() * pool.length) | 0];
-            if (pool.length > 1 && name === ctrl.curName) name = pool[(pool.indexOf(name) + 1) % pool.length];
-            ctrl.loadByName(name, 2.7);
-        };
-        ctrl.step = (dir) => {
-            const list = ctrl.browseArr();
-            if (!list.length) return;
-            let i = list.indexOf(ctrl.curName); if (i < 0) i = (dir > 0 ? -1 : 0);
-            i = (i + dir + list.length) % list.length;
-            ctrl.lastManual = performance.now();
-            ctrl.loadByName(list[i], 1.5);
-        };
-        ctrl.toggleFav = () => {
-            if (!ctrl.curName) return;
-            if (_bcFavorites.has(ctrl.curName)) _bcFavorites.delete(ctrl.curName);
-            else { _bcFavorites.add(ctrl.curName); _bcBanned.delete(ctrl.curName); }
-            _bcSaveLists(); _bcUpdatePanelPreset();
-        };
-        ctrl.banCur = () => {
-            if (!ctrl.curName) return;
-            if (_bcBanned.has(ctrl.curName)) {           // un-ban (two-way) — stay on it
-                _bcBanned.delete(ctrl.curName);
-                _bcSaveLists(); _bcUpdatePanelPreset();
-            } else {                                     // ban + advance off it
-                _bcBanned.add(ctrl.curName); _bcFavorites.delete(ctrl.curName);
-                _bcSaveLists(); ctrl.step(1);
-            }
-        };
-        _bcPrimary = ctrl;
-
-        _bcControllers.add(ctrl);
-        _bcEnsurePanel(wrap);
-        ctrl.applySettings();
-
-        _bcLoadLib().then(() => {
-            if (ctrl.dead) return;
-            const bc = _bcResolve();
-            if (!bc || typeof bc.createVisualizer !== 'function') { console.warn('[viz3d] Butterchurn global missing'); return; }
-            const Ctx = window.AudioContext || window.webkitAudioContext;
-            const sz = (sizeProvider && sizeProvider()) || { w: 1280, h: 720 };
-            // Browser (Docker/web app): REUSE the highway's existing shared
-            // analyser (the fog scenery's #audio / stems tap) via audioProvider,
-            // and build Butterchurn on that SAME AudioContext so connectAudio()
-            // doesn't fail cross-context. Desktop uses its own context fed by the
-            // guitar/mic input. `ownsActx` tracks whether WE created the context
-            // (so destroy() closes only contexts we own, never the shared one).
-            const fogAudio = _bcIsDesktop() ? null : (audioProvider ? audioProvider() : null);
-            ctrl.ownsActx = !(fogAudio && fogAudio.ctx);
-            ctrl.actx = (fogAudio && fogAudio.ctx) || new Ctx();
-            if (ctrl.actx.state === 'suspended' && ctrl.actx.resume) ctrl.actx.resume().catch(() => {});
-            // Seed the DRAWING BUFFER (canvas.width/height) to the device-pixel
-            // render size and report that SAME size to Butterchurn. Its on-screen
-            // pass viewports to the reported size but never sizes the output canvas
-            // itself — leaving the buffer at the 300x150 default blits the whole
-            // visualizer into a corner that CSS then stretches across the highway.
-            // pixelRatio:1 because DPR is now folded into the reported size, so
-            // buffer == viewport == internal texsize (no double-counting).
-            const _bcRatio0 = Math.min(window.devicePixelRatio || 1, 1.5);
-            const _bcW0 = Math.max(1, Math.round((sz.w || 1280) * _bcRatio0));
-            const _bcH0 = Math.max(1, Math.round((sz.h || 720) * _bcRatio0));
-            canvas.width = _bcW0; canvas.height = _bcH0;
-            ctrl.viz = bc.createVisualizer(ctrl.actx, canvas, {
-                width: _bcW0, height: _bcH0,
-                pixelRatio: 1, textureRatio: 1,
-            });
-            if (_bcIsDesktop()) {
-                try {
-                    ctrl.guitar = _bcGuitarFeed(ctrl.actx, (srcNode) => { try { if (ctrl.viz) ctrl.viz.connectAudio(srcNode); } catch (e) {} });
-                    console.log('[viz3d] bg: feeding GUITAR input into Butterchurn');
-                } catch (e) { console.warn('[viz3d] guitar feed failed', e); }
-            } else if (fogAudio && fogAudio.analyser) {
-                // The shared AnalyserNode is a passthrough — connecting it onward
-                // to Butterchurn's internal analyser doesn't disturb the fog's reads.
-                try { ctrl.viz.connectAudio(fogAudio.analyser); console.log('[viz3d] browser: Butterchurn tapping shared analyser (' + (fogAudio.source || 'core') + ')'); }
-                catch (e) { console.warn('[viz3d] shared-analyser connect failed', e); }
-            }
-            _bcLoadLists();
-            const presets = _bcPresets();
-            if (presets && typeof presets.getPresets === 'function') { ctrl.map = presets.getPresets(); ctrl.keys = Object.keys(ctrl.map); }
-            const pool0 = ctrl.pool();
-            ctrl.loadByName(pool0.length ? pool0[(Math.random() * pool0.length) | 0] : (ctrl.keys[0] || null), 0.0);
-            ctrl.cycle = setInterval(() => ctrl.autoTick(), 30000);
-            ctrl.connectedAnalyser = (fogAudio && fogAudio.analyser) || null;
-            console.log('[viz3d] Butterchurn ready, presets:', ctrl.keys.length);
-        }).catch((e) => {
-            // Async init failed (lib load, WebGL/context creation, etc.). Clean up
-            // the half-mounted controller so we don't leak an owned AudioContext /
-            // DOM layers, and mark it dead so _bcSyncMode can retry on a later
-            // mount instead of seeing a live-looking but non-functional bcCtrl.
-            console.error('[viz3d] Butterchurn load/init failed', e);
-            try { _bcReleaseCanvasGL(ctrl.canvas); } catch (_) {}
-            try { if (ctrl.guitar) { ctrl.guitar.stop(); ctrl.guitar = null; } } catch (_) {}
-            try { [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => { if (el && el.parentNode) el.parentNode.removeChild(el); }); } catch (_) {}
-            if (ctrl.ownsActx && ctrl.actx && typeof ctrl.actx.close === 'function') { try { ctrl.actx.close(); } catch (_) {} }
-            ctrl.actx = null; ctrl.viz = null; ctrl.dead = true;
-            _bcControllers.delete(ctrl);
-        });
-        // Size the Butterchurn output: set the canvas DRAWING BUFFER to the
-        // device-pixel render size AND report that same size, so buffer ==
-        // on-screen viewport == full fill. Butterchurn never sizes the output
-        // canvas itself; the previous code set only CSS size, leaving the buffer
-        // at the 300x150 default -> the viz showed a stretched lower-left corner
-        // (worse the larger the panel). Ratio reuses the highway's DPR budget.
-        function _bcApplySize(cssW, cssH) {
-            if (!(cssW > 0 && cssH > 0)) return;
-            ctrl.lastW = cssW; ctrl.lastH = cssH;
-            const ratio = Math.min(window.devicePixelRatio || 1, 1.5);
-            const bw = Math.max(1, Math.round(cssW * ratio)), bh = Math.max(1, Math.round(cssH * ratio));
-            if (canvas.width !== bw) canvas.width = bw;
-            if (canvas.height !== bh) canvas.height = bh;
-            const wpx = cssW + 'px', hpx = cssH + 'px';
-            // Confine ALL layers to exactly the highway-canvas rect so the opaque
-            // backdrop can't bleed over the transport bar above the highway.
-            [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => {
-                if (el) { el.style.width = wpx; el.style.height = hpx; el.style.right = 'auto'; el.style.bottom = 'auto'; }
-            });
-            if (ctrl.viz && ctrl.viz.setRendererSize) { try { ctrl.viz.setRendererSize(bw, bh); } catch (e) {} }
-        }
-        return {
-            applySettings() { ctrl.applySettings(); },
-            dead() { return ctrl.dead; },
-            ready() { return !!ctrl.viz; },
-            boundAnalyser() { return ctrl.connectedAnalyser || null; },
-            audioCtx() { return ctrl.actx; },
-            // Re-bind audio when the shared analyser changes (e.g. a stems song
-            // swap replaces the analyser). Same context → cheap reconnect; the
-            // caller handles a context change with a full rebuild (cross-context
-            // connectAudio is impossible — the visualizer is bound to one ctx).
-            reconnectAudio(a) {
-                if (!a || !a.analyser || !ctrl.viz) return false;
-                if (a.analyser === ctrl.connectedAnalyser) return true;
-                if (a.ctx && a.ctx !== ctrl.actx) return false; // needs rebuild
-                try { ctrl.viz.connectAudio(a.analyser); ctrl.connectedAnalyser = a.analyser; return true; } catch (e) { return false; }
-            },
-            chart(v) { if (ctrl.guitar && ctrl.guitar.setChart) ctrl.guitar.setChart(v); },
-            tint(hex, alpha) {
-                if (!ctrl.tint) return;
-                if (hex == null) { ctrl.tint.style.background = 'transparent'; return; }
-                const r = (hex >> 16) & 255, g = (hex >> 8) & 255, b = hex & 255;
-                ctrl.tint.style.background = 'rgba(' + r + ',' + g + ',' + b + ',' + (alpha || 0).toFixed(3) + ')';
-            },
-            render() {
-                const s = _bcLoadSettings();
-                if (!ctrl.viz || !s.enabled) return; // skip GPU work when the bg is off
-                const sz = sizeProvider && sizeProvider();
-                if (sz && sz.w > 0 && sz.h > 0 && (sz.w !== ctrl.lastW || sz.h !== ctrl.lastH)) {
-                    _bcApplySize(sz.w, sz.h);
-                }
-                try { ctrl.viz.render(); } catch (e) {}
-            },
-            resize(w, h) { _bcApplySize(w, h); },
-            destroy() {
-                ctrl.dead = true;
-                _bcControllers.delete(ctrl);
-                if (_bcPrimary === ctrl) { _bcPrimary = _bcControllers.values().next().value || null; _bcUpdatePanelPreset(); }
-                if (ctrl.cycle) { clearInterval(ctrl.cycle); ctrl.cycle = 0; }
-                if (ctrl.guitar) { ctrl.guitar.stop(); ctrl.guitar = null; }
-                // Release the Butterchurn WebGL context deterministically (don't
-                // wait for GC) so repeated mounts/toggles can't exhaust the
-                // browser's WebGL context cap (~16). Do it before removing the
-                // canvas from the DOM.
-                _bcReleaseCanvasGL(ctrl.canvas);
-                [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => { if (el && el.parentNode) el.parentNode.removeChild(el); });
-                ctrl.viz = null; ctrl.connectedAnalyser = null;
-                // Close the AudioContext only if we own it (desktop, or the
-                // browser fallback). The browser path normally reuses the
-                // highway's shared context, which the fog system owns — never
-                // close that. Without this, desktop leaks a new AudioContext per
-                // mount and hits the browser's ~6-context cap after a few toggles.
-                if (ctrl.ownsActx && ctrl.actx && typeof ctrl.actx.close === 'function') {
-                    try { ctrl.actx.close(); } catch (e) {}
-                }
-                ctrl.actx = null;
-                if (_bcControllers.size === 0) {
-                    if (_bcPanel && _bcPanel.parentNode) _bcPanel.parentNode.removeChild(_bcPanel);
-                    if (_bcPane && _bcPane.parentNode) _bcPane.parentNode.removeChild(_bcPane);
-                    _bcPanel = null; _bcPane = null; _bcListEl = null; _bcFilterEl = null; _bcPaneOpen = false;
-                } else if (_bcPrimary && _bcPrimary.wrap) {
-                    // Splitscreen: a controller other than this one is still
-                    // alive. The singleton panel was parented to THIS (now
-                    // destroyed) wrap, so re-home it onto the surviving primary's
-                    // wrap — otherwise the panel is orphaned on the dead wrap and
-                    // the surviving highway is left with no visualizer controls
-                    // (_bcEnsurePanel only runs at controller creation). It moves
-                    // the existing panel+pane when connected, or rebuilds them on
-                    // the survivor if this wrap was already detached.
-                    try { _bcEnsurePanel(_bcPrimary.wrap); _bcUpdatePanelPreset(); } catch (e) {}
-                }
-            },
-        };
-    }
-
-    // Selectable per-string color palettes (issue #10). Each palette has
-    // 8 entries to match MAX_RENDER_STRINGS so 6/7/8-string arrangements
-    // all index safely. Default is the canonical chart-format classic
-    // mapping (low E=red, A=yellow, D=blue, G=orange, B=green,
-    // high E=purple); Neon pushes saturation harder; Pastel desaturates
-    // for long-session comfort; Colorblind (high contrast) is derived from
-    // the chart format's built-in colorblind-mode palette, but this preset
-    // intentionally keeps some entries tuned for feedBack rather than
-    // reproducing every original hex value verbatim. The chart-format base
-    // values came from community reverse-engineering of the original chart
-    // files; do not treat the tuned values below as the exact original
-    // palette.
-    // In feedBack's index convention s=0 is the low E (thickest) and
-    // s=5 is the high E (thinnest), matching the chart format's native string
-    // indexing. Per-index ordering is preserved across all palettes so
-    // switching between them never reassigns a string to a different
-    // colour family. Indices 6/7 are supplementary slots used for
-    // 7/8-string arrangements.
-    // NOTE: settings.html mirrors these arrays in its hydration script
-    // for the palette-preview swatches — keep them in sync.
-    const PALETTES = {
-        default: [
-            0xe61f26, 0xecd234, 0x1096e6, 0xf18313,
-            0x3fc413, 0xb518d9, 0xff6bd5, 0x6bffe6,
-        ],
-        neon: [
-            0xff0030, 0xffe800, 0x0080ff, 0xff8030,
-            0x40ff50, 0xb050ff, 0xff40d0, 0x40ffd0,
-        ],
-        pastel: [
-            0xe89aa0, 0xefdf90, 0x9adfee, 0xefb898,
-            0xa6e0a8, 0xc4a6e0, 0xe0a6c8, 0xa6e0d8,
-        ],
-        colorblind_hc: [
-            0xa42424, 0xa3f300, 0x19abfc, 0xda7e41,
-            0x30d0a0, 0x7648a7, 0xff6bd5, 0x6bffe6,
-        ],
-    };
-    const PALETTE_IDS = Object.keys(PALETTES);
-    // User-defined per-string colors (core "Highway String Colors" theming).
-    // Persisted as a JSON hex array under the bg setting key 'customColors';
-    // when the active palette id is 'custom' the renderer resolves this into
-    // numeric hex, falling back to the default palette per missing index.
-    // Mutated in place by _resolveCustomPalette so the reference stays stable.
-    let _customPalette = PALETTES.default.slice();
-    function _h3dHexToInt(hex) {
-        if (typeof hex !== 'string') return null;
-        const t = hex.trim().replace(/^#/, '');
-        const full = t.length === 3 ? t[0] + t[0] + t[1] + t[1] + t[2] + t[2] : t;
-        if (!/^[0-9a-fA-F]{6}$/.test(full)) return null;
-        return parseInt(full, 16);
-    }
-    // Numeric (0xRRGGBB) darken/lighten — used to derive the gem-gradient
-    // top-highlight / bottom-shade stops from a custom per-string base color
-    // so the note bodies follow the custom palette (mirrors the 2D highway's
-    // dim/bright derivation). factor 0..1 keeps that fraction of each channel;
-    // lighten mixes t toward white.
-    function _clampByteI(n) { return n < 0 ? 0 : (n > 255 ? 255 : Math.round(n)); }
-    function _darkenInt(hex, factor) {
-        const r = (hex >> 16) & 0xff, g = (hex >> 8) & 0xff, b = hex & 0xff;
-        return (_clampByteI(r * factor) << 16) | (_clampByteI(g * factor) << 8) | _clampByteI(b * factor);
-    }
-    function _lightenInt(hex, t) {
-        const r = (hex >> 16) & 0xff, g = (hex >> 8) & 0xff, b = hex & 0xff;
-        return (_clampByteI(r + (255 - r) * t) << 16) | (_clampByteI(g + (255 - g) * t) << 8) | _clampByteI(b + (255 - b) * t);
-    }
-    // Default per-string gem gradient stops [topHighlight, bottomShade] —
-    // sampled from the original colour PNGs. Used verbatim for the built-in
-    // palettes (and for unchanged slots of a custom palette) so the stock look
-    // is byte-for-byte preserved; custom slots derive their stops from the
-    // chosen base color via _lightenInt/_darkenInt. Strings 6/7 have no entry
-    // and fall back to flat gNote.
-    const DEFAULT_GEM_GRADIENTS = [
-        [0xec0816, 0xbd0400], // 0 red
-        [0xefd20b, 0xceaa00], // 1 yellow
-        [0x0b93e9, 0x0e69b2], // 2 blue
-        [0xf77b0b, 0xdb5808], // 3 orange
-        [0x37c40b, 0x139305], // 4 green
-        [0xaf10db, 0x8907af], // 5 violet
-    ];
-    // Default palette at module scope so out-of-IIFE consumers (e.g. the
-    // out-of-range warning's reference to "palette size") still have a
-    // canonical length to compare against.
-    const S_COL = PALETTES.default;
-
-    const SCALE = 2.25;
-    const K = SCALE / 300;
-    // Horizontal stretch factor for fret X positions.  Increasing this widens
-    // the lane (frets, board plane, strings, notes, lane strip) without
-    // affecting K-based vertical dimensions (string gap, note height, camera).
-    const FRET_SCALE = SCALE * 1.1;
-
-    const NFRETS = 24;
-    const NSTR = 6;
-    /**
-     * Pure 12-semitone spacing compresses toward the bridge; multiply each
-     * segment **above** this fret by the factor so high positions stay
-     * slightly more playable/readable in 3D.
-     */
-    const FRET_SPACING_STRETCH_ABOVE12 = 1.1;
-    const FRET_SPACING_ANCHOR_F = 12;
-    // Per-string materials and projection meshes are built via S_COL.map(),
-    // so the renderer can only address strings 0..S_COL.length-1. Using a
-    // higher count would index undefined into mGlow/mStr/mSus/projMeshArr.
-    // Extend S_COL above to support more strings.
-    const MAX_RENDER_STRINGS = S_COL.length;
-
-    // Resolve the string count for the active arrangement. Prefer
-    // bundle.stringCount (exposed by feedBack core since #93 — derived
-    // from notes/chords/tuning, so it works for 5-string bass, 7- and
-    // 8-string guitar, etc.). Fall back to arrangement-name detection
-    // for older feedBack cores that don't emit the field. Clamp to the
-    // palette size so a malformed bundle or a 12-string chart doesn't
-    // index past the per-string material arrays.
-    function resolveStringCount(bundle) {
-        const sc = bundle && bundle.stringCount;
-        if (Number.isFinite(sc) && sc >= 1) {
-            return Math.min(Math.trunc(sc), MAX_RENDER_STRINGS);
-        }
-        return /bass/i.test(bundle?.songInfo?.arrangement || '') ? 4 : NSTR;
-    }
-
-    /** Chart-format tuning entries are semitone offsets from instrument standard. */
-    const _NOTE_NAMES_SHARP = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
-
-    // Open-string MIDI (thick → thin), matched to RS string index 0 low.
-    const _BASE_OPEN_MIDI_BASS4 = Object.freeze([28, 33, 38, 43]);
-    const _BASE_OPEN_MIDI_BASS5 = Object.freeze([23, 28, 33, 38, 43]);
-    const _BASE_OPEN_MIDI_GUITAR6 = Object.freeze([40, 45, 50, 55, 59, 64]);
-    const _BASE_OPEN_MIDI_GUITAR7 = Object.freeze([35, 40, 45, 50, 55, 59, 64]);
-    // F#/B/E standard extension — low string is a fifth below RS 7‑string low B.
-    const _BASE_OPEN_MIDI_GUITAR8 = Object.freeze([28, 35, 40, 45, 50, 55, 59, 64]);
-
-    function _baseOpenStringMidis(sc, arrangement) {
-        const isBass = /bass/i.test(arrangement || '');
-        if (sc === 4 && isBass) return _BASE_OPEN_MIDI_BASS4.slice();
-        if (sc === 4) return _BASE_OPEN_MIDI_GUITAR6.slice(0, 4);
-        if (sc === 5 && isBass) return _BASE_OPEN_MIDI_BASS5.slice();
-        if (sc === 5) return _BASE_OPEN_MIDI_GUITAR6.slice(0, 5);
-        if (sc === 7) return _BASE_OPEN_MIDI_GUITAR7.slice();
-        if (sc === 8) return _BASE_OPEN_MIDI_GUITAR8.slice();
-        if (Number.isFinite(sc) && sc > 8) {
-            const out = Array.from(_BASE_OPEN_MIDI_GUITAR8);
-            let last = out[out.length - 1];
-            while (out.length < sc) {
-                last += 5;
-                out.push(last);
-            }
-            return out.slice(0, sc);
-        }
-        const g6 = _BASE_OPEN_MIDI_GUITAR6.slice();
-        if (Number.isFinite(sc) && sc < 6 && sc >= 1) return g6.slice(0, sc);
-        return g6;
-    }
-
-    function _midiToPitchLabel(midi) {
-        const m = Math.round(midi);
-        const octave = Math.floor(m / 12) - 1;
-        const n = _NOTE_NAMES_SHARP[(m % 12 + 12) % 12];
-        return n + octave;
-    }
-
-    /**
-     * @param {number} nEffective string count clamped like nStr / resolveStringCount
-     * @param {Record<string, unknown>} songInfo WS song_info blob (subset)
-     */
-    function _openStringPitchLabelsForTuning(bundle, songInfo, nEffective) {
-        const n = Number.isFinite(nEffective) ? Math.min(Math.max(1, Math.trunc(nEffective)), MAX_RENDER_STRINGS) : resolveStringCount(bundle);
-        let tuning = (songInfo && songInfo.tuning) || bundle.tuning;
-        let cap = songInfo && songInfo.capo;
-        cap = Number.isFinite(cap) ? cap : (Number.isFinite(bundle.capo) ? bundle.capo : 0);
-        if (!Array.isArray(tuning)) tuning = [];
-
-        const base = _baseOpenStringMidis(n, songInfo?.arrangement);
-        const labels = [];
-        for (let s = 0; s < n; s++) {
-            const offRaw = tuning[s];
-            const off = Number.isFinite(offRaw) ? offRaw : 0;
-            const midi = (base[s] !== undefined ? base[s] : 40) + off + cap;
-            labels.push(_midiToPitchLabel(midi));
-        }
-        return labels;
-    }
-
-    const STR_THICK = 0.25 * K;
-
-    // Fret wires — bowed metal tubes (backported from highway_babylon's
-    // "hit-zone fret bars"). All frets share one bowed TubeGeometry whose
-    // middle (the middle strings) pushes away from the camera so the row of
-    // frets reads as wrapping a cylindrical neck — chart-format depth cue.
-    // Negative Z = away from camera (into the highway). All tunable.
-    const FRET_BOW_DZ = -1.2 * K;        // middle-of-span Z offset
-    const FRET_TUBE_RADIUS = STR_THICK * 0.75; // slightly thicker than a string
-    const FRET_TUBE_SEG = 12;            // tubular segments along the curve
-    // Radial segments (cross-section). 8 rather than 6: at FRET_TUBE_RADIUS the
-    // hexagonal facets of a 6-segment tube are visible along the top highlight.
-    // One shared geometry for all frets, so the extra segments are ~free.
-    const FRET_TUBE_RADIAL = 8;
-    // metalness kept moderate, NOT ~1.0: MeshStandardMaterial is PBR and the
-    // scene has no envMap, so a full-metal fret would reflect black and render
-    // dark (the nut/headstock use metalness 0.02 for the same reason). At ~0.4
-    // the lit albedo body survives while the directional light still throws a
-    // glossy specular streak across the rounded tube. The dim emissive floor
-    // keeps frets from going muddy far down the (fogged) neck.
-    const FRET_METALNESS = 0.4;          // lit steel / brass when gold
-    const FRET_ROUGHNESS = 0.3;
-    const FRET_EMISSIVE = 0x12141a;      // cool dim floor, never fully black
-
-    // Fret-wire tiers. Wires inside the active anchor lane (the frets the player
-    // is actually reading) sit bright; everything outside recedes. Kept far
-    // apart on purpose — a narrow gap reads as noise rather than as a focus cue.
-    const FRET_WIRE_ACTIVE_HEX = 0xD8A636; // gold; numeric twin of FRET_LABEL_GOLD_HEX
-    const FRET_WIRE_ACTIVE_OP = 0.9;
-    const FRET_WIRE_IDLE_HEX = 0x4A4A60;
-    const FRET_WIRE_IDLE_OP = 0.28;
-
-    // Hit flash: when a scorer (feedBack#254) confirms a note, the two wires
-    // bracketing its fret (f-1 and f) flash bright. Emissive is boosted as well
-    // as albedo — a MeshStandard fret with no envMap barely brightens from
-    // albedo alone, so without the emissive lift the "flash" reads as a shrug.
-    const FRET_WIRE_HIT_HEX = 0xFFFFFF;      // blown out to white at full flash
-    const FRET_WIRE_HIT_EMISSIVE = 0xFFE9B0; // hot warm-white glow
-    const FRET_WIRE_HIT_OP = 1.0;
-    // Emissive multiplier at full flash (baseline is 1). Pushing emissive past
-    // 1.0 is what actually makes the wire read as a light source rather than a
-    // brightly-lit object — the color alone saturates and stops there.
-    const FRET_WIRE_HIT_INTENSITY = 4.2;
-    // Seconds for a flash to fall to ~1/e once the provider stops reporting.
-    // The provider already fades its own `alpha` on a struck note; this tail
-    // just keeps the hand-off from popping, and smooths the frame-to-frame
-    // jitter of a held sustain (whose alpha tracks live input level).
-    const FRET_WIRE_HIT_DECAY = 0.32;
-
-    const S_BASE = 3 * K;
-    const S_GAP = 4 * K;
-
-    const AHEAD = 3.0;
-    const BEHIND = 0.5;
-    // How long a note/chord-frame stays renderable past the hit line while a
-    // note-state provider (feedBack#254) is attached. The provider's
-    // hit/miss verdict is asynchronous — the engine-side verifier reports it
-    // ~0.35-0.5 s after the line — so the default ~50 ms note linger /
-    // ~0.48 s chord linger lapses before the tint can apply. Drives both
-    // the outer-loop cull (ndVerdictT0) and the smart drawNote cull below.
-    const NOTEDETECT_GEM_VERDICT_WINDOW = 0.75;
-    // chDt threshold past the hit line at which the chord-frame scan
-    // gives up on an arpeggio-style frame whose constituents never come
-    // in. Must be < NOTEDETECT_GEM_VERDICT_WINDOW (the rim's draw life
-    // in detect mode); placing it at 0.55 s leaves ~0.2 s of the visible
-    // window for the latch to fire and skip subsequent scans.
-    const _ND_UNMATCHED_LATCH_AFTER = 0.55;
-    // Sample approach offsets dt in [0, AHEAD] into strips. Lane quads use
-    // z = dZ(dt) + TS*BEHIND = TS*(BEHIND - dt), while notes use z = dZ(n.t-now).
-    // So note hit line (z=0) aligns with dt=BEHIND, not dt=0. Chart time at
-    // lane parameter dt is now + dt - BEHIND (same z as a note at that time).
-    // Each strip’s <anchor> uses that chart time so the blue lane doesn’t
-    // switch ~BEHIND seconds before the XML <anchor time="…"/>.
-    const HWY_LANE_TIME_SLICES = 96;
-    /** Odd columns (1st/3rd/…) darker teal; even columns brighter blue. */
-    const HWY_LANE_STRIPE_ODD_HEX  = 0x103B5C;
-    const HWY_LANE_STRIPE_EVEN_HEX = 0x08283C;
-    /** Lane quad alpha: base + highwayIntensity * scale (readable on dark floor). */
-    const HWY_LANE_STRIPE_OP_BASE = 1.0;
-    const HWY_LANE_STRIPE_OP_INT  = 0;
-    /** Venue mode: slight near-lane contrast boost (visual only). */
-    const VENUE_LANE_OP_BOOST = 1.1;
-    /** Venue mode: gem emissive pop (~12%, visual only). */
-    const VENUE_GEM_EMISSIVE_MUL = 1.12;
-    /** Venue steady-state haze coefficient — kept low for raster bg plate. */
-    const VENUE_HAZE_STEADY = 0.008;
-    /** Venue backdrop pushed slightly farther for parallax depth. */
-    const VENUE_BACKDROP_DISTANCE_MUL = 1.06;
-    /** Note travel speed. */
-    const TS = 230 * K;
-
-    const RENDER_ORDER_LAYER_STACK = Object.freeze([
-        'CHORD_FILL',
-        'CHORD_STRUM_FILL',
-        'CHORD_STRUM_LINE',
-        'SUSTAIN_TRAIL',
-        'CHORD_FRAME',
-        'CHORD_EDGE_GLOW',
-        'CONNECTOR_LINE',
-        'FRET_COLUMN',
-        'ARP_CONNECTOR_LINE',
-        'NOTE_OUTLINE',
-        'NOTE_CORE',
-        'TECHNIQUE_MARKER',
-        'BOARD_STRING',
-        'BOARD_FRET_WIRE',
-        'NOTE_FRET_LABEL',
-        'ARP_NOTE_FRET_LABEL',
-        'CHORD_FRET_LABEL',
-    ]);
-    const RENDER_ORDER_LAYER_INDEX = Object.freeze(RENDER_ORDER_LAYER_STACK.reduce(
-        (indexByLayer, layerName, layerIndex) => {
-            indexByLayer[layerName] = layerIndex;
-            return indexByLayer;
-        },
-        Object.create(null)
-    ));
-
-    const RENDER_ORDER_AT_Z_ZERO = 700;
-    const RENDER_ORDER_FAR_CLAMP = 50;
-
-    /**
-     * Computes renderOrder from world depth plus a named layer.
-     * Closer objects receive larger values and paint over farther objects; the
-     * layer stack breaks ties at the same depth, keeping labels above note gems.
-     *
-     * The layer index is added as a sub-unit fraction (< 1) so the integer
-     * depth bucket STRICTLY dominates: a farther object can never outrank a
-     * nearer one merely because it sits on a higher layer. Adding the raw index
-     * (0..N-1) directly would let the ~N-wide layer span leak across depth
-     * buckets and re-introduce far-over-near bleed for notes within ~N draw
-     * units of each other. Fraction granularity (1/N ≈ 0.06) stays well above
-     * the 0.0001 intra-element sub-increments used at some call sites.
-     */
-    function renderOrderForLayerAtZ(worldZ, layerName) {
-        const layerIndex = RENDER_ORDER_LAYER_INDEX[layerName];
-        if (layerIndex === undefined) throw new Error(`Unknown 3D highway depth layer: ${layerName}`);
-        const depthRenderOrder = Math.max(
-            RENDER_ORDER_FAR_CLAMP,
-            Math.round(RENDER_ORDER_AT_Z_ZERO + worldZ / K)
-        );
-        return depthRenderOrder + layerIndex / RENDER_ORDER_LAYER_STACK.length;
-    }
-
-    /** Match `nextNoteByString` onset to this note (float + chart rounding; avoids ghost / glow flicker). */
-    const NEXT_ON_STRING_T_EPS = 0.06;
-    /** Fixed pre-impact ramp window for lead-note board ghosts (Primary + Upcoming slots). */
-    const GHOST_UPCOMING_WIN = 0.6;
-    /** Ghost starts at this fraction of full size/brightness and grows to 1.0 as it approaches. */
-    const PROJ_GROW_MIN = 0.45;
-    /**
-     * 3D highway post-strum tail — chord frame + ghost fret digit share the same
-     * hold and fade so timing stays consistent.
-     */
-    const CHORD_HWY_LINGER_S = 0.75;
-    /** Linear fade at end of `CHORD_HWY_LINGER_S` (applies to chord UI and board ghost numbers). */
-    const CHORD_HWY_FADE_S = 0.32;
-    const GHOST_HOLD_AFTER_ONSET = CHORD_HWY_LINGER_S;
-    const GHOST_FRET_LBL_FADE_S = CHORD_HWY_FADE_S;
-    /** Purple lane rails: extend past last matched chord/note so Z reaches frame end. */
-    const ARP_HWY_RAIL_END_TAIL_S = 0.38;
-    /** Keep 0 — chord/note-based ``shapeLo`` already aligns to the visible frame. */
-    const ARP_HWY_RAIL_START_LEAD_S = 0;
-    /** Drives emissive (`mGlow` / accent fill) for notes with `.ac`; matches drawNote `linger` cutoff (0.05). */
-    const ACCENT_NOTE_STR_GLOW = 3.55;
-    const ACCENT_NOTE_LINGER_EPS = 0.05;
-    /** Extra emissive layered on accent-only body material (`mAccentCore`), after `strGlow * glowMul`. */
-    const ACCENT_NOTE_FILL_BOOST = 2.55;
-    /** Accent rim draws brighter than normal string-coloured outlines (`mStrHitOutline`). */
-    const ACCENT_RIM_BASE_EMISSIVE = 3.45;
-    /** Outline / core scale bump vs normal gems (accent reads slightly larger). */
-    const ACCENT_RIM_XY_SCALE_MUL = 1.09;
-    const ACCENT_RIM_Z_SCALE_MUL = 1.06;
-    // Soft neon-style outer bloom (AdditiveBlending) — layered shells behind outline/core.
-    const ACCENT_HALO_OP_NEAR = 0.68;
-    const ACCENT_HALO_OP_MID = 0.42;
-    const ACCENT_HALO_OP_FAR = 0.24;
-    const ACCENT_HALO_XY_INNER = 1.36;
-    const ACCENT_HALO_XY_MID = 1.82;
-    const ACCENT_HALO_XY_OUTER = 2.32;
-    const ACCENT_HALO_Z_INNER = 1.05;
-    const ACCENT_HALO_Z_MID = 1.12;
-    const ACCENT_HALO_Z_OUTER = 1.22;
-
-    /**
-     * Post-hit tail fade shared by ghost fret digits and 3D chord UI: full
-     * opacity until (holdS − fadeS) after onset, then linear fade over fadeS;
-     * canceled when `nextSoon` — for ghosts: next note within `fadeS` of `now`;
-     * for chord frame: next chord onset lies in chart time [hold − fade, hold]
-     * after the current chord (so fade does not run into a same-window handoff).
-     * @param {number} dt chart time minus now (negative once struck)
-     * @param {number} fadeS linear fade duration (default: GHOST_FRET_LBL_FADE_S)
-     */
-    function hwyPostHitTailFadeMul(dt, holdS, nextSoon, fadeS = GHOST_FRET_LBL_FADE_S) {
-        if (nextSoon || dt >= 0) return 1;
-        const gone = -dt;
-        if (gone >= holdS) return 0;
-        const fS = Math.min(Math.max(fadeS, 1e-6), holdS);
-        const fadeStartT = Math.max(0, holdS - fS);
-        if (gone < fadeStartT) return 1;
-        return Math.max(0, 1 - (gone - fadeStartT) / fS);
-    }
-
-    // Shorter, flatter notes (joel style)
-    const NW = 5 * K, NH = 3 * K, ND = 0.25 * K;
-    // Sustain-trail X offset for fretted notes. Module-scoped + frozen
-    // so the hot path's `offsets.length` loop sees a stable singleton
-    // reference. The standalone-open-string path builds a fresh pair
-    // each call because its offset magnitude depends on the per-note
-    // `openWScale` (set in drawNote at line 7367 from the open-string
-    // body's lane width), so a module-scoped constant can't capture
-    // it; the allocation is the same one the prior code did via
-    // `const baseOff = NW * 3 * openWScale` plus the inline `[-, +]`
-    // literal in the chord-member branch — just consolidated.
-    const SINGLE_SUS_OFFSETS = Object.freeze([0]);
-    const BEND_HALFSTEP_WORLD_Y = S_GAP * 0.8;
-    const VIBRATO_HALF_WAVE_S = 0.08;
-    // Bend ribbon envelope: fraction of the sustain spent ramping up to
-    // the bent pitch, and releasing back down (rest is the held plateau).
-    const BEND_ENV_RISE_FRAC = 0.35;
-    const BEND_ENV_RELEASE_FRAC = 0.30;
-    const TREMOLO_BUMP_S = 0.06;
-
-    /** Longitudinal samples for sustain-technique prism (indexed BufferGeometry). */
-    const SLIDE_RIBBON_SAMPLES = 96;
-    /** Pre-built index buffer: `SLIDE_RIBBON_SAMPLES` × 8 tris × 3 verts. */
-    const SLIDE_RIBBON_INDICES = (() => {
-        const S = SLIDE_RIBBON_SAMPLES;
-        const idx = new Uint16Array(S * 24);
-        let o = 0;
-        for (let k = 0; k < S; k++) {
-            const b = k * 4;
-            const nx = (k + 1) * 4;
-            // Bottom (-Y outward)
-            idx[o++] = b; idx[o++] = b + 1; idx[o++] = nx + 1;
-            idx[o++] = b; idx[o++] = nx + 1; idx[o++] = nx;
-            // Top (+Y outward)
-            idx[o++] = b + 3; idx[o++] = nx + 3; idx[o++] = nx + 2;
-            idx[o++] = b + 3; idx[o++] = nx + 2; idx[o++] = b + 2;
-            // Left (-X outward)
-            idx[o++] = b; idx[o++] = nx; idx[o++] = nx + 3;
-            idx[o++] = b; idx[o++] = nx + 3; idx[o++] = b + 3;
-            // Right (+X outward)
-            idx[o++] = b + 1; idx[o++] = b + 2; idx[o++] = nx + 2;
-            idx[o++] = b + 1; idx[o++] = nx + 2; idx[o++] = nx + 1;
-        }
-        return idx;
-    })();
-    // Three r170's setIndex() only wraps plain Arrays into Uint16BufferAttribute;
-    // typed-array input gets assigned raw onto .index, which trips WebGL's
-    // byteLength check. Convert once at module init so each pooled geometry
-    // reuses the same Array reference instead of allocating per mesh.
-    const SLIDE_RIBBON_INDICES_ARR = Array.from(SLIDE_RIBBON_INDICES);
-    const N_RAD = 1.5 * K;
-    const SW = 2 * K, SH = 1.5 * K;
-
-    const CAM_H_BASE = 190 * K;
-    const CAM_DIST_BASE = 240 * K;
-    const REF_ASPECT = 16 / 9;
-    const FOCUS_D = 600 * K;
-    const CAM_LERP_BASE = 0.02;
-
-    // Base vertical field of view (deg). THREE's PerspectiveCamera fov is the
-    // VERTICAL angle; horizontal follows from the aspect ratio. At a normal
-    // ~16:9 pane this gives a ~102° horizontal cone. On an ultra-wide pane
-    // (top/bottom 2-player split → full-width/half-height → ~32:9) that
-    // horizontal cone balloons past 130° and squeezes the fixed-width neck into
-    // a central sliver. The optional horizontal-FOV-hold path below counters
-    // that by lowering the effective vertical fov as the pane widens.
-    const BASE_VFOV = 70;
-    // Horizontal-FOV-hold ("Hor+") defaults. At/under HORPLUS_START_ASPECT the
-    // effective vertical fov equals BASE_VFOV (exact no-op); past it the
-    // vertical fov drops to keep the horizontal cone ~constant so the neck
-    // fills a wide pane. HORPLUS_MIN_VFOV floors the result on pathological
-    // aspects. Engaged only via the window.__h3dAspectTune bridge (default off).
-    const HORPLUS_START_ASPECT = 16 / 9;
-    const HORPLUS_MIN_VFOV = 28;
-
-    // Zoom-dependent framing — height (h*) and depth (dist*) multipliers
-    // applied to cam.position. Interpolated by `dist`:
-    //   NEAR = tight view (nut position, span<=4 -> dist~=93*K): lower/closer.
-    //   FAR  = wide view (midpoint fret 1<->20 -> dist~=141*K): higher/pulled back
-    //          to fit the whole neck.
-    // Outside this range the values clamp at the endpoints.
-    const CAM_FRAME_DIST_NEAR = 93 * K;
-    const CAM_FRAME_DIST_FAR  = 141 * K;
-    const CAM_FRAME_H_NEAR = 0.75;
-    const CAM_FRAME_H_FAR  = 1.00;
-    const CAM_FRAME_D_NEAR = 0.575;
-    const CAM_FRAME_D_FAR  = 0.60;
-    // Fret-row fit guard. The heat-coloured fret-number row is a band drawn
-    // BELOW the board (at sY(lowest) - S_GAP*1.4). The lower-third framing
-    // anchors the board CENTRE, not that row, so a tight zoom on a centred span
-    // (worst mid-neck — fine pushed to either end of the neck) drops the row off
-    // the bottom edge. Tilt can't add vertical room there (it would only trade a
-    // bottom clip for a top clip), so camUpdate dollies the camera back just
-    // enough to bring the row back into frame — auto-sized, capped, hysteretic.
-    const FRET_ROW_FIT_NDC_MIN   = -0.86;  // keep the row anchor at/above this NDC y (>-1 = on screen)
-    const FRET_ROW_FIT_DEADBAND  = 0.06;   // headroom past the min before the dolly relaxes (anti-hunt)
-    const FRET_ROW_FIT_BOOST_MAX = 1.6;    // cap the pull-back so the zoom can't pop (never dolly back > +60%)
-
-    // Camera-X targeting (issue #34). The visible AHEAD = 4.0 s window is
-    // far too coarse for picking where the camera should sit — a single
-    // 17th-fret bend 2.5 s away yanks tgtX several frets even though the
-    // immediate playing area hasn't moved. These constants are bounds for
-    // a smoothing dial (0 = twitchy, 1 = calm); the runtime lerps between
-    // the pair using the user's `cameraSmoothing` setting.
-    const CAM_TGT_BEHIND   = 0.2;   // s behind hit line for X targeting
-    const CAM_TGT_AHEAD_T  = 2.0;   // s — twitchy: longer lookahead (more reactive)
-    const CAM_TGT_AHEAD_C  = 0.7;   // s — calm: shorter lookahead (ignore distant outliers)
-    const CAM_TGT_TAU_T    = 0.35;  // s — twitchy: short recency time-constant
-    const CAM_TGT_TAU_C    = 0.9;   // s — calm: longer time-constant (averages more)
-    const CAM_TGT_HYST_T   = 0.25;  // frets — twitchy: tiny dead zone
-    const CAM_TGT_HYST_C   = 5.0;   // frets — calm: ~5-fret dead zone, wide
-                                    // enough to swallow chord-to-chord
-                                    // alternations across a 6-fret span
-                                    // (e.g. Am ↔ D in first position).
-
-    // Zoom (tgtDist) damping. Controlled by its own `zoomSmoothing` setting
-    // so X-pan and zoom-pull-back can be tuned independently. New users
-    // (and existing users who never wrote zoomSmoothing) inherit
-    // cameraSmoothing's value on first read, so default behaviour is
-    // unchanged from when zoom + X shared a single slider.
-    const CAM_DIST_HYST_T  = 0.5;   // fret-span — twitchy: minimal dead zone
-    const CAM_DIST_HYST_C  = 5.0;   // fret-span — calm: 5-fret span change required
-
-    // Vertical-tilt damping. Drives the tgtLookY self-correction loop in
-    // camUpdate(): how far the fretboard's NDC Y can drift from
-    // DESIRED_NDC_Y before we nudge the camera, and how strongly each
-    // nudge corrects. Twitchy = narrow band + strong correction (re-frame
-    // aggressively); calm = wide band + weak correction (let small drift
-    // ride). Driven by `tiltSmoothing`, mirrors cameraSmoothing on first
-    // read like zoomSmoothing does.
-    // Bounds chosen so the midpoint (tiltSmoothing=0.5) reproduces the
-    // pre-PR hardcoded behaviour (band=0.15, str=0.5). Without that, a
-    // fresh install would silently change the vertical-tilt feel even
-    // though the PR description promises "default behaviour unchanged."
-    const CAM_TILT_BAND_T  = 0.05;  // NDC — twitchy: narrow tolerance
-    const CAM_TILT_BAND_C  = 0.25;  // NDC — calm: wide tolerance, fewer corrections
-    const CAM_TILT_STR_T   = 0.8;   // multiplier — twitchy: strong nudge per correction
-    const CAM_TILT_STR_C   = 0.2;   // multiplier — calm: weak nudge per correction
-
-    // Lock-low zoom range. The cameraLockZoom slider (0..1) blends between
-    // these two multipliers and scales the locked tgtDist. Defaults pick
-    // 1.0× at slider=0.5 so the previous locked view is the midpoint.
-    const CAM_LOCK_ZOOM_MIN = 0.55;  // slider=0 — closest, biggest fretboard
-    const CAM_LOCK_ZOOM_MAX = 1.45;  // slider=1 — furthest
-    const CAM_LOCK_CENTER_FRET = 6;  // default camera X center (first-position midpoint)
-
-    // ── 3D preview: lookahead fret bounds + smoothed focal X / span ─────────
-    /** User-selectable via `cameraMode`. Legacy `classic` in storage maps to `steady`. */
-    const CAMERA_MODE_IDS = ['steady', 'lookahead'];
-    const CAM_LOOKAHEAD_SEC = 3.0;       // fallback when no beats/measures are available
-    const CAM_LOOKAHEAD_MEASURES = 9;    // lookahead window = N measures ahead
-    const CAM_FOCUS_BLEND_RATE = 0.7;
-    const CAM_FRET_EDGE_BLEND = 0.1;
-    const DEFAULT_LOOKAHEAD_FRET_SPAN = 4;
-    /** Schmitt: avoid lock↔dynamic flicker when lookahead maxF jitters at the 12th fret. */
-    const LOOKAHEAD_LOCK_RELEASE_MAXF = 13;
-    const LOOKAHEAD_LOCK_ENGAGE_MAXF = 10;
-    // Note: we deliberately do NOT scale the camUpdate lerp speed with
-    // cameraSmoothing. Smoothing widens the hysteresis dead zones so the
-    // camera stays put through small/repetitive shifts; but when a shift
-    // *does* clear the gate (a real jump to a far fret), we want the slide
-    // to be snappy, not lethargic. The dead zone gates "should we move?",
-    // the BPM-scaled lerp answers "how fast" — keeping those orthogonal
-    // gives the right feel.
-
-    const FOG_START = 200 * K;
-    const FOG_END = 670 * K;
-
-    const DOTS = [3, 5, 7, 9, 12, 15, 17, 19, 21, 24];
-    const DDOTS = new Set([12, 24]);
-    const INLAY_LABEL_FRETS = [3, 5, 7, 9, 12, 15, 17, 19, 22, 24]; // 22 not 21: intentional display choice
-
-    // Fret-column reference markers: floor-aligned fret-number sprites
-    // that scroll toward the hit line every Nth measure. When the chart
-    // has <anchor>, the row uses the inlay cadence (DOTS) around the
-    // anchor fret: two marker positions before and three after the
-    // snapped cadence cell (e.g. anchor fret 7 → 3,5,7,9,12,15).
-    const FRET_COL_MARKER_ANCHOR_BACK = 2;
-    const FRET_COL_MARKER_ANCHOR_FWD = 3;
-
-    /**
-     * @param {number} anchorFret Chart anchor `.fret` (world start fret).
-     * @param {number[]} [cadence] Ascending frets (e.g. DOTS).
-     * @returns {number[]}
-     */
-    function fretColumnMarkersForAnchor(anchorFret, cadence = DOTS) {
-        const f0 = Math.round(Number(anchorFret));
-        if (!Number.isFinite(f0) || cadence.length === 0) return cadence.slice();
-        let iBest = 0;
-        let dBest = Infinity;
-        for (let i = 0; i < cadence.length; i++) {
-            const d = Math.abs(cadence[i] - f0);
-            if (d < dBest || (d === dBest && cadence[i] < cadence[iBest])) {
-                dBest = d;
-                iBest = i;
-            }
-        }
-        const i0 = Math.max(0, iBest - FRET_COL_MARKER_ANCHOR_BACK);
-        const i1 = Math.min(cadence.length, iBest + FRET_COL_MARKER_ANCHOR_FWD + 1);
-        return cadence.slice(i0, i1);
-    }
-
-    // Fast integer key for (t, s) pairs — avoids per-frame string allocation in
-    // hot-path Set lookups. Encodes chart time in 0.1 ms steps (sufficient for
-    // chart-format note precision) combined with the string index.
-    // t range 0–600 s → 0–6,000,000; * 10 + s(0–7) = max 60,000,007 < 2^53 ✓.
-    // The |0 truncates to int32 but the outer multiply stays in float64, so the
-    // key is always a safe JS integer for songs ≤ 214,748 s (well above any song).
-    function _noteKey(t, s) { return ((t * 10000 + 0.5) | 0) * 10 + s; }
-
-    // Binary lower-bound: returns the first index i in arr where arr[i].t >= t.
-    // Assumes arr is sorted ascending by .t (bundle.notes / bundle.chords always are).
-    // Byte-identical to core's bundle.lowerBoundT — kept as a local because this
-    // plugin must run on downlevel hosts whose bundles don't carry the helper
-    // (it's called from ~30 sites incl. top-level helpers that don't receive a
-    // bundle). New code that already holds a bundle should prefer
-    // bundle.lowerBoundT / bundle.lowerBoundTime.
-    function lowerBoundT(arr, t) {
-        let lo = 0, hi = arr.length;
-        while (lo < hi) {
-            const mid = (lo + hi) >>> 1;
-            if (arr[mid].t < t) lo = mid + 1;
-            else hi = mid;
-        }
-        return lo;
-    }
-
-    // Last arrangement <anchor> at or before chart time `t` (sorted by .time).
-    // Mirrors static/highway.js getAnchorAt — until t reaches the first anchor’s
-    // time, the first anchor still defines fret/width.
-    // Binary search: this is called inside per-frame loops (lane slicing,
-    // lookahead sampling, marker spawning), so the linear scan was O(samples *
-    // numAnchors) on dense charts.
-    function getChartAnchorAt(anchorArr, t) {
-        if (!anchorArr || !anchorArr.length) return null;
-        let lo = 0, hi = anchorArr.length;
-        while (lo < hi) {
-            const mid = (lo + hi) >>> 1;
-            if (anchorArr[mid].time <= t) lo = mid + 1;
-            else hi = mid;
-        }
-        return lo === 0 ? anchorArr[0] : anchorArr[lo - 1];
-    }
-
-    /** @returns {{ dMin: number, dMax: number } | null} */
-    function laneBoundsFromAnchor(anc) {
-        if (!anc) return null;
-        let fStart = Math.round(Number(anc.fret));
-        // Match anchorPlayedFretInclusiveSpan(): fret 0 (and below) clamps
-        // to 1, otherwise the lane span ends up one fret narrower than the
-        // played-fret span / label highlighting on charts that emit
-        // <anchor fret="0" width="N">.
-        if (!Number.isFinite(fStart) || fStart < 1) fStart = 1;
-        let w = Number(anc.width);
-        if (!Number.isFinite(w)) w = 4;
-        w = Math.max(1, Math.round(w));
-        const fLast = Math.min(NFRETS, fStart + w - 1);
-        const dMin = Math.max(0, fStart - 1);
-        const dMax = Math.min(NFRETS, fLast);
-        return { dMin, dMax };
-    }
-
-    /** Same horizontal span as the dynamic highway lane: anchor at chart time `t`. */
-    function anchorLaneBoundsAt(anchorArr, t) {
-        if (!anchorArr || !anchorArr.length) return null;
-        return laneBoundsFromAnchor(getChartAnchorAt(anchorArr, t));
-    }
-
-    /**
-     * Inclusive chart-fret indices for the playing window (anchor `fret` + `width`),
-     * e.g. fret=5 width=4 → 5..8. Unlike {@link laneBoundsFromAnchor}'s `dMin`/`dMax`
-     * (diagram wire span), these are the labels shown on gems / row numbers.
-     * @returns {{ f0: number, f1: number } | null}
-     */
-    function anchorPlayedFretInclusiveSpan(anc) {
-        if (!anc) return null;
-        let f0 = Math.round(Number(anc.fret));
-        if (!Number.isFinite(f0) || f0 < 1) f0 = 1;
-        let w = Number(anc.width);
-        if (!Number.isFinite(w)) w = 4;
-        w = Math.max(1, Math.round(w));
-        const f1 = Math.min(NFRETS, f0 + w - 1);
-        return { f0, f1 };
-    }
-
-    function anchorPlayedFretSpanAt(anchorArr, t) {
-        if (!anchorArr || !anchorArr.length) return null;
-        return anchorPlayedFretInclusiveSpan(getChartAnchorAt(anchorArr, t));
-    }
-
-    const FRET_COOLDOWN = 0.5; // seconds a lane fret stays active after last note
-
-    const DIAG_LINGER_S    = 0.55;
-    const DIAG_ENTRANCE_S  = 0.20;
-    const DIAG_CROSSFADE_S = 0.15;
-    const DIAG_SIZE_MIN    = 0.08;
-    const DIAG_SIZE_MAX    = 0.16;
-    const DIAG_CELL_MAX    = 34;
-    // 'bl' and 'br' removed — diagram is top-only. Legacy localStorage values
-    // that contain 'bl'/'br' will fall back to BG_DEFAULTS.chordDiagramPosition
-    // via _bgCoerce (which rejects values not in this list).
-    const CHORD_DIAG_POSITION_IDS = ['tl', 'tr'];
-
-    /** Default chord-box rim / fill gradient (teal family). */
-    const CHORD_BOX_TEAL_HEX = 0x00d2d5;
-    const CHORD_BOX_TEAL_DARK_HEX = 0x003c3d;
-    /** Frame edge quads: premultiplied-ish alpha match (~128/255). */
-    const CHORD_BOX_EDGE_ALPHA = 128 / 255;
-    /** Interior gradient strip alpha on both stops (~32/255). */
-    const CHORD_BOX_FILL_GRAD_ALPHA = 32 / 255;
-    /** Arpeggio interior wash; dedicated gradient tex so teal map doesn’t dominate. */
-    const ARPEGGIO_BOX_BLUE_HEX = 0x454BB6;
-    const ARPEGGIO_BOX_BLUE_DARK_HEX = 0x2D3190;
-    /** Arpeggio rim accent and lane tint. */
-    const ARPEGGIO_RIM_BLUE_HEX = 0x454BB6;
-    /** Post-hit chord-frame rim tints driven by the note-state provider
-     *  (feedBack#254). Applied only to the teal frame during the linger
-     *  fade (chDt <= 0) when a scorer is attached.
-     *  Matches the gem hit/miss colours so chord frame and note body
-     *  give a consistent signal:
-     *    hit  → neon spring-green 0x22ff88 (same as mHitBright).
-     *    miss → hot magenta-red 0xff0066 (same as mMissOutline). */
-    const CHORD_BOX_HIT_BRIGHT_HEX  = 0x22ff88;
-    const CHORD_BOX_MISS_DARK_HEX   = 0xff0066;
-
-    /** Fret-number label tints — gold on approaching/active notes, muted blue when idle. */
-    const FRET_LABEL_GOLD_HEX = '#D8A636';
-    const FRET_LABEL_IDLE_HEX = '#9ab8cc';
-
-    /** 3D chord-box rim bars (thin on all chords, including repeats in a sequence). */
-    const CHORD_FRAME_RIM_MIN = 0.055;       // × K — floor thickness
-    const CHORD_FRAME_RIM_FRAC_H = 0.028;    // × fullChordBoxH
-    const CHORD_FRAME_RIM_Z_MIN = 0.048;      // × K — depth squash
-    const CHORD_FRAME_RIM_Z_SCAL = 0.68;     // thickZ scales with ft
-    /**
-     * Highway arpeggio frame uses ``inferArpeggioFromNotePattern`` only inside this
-     * window around ``ch.t``. Hand-shape spans can cover many seconds and several
-     * separate strums of the same voicing; a full-span scan mis-detects arpeggio
-     * from beats that belong to different chord rows.
-     */
-    const ARP_FRAME_ONSET_PAD_S = 0.06;
-    const ARP_FRAME_ONSET_CLUSTER_S = 0.26;
-    /**
-     * The chart format encodes fast alternating power chords (e.g. D5/D#5 gallops) as
-     * very short ``<handShape>`` rows (~0.05–0.2 s). Note-stream arpeggio
-     * inference must not treat strum spread across strings as arpeggio there —
-     * it false-triggers lavender highway rails / frames (see Frantic ~2:36).
-     */
-    const ARP_INFER_MIN_HAND_SHAPE_SPAN_S = 0.21;
-    /**
-     * In a **short** chart window, chord strums (same voicing, strings picked
-     * within ~30–45 ms) barely exceed this total spread; real arpeggios in that
-     * window are usually slower across strings OR have 4+ plucks.
-     */
-    const ARP_INFER_STRUM_VS_ARP_SPREAD_MIN_S = 0.047;
-    /**
-     * If more than ``shape.size + ARP_INFER_MULTI_STRUM_HIT_SLACKS`` matching picks
-     * sit inside a non-trivial hand-shape window, the chart is almost certainly
-     * **repeated strums** of the same chord (or gallops), not one arpeggio sweep.
-     */
-    const ARP_INFER_MULTI_STRUM_HIT_SLACK = 2;
-    /** ``timeWin`` span above which we apply the multi-strum hit-count cap. */
-    const ARP_INFER_MULTI_STRUM_WIN_MIN_S = 0.26;
-    /**
-     * Minimum staggered hits inside a hand-shape window for note-stream arpeggio
-     * inference. A genuine arpeggio sweeps several strings of the held shape;
-     * a 2-note melodic motif inside a multi-string ``<handShape>`` (e.g. Jackson 5
-     * "I Want You Back" ~0:27 — Fm7 transition fingering with two plucks on
-     * strings 4–5) earlier registered as arpeggio and produced a stray lavender
-     * chord frame + purple lane outer dividers. Cap at ``min(shape.size, 3)``
-     * so 2-string voicings still infer normally and 3+ string templates need
-     * a real sweep.
-     */
-    const ARP_INFER_MIN_HITS_VS_SHAPE_CAP = 3;
-
-    /* ======================================================================
-     *  Pure helpers
-     * ====================================================================== */
-
-    // Logarithmic spacing — mirrors real guitar fret geometry (12th root of 2).
-    const _fretXLog = f => {
-        if (f <= 0) return 0;
-        const raw = FRET_SCALE - FRET_SCALE / Math.pow(2, f / 12);
-        if (f <= FRET_SPACING_ANCHOR_F) return raw;
-        const rawAnchor = FRET_SCALE - FRET_SCALE / Math.pow(2, FRET_SPACING_ANCHOR_F / 12);
-        return rawAnchor + (raw - rawAnchor) * FRET_SPACING_STRETCH_ABOVE12;
-    };
-    // Uniform spacing — same column width per fret (chart-format style).
-    // Total board width equals the logarithmic NFRETS position for consistency.
-    const _fretXUniStep = _fretXLog(NFRETS) / NFRETS;
-    const _fretXUni = f => f <= 0 ? 0 : f * _fretXUniStep;
-
-    let _h3dFretUniform = true;
-    try { _h3dFretUniform = localStorage.getItem('highway_3d.fretSpacing') !== 'logarithmic'; } catch (_) {}
-    const fretX = f => _h3dFretUniform ? _fretXUni(f) : _fretXLog(f);
-
-    window.h3dSetFretSpacing = mode => {
-        // Validate against the two supported modes before persisting so an
-        // unexpected input can't leave an invalid value in localStorage
-        // (mirrors h3dBgSetFretNumberGhostScope's allowlist guard). No-op
-        // when the stored mode is already what was requested.
-        const m = mode === 'logarithmic' ? 'logarithmic' : 'uniform';
-        try {
-            if (localStorage.getItem('highway_3d.fretSpacing') === m) return;
-            localStorage.setItem('highway_3d.fretSpacing', m);
-        } catch (_) {}
-        // Apply live rather than reloading the page — a full page reload
-        // reboots the SPA to the home screen (index.html's `.screen.active`),
-        // ejecting the user from Settings. Rebind the module-scope flag so
-        // panels mounted later this session pick up the new mode, recompute
-        // the fretX-derived scalars, then broadcast a change so every mounted
-        // panel rebuilds its board. Same live-update path as every other
-        // 3D-highway setting.
-        _h3dFretUniform = (m !== 'logarithmic');
-        _recomputeFretSpacingDerived();
-        _bgEmitChange('fretSpacing');
-    };
-
-    const fretMid = f => (f <= 0 ? -2 * K : (fretX(f - 1) + fretX(f)) / 2);
-    /** World-space width of fret column (wires f−1 .. f); used to scale row markers past ~12. */
-    function fretColumnWorldW(f) {
-        const fi = Math.round(Number(f));
-        if (!Number.isFinite(fi) || fi <= 0) return Math.abs(fretX(1) - fretX(0));
-        const lo = Math.min(NFRETS, Math.max(1, fi));
-        return Math.abs(fretX(lo) - fretX(lo - 1));
-    }
-    /** Reference column (~mid board): prior fixed K-based sprites matched this neighborhood. */
-    const FRET_LABEL_SCALE_REF_FRET = 5;
-    // `let` (not `const`): recomputed by _recomputeFretSpacingDerived when the
-    // user flips Uniform/Logarithmic at runtime so label scaling tracks the
-    // new geometry without a page reload.
-    let _fretLabelScaleRefW = Math.max(1e-8, fretColumnWorldW(FRET_LABEL_SCALE_REF_FRET));
-    function fretLabelScaleForFret(f) {
-        const w = fretColumnWorldW(f);
-        const m = w / _fretLabelScaleRefW;
-        return Math.max(0.32, Math.min(1.45, m));
-    }
-    const dZ = dt => -dt * TS;
-
-    /**
-     * Pitched slide uses `sl`, unpitched uses `slu` (slide-to vs unpitched slide fields).
-     * Prefer `sl` when both are present — matches RS wire.
-     * @returns {{ endFret: number, unpitched: boolean } | null}
-     */
-    function slideTrailEnd(n) {
-        const sl = n.sl;
-        const slu = n.slu;
-        if (Number.isFinite(sl) && sl >= 0) {
-            return { endFret: sl | 0, unpitched: false };
-        }
-        if (Number.isFinite(slu) && slu >= 0) {
-            return { endFret: slu | 0, unpitched: true };
-        }
-        return null;
-    }
-
-    /**
-     * Lateral slide offset along the fretboard during sustain — easing
-     * mirrors the pitched/unpitched slide offset convention above.
-     * @param {{ endFret: number, unpitched: boolean } | null} [st_] from slideTrailEnd
-     */
-    function slideOffsetWorldX(n, chartTime, st_) {
-        const st = st_ || slideTrailEnd(n);
-        if (!st || n.f <= 0 || !(n.sus > 0)) return 0;
-        const denom = Math.max(n.sus, 1e-6);
-        const p = Math.max(0, Math.min(1, (chartTime - n.t) / denom));
-        const startX = fretMid(n.f);
-        const endX = fretMid(st.endFret);
-        const w = st.unpitched
-            ? 1 - Math.sin((1 - p) * Math.PI / 2)
-            : Math.pow(Math.sin(p * Math.PI / 2), 3);
-        return (endX - startX) * w;
-    }
-
-    // Camera tgtDist building blocks. Both the dynamic (camera-follow)
-    // and locked (frets 1-12) branches compose tgtDist from these, so
-    // any future tuning of the base zoom curve or low-fret pullback
-    // lands in both branches without drift.
-    //   span    — camDistMax - camDistMin in fret-span units
-    //   minFret — lowest fretted note in the camera window (or 1 for
-    //             the locked branch, which assumes nut chords)
-    const camBaseDistU = span => 65 + Math.max(span, 4) * 3;
-    const camLowFretPullbackU = minFret => Math.max(0, 5 - minFret) * 4;
-
-    // World-units-per-fret near mid-neck. Used by the camera-X hysteresis
-    // gate (issue #34) to convert a fret-equivalent dead zone into world
-    // units. Pure function of SCALE — hoist out of update()'s hot path.
-    // `let` (not `const`): recomputed alongside _fretLabelScaleRefW when the
-    // fret-spacing mode flips at runtime — see _recomputeFretSpacingDerived.
-    let FRET_WIDTH_MID = fretX(7) - fretX(6);
-
-    // Recompute the fretX-derived scalars baked at module init. Called from
-    // h3dSetFretSpacing after _h3dFretUniform flips so label scaling and the
-    // camera hysteresis threshold track the newly chosen spacing — the live
-    // alternative to the old location.reload(), which ejected the user from
-    // Settings back to the home screen.
-    function _recomputeFretSpacingDerived() {
-        _fretLabelScaleRefW = Math.max(1e-8, fretColumnWorldW(FRET_LABEL_SCALE_REF_FRET));
-        FRET_WIDTH_MID = fretX(7) - fretX(6);
-    }
-
-    function computeBPM(beats, t) {
-        if (!beats || beats.length < 2) return 120;
-        let lo = 0, hi = beats.length;
-        while (lo < hi) {
-            const mid = (lo + hi) >> 1;
-            if (beats[mid].time < t) lo = mid + 1; else hi = mid;
-        }
-        let closest = lo;
-        if (lo === beats.length) closest = beats.length - 1;
-        else if (lo > 0 && Math.abs(beats[lo - 1].time - t) < Math.abs(beats[lo].time - t)) closest = lo - 1;
-        const start = Math.max(0, closest - 2);
-        const end = Math.min(beats.length - 1, closest + 2);
-        let sum = 0, count = 0;
-        for (let i = start; i < end; i++) {
-            const dt = beats[i + 1].time - beats[i].time;
-            if (dt > 0) { sum += dt; count++; }
-        }
-        return count > 0 && sum > 0 ? 60 / (sum / count) : 120;
-    }
-
-    // Build a horizontal gaussian DataTexture for the sustain-rail bloom effect.
-    // Returns a W×1 RGBA texture where alpha follows exp(-0.5*(u−0.5)²/σ²),
-    // peaking at 1.0 in the centre. With the default σ=0.28 the edges retain
-    // ~0.20 alpha (not fully transparent) — a deliberately soft, wide falloff
-    // so the additive bloom fades gradually rather than cutting off sharply.
-    // Power-of-two width keeps WebGL mipmapping happy.
-    function _makeGaussTex(ThreeLib, w = 128, sigma = 0.28) {
-        const data = new Uint8Array(w * 4);
-        for (let i = 0; i < w; i++) {
-            const u = i / (w - 1);
-            const d = (u - 0.5) / sigma;
-            const v = Math.exp(-0.5 * d * d);
-            const a = Math.round(v * 255);
-            data[i * 4]     = 255;
-            data[i * 4 + 1] = 255;
-            data[i * 4 + 2] = 255;
-            data[i * 4 + 3] = a;
-        }
-        const tex = new ThreeLib.DataTexture(data, w, 1, ThreeLib.RGBAFormat);
-        // LinearFilter on both axes so the bloom plane interpolates smoothly
-        // when scaled — the default NearestFilter causes visible banding.
-        tex.magFilter = ThreeLib.LinearFilter;
-        tex.minFilter = ThreeLib.LinearFilter;
-        tex.needsUpdate = true;
-        return tex;
-    }
-
-    /* ======================================================================
-     *  Three.js module — lazily loaded, memoized
-     * ====================================================================== */
-
-    let T = null;
-    let threeLoadPromise = null;
-    function loadThree() {
-        if (!threeLoadPromise) {
-            threeLoadPromise = import(THREE_URL)
-                .then(mod => { T = mod; return mod; })
-                .catch(() => import(THREE_CDN)
-                    .then(mod => { T = mod; return mod; })
-                    .catch(e => {
-                        console.error('[3D-Hwy] Three.js load failed:', e);
-                        threeLoadPromise = null;
-                        throw e;
-                    }));
-        }
-        return threeLoadPromise;
-    }
-
-    /* ======================================================================
-     *  Splitscreen helpers
-     * ====================================================================== */
-
-    function _ssActive() {
-        const ss = window.feedBackSplitscreen;
-        if (!ss || typeof ss.isActive !== 'function' || !ss.isActive()) return false;
-        return typeof ss.isCanvasFocused === 'function'
-            && typeof ss.onFocusChange === 'function'
-            && typeof ss.offFocusChange === 'function';
-    }
-
-    function _ssIsCanvasFocused(highwayCanvas) {
-        const ss = window.feedBackSplitscreen;
-        if (!_ssActive()) return true;
-        return !!(ss && typeof ss.isCanvasFocused === 'function' &&
-            ss.isCanvasFocused(highwayCanvas));
-    }
-
-    // Shortcut for the wide-pane framing tuner. Opens/closes the floating panel
-    // (the A/B on/off and the per-pane target live inside it now). Registered
-    // once per session via a module-level guard (it drives shared module state,
-    // so per-instance registration would stack duplicate handlers and cancel
-    // itself out); it's a harmless debug control, so it is never unregistered.
-    // No-ops where the core shortcut API isn't present (older core / borrowed
-    // contexts).
-    let _tunerShortcutRegistered = false;
-    function _registerTunerShortcut() {
-        if (_tunerShortcutRegistered) return;
-        if (typeof window.registerShortcut !== 'function') return;
-        _tunerShortcutRegistered = true;
-        try {
-            window.registerShortcut({
-                key: 'A',   // uppercase e.key → produced with Shift held (Shift+A)
-                description: '3D Highway: open/close wide-pane framing tuner (Shift+A)',
-                scope: 'player',
-                handler: () => {
-                    // Open/close the live tuner panel. The A/B on/off and the
-                    // per-pane target now live in the panel itself, so the
-                    // shortcut is just a dismiss/reveal.
-                    _toggleAspectPanel();
-                },
-            });
-        } catch (e) {
-            _tunerShortcutRegistered = false;   // allow a later retry if it threw
-        }
-    }
-
-    // ── Wide-pane framing: live tuner bridge + panel ──────────────────────────
-    // window.__h3dAspectTune is the single source of truth the renderer reads
-    // each frame (see effectiveVfov + camUpdate). The defaults reproduce the
-    // current framing exactly (enabled:false). Values persist to localStorage so
-    // a tuning session survives reloads; the floating panel (Shift+A) writes the
-    // same object live. All of this is a debug aid — none of it runs unless the
-    // user opts in.
-    // Versioned key: the first iteration shipped a broken default (enabled:true,
-    // baseVfov:30) and may have persisted it. Bumping the key ignores that stale
-    // state so the corrected default-off config actually takes effect.
-    const _ASPECT_LS = 'h3d_aspect_tune2';
-    // Working defaults. Default OFF, so out of the box this is an exact no-op —
-    // every pane renders byte-for-byte as before (effectiveVfov returns
-    // BASE_VFOV and the pose nudges gate off). The config is also coherent when
-    // a tester turns it ON via Shift+A: baseVfov == BASE_VFOV so normal ~16:9
-    // panes (single-player, most 2x2) stay at 70° even enabled, and only panes
-    // wider than startAspect (2.25) engage the Hor+ hold; blend:1 makes that
-    // hold actually take effect; minVfovDeg (28) sits below baseVfov so the floor
-    // is a real floor. The pose nudges are the in-progress wide-pane look a
-    // tester sees once enabled. localStorage overrides all of this per machine.
-    const _ASPECT_DEFAULTS = {
-        enabled: false, baseVfov: BASE_VFOV, startAspect: 2.25, hfovDeg: null,
-        blend: 1, minVfovDeg: HORPLUS_MIN_VFOV, splitOnly: false,
-        heightMul: 0.30, distMul: 0.95, pitchAdd: -1.5, lookDepthMul: 1,
-    };
-    // Slider specs (numeric fields). Checkboxes (enabled/splitOnly) + the hfov
-    // override are handled separately in the panel builder. Ranges are wide on
-    // purpose — this is a tuning aid, the no-op default sits mid-range.
-    const _ASPECT_FIELDS = [
-        { k: 'baseVfov',     label: 'Base vFOV°',   min: 18,  max: 90,  step: 1 },
-        { k: 'startAspect',  label: 'Start aspect', min: 1.0, max: 4.0, step: 0.05 },
-        { k: 'blend',        label: 'Blend',        min: 0,   max: 1,   step: 0.05 },
-        { k: 'minVfovDeg',   label: 'Min vFOV°',    min: 10,  max: 60,  step: 1 },
-        { k: 'heightMul',    label: 'Height ×',     min: 0.1, max: 2.5, step: 0.05 },
-        { k: 'distMul',      label: 'Dolly ×',      min: 0.2, max: 3.0, step: 0.05 },
-        { k: 'pitchAdd',     label: 'Pitch +',      min: -40, max: 40,  step: 0.5 },
-        // Aims the camera further down the neck (>1) or pulls the aim back (<1).
-        // This is the lever that flattens the mid-distance "hump" toward a
-        // straight gradual recede.
-        { k: 'lookDepthMul', label: 'Look depth',   min: 0.2, max: 3.0, step: 0.05 },
-    ];
-    let _aspectPanelEl = null;        // the floating panel root (built once)
-    let _aspectPanelRO = null;        // readout <div>
-    let _aspectPanelRAF = 0;          // readout poll handle
-    let _aspectTargetSel = null;      // the "Target" <select>
-    let _aspectTgtRow = null;         // the Target row (hidden when only one pane)
-    let _aspectHfovCb = null;         // hfov-override checkbox (synced explicitly)
-    let _aspectHfovSl = null;         // hfov-override slider
-    // Which pane the panel edits. '' = all panes (writes the shared base object);
-    // a pane key ('arr:<name>' or the fallback 'pane:<uid>') writes that pane's
-    // sparse override, so one split pane can be framed independently.
-    let _aspectEditTarget = '';
-    // Bumped when the SET of live panes changes (add/prune) so the panel rebuilds
-    // the Target dropdown — never on a per-frame label re-report, which would
-    // flicker the <select>.
-    let _aspectPanesDirty = true;
-    // Monotonic counter for the per-instance fallback key (when a pane has no
-    // arrangement name to key by).
-    let _aspectPaneCounter = 0;
-    function _aspectNowMs() {
-        try { if (performance && performance.now) return performance.now(); } catch (e) {}
-        try { return Date.now(); } catch (e) { return 0; }   // keep pruning functional
-    }
-    // Pane key: prefer the arrangement name ('arr:Bass') so a pane's framing is
-    // stable across songs AND distinct between split panes, with no dependency on
-    // the external splitscreen panel index (which isn't always available). Fall
-    // back to a per-instance id ('pane:3') when there's no arrangement.
-    function _aspectPaneKey(arrangement, uid) {
-        const a = (typeof arrangement === 'string') ? arrangement.trim() : '';
-        return a ? ('arr:' + a) : ('pane:' + uid);
-    }
-    // Human label derived from the key.
-    function _aspectPaneLabel(paneKey) {
-        if (paneKey.slice(0, 4) === 'arr:') return paneKey.slice(4);
-        if (paneKey.slice(0, 5) === 'pane:') return 'Pane ' + paneKey.slice(5);
-        return paneKey;
-    }
-
-    // Get-or-create the shared bridge object, seeded from defaults + localStorage.
-    // May carry a sparse `__panels` map of per-pane overrides.
-    function _aspectTune() {
-        let t = window.__h3dAspectTune;
-        if (!t || typeof t !== 'object') {
-            t = Object.assign({}, _ASPECT_DEFAULTS);
-            try {
-                const raw = localStorage.getItem(_ASPECT_LS);
-                if (raw) Object.assign(t, JSON.parse(raw));
-            } catch (e) {}
-            window.__h3dAspectTune = t;
-        }
-        return t;
-    }
-    // Bumped on every tune mutation (all writes funnel through _aspectPersist) so
-    // the per-pane resolve cache below can invalidate cheaply.
-    let _aspectRev = 0;
-    function _aspectPersist() {
-        _aspectRev++;
-        try {
-            const t = _aspectTune(), out = {};
-            Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = t[k]; });
-            // Persist per-pane overrides keyed by arrangement ('arr:*') only, so a
-            // pane's framing carries across songs. Instance-id fallback keys
-            // ('pane:*') are session-only — persisting them would leak a new key
-            // every reload.
-            if (t.__panels) {
-                const p = {}; let any = false;
-                Object.keys(t.__panels).forEach((k) => {
-                    if (k.slice(0, 4) === 'arr:') { p[k] = t.__panels[k]; any = true; }
-                });
-                if (any) out.__panels = p;
-            }
-            localStorage.setItem(_ASPECT_LS, JSON.stringify(out));
-        } catch (e) {}
-    }
-
-    // Resolve the effective tune for a pane: the shared base, with that pane's
-    // override keys (if any) laid on top. Called every frame per renderer, so the
-    // merged object is memoized per pane and only rebuilt when the tune mutates
-    // (_aspectRev changes). Panes with no override return the base directly (no
-    // allocation).
-    const _aspectResolveCache = new Map();   // paneKey -> { rev, obj }
-    function _resolveTuneFor(paneKey) {
-        const base = _aspectTune();
-        const ov = base.__panels && base.__panels[paneKey];
-        if (!ov) return base;
-        const c = _aspectResolveCache.get(paneKey);
-        if (c && c.rev === _aspectRev) return c.obj;
-        const out = {};
-        Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = (k in ov) ? ov[k] : base[k]; });
-        _aspectResolveCache.set(paneKey, { rev: _aspectRev, obj: out });
-        return out;
-    }
-    // Record a live pane so the Target dropdown can list it. Called every frame
-    // by each renderer with its pane key. `seen` is refreshed each call for
-    // pruning; the dropdown is only marked dirty when a pane is newly added — not
-    // on every re-report, which would flicker the <select>.
-    function _aspectRegisterPane(paneKey) {
-        const reg = window.__h3dAspectPanes || (window.__h3dAspectPanes = {});
-        const label = _aspectPaneLabel(paneKey);
-        let e = reg[paneKey];
-        if (!e) { e = reg[paneKey] = { label, seen: 0 }; _aspectPanesDirty = true; }
-        else if (e.label !== label) { e.label = label; _aspectPanesDirty = true; }
-        e.seen = _aspectNowMs();
-    }
-    // Drop panes not reported recently (song change, split teardown, pane close).
-    function _aspectPrunePanes() {
-        const reg = window.__h3dAspectPanes;
-        if (!reg) return;
-        const now = _aspectNowMs();
-        const ro = window.__h3dAspectReadout;
-        Object.keys(reg).forEach((k) => {
-            if (now - (reg[k].seen || 0) > 1500) {
-                delete reg[k];
-                // Prune the matching readout slot so it can't grow unbounded as
-                // songs/arrangements churn, and drop a dangling __last pointer.
-                if (ro) { delete ro[k]; if (ro.__last === k) delete ro.__last; }
-                _aspectPanesDirty = true;
-            }
-        });
-    }
-
-    // True while _syncAspectPanel is programmatically refreshing controls, so the
-    // synthetic 'input' events it dispatches to update labels don't write back
-    // into the tune (which would populate a full override for every field and
-    // spam localStorage). Real user input runs with this false.
-    let _aspectSyncing = false;
-    // Read/write against the current edit target ('' → base, else pane override).
-    function _aspectReadVal(k) {
-        const base = _aspectTune();
-        if (!_aspectEditTarget) return base[k];
-        const ov = base.__panels && base.__panels[_aspectEditTarget];
-        return (ov && (k in ov)) ? ov[k] : base[k];
-    }
-    function _aspectWriteVal(k, v) {
-        const base = _aspectTune();
-        if (!_aspectEditTarget) { base[k] = v; }
-        else {
-            const m = base.__panels || (base.__panels = {});
-            (m[_aspectEditTarget] || (m[_aspectEditTarget] = {}))[k] = v;
-        }
-        _aspectPersist();
-    }
-    // Clear a field: for the base target set the explicit auto value (null); for a
-    // pane target delete the override key so the pane re-inherits the base value
-    // (and drop the pane's override object once it's empty).
-    function _aspectClearVal(k) {
-        const base = _aspectTune();
-        if (!_aspectEditTarget) { base[k] = null; }
-        else {
-            const m = base.__panels, ov = m && m[_aspectEditTarget];
-            if (ov) { delete ov[k]; if (!Object.keys(ov).length) delete m[_aspectEditTarget]; }
-        }
-        _aspectPersist();
-    }
-
-    // (Re)build the Target dropdown from the live pane registry, preserving the
-    // current selection when it's still valid.
-    function _aspectBuildTargets() {
-        if (!_aspectTargetSel) return;
-        // Don't yank a dropdown the user is actively interacting with — leave it
-        // dirty and rebuild on a later tick once it's no longer focused.
-        if (document.activeElement === _aspectTargetSel) return;
-        const reg = window.__h3dAspectPanes || {};
-        const keys = Object.keys(reg).sort();
-        _aspectTargetSel.innerHTML = '';
-        const all = document.createElement('option');
-        all.value = ''; all.textContent = keys.length > 1 ? 'All panes' : 'All';
-        _aspectTargetSel.appendChild(all);
-        keys.forEach((pk) => {
-            const o = document.createElement('option');
-            o.value = pk; o.textContent = reg[pk].label;
-            _aspectTargetSel.appendChild(o);
-        });
-        // Force the edit target back to "All" when the Target row is hidden
-        // (single pane) or the selected pane is gone — otherwise a stale pane
-        // target would silently route edits into a hidden (and persistent
-        // arr:*) override in single-player.
-        if (keys.length <= 1 || (_aspectEditTarget && !reg[_aspectEditTarget])) {
-            _aspectEditTarget = '';
-        }
-        _aspectTargetSel.value = _aspectEditTarget;
-        // The Target row only matters with more than one pane (a split). With a
-        // single pane there's nothing to disambiguate, so hide it.
-        if (_aspectTgtRow) _aspectTgtRow.style.display = keys.length > 1 ? '' : 'none';
-        _aspectPanesDirty = false;
-    }
-
-    function _ensureAspectPanel() {
-        if (_aspectPanelEl || typeof document === 'undefined') return;
-        const wrap = document.createElement('div');
-        wrap.id = 'h3d-aspect-tuner';
-        wrap.style.cssText = [
-            'position:fixed', 'top:64px', 'right:12px', 'z-index:99999',
-            'width:236px', 'padding:10px 12px', 'border-radius:8px',
-            'background:rgba(12,18,28,0.92)', 'border:1px solid rgba(120,150,200,0.35)',
-            'box-shadow:0 6px 24px rgba(0,0,0,0.5)', 'color:#cfe0f5',
-            'font:11px/1.35 system-ui,sans-serif', 'user-select:none',
-            'pointer-events:auto',
-        ].join(';');
-
-        // Header: title + close (×). Close hides the panel; the feature keeps
-        // whatever enabled state it had — this is a dismiss, not an A/B toggle.
-        const hdr = document.createElement('div');
-        hdr.style.cssText = 'display:flex;align-items:center;justify-content:space-between;margin-bottom:6px;';
-        const title = document.createElement('div');
-        title.textContent = 'Wide-pane framing';
-        title.style.cssText = 'font-weight:700;color:#e8c040;';
-        const close = document.createElement('button');
-        close.type = 'button';                 // never submit if nested in a <form>
-        close.textContent = '×';
-        close.title = 'Close (Shift+A)';
-        close.setAttribute('aria-label', 'Close');
-        close.style.cssText = 'border:none;background:transparent;color:#cfe0f5;font-size:17px;line-height:1;cursor:pointer;padding:0 2px;';
-        close.addEventListener('click', () => _setAspectPanelVisible(false));
-        hdr.appendChild(title); hdr.appendChild(close); wrap.appendChild(hdr);
-
-        // Target selector — which pane the controls below edit.
-        const tgtRow = document.createElement('div'); tgtRow.style.cssText = 'margin:2px 0 7px;';
-        _aspectTgtRow = tgtRow;
-        const tgtLab = document.createElement('div');
-        tgtLab.textContent = 'Target'; tgtLab.style.cssText = 'color:#9fb0c8;margin-bottom:2px;';
-        _aspectTargetSel = document.createElement('select');
-        _aspectTargetSel.setAttribute('aria-label', 'Target pane');
-        _aspectTargetSel.style.cssText = 'width:100%;background:rgba(30,44,66,0.9);color:#cfe0f5;border:1px solid rgba(120,150,200,0.4);border-radius:4px;padding:3px;';
-        _aspectTargetSel.addEventListener('change', () => {
-            _aspectEditTarget = _aspectTargetSel.value; _syncAspectPanel();
-        });
-        tgtRow.appendChild(tgtLab); tgtRow.appendChild(_aspectTargetSel); wrap.appendChild(tgtRow);
-        _aspectBuildTargets();
-
-        // enabled + splitOnly checkboxes (per-target)
-        [['enabled', 'Enabled'], ['splitOnly', 'Split panes only']].forEach(([k, lbl]) => {
-            const row = document.createElement('label');
-            row.style.cssText = 'display:flex;align-items:center;gap:6px;margin:2px 0;cursor:pointer;';
-            const cb = document.createElement('input');
-            cb.type = 'checkbox'; cb.checked = !!_aspectReadVal(k); cb.dataset.k = k;
-            cb.addEventListener('change', () => { _aspectWriteVal(k, cb.checked); });
-            const span = document.createElement('span'); span.textContent = lbl;
-            row.appendChild(cb); row.appendChild(span); wrap.appendChild(row);
-        });
-
-        // numeric sliders (per-target)
-        _ASPECT_FIELDS.forEach((f) => {
-            const row = document.createElement('div');
-            row.style.cssText = 'margin:5px 0;';
-            const head = document.createElement('div');
-            head.style.cssText = 'display:flex;justify-content:space-between;';
-            const lab = document.createElement('span'); lab.textContent = f.label;
-            const val = document.createElement('span');
-            val.style.cssText = 'color:#8fb6ff;font-variant-numeric:tabular-nums;';
-            head.appendChild(lab); head.appendChild(val); row.appendChild(head);
-            const sl = document.createElement('input');
-            sl.type = 'range'; sl.min = f.min; sl.max = f.max; sl.step = f.step;
-            const rv = _aspectReadVal(f.k);
-            sl.value = Number.isFinite(rv) ? rv : _ASPECT_DEFAULTS[f.k];
-            sl.dataset.k = f.k;
-            sl.style.cssText = 'width:100%;';
-            const show = () => { val.textContent = (+sl.value).toFixed(f.step < 1 ? 2 : 0); };
-            show();
-            sl.addEventListener('input', () => {
-                show();                                   // label always refreshes
-                if (!_aspectSyncing) _aspectWriteVal(f.k, parseFloat(sl.value));
-            });
-            row.appendChild(sl); wrap.appendChild(row);
-        });
-
-        // hfov override (checkbox enables a slider; off → hfovDeg=null = auto)
-        {
-            const row = document.createElement('div'); row.style.cssText = 'margin:5px 0;';
-            const head = document.createElement('label');
-            head.style.cssText = 'display:flex;align-items:center;gap:6px;cursor:pointer;';
-            const cb = document.createElement('input');
-            cb.type = 'checkbox'; cb.checked = Number.isFinite(_aspectReadVal('hfovDeg'));
-            const lbl = document.createElement('span'); lbl.textContent = 'Override held hFOV°';
-            head.appendChild(cb); head.appendChild(lbl); row.appendChild(head);
-            const sl = document.createElement('input');
-            sl.type = 'range'; sl.min = 40; sl.max = 160; sl.step = 1;
-            const hv = _aspectReadVal('hfovDeg');
-            sl.value = Number.isFinite(hv) ? hv : 102;
-            sl.disabled = !cb.checked;
-            sl.style.cssText = 'width:100%;';
-            cb.addEventListener('change', () => {
-                if (_aspectSyncing) return;
-                sl.disabled = !cb.checked;
-                if (cb.checked) _aspectWriteVal('hfovDeg', parseFloat(sl.value));
-                else _aspectClearVal('hfovDeg');   // base → auto (null); pane → re-inherit base
-            });
-            sl.addEventListener('input', () => {
-                if (!_aspectSyncing && cb.checked) _aspectWriteVal('hfovDeg', parseFloat(sl.value));
-            });
-            row.appendChild(sl); wrap.appendChild(row);
-            _aspectHfovCb = cb; _aspectHfovSl = sl;
-        }
-
-        // live readout
-        _aspectPanelRO = document.createElement('div');
-        _aspectPanelRO.style.cssText = 'margin-top:6px;padding-top:6px;border-top:1px solid rgba(120,150,200,0.25);color:#9fb;font-variant-numeric:tabular-nums;';
-        _aspectPanelRO.textContent = 'aspect — · vFOV —';
-        wrap.appendChild(_aspectPanelRO);
-
-        // buttons
-        const btnRow = document.createElement('div');
-        btnRow.style.cssText = 'display:flex;gap:6px;margin-top:8px;';
-        const mkBtn = (txt, fn) => {
-            const b = document.createElement('button');
-            b.type = 'button';                 // never submit if nested in a <form>
-            b.textContent = txt;
-            b.style.cssText = 'flex:1;padding:4px 0;border-radius:5px;border:1px solid rgba(120,150,200,0.4);background:rgba(40,60,90,0.6);color:#cfe0f5;cursor:pointer;font:11px system-ui;';
-            b.addEventListener('click', fn);
-            return b;
-        };
-        // Reset: for "All" restores the shared defaults exactly; for a pane
-        // clears that pane's override so it inherits the shared base again. Panel
-        // visibility is independent (Shift+A / ×), so Reset doesn't force it open.
-        btnRow.appendChild(mkBtn('Reset', () => {
-            const base = _aspectTune();
-            if (!_aspectEditTarget) {
-                Object.keys(_ASPECT_DEFAULTS).forEach((k) => { base[k] = _ASPECT_DEFAULTS[k]; });
-            } else if (base.__panels) {
-                delete base.__panels[_aspectEditTarget];
-            }
-            _aspectPersist(); _syncAspectPanel();
-        }));
-        // Copy: the resolved values for the current target, as JSON.
-        btnRow.appendChild(mkBtn('Copy', () => {
-            const r = _aspectEditTarget ? _resolveTuneFor(_aspectEditTarget) : _aspectTune();
-            const out = {};
-            Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = r[k]; });
-            const json = JSON.stringify(out, null, 2);
-            try { console.log('[h3d] wide-pane framing values (' + (_aspectEditTarget || 'all') + '):\n' + json); } catch (e) {}
-            try { if (navigator.clipboard) navigator.clipboard.writeText(json); } catch (e) {}
-        }));
-        wrap.appendChild(btnRow);
-
-        document.body.appendChild(wrap);
-        _aspectPanelEl = wrap;
-        _aspectPanelEl.style.display = 'none';
-    }
-
-    // Push the current target's values back into the panel controls (after Reset,
-    // a target switch, or an external edit). Cheap; only runs on demand.
-    function _syncAspectPanel() {
-        if (!_aspectPanelEl) return;
-        _aspectBuildTargets();
-        // Guard so the synthetic 'input' events below only refresh labels and
-        // don't write the read-back values into the target (which would turn a
-        // sparse pane override into a full one and spam localStorage).
-        _aspectSyncing = true;
-        try {
-            _aspectPanelEl.querySelectorAll('input[type=checkbox][data-k]').forEach((cb) => {
-                cb.checked = !!_aspectReadVal(cb.dataset.k);
-            });
-            _aspectPanelEl.querySelectorAll('input[type=range][data-k]').forEach((sl) => {
-                const v = _aspectReadVal(sl.dataset.k);
-                if (Number.isFinite(v)) sl.value = v;
-                sl.dispatchEvent(new Event('input'));   // refresh the value label only
-            });
-            if (_aspectHfovCb) {
-                const hv = _aspectReadVal('hfovDeg');
-                _aspectHfovCb.checked = Number.isFinite(hv);
-                _aspectHfovSl.disabled = !_aspectHfovCb.checked;
-                if (Number.isFinite(hv)) _aspectHfovSl.value = hv;
-            }
-        } finally {
-            _aspectSyncing = false;
-        }
-    }
-
-    function _setAspectPanelVisible(on) {
-        _ensureAspectPanel();
-        if (!_aspectPanelEl) return;
-        _aspectPanelEl.style.display = on ? 'block' : 'none';
-        window.__h3dAspectPanelOpen = !!on;        // gates the per-frame readout publish
-        // Prune before the first build so panes from a prior song/split don't
-        // flash in the dropdown until the first RAF tick.
-        if (on) { _aspectPrunePanes(); _aspectBuildTargets(); }
-        if (on && !_aspectPanelRAF) {
-            const tick = () => {
-                if (!window.__h3dAspectPanelOpen) { _aspectPanelRAF = 0; return; }
-                _aspectPrunePanes();
-                if (_aspectPanesDirty) _aspectBuildTargets();
-                const ro = window.__h3dAspectReadout;
-                if (_aspectPanelRO && ro) {
-                    const key = _aspectEditTarget || ro.__last;
-                    const e = key && ro[key];
-                    if (e && Number.isFinite(e.aspect)) {
-                        _aspectPanelRO.textContent =
-                            'aspect ' + e.aspect.toFixed(2) + ' · vFOV ' + e.vfov.toFixed(1) + '°';
-                    }
-                }
-                _aspectPanelRAF = requestAnimationFrame(tick);
-            };
-            _aspectPanelRAF = requestAnimationFrame(tick);
-        }
-    }
-    // Toggle the panel open/closed (the Shift+A dismiss/reveal).
-    function _toggleAspectPanel() {
-        _ensureAspectPanel();
-        const open = !(_aspectPanelEl && _aspectPanelEl.style.display !== 'none');
-        _setAspectPanelVisible(open);
-        if (open) _syncAspectPanel();
-    }
-
-    /* ======================================================================
-     *  Background animations (issue #13)
-     *
-     *  Audio-reactive ambient scenery in the fog band beyond the highway.
-     *  Module-level singletons share an AudioContext + AnalyserNode tap on
-     *  the feedBack core <audio id="audio"> element across all panel
-     *  instances; per-panel settings live in localStorage with a global
-     *  fallback so settings.html drives a single default while per-panel
-     *  overrides (h3d_bg_panel<idx>_*) can be set for splitscreen layouts.
-     *
-     *  Caveat: createMediaElementSource() can only be called once per
-     *  element. 3dhighway owns that source for now; future plugins
-     *  needing an analyser will have to share through a core API.
-     * ====================================================================== */
-
-    // Returned from _bgReadBands when reactive=false or analyser
-    // unavailable; shared so the per-frame non-reactive path doesn't
-    // allocate. Declared up-front because _bgBandsCache initializes to
-    // it during the same IIFE execution pass.
-    const BG_ZERO_BANDS = Object.freeze({ bass: 0, mid: 0, treble: 0 });
-
-    // Module-level AudioContext singleton. Intentionally never torn
-    // down: createMediaElementSource(<audio>) is irrevocable — once
-    // called, the element's audio is permanently routed through this
-    // context for the page's lifetime. Closing the context would
-    // silence playback. The leak (one AudioContext + one AnalyserNode,
-    // a few KB) is the cost of having a plugin tap audio at all.
-    let _bgAudio = null;
-    // The core (#audio-tap) cache is held separately from the stems cache so
-    // we can switch back to it without re-calling createMediaElementSource on
-    // #audio — that call is one-shot per element, and a second one throws
-    // InvalidStateError (which would then be marked permanent and disable
-    // reactivity forever on legacy songs after any sloppak detour).
-    let _bgAudioCore = null;
-    let _bgAudioFailedAt = 0;  // performance.now() of last failure, 0 = never
-    const _BG_AUDIO_RETRY_MS = 1000;
-    // _bgReadBands sums bins 0..7 (bass), 8..39 (mid), 40..127 (treble),
-    // so the frequency buffer must hold at least 128 bins regardless of
-    // the source analyser's fftSize.
-    const BG_FREQ_BINS = 128;
-    const _bgBridgeKeys = new Map();
-    function _bgRecordAudioBridge(bridgeId, legacySurface, outcome = 'handled', reason = '', status = 'used') {
-        const key = `${outcome}:${status}:${reason}`;
-        if (_bgBridgeKeys.get(bridgeId) === key) return;
-        _bgBridgeKeys.set(bridgeId, key);
-        const session = window.feedBack && window.feedBack.audioSession;
-        if (!session || typeof session.recordBridgeHit !== 'function') return;
-        try {
-            session.recordBridgeHit({
-                domain: 'audio-mix',
-                bridgeId,
-                legacySurface,
-                participantId: 'highway_3d',
-                outcome,
-                status,
-                reason,
-            });
-        } catch (_) { /* diagnostics are best-effort */ }
-    }
-
-    function _bgGetAnalyser() {
-        // Prefer the stems plugin's side-chain analyser when a sloppak is
-        // loaded. As of feedBack-plugin-stems 0.5.0 (sample-locked playback)
-        // the #audio element is a silent virtual transport on sloppaks, so
-        // tapping it sees only silence; the stems mix is exposed at
-        // window.feedBack.stems.getAnalyser() instead. The stems plugin
-        // creates and destroys that AnalyserNode per song, so we re-check
-        // each call and key the cache on its identity — when the node
-        // changes (song switch), the cache is replaced automatically.
-        const stemsApi = window.feedBack && window.feedBack.stems;
-        const stemsAnalyser = (stemsApi && typeof stemsApi.getAnalyser === 'function')
-            ? stemsApi.getAnalyser() : null;
-        if (stemsAnalyser) {
-            if (!_bgAudio || _bgAudio.source !== 'stems' || _bgAudio.analyser !== stemsAnalyser) {
-                // Adopt the live stems analyser. Do NOT close its context — it's
-                // shared with stem playback and the stems plugin owns its
-                // lifecycle. No play-event resume hooks either; the stems
-                // plugin manages context resume itself.
-                _bgAudio = {
-                    ctx: stemsAnalyser.context,
-                    analyser: stemsAnalyser,
-                    // _bgReadBands reads bins 0..127 unconditionally. Always
-                    // allocate at least 128 bytes so a smaller analyser (e.g.
-                    // fftSize < 256) can't leave undefined values in the loop.
-                    freq: new Uint8Array(Math.max(BG_FREQ_BINS, stemsAnalyser.frequencyBinCount)),
-                    source: 'stems',
-                };
-                _bgRecordAudioBridge('audio-mix.analyser', 'window.feedBack.stems.getAnalyser', 'handled', '', 'stems');
-            }
-            return _bgAudio;
-        }
-        // No sloppak active — drop a stale stems-sourced cache, restoring the
-        // core-tap cache if we'd already built one. Without this, the next
-        // step would try to createMediaElementSource(#audio) a second time
-        // (one-shot per element) and throw InvalidStateError — disabling
-        // reactivity for the rest of the page lifetime.
-        if (_bgAudio && _bgAudio.source === 'stems') _bgAudio = _bgAudioCore;
-
-        if (_bgAudio && !_bgAudio.failed) return _bgAudio;
-        if (_bgAudio && _bgAudio.failed) {
-            // Distinguish permanent failures from transient ones.
-            // InvalidStateError on createMediaElementSource means the
-            // <audio> element is already tapped by another consumer —
-            // there's no recovering from that without a page reload, so
-            // don't retry. Transient failures (NotAllowedError before
-            // first user gesture, etc.) get a once-per-second retry so
-            // reactivity recovers once the blocking condition clears.
-            if (_bgAudio.permanent) return null;
-            if (performance.now() - _bgAudioFailedAt < _BG_AUDIO_RETRY_MS) return null;
-        }
-        const audio = document.getElementById('audio');
-        if (!audio) return null;
-        // Shared tap: createMediaElementSource is one-shot per element, so
-        // the FIRST visualizer to tap #audio publishes it at
-        // window.__feedBackAudioTap and every later one (this plugin, the
-        // drum/keys 3D highways) adopts it instead of throwing
-        // InvalidStateError when visualizers are switched or mixed in
-        // splitscreen.
-        const sharedTap = window.__feedBackAudioTap;
-        if (sharedTap && sharedTap.analyser && sharedTap.mediaEl === audio) {
-            _bgAudio = {
-                ctx: sharedTap.ctx,
-                analyser: sharedTap.analyser,
-                freq: new Uint8Array(Math.max(BG_FREQ_BINS, sharedTap.analyser.frequencyBinCount)),
-                source: 'core',
-            };
-            _bgAudioCore = _bgAudio;
-            _bgRecordAudioBridge('audio-mix.analyser', 'shared #audio analyser tap', 'handled', '', 'core');
-            return _bgAudio;
-        }
-        // Hoist ctx out of the try so we can close() it if a later step
-        // throws (e.g. createMediaElementSource on an element that
-        // already has a source node). Otherwise the AudioContext leaks.
-        let ctx = null;
-        try {
-            const Ctx = window.AudioContext || window.webkitAudioContext;
-            if (!Ctx) throw new Error('Web Audio API not available');
-            ctx = new Ctx();
-            const source = ctx.createMediaElementSource(audio);
-            const analyser = ctx.createAnalyser();
-            analyser.fftSize = 256;
-            source.connect(analyser);
-            analyser.connect(ctx.destination);
-            _bgAudio = { ctx, analyser, freq: new Uint8Array(Math.max(BG_FREQ_BINS, analyser.frequencyBinCount)), source: 'core' };
-            try { window.__feedBackAudioTap = { ctx, analyser, mediaEl: audio }; } catch (_) {}
-            _bgRecordAudioBridge('audio-mix.analyser', 'HTMLAudioElement analyser tap', 'handled', '', 'core');
-            // Remember the core analyser so a later stems-then-back-to-core
-            // transition can re-use it instead of re-tapping #audio (which
-            // would throw InvalidStateError on the one-shot per element).
-            _bgAudioCore = _bgAudio;
-            // Browsers with autoplay restrictions hand back a suspended
-            // AudioContext; createMediaElementSource then routes the
-            // <audio> through that suspended graph and playback goes
-            // silent (and the analyser reads zeros) until we resume.
-            // Try once now (fine if the page already had a user gesture)
-            // and again on every play event so the first successful
-            // user-initiated play unblocks the graph.
-            const resume = () => {
-                if (ctx.state === 'suspended' && typeof ctx.resume === 'function') {
-                    ctx.resume().catch(() => { /* no gesture yet, retry on next play */ });
-                }
-            };
-            resume();
-            audio.addEventListener('play', resume);
-            return _bgAudio;
-        } catch (e) {
-            if (ctx && typeof ctx.close === 'function') {
-                try { ctx.close(); } catch (_) { /* close errors during failure path are noise */ }
-            }
-            console.warn('[3D-Hwy] failed to set up audio analyser:', e);
-            const permanent = !!(e && e.name === 'InvalidStateError');
-            _bgRecordAudioBridge('audio-mix.analyser', 'HTMLAudioElement analyser tap', 'failed', e && e.message ? e.message : String(e), permanent ? 'permanent-failure' : 'transient-failure');
-            _bgAudio = { failed: true, permanent };
-            _bgAudioFailedAt = performance.now();
-            return null;
-        }
-    }
-
-    // Bands cache: in splitscreen, every panel asks for bands per frame.
-    // The analyser is shared, so the answer is identical — cache for a
-    // few ms so 4-up splitscreen pays one getByteFrequencyData + one sum
-    // pass per frame instead of four.
-    const _BG_BANDS_CACHE_MS = 5;
-    let _bgBandsLastT = -Infinity;
-    // Mutable cache reused across reads — refreshing in place keeps the
-    // per-frame allocation count at zero. Style.update() uses the bands
-    // synchronously within the same frame so the live-mutation contract
-    // is safe.
-    const _bgBandsCache = { bass: 0, mid: 0, treble: 0 };
-    function _bgReadBands() {
-        const a = _bgGetAnalyser();
-        if (!a) return BG_ZERO_BANDS;
-        const t = performance.now();
-        if (t - _bgBandsLastT < _BG_BANDS_CACHE_MS) return _bgBandsCache;
-        _bgBandsLastT = t;
-        a.analyser.getByteFrequencyData(a.freq);
-        let bass = 0, mid = 0, treble = 0;
-        for (let i = 0; i < 8; i++) bass += a.freq[i];
-        for (let i = 8; i < 40; i++) mid += a.freq[i];
-        for (let i = 40; i < 128; i++) treble += a.freq[i];
-        _bgBandsCache.bass = bass / (8 * 255);
-        _bgBandsCache.mid = mid / (32 * 255);
-        _bgBandsCache.treble = treble / (88 * 255);
-        return _bgBandsCache;
-    }
-
-    const BG_DEFAULTS = { style: 'particles', intensity: 0.5, reactive: true, palette: 'default', bgTheme: 'default', hwTheme: 'default', showFretOnNote: true, fretNumberGhostScope: 'chords', cameraSmoothing: 0.5, zoomSmoothing: 0.5, tiltSmoothing: 0.5, cameraLockLow: false, cameraLockZoom: 0.5, cameraMode: 'lookahead', nutHeadstockVisible: true, tuningLabelsVisible: true, nutColor: '#f5f3f0', headstockColor: '#d4b48a', textSize: 0.5, vibrancy: 0.85, glow: 0.25, customImageDataUrl: '', customImageName: '', customVideoName: '', chordDiagramVisible: true, chordDiagramSize: 0.5, chordDiagramPosition: 'tl', fretColumnMarkerCadence: 1, projectionVisible: true, inlayLabelsVisible: false, sectionLabelsOnHighway: false, sectionHudVisible: false, sectionHudPosition: 'tr', sectionHudSize: 0.5, toneHudVisible: false, toneHudPosition: 'tl', toneHudSize: 0.5, fpsVisible: false, fretDividersVisible: true, slideArrowApproachVisible: true, slideArrowNeckVisible: true, slideArrowChainPreviewVisible: true, hitFx: 0.7, sparks: true, cinematic: true, verdictMarks: true, timingFx: true, streakFx: true, bloom: true };
-    // User-selectable, persistable bg styles — must mirror settings.html's
-    // VALID_STYLES. 'venue' is deliberately NOT here: it is an internal effective
-    // style reached only via _venueSceneOverride (the viz-picker Venue flow), so
-    // _bgCoerce must reject a stored h3d_bg_style='venue' — otherwise venue could
-    // mount outside that flow and settings.html (which can't represent 'venue')
-    // would be unable to switch back. BG_STYLES still has a 'venue' renderer entry.
-    const BG_STYLE_IDS = ['off', 'particles', 'silhouettes', 'lights', 'geometric', 'butterchurn', 'image', 'video'];
-    // Scene color themes — TWO INDEPENDENT AXES sharing one palette family.
-    // The combined `BG_THEMES` table below is the single source of truth; each
-    // entry carries the colors for BOTH axes, but the two axes are selected and
-    // applied SEPARATELY (two dropdowns, two settings keys):
-    //   • BACKGROUND axis (setting key `bgTheme`) owns:
-    //       clear — WebGL clear color (the empty background behind everything)
-    //       fog   — distance fog tint (kept === clear so the horizon dissolves
-    //               cleanly instead of showing a seam)
-    //   • HIGHWAY axis (setting key `hwTheme`) owns:
-    //       board   — the fretboard / highway-surface plane color
-    //       lane    — the lit highway lane strip under the gems (optional)
-    //       laneDim — the lane's dimmer alternating row (optional)
-    // Because both axes read from the SAME id-set (the keys of this table), ANY
-    // background id can mix with ANY highway id (e.g. Deep Focus background +
-    // Cathode Green highway); picking the SAME id in both gives the original
-    // "matched" combined look. _bgBackgroundColors()/_bgHighwayColors() below
-    // are the per-axis accessors; both fall back to 'default' for unknown ids.
-    // 'default' reproduces the original look byte-for-byte on BOTH axes, so
-    // existing users (and anyone who never touches either setting) see no
-    // change. A migration in _bgLoadSettings() makes an existing single-`bgTheme`
-    // pick drive BOTH axes until the user diverges them, so upgrades are
-    // visually identical too. All themes keep the board very dark and the
-    // background dark so the bright per-string note gems, lane, and labels
-    // retain contrast. NOTE: settings.html mirrors these ids in its
-    // VALID_BG_THEMES set (shared by both dropdowns) — keep them in sync.
-    // Optional `lane` / `laneDim` fields retint the lit highway lane strip + its
-    // dimmer alternating row. A theme that omits them falls back to the stock
-    // blue lane (HWY_LANE_STRIPE_ODD_HEX / _EVEN_HEX); only 'default' relies on
-    // that fallback (so its output stays byte-identical). Every other theme sets
-    // its own lane so the Highway axis is visibly distinct entry-to-entry — the
-    // near-black neutral boards alone aren't separable, so the lane carries it.
-    // See _applyBgTheme().
-    const BG_THEMES = {
-        default:    { clear: 0x101820, fog: 0x101820, board: 0x08080e },
-        // Cool navy surface + a brighter pure-blue lane, so it reads distinct
-        // from 'default' (neutral board + stock teal-blue lane) on the Highway axis.
-        midnight:   { clear: 0x0a0e1a, fog: 0x0a0e1a, board: 0x080d1c, lane: 0x244fae, laneDim: 0x122a5e },
-        // Lighter NEUTRAL-grey surface + a steel-grey lane — the only mid-dark
-        // neutral board, so the surface itself is visibly different from the
-        // near-black neutrals around it (board kept dark enough for gem contrast).
-        charcoal:   { clear: 0x16181c, fog: 0x16181c, board: 0x141417, lane: 0x525a66, laneDim: 0x282d34 },
-        deeppurple: { clear: 0x140a1e, fog: 0x140a1e, board: 0x0b0610, lane: 0x3a1f6e, laneDim: 0x1f1040 },
-        forest:     { clear: 0x0a1614, fog: 0x0a1614, board: 0x06100c, lane: 0x15602a, laneDim: 0x0a3318 },
-        // Warm dark neutral (espresso/umber) — the first non-cool scene.
-        warmslate:  { clear: 0x1c130b, fog: 0x1c130b, board: 0x0e0805, lane: 0x5e3a12, laneDim: 0x341f0a },
-        // Recessive near-black neutral (a hair above #000000, ~zero chroma) —
-        // maximizes gem-vs-board contrast; a clean stage/stream look. Purest-dark
-        // board + a clean steel-cyan lane (brighter/cooler than 'default's muted
-        // teal-blue) so the Highway axis reads clearly distinct from default.
-        deepfocus:  { clear: 0x0c0c0d, fog: 0x0c0c0d, board: 0x060606, lane: 0x2f7fa0, laneDim: 0x163c4e },
-        // Calm dark teal — blue-dominant so it reads distinct from the navy
-        // 'midnight' and the green 'forest'.
-        deepsea:    { clear: 0x06222b, fog: 0x06222b, board: 0x03141a, lane: 0x0e5a63, laneDim: 0x063338 },
-        // Retro CRT glow — a warm AMBER phosphor cast (the classic amber
-        // terminal). Amber rather than green so a phosphor board can't crush
-        // green/teal gems, and so it stays clearly distinct from 'forest' and
-        // 'deepsea'. Board stays very dark / low-chroma to keep gems popping.
-        cathode:    { clear: 0x140b03, fog: 0x140b03, board: 0x0c0702, lane: 0x6e4a0e, laneDim: 0x3a2806 },
-        // Retro CRT GREEN phosphor — leaned more saturated / cyan-green than
-        // 'forest' so it reads as a terminal, not woodland (dRGB 35 vs forest,
-        // 32 vs deepsea). Phosphor-green board + green lane. Verified to keep
-        // green/teal gems legible (green-on-green floor CR ~2.2).
-        cathodegreen: { clear: 0x07301a, fog: 0x07301a, board: 0x031a0c, lane: 0x0e6e2a, laneDim: 0x073a18 },
-        // Warm hearth — the first warm-RED scene, pairs with the Ember/Sunrise
-        // strings. Deep red, pushed away from the amber 'cathode'/'warmslate'
-        // (dRGB ~26 from cathode). Ember-red lane.
-        hearth:     { clear: 0x280806, fog: 0x280806, board: 0x1a0606, lane: 0x7a2410, laneDim: 0x3f1409 },
-    };
-    const BG_THEME_IDS = Object.keys(BG_THEMES);
-    // Shared lookup for the combined entry (both axes are keyed by the same id
-    // set, so a single id list / coerce check validates either axis).
-    function _bgThemeColors(id) { return BG_THEMES[id] || BG_THEMES.default; }
-    // Per-axis accessors. Background reads clear/fog; highway reads
-    // board/lane/laneDim. They alias the same table — splitting at read-time
-    // keeps one source of truth while letting the two dropdowns pick freely.
-    function _bgBackgroundColors(id) { return _bgThemeColors(id); }
-    function _bgHighwayColors(id) { return _bgThemeColors(id); }
-    const VENUE_SCENE_ASSET_BASE = '/static/assets/venue/themes/small-club/';
-    const VENUE_BG_PLATE_PNG = 'bg-plate.png';
-    const VENUE_BG_PLATE_WEBP = 'bg-plate.webp';
-    const VENUE_INSTRUMENT_PLATES = {
-        guitar: { webp: 'guitar-pov-bg.webp', png: 'guitar-pov-bg.png' },
-        bass: { webp: 'bass-pov-bg.webp', png: 'bass-pov-bg.png' },
-        drums: { webp: 'drums-pov-bg.webp', png: 'drums-pov-bg.png' },
-        piano: { webp: 'piano-pov-bg.webp', png: 'piano-pov-bg.png' },
-        vocals: { webp: 'vocals-pov-bg.webp', png: 'vocals-pov-bg.png' },
-    };
-    let _venueSceneOverride = false;
-    let _venueMoodState = 'idle';
-    let _venueInstrumentPov = 'guitar';
-    let _venueMotionMode = 'subtle';
-    let _venuePlateUrl = '';
-    let _venueSceneAssetsLoaded = false;
-    let _venueSceneLoadFailed = false;
-    const _venueTextureCache = new Map();
-    // Crowd video layers (career mode). venue-crowd.js owns the <video>
-    // elements and the crossfade timing; the renderer only maps them onto
-    // two planes in front of the static plate. _venueCrowdRev bumps on any
-    // element (re)assignment so update() knows to rebind textures.
-    const _venueCrowdVideos = [null, null];
-    let _venueCrowdMix = 0;
-    let _venueCrowdRev = 0;
-
-    function _bgVenueMoodCoeffs(state) {
-        const s = String(state || 'idle').toLowerCase();
-        if (s === 'fire' || s === 'strong') {
-            return { light: 1.0, crowd: 0, haze: 0.012, warmth: 1.02 };
-        }
-        if (s === 'recovery' || s === 'smoke') {
-            return { light: 0.55, crowd: 0, haze: 0.032, warmth: 0.94 };
-        }
-        return { light: 0.72, crowd: 0, haze: VENUE_HAZE_STEADY, warmth: 0.96 };
-    }
-
-    function _venueResolvePovFromInput(input) {
-        if (typeof window !== 'undefined' && window.v3VenueInstrumentPov &&
-            typeof window.v3VenueInstrumentPov.resolveVenueInstrumentPov === 'function') {
-            return window.v3VenueInstrumentPov.resolveVenueInstrumentPov(input);
-        }
-        const s = String(input == null ? '' : input).trim().toLowerCase();
-        if (!s) return 'guitar';
-        if (/\b(drums?)\b/.test(s)) return 'drums';
-        if (/\b(bass)\b/.test(s)) return 'bass';
-        if (/\b(piano|keys|keyboard)\b/.test(s)) return 'piano';
-        if (/\b(karaoke|vocal|vocals|lyric|lyrics|sing|singing)\b/.test(s)) return 'vocals';
-        if (/\b(lead|rhythm|guitar|combo)\b/.test(s)) return 'guitar';
-        return 'guitar';
-    }
-
-    function _venueMotionProfile(mode) {
-        if (typeof window !== 'undefined' && window.v3VenueMoodFx &&
-            typeof window.v3VenueMoodFx.venueMotionProfile === 'function') {
-            return window.v3VenueMoodFx.venueMotionProfile(mode);
-        }
-        const m = String(mode || 'subtle').toLowerCase();
-        if (m === 'off') {
-            return { breathe: 0, parallax: 0, hazeDrift: 0, warmthPulse: 0, shimmer: 0 };
-        }
-        if (m === 'full') {
-            return { breathe: 0.014, parallax: 0.010, hazeDrift: 0.020, warmthPulse: 0.028, shimmer: 0.10 };
-        }
-        return { breathe: 0.005, parallax: 0.004, hazeDrift: 0.007, warmthPulse: 0.010, shimmer: 0.04 };
-    }
-
-    function _venuePrefersReducedMotion() {
-        if (typeof window !== 'undefined' && window.v3VenueMoodFx &&
-            typeof window.v3VenueMoodFx.prefersReducedMotion === 'function') {
-            return window.v3VenueMoodFx.prefersReducedMotion();
-        }
-        return false;
-    }
-
-    function _venueEffectiveMotionMode() {
-        if (!_venueSceneOverride) return 'off';
-        if (_venuePrefersReducedMotion()) return 'off';
-        return _venueMotionMode;
-    }
-
-    function _venueApplyFakeDepthMotion(s, coeffs, t) {
-        const motion = _venueMotionProfile(_venueEffectiveMotionMode());
-        if (!motion.breathe && !motion.parallax && !motion.hazeDrift && !motion.warmthPulse) {
-            if (s.haze && s.haze.mesh) {
-                s.haze.mesh.position.set(s.haze.baseX, s.haze.baseY, s.haze.baseZ);
-            }
-            return motion;
-        }
-        const breath = Math.sin(t * 0.38);
-        const parallax = Math.sin(t * 0.21);
-        const shimmer = Math.sin(t * 0.55);
-        if (s.backdrop && s.backdrop.loaded && s.backdrop.mesh) {
-            const mesh = s.backdrop.mesh;
-            const vh = s.backdrop.lastVisibleHeight || 1;
-            const vw = s.backdrop.lastVisibleWidth || vh;
-            const offX = parallax * motion.parallax * vh;
-            const offY = breath * motion.breathe * vh * 0.35;
-            mesh.position.x += offX;
-            mesh.position.y += offY;
-            const scaleMul = 1 + breath * motion.breathe * 2.5;
-            mesh.scale.set(vw * scaleMul, vh * scaleMul, 1);
-            if (s.backdrop.mat) {
-                const warm = coeffs.warmth;
-                const warmPulse = 1 + shimmer * motion.warmthPulse;
-                s.backdrop.mat.color.setRGB(
-                    warm * warmPulse,
-                    warm * 0.98 * warmPulse,
-                    warm * 0.95 * (1 + shimmer * motion.warmthPulse * 0.6),
-                );
-            }
-        } else if (s.backdrop && s.backdrop.mat) {
-            const warm = coeffs.warmth;
-            s.backdrop.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
-        }
-        if (s.haze && s.haze.mesh) {
-            const driftX = Math.sin(t * 0.18) * motion.hazeDrift * 8 * K;
-            const driftY = Math.cos(t * 0.14) * motion.hazeDrift * 4 * K;
-            s.haze.mesh.position.set(
-                s.haze.baseX + driftX,
-                s.haze.baseY + driftY,
-                s.haze.baseZ,
-            );
-            if (s.haze.mat) {
-                const baseOp = (s.haze.baseOp || VENUE_HAZE_STEADY) * (coeffs.haze / VENUE_HAZE_STEADY);
-                s.haze.mat.opacity = baseOp * (1 + shimmer * motion.shimmer * 0.12);
-            }
-        }
-        return motion;
-    }
-
-    function _venuePlateUrlChain(pov) {
-        const plate = VENUE_INSTRUMENT_PLATES[pov] || VENUE_INSTRUMENT_PLATES.guitar;
-        const base = VENUE_SCENE_ASSET_BASE;
-        return [
-            base + plate.webp,
-            base + plate.png,
-            base + VENUE_BG_PLATE_WEBP,
-            base + VENUE_BG_PLATE_PNG,
-        ];
-    }
-
-    function _venueLoadCachedTexture(loader, url, onSuccess, onFail) {
-        const cached = _venueTextureCache.get(url);
-        if (cached) {
-            onSuccess(cached, url);
-            return;
-        }
-        loader.load(
-            url,
-            (tex) => {
-                _venueTextureCache.set(url, tex);
-                onSuccess(tex, url);
-            },
-            undefined,
-            onFail,
-        );
-    }
-
-    function _venueApplyPlateTexture(backdrop, tex, url) {
-        backdrop.tex = tex;
-        backdrop.plateUrl = url;
-        _venuePlateUrl = url;
-        backdrop.mat.map = tex;
-        backdrop.mat.needsUpdate = true;
-        if (backdrop.applyCoverCrop) backdrop.applyCoverCrop();
-        backdrop.loaded = true;
-        backdrop.mesh.visible = true;
-    }
-
-    function _venueLoadPlateForPov(loader, pov, backdrop, onSuccess, onFail) {
-        const chain = _venuePlateUrlChain(pov);
-        let idx = 0;
-        function tryNext() {
-            if (idx >= chain.length) {
-                onFail();
-                return;
-            }
-            const url = chain[idx++];
-            _venueLoadCachedTexture(loader, url, (tex, loadedUrl) => {
-                _venueApplyPlateTexture(backdrop, tex, loadedUrl);
-                onSuccess(tex, loadedUrl);
-            }, tryNext);
-        }
-        tryNext();
-    }
-
-    function _venueSwapPlateIfNeeded(s) {
-        if (!s || s.failed || s.plateLoading || !s.loader || !s.backdrop) return;
-        const pov = _venueInstrumentPov;
-        if (s.instrumentPov === pov && s.backdrop.loaded) return;
-        s.plateLoading = true;
-        _venueLoadPlateForPov(
-            s.loader,
-            pov,
-            s.backdrop,
-            () => {
-                s.instrumentPov = pov;
-                s.plateLoading = false;
-                s.loaded = true;
-                _venueSceneAssetsLoaded = true;
-                _venueSceneLoadFailed = false;
-                // The POV may have changed while this load was in flight (the
-                // plateLoading latch made concurrent swaps no-op). Re-sync to the
-                // current target so the backdrop isn't stranded on a stale plate.
-                if (_venueInstrumentPov !== pov) _venueSwapPlateIfNeeded(s);
-            },
-            () => {
-                s.plateLoading = false;
-                if (s.backdrop.loaded) return;
-                s.failed = true;
-                _venueSceneLoadFailed = true;
-                _venueSceneAssetsLoaded = false;
-                console.warn('[venue-scene] failed to load venue bg plate for pov ' + pov);
-                _venueSceneOverride = false;
-                _bgEmitChange('venueScene');
-                try {
-                    if (typeof window !== 'undefined' && window.v3VenueScene3d &&
-                        typeof window.v3VenueScene3d.onAssetsFailed === 'function') {
-                        window.v3VenueScene3d.onAssetsFailed('failed to load venue bg plate');
-                    }
-                } catch (_) { /* visual-only */ }
-            },
-        );
-    }
-    const FRET_NUMBER_GHOST_SCOPE_IDS = ['chords', 'all'];
-
-    /**
-     * localStorage panel key for per-panel background settings ('main' or
-     * 'panel<index>'). Defensive on the splitscreen global-name rename in flight,
-     * and throw-safe on panelIndexFor — same as _freeCamFor — so a misbehaving
-     * splitscreen build can't take down background-settings resolution. Only a
-     * non-negative integer index yields a 'panel<N>' key; anything else (null,
-     * NaN, negative, non-integer) falls back to 'main' so a bad index can never
-     * mint a bogus "panelNaN"-style key.
-     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
-     * @returns {string} 'main' or 'panel<index>'
-     */
-    function _bgPanelKey(canvas) {
-        const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
-        let idx = null;
-        if (ss && typeof ss.panelIndexFor === 'function') {
-            try { idx = ss.panelIndexFor(canvas); } catch (e) { idx = null; }
-        }
-        return (Number.isInteger(idx) && idx >= 0) ? 'panel' + idx : 'main';
-    }
-
-    /**
-     * Camera Director bridge resolver. Prefers THIS panel's per-panel camera under
-     * splitscreen (window.__h3dCamCtlPanels[panelIndex]) and falls back to the
-     * single global (window.__h3dCamCtl); returns null when Camera Director is
-     * absent → 100% stock framing. Defensive on the splitscreen global-name rename
-     * in flight (feedBackSplitscreen vs slopsmithSplitscreen); throw-safe on
-     * panelIndexFor. Mirrors the panel resolution in _bgPanelKey.
-     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
-     * @returns {object|null} the resolved free-camera bridge, or null
-     */
-    function _freeCamFor(canvas) {
-        const map = window.__h3dCamCtlPanels;
-        if (map) {
-            const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
-            if (ss && typeof ss.panelIndexFor === 'function') {
-                try {
-                    const i = ss.panelIndexFor(canvas);
-                    // Only a non-negative integer indexes the map (same hardening
-                    // as _bgPanelKey) — a non-int / negative / string index must not
-                    // resolve an unintended/inherited property; fall through then.
-                    if (Number.isInteger(i) && i >= 0 && map[i]) return map[i];
-                } catch (e) { /* ignore */ }
-            }
-        }
-        return window.__h3dCamCtl || null;
-    }
-    // In-memory fallback for when localStorage is blocked (private mode,
-    // sandboxed iframes, some test runners). _bgWriteGlobal stages the
-    // value here unconditionally, so it always reflects the most recent
-    // in-session intent — _bgReadSetting prefers it over the global
-    // localStorage slot to avoid serving a stale persisted value when
-    // a write failed silently (quota exceeded, etc.). Per-panel
-    // localStorage overrides still win because they're an explicit
-    // per-instance opt-out and shouldn't be shadowed by a global edit.
-    const _bgMemFallback = Object.create(null);
-    function _bgReadSetting(panelKey, key) {
-        let panelVal = null;
-        let globalVal = null;
-        try {
-            // 'palette' + 'customColors' are GLOBAL-only: the per-panel palette
-            // control was removed in favour of the global "Highway String Colors"
-            // UI, so a panel must never be shadowed by a stale per-panel override
-            // (h3d_bg_panel<idx>_palette / _customColors). Neither is a
-            // BG_DEFAULTS key, so per-panel scoping never applied to them.
-            if (key !== 'palette' && key !== 'customColors') {
-                panelVal = localStorage.getItem('h3d_bg_' + panelKey + '_' + key);
-            }
-            globalVal = localStorage.getItem('h3d_bg_' + key);
-        } catch (_) { /* storage blocked — both stay null */ }
-        if (panelVal !== null && panelVal !== undefined) return _bgCoerce(key, panelVal);
-        // Prefer the in-memory staged value over the persisted global slot.
-        // _bgWriteGlobal always writes to _bgMemFallback first, so the
-        // memory value is at least as fresh as the persisted one.
-        if (key in _bgMemFallback) return _bgCoerce(key, _bgMemFallback[key]);
-        if (globalVal !== null && globalVal !== undefined) return _bgCoerce(key, globalVal);
-        return BG_DEFAULTS[key];
-    }
-    // Shared "stored string -> bool" coercion for every boolean
-    // setting. Mirrors settings.html's coerceBool so the renderer and
-    // the UI hydration always agree on what a corrupted/unknown value
-    // means (fall back to default rather than silently flipping to
-    // false). Add new boolean keys to BG_DEFAULTS and they pick this
-    // up via the dispatch below.
-    const _BG_BOOL_KEYS = new Set(['reactive', 'showFretOnNote', 'cameraLockLow', 'inlayLabelsVisible', 'sectionLabelsOnHighway', 'sectionHudVisible', 'nutHeadstockVisible', 'tuningLabelsVisible', 'projectionVisible', 'chordDiagramVisible', 'fpsVisible', 'toneHudVisible', 'fretDividersVisible', 'slideArrowApproachVisible', 'slideArrowNeckVisible', 'slideArrowChainPreviewVisible', 'sparks', 'cinematic', 'verdictMarks', 'timingFx', 'streakFx', 'bloom']);
-    function _bgCoerceBool(val, fallback) {
-        if (val === 'true' || val === '1') return true;
-        if (val === 'false' || val === '0') return false;
-        return fallback;
-    }
-    // Settings stored as 0..1 floats. cameraSmoothing controls X-pan
-    // hysteresis; zoomSmoothing the zoom dead zone; tiltSmoothing the
-    // vertical-tilt deadband + correction strength. All three slider-
-    // shaped settings share the same parse + clamp behaviour.
-    const _BG_FLOAT_KEYS = new Set(['intensity', 'cameraSmoothing', 'zoomSmoothing', 'tiltSmoothing', 'cameraLockZoom', 'textSize', 'vibrancy', 'glow', 'chordDiagramSize', 'sectionHudSize', 'toneHudSize', 'hitFx']);
-    function _bgCoerce(key, val) {
-        if (_BG_FLOAT_KEYS.has(key)) {
-            const n = parseFloat(val);
-            return Number.isFinite(n) ? Math.max(0, Math.min(1, n)) : BG_DEFAULTS[key];
-        }
-        if (_BG_BOOL_KEYS.has(key)) return _bgCoerceBool(val, BG_DEFAULTS[key]);
-        if (key === 'style') return BG_STYLE_IDS.includes(val) ? val : BG_DEFAULTS.style;
-        if (key === 'palette') return (PALETTE_IDS.includes(val) || val === 'custom') ? val : BG_DEFAULTS.palette;
-        if (key === 'bgTheme') return BG_THEME_IDS.includes(val) ? val : BG_DEFAULTS.bgTheme;
-        // Highway axis shares the same id-set as the background axis.
-        if (key === 'hwTheme') return BG_THEME_IDS.includes(val) ? val : BG_DEFAULTS.hwTheme;
-        if (key === 'chordDiagramPosition')
-            return CHORD_DIAG_POSITION_IDS.includes(val) ? val : BG_DEFAULTS.chordDiagramPosition;
-        if (key === 'sectionHudPosition')
-            return ['tl', 'tr', 'bl', 'br'].includes(val) ? val : BG_DEFAULTS.sectionHudPosition;
-        if (key === 'toneHudPosition')
-            return ['tl', 'tr', 'bl', 'br'].includes(val) ? val : BG_DEFAULTS.toneHudPosition;
-        if (key === 'cameraMode') {
-            if (val === 'classic') val = 'steady';
-            return CAMERA_MODE_IDS.includes(val) ? val : BG_DEFAULTS.cameraMode;
-        }
-        if (key === 'fretNumberGhostScope')
-            return FRET_NUMBER_GHOST_SCOPE_IDS.includes(val) ? val : BG_DEFAULTS.fretNumberGhostScope;
-        if (key === 'nutColor' || key === 'headstockColor') {
-            if (typeof val !== 'string') return BG_DEFAULTS[key];
-            const t = val.trim();
-            if (/^#[0-9a-fA-F]{6}$/.test(t)) return t.toLowerCase();
-            return BG_DEFAULTS[key];
-        }
-        if (key === 'fretColumnMarkerCadence') {
-            const n = parseInt(val, 10);
-            if (!Number.isFinite(n)) return BG_DEFAULTS.fretColumnMarkerCadence;
-            return Math.max(0, Math.min(16, n));
-        }
-        return val;
-    }
-
-    // Mirror-at-first-read fallback: returns true if the user has ever
-    // explicitly written `key` (per-panel, in-memory, or global). When
-    // false, callers should treat the value as "unset" — useful for
-    // zoomSmoothing / tiltSmoothing which inherit cameraSmoothing's
-    // value the first time they're read so existing users who calmed
-    // the camera don't lose calmness on the new axes by default.
-    function _bgHasStored(panelKey, key) {
-        try {
-            if (localStorage.getItem('h3d_bg_' + panelKey + '_' + key) != null) return true;
-        } catch (_) {}
-        if (key in _bgMemFallback) return true;
-        try {
-            if (localStorage.getItem('h3d_bg_' + key) != null) return true;
-        } catch (_) {}
-        return false;
-    }
-    function _bgWriteGlobal(key, val) {
-        const s = String(val);
-        // Stage in memory FIRST so _bgReadSetting's "memory beats global
-        // localStorage" precedence has a true freshness guarantee even
-        // if localStorage.setItem throws partway through. Without this
-        // ordering, a quota exception thrown after the persisted slot
-        // was already mutated would leave a stale value in localStorage
-        // that's newer than _bgMemFallback.
-        _bgMemFallback[key] = s;
-        try { localStorage.setItem('h3d_bg_' + key, s); } catch (_) { /* storage blocked */ }
-        _bgEmitChange(key);
-    }
-
-    // Pub-sub so settings.html can update live across all panel instances.
-    const _bgListeners = new Set();
-    function _bgSubscribe(fn) { _bgListeners.add(fn); }
-    function _bgUnsubscribe(fn) { _bgListeners.delete(fn); }
-    function _bgEmitChange(key) {
-        for (const fn of _bgListeners) {
-            try { fn(key); } catch (e) { console.error('[3D-Hwy] bg listener threw', e); }
-        }
-    }
-
-    // Settings.html setters — global keys; per-panel overrides via direct
-    // localStorage edits today, runtime UI in a follow-up.
-    window.h3dBgSetStyle = (v) => _bgWriteGlobal('style', v);
-    window.h3dBgSetIntensity = (v) => _bgWriteGlobal('intensity', v);
-    window.h3dBgSetReactive = (v) => _bgWriteGlobal('reactive', !!v);
-    window.h3dBgSetPalette = (v) => _bgWriteGlobal('palette', v);
-    // BACKGROUND scene-color axis (clear + fog only). Validated against
-    // BG_THEME_IDS in _bgCoerce; the listener re-applies clear/fog live and
-    // independently of the highway axis.
-    window.h3dBgSetBgTheme = (v) => {
-        const s = String(v);
-        _bgWriteGlobal('bgTheme', BG_THEME_IDS.includes(s) ? s : BG_DEFAULTS.bgTheme);
-    };
-    // HIGHWAY scene-color axis (board + lane + laneDim). Same id-set as the
-    // background axis, so any highway can mix with any background. The listener
-    // re-applies the board plane + lane live and independently.
-    window.h3dBgSetHwTheme = (v) => {
-        const s = String(v);
-        _bgWriteGlobal('hwTheme', BG_THEME_IDS.includes(s) ? s : BG_DEFAULTS.hwTheme);
-    };
-    // Apply a user-defined per-string color set (core theming UI). `hexArray`
-    // is up to 8 hex strings; invalid/missing entries fall back to the default
-    // palette per index. Writes the colors, then flips the palette to 'custom'
-    // — the palette listener retints all materials + rebuilds the board live.
-    // Pass null/[] then h3dBgSetPalette('default') to revert.
-    window.h3dBgSetStringColors = (hexArray) => {
-        const arr = Array.isArray(hexArray) ? hexArray : [];
-        const norm = [];
-        for (let i = 0; i < MAX_RENDER_STRINGS; i++) {
-            const n = _h3dHexToInt(arr[i]);
-            norm[i] = (n != null) ? '#' + n.toString(16).padStart(6, '0') : null;
-        }
-        _bgWriteGlobal('customColors', JSON.stringify(norm));
-        _bgWriteGlobal('palette', 'custom');
-    };
-    window.h3dBgSetShowFretOnNote = (v) => _bgWriteGlobal('showFretOnNote', !!v);
-    window.h3dBgSetFretNumberGhostScope = (v) => {
-        const s = String(v);
-        _bgWriteGlobal('fretNumberGhostScope', FRET_NUMBER_GHOST_SCOPE_IDS.includes(s) ? s : BG_DEFAULTS.fretNumberGhostScope);
-    };
-    window.h3dBgSetCameraSmoothing = (v) => _bgWriteGlobal('cameraSmoothing', v);
-    window.h3dBgSetZoomSmoothing = (v) => _bgWriteGlobal('zoomSmoothing', v);
-    window.h3dBgSetTiltSmoothing = (v) => _bgWriteGlobal('tiltSmoothing', v);
-    window.h3dBgSetCameraLockLow = (v) => _bgWriteGlobal('cameraLockLow', !!v);
-    window.h3dBgSetCameraLockZoom = (v) => _bgWriteGlobal('cameraLockZoom', v);
-    window.h3dBgSetCameraMode = (v) => {
-        let s = String(v);
-        if (s === 'classic') s = 'steady';
-        _bgWriteGlobal('cameraMode', s);
-    };
-    window.h3dBgSetNutHeadstockVisible = (v) => _bgWriteGlobal('nutHeadstockVisible', !!v);
-    window.h3dBgSetTuningLabelsVisible = (v) => _bgWriteGlobal('tuningLabelsVisible', !!v);
-    window.h3dBgSetNutColor = (v) => _bgWriteGlobal('nutColor', v);
-    window.h3dBgSetHeadstockColor = (v) => _bgWriteGlobal('headstockColor', v);
-    window.h3dBgSetTextSize = (v) => _bgWriteGlobal('textSize', v);
-    window.h3dBgSetVibrancy = (v) => _bgWriteGlobal('vibrancy', v);
-    window.h3dBgSetGlow     = (v) => _bgWriteGlobal('glow', v);
-    window.h3dBgSetHitFx        = (v) => _bgWriteGlobal('hitFx', v);
-    window.h3dBgSetSparks       = (v) => _bgWriteGlobal('sparks', !!v);
-    window.h3dBgSetCinematic    = (v) => _bgWriteGlobal('cinematic', !!v);
-    window.h3dBgSetVerdictMarks = (v) => _bgWriteGlobal('verdictMarks', !!v);
-    window.h3dBgSetTimingFx     = (v) => _bgWriteGlobal('timingFx', !!v);
-    window.h3dBgSetStreakFx     = (v) => _bgWriteGlobal('streakFx', !!v);
-    window.h3dBgSetBloom        = (v) => _bgWriteGlobal('bloom', !!v);
-    window.h3dBgSetToneHudVisible   = (v) => _bgWriteGlobal('toneHudVisible', !!v);
-    window.h3dBgSetToneHudPosition  = (v) => _bgWriteGlobal('toneHudPosition', v);
-    window.h3dBgSetToneHudSize      = (v) => _bgWriteGlobal('toneHudSize', v);
-    window.h3dBgSetFpsVisible           = (v) => _bgWriteGlobal('fpsVisible', !!v);
-    window.h3dBgSetFretDividersVisible  = (v) => _bgWriteGlobal('fretDividersVisible', !!v);
-    window.h3dBgSetChordDiagramVisible  = (v) => _bgWriteGlobal('chordDiagramVisible', !!v);
-    window.h3dBgSetChordDiagramSize     = (v) => _bgWriteGlobal('chordDiagramSize', v);
-    window.h3dBgSetChordDiagramPosition = (v) => _bgWriteGlobal('chordDiagramPosition', v);
-    window.h3dBgSetFretColumnMarkerCadence = (v) => _bgWriteGlobal('fretColumnMarkerCadence', v);
-    window.h3dBgSetInlayLabelsVisible = (v) => _bgWriteGlobal('inlayLabelsVisible', !!v);
-    window.h3dBgSetSectionLabelsOnHighway = (v) => _bgWriteGlobal('sectionLabelsOnHighway', !!v);
-    window.h3dBgSetSectionHudVisible      = (v) => _bgWriteGlobal('sectionHudVisible', !!v);
-    window.h3dBgSetSectionHudPosition     = (v) => _bgWriteGlobal('sectionHudPosition', v);
-    window.h3dBgSetSectionHudSize         = (v) => _bgWriteGlobal('sectionHudSize', v);
-    window.h3dBgSetProjectionVisible      = (v) => _bgWriteGlobal('projectionVisible', !!v);
-    window.h3dBgSetSlideArrowApproachVisible = (v) => _bgWriteGlobal('slideArrowApproachVisible', !!v);
-    window.h3dBgSetSlideArrowNeckVisible     = (v) => _bgWriteGlobal('slideArrowNeckVisible', !!v);
-    window.h3dBgSetSlideArrowChainPreviewVisible = (v) => _bgWriteGlobal('slideArrowChainPreviewVisible', !!v);
-    // Custom image asset for the 'image' bg style (#19). Composite setter:
-    // writes both the data URL (the bytes that drive the texture) and the
-    // display filename, each emitting a change event. The listener
-    // rebuilds on customImageDataUrl change when the image style is
-    // active; customImageName is display-only and skips rebuild.
-    window.h3dBgSetCustomImage = (asset) => {
-        const a = asset || {};
-        _bgWriteGlobal('customImageDataUrl', a.dataUrl || '');
-        _bgWriteGlobal('customImageName', a.name || '');
-    };
-    window.h3dBgClearCustomImage = () => {
-        _bgWriteGlobal('customImageDataUrl', '');
-        _bgWriteGlobal('customImageName', '');
-    };
-    // Custom video asset for the 'video' bg style (#19 follow-up).
-    // Bytes live on disk under {config_dir}/plugin_uploads/highway_3d/
-    // and are served by routes.py — localStorage only stores the
-    // filename, which the renderer maps to the served URL. Single
-    // global slot; the file picker in settings.html POSTs to the
-    // upload route and then calls this setter with the response name.
-    window.h3dBgSetCustomVideo = (asset) => {
-        _bgWriteGlobal('customVideoName', (asset && asset.name) || '');
-    };
-    window.h3dBgClearCustomVideo = () => _bgWriteGlobal('customVideoName', '');
-    window.h3dVenueSceneSetActive = (on) => {
-        const next = !!on;
-        if (_venueSceneOverride === next) return;
-        _venueSceneOverride = next;
-        if (!next) {
-            _venueSceneAssetsLoaded = false;
-            _venueSceneLoadFailed = false;
-        }
-        _bgEmitChange('venueScene');
-    };
-    window.h3dVenueSceneSetMood = (state) => {
-        _venueMoodState = String(state || 'idle').toLowerCase();
-    };
-    // Crowd video layers (career mode) — see venue-crowd.js. Layer 0/1 are
-    // two coplanar backdrop planes; mix selects between them (0 → layer 0,
-    // 1 → layer 1) so the caller can crossfade loop videos.
-    window.h3dVenueBackdropSetVideo = (layer, videoEl) => {
-        const i = layer ? 1 : 0;
-        const el = videoEl || null;
-        if (_venueCrowdVideos[i] === el) return;
-        _venueCrowdVideos[i] = el;
-        _venueCrowdRev++;
-    };
-    window.h3dVenueBackdropSetMix = (mix) => {
-        const v = Number(mix);
-        _venueCrowdMix = Number.isFinite(v) ? Math.max(0, Math.min(1, v)) : 0;
-    };
-    window.h3dVenueSceneSetInstrumentPov = (input) => {
-        const next = _venueResolvePovFromInput(input);
-        if (_venueInstrumentPov === next) return;
-        _venueInstrumentPov = next;
-        _bgEmitChange('venueInstrumentPov');
-    };
-    window.h3dVenueSceneSetMotionMode = (mode) => {
-        const next = String(mode || 'subtle').toLowerCase();
-        const allowed = { off: 1, subtle: 1, full: 1 };
-        _venueMotionMode = allowed[next] ? next : 'subtle';
-    };
-    window.h3dVenueSceneGetState = () => {
-        const motionMode = _venueEffectiveMotionMode();
-        const motionProfile = _venueMotionProfile(motionMode);
-        return {
-            active: _venueSceneOverride,
-            mood: _venueMoodState,
-            instrumentPov: _venueInstrumentPov,
-            motionMode: _venueMotionMode,
-            motionEffective: motionMode,
-            motionEnabled: motionMode !== 'off',
-            motionIntensity: motionProfile.breathe + motionProfile.parallax + motionProfile.hazeDrift,
-            motionProfile,
-            plateUrl: _venuePlateUrl || null,
-            assetsLoaded: _venueSceneAssetsLoaded,
-            loadFailed: _venueSceneLoadFailed,
-        };
-    };
-    // Back-compat alias for any caller that picked up the original
-    // (inconsistent) name during this PR's review window.
-    window.h3dSetPalette = window.h3dBgSetPalette;
-
-    // Procedural silhouette bitmap, drawn once and shared across panels.
-    // The Canvas2D bitmap is module-level (cheap, CPU-only); each layer
-    // wraps it in its own CanvasTexture so per-layer texture.offset.x
-    // can drive a seam-free scroll without coupling to other layers /
-    // panels (a shared CanvasTexture would synchronize all offsets).
-    let _silCanvas = null;
-    function _bgEnsureSilhouetteCanvas() {
-        if (_silCanvas) return _silCanvas;
-        const c = document.createElement('canvas');
-        c.width = 1024; c.height = 64;
-        const cx = c.getContext('2d');
-        if (!cx) {
-            // Restrictive environments (some sandboxed iframes, headless
-            // tests) can return null. Without a guard, the clearRect/
-            // fillRect calls below would throw TypeError and the silhouette
-            // style would never become available.
-            throw new Error('[3D-Hwy] 2D canvas context unavailable for silhouette texture');
-        }
-        cx.clearRect(0, 0, c.width, c.height);
-        cx.fillStyle = '#000814';
-        let x = 0;
-        while (x < c.width) {
-            const w = 8 + Math.random() * 30;
-            const h = 20 + Math.random() * 40;
-            cx.fillRect(x, c.height - h, w, h);
-            x += w + Math.random() * 10;
-        }
-        _silCanvas = c;
-        return c;
-    }
-
-    // Helpers shared by the asset-driven bg styles (image, video).
-    // Both render a "stage backdrop" plane that's full-bleed: sized
-    // each frame to fill the camera's view frustum at a fixed
-    // distance and positioned to track the camera (so the user's
-    // image/video reads as the entire visible BG, with highway and
-    // notes painting on top via renderOrder).
-    //
-    // Distance is chosen far enough back that no note ever lands
-    // beyond it; depthWrite=false on the plane material plus
-    // renderOrder=-1 means notes still paint on top regardless.
-    const BG_BACKDROP_DISTANCE = FOG_END * 0.95;
-
-    // Module-level scratch vector reused each frame to avoid GC
-    // churn from per-frame Vector3 allocation. Only valid for the
-    // duration of a single update() call.
-    const _bgBackdropTmp = (() => {
-        // Lazily created when T is available (T isn't bound at module
-        // parse time — initScene assigns it inside loadThree().then).
-        // Returning a getter that allocates on first read keeps the
-        // dependency timing clean.
-        let v = null;
-        return () => v || (v = new T.Vector3());
-    })();
-
-    // Frustum-fit a plane mesh: scale a unit PlaneGeometry to exactly
-    // fill the camera's view at the configured distance, then position
-    // it `distance` units in front of the camera and orient it so the
-    // texture faces the camera. Called whenever cam.aspect changes
-    // (resize) and to position-track the camera each frame.
-    function _bgFitBackdropPlane(state) {
-        const cam = state.cam;
-        const d = state.distance;
-        const halfFovRad = cam.fov * Math.PI / 360;
-        const visibleHeight = 2 * Math.tan(halfFovRad) * d;
-        const visibleWidth = visibleHeight * cam.aspect;
-        if (state.lastAspect !== cam.aspect ||
-            state.lastVisibleHeight !== visibleHeight) {
-            state.mesh.scale.set(visibleWidth, visibleHeight, 1);
-            state.lastAspect = cam.aspect;
-            state.lastVisibleHeight = visibleHeight;
-            state.lastVisibleWidth = visibleWidth;
-            // Aspect change shifts the cover-crop ratio; re-apply.
-            if (state.applyCoverCrop) state.applyCoverCrop();
-        }
-        // Track camera each frame: position = cam.position +
-        // cam.forward * distance, orient toward camera.
-        const fwd = cam.getWorldDirection(_bgBackdropTmp());
-        state.mesh.position.copy(cam.position).addScaledVector(fwd, d);
-        state.mesh.lookAt(cam.position);
-    }
-
-    // Cover-crop a texture to the plane aspect: the larger axis fills
-    // the plane (cropped if needed), centered. For wider-than-plane
-    // textures the X offset is left at the centered value but the
-    // image style's drift loop overwrites it per frame; the video
-    // style leaves it centered.
-    function _bgCoverCrop(tex, srcW, srcH, planeAspect) {
-        if (srcW <= 0 || srcH <= 0) return;
-        tex.repeat.set(1, 1);
-        tex.offset.set(0, 0);
-        const srcAspect = srcW / srcH;
-        if (srcAspect > planeAspect) {
-            tex.repeat.x = planeAspect / srcAspect;
-            tex.offset.x = (1 - tex.repeat.x) * 0.5;
-        } else {
-            tex.repeat.y = srcAspect / planeAspect;
-            tex.offset.y = (1 - tex.repeat.y) * 0.5;
-        }
-        tex.needsUpdate = true;
-    }
-
-    // Background-style registry. Each entry returns a per-panel state
-    // object from build() and reads from it in update() / teardown().
-    // T (THREE) is set by the time these are invoked (initScene runs
-    // inside loadThree().then).
-    const BG_STYLES = {
-        off: {
-            build() { return null; },
-            update() {},
-            teardown() {},
-        },
-        particles: {
-            build(scene, settings) {
-                const N = Math.max(20, Math.floor(80 + 200 * settings.intensity));
-                const positions = new Float32Array(N * 3);
-                for (let i = 0; i < N; i++) {
-                    positions[i * 3] = (Math.random() - 0.5) * 800 * K;
-                    positions[i * 3 + 1] = (Math.random() - 0.4) * 80 * K;
-                    // Spawn within the visible fog range. Fog reaches
-                    // its far limit at FOG_END * 1.2 from the camera,
-                    // and cam.position.z is updated each frame in
-                    // camUpdate() (`dist * 0.75`, where dist tracks
-                    // aspectScale). Anything beyond that camera-relative
-                    // distance gets fully fogged out, so the cutoff in
-                    // world z is dynamic — the earlier "push past notes"
-                    // fix placed particles at -FOG_END * (0.95..1.20)
-                    // which sat past fog far at any camera z, making
-                    // them invisible. renderOrder = -1 on the bg stage
-                    // already keeps particles behind notes regardless
-                    // of z, so depth-based separation wasn't needed and
-                    // was actively breaking visibility.
-                    positions[i * 3 + 2] = -FOG_START - Math.random() * (FOG_END - FOG_START) * 0.85;
-                }
-                const geo = new T.BufferGeometry();
-                geo.setAttribute('position', new T.BufferAttribute(positions, 3));
-                const mat = new T.PointsMaterial({
-                    // size 5*K (bumped from 1.5*K). At distance ~700*K
-                    // with sizeAttenuation the prior sprite shrank
-                    // below 2 pixels — practically invisible against
-                    // dark fog. 5*K reads as a small bright dot.
-                    // Build-time opacity is overridden every frame in
-                    // update() — the runtime formula is the source of
-                    // truth.
-                    color: 0xa0c0ff, size: 5 * K, transparent: true,
-                    blending: T.AdditiveBlending, depthWrite: false, sizeAttenuation: true,
-                });
-                const points = new T.Points(geo, mat);
-                scene.add(points);
-                return { points, geo, mat, N };
-            },
-            update(s, bands, dt) {
-                const positions = s.geo.attributes.position.array;
-                const dx = dt * (3 + bands.mid * 12) * K;
-                for (let i = 0; i < s.N; i++) {
-                    positions[i * 3] += dx;
-                    if (positions[i * 3] > 400 * K) positions[i * 3] -= 800 * K;
-                }
-                s.geo.attributes.position.needsUpdate = true;
-                // Bumped opacity floor 0.4 → 0.55 + treble headroom
-                // 0.4 → 0.45 so particles read as visible specks even
-                // when bgReactive is false / treble≈0 (was effectively
-                // 0.4 floor, below noise floor against dark fog).
-                s.mat.opacity = 0.55 + bands.treble * 0.45;
-            },
-            teardown(s) {
-                if (!s) return;
-                s.points.parent?.remove(s.points);
-                s.geo.dispose();
-                s.mat.dispose();
-            },
-        },
-        silhouettes: {
-            build(scene, settings) {
-                const canvas = _bgEnsureSilhouetteCanvas();
-                // Inside the visible fog range. Fog far = FOG_END * 1.2
-                // from the camera, and cam.position.z is dynamic
-                // (camUpdate() sets `dist * 0.75`). renderOrder = -1
-                // on the bg stage handles "behind notes" regardless
-                // of z. Spread the three layers across the back half
-                // of the visible fog band for parallax separation.
-                const depths = [-FOG_END * 0.55, -FOG_END * 0.70, -FOG_END * 0.85];
-                const layers = [];
-                const allocated = [];
-                try {
-                    for (const z of depths) {
-                        // Per-layer CanvasTexture wrapping the shared
-                        // canvas: lets each layer scroll independently
-                        // via texture.offset.x without coupling to its
-                        // siblings or to other panels.
-                        const tex = new T.CanvasTexture(canvas);
-                        tex.wrapS = T.RepeatWrapping;
-                        const geo = new T.PlaneGeometry(800 * K, 50 * K);
-                        const mat = new T.MeshBasicMaterial({
-                            map: tex, transparent: true, opacity: 0.4, depthWrite: false,
-                        });
-                        const mesh = new T.Mesh(geo, mat);
-                        mesh.position.set(0, -10 * K, z);
-                        scene.add(mesh);
-                        // Parallax: nearer layers move more than farther
-                        // ones (perspective). distance = -z; small d ->
-                        // large parallax. Scaled so the nearest sits
-                        // around 0.32 and farthest around 0.18.
-                        const distance = -z;
-                        const parallax = Math.max(0.05, 1 - distance / (FOG_END * 1.4));
-                        const layer = { mesh, geo, mat, tex, z, drift: 0, parallax };
-                        layers.push(layer);
-                        allocated.push(layer);
-                    }
-                    return { layers, intensity: settings.intensity };
-                } catch (e) {
-                    // Build threw partway — clean up any per-layer
-                    // textures we already created. _bgMountStyle's catch
-                    // disposes the stage tree's meshes, but a partial-
-                    // build's CanvasTextures aren't reachable from any
-                    // mesh yet, so this catch owns them.
-                    for (const L of allocated) {
-                        L.tex?.dispose?.();
-                    }
-                    throw e;
-                }
-            },
-            update(s, bands, dt) {
-                // Intensity multiplier: 0 dims to ~50% of base, 1
-                // brightens to ~120%. Below-base values still leave the
-                // silhouettes faintly visible so users know the style
-                // is on; above-base lets the layers read as a real
-                // backdrop on louder passages.
-                const intensityMul = 0.5 + s.intensity * 0.7;
-                for (const L of s.layers) {
-                    // Scroll via texture.offset.x with RepeatWrapping —
-                    // unbounded, no modulus snap. The mesh stays put;
-                    // the texture wraps continuously across the visible
-                    // surface. (offset is in normalized texture space,
-                    // so we keep it small and let the wrap do the job.)
-                    L.drift += dt * (0.05 + bands.mid * 0.15) * L.parallax;
-                    L.mat.map.offset.x = L.drift;
-                    L.mesh.position.y = -10 * K + bands.bass * 4 * K;
-                    L.mat.opacity = (0.25 + 0.5 * L.parallax) * intensityMul;
-                }
-            },
-            teardown(s) {
-                if (!s) return;
-                for (const L of s.layers) {
-                    L.mesh.parent?.remove(L.mesh);
-                    L.geo.dispose();
-                    L.mat.dispose();
-                    L.tex.dispose();
-                }
-            },
-        },
-        lights: {
-            build(scene, settings) {
-                // Lights count scales 6 → 14 over intensity 0 → 1.
-                // _bgCoerce clamps intensity to [0,1] before it reaches
-                // here, so no further clamp is needed.
-                const N = Math.floor(6 + 8 * settings.intensity);
-                const lights = [];
-                // Palette comes from the calling panel's settings so
-                // each splitscreen panel picks its own (issue #10).
-                // Falls back to the default palette if the caller
-                // doesn't supply one (e.g. an older code path).
-                const palette = settings.palette || PALETTES.default;
-                for (let i = 0; i < N; i++) {
-                    const color = palette[i % palette.length];
-                    // 30*K plane reads as a real stage glow at distance.
-                    // Build-time opacity is overridden every frame in
-                    // update() — the runtime formula is the source of
-                    // truth.
-                    const geo = new T.PlaneGeometry(30 * K, 30 * K);
-                    const mat = new T.MeshBasicMaterial({
-                        color, transparent: true,
-                        blending: T.AdditiveBlending, depthWrite: false,
-                    });
-                    const mesh = new T.Mesh(geo, mat);
-                    mesh.position.set(
-                        (Math.random() - 0.5) * 600 * K,
-                        (Math.random() - 0.3) * 80 * K,
-                        // Inside visible fog range; renderOrder = -1
-                        // keeps lights behind notes regardless of z.
-                        -FOG_START - Math.random() * (FOG_END - FOG_START) * 0.85
-                    );
-                    scene.add(mesh);
-                    lights.push({ mesh, geo, mat, baseScale: 1 + Math.random() * 0.5, phase: Math.random() * Math.PI * 2 });
-                }
-                return { lights };
-            },
-            update(s, bands, dt, t) {
-                // Bumped opacity floor 0.35 → 0.55 + treble headroom
-                // 0.3 → 0.4 so lights read as visible stage glows at
-                // distance instead of faint specks (was effectively
-                // 0.35 floor since the build-time bump was overridden
-                // by this formula).
-                for (const L of s.lights) {
-                    const pulse = 1 + bands.bass * 1.5 + Math.sin(t * 1.5 + L.phase) * 0.2;
-                    L.mesh.scale.set(L.baseScale * pulse, L.baseScale * pulse, 1);
-                    L.mat.opacity = 0.55 + bands.treble * 0.4;
-                }
-            },
-            teardown(s) {
-                if (!s) return;
-                for (const L of s.lights) {
-                    L.mesh.parent?.remove(L.mesh);
-                    L.geo.dispose();
-                    L.mat.dispose();
-                }
-            },
-        },
-        geometric: {
-            build(scene, settings) {
-                const meshes = [];
-                // Bumped opacity floor (0.25 → 0.45) + ceiling so the
-                // wireframes read as real shapes instead of barely-
-                // there ghosts at low intensity.
-                const op = 0.45 + 0.25 * settings.intensity;
-                const ico = new T.Mesh(
-                    new T.IcosahedronGeometry(30 * K, 1),
-                    new T.MeshBasicMaterial({ color: 0x6080c0, wireframe: true, transparent: true, opacity: op, depthWrite: false }),
-                );
-                // Inside visible fog range; renderOrder = -1 keeps
-                // wireframes behind notes regardless of z.
-                ico.position.set(-100 * K, 30 * K, -FOG_END * 0.65);
-                scene.add(ico);
-                meshes.push(ico);
-                const torus = new T.Mesh(
-                    new T.TorusGeometry(22 * K, 4 * K, 6, 12),
-                    new T.MeshBasicMaterial({ color: 0xc06080, wireframe: true, transparent: true, opacity: op * 0.9, depthWrite: false }),
-                );
-                torus.position.set(120 * K, 20 * K, -FOG_END * 0.75);
-                scene.add(torus);
-                meshes.push(torus);
-                return { meshes };
-            },
-            update(s, bands, dt) {
-                const speed = 0.2 + bands.mid * 0.4;
-                const pulse = 1 + bands.bass * 0.25;
-                for (const m of s.meshes) {
-                    m.rotation.x += dt * speed * 0.3;
-                    m.rotation.y += dt * speed * 0.4;
-                    m.scale.setScalar(pulse);
-                }
-            },
-            teardown(s) {
-                if (!s) return;
-                for (const m of s.meshes) {
-                    m.parent?.remove(m);
-                    m.geometry.dispose();
-                    m.material.dispose();
-                }
-            },
-        },
-        // Venue visualization — generated small-club raster bg plate
-        // behind the highway. Activated via h3dVenueSceneSetActive(true)
-        // when Visualization = Venue; does not persist as a user bg style.
-        venue: {
-            build(scene, settings) {
-                const coeffs = _bgVenueMoodCoeffs(_venueMoodState);
-                const state = {
-                    backdrop: null,
-                    haze: null,
-                    loader: null,
-                    instrumentPov: _venueInstrumentPov,
-                    plateLoading: false,
-                    pending: 1,
-                    loaded: false,
-                    failed: false,
-                };
-
-                function _venueMarkLoaded() {
-                    state.pending--;
-                    if (state.pending <= 0 && !state.failed) {
-                        state.loaded = true;
-                        _venueSceneAssetsLoaded = true;
-                        _venueSceneLoadFailed = false;
-                        try {
-                            if (typeof window !== 'undefined' && window.v3VenueScene3d &&
-                                typeof window.v3VenueScene3d.onAssetsLoaded === 'function') {
-                                window.v3VenueScene3d.onAssetsLoaded();
-                            }
-                        } catch (_) { /* visual-only */ }
-                    }
-                }
-                function _venueMarkFailed(msg) {
-                    if (state.failed) return;
-                    state.failed = true;
-                    _venueSceneLoadFailed = true;
-                    _venueSceneAssetsLoaded = false;
-                    console.warn('[venue-scene] ' + msg);
-                    _venueSceneOverride = false;
-                    _bgEmitChange('venueScene');
-                    try {
-                        if (typeof window !== 'undefined' && window.v3VenueScene3d &&
-                            typeof window.v3VenueScene3d.onAssetsFailed === 'function') {
-                            window.v3VenueScene3d.onAssetsFailed(msg);
-                        }
-                    } catch (_) { /* visual-only */ }
-                }
-
-                const loader = new T.TextureLoader();
-                state.loader = loader;
-                const backdrop = {
-                    mesh: null, geo: null, mat: null, tex: null,
-                    cam: settings.cam, distance: BG_BACKDROP_DISTANCE * VENUE_BACKDROP_DISTANCE_MUL,
-                    lastAspect: 0, lastVisibleHeight: 0, lastVisibleWidth: 0, loaded: false,
-                };
-                backdrop.geo = new T.PlaneGeometry(1, 1);
-                backdrop.mat = new T.MeshBasicMaterial({
-                    color: 0xffffff, transparent: false, depthWrite: false, fog: false,
-                });
-                backdrop.mesh = new T.Mesh(backdrop.geo, backdrop.mat);
-                backdrop.mesh.visible = false;
-                scene.add(backdrop.mesh);
-                state.backdrop = backdrop;
-                backdrop.applyCoverCrop = function () {
-                    if (!backdrop.tex || !backdrop.tex.image) return;
-                    _bgCoverCrop(
-                        backdrop.tex,
-                        backdrop.tex.image.width || 0,
-                        backdrop.tex.image.height || 0,
-                        backdrop.cam.aspect,
-                    );
-                };
-                _venueLoadPlateForPov(
-                    loader,
-                    _venueInstrumentPov,
-                    backdrop,
-                    () => _venueMarkLoaded(),
-                    () => _venueMarkFailed('failed to load small-club bg plate'),
-                );
-
-                // Crowd video planes (career mode): two crossfading layers
-                // just in front of the static plate (which stays mounted as
-                // the no-pack / load-failure fallback). Textures bind lazily
-                // in update() when venue-crowd.js assigns video elements.
-                state.crowd = { layers: [], rev: -1 };
-                for (let i = 0; i < 2; i++) {
-                    const geo = new T.PlaneGeometry(1, 1);
-                    const mat = new T.MeshBasicMaterial({
-                        color: 0xffffff, transparent: true, opacity: 0,
-                        depthWrite: false, fog: false,
-                    });
-                    const mesh = new T.Mesh(geo, mat);
-                    mesh.visible = false;
-                    // Layer 1 sits nearest so three.js's back-to-front
-                    // transparent sort draws it after layer 0.
-                    const layer = {
-                        mesh, geo, mat, tex: null, videoEl: null,
-                        cam: settings.cam,
-                        distance: BG_BACKDROP_DISTANCE * (i === 0 ? 1.04 : 1.03),
-                        lastAspect: 0, lastVisibleHeight: 0,
-                    };
-                    layer.applyCoverCrop = function () {
-                        if (!layer.videoEl || !layer.tex) return;
-                        _bgCoverCrop(
-                            layer.tex,
-                            layer.videoEl.videoWidth || 0,
-                            layer.videoEl.videoHeight || 0,
-                            layer.cam.aspect,
-                        );
-                    };
-                    scene.add(mesh);
-                    state.crowd.layers.push(layer);
-                }
-
-                const hazeGeo = new T.PlaneGeometry(280 * K, 40 * K);
-                const hazeMat = new T.MeshBasicMaterial({
-                    color: 0x101820, transparent: true, opacity: coeffs.haze,
-                    depthWrite: false, fog: false,
-                });
-                const hazeMesh = new T.Mesh(hazeGeo, hazeMat);
-                hazeMesh.position.set(0, -12 * K, -FOG_END * 0.70);
-                scene.add(hazeMesh);
-                state.haze = {
-                    mesh: hazeMesh, geo: hazeGeo, mat: hazeMat, baseOp: coeffs.haze,
-                    baseX: 0, baseY: -12 * K, baseZ: -FOG_END * 0.70,
-                };
-
-                return state;
-            },
-            update(s, bands, dt, t) {
-                if (!s || s.failed) return;
-                _venueSwapPlateIfNeeded(s);
-                const coeffs = _bgVenueMoodCoeffs(_venueMoodState);
-                if (s.backdrop && s.backdrop.loaded) {
-                    _bgFitBackdropPlane(s.backdrop);
-                }
-                const motion = _venueApplyFakeDepthMotion(s, coeffs, t);
-                if (s.backdrop && s.backdrop.loaded && s.backdrop.mat && !motion.breathe && !motion.warmthPulse) {
-                    const warm = coeffs.warmth;
-                    s.backdrop.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
-                }
-                if (s.haze && s.haze.mat && !motion.hazeDrift && !motion.shimmer) {
-                    s.haze.mat.opacity = (s.haze.baseOp || VENUE_HAZE_STEADY)
-                        * (coeffs.haze / VENUE_HAZE_STEADY);
-                }
-                if (s.crowd) {
-                    // Rebind VideoTextures when venue-crowd.js (re)assigns
-                    // elements. VideoTexture samples the element every frame,
-                    // so a src change on the same element needs no rebind.
-                    if (s.crowd.rev !== _venueCrowdRev) {
-                        s.crowd.rev = _venueCrowdRev;
-                        s.crowd.layers.forEach((layer, i) => {
-                            const el = _venueCrowdVideos[i];
-                            if (layer.videoEl === el) return;
-                            if (layer.tex) { layer.mat.map = null; layer.tex.dispose(); layer.tex = null; }
-                            layer.videoEl = el;
-                            layer.lastAspect = 0; // force refit + recrop
-                            if (el) {
-                                const tex = new T.VideoTexture(el);
-                                tex.colorSpace = T.SRGBColorSpace;
-                                tex.wrapS = T.ClampToEdgeWrapping;
-                                tex.wrapT = T.ClampToEdgeWrapping;
-                                tex.minFilter = T.LinearFilter;
-                                tex.magFilter = T.LinearFilter;
-                                tex.generateMipmaps = false;
-                                layer.tex = tex;
-                                layer.mat.map = tex;
-                            }
-                            layer.mat.needsUpdate = true;
-                        });
-                    }
-                    const warm = coeffs.warmth;
-                    s.crowd.layers.forEach((layer, i) => {
-                        const el = layer.videoEl;
-                        // videoWidth === 0 until metadata lands — showing the
-                        // plane before that paints a black flash over the plate.
-                        const ready = !!el && el.videoWidth > 0;
-                        // venue-crowd.js swaps src on the same element (loop ↔
-                        // stinger); a new intrinsic size needs a fresh
-                        // cover-crop, which _bgFitBackdropPlane only reapplies
-                        // on camera aspect changes.
-                        if (ready && (layer.lastVidW !== el.videoWidth ||
-                                      layer.lastVidH !== el.videoHeight)) {
-                            layer.lastVidW = el.videoWidth;
-                            layer.lastVidH = el.videoHeight;
-                            layer.applyCoverCrop();
-                        }
-                        // Layer 0 (rear) stays fully opaque whenever any of the
-                        // fade involves it: two half-transparent layers would
-                        // let the static plate behind bleed through (~25% at
-                        // mid-fade). The crossfade is therefore layer 1 (front)
-                        // fading over an opaque layer 0 — in both directions.
-                        const opacity = i === 0
-                            ? (_venueCrowdMix < 0.999 ? 1 : 0)
-                            : _venueCrowdMix;
-                        layer.mat.opacity = opacity;
-                        layer.mesh.visible = ready && opacity > 0.01;
-                        if (layer.mesh.visible) {
-                            layer.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
-                            _bgFitBackdropPlane(layer);
-                        }
-                    });
-                }
-            },
-            teardown(s) {
-                if (!s) return;
-                _venueSceneAssetsLoaded = false;
-                for (const key of ['backdrop', 'haze']) {
-                    const p = s[key];
-                    if (!p) continue;
-                    p.mesh?.parent?.remove(p.mesh);
-                    p.geo?.dispose?.();
-                    if (p.mat) {
-                        p.mat.map = null;
-                        p.mat.dispose?.();
-                    }
-                }
-                // Crowd planes: this style owns the VideoTextures; the
-                // <video> elements belong to venue-crowd.js and survive.
-                if (s.crowd) {
-                    for (const layer of s.crowd.layers) {
-                        layer.mesh?.parent?.remove(layer.mesh);
-                        layer.geo?.dispose?.();
-                        if (layer.mat) {
-                            layer.mat.map = null;
-                            layer.mat.dispose?.();
-                        }
-                        layer.tex?.dispose?.();
-                    }
-                }
-                // Dispose the cached plate textures too — the module-level cache
-                // otherwise keeps every loaded POV plate GPU-resident for the
-                // page lifetime (steady VRAM growth across POV/arrangement swaps).
-                try {
-                    _venueTextureCache.forEach((tex) => { tex?.dispose?.(); });
-                } catch (_) { /* visual-only */ }
-                _venueTextureCache.clear();
-            },
-        },
-        // Custom image backdrop (#19). User uploads a JPG/PNG/WebP
-        // through settings.html; the bytes are persisted as a base64
-        // data URL in localStorage under h3d_bg_customImageDataUrl and
-        // passed in via settings.customImageDataUrl. Renders as a
-        // PlaneGeometry in the silhouette parallax band, "cover" cropped
-        // (via texture.repeat / offset) so non-matching aspects fill
-        // the plane without distortion. Slow horizontal drift on
-        // texture.offset.x for life. When no asset is uploaded, build
-        // returns null and the style is inert (settings.html disables
-        // the picker option in that case).
-        image: {
-            build(scene, settings) {
-                // Upfront validation: only accept the same raster image
-                // formats settings.html lets the user upload (jpeg /
-                // png / webp). Without this, a corrupt localStorage
-                // value (truncated base64, wrong scheme, plain string)
-                // OR an unsupported type (e.g. data:image/svg+xml)
-                // reaches TextureLoader and can fail asynchronously
-                // after the plane has been mounted — a silent black
-                // backdrop with no clear cause. Returning null here
-                // treats invalid bytes the same as "no asset uploaded":
-                // style is inert, the user can clear and re-upload
-                // from settings.html.
-                const dataUrl = (typeof settings.customImageDataUrl === 'string')
-                    ? settings.customImageDataUrl.trim() : '';
-                if (!/^data:image\/(jpeg|png|webp);/i.test(dataUrl)) return null;
-                // Renderer-side encoded-length cap. settings.html
-                // enforces the same limit on upload, but a manually
-                // edited localStorage value (or legacy data from
-                // before the upload guard existed) could still feed
-                // an arbitrarily large data URL into TextureLoader
-                // and burn memory / CPU during decode. Treat overlong
-                // values as "no asset" — style is inert, user can
-                // clear and re-upload from settings.
-                if (dataUrl.length > 2.5 * 1024 * 1024) return null;
-                // Renderer-side decompression-bomb caps. Mirror
-                // settings.html's upload-time guard so a manual
-                // localStorage edit (or legacy data from before that
-                // guard existed) can't sneak a 50000×50000 PNG past
-                // and OOM the GPU on texture upload.
-                const MAX_IMAGE_DIM = 4096;
-                const MAX_IMAGE_PIXELS = 16 * 1024 * 1024;
-                // Full-bleed backdrop: unit plane, scaled per frame in
-                // _bgFitBackdropPlane to fill the camera's view at
-                // BG_BACKDROP_DISTANCE. fog: false so the backdrop
-                // shows in full color; notes drawn on top still pick
-                // up atmospheric fog as before.
-                const state = {
-                    mesh: null, geo: null, mat: null, tex: null,
-                    drift: 0.5, intensity: settings.intensity, loaded: false,
-                    cam: settings.cam, distance: BG_BACKDROP_DISTANCE,
-                    lastAspect: 0, lastVisibleHeight: 0,
-                };
-                // Helper closure for cover-crop refresh — called both
-                // on async decode (initial) and from _bgFitBackdropPlane
-                // when the camera aspect changes (resize).
-                state.applyCoverCrop = function () {
-                    if (!state.tex || !state.tex.image) return;
-                    _bgCoverCrop(
-                        state.tex,
-                        state.tex.image.width  || 0,
-                        state.tex.image.height || 0,
-                        state.cam.aspect,
-                    );
-                };
-                const tex = new T.TextureLoader().load(
-                    dataUrl,
-                    (loaded) => {
-                        // Image dimensions are only known after async decode.
-                        const imgW = loaded.image?.width  || 0;
-                        const imgH = loaded.image?.height || 0;
-                        if (imgW > MAX_IMAGE_DIM || imgH > MAX_IMAGE_DIM || (imgW * imgH) > MAX_IMAGE_PIXELS) {
-                            // Bail before the texture gets uploaded to
-                            // the GPU (Three.js uploads on first render
-                            // of a visible mesh — hiding the mesh here
-                            // skips that). Disposing the texture too,
-                            // belt-and-suspenders, in case anything
-                            // else holds a reference.
-                            console.warn('[3D-Hwy] custom image dimensions too large to render', imgW + 'x' + imgH);
-                            if (state.mesh) state.mesh.visible = false;
-                            loaded.dispose();
-                            return;
-                        }
-                        state.applyCoverCrop();
-                        // Reset drift to the centered triangle-wave
-                        // phase now that repeat.x is final. Without
-                        // this reset, drift accumulated during the
-                        // async decode would phase-shift the initial
-                        // offset by a non-deterministic amount —
-                        // wider images would open at whatever crop
-                        // the elapsed-decode-time happened to land on.
-                        state.drift = 0.5;
-                        state.loaded = true;
-                    },
-                    undefined,
-                    // Async-failure path: the upfront regex catches the
-                    // common "corrupted/truncated bytes" case, but a
-                    // valid-looking data URL can still fail to decode
-                    // (e.g. wrong MIME / unsupported codec). Hide the
-                    // mesh so we don't paint a frozen blank plane on
-                    // top of fog, and log so the failure isn't silent.
-                    (err) => {
-                        console.error('[3D-Hwy] custom image decode failed', err);
-                        if (state.mesh) state.mesh.visible = false;
-                    },
-                );
-                tex.colorSpace = T.SRGBColorSpace;
-                // ClampToEdge on both axes — user uploads are non-
-                // power-of-two in general, and WebGL1 rejects RepeatWrapping
-                // on NPOT textures (renders black or emits GL errors). The
-                // drift logic below uses a triangle-wave so the offset
-                // stays inside [0, 1-repeat] and never needs wrap.
-                tex.wrapS = T.ClampToEdgeWrapping;
-                tex.wrapT = T.ClampToEdgeWrapping;
-                // User uploads aren't power-of-two in general; mipmaps
-                // are noisy for a single static backdrop and burn memory.
-                tex.generateMipmaps = false;
-                tex.minFilter = T.LinearFilter;
-                tex.magFilter = T.LinearFilter;
-                const geo = new T.PlaneGeometry(1, 1);
-                const mat = new T.MeshBasicMaterial({
-                    map: tex, transparent: false, depthWrite: false, fog: false,
-                });
-                const mesh = new T.Mesh(geo, mat);
-                scene.add(mesh);
-                state.mesh = mesh;
-                state.geo  = geo;
-                state.mat  = mat;
-                state.tex  = tex;
-                // Initial fit so the first frame is correctly sized
-                // and positioned, even if update() hasn't run yet.
-                _bgFitBackdropPlane(state);
-                return state;
-            },
-            update(s, bands, dt) {
-                if (!s) return;
-                // Track camera position / aspect every frame. The
-                // helper resizes the plane and refreshes cover-crop
-                // when aspect changes, and re-positions the plane to
-                // stay BG_BACKDROP_DISTANCE in front of the camera.
-                _bgFitBackdropPlane(s);
-                // Skip drift advance until the texture has finished
-                // decoding. Without this guard, drift accumulates
-                // during the async load while repeat.x is still 1
-                // (its default), and once the cover-crop applies the
-                // image opens at a phase-shifted offset whose value
-                // depends on how long the decode took — the
-                // "centered start" intent becomes non-deterministic.
-                if (!s.loaded) return;
-                // Triangle-wave ping-pong drift inside the cropped slack.
-                // ClampToEdge on wrapS means we cannot wrap across the
-                // texture boundary (would render edge pixels stretched);
-                // ping-pong oscillates the visible window between the
-                // image's left and right edges, which gives the same
-                // "alive" feel without the WebGL1 NPOT-Repeat hazard.
-                // Slack is the horizontal margin between the cropped
-                // window and the texture edges; for taller-than-plane
-                // images repeat.x stays 1, slack collapses to 0, and
-                // the offset stays at 0 — the image sits still, which
-                // is correct (it's already filling horizontally).
-                s.drift += dt * 0.02 * s.intensity;
-                const slack = Math.max(0, 1 - s.tex.repeat.x);
-                // Period of 2 drift units ≈ 100 s at intensity = 0.5;
-                // gentle, cinematic. cyc ∈ [0, 2), tri ∈ [0, 1] then back.
-                const cyc = ((s.drift % 2) + 2) % 2;
-                const tri = cyc < 1 ? cyc : 2 - cyc;
-                s.tex.offset.x = tri * slack;
-            },
-            teardown(s) {
-                if (!s) return;
-                s.mesh.parent && s.mesh.parent.remove(s.mesh);
-                s.geo.dispose();
-                s.mat.dispose();
-                // This style owns the texture lifecycle (per the comment
-                // at _bgDisposeGroupTree: tree dispose does NOT touch
-                // material.map textures).
-                s.tex.dispose();
-            },
-        },
-        // Custom video backdrop (#19 follow-up). User uploads a
-        // .mp4/.webm via settings.html; routes.py stores it on disk and
-        // serves a same-origin URL (avoids CORS taint on VideoTexture).
-        // localStorage holds only the filename — bytes live in
-        // {config_dir}/plugin_uploads/highway_3d/. Per-panel video
-        // element so each panel can mount/teardown independently;
-        // browsers cache the video bytes after first fetch so multi-
-        // panel splitscreen pays only the decoder cost, not the
-        // network or disk-read cost.
-        video: {
-            build(scene, settings) {
-                // Lowercase before validation so a manual localStorage
-                // edit like `current.MP4` doesn't pass a case-insensitive
-                // regex check and then 404 against the server, which
-                // only ever produces and serves lowercase
-                // current.<ext> (the upload route lowercases the
-                // extension; routes.py's GET pattern is case-sensitive).
-                const filename = (typeof settings.customVideoName === 'string')
-                    ? settings.customVideoName.trim().toLowerCase() : '';
-                // Strict pattern matches routes.py's deterministic
-                // single-slot naming. Any other shape (corrupt
-                // localStorage, future schema change) → style is
-                // inert, no <video> created, no orphan request to a
-                // 404 endpoint.
-                if (!/^current\.(mp4|webm)$/.test(filename)) return null;
-                const url = '/api/plugins/highway_3d/files/' + filename;
-
-                // Track partial allocations so a throw between any of
-                // them can clean up. _bgMountStyle's failure path
-                // disposes the stage tree but explicitly does NOT
-                // dispose textures (per the comment at
-                // _bgDisposeGroupTree), and the <video> element is
-                // parented to document.body — not the stage — so
-                // neither would be reached without an explicit catch.
-                let videoEl = null, tex = null, geo = null, mat = null, mesh = null;
-                try {
-                    // muted + playsInline + autoplay is the cross-
-                    // browser recipe that bypasses gesture requirements
-                    // (Chrome, Firefox, Safari desktop + mobile).
-                    // preload='auto' lets the first frame land before
-                    // play() is called. src is deliberately NOT set
-                    // yet — we want every piece of state (mesh, tex)
-                    // to exist before the browser can fire
-                    // loadedmetadata or error events on a cached
-                    // resource. The handlers close over state.tex /
-                    // state.mesh; setting src first would create a
-                    // window where a fast cache hit could fire an
-                    // event into half-initialized state.
-                    videoEl = document.createElement('video');
-                    // No crossOrigin attribute: the URL is same-origin
-                    // (/api/plugins/highway_3d/files/…), so VideoTexture
-                    // never sees a tainted canvas. Setting
-                    // `crossOrigin = "anonymous"` would also strip
-                    // cookies from the fetch, which would 401 against
-                    // any cookie-protected feedBack deployment. If
-                    // this ever needs to fetch cross-origin, switch
-                    // to `use-credentials` AND have the server send
-                    // the matching CORS headers.
-                    videoEl.muted = true;
-                    videoEl.playsInline = true;
-                    videoEl.loop = true;
-                    videoEl.autoplay = true;
-                    videoEl.preload = 'auto';
-                    videoEl.style.display = 'none';
-                    document.body.appendChild(videoEl);
-
-                    // Build mesh + texture before registering listeners
-                    // and before setting src. By the time loadedmetadata
-                    // or error can fire, state.tex and state.mesh are
-                    // both populated.
-                    tex = new T.VideoTexture(videoEl);
-                    tex.colorSpace = T.SRGBColorSpace;
-                    tex.wrapS = T.ClampToEdgeWrapping;
-                    tex.wrapT = T.ClampToEdgeWrapping;
-                    tex.minFilter = T.LinearFilter;
-                    tex.magFilter = T.LinearFilter;
-                    tex.generateMipmaps = false;
-                    geo = new T.PlaneGeometry(1, 1);
-                    mat = new T.MeshBasicMaterial({
-                        map: tex, transparent: false, depthWrite: false, fog: false,
-                    });
-                    mesh = new T.Mesh(geo, mat);
-                    scene.add(mesh);
-
-                    // Full-bleed backdrop: scaled and positioned each
-                    // frame in update() via _bgFitBackdropPlane.
-                    // cam + distance + lastAspect / lastVisibleHeight
-                    // power that helper.
-                    const state = {
-                        videoEl, mesh, geo, mat, tex,
-                        cam: settings.cam, distance: BG_BACKDROP_DISTANCE,
-                        lastAspect: 0, lastVisibleHeight: 0,
-                    };
-                    state.applyCoverCrop = function () {
-                        if (!state.videoEl) return;
-                        _bgCoverCrop(
-                            state.tex,
-                            state.videoEl.videoWidth  || 0,
-                            state.videoEl.videoHeight || 0,
-                            state.cam.aspect,
-                        );
-                    };
-
-                    // Cover-crop math runs on loadedmetadata since
-                    // video dimensions aren't known until then.
-                    // _bgFitBackdropPlane will also re-apply when the
-                    // camera aspect changes.
-                    videoEl.addEventListener('loadedmetadata', () => {
-                        state.applyCoverCrop();
-                    });
-                    videoEl.addEventListener('error', () => {
-                        // Fired for: codec unsupported, 404 from
-                        // server, truncated file, etc. Hide the mesh
-                        // so we don't paint a frozen blank plane on
-                        // top of fog.
-                        console.error('[3D-Hwy] custom video load failed', videoEl.error);
-                        state.mesh.visible = false;
-                    });
-
-                    // Set src last — this is what triggers the async
-                    // load. With handlers and state in place, any
-                    // synchronous-feeling event from a cached resource
-                    // is still safely received and handled.
-                    videoEl.src = url;
-
-                    // play() can reject for transient reasons (tab
-                    // backgrounded at mount time, low-power mode,
-                    // brief autoplay-policy timing window) even with
-                    // muted + autoplay set — but the browser retries
-                    // on its own once conditions improve (visibility
-                    // change, foregrounding, gesture). Real load /
-                    // codec failures come through the `error` event
-                    // we registered above and DO hide the mesh. So
-                    // just log here and leave the mesh visible; the
-                    // next ready frame will paint.
-                    videoEl.play().catch((err) => {
-                        console.warn('[3D-Hwy] custom video play() rejected (will retry on visibility/gesture)', err);
-                    });
-                    // Initial fit so the first frame is correctly
-                    // sized and positioned even before update() runs.
-                    _bgFitBackdropPlane(state);
-                    return state;
-                } catch (err) {
-                    // Best-effort cleanup of whatever was allocated
-                    // before the throw. Each step is independently
-                    // guarded so a secondary failure (e.g. dispose
-                    // throwing on an already-disposed object) can't
-                    // mask the original error.
-                    try {
-                        if (videoEl) {
-                            videoEl.pause();
-                            videoEl.removeAttribute('src');
-                            videoEl.load();
-                            if (videoEl.parentNode) videoEl.parentNode.removeChild(videoEl);
-                        }
-                    } catch (_) { /* ignore */ }
-                    try { if (mesh && mesh.parent) mesh.parent.remove(mesh); } catch (_) { /* ignore */ }
-                    try { if (geo) geo.dispose(); } catch (_) { /* ignore */ }
-                    try { if (mat) mat.dispose(); } catch (_) { /* ignore */ }
-                    try { if (tex) tex.dispose(); } catch (_) { /* ignore */ }
-                    throw err;
-                }
-            },
-            update(s) {
-                if (!s) return;
-                // VideoTexture auto-updates from the playing element —
-                // Three.js samples the current frame each render. No
-                // per-frame texture mutation here. Drift on offset.x
-                // is intentionally omitted: the video's own motion is
-                // the "life", drifting the crop on top would feel
-                // busy and compete with playback. The only per-frame
-                // work is keeping the plane camera-locked and resized
-                // when aspect changes (handled inside the helper).
-                _bgFitBackdropPlane(s);
-            },
-            teardown(s) {
-                if (!s) return;
-                if (s.videoEl) {
-                    try { s.videoEl.pause(); } catch (_) {}
-                    s.videoEl.removeAttribute('src');
-                    // load() with no src tells the browser to release
-                    // any decoder/buffer state for this element.
-                    try { s.videoEl.load(); } catch (_) {}
-                    if (s.videoEl.parentNode) s.videoEl.parentNode.removeChild(s.videoEl);
-                }
-                if (s.mesh) s.mesh.parent && s.mesh.parent.remove(s.mesh);
-                if (s.geo) s.geo.dispose();
-                if (s.mat) s.mat.dispose();
-                if (s.tex) s.tex.dispose();
-            },
-        },
-    };
-
-    /* ======================================================================
-     *  Per-instance counter
-     * ====================================================================== */
-
-    let _nextInstanceId = 0;
-
-    /* ======================================================================
-     *  Factory — feedBack#36 setRenderer contract
-     * ====================================================================== */
-
-    function createFactory() {
-        const _instanceId = ++_nextInstanceId;
-
-        // ── Per-instance Three.js state ───────────────────────────────────
-        let scene = null, cam = null, ren = null;
-        let wrap = null;
-        // WebGL context-loss recovery. Switching the active window / alt-tabbing
-        // (especially on Windows) can trigger a GPU context reset; with no
-        // handler the lost context escalates into a render-process crash. The
-        // listeners (bound in initScene on ren.domElement, removed in teardown)
-        // preventDefault the loss so the browser keeps the context restorable,
-        // _ctxLost gates draw() off the dead context, and on restore we reset the
-        // viewport + resume (Three re-uploads scene resources on the next render).
-        let _ctxLost = false;
-        let _onCtxLost = null, _onCtxRestored = null;
-        let bcCtrl = null; // Butterchurn audio-reactive background (the 'butterchurn' bg-style)
-        let _chartEnv = 0, _chartPrevT = -1, _bcBeatIdx = 0, _bcNoteIdx = 0, _bcChordIdx = 0, _bcTintTarget = null;
-        let _tintR = 20, _tintG = 24, _tintB = 40; // smoothed instrument-color tint for the bg
-        // highway:visibility listener (feedBack#246). Hides the .h3d-wrap
-        // overlay when feedBack's canvas is display:none'd (splitscreen
-        // case). Without this, the wrap is a *sibling* of #highway so
-        // hiding #highway leaves the WebGL scene painting full-screen.
-        // Bound in initScene after wrap creation, unbound in destroy().
-        let _visibilityHandler = null;
-        // highway:canvas-replaced listener — keeps highwayCanvas up to
-        // date across context-type swaps (e.g. swapping back to a 2D
-        // viz). The visibility handler's identity gate (event.detail.
-        // canvas === highwayCanvas) would otherwise stop matching
-        // after the swap; this listener follows the documented plugin
-        // contract from CLAUDE.md.
-        let _canvasReplacedHandler = null;
-        let ambLight = null, dirLight = null;
-        let fretG = null, tuningLblG = null, noteG = null, beatG = null, lblG = null;
-        let gNote = null, gSus = null, gBeat = null, gTapChevron = null;
-        // Per-string gradient gem geometries (index 0..5). Built in initScene
-        // from sampled colour PNGs; each carries a per-vertex colour attribute.
-        let gNoteGrad = [];
-        let mStr = [], mGlow = [], mSus = [], mStrHitOutline = [], mAccentOutline = [], mAccentCore = [], mAccentHaloNear = [], mAccentHaloMid = [], mAccentHaloFar = [];
-        // Pre-built accent-halo shell descriptors per string. Populated after
-        // mAccentHaloFar/Mid/Near are materialised; consumed in drawNote()'s
-        // hot path so the inner per-note `accentShells = [...]` array literal
-        // (3 plain-object allocations per accent gem per frame) is replaced
-        // by a stable read. Index 0 = outer, 1 = mid, 2 = near.
-        let _accentShellsByString = [];
-        let mWhiteOutline = null, mSusOutline = null;
-        // Dedicated sustain-trail outline material for the hit verdict.
-        // Drawn at opacity 0.45 — lower than mSusOutline (0.75) so the
-        // bright green emissive doesn't tint the body interior, and the
-        // verdict shows mostly on the outline fringe past the body edges.
-        // Only the hit-side rim ships; the verdict on miss is carried by
-        // mMissOutline (the gem-border material) instead of a dedicated
-        // sustain outline — matches the "outline-only verdict, body retains
-        // string colour" doctrine for the rest of the rendering path.
-        let mHitSusOutline = null;
-        // Shared materials for the legato technique meshes — one per geometry
-        // type, reused across every pooled mesh instance to avoid per-mesh
-        // material allocation in dense HO/PO/tap passages. Allocated in
-        // initScene() alongside the other scene materials and disposed in
-        // teardown.
-        let mTapChevron = null;
-        // Barre indicator material (white vertical line at the barre fret
-        // during chord linger). Promoted from inline pool-factory authoring
-        // to a named module-scope reference so _applyGlow() can mutate
-        // emissiveIntensity in place when the user drags the glow slider.
-        let mBarre = null;
-        // Notedetect feedback outlines (issue #9). Created in initScene
-        // alongside mWhiteOutline; swapped onto the note's outline mesh
-        // when a recent notedetect:hit / :miss event matches the note's
-        // (s, f, t). The miss gem border uses mMissOutline; the hit side
-        // uses per-string mHitBright[s] for the cyan-shifted flash.
-        let mMissOutline = null;
-        // Per-string hit verdict material used for outline + lateral face fill.
-        // Built in initScene() after mGlow. Array share the same material
-        // instances so outline and face fill always match exactly.
-        let mHitBright = [], mHitBrightArrays = [];
-        // [verdict glow] Per-frame accumulation of the note-state provider's
-        // alpha (note_detect drives this from the live input level for held
-        // sustains, and as a time-fade for fresh strikes). Applied at the top of
-        // update() to scale the verdict-glow materials' emissiveIntensity so the
-        // gem brightness tracks how hard the string is actually ringing. Stays
-        // at "no provider" (vg = 1, unchanged brightness) for the legacy event
-        // path or when note_detect is off.
-        let _ndVerdictMaxAlpha = 0;
-        let _ndVerdictSawAlpha = false;
-        // Magenta-red face fill for miss — see initScene() for construction
-        // (uses mMissOutline ×4 + mEdgeTransparent ×2).
-        let mMissEdgeArrays = null;
-        let mEdgeTransparent = null;
-        let pSusOutline = null, pNoteEdge = null;
-        let projMeshArr = null;
-        let _probe = null;
-        /** Snapshotted in update() for drawNote() ghost / glow (single source vs per-caller isNext). */
-        let _drawNextByString = null;
-        /** Most-recent past event time per string (within 0.6 s back), for _nextAnyT deadline. */
-        let _drawRecentByString = null;
-        /** Snapshotted in update() — drawNote() is a sibling of update(), not nested in its closure. */
-        let _drawChordTemplates = null;
-        /** Ditto — drawNote() needs the anchors to resolve the lane's outer
-         * wires for an open note's hit flash (an open note has no fret of its
-         * own; its slab spans the lane, so the lane edges are what bracket it). */
-        let _drawAnchors = null;
-        /** Teaching marks sd/ch overlay pref (§6.2.2), mirrored from the 2D
-         * highway's `teachingMarksVisible` bundle flag. */
-        let _drawTeachingMarks = false;
-        /** Fret-hand finger (fg) hint pref, mirrored from the 2D highway's
-         * `fingerHintsVisible` bundle flag — default on (shown unless an explicit
-         * false), hideable independently of the sd/ch overlays. */
-        let _showFingerHints = true;
-        let _laneTargetColor = null;
-        let _renderScale = 1;
-        let lyricsCanvas = null, lyricsCtx = null;
-        // FPS counter overlay. EMA-smoothed over ~30 frames so the readout doesn't
-        // jitter every rAF tick. Controlled by the 'fpsVisible' setting (BG_DEFAULTS).
-        // Legacy 'h3d_showFps' localStorage key and window.h3dShowFps are no longer
-        // consulted — use the Settings → 3D Highway — Camera → Show FPS counter checkbox.
-        let _fpsLastT = 0;
-        let _fpsEma = 0;
-        let _fpsDisplay = 0;
-        let _fpsLastSampleT = 0;
-        // The FPS readout is pinned top-right of the highway overlay — the same
-        // corner the v3 player chrome stacks its persistent "Up Next" pill and
-        // live-performance HUD into, on a higher layer that paints over the
-        // canvas. So out of the box the readout sits *behind* that chrome and
-        // can't be read (exactly when you've turned it on to judge perf). Rather
-        // than relocate it (testers look top-right), we drop it just BELOW
-        // whichever of that chrome is showing. Refs are resolved once and cached
-        // — never a per-frame querySelector (see CLAUDE.md "never run DOM queries
-        // on a per-frame path") — and re-resolved only when a node detaches.
-        let _v3HudEls = null;
-        // Returns the bottom edge (in overlay-canvas px, which are 1:1 CSS px on
-        // this overlay) of the lowest visible top-right v3 chrome element, or 0
-        // when none apply (classic v2 UI, or all hidden). Only called while the
-        // FPS readout is actually drawn, so the layout reads cost nothing in the
-        // common (counter-off) case.
-        function _v3TopRightChromeBottom() {
-            if (typeof document === 'undefined' || !highwayCanvas) return 0;
-            // Only the v3 chrome stacks persistent HUD elements over the canvas's
-            // top-right. Gate on the documented detector so this is a strict no-op
-            // in classic v2 (where 'hud-time' also exists but sits elsewhere).
-            if (!(window.feedBack && window.feedBack.uiVersion === 'v3')) return 0;
-            if (!_v3HudEls || _v3HudEls.some((el) => el && !el.isConnected)) {
-                _v3HudEls = ['v3-upnext', 'v3-live-performance-hud', 'hud-time']
-                    .map((id) => document.getElementById(id));
-            }
-            const top = highwayCanvas.getBoundingClientRect().top;
-            let maxBottom = 0;
-            for (const el of _v3HudEls) {
-                // offsetParent === null ⇒ display:none (a `.hidden` pill/HUD) or
-                // not laid out — don't duck under something that isn't shown.
-                if (!el || el.offsetParent === null) continue;
-                const b = el.getBoundingClientRect().bottom - top;
-                if (b > maxBottom) maxBottom = b;
-            }
-            return maxBottom;
-        }
-        let _diagChord            = null;
-        // Chord diagram render cache. Keys: static layout inputs joined as a
-        // string. Values: OffscreenCanvas (or <canvas>) rendered at opacity=1
-        // entranceT=1 — composited each frame via drawImage + globalAlpha.
-        // Cleared on canvas resize (bx/by depend on canvasW/H/lyricsBottom)
-        // and on teardown/destroy.
-        const _diagRenderCache = new Map();
-        // Cap chosen to cover the ~5–6 active chord shapes per phrase while
-        // keeping the cached-OffscreenCanvas footprint bounded (~50 MB per
-        // panel at typical 1920×1080). A structural fix — caching a
-        // tightly-sized box surface instead of the full overlay canvas —
-        // is tracked as a follow-up.
-        const _DIAG_CACHE_MAX  = 6;
-        let pSusRail = null, gSusRail = null, mSusRailBase = null;
-        let pSusRailBloom = null, gSusRailBloom = null, mSusRailBloomBase = null, _bloomGaussTex = null;
-        let pTechPlane = null, gTechPlane = null;
-
-        // ── InstancedMesh for PM/FH X markers ────────────────────────────────
-        // Replaces pTechPlane pool entries for PM and FH mute techniques,
-        // collapsing O(visible-muted-notes) draw calls to 2 per type.
-        // pTechPlane pool is still used for H/P triangles, harmonics and bends.
-        let imPMTech = null, imFHTech = null;
-        let _imGPMTech = null, _imGFHTech = null; // cloned geometries (own instanceAlpha attr)
-        let _imPMTechMat = null, _imFHTechMat = null;
-        const IM_TECH_CAP = 256;
-        const _imPMTechAlphaArr = new Float32Array(IM_TECH_CAP);
-        const _imFHTechAlphaArr = new Float32Array(IM_TECH_CAP);
-        let _imPMTechCount = 0, _imFHTechCount = 0;
-
-        // ── InstancedMesh for chord strum indicators ──────────────────────────
-        // Replaces pPMXFill, pMuteXLines, pFHXFill, pFHXLines pools.
-        // Fixed renderOrder per type — no per-instance sort needed.
-        let imPMXFill = null, imPMXLines = null, imFHXFill = null, imFHXLines = null;
-        let _imPMXFillMat = null, _imPMXLinesMat = null;
-        let _imFHXFillMat = null, _imFHXLinesMat = null;
-        const IM_STRUM_CAP = 64;
-        const _imPMXFillAlphaArr  = new Float32Array(IM_STRUM_CAP);
-        const _imPMXLinesAlphaArr = new Float32Array(IM_STRUM_CAP);
-        const _imFHXFillAlphaArr  = new Float32Array(IM_STRUM_CAP);
-        const _imFHXLinesAlphaArr = new Float32Array(IM_STRUM_CAP);
-        let _imPMXFillCount = 0, _imPMXLinesCount = 0, _imFHXFillCount = 0, _imFHXLinesCount = 0;
-
-        // Temporaries for InstancedMesh matrix composition — allocated once in
-        // initScene() after Three.js loads, reused every frame without allocation.
-        let _imM4 = null, _imPos = null, _imSca = null, _imQ = null, _imAZ = null, _imColor = null;
-
-        let _diagPrev             = null;
-        let _diagPrevOpacity      = 0;
-        let _diagPrevStartOpacity = 0;
-        let _diagPrevStartT       = null;  // bundle.currentTime when crossfade began (drives rewindable fade)
-        let _diagEntranceT        = 1.0;
-        let _diagLastKey          = null;  // chord identity: name + '|' + frets.join(',')
-        // Per-wave cache for fret-column reference markers. Keyed by the
-        // wave's beat timestamp. We snapshot { hasLow, hasHigh, fretList,
-        // anchorKeyed } at first sight of a wave so its render gate stays consistent through the
-        // wave's flight even as activeFrets shifts mid-song. Entries are
-        // pruned each frame once their wave has passed `now`.
-        let _fretMarkerWaveCache = new Map();
-        // Per-frame booleans: handShapes[i] passes inferArpeggioFromNotePattern
-        // once (see fillArpeggioGhostInferFlags) so the note loop skips O(hs×notes)
-        // rescans — ref fillArpeggioGhostInferFlags in update().
-        let _arpGhostHsInferScratch = [];
-        // Handshape start-times where ghost fret numbers show but [ ] brackets are suppressed
-        // (synth-chord onset-match cases — not genuine arpeggios).
-        let _arpSynthOnsetHsSet = new Set();
-        /** Per-frame: ``handShapeIsArpeggioForLaneRail`` baked once — lane slices were O(96 × hs × infer). */
-        let _arpLaneRailHsScratch = [];
-        let _arpRailBoundLoScratch = [];
-        let _arpRailBoundHiScratch = [];
-
-        // ── Cross-frame caches for chart-static derivations ──────────────
-        // The merge + arp-flag fills below depend only on chart-static
-        // input arrays (handShapes / chords / chordTemplates / notes),
-        // not on `now`. The bundle hands us the same array refs every
-        // frame within an arrangement, so we can skip the recompute when
-        // the inputs are identity-equal to the previous frame's. On dense
-        // arrangements this avoids per-frame Set construction, nested
-        // O(hs × notes) scans, and a sort — significant FPS recovery.
-        let _mergeCacheResult = null;
-        let _mergeCacheChordsRef = null;
-        let _mergeCacheHsRef = null;
-        let _mergeCacheTplRef = null;
-
-        // Fret connector-label visibility cache: tracks which (time, fret)
-        // pairs may show their indicator number per the measure-skip rule
-        // (show only the first note with a given fret in a measure; suppress
-        // the same fret for the following measure, then allow it again).
-        let _fretLabelAllowed = new Set();
-        let _fretLabelNotesRef = null;
-        // Cache of measure-start times (beats with measure !== -1), rebuilt when
-        // the beats array changes. Drives the camera lookahead window
-        // (CAM_LOOKAHEAD_MEASURES measures instead of a fixed number of seconds).
-        let _measureStarts = [];
-        let _measureStartsRef = null;
-        // Frame-level dedup: tracks which (40ms-rounded-time, fret) pairs have already
-        // rendered a label this frame so that multiple strings at the same fret/onset
-        // (arpeggio chords, synthetic chords) never produce stacked duplicate labels.
-        const _frameLabeledKeys = new Set();
-
-        let _arpGhostInferRefHs = null;
-        let _arpGhostInferRefNotes = null;
-        let _arpGhostInferRefTpl = null;
-
-        // Slide-target gem suppression. A Set of "t_s" keys for notes in
-        // bundle.notes that are the linkNext destination of a preceding note
-        // (single or chord). The gem is suppressed (skipBody=true) but the
-        // sustain/slide trail still renders so the slide motion stays visible.
-        let _slideTargetSet = null;
-        let _slideTargetNotesRef = null;
-        let _slideTargetChordsRef = null;
-
-        let _laneRailFlagsRefHs = null;
-        let _laneRailFlagsRefTpl = null;
-
-        let _laneRailBoundsRefHs = null;
-        let _laneRailBoundsRefChords = null;
-        let _laneRailBoundsRefTpl = null;
-        let _laneRailBoundsRefNotes = null;
-        let _lastHwW = 0, _lastHwH = 0;
-        // Frame counter for throttling the CSS-box drift check in draw()
-        // (getBoundingClientRect is a forced layout read; see the comment
-        // at the check).
-        let _boxCheckCountdown = 0;
-        // Last logical (CSS px) size handed to applySize(). #highway is a
-        // flex:1 item, so its real rendered box (canvasSize()) can change as
-        // the player layout settles after a song opens WITHOUT the backing
-        // store (canvas.width) changing — which the _lastHwW/H check below
-        // would miss. Tracking the applied logical size lets draw() detect
-        // that CSS-box drift and re-frame, instead of the user having to
-        // un/re-maximize the window.
-        let _appliedW = 0, _appliedH = 0;
-        // Last pane aspect (w/h) handed to the camera, cached so camUpdate can
-        // recompute the horizontal-FOV-hold each frame (and react to live
-        // __h3dAspectTune edits) without waiting for a resize. 0 until first
-        // applySize().
-        let _paneAspect = 0;
-        // Per-instance fallback id for the wide-pane tuner's pane key, used only
-        // when this pane has no arrangement name to key by. Assigned once in
-        // init(); overrides keyed off arrangement persist across songs, this
-        // fallback is session-only.
-        let _paneUid = 0;
-        // True once applySize() has pinned the .h3d-wrap overlay to the
-        // highway canvas's offset box. Stays false while the canvas has no
-        // layout yet (init() can run before #highway has a real box, where
-        // applySize falls back to the parent-panel size and only sets the
-        // wrap height). The rAF loop re-pins once the canvas lays out even
-        // when the logical render size is unchanged — otherwise the overlay
-        // would stay at top:0;left:0;right:0 and expose a strip of #highway.
-        let _wrapPinned = false;
-        let mBeatM = null, mBeatQ = null;
-        let txtCache = {};
-        // Cloned sprite materials cached on individual sprite instances
-        // (e.g. pmMark._pmMat). pLbl pool reuses sprites across labels,
-        // so when a sprite is later assigned a different material the
-        // _pmMat stays referenced on the sprite itself but isn't reached
-        // by the scene.traverse-based dispose. Track them here so
-        // teardown can dispose them explicitly.
-        const _ownedClonedMats = [];
-        // Per-mesh technique-marker clones — keyed by mesh, disposed when
-        // the source sprite's map changes or on teardown. Replaces the old
-        // unbounded push-per-frame approach in _spriteMat2MeshMat.
-        const _techMeshMatClones = new Set();
-        // Shared (non-clone) materials and geometries that pool factories
-        // reference but that aren't guaranteed to be reachable via
-        // scene.traverse() — e.g. mLaneEven is only reached if at least one
-        // even-numbered fret stripe ever spawns. Track them here so teardown
-        // disposes the GPU resource regardless.
-        const _ownedSharedMats = [];
-        const _ownedSharedGeos = [];
-
-        // Background animation state (issue #13). bgGroup is the parent
-        // container for all bg meshes so teardown is one remove + dispose
-        // pass. bgState is the active style's per-panel state object.
-        let bgGroup = null, bgStage = null, bgState = null;
-        let bgMountedStyleId = null;
-        let bgStyleId = 'particles', bgIntensity = 0.5, bgReactive = true;
-        // Active scene color theme (background + highway surface). Read in
-        // _bgLoadSettings, applied by _applyBgTheme (clear + fog + board plane).
-        let bgThemeId = 'default';   // BACKGROUND axis (clear + fog)
-        let hwThemeId = 'default';   // HIGHWAY axis (board + lane + laneDim)
-        // Board (fretboard/highway-surface) plane material — kept so the theme
-        // can recolor it live without rebuilding the board. Set in buildBoard().
-        let _boardPlaneMat = null;
-        // Per-render opt-out for plugins borrowing the highway as a viz: when the
-        // mount bundle sets bgReactive === false, suppress the audio-reactive
-        // background for THIS instance only (no shared h3d_bg_* write). Captured
-        // from the bundle in init(); applied in _bgLoadSettings() so it survives
-        // later setting reloads. See init() for the rationale.
-        let _bgReactiveOptOut = false;
-        // Active palette for this panel (issue #10). Materials and per-
-        // frame color reads inside createFactory all consult this rather
-        // than the module-level S_COL, so a palette swap re-tints the
-        // panel live without touching module-level state.
-        let activePalette = PALETTES.default;
-        // Content signature of the colors last applied to materials; lets
-        // _bgLoadSettings force a retint when the in-place custom palette
-        // changes values without changing array identity.
-        let _bgPaletteSig = '';
-        // Fret digits on the board ghost (hollow preview at Z=0), not on
-        // flying note bodies — see fretNumberGhostScope for chord-hand vs all.
-        let showFretOnNote = false;
-        let fretNumberGhostScope = 'chords';
-        // Camera-X smoothing dial (issue #34). 0 = twitchy (track every
-        // upcoming fret), 1 = calm (ignore small intra-cluster shifts).
-        // Cached here and refreshed via the bg listener to avoid a
-        // per-frame localStorage hit inside update().
-        let cameraSmoothing = 0.5;
-        // Per-axis follow-ups: zoom (tgtDist hysteresis) and vertical-tilt
-        // (tgtLookY NDC self-correction) each get their own dial. Same
-        // 0..1 shape; same caching pattern. Both mirror cameraSmoothing's
-        // value when not explicitly stored, so existing users who only
-        // ever moved the camera-smoothing slider get the same calmness on
-        // the new axes by default.
-        let zoomSmoothing = 0.5;
-        let tiltSmoothing = 0.5;
-        // Camera lock: when true, pin the camera to a fixed wide view of
-        // frets 1-12 unless an upcoming note would otherwise be off-screen.
-        // The lock disengages while any note above fret 12 is in the
-        // lookahead window so the camera can briefly widen to include it,
-        // then re-engages once the high note ages out.
-        let cameraLockLow = false;
-        // Zoom-level for the locked view. Slider 0..1 maps to a multiplier
-        // on the locked tgtDist: 0 → CAM_LOCK_ZOOM_MIN (closest, biggest
-        // fretboard), 0.5 → 1.0× (the default locked view), 1 → CAM_LOCK_ZOOM_MAX
-        // (furthest). Inactive when the lock isn't engaged.
-        let cameraLockZoom = 0.5;
-        /** 'steady' = recency-weighted centroid + hysteresis (#34); 'lookahead' = wide preview window + smooth focal. */
-        let cameraMode = BG_DEFAULTS.cameraMode;
-        // Global text-size multiplier for in-scene text sprites (chord
-        // names, fret labels, section banners, technique markers, etc.).
-        // Slider is 0..1; mapped to a 0.5..1.5× multiplier with 0.5 = 1.0×
-        // (current default behaviour). _textSizeMul is the materialized
-        // multiplier — refreshed once per frame at the top of update()
-        // and consumed by every text-sprite scale.set call inside update
-        // and drawNote.
-        let textSize = 0.5;
-        let _textSizeMul = 1.0;
-        let _textSizeMulApplied = -1;
-        // Visual look dials (issue: pastel/washed-out feel + too-much-glow
-        // complaint). vibrancy raises idle string/note opacity and de-whites
-        // the hit-note body; glow scales every emissive contribution +
-        // projection glow layer opacity. Sliders are 0..1; defaults lean
-        // vivid + minimal-glow to match the requested out-of-box look.
-        // _vibrancyIdleOp / _vibrancyProjOp are cached so
-        // updateStringHighlights() and drawNote() don't recompute the
-        // linear blend every frame.
-        let vibrancy            = BG_DEFAULTS.vibrancy;
-        let glowMul             = BG_DEFAULTS.glow;
-        let _hitFx              = BG_DEFAULTS.hitFx;
-        let _sparks             = BG_DEFAULTS.sparks;
-        let _cinematic          = BG_DEFAULTS.cinematic;
-        let _verdictMarks       = BG_DEFAULTS.verdictMarks;
-        let _timingFx           = BG_DEFAULTS.timingFx;
-        let _streakFx           = BG_DEFAULTS.streakFx;
-        let _bloom              = BG_DEFAULTS.bloom;
-        let _composer = null, _bloomPass = null, _bloomLoad = null, _bloomW = 0, _bloomH = 0;
-        let _sparkPts = null, _sparkPos = null, _sparkCol = null, _sparkVel = null, _sparkLife = null;
-        const _SPARK_N = 256;
-        const _sparkSeen = new Map();     // note-key -> expiry; one burst per hit
-        let _juiceLastT = 0;              // frame-dt clock for the juice layer
-        let _streakHits = 0, _streakHeat = 0;  // #7 consecutive-hit escalation
-        let fpsVisible           = BG_DEFAULTS.fpsVisible;
-        let fretDividersVisible  = BG_DEFAULTS.fretDividersVisible;
-        let chordDiagramVisible  = BG_DEFAULTS.chordDiagramVisible;
-        let chordDiagramSize     = BG_DEFAULTS.chordDiagramSize;
-        let chordDiagramPosition = BG_DEFAULTS.chordDiagramPosition;
-        let fretColumnMarkerCadence = BG_DEFAULTS.fretColumnMarkerCadence;
-        let inlayLabelsVisible = BG_DEFAULTS.inlayLabelsVisible;
-        let sectionLabelsOnHighway = BG_DEFAULTS.sectionLabelsOnHighway;
-        let sectionHudVisible      = BG_DEFAULTS.sectionHudVisible;
-        let sectionHudPosition     = BG_DEFAULTS.sectionHudPosition;
-        let sectionHudSize         = BG_DEFAULTS.sectionHudSize;
-        let toneHudVisible         = BG_DEFAULTS.toneHudVisible;
-        let toneHudPosition        = BG_DEFAULTS.toneHudPosition;
-        let toneHudSize            = BG_DEFAULTS.toneHudSize;
-        let nutHeadstockVisible    = BG_DEFAULTS.nutHeadstockVisible;
-        let tuningLabelsVisible    = BG_DEFAULTS.tuningLabelsVisible;
-        let nutColor               = BG_DEFAULTS.nutColor;
-        let headstockColor         = BG_DEFAULTS.headstockColor;
-        let projectionVisible      = BG_DEFAULTS.projectionVisible;   // board "note preview" ghost on the fretboard
-        let slideArrowApproachVisible = BG_DEFAULTS.slideArrowApproachVisible; // slide-direction arrow riding with the note/gem
-        let slideArrowNeckVisible      = BG_DEFAULTS.slideArrowNeckVisible;    // slide-direction arrow preview on the neck
-        let slideArrowChainPreviewVisible = BG_DEFAULTS.slideArrowChainPreviewVisible; // early neck preview for chained/multi-leg slides
-        let _vibrancyIdleOp = 0.4  + 0.6  * BG_DEFAULTS.vibrancy;
-        let _vibrancyProjOp = 0.15 + 0.35 * BG_DEFAULTS.vibrancy;
-        // Custom image asset (issue #19). Data URL is the bytes that
-        // drive the 'image' bg style's texture; name is display-only
-        // metadata that settings.html shows next to the file picker.
-        let bgCustomImageDataUrl = '';
-        let bgCustomImageName = '';
-        // Custom video asset (issue #19 follow-up). Stores the
-        // server-side filename only; bytes live on disk via routes.py.
-        // The renderer composes the served URL from this filename in
-        // BG_STYLES.video.build.
-        let bgCustomVideoName = '';
-        let _bgListener = null;
-        let _bgLastT = 0;  // ms timestamp for dt
-
-        // Notedetect feedback (issue #9). Per-panel mark queues populated
-        // by two event sources: (a) legacy `notedetect:hit` /
-        // `notedetect:miss` window CustomEvents, and (b) FeedBack
-        // event-bus `note:hit` / `note:miss` events (subscribed in
-        // initScene() when window.feedBack exposes both `on` and `off`).
-        // Both sources feed the same _ndPushMark() helper which dedupes
-        // dual emissions. drawNote looks up its (s, f, t) against these
-        // arrays each frame and swaps the outline material when a match
-        // is current. Marks expire after _ND_TTL_MS so the visual flash
-        // is brief. Marks self-prune unconditionally in the listener and
-        // once per frame in update() to keep the arrays small.
-        const _ND_TTL_MS = 500;
-        const _ND_TIME_EPS = 0.01;
-        let _ndHitMarks = [];
-        let _ndMissMarks = [];
-        let _ndOnHit = null, _ndOnMiss = null;
-        let _ndOnBusHit = null, _ndOnBusMiss = null;
-        let _ndLabels = [];
-        // Per-chord-occurrence verdict latch for the chord-frame rim
-        // tint. Once a chord is observed all-hit/active during its linger
-        // fade we latch 'green' here so subsequent frames can't undo it
-        // as individual constituent glows decay and getNoteState starts
-        // returning null again (which would otherwise flicker the rim
-        // back to red mid-linger). Keyed by `${ch.id}|${ch.t}` — ch.id
-        // alone is the chord *template* id and is reused across every
-        // occurrence of the same shape, so id-only latching would bleed
-        // a single clean grab onto every later occurrence of that chord.
-        // Pre-hit-line invalidation (chDt > 0 path in the rim selection)
-        // evicts a chord's latch the next time it's seen approaching, so
-        // loops/rewinds re-judge from scratch and the Map can't grow
-        // beyond the current pre-hit-line frontier. Also cleared in
-        // destroy().
-        let _chordVerdicts = new Map();
-        // Previous-frame `now` for the chord-verdicts pruner — on a
-        // backward seek the latches behind that time become "future"
-        // entries the forward-only prune can't reach, so we wipe the
-        // map instead of paying an O(n) scan per frame to find them.
-        let _chordVerdictsLastNow = null;
-        // Numeric encoding for the _chordVerdicts key — replaces
-        // ``${ch.id}|${ch.t}`` which allocated a string per chord per
-        // frame in detect mode. Encoded so the key is monotonic in
-        // chord time and the prune sweep can compare keys directly
-        // (no parseFloat / String.slice). The time component sits in
-        // the upper bits; chord-template ids share the lower 1e6 slot
-        // and ch.id == null reserves idSlot 0 (no real chord id can
-        // collide with it because real ids encode as id + 1).
-        // ``time * 1e4`` keeps a 0.1 ms resolution — more than enough
-        // to disambiguate distinct chord onsets — and stays under the
-        // safe-integer limit for any realistic song length.
-        const _CV_KEY_TIME_MUL = 1e4;
-        const _CV_KEY_TIME_SLOT = 1e6;
-        function _encodeChordVerdictKey(ch) {
-            const tSlot = Math.round(ch.t * _CV_KEY_TIME_MUL) * _CV_KEY_TIME_SLOT;
-            const idSlot = ch.id != null ? ((Number(ch.id) | 0) + 1) : 0;
-            return tSlot + idSlot;
-        }
-        // Per-frame timestamp captured by update() and used by its
-        // prune pass for the notedetect mark arrays. drawNote itself
-        // no longer reads it — pruning lives once per frame so
-        // drawNote's hot path is just the bounded (s, f, t) match.
-        let _ndFrameNowMs = 0;
-        // feedBack#254 — core's per-note judgment provider, captured
-        // from `bundle.getNoteState` at the top of each update(). When
-        // present it's authoritative over the event-driven marks above:
-        // 'hit'/'active' → bright string-tinted outline (mGlow[s]) +
-        // bright body + glowing sustain trail + a contained sparkle on
-        // the overlay (a held sustain keeps glowing/sparkling for as
-        // long as it stays 'active'); 'miss' → red outline (mMissOutline)
-        // + suppressed body. null on cores without the API or songs
-        // with no scorer registered. Older note_detect builds that only
-        // emit notedetect:hit/miss events still work via _ndHitMarks.
-        let _ndGetNoteState = null;
-        let _ndHasProvider = false;  // true iff a note-state provider is registered (feedBack#254)
-        // Sustain verdict latch — persists a provider's hit/miss verdict for the
-        // full duration of a sustained note. Once hitGlowDuration expires the
-        // provider stops returning state; the latch re-injects the last verdict
-        // so the green/red color stays alive until susEnd.
-        // Key: Math.round(n.t * 1e4) * 10 + n.s  (matches _ghostPrevBuf scheme)
-        // Value: 'hit' | 'hit-live' | 'miss'  ('hit-live' = a live provider hit,
-        // tagged live:true, which is NOT re-injected once the provider goes
-        // silent — see the live-latch handling in the per-gem loop below).
-        let _susVerdictLatch = new Map();
-
-        // ── Score FX (notedetect game-scoring layer, notedetect ≥1.13) ──
-        // Two channels: (1) per-note "+N" score pops, sourced from the
-        // note-state provider's new { points, mult, popKey } fields at the
-        // moment a gem's verdict lands; (2) session-level bursts/pulses from
-        // the new `notedetect:fx` event (streak milestones, multiplier tier
-        // changes, streak breaks). Everything renders on the 2D overlay
-        // canvas (same layer as drawNotedetectLabels) — no Three.js objects,
-        // no txtMat() cache entries, nothing to dispose. Pools are fixed-
-        // size slot arrays created once per factory instance; when all slots
-        // are busy a new effect is simply dropped.
-        const _FX_POP_LIFE_MS = 700;
-        const _FX_BURST_LIFE_MS = 900;
-        const _FX_BURST_N = 36;
-        const _fxPops = Array.from({ length: 24 }, () => (
-            { active: false, x: 0, y: 0, z: 0, bornMs: 0, text: '', mult: 1 }
-        ));
-        const _fxBursts = Array.from({ length: 4 }, () => ({
-            active: false, bornMs: 0,
-            px: new Float32Array(_FX_BURST_N), py: new Float32Array(_FX_BURST_N),
-            vx: new Float32Array(_FX_BURST_N), vy: new Float32Array(_FX_BURST_N),
-        }));
-        // popKey -> expiry ms. Dedupes pops (chord members share the chord's
-        // popKey; sustains keep returning points for the whole glow window).
-        const _fxSeen = new Map();
-        let _fxOnFx = null;          // notedetect:fx listener (window)
-        let _fxOnSkin = null;        // notedetect:skin bus listener
-        // Generation counter: bumped by teardown() so the deferred window-
-        // copy fallback (a zero-delay task the listener removal can't cancel)
-        // bails instead of re-arming ring/burst state after teardown — or,
-        // worse, leaking a stale event into a subsequent init's fresh state.
-        let _fxGen = 0;
-        let _fxLastFxDetail = null;  // reference dedup: window + instanceRoot dispatches share one detail
-        // Details seen via element-scoped (bubbled) dispatch. A WeakSet, not a
-        // single slot: one judged hit can emit several fx in the same task
-        // (milestone + multiplier tier-up), and the deferred window-copy
-        // fallback for the FIRST must still see that its element copy arrived
-        // after the SECOND overwrote any last-detail slot. GC reclaims
-        // entries once notedetect drops the detail objects.
-        let _fxElemSeen = new WeakSet();
-        let _fxRingMs = -1e9;        // multiplier ring-pulse anchor
-        let _fxRingMult = 1;
-        let _fxBreakMs = -1e9;       // streak-break flicker anchor
-        // Canvas-side palette per notedetect skin (mirrors the accents in
-        // notedetect's assets/plugin.css; fonts are document-loaded by that
-        // stylesheet so the overlay canvas can use the family names).
-        const _FX_PALETTES = {
-            neon:    { accent: '#00f0ff', accent2: '#ff2ec4', miss: '#ff4444', font: 'Orbitron' },
-            esports: { accent: '#e8b43a', accent2: '#f5f5f4', miss: '#f87171', font: 'Rajdhani' },
-            metal:   { accent: '#ffb347', accent2: '#ff6b35', miss: '#ef4444', font: 'Russo One' },
-        };
-        let _fxPalette = _FX_PALETTES.neon;
-        function _fxResolvePalette() {
-            let skin = null;
-            try { skin = localStorage.getItem('feedBack_notedetect_skin'); } catch (e) {}
-            _fxPalette = _FX_PALETTES[skin] || _FX_PALETTES.neon;
-        }
-        function _fxSpawnPop(popKey, points, mult, x, y, z) {
-            if (_fxSeen.has(popKey)) return;
-            const nowMs = _ndFrameNowMs || performance.now();
-            _fxSeen.set(popKey, nowMs + 4000);
-            for (let i = 0; i < _fxPops.length; i++) {
-                const p = _fxPops[i];
-                if (p.active) continue;
-                p.active = true;
-                p.x = x; p.y = y; p.z = z;
-                p.bornMs = nowMs;
-                p.text = '+' + points;
-                p.mult = mult || 1;
-                return;
-            }
-        }
-        function _fxSpawnBurst(nowMs) {
-            for (let i = 0; i < _fxBursts.length; i++) {
-                const b = _fxBursts[i];
-                if (b.active) continue;
-                b.active = true;
-                b.bornMs = nowMs;
-                for (let j = 0; j < _FX_BURST_N; j++) {
-                    const a = (j / _FX_BURST_N) * Math.PI * 2;
-                    const sp = 2 + (j % 5) * 0.8;
-                    b.px[j] = 0; b.py[j] = 0;
-                    b.vx[j] = Math.cos(a) * sp;
-                    b.vy[j] = Math.sin(a) * sp - 1.2;
-                }
-                return;
-            }
-        }
-        function _fxHandle(d) {
-            // Reference dedup — notedetect dispatches the SAME detail object
-            // on window and on its instanceRoot; whichever arrives first wins.
-            if (d === _fxLastFxDetail) return;
-            _fxLastFxDetail = d;
-            const nowMs = performance.now();
-            if (d.fxType === 'milestone') {
-                _fxSpawnBurst(nowMs);
-            } else if (d.fxType === 'multiplier' && d.mult > (d.prevMult || 1)) {
-                _fxRingMs = nowMs;
-                _fxRingMult = d.mult;
-            } else if (d.fxType === 'streakBreak') {
-                _fxBreakMs = nowMs;
-            }
-        }
-
-        // Object pools
-        let pNote, pSus, pLbl, pBeat, pSec;
-        let pFretLbl, pLane, pLaneDivider;
-        // Shared materials/geometry for the lane stripes — see initScene().
-        // Hoisted so draw() can reference them when assigning per-stripe.
-        let mLaneOdd = null, mLaneEven = null, gLanePlane = null;
-        /** Lane fret dividers: default white vs arpeggio frame tint on outer wires only. */
-        let mLaneDivider = null, mLaneDividerArp = null, mLaneDividerExt = null;
-        /** Shared XY plane for ghost fret digits (lies on board like proj, not billboarding). */
-        let gGhostFretPlane = null, pGhostFretLbl = null;
-        // Anchor-driven lane scratch buffers. Per-frame the loop builds up
-        // to HWY_LANE_TIME_SLICES segments, but consecutive slices that share
-        // an anchor (the common case) collapse into the same entry. Held as
-        // four parallel arrays so the per-frame work allocates nothing once
-        // the buffers reach their steady-state size.
-        const _laneSegDMin = [];
-        const _laneSegDMax = [];
-        const _laneSegZ0 = [];
-        const _laneSegZ1 = [];
-        /** Chart-time span per merged lane segment (for per-slice arpeggio rail tint). */
-        const _laneSegTLo = [];
-        const _laneSegTHi = [];
-        const _laneSegArp = [];
-        let _laneSegLen = 0;
-        let pChordBox, pChordFrameFill, pChordLbl, pBarreLine, pArpBracket, pPMXFill, pFHXFill;
-        let gPMXFill = null; // shared geometry for PM X fill — disposed in teardown
-        let gFHXFill = null; // shared geometry for FH X fill — disposed in teardown
-        let gPMXLines = null, pMuteXLines = null; // PM X lines combined geometry (8 segs as quads)
-        let gFHXLines = null, pFHXLines = null;   // FH X lines combined geometry
-        let pNoteFretLabel, pConnectorLine, pDropLine, pTapChevron, pAccentHalo;
-        let pTeachMarkLbl;  // teaching marks fg/sd label sprites (§6.2.2)
-        let pHaloBar = null, gHaloBar = null; // gradient halo bar geometry — replaces per-shell pChordAccentHalo
-        let gArpBracket = null; // shared 1×1×1 box geometry for pArpBracket; built once, disposed in teardown
-        let pSusRibbon = null, pSusRibbonOl = null;
-        let pFretColMarker;
-        /** Horizontal gradient for chord box interior fill. */
-        let chordFrameGradTex = null;
-        /** Lavender gradient for arpeggio box interior (cyan × lavender blend — fades back to cyan). */
-        let chordFrameGradTexArp = null;
-
-        // Dynamic glowing string meshes (BoxGeometry, one per string)
-        let stringLines = [];
-        // Static thin-line glow layer behind each string (one Line per
-        // string). Retained so _applyVibrancy() can mutate opacity in
-        // place — without this the layer stays at its built-in opacity
-        // until the next palette change rebuilds buildBoard().
-        let stringLineGlows = [];
-        // One MeshStandardMaterial per fret wire (index = fret 0..NFRETS).
-        // Updated each frame to gold when inside the active anchor range,
-        // gray otherwise. Reset to [] on every buildBoard() rebuild.
-        let fretWireMats = [];
-        // Shared bowed TubeGeometry for all fret wires (centered at x=0;
-        // each fret mesh only differs by position). Disposed on rebuild +
-        // teardown. See FRET_BOW_DZ constants.
-        let fretTubeGeo = null;
-        /** Nut + headstock 3D subtree; visibility toggled from settings without rebuild. */
-        let nutHeadstockGroup = null;
-        /** Left edge X of drawable string meshes; updated in buildBoard() at nut / fret junction. */
-        let boardStringStartX = fretX(0);
-        /** Open-string label column X — over headstock, left of nut (set in buildBoard()). */
-        let boardTuningLabelX = -4.2 * K;
-        // Fret inlay number label sprites (one per INLAY_LABEL_FRETS entry).
-        // Retained so update() can rescale them live when _textSizeMul changes.
-        let _inlayLabels = [];
-        // Cloned SpriteMaterials for the inlay labels — disposed on rebuild and
-        // destroy() to prevent GPU leaks across palette changes or panel reuse.
-        let _inlayMats = [];
-        // Open-string tuning labels beside the headstock (issue: per-song tuning).
-        let _tuningLabelSprites = [], _tuningLabelMats = [];
-        let _lastOpenStringLblSig = '';
-        // Cheap-key cache for _syncOpenStringPitchLabels: skip the expensive
-        // labels-array + signature-string build when the inputs that actually
-        // change the labels haven't changed reference/value since last frame.
-        let _lastSyncTuningRef = undefined;
-        let _lastSyncBundleTuningRef = undefined;
-        let _lastSyncCapo = NaN;
-        let _lastSyncArrIdx = undefined;
-        let _lastSyncPaletteRef = null;
-        let _lastSyncNStr = -1;
-        let _lastSyncTextSizeMul = NaN;
-        let _lastSyncStartX = NaN;
-        let _lastSyncLabelX = NaN;
-        // Scratch Color used by _applyVibrancy() to avoid allocating a
-        // fresh THREE.Color each time the user drags a slider.
-        // Allocated lazily once Three.js is loaded inside initScene().
-        let _paletteColorTmp = null;
-        // Per-fret last-active timestamp for lane persistence
-        let fretLastActiveTime = new Array(NFRETS + 1).fill(0);
-
-        // Active string count for the current arrangement (resolved each
-        // frame from bundle.stringCount and clamped to MAX_RENDER_STRINGS).
-        let nStr = NSTR;
-        // Set true once a chart with out-of-range s indices has triggered
-        // its warning. Reset only on teardown or when nStr changes (e.g.
-        // arrangement switch from guitar to bass) — same-nStr songs share
-        // the suppression, which is fine for what is purely a developer
-        // aid log.
-        let _oobStringWarned = false;
-
-        // Per-string bounds check used by every loop that indexes a
-        // per-string array (noteState.*, nextNoteByString, lastFretForString,
-        // mStr/mGlow/mSus, ...). Skipping out-of-range s upstream keeps
-        // sparse-array extension out of those arrays AND keeps drawNote's
-        // material lookup safe in one place.
-        function validString(s) {
-            const ok = Number.isInteger(s) && s >= 0 && s < nStr;
-            if (!ok && !_oobStringWarned) {
-                _oobStringWarned = true;
-                let msg = '[3D-Hwy] dropping notes with s out of range [0,' + nStr + ')';
-                if (nStr === S_COL.length) msg += ' (extended-range chart beyond palette size)';
-                console.warn(msg);
-            }
-            return ok;
-        }
-
-        // filter() allocates a new array per chord per frame, even though
-        // the vast majority of charts have no out-of-range strings. Scan
-        // first; only allocate when there's actually something to drop.
-        // The unfiltered array is reused as-is in the common case.
-        //
-        // Result is cached by ``ch.notes`` identity — call sites (chord
-        // render loop, camera pre-pass, strGlow / accent prepasses, cjNext
-        // peek) hit the same chord-notes array many times per frame, and
-        // the array contents are chart-static for the lifetime of the
-        // arrangement. The cache stores either the input array itself
-        // (common case) or the filtered copy, so the identity-preservation
-        // contract callers depend on is unchanged.
-        // NOTE: this cache (and _chordSigCache / _chordShapeCache below) keys on
-        // the notes/chord object but its result depends on validString() →
-        // nStr. If first computed while nStr is still the default 6 (an early
-        // frame before song_info applies stringCount), string-6+ notes get
-        // filtered out and would stay gone forever. The nStr-change handler
-        // resets all three via _resetStringDependentCaches() so extended-range
-        // (7+ string) charts recompute once the real string count arrives.
-        let _filterValidNotesCache = new WeakMap();
-        function filterValidNotes(notes) {
-            const cached = _filterValidNotesCache.get(notes);
-            if (cached !== undefined) return cached;
-            let filtered = notes;
-            for (let i = 0; i < notes.length; i++) {
-                if (!validString(notes[i].s)) {
-                    filtered = notes.filter(cn => validString(cn.s));
-                    break;
-                }
-            }
-            _filterValidNotesCache.set(notes, filtered);
-            return filtered;
-        }
-
-        /**
-         * Normalized fingering signature for chord repeat-run detection, or null.
-         * Cached via WeakMap so the sort+join only runs once per unique chord object
-         * across all frames — chart data never changes after load.
-         */
-        let _chordSigCache = new WeakMap();
-        function chordShapeSignature(ch) {
-            if (!ch?.notes) return null;
-            if (_chordSigCache.has(ch)) return _chordSigCache.get(ch);
-            const chordNotes = filterValidNotes(ch.notes);
-            let sig = null;
-            if (chordNotes.length > 0) {
-                sig = chordNotes.slice().sort((a, b) => a.s - b.s).map(n => `${n.s}:${n.f}`).join('|');
-            }
-            _chordSigCache.set(ch, sig);
-            return sig;
-        }
-
-        // ── Per-frame scratch arrays (hoisted to avoid per-frame allocation) ─────
-        // Sized to MAX_RENDER_STRINGS / NFRETS+1 — always large enough for any
-        // arrangement. We fill only [0..nStr) each frame and reset with .fill().
-        // Holding these at closure scope keeps them in a GC root; the engine can
-        // keep them hot in L1/L2 across frames, and no allocation pressure from
-        // update() itself.
-        const _scrStringSustain      = new Array(MAX_RENDER_STRINGS).fill(false);
-        const _scrStringAnticipation = new Array(MAX_RENDER_STRINGS).fill(0);
-        const _scrFretHeat           = new Array(NFRETS + 1).fill(0);
-        // Fret-wire hit flash. _fwHitIn is per-frame (cleared with the rest of
-        // the frame state, written by drawNote when a provider confirms a note);
-        // _fwHitGlow persists across frames so the flash can decay smoothly
-        // rather than snapping off the frame the provider goes quiet.
-        const _fwHitIn               = new Float32Array(NFRETS + 1);
-        const _fwHitGlow             = new Float32Array(NFRETS + 1);
-        // Per-frame chord accumulator. A chord flashes only the OUTERMOST wires
-        // of its shape, but drawNote() sees one chord note at a time and can't
-        // know the span — so hits accumulate here keyed by chord, and the flash
-        // pass (which runs after every draw loop) resolves min/max into wires.
-        // Typically 0-2 entries: only chords with a confirmed hit land here.
-        const _fwChordAcc            = new Map();
-        let _fwHitPrevTime = -Infinity; // chart time of the last decay step
-        let _fwHitColor = null;         // T.Color scratch (built in initScene)
-        let _fwHitEmissive = null;
-        const _scrStrGlow            = new Array(MAX_RENDER_STRINGS).fill(0.5);
-        const _scrAccentFillBoost    = new Array(MAX_RENDER_STRINGS).fill(0);
-        const _scrNextNoteByString   = new Array(MAX_RENDER_STRINGS).fill(null);
-        const _scrLastFretForString  = new Array(MAX_RENDER_STRINGS).fill(undefined);
-        // Scratch buffer for the recent-past-event prepass (~0.6 s back) — avoids
-        // re-allocating a per-string Array every frame. Re-filled with -Infinity
-        // at the top of each prepass run.
-        const _scrRecentByString     = new Array(MAX_RENDER_STRINGS).fill(-Infinity);
-        // Scratch buffers for the ghost-preview gap prepass — refilled each
-        // frame to avoid the `new Array(nStr)` + `Object.create(null)` churn.
-        // The Map is cleared at the top of the prepass; live entries are
-        // consumed by drawNote() reads later in the same frame.
-        const _scrGhostLastT         = new Array(MAX_RENDER_STRINGS).fill(-Infinity);
-        const _scrGhostPrevBuf       = new Map();
-        // Per-string count of upcoming-ghost slots (1/2) claimed so far this
-        // frame (board ghost — up to 3 simultaneous previews per string).
-        // Reset to 0 each frame alongside the other pool .reset() calls.
-        const _scrGhostUpcomingCount = new Array(MAX_RENDER_STRINGS).fill(0);
-        // Hoisted scratch for the arp-bracket dedupe within a single draw().
-        // Keys are `${chordId}:${occurrenceStart}` strings (cheap to build, low
-        // cardinality per frame); values are Sets of string-indices that have
-        // already drawn brackets in the AHEAD note-stream pass. Cleared at the
-        // top of every chord pass so the Set objects (and the outer Map) are
-        // reused across frames instead of reallocated.
-        const _scrNoteStreamBracketStrings = new Map();
-        // Scratch object reused for chord-note drawNote calls so `{ ...cn, t: ch.t }`
-        // doesn't allocate a new object per chord note per frame.
-        const _scrChordNote = {};
-        // Scratch objects for the nextNoteByString prepass — chord notes need
-        // a merged `{ ...cn, t: ch.t }` object, but spread allocates every frame.
-        // One scratch object per string (max MAX_RENDER_STRINGS) is safe because:
-        // (a) the prepass writes each string's entry at most once per frame,
-        // (b) drawNote() reads nxFrame.t before the next frame's prepass can overwrite.
-        const _scrNextNoteByStringData = Array.from({ length: MAX_RENDER_STRINGS }, () => ({}));
-        // Reusable Set for arpeggio persistence key lookup — cleared each frame
-        // instead of reallocating a new Set.
-        const _scrArpPersistKeys = new Set();
-        // Reusable Set for active-fret cooldown tracking — cleared each frame.
-        const _scrActiveFrets = new Set();
-        // Reusable scratch for barre atMinFretStrings computation — avoids the
-        // [...chShape].filter().map().sort() chain (3 allocations per chord per frame).
-        const _scrAtMinFretArr = new Array(MAX_RENDER_STRINGS).fill(0);
-        let _scrAtMinFretLen = 0;
-        // Sorted scalar view of "next event time per string ∪ recent event
-        // time per string" — populated once per frame in update() after
-        // _drawNextByString and _drawRecentByString are set. drawNote() and
-        // the chord render loop both need "earliest event time strictly
-        // greater than t" to deadline-cap gem visibility; the previous
-        // implementation re-scanned both per-string arrays (2 * nStr
-        // lookups) per note/chord per frame, which is hot in dense
-        // PM/FH/arpeggio passages. With this scratch the same query is
-        // O(log N) over at most 2 * MAX_RENDER_STRINGS = 16 entries via
-        // _firstEventTimeGreaterThan(). Capacity is fixed (Float64Array)
-        // to keep the buffer in stable memory; _scrEventTimesLen tracks
-        // the live prefix.
-        const _scrEventTimes    = new Float64Array(MAX_RENDER_STRINGS * 2);
-        let   _scrEventTimesLen = 0;
-        function _firstEventTimeGreaterThan(t) {
-            let lo = 0, hi = _scrEventTimesLen;
-            while (lo < hi) {
-                const mid = (lo + hi) >>> 1;
-                if (_scrEventTimes[mid] <= t) lo = mid + 1;
-                else hi = mid;
-            }
-            return lo < _scrEventTimesLen ? _scrEventTimes[lo] : Infinity;
-        }
-
-        // Camera state
-        let _leftyCached = false;
-        const xFret = f => (_leftyCached ? -fretX(f) : fretX(f));
-        const xFretMid = f => (_leftyCached ? -fretMid(f) : fretMid(f));
-        const boardSpanX = () => {
-            const x0 = xFret(0);
-            const xN = xFret(NFRETS);
-            return {
-                min: Math.min(x0, xN),
-                max: Math.max(x0, xN),
-                center: (x0 + xN) / 2,
-                width: Math.abs(xN - x0),
-            };
-        };
-
-        let tgtX = xFretMid(CAM_LOCK_CENTER_FRET), curX = xFretMid(CAM_LOCK_CENTER_FRET);
-        let tgtDist = CAM_DIST_BASE, curDist = CAM_DIST_BASE;
-        // Dolly-back multiplier applied to the curDist lerp target by camUpdate's
-        // fret-row fit guard. 1 = no extra pull-back (the common case); rises
-        // toward FRET_ROW_FIT_BOOST_MAX only when a tight, centred zoom would push
-        // the fret-number row past the bottom edge, then relaxes back to 1.
-        let _fretRowFitBoost = 1;
-        // Last committed lowFretBonus contribution baked into tgtDist
-        // (see candidateDist block — bonus is applied on top of the
-        // hysteresis-gated base).
-        let prevLowFretBonus = 0;
-        // Tracks whether the camera lock was active on the previous
-        // frame, so the dynamic branch can bypass zoom hysteresis on
-        // the first frame after a lock release. Without this, a >12
-        // fret note that disengaged the lock could be swallowed by
-        // the dead zone and the camera would fail to widen — a UX
-        // promise of the lock toggle.
-        let prevLockActive = false;
-        let tgtLookY = 0, curLookY = 0;   // lerped look-at Y for self-correcting camera
-        let aspectScale = 1;
-        // _camSnapped / _camPreScanned / _songKey: together they gate the first-data snap.
-        //
-        // On the first update() frame where bundle.notes is available,
-        // _camPreScanned is set and the full notes array is scanned (O(N), once)
-        // to check whether ANY fretted note (f > 0) exists.  If none do (e.g. an
-        // all-open-string bass arrangement), _camSnapped is set to true immediately
-        // so the per-frame pre-pass is disabled for the entire song.
-        //
-        // For charts that do have fretted notes, a lightweight O(window) pre-pass
-        // runs before any drawNote() call on every frame until the first frame
-        // where fretted notes appear in the camera targeting window (preWSum > 0).
-        // At that point curX/curDist are snapped directly to the computed targets,
-        // eliminating the camera swoop for songs with long silent intros.
-        //
-        // Once _camSnapped is true it is never cleared for the current song; the
-        // pre-pass is a permanent no-op thereafter and the camera reverts to
-        // normal lerp-based tracking for the rest of the song.
-        //
-        // _songKey tracks the active song/arrangement so the snap state resets
-        // automatically when the user switches songs or arrangements via
-        // reconnect() (which does not call renderer.destroy/init).
-        let _camSnapped = false;
-        let _camPreScanned = false;
-        let _songKey = null;
-        // Smooth lookahead camera: fused world-X and displayed fret-span.
-        let _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
-        let _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
-        let _lookaheadCamPrevNow = null;
-        let _lookaheadLowBonusU = 0;
-        let _lookaheadHiNeckLatch = false;
-
-        // ── Sub-frame clock smoothing ─────────────────────────────────────
-        // bundle.currentTime is the browser's audio.currentTime, which only
-        // refreshes every ~20–23 ms — coarser than a 60/144 Hz rAF frame. Fed
-        // straight into note Z-positions it makes the whole highway step in
-        // micro-jumps (1–2 static frames, then a jump), most visible as a
-        // "stutter" across a dense wall of repeated chords even when FPS is
-        // steady. smoothNow() interpolates forward with performance.now()
-        // between distinct audio samples (mirroring core highway.js
-        // getTime()), tracking the observed playback rate so the speed slider
-        // stays accurate, and falls back to the raw value on pause / seek /
-        // stall so the scroll never drifts against silent audio.
-        let _clkAudioT = NaN;   // last distinct bundle.currentTime sample
-        let _clkPerf = NaN;     // performance.now() when that sample arrived
-        let _clkRate = 1;       // observed chart-seconds per real-second
-        let _frameNow = 0;      // smoothed time for THIS frame (update → camUpdate)
-
-        // Low-overdraw sustain rendering (DEFAULT since perf profiling on
-        // dense palm-mute / fret-hand-mute passages). Those sections are GPU
-        // fill-bound: the transparent sustain trails/rails stack many blended
-        // fragments. Profiling (pinned A/B loop) showed ren.render() p50 at
-        // ~7.5 ms vs ~5.9 ms with all the sustain extras off. The additive
-        // rail bloom halo (wide gaussian planes, additive blending) is the
-        // single most expensive per-pixel contributor, so the lean default
-        // drops ONLY the bloom. The trail/ribbon white OUTLINE (mSusOutline,
-        // with hit/miss colour) is kept — it's a thin, cheap layer and gives
-        // tails their border, so it's worth the small fill cost. Opt back into
-        // the full look (re-enable the rail bloom) per browser, no rebuild:
-        //   localStorage.h3d_full_sus = '1'   // re-enable rail bloom halo
-        //   delete localStorage.h3d_full_sus  // back to lean default
-        // Polled at ~1 Hz at the top of update() (perf: localStorage reads
-        // are synchronous) so the console flag still takes effect live.
-        // The bloom pool/material/gaussian texture are kept intact
-        // (still pinned by the bloom unit tests and used by the opt-out path).
-        let _leanSus = true;
-        let _leanSusPollCounter = 0;
-
-        // Lifecycle flags
-        let _isReady = false;
-        let _destroyed = false;
-        let _invertedCached = false;
-        let _invertedForBoard = false;
-        let _leftyForBoard = false;
-        let _initToken = 0;
-        let highwayCanvas = null;
-
-        // ── Focus state (splitscreen dim) ─────────────────────────────────
-        let _focusSubscribed = false;
-        let _isFocused = true;
-        const _onFocusChange = () => _updateFocusState();
-
-        function _unsubscribeFocus() {
-            if (!_focusSubscribed) return;
-            const ss = window.feedBackSplitscreen;
-            if (ss && typeof ss.offFocusChange === 'function') ss.offFocusChange(_onFocusChange);
-            _focusSubscribed = false;
-        }
-
-        function _updateFocusState() {
-            if (_destroyed || !_isReady) return;
-            const focused = _ssIsCanvasFocused(highwayCanvas);
-            if (focused === _isFocused) return;
-            _isFocused = focused;
-            if (ambLight) ambLight.intensity = focused ? 0.85 : 0.4;
-            if (dirLight) dirLight.intensity = focused ? 0.8 : 0.35;
-        }
-
-        // ── String-to-Y (respects invert) ─────────────────────────────────
-        const sY = s => S_BASE + (_invertedCached ? s : (nStr - 1 - s)) * S_GAP;
-
-        // ── Text-sprite cache ──────────────────────────────────────────────
-        // ── Text-sprite style presets ─────────────────────────────────────
-        // Each preset describes how a class of label is rasterised.
-        // Tweak per-class look here (font, outline color/width, source
-        // canvas size). `wide` toggles a long aspect ratio for multi-char
-        // labels (chord/section names, "↑1/2", "~~~").
-        //
-        // Knobs:
-        //   font        — full CSS font shorthand (weight + size + family)
-        //   wideFont    — same, used when caller passes wide=true
-        //   srcH        — source-canvas height in px (square; wide=4×).
-        //                 Keep power-of-two so WebGL1 / Three.js retain
-        //                 mipmaps + linear-mip-linear filtering — NPOT
-        //                 textures silently fall back to no-mipmap and
-        //                 shimmer at distance.
-        //   stroke      — outline color (null = no outline)
-        //   strokeW     — outline line-width in source-canvas px
-        //   shadow      — { color, blur, dx, dy } or null
-        const TXT_STYLES = {
-            // The two fret-number sets the user wants to pop hardest.
-            fretRow: {
-                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                srcH: 256, stroke: '#0a1018', strokeW: 18,
-                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
-            },
-            noteFret: {
-                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                srcH: 256, stroke: '#0a1018', strokeW: 18,
-                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
-            },
-            // Ghost-fret labels on the board projection: same weight/size/outline
-            // as noteFret, but uses textAlign='center'; textBaseline='middle'
-            // (the standard branch in txtMat) so the glyph is truly centred on
-            // the PlaneGeometry UV. inkCenterFret's actualBoundingBox path is
-            // intentionally NOT activated for this style — that path was designed
-            // for Sprites and shifts the canvas origin, which causes visible
-            // lower-left drift on Mesh + MeshBasicMaterial (UV-direct mapping).
-            ghostFret: {
-                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
-                srcH: 256, stroke: '#0a1018', strokeW: 18,
-                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
-            },
-            // Chord names — gold script-style label, lighter outline keeps
-            // the colour readable.
-            chord: {
-                font:     'bold 80px sans-serif',
-                wideFont: 'bold 64px sans-serif',
-                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
-            },
-            // Section banners ("Verse", "Chorus") — same as chord weight.
-            section: {
-                font:     'bold 80px sans-serif',
-                wideFont: 'bold 64px sans-serif',
-                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
-            },
-            // Technique markers (pinch-harmonic icon, PM, AC, H/P/T, etc.).
-            technique: {
-                font:     'bold 80px sans-serif',
-                wideFont: 'bold 64px sans-serif',
-                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
-            },
-            // Open-string "0" label on the note body itself.
-            open: {
-                font:     'bold 80px sans-serif',
-                wideFont: 'bold 64px sans-serif',
-                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
-            },
-        };
-
-        function txtMat(text, col, wide, style) {
-            const sName = style || 'technique';
-            const k = sName + '|' + (wide ? 'W' : '') + text + '|' + col;
-            if (txtCache[k]) return txtCache[k];
-            const sp = TXT_STYLES[sName] || TXT_STYLES.technique;
-            const h  = sp.srcH;
-            const str = String(text);
-            const font = wide ? sp.wideFont : sp.font;
-
-            let w = wide ? h * 4 : h;
-
-            if (!wide && sName === 'noteFret') {
-                // Wide labels (D#2, Bb3) need a canvas wider than srcH; cap so
-                // glyphs stay centred at (w/2, h/2) without edge clipping.
-                const probe = document.createElement('canvas').getContext('2d');
-                probe.font = font;
-                const tw = probe.measureText(str).width;
-                let pad = 0;
-                if (sp.stroke && sp.strokeW > 0) pad += sp.strokeW * 2;
-                if (sp.shadow) {
-                    pad += Math.abs(sp.shadow.dx) + sp.shadow.blur * 2;
-                }
-                w = Math.min(12 * h, Math.max(h, Math.ceil(tw + pad)));
-            }
-
-            const c  = document.createElement('canvas');
-            c.width = w; c.height = h;
-            const x = c.getContext('2d');
-            x.font = font;
-            // Fret / open-string digits: anchor from actualBoundingBox so the
-            // glyph sits at the true optical centre of the canvas (fixes
-            // sprites looking off-centre inside the board ghost and elsewhere).
-            const inkCenterFret = !wide && (sName === 'noteFret' || sName === 'open');
-            // Ghost fret labels live on a PlaneGeometry Mesh (UV-direct), not a Sprite
-            // billboard.  Sprites tolerate slight canvas off-centering because Three.js
-            // centres them at their world position; a Mesh does not — the digit lands
-            // wherever it sits in UV space.  Use the advance-width centre as the initial
-            // pen position and then correct for any ink asymmetry via actualBoundingBox.
-            const inkCenterGhost = !wide && sName === 'ghostFret';
-            let drawX = w / 2;
-            let drawY = h / 2;
-            if (inkCenterFret) {
-                x.textAlign = 'left';
-                x.textBaseline = 'alphabetic';
-                const m = x.measureText(str);
-                const L = m.actualBoundingBoxLeft;
-                const R = m.actualBoundingBoxRight;
-                const A = m.actualBoundingBoxAscent;
-                const D = m.actualBoundingBoxDescent;
-                if (
-                    L != null && R != null && A != null && D != null &&
-                    Number.isFinite(L) && Number.isFinite(R) &&
-                    Number.isFinite(A) && Number.isFinite(D)
-                ) {
-                    const inkW = R - L;
-                    drawX = (w - inkW) / 2 - L;
-                    drawY = (h + A - D) / 2;
-                    // Tab digits sit visually a hair low vs bbox (stroke/shadow);
-                    // small canvas nudge keeps sprites centred on the board ghost.
-                    if (sName === 'noteFret') drawY -= h * 0.028;
-                } else {
-                    x.textAlign = 'center';
-                    x.textBaseline = 'middle';
-                    drawX = w / 2;
-                    drawY = h / 2;
-                }
-            } else if (inkCenterGhost) {
-                // Alpha-weighted centroid approach on FILL-ONLY ink (no shadow, no
-                // stroke) to find the true ink centre of mass without contamination
-                // from the isotropic shadow blur.  For Arial Black "1" the shadow from
-                // the thin upper-left flag bleeds leftward and cancels part of the
-                // rightward correction when we include it in the scan.  Measuring fill
-                // alone isolates the actual glyph shape.
-                // 1. Draw fill-only (no shadow, no stroke) at (w/2, h/2) on temp canvas.
-                // 2. Compute Σ(px·alpha) / Σ(alpha) → ink centroid.
-                // 3. Shift drawX/drawY so centroid lands exactly at (w/2, h/2).
-                // Max 4 unique digits (1–4) → cache-miss runs at most 4 times ever.
-                x.textAlign = 'center';
-                x.textBaseline = 'middle';
-                try {
-                    const tmpC = document.createElement('canvas');
-                    tmpC.width = w; tmpC.height = h;
-                    const tc = tmpC.getContext('2d');
-                    tc.font = font;
-                    tc.textAlign = 'center';
-                    tc.textBaseline = 'middle';
-                    // Deliberately NO shadow and NO stroke — shadow spreads isotropically
-                    // and muddles the centroid; fill alone gives the cleanest reading.
-                    tc.fillStyle = '#ffffff';
-                    tc.fillText(str, w / 2, h / 2);
-                    const id = tc.getImageData(0, 0, w, h).data;
-                    // Alpha-weighted centroid — heavier ink pixels (thick vertical stem
-                    // of "1") outweigh thin/sparse pixels (diagonal flag), producing the
-                    // correct perceptual centre rather than the geometric bbox midpoint.
-                    let sumX = 0, sumY = 0, sumA = 0;
-                    for (let py = 0; py < h; py++) {
-                        for (let px = 0; px < w; px++) {
-                            const a = id[(py * w + px) * 4 + 3];
-                            if (a > 4) { sumX += px * a; sumY += py * a; sumA += a; }
-                        }
-                    }
-                    if (sumA > 0) {
-                        // shift pen so centroid → canvas centre, then add a small
-                        // extra rightward nudge (8 %) so the vertical stroke of
-                        // narrow digits like "1" sits visually at gem centre rather
-                        // than the advance-width centre (which may be slightly left
-                        // of the dominant ink mass for Arial Black numerals).
-                        drawX = w / 2 + (w / 2 - sumX / sumA) + w * 0.08;
-                        drawY = h / 2 + (h / 2 - sumY / sumA);
-                    }
-                } catch (_) { /* fallback: draw at (w/2, h/2) */ }
-                // x (real canvas) still has textAlign='center'; textBaseline='middle'
-            } else {
-                x.textAlign = 'center';
-                x.textBaseline = 'middle';
-            }
-            if (sp.shadow) {
-                x.shadowColor   = sp.shadow.color;
-                x.shadowBlur    = sp.shadow.blur;
-                x.shadowOffsetX = sp.shadow.dx;
-                x.shadowOffsetY = sp.shadow.dy;
-            }
-            if (sp.stroke && sp.strokeW > 0) {
-                x.lineJoin    = 'round';
-                x.miterLimit  = 2;
-                x.strokeStyle = sp.stroke;
-                x.lineWidth   = sp.strokeW;
-                x.strokeText(str, drawX, drawY);
-            }
-            x.fillStyle = col;
-            x.fillText(str, drawX, drawY);
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c),
-                transparent: true,
-                // depthTest:false means later geometry never *fails* depth
-                // against these sprites, but without depthWrite:false the
-                // sprites still write to the depth buffer (Three.js default
-                // is depthWrite:true even for SpriteMaterial). That can
-                // make subsequent sprites/labels vanish — match the
-                // pattern used by the other sprite materials in this file.
-                depthTest: false,
-                depthWrite: false,
-            });
-            txtCache[k] = mat;
-            return mat;
-        }
-
-        function pinchHarmonicMat(col) {
-            const baseCol = new T.Color(col != null ? col : '#ffd84d');
-            // v5 — compact concentric ellipses:
-            //   1. black outer border  rx=0.430h ry=0.255h
-            //   2. string-color body   rx=0.418h ry=0.232h
-            //   3. black inner ring    rx=0.407h ry=0.218h
-            //   4. string-color inner  rx=0.264h ry=0.218h
-            //   5. black center dot    rx=0.134h ry=0.120h
-            const k = 'technique|pinchHarmonicIcon|rs2014-v5b|' + baseCol.getHexString();
-            if (txtCache[k]) return txtCache[k];
-
-            const h = 512;
-            const c = document.createElement('canvas');
-            c.width = h; c.height = h;
-            const x = c.getContext('2d');
-            const TAU = Math.PI * 2;
-            const colStr = `rgb(${Math.round(baseCol.r * 255)},${Math.round(baseCol.g * 255)},${Math.round(baseCol.b * 255)})`;
-
-            x.clearRect(0, 0, h, h);
-            x.save();
-            x.translate(h / 2, h / 2);
-
-            // Form 1 — black outer border
-            x.fillStyle = '#000000';
-            x.beginPath(); x.ellipse(0, 0, h * 0.430, h * 0.255, 0, 0, TAU); x.fill();
-
-            // Form 2 — string-color main body
-            x.fillStyle = colStr;
-            x.beginPath(); x.ellipse(0, 0, h * 0.418, h * 0.232, 0, 0, TAU); x.fill();
-
-            // Form 3 — black inner ring
-            x.fillStyle = '#000000';
-            x.beginPath(); x.ellipse(0, 0, h * 0.407, h * 0.218, 0, 0, TAU); x.fill();
-
-            // Form 4 — string-color inner spot (narrower)
-            x.fillStyle = colStr;
-            x.beginPath(); x.ellipse(0, 0, h * 0.2637, h * 0.218, 0, 0, TAU); x.fill();
-
-            // Form 5 — black center dot
-            x.fillStyle = '#000000';
-            x.beginPath(); x.ellipse(0, 0, h * 0.134, h * 0.120, 0, 0, TAU); x.fill();
-
-            x.restore();
-
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c),
-                transparent: true,
-                depthTest: false,
-                depthWrite: false,
-            });
-            txtCache[k] = mat;
-            return mat;
-        }
-
-        function naturalHarmonicMat() {
-            const k = 'technique|naturalHarmonicIcon|pink-ring-v3';
-            if (txtCache[k]) return txtCache[k];
-
-            const h = 256;
-            const c = document.createElement('canvas');
-            c.width = h; c.height = h;
-            const x = c.getContext('2d');
-            const cx = h / 2;
-            const cy = h / 2;
-            const TAU = Math.PI * 2;
-
-            x.clearRect(0, 0, h, h);
-
-            const glow = x.createRadialGradient(cx, cy, h * 0.03, cx, cy, h * 0.47);
-            glow.addColorStop(0, 'rgba(255,170,255,0.14)');
-            glow.addColorStop(0.55, 'rgba(0,0,0,0.22)');
-            glow.addColorStop(1, 'rgba(0,0,0,0)');
-            x.fillStyle = glow;
-            x.beginPath();
-            x.arc(cx, cy, h * 0.44, 0, TAU);
-            x.fill();
-
-            x.shadowColor = 'rgba(0,0,0,0.85)';
-            x.shadowBlur = 14;
-            x.fillStyle = 'rgba(255, 255, 255, 0.96)';
-            x.beginPath();
-            x.arc(cx, cy, h * 0.31, 0, TAU);
-            x.fill();
-
-            // Punch out the inner gap so the icon reads as a bright ring.
-            x.shadowBlur = 0;
-            x.globalCompositeOperation = 'destination-out';
-            x.beginPath();
-            x.arc(cx, cy, h * 0.20, 0, TAU);
-            x.fill();
-            x.globalCompositeOperation = 'source-over';
-
-            x.shadowColor = 'rgba(0, 0, 0, 0.7)';
-            x.shadowBlur = 10;
-            x.strokeStyle = 'rgba(255, 255, 255, 0.98)';
-            x.lineWidth = 8;
-            x.beginPath();
-            x.arc(cx, cy, h * 0.255, 0, TAU);
-            x.stroke();
-
-            x.shadowColor = 'rgba(0,0,0,0)';
-            x.fillStyle = 'rgba(255, 255, 255, 0.98)';
-            x.beginPath();
-            x.arc(cx, cy, h * 0.12, 0, TAU);
-            x.fill();
-
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c),
-                transparent: true,
-                depthTest: false,
-                depthWrite: false,
-                opacity: 0.96,
-            });
-            txtCache[k] = mat;
-            return mat;
-        }
-
-        // Only two PM/FH variants exist (palm-mute = black-on-white,
-        // fret-hand mute = white-on-black). drawNote() hits muteXMat per
-        // muted chord-note per frame, so dense PM/FH passages were paying
-        // for a string concat + Map lookup on every call. Hoist both
-        // SpriteMaterial refs and short-circuit before touching the cache.
-        // They're populated lazily on first use; teardown still reaches
-        // them via the shared ``txtCache`` because muteXMat writes there.
-        let _pmXSpriteMat = null;
-        let _fhXSpriteMat = null;
-        function palmMuteXSpriteMat() {
-            return _pmXSpriteMat ?? (_pmXSpriteMat = muteXMat('#000000', '#ffffff'));
-        }
-        function fretHandMuteXSpriteMat() {
-            return _fhXSpriteMat ?? (_fhXSpriteMat = muteXMat('#ffffff', '#000000'));
-        }
-
-        function muteXMat(fillCol, strokeCol) {
-            const k = 'technique|muteX|v2|' + String(fillCol) + '|' + String(strokeCol);
-            if (txtCache[k]) return txtCache[k];
-
-            // lineCap:'square' gives flat tips. For a 45° diagonal the square-cap
-            // corners sit at ±outerW/2 rotated 45° from the endpoint — they land
-            // outside the canvas unless pad ≥ outerW/√2 (the common mistake is
-            // using outerW/2, which is too small). With the correct pad the white
-            // cap is fully inside the canvas and the border is visible at every tip.
-            const h = 512;
-            const outerW = 132, innerW = 114;
-            // pad must satisfy: pad ≥ outerW / Math.SQRT2  (≈ outerW × 0.707)
-            const pad = Math.ceil(outerW / Math.SQRT2) + 2; // 96
-            const c = document.createElement('canvas');
-            c.width = h; c.height = h;
-            const x = c.getContext('2d');
-
-            x.clearRect(0, 0, h, h);
-            x.lineCap = 'square';
-
-            // Draw each diagonal in its own stroke() call — caps of the two
-            // diagonals don't interact, and the white outer is drawn before the
-            // black inner so the border is clean at every edge and tip.
-            x.strokeStyle = strokeCol;
-            x.lineWidth = outerW;
-            x.beginPath(); x.moveTo(pad, pad); x.lineTo(h - pad, h - pad); x.stroke();
-            x.beginPath(); x.moveTo(h - pad, pad); x.lineTo(pad, h - pad); x.stroke();
-
-            x.strokeStyle = fillCol;
-            x.lineWidth = innerW;
-            x.beginPath(); x.moveTo(pad, pad); x.lineTo(h - pad, h - pad); x.stroke();
-            x.beginPath(); x.moveTo(h - pad, pad); x.lineTo(pad, h - pad); x.stroke();
-
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c),
-                transparent: true,
-                depthTest: false,
-                depthWrite: false,
-            });
-            txtCache[k] = mat;
-            return mat;
-        }
-
-        // Technique-marker sprite materials (triangle / chevron). Keyed by a
-        // packed NUMBER, not a string — triMat/bendChevronMat are called from
-        // the drawNote hot path, so a string cache key would allocate per
-        // note per frame. Disposed in teardown. `hex` is a 0xRRGGBB number;
-        // the low nibble of the key tags the variant (0 ▲, 1 ▼, 3-6 chevron
-        // step-count) so triangle and chevron entries can't collide.
-        const _techMatCache = new Map();
-
-        // Hammer-on / pull-off triangle marker: a white ▲ (up) / ▼ (down)
-        // with a thick border in the gem's string colour.
-        function triMat(up, hex) {
-            const h = (hex >>> 0) & 0xffffff;
-            const key = h * 16 + (up ? 0 : 1);
-            const cached = _techMatCache.get(key);
-            if (cached) return cached;
-            const S = 256, m = S * 0.15;
-            const c = document.createElement('canvas');
-            c.width = c.height = S;
-            const g = c.getContext('2d');
-            g.beginPath();
-            if (up) { g.moveTo(S / 2, m); g.lineTo(S - m, S - m); g.lineTo(m, S - m); }
-            else    { g.moveTo(S / 2, S - m); g.lineTo(S - m, m); g.lineTo(m, m); }
-            g.closePath();
-            g.lineJoin = 'round';
-            g.fillStyle = '#ffffff';
-            g.fill();
-            g.lineWidth = S * 0.122;
-            g.strokeStyle = '#' + (hex >>> 0).toString(16).padStart(6, '0');
-            g.stroke();
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c), transparent: true,
-                depthTest: false, depthWrite: false,
-            });
-            _techMatCache.set(key, mat);
-            return mat;
-        }
-
-        // Strength-of-bend chevron stack: `steps` (1-4) chevrons in the gem's
-        // string colour (chart-format bend notation — 1 per half-step).
-        function bendChevronMat(steps, hex) {
-            const h = (hex >>> 0) & 0xffffff;
-            const key = h * 16 + 2 + steps;   // steps 1-4 → low nibble 3-6
-            const cached = _techMatCache.get(key);
-            if (cached) return cached;
-            const S = 256;
-            const c = document.createElement('canvas');
-            c.width = c.height = S;
-            const g = c.getContext('2d');
-            g.strokeStyle = '#' + (hex >>> 0).toString(16).padStart(6, '0');
-            g.lineWidth = S * 0.10;
-            g.lineJoin = g.lineCap = 'round';
-            const padX = S * 0.18;
-            const rowH = S / steps;
-            const amp = Math.min(rowH * 0.55, S * 0.24);
-            for (let i = 0; i < steps; i++) {
-                const cy = (i + 0.5) * rowH;
-                g.beginPath();
-                g.moveTo(padX, cy + amp * 0.5);
-                g.lineTo(S / 2, cy - amp * 0.5);
-                g.lineTo(S - padX, cy + amp * 0.5);
-                g.stroke();
-            }
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c), transparent: true,
-                depthTest: false, depthWrite: false,
-            });
-            _techMatCache.set(key, mat);
-            return mat;
-        }
-
-        // Darken a 0xRRGGBB colour by `factor` (0..1) for the slide-arrow
-        // marker — full string colour is too bright next to the gem.
-        function darkenHex(hex, factor) {
-            const h = (hex >>> 0) & 0xffffff;
-            const r = Math.round(((h >> 16) & 0xff) * factor);
-            const g = Math.round(((h >> 8) & 0xff) * factor);
-            const b = Math.round((h & 0xff) * factor);
-            return (r << 16) | (g << 8) | b;
-        }
-
-        // Slide-direction arrow (›/‹): a filled triangle pointing toward the
-        // slide's destination fret, in the gem's (darkened) string colour.
-        // `hex` here is already the darkened colour — keep its own cache-key
-        // nibble range (8/9) so it can't collide with triMat (0/1) or
-        // bendChevronMat (3-6).
-        function slideArrowMat(pointRight, hex) {
-            const h = (hex >>> 0) & 0xffffff;
-            const key = h * 16 + 8 + (pointRight ? 0 : 1);
-            const cached = _techMatCache.get(key);
-            if (cached) return cached;
-            const S = 256, m = S * 0.18;
-            const c = document.createElement('canvas');
-            c.width = c.height = S;
-            const g = c.getContext('2d');
-            g.beginPath();
-            if (pointRight) { g.moveTo(S - m, S / 2); g.lineTo(m, m); g.lineTo(m, S - m); }
-            else            { g.moveTo(m, S / 2); g.lineTo(S - m, m); g.lineTo(S - m, S - m); }
-            g.closePath();
-            g.fillStyle = '#' + h.toString(16).padStart(6, '0');
-            g.fill();
-            const mat = new T.SpriteMaterial({
-                map: new T.CanvasTexture(c), transparent: true,
-                depthTest: false, depthWrite: false,
-            });
-            _techMatCache.set(key, mat);
-            return mat;
-        }
-
-        function _meshMatForGhostFretDigit(spriteMat) {
-            let mb = spriteMat.userData.h3dGhostFretMeshMat;
-            if (!mb) {
-                mb = new T.MeshBasicMaterial({
-                    map: spriteMat.map,
-                    transparent: true,
-                    depthTest: false,
-                    depthWrite: false,
-                });
-                spriteMat.userData.h3dGhostFretMeshMat = mb;
-            }
-            return mb;
-        }
-
-        /**
-         * Convert any SpriteMaterial to a MeshBasicMaterial that shares its canvas
-         * texture, so technique markers can be applied to a rotatable PlaneGeometry
-         * mesh instead of a billboard Sprite. Cached on userData to avoid allocations.
-         *
-         * The cache is multi-entry: each pTechPlane mesh holds a Map<sm.map,
-         * clone> so a recycled mesh that's used for several techniques
-         * (hammer-on, palm-mute, harmonic, bend...) across frames keeps a
-         * clone for each one rather than disposing-and-recloning on every
-         * switch. With nStr-wide chords containing mixed PM/FH/HO/HP
-         * markers this collapses the per-frame allocation entirely while
-         * still being bounded — the per-mesh Map has at most one entry per
-         * distinct technique × colour the mesh has ever been used for.
-         */
-        function _spriteMat2MeshMat(mesh, sm) {
-            let perMesh = mesh.userData.h3dTechMeshMatCloneByMap;
-            if (perMesh) {
-                const hit = perMesh.get(sm.map);
-                if (hit) return hit;
-            }
-
-            let base = sm.userData.h3dTechMeshMat;
-            if (!base) {
-                base = new T.MeshBasicMaterial({
-                    map: sm.map,
-                    transparent: true,
-                    // depthTest: false — cross-note Z ordering is handled by
-                    // per-note renderOrderForLayerAtZ(...) calls rather than the
-                    // depth buffer. This is necessary because close notes often use
-                    // mGlow (depthWrite:false), so the depth buffer can't reliably
-                    // occlude far markers near the hit line. With per-note renderOrder,
-                    // far labels render first and close note geometry renders last,
-                    // appearing on top without depthTest.
-                    depthTest: false,
-                    depthWrite: false,
-                    // forceSinglePass accompanies EVERY transparent DoubleSide
-                    // material in this file: without it, Three r158+ renders
-                    // each such object in TWO passes (back side then front),
-                    // setting material.needsUpdate on both — which forces a
-                    // full getParameters/program-cache lookup per object per
-                    // frame (profiled at ~4% of throttled main-thread time)
-                    // and doubles the draw calls. The two-pass path exists to
-                    // fix self-occlusion sorting on closed transparent meshes;
-                    // all our DoubleSide materials are flat unlit quads
-                    // (labels, rails, frames, lanes) where it buys nothing.
-                    side: T.DoubleSide, forceSinglePass: true,
-                });
-                sm.userData.h3dTechMeshMat = base;
-            }
-            // First conversion for this mesh: the pTechPlane pool factory gave
-            // it a placeholder MeshBasicMaterial that the caller is about to
-            // overwrite with the clone below. Dispose it now — once
-            // mesh.material is reassigned the placeholder is orphaned and
-            // teardown's scene.traverse() pass can no longer reach it, so it
-            // would leak one GPU material per pooled mesh for the renderer's
-            // lifetime.
-            if (!perMesh && mesh.material && mesh.material !== base) {
-                mesh.material.dispose?.();
-            }
-            if (!perMesh) {
-                perMesh = new Map();
-                mesh.userData.h3dTechMeshMatCloneByMap = perMesh;
-            }
-            const clone = base.clone();
-            perMesh.set(sm.map, clone);
-            _techMeshMatClones.add(clone);
-            return clone;
-        }
-
-        function _disposeOpenStringPitchSprites() {
-            // Tuning-label materials are clones of cached txtMat() entries, so
-            // they share the .map (CanvasTexture) with the canonical txtCache
-            // material. Disposing the map here would invalidate every other
-            // material that references the same cached glyph; teardown()'s
-            // txtCache loop is the single owner of those textures.
-            for (const m of _tuningLabelMats) {
-                try { m.dispose(); } catch (_) { /* idempotent */ }
-            }
-            _tuningLabelMats = [];
-            _tuningLabelSprites = [];
-            _lastOpenStringLblSig = '';
-            if (!tuningLblG) return;
-            while (tuningLblG.children.length) tuningLblG.remove(tuningLblG.children[0]);
-        }
-
-        function _openStringLabelSignature(bundle, labels) {
-            const si = bundle && bundle.songInfo;
-            const tun = si && si.tuning;
-            let tStr = '';
-            if (Array.isArray(tun)) tStr = tun.slice(0, labels.length).join(',');
-            else if (bundle && Array.isArray(bundle.tuning)) tStr = bundle.tuning.slice(0, labels.length).join(',');
-            const capo =
-                si && Number.isFinite(si.capo) ? si.capo
-                    : (bundle && Number.isFinite(bundle.capo) ? bundle.capo : '');
-            const arrIdx = si && si.arrangement_index != null ? si.arrangement_index : '';
-            let palSig = '';
-            const nLab = labels.length;
-            if (activePalette) {
-                // activePalette entries are numeric hex (PALETTES) or already hex strings;
-                // convert without instantiating T.Color per string — this signature is
-                // built every frame inside _syncOpenStringPitchLabels.
-                const lim = Math.min(activePalette.length, nLab);
-                for (let i = 0; i < lim; i++) {
-                    if (i > 0) palSig += '/';
-                    const c = activePalette[i];
-                    palSig += typeof c === 'number' ? (c >>> 0).toString(16) : String(c);
-                }
-            }
-            return `${nStr}|${capo}|${tStr}|${arrIdx}|${labels.join(',')}|${palSig}|${_textSizeMul.toFixed(3)}|${boardStringStartX.toFixed(6)}|${boardTuningLabelX.toFixed(6)}`;
-        }
-
-        function _syncOpenStringPitchLabels(bundle) {
-            if (!tuningLblG || !T || !bundle) return;
-            if (!tuningLabelsVisible) {
-                tuningLblG.visible = false;
-                if (_tuningLabelSprites.length) _disposeOpenStringPitchSprites();
-                _lastOpenStringLblSig = '';
-                return;
-            }
-            tuningLblG.visible = true;
-            // Cheap-key fast path: compare the inputs that drive the label content
-            // against last frame. The signature string + labels array build are
-            // both per-frame allocators, so skipping them when nothing changed
-            // saves a chunk of GC pressure in the hot render loop.
-            const si = bundle.songInfo;
-            const tunRef = (si && Array.isArray(si.tuning)) ? si.tuning : null;
-            const bundleTunRef = Array.isArray(bundle.tuning) ? bundle.tuning : null;
-            const capo =
-                si && Number.isFinite(si.capo) ? si.capo
-                    : (Number.isFinite(bundle.capo) ? bundle.capo : NaN);
-            const arrIdx = si && si.arrangement_index != null ? si.arrangement_index : undefined;
-            if (
-                _tuningLabelSprites.length === nStr &&
-                _lastSyncTuningRef === tunRef &&
-                _lastSyncBundleTuningRef === bundleTunRef &&
-                Object.is(_lastSyncCapo, capo) &&
-                _lastSyncArrIdx === arrIdx &&
-                _lastSyncPaletteRef === activePalette &&
-                _lastSyncNStr === nStr &&
-                _lastSyncTextSizeMul === _textSizeMul &&
-                _lastSyncStartX === boardStringStartX &&
-                _lastSyncLabelX === boardTuningLabelX
-            ) return;
-            // One of the inputs changed — fall through to the canonical signature
-            // check (catches value-equal-but-different-ref tuning arrays).
-            const labels = _openStringPitchLabelsForTuning(bundle, si, nStr);
-            const sig = _openStringLabelSignature(bundle, labels);
-            // Refresh cheap-key cache regardless of signature outcome so future
-            // frames can fast-path even when the sig matched.
-            _lastSyncTuningRef = tunRef;
-            _lastSyncBundleTuningRef = bundleTunRef;
-            _lastSyncCapo = capo;
-            _lastSyncArrIdx = arrIdx;
-            _lastSyncPaletteRef = activePalette;
-            _lastSyncNStr = nStr;
-            _lastSyncTextSizeMul = _textSizeMul;
-            _lastSyncStartX = boardStringStartX;
-            _lastSyncLabelX = boardTuningLabelX;
-            if (sig === _lastOpenStringLblSig && _tuningLabelSprites.length === nStr) return;
-            _disposeOpenStringPitchSprites();
-            _lastOpenStringLblSig = sig;
-            // Left of nut/cordas — centered on headstock mass so text does not sit on the strings.
-            const labelX = boardTuningLabelX;
-            const zLabel = -0.08 * K;
-            const scalePx = 2.42 * _textSizeMul * K;
-            for (let s = 0; s < nStr; s++) {
-                const hex = '#' + new T.Color(activePalette[s % activePalette.length]).getHexString();
-                const mat = txtMat(labels[s] || '?', hex, false, 'noteFret').clone();
-                mat.depthTest = false;
-                mat.depthWrite = false;
-                mat.transparent = true;
-                const sp = new T.Sprite(mat);
-                sp.center.set(0, 0.5);
-                sp.scale.set(scalePx, scalePx, 1);
-                sp.position.set(labelX, sY(s), zLabel);
-                sp.renderOrder = 8;
-                tuningLblG.add(sp);
-                _tuningLabelSprites.push(sp);
-                _tuningLabelMats.push(mat);
-            }
-        }
-
-        // ── Object pool ────────────────────────────────────────────────────
-        // ── Opt-in perf bench harness (feedBack#226) ──────────────────────
-        // Enable with `?h3dbench=1` on the player URL. Aggregates per-segment
-        // timings of update() into a console.log every _PB_REPORT_MS.
-        //
-        // When the bench is OFF, pbBeg/pbEnd/pbReportTick are bound to a
-        // single shared empty function literal when this renderer
-        // instance is created (createHighway() runs once per panel, not
-        // once per module load) — V8 typically inlines empty bodies and
-        // the call sites have minimized overhead in the hot path.
-        // (Previously they had `if (!_perfBench) return;` guards, which
-        // still cost a function-call frame per mark site per frame;
-        // Copilot review on #413.) Inlining is a JIT heuristic, not a
-        // language guarantee.
-        const _perfBench = (() => {
-            try { return new URLSearchParams(location.search).get('h3dbench') === '1'; }
-            catch (_) { return false; }
-        })();
-        let pbBeg, pbEnd, pbReportTick;
-        if (_perfBench) {
-            const _PB_NAMES = ['frame', 'state', 'next', 'mat', 'noteDraw', 'chordDraw', 'render'];
-            const _pbStart = new Float64Array(_PB_NAMES.length);
-            const _pbAcc = _PB_NAMES.map(() => []);
-            const _PB_REPORT_MS = 5000;
-            let _pbReportStart = 0;
-            let _pbFrameCount = 0;
-            pbBeg = function pbBeg(idx) { _pbStart[idx] = performance.now(); };
-            pbEnd = function pbEnd(idx) {
-                _pbAcc[idx].push(performance.now() - _pbStart[idx]);
-            };
-            pbReportTick = function pbReportTick() {
-                const now = performance.now();
-                if (_pbReportStart === 0) {
-                    // First call: discard the sample(s) that already
-                    // landed in _pbAcc from the very first frame's
-                    // pbEnd() calls, so fps and segment stats span the
-                    // same frame set on every reported window.
-                    _pbReportStart = now;
-                    _pbFrameCount = 0;
-                    for (let i = 0; i < _PB_NAMES.length; i++) _pbAcc[i].length = 0;
-                    return;
-                }
-                _pbFrameCount++;
-                if (now - _pbReportStart < _PB_REPORT_MS) return;
-                const dur = now - _pbReportStart;
-                const fps = (_pbFrameCount / dur * 1000).toFixed(1);
-                const parts = [];
-                for (let i = 0; i < _PB_NAMES.length; i++) {
-                    const arr = _pbAcc[i];
-                    if (!arr.length) { parts.push(`${_PB_NAMES[i]}=-`); continue; }
-                    arr.sort((a, b) => a - b);
-                    const n = arr.length;
-                    // Nearest-rank: ceil(p · n) - 1, clamped to [0, n-1].
-                    // Avoids the off-by-one where Math.floor(n * 0.95)
-                    // returns the last element (effectively the max)
-                    // for small samples (e.g. n=20 → idx 19).
-                    const p50 = arr[Math.max(0, Math.ceil(0.50 * n) - 1)];
-                    const p95 = arr[Math.max(0, Math.ceil(0.95 * n) - 1)];
-                    const mx = arr[n - 1];
-                    parts.push(`${_PB_NAMES[i]} p50=${p50.toFixed(2)} p95=${p95.toFixed(2)} max=${mx.toFixed(2)}`);
-                    arr.length = 0;
-                }
-                console.log(`[h3dbench] ${fps}fps (${_pbFrameCount} frames) over ${(dur/1000).toFixed(1)}s — ${parts.join(' | ')}`);
-                _pbReportStart = now;
-                _pbFrameCount = 0;
-            };
-        } else {
-            pbBeg = pbEnd = pbReportTick = function () {};
-        }
-
-        function pool(parent, mk) {
-            const a = [];
-            let n = 0;
-            return {
-                get() {
-                    if (n < a.length) {
-                        const o = a[n++];
-                        o.visible = true;
-                        if (o.center && o.center.isVector2) o.center.set(0.5, 0.5);
-                        return o;
-                    }
-                    const o = mk(); parent.add(o); a.push(o); n++; return o;
-                },
-                reset() { for (let i = 0; i < n; i++) a[i].visible = false; n = 0; },
-                // Pre-allocate `cap` slots at construction so the first dense
-                // playback frames don't pay the new-Mesh allocation cost
-                // mid-RAF (felt as a stall on 7/8-string charts where the
-                // visible-note count outruns the lazy-grow path). Lazy growth
-                // past `cap` still works — this is amortisation, not a cap.
-                //
-                // Coerce `cap` to a non-negative int32: a float would still
-                // work but a callsite passing `Infinity` (or `NaN`) would
-                // otherwise spin the while-loop until OOM. `cap | 0`
-                // truncates floats, clamps Infinity → 0, and turns NaN → 0;
-                // Math.max(0, …) keeps negatives out.
-                warm(cap) {
-                    // Local rename to avoid shadowing the pool's outer
-                    // `n` (the in-use index advanced by get() / reset()).
-                    const targetLen = Math.max(0, cap | 0);
-                    while (a.length < targetLen) { const o = mk(); o.visible = false; parent.add(o); a.push(o); }
-                    return this;
-                },
-            };
-        }
-
-        // Returns indices of the longest consecutive run in a sorted integer
-        // array as { start, len } — `sorted[start..start+len)` is the run.
-        // Avoids the two per-call sub-array allocations of the previous
-        // implementation (best + cur arrays grown via .push), at the cost
-        // of one small 2-key result object. Net: callers in the chord-
-        // diagram render path no longer churn arrays per visible chord.
-        function longestConsecutiveRun(sorted) {
-            let bestStart = -1, bestLen = 0;
-            let curStart = -1, curLen = 0;
-            for (let i = 0; i < sorted.length; i++) {
-                if (curLen === 0 || sorted[i] === sorted[curStart + curLen - 1] + 1) {
-                    if (curLen === 0) curStart = i;
-                    curLen++;
-                } else {
-                    if (curLen > bestLen) { bestLen = curLen; bestStart = curStart; }
-                    curStart = i; curLen = 1;
-                }
-            }
-            if (curLen > bestLen) { bestLen = curLen; bestStart = curStart; }
-            return { start: bestStart, len: bestLen };
-        }
-
-        /* ── Lyrics overlay (2D canvas on top of WebGL) ─────────────────── */
-        function drawChordDiagram(ctx, opts) {
-            const {
-                name, frets,
-                opacity = 1,
-                entranceT = 1.0,
-                canvasW = 600, canvasH = 400,
-                inverted = false,
-                sizeSlider = 0.5,
-                position = 'tl',
-                nStr = 6,
-                lyricsBottom = 0,
-                stackOffset = 0,
-            } = opts;
-
-            // Responsive sizing — CELL derived from panel height + user slider.
-            // COLS is the resolved string count from the caller (via resolveStringCount)
-            // so bass (4), extended (7/8) arrangements render correctly.
-            const COLS = nStr, ROWS = 4;
-            // Minimum column span required for PATH B (bracket extension / detection).
-            // Math.min(COLS-1, 4) scales with string count:
-            //   4-string bass → 3  (max possible span, so 2-4-4-2 shapes qualify)
-            //   6-string      → 4  (excludes D major span=2 / common 2-string coincidences)
-            //   8-string      → 4  (muted outer strings still leave span ≥ 4 for real barres)
-            const MIN_BARRE_SPAN = Math.min(COLS - 1, 4);
-            // Maps diagram column index → chord-template frets-array index.
-            // Templates are high-e-first: frets[0]=high e, frets[COLS-1]=low E.
-            // Non-inverted display (col 0 = high e): getStrIdx(0) = 0        → frets[0]      = high e.
-            // Inverted display     (col 0 = low E):  getStrIdx(0) = COLS-1   → frets[COLS-1] = low E.
-            const getStrIdx = col => inverted ? (COLS - 1 - col) : col;
-            const sizeF  = DIAG_SIZE_MIN + (DIAG_SIZE_MAX - DIAG_SIZE_MIN) * sizeSlider;
-
-            // startFret / isFirstPos must be known before CELL so that fretLabelW
-            // can be measured and factored into the width cap.  The old
-            // canvasW/(COLS+1.5) guard only approximated 2*PAD and ignored the
-            // extra left padding reserved for non-first-position "Nfr" labels.
-            const playedFrets = frets.filter(f => f > 0);
-            const minFret     = playedFrets.length > 0 ? Math.min(...playedFrets) : 1;
-            const startFret   = Math.max(1, minFret);
-            const isFirstPos  = startFret === 1;
-
-            // Phase 1 — height + hard-cap estimate, used only to size the label font.
-            // Cap against the vertical space available below lyricsBottom so that the
-            // diagram does not overflow into the lyrics banner on short split panels with
-            // wrapped lyric rows.  Only top-corner positions can overlap the lyrics banner,
-            // so lyricsBottom is only subtracted when position is 'tl' or 'tr'; for 'bl'
-            // and 'br' the full canvas height is available.
-            // Clamp to at least 1 so font/box calculations never receive 0-px input
-            // on very short panels (e.g. tiny split cells < 44 px tall).
-            const isTopCorner = position === 'tl' || position === 'tr';
-            const availH  = canvasH - (isTopCorner ? lyricsBottom : 0);
-            const cellEst = Math.max(1, Math.min(
-                Math.round(availH * sizeF / (ROWS + 3)),
-                DIAG_CELL_MAX,
-            ));
-            // Extra left padding for the "Nfr" label on non-first-position chords.
-            // Measured with ctx.measureText at cellEst so the estimate is exact.
-            let fretLabelW = 0;
-            if (!isFirstPos) {
-                // Measure inside a save/restore so this font assignment does not
-                // leak to the caller (the outer ctx.save() happens after CELL is derived).
-                ctx.save();
-                ctx.font = `italic ${Math.round(cellEst * 0.55)}px sans-serif`;
-                fretLabelW = Math.ceil(ctx.measureText(startFret + 'fr').width) + 6;
-                ctx.restore();
-            }
-
-            // Phase 2 — final CELL: cap against panel height, hard max, and panel width.
-            // Two width constraints are needed because PAD has a hard floor of 6:
-            //   A) when PAD = CELL*0.65 (large CELL):  CELL*(COLS+0.3) + fretLabelW ≤ canvasW
-            //   B) when PAD = 6 floor (small CELL):    CELL*(COLS-1)  + 12 + fretLabelW ≤ canvasW
-            // Both are included so boxW ≤ canvasW in every regime.
-            // fretLabelW was measured at cellEst ≥ CELL, so the cap is conservative.
-            const CELL   = Math.max(1, Math.min(
-                cellEst,
-                Math.floor((canvasW - fretLabelW) / (COLS + 0.3)),
-                Math.floor((canvasW - 2 * 6 - fretLabelW) / Math.max(1, COLS - 1)),
-            ));
-            const HEADER = Math.round(CELL * 1.6);
-            const MARKER = Math.round(CELL * 0.7);
-            const DOT_R  = CELL * 0.3;
-            const PAD    = Math.max(6, Math.round(CELL * 0.65));
-            const gridW  = CELL * (COLS - 1);
-            const gridH  = CELL * ROWS;
-
-            const PAD_L  = PAD + fretLabelW;
-
-            const boxW   = gridW + PAD_L + PAD;
-            const boxH   = HEADER + MARKER + gridH + PAD;
-
-            // Anchor to chosen corner. Top positions get extra vertical offset
-            // to clear the timeline plugin and song name displayed at the top.
-            // lyricsBottom is the actual bottom Y of the lyrics banner (returned by
-            // drawLyrics), so TOP_Y steps down past all lyric rows regardless of
-            // how many wrap lines the current panel width produces.
-            const E    = PAD;
-            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
-            let bx, by;
-            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
-            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
-            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
-            else                        { bx = E; by = TOP_Y + stackOffset; }
-
-            // Clamp so the box never bleeds off-canvas on narrow panels or wide string counts.
-            bx = Math.max(0, Math.min(canvasW - boxW, bx));
-            by = Math.max(0, Math.min(canvasH - boxH, by));
-
-            // Guard: the canvasH–boxH clamp above can push `by` above lyricsBottom when
-            // wrapped lyrics consume nearly the full panel height.  This applies to ALL
-            // corner positions: a bottom-corner diagram anchored near the canvas bottom can
-            // still reach up into the lyrics banner on very short or narrow panels where
-            // boxH is larger than the space below the lyrics.  In those cases skip drawing
-            // entirely rather than painting on top of the lyrics banner.
-            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
-
-            const gx = bx + PAD_L, gy = by + HEADER + MARKER;
-
-            // Ease-out quadratic entrance scale: 0.85 → 1.0.
-            const scale = 1 - 0.15 * (1 - entranceT) * (1 - entranceT);
-
-            ctx.save();
-            ctx.globalAlpha = opacity;
-
-            if (scale !== 1.0) {
-                const cx = bx + boxW / 2, cy = by + boxH / 2;
-                ctx.translate(cx, cy);
-                ctx.scale(scale, scale);
-                ctx.translate(-cx, -cy);
-            }
-
-            // Background + border.
-            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
-            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
-
-            // Split-root typography: "Dm7" → "D" large bold + "m7" smaller.
-            const rootMatch = name.match(/^([A-G][#b]?)(.*)/);
-            const root    = rootMatch ? rootMatch[1] : name;
-            const quality = rootMatch ? rootMatch[2] : '';
-            const rootSize = Math.round(CELL * 1.25);
-            const qualSize = Math.round(rootSize * 0.65);
-            ctx.textBaseline = 'middle';
-            const nameY = by + HEADER * 0.55;
-            ctx.font = `bold ${rootSize}px sans-serif`;
-            const rootW = ctx.measureText(root).width;
-            ctx.font = `${qualSize}px sans-serif`;
-            const qualW = quality ? ctx.measureText(quality).width : 0;
-            const nameBlockW = rootW + (quality ? qualW + 2 : 0);
-            const nameStartX = bx + boxW / 2 - nameBlockW / 2;
-            ctx.fillStyle = '#e8d080';
-            ctx.font = `bold ${rootSize}px sans-serif`;
-            ctx.textAlign = 'left';
-            ctx.fillText(root, nameStartX, nameY);
-            if (quality) {
-                ctx.font = `${qualSize}px sans-serif`;
-                ctx.fillStyle = 'rgba(232,208,128,0.75)';
-                ctx.fillText(quality, nameStartX + rootW + 2, nameY);
-            }
-
-            // Nut: CELL-proportional filled rect + subtle highlight line.
-            // Thickness is 40% of CELL, floored at 2 px so it stays visible on
-            // the smallest diagrams (CELL=1 on compact split panels).
-            const NUT_H = Math.round(Math.max(2, CELL * 0.4));
-            if (isFirstPos) {
-                ctx.fillStyle = '#ffffff';
-                ctx.fillRect(gx, gy - NUT_H, gridW, NUT_H);
-                ctx.fillStyle = 'rgba(255,255,255,0.4)';
-                ctx.fillRect(gx, gy - NUT_H, gridW, Math.max(1, Math.round(NUT_H * 0.25)));
-            }
-
-            // Fret label for non-first-position chords.
-            if (!isFirstPos) {
-                ctx.fillStyle = 'rgba(220,200,120,0.9)';
-                ctx.font = `italic ${Math.round(CELL * 0.55)}px sans-serif`;
-                ctx.textAlign = 'right';
-                ctx.textBaseline = 'middle';
-                ctx.fillText(startFret + 'fr', gx - 4, gy + CELL * 0.5);
-            }
-
-            // Fret lines.
-            ctx.strokeStyle = 'rgba(255,255,255,0.22)'; ctx.lineWidth = 1;
-            for (let r = (isFirstPos ? 1 : 0); r <= ROWS; r++) {
-                ctx.beginPath();
-                ctx.moveTo(gx, gy + r * CELL);
-                ctx.lineTo(gx + gridW, gy + r * CELL);
-                ctx.stroke();
-            }
-
-            // String lines with varying weight: low E heavier, high e lighter.
-            // With getStrIdx(col) = col (non-inverted): col 0 (high e) → strIdx=0 → t=0 thin;
-            // col COLS-1 (low E) → strIdx=COLS-1 → t=1 thick. Inverted mode naturally mirrors.
-            // Weights scale with CELL so strings never bleed into adjacent columns on
-            // small-CELL diagrams (e.g. CELL=1 on compact split panels).
-            for (let col = 0; col < COLS; col++) {
-                const strIdx = getStrIdx(col);
-                const t = COLS > 1 ? strIdx / (COLS - 1) : 1;  // 1=low E (thick), 0=high e (thin); guard COLS=1
-                ctx.lineWidth = Math.max(0.5, CELL * (0.05 + t * 0.10));
-                ctx.strokeStyle = 'rgba(255,255,255,0.3)';
-                ctx.beginPath();
-                ctx.moveTo(gx + col * CELL, gy);
-                ctx.lineTo(gx + col * CELL, gy + ROWS * CELL);
-                ctx.stroke();
-            }
-
-            // Barre detection — two complementary paths:
-            //
-            // PATH A (F-shape / mini-barre): at least two ADJACENT columns are at startFret.
-            //   Bracket is initially set to the consecutive run's own endpoints (not the full
-            //   startFretCols range) so isolated bass notes at the same fret can't pull the
-            //   bracket across an open gap (e.g. "2 0 2 2 0 0" stays bracketed at cols 2..3).
-            //
-            // PATH B (full-span barre / extension):
-            //   When PATH A fired: extend the bracket outward to the full outer startFret span
-            //     if the span ≥ MIN_BARRE_SPAN and every column between the outer startFret
-            //     columns is fretted (f > 0).
-            //   When PATH A did NOT fire: detect standalone full barres (e.g. x24442, x46654)
-            //     where only the two outermost strings sit at startFret.  An additional check
-            //     ensures that no intermediate column is itself at startFret — this rules out
-            //     alternating-fret voicings like "1 3 1 3 1 0" (col 2 at startFret would fire
-            //     incorrectly) while still catching B-major-style shapes where the barre
-            //     finger covers only the outer two strings.
-            //
-            // Templates are high-e-first: frets[0]=high e, frets[COLS-1]=low E.
-            // Examples (6-string, MIN_BARRE_SPAN=4):
-            //   F major [1,1,2,3,3,1]: PATH A run=[4,5] → bracket 4..5; PATH B span=5, all fretted → extends to 0..5 ✓
-            //   B major x24442:        PATH A no run; PATH B span=4, all fretted, no inner at startFret → 1..5 ✓
-            //   mini-A  x02220:        PATH A run=[2,3,4] → bracket 2..4; PATH B span=2<4 → no extension ✓
-            //   D major xx0232:        PATH A run length=1 → no PATH A; PATH B span<4 → no bracket ✓
-            //   2 0 2 2 0 0:           PATH A run=[2,3] → bracket 2..3; PATH B span=3<4 → no extension ✓
-            //   1 3 1 3 1 0:           PATH A no run; PATH B: inner col 2 at startFret → no bracket ✓
-            const startFretCols = [];
-            for (let col = 0; col < COLS; col++) {
-                if (frets[getStrIdx(col)] === startFret) startFretCols.push(col);
-            }
-            const barreRun = longestConsecutiveRun(startFretCols);
-            let hasBarreArc = barreRun.len >= 2;   // PATH A
-            let barreMinCol = hasBarreArc ? startFretCols[barreRun.start] : -1;
-            let barreMaxCol = hasBarreArc ? startFretCols[barreRun.start + barreRun.len - 1] : -1;
-
-            if (startFretCols.length >= 2) {             // PATH B
-                const minC = startFretCols[0];
-                const maxC = startFretCols[startFretCols.length - 1];
-                if (maxC - minC >= MIN_BARRE_SPAN) {
-                    let allFretted = true;
-                    for (let col = minC; col <= maxC; col++) {
-                        if (frets[getStrIdx(col)] <= 0) { allFretted = false; break; }
-                    }
-                    if (allFretted) {
-                        if (hasBarreArc) {
-                            // PATH A fired: always safe to extend to full outer span.
-                            barreMinCol = minC;
-                            barreMaxCol = maxC;
-                        } else {
-                            // PATH A did not fire: only draw a bracket when no intermediate
-                            // column sits at startFret.  Intermediate startFret columns would
-                            // indicate a scattered/alternating voicing rather than a clean
-                            // outer-edge barre (e.g. "1 3 1 3 1 0" has col 2 at startFret).
-                            let noInnerAtStartFret = true;
-                            for (let col = minC + 1; col < maxC; col++) {
-                                if (frets[getStrIdx(col)] === startFret) { noInnerAtStartFret = false; break; }
-                            }
-                            if (noInnerAtStartFret) {
-                                hasBarreArc = true;
-                                barreMinCol = minC;
-                                barreMaxCol = maxC;
-                            }
-                        }
-                    }
-                }
-            }
-            if (hasBarreArc) {
-                const barreY   = gy + CELL * 0.5;
-                const capH     = CELL * 0.22;  // vertical offset from barreY to the bracket line
-                const capHalf  = Math.max(1, Math.round(CELL * 0.3)); // half-height of the vertical end caps
-                // Straight bracket: a horizontal line with short vertical end caps.
-                // Stroke scales with CELL so it doesn't swamp tiny cells (floor at 1 px).
-                ctx.strokeStyle = 'rgba(255,255,255,0.6)'; ctx.lineWidth = Math.max(1, CELL * 0.2);
-                ctx.beginPath();
-                ctx.moveTo(gx + barreMinCol * CELL, barreY - capH);
-                ctx.lineTo(gx + barreMaxCol * CELL, barreY - capH);
-                ctx.stroke();
-                ctx.beginPath();
-                ctx.moveTo(gx + barreMinCol * CELL, barreY - capH - capHalf);
-                ctx.lineTo(gx + barreMinCol * CELL, barreY - capH + capHalf);
-                ctx.stroke();
-                ctx.beginPath();
-                ctx.moveTo(gx + barreMaxCol * CELL, barreY - capH - capHalf);
-                ctx.lineTo(gx + barreMaxCol * CELL, barreY - capH + capHalf);
-                ctx.stroke();
-            }
-
-            // Open/muted markers + finger dots.
-            // Non-inverted: col 0 = high e → getStrIdx(0)=0 → frets[0]; col COLS-1 = low E → frets[COLS-1].
-            // Inverted:     col 0 = low E → getStrIdx(0)=COLS-1 → frets[COLS-1]; col COLS-1 = high e → frets[0].
-            for (let col = 0; col < COLS; col++) {
-                const f = frets[getStrIdx(col)];
-                const sx = gx + col * CELL;
-                const markerY = gy - MARKER * 0.5;
-                if (f < 0) {
-                    const r = CELL * 0.20;
-                    ctx.strokeStyle = '#cc4444'; ctx.lineWidth = 1.5;
-                    ctx.beginPath(); ctx.moveTo(sx - r, markerY - r); ctx.lineTo(sx + r, markerY + r); ctx.stroke();
-                    ctx.beginPath(); ctx.moveTo(sx + r, markerY - r); ctx.lineTo(sx - r, markerY + r); ctx.stroke();
-                } else if (f === 0) {
-                    ctx.strokeStyle = '#88bbff'; ctx.lineWidth = 1.5;
-                    ctx.beginPath(); ctx.arc(sx, markerY, CELL * 0.22, 0, Math.PI * 2); ctx.stroke();
-                } else {
-                    const row = f - startFret;
-                    if (row >= 0 && row < ROWS) {
-                        const isBarreCol = hasBarreArc && f === startFret &&
-                                           col >= barreMinCol && col <= barreMaxCol;
-                        ctx.shadowColor = 'rgba(0,0,0,0.5)';
-                        ctx.shadowBlur = Math.min(4, CELL * 0.4);
-                        ctx.shadowOffsetX = Math.max(0.5, CELL * 0.1);
-                        ctx.shadowOffsetY = Math.max(0.5, CELL * 0.1);
-                        ctx.fillStyle = isBarreCol ? 'rgba(255,255,255,0.85)' : '#ffffff';
-                        ctx.beginPath();
-                        ctx.arc(sx, gy + row * CELL + CELL * 0.5, DOT_R, 0, Math.PI * 2);
-                        ctx.fill();
-                        ctx.shadowColor = 'transparent'; ctx.shadowBlur = 0;
-                        ctx.shadowOffsetX = 0; ctx.shadowOffsetY = 0;
-                    }
-                }
-            }
-            ctx.restore();
-            return boxH;
-        }
-
-        // Cached wrapper for drawChordDiagram. When entranceT === 1 (scale
-        // transform is identity) the diagram is rendered once to an
-        // OffscreenCanvas and reused every subsequent frame via drawImage +
-        // globalAlpha. During the 0.2 s entrance animation (entranceT < 1)
-        // the scale transform is non-trivial so we fall through to a fresh
-        // render — that window is ~12 frames at 60 fps, negligible.
-        //
-        // Returns boxH (diagram card height in px) so the draw loop can
-        // accumulate per-corner stack offsets when multiple overlays share
-        // the same corner position.
-        function _drawDiagramCached(ctx, opts) {
-            const { opacity = 1, entranceT = 1.0, canvasW, canvasH } = opts;
-            if (opacity <= 0) return 0;
-            if (entranceT < 1.0) {
-                return drawChordDiagram(ctx, opts) || 0;
-            }
-            const { name, frets, nStr, inverted, sizeSlider, position, lyricsBottom = 0, stackOffset = 0 } = opts;
-            const key = name + '|' + (frets || []).join(',') + '|' + nStr + '|' +
-                        (inverted ? 1 : 0) + '|' + sizeSlider + '|' + position + '|' +
-                        canvasW + '|' + canvasH + '|' + lyricsBottom + '|' + stackOffset;
-            let entry = _diagRenderCache.get(key);
-            if (!entry) {
-                let oc;
-                try { oc = new OffscreenCanvas(canvasW, canvasH); }
-                catch (_) { oc = document.createElement('canvas'); oc.width = canvasW; oc.height = canvasH; }
-                const boxH = drawChordDiagram(oc.getContext('2d'), { ...opts, opacity: 1, entranceT: 1 }) || 0;
-                if (_diagRenderCache.size >= _DIAG_CACHE_MAX) {
-                    _diagRenderCache.delete(_diagRenderCache.keys().next().value);
-                }
-                entry = { oc, boxH };
-                _diagRenderCache.set(key, entry);
-            }
-            ctx.save();
-            ctx.globalAlpha = opacity;
-            ctx.drawImage(entry.oc, 0, 0);
-            ctx.restore();
-            return entry.boxH;
-        }
-
-        // Two-line section card. Top line is "Now: <current>", bottom line
-        // is "Up Next: <next> in <countdown>". Explicit labels disambiguate
-        // current vs upcoming — earlier single-line variant rendered both
-        // states with the same word and was confusing during playback.
-        //
-        // Returns boxH on draw, 0 when nothing rendered. Position / size
-        // mirror the chord-diagram contract: 'tl' / 'tr' / 'bl' / 'br'
-        // anchor corners, sizeSlider in [0,1] scales card height.
-        //
-        // Hidden when:
-        //   - no sections array, or
-        //   - playback has not yet reached the first section AND there's
-        //     no upcoming-only fallback rendered (we still show "Up Next"
-        //     during the pre-roll so the user sees what's coming).
-        function drawSectionHud(ctx, opts) {
-            const {
-                sections, currentTime,
-                canvasW, canvasH,
-                position = 'tr',
-                sizeSlider = 0.5,
-                lyricsBottom = 0,
-                stackOffset = 0,
-            } = opts;
-            if (!sections || !sections.length) return 0;
-
-            // sections are time-ordered server-side; single forward scan.
-            let curIdx = -1;
-            for (let i = 0; i < sections.length; i++) {
-                if (sections[i].time <= currentTime) curIdx = i;
-                else break;
-            }
-            const cur  = curIdx >= 0 ? sections[curIdx] : null;
-            const next = (curIdx + 1 < sections.length) ? sections[curIdx + 1] : null;
-            // Pre-first-section: nothing playing yet but next is coming —
-            // still useful to render "Up Next" alone so the user gets the
-            // anticipatory cue during the song's intro silence.
-            if (!cur && !next) return 0;
-
-            const nowName = cur ? cur.name : '';
-            // Render countdown as a separate span so it can take a calmer
-            // grey-white treatment while the section name itself stays
-            // cyan. Combining them into one string would inherit the cyan
-            // fill across both, defeating the visual hierarchy promised
-            // in the FR.
-            let nextName = '';
-            let nextCountdown = '';
-            if (next) {
-                const dt = next.time - currentTime;
-                nextName = next.name;
-                nextCountdown = dt > 10
-                    ? 'in ' + Math.round(dt) + 's'
-                    : 'in ' + Math.max(0, dt).toFixed(1) + 's';
-            }
-
-            const sizeF = 0.65 + 0.85 * sizeSlider; // 0.65 .. 1.5
-            const baseH = Math.max(34, Math.min(72, Math.round(canvasH * 0.085 * sizeF)));
-            const PAD_X = Math.round(baseH * 0.45);
-            const PAD_Y = Math.round(baseH * 0.20);
-            // Per-text-element scale applied to nameSize / tagSize / lineH
-            // when the unscaled card would overflow a narrow panel
-            // (splitscreen quad layout, ultra-tall portrait). Computed
-            // below from the measured contentW vs the available width.
-            let textScale = 1.0;
-            const baseLineH    = Math.round(baseH * 0.46);
-            const baseNameSize = Math.round(baseH * 0.36);
-            const baseTagSize  = Math.round(baseH * 0.24);
-            const baseTagGap   = Math.round(baseH * 0.14);
-
-            const TAG_NOW  = 'Now:';
-            const TAG_NEXT = 'Up Next:';
-
-            // Phase-1 measurement at the unscaled font sizes — used to
-            // decide whether textScale needs to drop, and to lay out the
-            // final draw at whatever scale we land on.
-            ctx.save();
-            ctx.font = `${baseTagSize}px sans-serif`;
-            const tagNowWBase  = ctx.measureText(TAG_NOW).width;
-            const tagNextWBase = ctx.measureText(TAG_NEXT).width;
-            const countdownWBase = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
-            ctx.font = `bold ${baseNameSize}px sans-serif`;
-            const nowNameWBase  = nowName  ? ctx.measureText(nowName).width  : 0;
-            const nextNameWBase = nextName ? ctx.measureText(nextName).width : 0;
-            ctx.restore();
-
-            const lineNowWBase  = nowName  ? tagNowWBase  + baseTagGap + nowNameWBase  : 0;
-            const lineNextWBase = nextName
-                ? tagNextWBase + baseTagGap + nextNameWBase
-                  + (nextCountdown ? baseTagGap + countdownWBase : 0)
-                : 0;
-            const contentWBase  = Math.max(lineNowWBase, lineNextWBase);
-            const numLines = (nowName ? 1 : 0) + (nextName ? 1 : 0);
-            if (numLines === 0) return 0;
-
-            // Target width budget: cap at canvasW - 16 and reserve PAD_X
-            // either side. If contentWBase exceeds the budget, scale the
-            // font proportionally — clamped to 0.55 so labels stay legible
-            // even on extreme split-panel widths.
-            const maxBoxW = Math.max(40, canvasW - 16);
-            const availContentW = Math.max(1, maxBoxW - PAD_X * 2);
-            if (contentWBase > availContentW) {
-                textScale = Math.max(0.55, availContentW / contentWBase);
-            }
-
-            const lineH    = Math.max(1, Math.round(baseLineH    * textScale));
-            const nameSize = Math.max(1, Math.round(baseNameSize * textScale));
-            const tagSize  = Math.max(1, Math.round(baseTagSize  * textScale));
-            const TAG_GAP  = Math.max(1, Math.round(baseTagGap   * textScale));
-
-            // Phase-2 re-measurement at the scaled font sizes for the
-            // final layout. measureText doesn't scale linearly with font
-            // size on every glyph, so re-measuring is cheaper than
-            // multiplying the base widths by textScale and risking a
-            // half-pixel overflow.
-            ctx.save();
-            ctx.font = `${tagSize}px sans-serif`;
-            const tagNowW  = ctx.measureText(TAG_NOW).width;
-            const tagNextW = ctx.measureText(TAG_NEXT).width;
-            const countdownW = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
-            ctx.font = `bold ${nameSize}px sans-serif`;
-            const nowNameW  = nowName  ? ctx.measureText(nowName).width  : 0;
-            const nextNameW = nextName ? ctx.measureText(nextName).width : 0;
-            ctx.restore();
-
-            const lineNowW  = nowName  ? tagNowW  + TAG_GAP + nowNameW  : 0;
-            const lineNextW = nextName
-                ? tagNextW + TAG_GAP + nextNameW + (nextCountdown ? TAG_GAP + countdownW : 0)
-                : 0;
-            const contentW = Math.max(lineNowW, lineNextW);
-
-            const boxW = Math.min(maxBoxW, Math.round(contentW + PAD_X * 2));
-            const boxH = Math.round(numLines * lineH + PAD_Y * 2);
-
-            const E = Math.round(baseH * 0.25);
-            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
-            let bx, by;
-            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
-            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
-            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
-            else                        { bx = E; by = TOP_Y + stackOffset; }
-            bx = Math.max(0, Math.min(canvasW - boxW, bx));
-            by = Math.max(0, Math.min(canvasH - boxH, by));
-            // Suppress overlap with the wrapped lyrics banner regardless
-            // of corner. Bottom-corner cards on short panels can still
-            // reach up into the banner once boxH exceeds the space below
-            // the lyrics — same shape the chord diagram uses.
-            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
-
-            ctx.save();
-            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
-            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
-
-            ctx.textBaseline = 'middle';
-            ctx.textAlign = 'left';
-
-            // Layout each line with tag left-aligned, name in cyan after a
-            // small gap. Both lines share the same x origin (bx + PAD_X)
-            // so the tag column visually aligns vertically.
-            const lineX = bx + PAD_X;
-            let lineY = by + PAD_Y + lineH / 2;
-            const TAG_COLOR = 'rgba(180,190,205,0.85)';
-            const NAME_COLOR = '#00cccc';
-            const TIME_COLOR = 'rgba(220,225,235,0.9)';
-
-            if (nowName) {
-                ctx.font = `${tagSize}px sans-serif`;
-                ctx.fillStyle = TAG_COLOR;
-                ctx.fillText(TAG_NOW, lineX, lineY);
-                ctx.font = `bold ${nameSize}px sans-serif`;
-                ctx.fillStyle = NAME_COLOR;
-                ctx.fillText(nowName, lineX + tagNowW + TAG_GAP, lineY);
-                lineY += lineH;
-            }
-            if (nextName) {
-                ctx.font = `${tagSize}px sans-serif`;
-                ctx.fillStyle = TAG_COLOR;
-                ctx.fillText(TAG_NEXT, lineX, lineY);
-                const nextX = lineX + tagNextW + TAG_GAP;
-                ctx.font = `bold ${nameSize}px sans-serif`;
-                ctx.fillStyle = NAME_COLOR;
-                ctx.fillText(nextName, nextX, lineY);
-                if (nextCountdown) {
-                    ctx.font = `${tagSize}px sans-serif`;
-                    ctx.fillStyle = TIME_COLOR;
-                    ctx.fillText(nextCountdown, nextX + nextNameW + TAG_GAP, lineY);
-                }
-            }
-            ctx.restore();
-            return boxH;
-        }
-
-        // Tone-change HUD — card showing the active tone and the next upcoming
-        // tone with a countdown. Mirrors drawSectionHud's layout contract
-        // (position, size slider, lyricsBottom) but uses an amber accent colour
-        // so it reads as distinct from the cyan section card.
-        function drawToneHud(ctx, opts) {
-            const {
-                toneChanges, toneBase = '',
-                currentTime,
-                canvasW, canvasH,
-                position = 'tl',
-                sizeSlider = 0.5,
-                lyricsBottom = 0,
-                stackOffset = 0,
-            } = opts;
-
-            // Resolve active tone: toneBase before all changes, else the most
-            // recent change at or before currentTime.
-            // toneChanges items use { t, name } (not { time, name }) — both
-            // the legacy import path (server.py xml_tone_changes) and the sloppak
-            // path (lib/tones.py sloppak_tone_changes) emit "t" as the key.
-            let curName = toneBase;
-            let nextChange = null;
-            if (toneChanges && toneChanges.length) {
-                for (let i = 0; i < toneChanges.length; i++) {
-                    if (toneChanges[i].t <= currentTime) {
-                        curName = toneChanges[i].name;
-                    } else {
-                        nextChange = toneChanges[i];
-                        break;
-                    }
-                }
-            }
-            if (!curName && !nextChange) return 0;
-
-            let nextName = '';
-            let nextCountdown = '';
-            if (nextChange) {
-                const dt = nextChange.t - currentTime;
-                nextName = nextChange.name;
-                nextCountdown = dt > 10
-                    ? 'in ' + Math.round(dt) + 's'
-                    : 'in ' + Math.max(0, dt).toFixed(1) + 's';
-            }
-
-            const sizeF = 0.65 + 0.85 * sizeSlider;
-            const baseH = Math.max(34, Math.min(72, Math.round(canvasH * 0.085 * sizeF)));
-            const PAD_X = Math.round(baseH * 0.45);
-            const PAD_Y = Math.round(baseH * 0.20);
-            let textScale = 1.0;
-            const baseLineH    = Math.round(baseH * 0.46);
-            const baseNameSize = Math.round(baseH * 0.36);
-            const baseTagSize  = Math.round(baseH * 0.24);
-            const baseTagGap   = Math.round(baseH * 0.14);
-
-            const TAG_CUR  = 'Tone:';
-            const TAG_NEXT = 'Next:';
-
-            ctx.save();
-            ctx.font = `${baseTagSize}px sans-serif`;
-            const tagCurWBase  = ctx.measureText(TAG_CUR).width;
-            const tagNextWBase = ctx.measureText(TAG_NEXT).width;
-            const countdownWBase = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
-            ctx.font = `bold ${baseNameSize}px sans-serif`;
-            const curNameWBase  = curName  ? ctx.measureText(curName).width  : 0;
-            const nextNameWBase = nextName ? ctx.measureText(nextName).width : 0;
-            ctx.restore();
-
-            const lineCurWBase  = curName  ? tagCurWBase  + baseTagGap + curNameWBase  : 0;
-            const lineNextWBase = nextName
-                ? tagNextWBase + baseTagGap + nextNameWBase
-                  + (nextCountdown ? baseTagGap + countdownWBase : 0)
-                : 0;
-            const contentWBase = Math.max(lineCurWBase, lineNextWBase);
-            const numLines = (curName ? 1 : 0) + (nextName ? 1 : 0);
-            if (numLines === 0) return 0;
-
-            const maxBoxW = Math.max(40, canvasW - 16);
-            const availContentW = Math.max(1, maxBoxW - PAD_X * 2);
-            if (contentWBase > availContentW) {
-                textScale = Math.max(0.55, availContentW / contentWBase);
-            }
-
-            const lineH    = Math.max(1, Math.round(baseLineH    * textScale));
-            const nameSize = Math.max(1, Math.round(baseNameSize * textScale));
-            const tagSize  = Math.max(1, Math.round(baseTagSize  * textScale));
-            const TAG_GAP  = Math.max(1, Math.round(baseTagGap   * textScale));
-
-            ctx.save();
-            ctx.font = `${tagSize}px sans-serif`;
-            const tagCurW  = ctx.measureText(TAG_CUR).width;
-            const tagNextW = ctx.measureText(TAG_NEXT).width;
-            const countdownW = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
-            ctx.font = `bold ${nameSize}px sans-serif`;
-            const curNameW  = curName  ? ctx.measureText(curName).width  : 0;
-            const nextNameW = nextName ? ctx.measureText(nextName).width : 0;
-            ctx.restore();
-
-            const lineCurW  = curName  ? tagCurW  + TAG_GAP + curNameW  : 0;
-            const lineNextW = nextName
-                ? tagNextW + TAG_GAP + nextNameW + (nextCountdown ? TAG_GAP + countdownW : 0)
-                : 0;
-            const contentW = Math.max(lineCurW, lineNextW);
-
-            const boxW = Math.min(maxBoxW, Math.round(contentW + PAD_X * 2));
-            const boxH = Math.round(numLines * lineH + PAD_Y * 2);
-
-            const E = Math.round(baseH * 0.25);
-            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
-            let bx, by;
-            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
-            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
-            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
-            else                        { bx = E; by = TOP_Y + stackOffset; } // 'tl' default
-            bx = Math.max(0, Math.min(canvasW - boxW, bx));
-            by = Math.max(0, Math.min(canvasH - boxH, by));
-            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
-
-            ctx.save();
-            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
-            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
-            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
-
-            ctx.textBaseline = 'middle';
-            ctx.textAlign = 'left';
-
-            const lineX = bx + PAD_X;
-            let lineY = by + PAD_Y + lineH / 2;
-            const TAG_COLOR  = 'rgba(180,190,205,0.85)';
-            const NAME_COLOR = '#ff9a3c'; // amber — distinct from section cyan
-            const TIME_COLOR = 'rgba(220,225,235,0.9)';
-
-            if (curName) {
-                ctx.font = `${tagSize}px sans-serif`;
-                ctx.fillStyle = TAG_COLOR;
-                ctx.fillText(TAG_CUR, lineX, lineY);
-                ctx.font = `bold ${nameSize}px sans-serif`;
-                ctx.fillStyle = NAME_COLOR;
-                ctx.fillText(curName, lineX + tagCurW + TAG_GAP, lineY);
-                lineY += lineH;
-            }
-            if (nextName) {
-                ctx.font = `${tagSize}px sans-serif`;
-                ctx.fillStyle = TAG_COLOR;
-                ctx.fillText(TAG_NEXT, lineX, lineY);
-                const nextX = lineX + tagNextW + TAG_GAP;
-                ctx.font = `bold ${nameSize}px sans-serif`;
-                ctx.fillStyle = NAME_COLOR;
-                ctx.fillText(nextName, nextX, lineY);
-                if (nextCountdown) {
-                    ctx.font = `${tagSize}px sans-serif`;
-                    ctx.fillStyle = TIME_COLOR;
-                    ctx.fillText(nextCountdown, nextX + nextNameW + TAG_GAP, lineY);
-                }
-            }
-            ctx.restore();
-            return boxH;
-        }
-
-        // Lyrics layout cache — measureText per syllable + row wrapping
-        // only changes when the displayed line(s), font size, or canvas
-        // width change, not per frame. Keyed below; the per-frame work is
-        // just drawing over the cached widths.
-        let _lyrRowsCache = null;
-
-        function drawLyrics(lyrics, currentTime, ctx, W, H) {
-            if (!lyrics._lines) {
-                const lines = [];
-                let line = null, word = null;
-                const flushWord = () => { if (word && word.length) line.words.push(word); word = null; };
-                const flushLine = () => { flushWord(); if (line && line.words.length) lines.push(line); line = null; };
-                for (let i = 0; i < lyrics.length; i++) {
-                    const l = lyrics[i];
-                    const raw = l.w || '';
-                    const endsLine = raw.endsWith('+');
-                    const continuesWord = raw.endsWith('-');
-                    if (line && i > 0 && l.t - (lyrics[i - 1].t + lyrics[i - 1].d) > 4.0) flushLine();
-                    if (!line) line = { words: [], start: l.t, end: l.t + l.d };
-                    if (!word) word = [];
-                    word.push(l);
-                    line.end = Math.max(line.end, l.t + l.d);
-                    if (!continuesWord) flushWord();
-                    if (endsLine) flushLine();
-                }
-                flushLine();
-                lyrics._lines = lines;
-            }
-            const allLines = lyrics._lines;
-            if (!allLines.length) return 0;
-
-            let currentIdx = -1;
-            for (let i = 0; i < allLines.length; i++) {
-                if (allLines[i].start <= currentTime) currentIdx = i;
-                else break;
-            }
-            if (currentIdx === -1) {
-                if (allLines[0].start - currentTime > 2.0) return 0;
-                currentIdx = 0;
-            }
-            const currentLine = allLines[currentIdx];
-            const nextLine = allLines[currentIdx + 1] || null;
-            const gapToNext = nextLine ? (nextLine.start - currentLine.end) : Infinity;
-            if (currentTime > currentLine.end + 0.5 && gapToNext > 3.0) return 0;
-
-            const linesToShow = [currentLine];
-            if (nextLine && gapToNext <= 3.0) linesToShow.push(nextLine);
-
-            const fontSize = Math.max(18, H * 0.028) | 0;
-            const lineY = H * 0.04;
-            const sylText = s => { const t = s.w || ''; return (t.endsWith('+') || t.endsWith('-')) ? t.slice(0, -1) : t; };
-
-            ctx.font = `bold ${fontSize}px sans-serif`;
-            let rows, spaceWidth, bgWidth;
-            const _lc = _lyrRowsCache;
-            if (_lc && _lc.lyricsRef === lyrics && _lc.idx === currentIdx
-                && _lc.shown === linesToShow.length
-                && _lc.fontSize === fontSize && _lc.W === W) {
-                rows = _lc.rows; spaceWidth = _lc.spaceWidth; bgWidth = _lc.bgWidth;
-            } else {
-                spaceWidth = ctx.measureText(' ').width;
-                const maxWidth = W * 0.8;
-
-                rows = [];
-                for (const authoredLine of linesToShow) {
-                    let row = [], rowWidth = 0;
-                    for (const wordSyls of authoredLine.words) {
-                        const parts = [];
-                        let wordWidth = 0;
-                        for (const s of wordSyls) {
-                            const text = sylText(s);
-                            const w = ctx.measureText(text).width;
-                            parts.push({ syl: s, text, width: w });
-                            wordWidth += w;
-                        }
-                        const advance = wordWidth + spaceWidth;
-                        if (row.length > 0 && rowWidth + advance > maxWidth) { rows.push(row); row = []; rowWidth = 0; }
-                        row.push({ parts, advance });
-                        rowWidth += advance;
-                    }
-                    if (row.length) rows.push(row);
-                }
-
-                bgWidth = 0;
-                for (const row of rows) {
-                    const rw = row.reduce((s, w) => s + w.advance, 0) - spaceWidth;
-                    if (rw > bgWidth) bgWidth = rw;
-                }
-                bgWidth = Math.min(bgWidth + 30, W * 0.85);
-                _lyrRowsCache = {
-                    lyricsRef: lyrics, idx: currentIdx,
-                    shown: linesToShow.length, fontSize, W,
-                    rows, spaceWidth, bgWidth,
-                };
-            }
-
-            const rowHeight = fontSize + 6;
-            const totalHeight = rows.length * rowHeight + 10;
-
-            ctx.fillStyle = 'rgba(0,0,0,0.7)';
-            ctx.beginPath();
-            const bx = W / 2 - bgWidth / 2, by = lineY - 4, br = 8;
-            ctx.moveTo(bx + br, by); ctx.lineTo(bx + bgWidth - br, by);
-            ctx.quadraticCurveTo(bx + bgWidth, by, bx + bgWidth, by + br);
-            ctx.lineTo(bx + bgWidth, by + totalHeight - br);
-            ctx.quadraticCurveTo(bx + bgWidth, by + totalHeight, bx + bgWidth - br, by + totalHeight);
-            ctx.lineTo(bx + br, by + totalHeight);
-            ctx.quadraticCurveTo(bx, by + totalHeight, bx, by + totalHeight - br);
-            ctx.lineTo(bx, by + br);
-            ctx.quadraticCurveTo(bx, by, bx + br, by);
-            ctx.closePath();
-            ctx.fill();
-
-            ctx.textAlign = 'left';
-            ctx.textBaseline = 'top';
-            for (let r = 0; r < rows.length; r++) {
-                const row = rows[r];
-                const rowWidth = row.reduce((s, w) => s + w.advance, 0) - spaceWidth;
-                let xPos = W / 2 - rowWidth / 2;
-                const yPos = lineY + r * rowHeight + 2;
-                for (const w of row) {
-                    for (const part of w.parts) {
-                        const l = part.syl;
-                        const isActive = currentTime >= l.t && currentTime < l.t + l.d;
-                        const isPast = currentTime >= l.t + l.d;
-                        ctx.fillStyle = isActive ? '#4ae0ff' : isPast ? '#8899aa' : '#556677';
-                        ctx.font = `${isActive ? 'bold' : 'normal'} ${fontSize}px sans-serif`;
-                        ctx.fillText(part.text, xPos, yPos);
-                        xPos += part.width;
-                    }
-                    xPos += spaceWidth;
-                }
-            }
-            // Return the actual bottom Y of the rendered background box so callers
-            // (e.g. drawChordDiagram) can avoid overlapping it.
-            return Math.round(by + totalHeight);
-        }
-
-        /* ── Scene initialisation ─────────────────────────────────────────── */
-        function initScene() {
-            if (!highwayCanvas || !highwayCanvas.parentNode) {
-                console.error('[3D-Hwy] initScene: canvas has no parent; aborting');
-                return false;
-            }
-
-            // Reset per-song lane state
-            fretLastActiveTime.fill(0);
-
-            wrap = document.createElement('div');
-            wrap.id = 'h3d-wrap-' + _instanceId;
-            wrap.className = 'h3d-wrap';
-            wrap.dataset.h3dInstance = String(_instanceId);
-            wrap.style.cssText = 'position:absolute;top:0;left:0;right:0;z-index:2;pointer-events:none;';
-            // Mark this instance as the primary tour target so the tour engine
-            // always spotlights a unique element (selector '.h3d-wrap[data-h3d-primary]')
-            // rather than the first of potentially many splitscreen wraps.
-            document.querySelectorAll('.h3d-wrap[data-h3d-primary]').forEach(
-                el => el.removeAttribute('data-h3d-primary'));
-            wrap.setAttribute('data-h3d-primary', '');
-            highwayCanvas.parentNode.insertBefore(wrap, highwayCanvas.nextSibling);
-
-            // Subscribe to highway:visibility (feedBack#246) so the
-            // .h3d-wrap overlay hides in sync with the feedBack canvas.
-            // The wrap is a sibling of #highway, so display:none on
-            // #highway leaves us painting full-screen otherwise.
-            // Guarded lazy bind: tolerate hosts that don't yet expose
-            // feedBack.on/off (older feedBack versions, headless
-            // tests).
-            if (window.feedBack
-                && typeof window.feedBack.on === 'function'
-                && typeof window.feedBack.off === 'function') {
-                _visibilityHandler = (e) => {
-                    if (!wrap) return;
-                    // Filter by canvas identity (splitscreen-safe).
-                    // Each createHighway() instance emits its own
-                    // visibility events on the shared feedBack bus —
-                    // without this gate, one hidden panel would also
-                    // hide every other panel's 3D overlay.
-                    if (!e || !e.detail || e.detail.canvas !== highwayCanvas) return;
-                    const v = e.detail.visible;
-                    wrap.style.display = v === false ? 'none' : '';
-                };
-                try {
-                    window.feedBack.on('highway:visibility', _visibilityHandler);
-                } catch (e) {
-                    _visibilityHandler = null;
-                }
-                // Track canvas-replaced so the visibility handler's
-                // identity gate continues to match after core swaps the
-                // <canvas> element for a context-type change.
-                _canvasReplacedHandler = (e) => {
-                    if (!e || !e.detail) return;
-                    // Only update if the swap involves OUR canvas — in
-                    // splitscreen each panel has its own canvas.
-                    if (e.detail.oldCanvas !== highwayCanvas) return;
-                    highwayCanvas = e.detail.newCanvas;
-                    // Re-sync wrap visibility from the new canvas in
-                    // case its initial displayed-state differs.
-                    if (wrap) {
-                        const v = highwayCanvas && highwayCanvas.offsetParent !== null;
-                        wrap.style.display = v ? '' : 'none';
-                    }
-                };
-                try {
-                    window.feedBack.on('highway:canvas-replaced', _canvasReplacedHandler);
-                } catch (e) {
-                    _canvasReplacedHandler = null;
-                }
-                // Sync once at bind time: the event is transition-only,
-                // so if the canvas was already hidden when we mounted
-                // (e.g. plugin loaded while splitscreen was active),
-                // we'd never receive an emit and would leave the wrap
-                // visible. Compute from the local highwayCanvas (not
-                // window.highway.isVisible) so splitscreen panels get
-                // their own per-instance answer instead of inheriting
-                // the main highway's state.
-                if (_visibilityHandler) {
-                    try {
-                        const initialVisible = highwayCanvas
-                            && highwayCanvas.offsetParent !== null;
-                        wrap.style.display = initialVisible ? '' : 'none';
-                    } catch (e) { /* ignore — initial sync is best-effort */ }
-                }
-            }
-
-            // powerPreference hints the platform to use the discrete /
-            // high-performance GPU and a higher power profile for this WebGL
-            // context. On laptops / iGPU+dGPU machines (Windows, macOS) it
-            // steers GPU selection to the dGPU; on single-dGPU desktops it
-            // requests the high-performance power profile. (It does not by
-            // itself force NVIDIA's utilisation-driven clock ramp on Linux.)
-            ren = new T.WebGLRenderer({ antialias: true, powerPreference: 'high-performance', alpha: true });
-            _probe = new T.Vector3();
-            ren.setClearColor(0x101820, _bcActive() ? 0 : 1);
-            wrap.appendChild(ren.domElement);
-
-            // WebGL context-loss recovery (see the _ctxLost declaration). Bound
-            // on Three's own canvas — the context that actually resets on a GPU
-            // reset / alt-tab. preventDefault() keeps the context restorable
-            // instead of letting the loss escalate to a render-process crash;
-            // _ctxLost then makes draw() bail so no GL work runs on the dead
-            // context; on restore we reset the viewport and resume (Three
-            // re-uploads geometry/materials/textures lazily on the next render).
-            _onCtxLost = (e) => {
-                if (e && typeof e.preventDefault === 'function') e.preventDefault();
-                _ctxLost = true;
-                console.warn('[3D-Hwy] WebGL context lost — pausing render until it is restored.');
-            };
-            _onCtxRestored = () => {
-                _ctxLost = false;
-                console.warn('[3D-Hwy] WebGL context restored — resuming render.');
-                try { const s = canvasSize(highwayCanvas); if (s.w > 0 && s.h > 0) applySize(s.w, s.h); } catch (err) {}
-            };
-            ren.domElement.addEventListener('webglcontextlost', _onCtxLost, false);
-            ren.domElement.addEventListener('webglcontextrestored', _onCtxRestored, false);
-
-            lyricsCanvas = document.createElement('canvas');
-            lyricsCanvas.style.cssText = 'position:absolute;top:0;left:0;pointer-events:none;z-index:1;';
-            lyricsCtx = lyricsCanvas.getContext('2d');
-            wrap.appendChild(lyricsCanvas);
-
-            scene = new T.Scene();
-            scene.fog = new T.Fog(0x101820, FOG_START * 0.8, FOG_END * 1.2);
-
-            cam = new T.PerspectiveCamera(BASE_VFOV, 1, 0.01, FOG_END * 3);
-
-            ambLight = new T.AmbientLight(0xffffff, 0.85);
-            scene.add(ambLight);
-            dirLight = new T.DirectionalLight(0xffffff, 0.8);
-            dirLight.position.set(40 * K, 120 * K, 80 * K);
-            scene.add(dirLight);
-            _applyCinematic();
-
-            fretG = new T.Group(); scene.add(fretG);
-            tuningLblG = new T.Group(); scene.add(tuningLblG);
-            noteG = new T.Group(); scene.add(noteG);
-            // Hit sparks (#3): a pooled additive Points cloud; a small burst fires at a
-            // gem on a verified hit (spawned in the verdict block, advanced in the render loop).
-            _sparkPos = new Float32Array(_SPARK_N * 3); _sparkCol = new Float32Array(_SPARK_N * 3);
-            _sparkVel = new Float32Array(_SPARK_N * 3); _sparkLife = new Float32Array(_SPARK_N);
-            {
-                const sg = new T.BufferGeometry();
-                sg.setAttribute('position', new T.BufferAttribute(_sparkPos, 3).setUsage(T.DynamicDrawUsage));
-                sg.setAttribute('color', new T.BufferAttribute(_sparkCol, 3).setUsage(T.DynamicDrawUsage));
-                const sm = new T.PointsMaterial({ size: 1.0 * K, vertexColors: true, transparent: true, opacity: 0.8, depthWrite: false, blending: T.AdditiveBlending, sizeAttenuation: true });
-                _sparkPts = new T.Points(sg, sm); _sparkPts.frustumCulled = false; _sparkPts.renderOrder = 8;
-                scene.add(_sparkPts);
-            }
-            beatG = new T.Group(); scene.add(beatG);
-            lblG = new T.Group(); scene.add(lblG);
-
-            // Rectangular note geometry
-            gNote = new T.BoxGeometry(NW, NH, ND);
-            // Per-string vertical gradient gems — colours sampled from the
-            // original colour PNGs (top highlight → deeper bottom). Each gradient
-            // string gets its own BoxGeometry clone carrying a per-vertex colour
-            // attribute; the gem core swaps to gNoteGrad[s] in drawNote while its
-            // material (mStr[s]) is white + vertexColors:true so the gradient
-            // shows pure. Strings 6/7 have no entry and fall back to flat gNote.
-            gNoteGrad = DEFAULT_GEM_GRADIENTS.map(([topHex, botHex]) => {
-                const g = new T.BoxGeometry(NW, NH, ND);
-                const _pos = g.attributes.position;
-                const _colors = new Float32Array(_pos.count * 3);
-                const _topCol = new T.Color(topHex);
-                const _botCol = new T.Color(botHex);
-                const _tmpCol = new T.Color();
-                const _halfH = NH / 2;
-                for (let i = 0; i < _pos.count; i++) {
-                    const t = (_pos.getY(i) + _halfH) / (2 * _halfH); // 0 bottom..1 top
-                    _tmpCol.copy(_botCol).lerp(_topCol, t);
-                    _colors[i * 3] = _tmpCol.r;
-                    _colors[i * 3 + 1] = _tmpCol.g;
-                    _colors[i * 3 + 2] = _tmpCol.b;
-                }
-                g.setAttribute('color', new T.BufferAttribute(_colors, 3));
-                _ownedSharedGeos.push(g);
-                return g;
-            });
-            // Seed gem colors from whatever palette is active at mount (custom
-            // colors recolor the gem bodies just like the strings/trails).
-            _recolorGemGradients();
-
-            /** Filled ring matching flying-note outline (1.1) minus core (1.0); hollow centre. */
-            function mkGhostFrameGeometry() {
-                const ow = NW * 1.1;
-                const oh = NH * 1.1;
-                const iw = NW;
-                const ih = NH;
-                const depth = ND * 2.8;
-                const shape = new T.Shape();
-                shape.moveTo(-ow / 2, -oh / 2);
-                shape.lineTo(-ow / 2, oh / 2);
-                shape.lineTo(ow / 2, oh / 2);
-                shape.lineTo(ow / 2, -oh / 2);
-                shape.lineTo(-ow / 2, -oh / 2);
-                const hole = new T.Path();
-                hole.moveTo(-iw / 2, -ih / 2);
-                hole.lineTo(iw / 2, -ih / 2);
-                hole.lineTo(iw / 2, ih / 2);
-                hole.lineTo(-iw / 2, ih / 2);
-                hole.lineTo(-iw / 2, -ih / 2);
-                shape.holes.push(hole);
-                const g = new T.ExtrudeGeometry(shape, { depth, bevelEnabled: false });
-                g.translate(0, 0, -depth / 2);
-                return g;
-            }
-
-            gSus = new T.BoxGeometry(1, 1, 1);
-            gBeat = new T.BufferGeometry().setFromPoints(
-                [new T.Vector3(0, 0, 0), new T.Vector3(1, 0, 0)],
-            );
-            // Tap chevron (open V pointing downward) — filled outline for extrusion into a solid mesh
-
-            const chevronShape = new T.Shape();
-
-            // Adjusting points for a "stubby" look
-            // Width: increased to +/- 0.8 for a broader look
-            // Height: capped at 0.2 to make it significantly shorter
-            chevronShape.moveTo(-0.6, 0.3);   // Top left point (further out, lower down)
-            chevronShape.lineTo(0, -0.1);     // Interior vertex (shallower V)
-            chevronShape.lineTo(0.6, 0.3);    // Top right point (further out, lower down)
-
-            chevronShape.lineTo(0.8, 0.0);    // Right outer thickness point
-            chevronShape.lineTo(0, -0.3);     // Bottom vertex / Outer point (less deep)
-            chevronShape.lineTo(-0.8, 0.0);   // Left outer thickness point
-
-            chevronShape.closePath();
-
-            // Create the 3D mesh geometry with a small depth
-            gTapChevron = new T.ExtrudeGeometry(chevronShape, {
-                depth: 0.04 * K,
-                bevelEnabled: false,
-            });
-
-            // Optional: Center the geometry if the pivot point feels off
-            gTapChevron.computeBoundingBox();
-            const centerOffset = -0.5 * (gTapChevron.boundingBox.max.y + gTapChevron.boundingBox.min.y);
-            gTapChevron.translate(0, centerOffset, 0);
-
-            // String materials. Strings 0..5 use a per-vertex gradient (color is
-            // white so the gradient baked into gNoteGrad[s] shows pure); strings
-            // 6/7 keep a flat colour (vertexColors:false ignores the attribute).
-            mStr = activePalette.map((c, i) => new T.MeshBasicMaterial({
-                color: i < 6 ? 0xffffff : c,
-                vertexColors: i < 6,
-                transparent: true, opacity: 1.0,
-            }));
-            mGlow = activePalette.map(c => new T.MeshLambertMaterial({
-                color: 0xffffff, emissive: c, emissiveIntensity: 1.5,
-                transparent: true, opacity: 1.0, depthWrite: false,
-            }));
-            _laneTargetColor = new T.Color(0x4488ff);
-            _fwHitColor = new T.Color(FRET_WIRE_HIT_HEX);
-            _fwHitEmissive = new T.Color(FRET_WIRE_HIT_EMISSIVE);
-            _fwHitGlow.fill(0);
-            _fwHitPrevTime = -Infinity;
-            mSus = activePalette.map(c => new T.MeshLambertMaterial({
-                color: c, transparent: true, opacity: 0.35,
-            }));
-            mWhiteOutline = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.6, transparent: true, opacity: 1.0, depthWrite: false });
-            const _outlineColors = [0xFF5552, 0xFFF352, 0x31CAFF, 0xFFAE31, 0x84FF42, 0xE639FF];
-            const _outlinePalette = activePalette.map((c, i) => _outlineColors[i] ?? c);
-            mStrHitOutline = _outlinePalette.map(c => new T.MeshLambertMaterial({
-                color: c, emissive: c, emissiveIntensity: 1.0,
-                transparent: true, opacity: 1.0, depthWrite: false,
-            }));
-            // Stronger coloured rim + body for accented notes (.ac); drawNote swaps these in behind ND hit/miss.
-            mAccentOutline = activePalette.map(c => new T.MeshLambertMaterial({
-                color: c, emissive: c, emissiveIntensity: ACCENT_RIM_BASE_EMISSIVE,
-                transparent: true, opacity: 1.0, depthWrite: false,
-            }));
-            // Same colour response as mGlow (vibrancy lerp) but separate emissive drive for extra accent punch.
-            mAccentCore = activePalette.map(c => new T.MeshLambertMaterial({
-                color: 0xffffff, emissive: c, emissiveIntensity: 1.5,
-                transparent: true, opacity: 1.0, depthWrite: false,
-            }));
-            const mkAccentHaloMats = (baseOp) => activePalette.map(c => new T.MeshBasicMaterial({
-                color: new T.Color(c),
-                transparent: true,
-                opacity: baseOp,
-                depthWrite: false,
-                depthTest: true,
-                blending: T.AdditiveBlending,
-                side: T.DoubleSide, forceSinglePass: true,
-                fog: true,
-            }));
-            mAccentHaloNear = mkAccentHaloMats(ACCENT_HALO_OP_NEAR);
-            mAccentHaloMid = mkAccentHaloMats(ACCENT_HALO_OP_MID);
-            mAccentHaloFar = mkAccentHaloMats(ACCENT_HALO_OP_FAR);
-            // Frozen per-string shell descriptors — see _accentShellsByString
-            // declaration. Materials live for the renderer's lifetime, so
-            // these refs stay valid until teardown() clears them.
-            _accentShellsByString = mAccentHaloFar.map((_, s) => Object.freeze([
-                Object.freeze({ mat: mAccentHaloFar[s],  ixy: ACCENT_HALO_XY_OUTER, iz: ACCENT_HALO_Z_OUTER, zK: 0.012 }),
-                Object.freeze({ mat: mAccentHaloMid[s],  ixy: ACCENT_HALO_XY_MID,   iz: ACCENT_HALO_Z_MID,   zK: 0.008 }),
-                Object.freeze({ mat: mAccentHaloNear[s], ixy: ACCENT_HALO_XY_INNER, iz: ACCENT_HALO_Z_INNER, zK: 0.005 }),
-            ]));
-            // Chord/arpeggio frame accent bloom — single gradient bar geometry.
-            // The 4 bloom shells (expand=1.00/1.10/1.25/1.45, op=0.90/0.65/0.38/0.18)
-            // are baked into vertex colours as their additive sum at each Y level,
-            // so one mesh per bar replaces 4 per-shell meshes (16→4 draw calls/chord).
-            // Normalised Y = ±(expand / EXPAND_MAX); EXPAND_MAX = 1.45.
-            // Values > 1.0 in the Float32Array buffer are intentional: WebGL passes
-            // them to the shader unchanged, and additive blending clips naturally.
-            if (!gHaloBar) {
-                // Y levels (normalised): ±(shell_expand / 1.45)
-                //   ±0.690 = shell 1 edge  ±0.759 = shell 2  ±0.862 = shell 3  ±1.0 = shell 4
-                // Brightness = additive sum of all shells covering that band:
-                //   |y| < 0.690 → all 4: 0.90+0.65+0.38+0.18 = 2.11
-                //   |y| < 0.759 → 3 shells: 0.65+0.38+0.18 = 1.21
-                //   |y| < 0.862 → 2 shells: 0.38+0.18 = 0.56
-                //   |y| ≤ 1.000 → shell 4 only: 0.18
-                // prettier-ignore
-                const YS = [-1.000, -0.862, -0.759, -0.690,  0.690, 0.759, 0.862, 1.000];
-                // prettier-ignore
-                const BS = [ 0.18,   0.56,   1.21,   2.11,   2.11,  1.21,  0.56,  0.18 ];
-                const N = YS.length;
-                const pos = new Float32Array(N * 2 * 3);
-                const col = new Float32Array(N * 2 * 3);
-                const idx = new Uint16Array((N - 1) * 6);
-                for (let i = 0; i < N; i++) {
-                    const y = YS[i], b = BS[i];
-                    const li = (i * 2 + 0) * 3, ri = (i * 2 + 1) * 3;
-                    pos[li]=-1; pos[li+1]=y; pos[li+2]=0;
-                    col[li]=b;  col[li+1]=b; col[li+2]=b;
-                    pos[ri]=+1; pos[ri+1]=y; pos[ri+2]=0;
-                    col[ri]=b;  col[ri+1]=b; col[ri+2]=b;
-                }
-                for (let i = 0; i < N - 1; i++) {
-                    const ii = i * 6, v = i * 2;
-                    idx[ii+0]=v+0; idx[ii+1]=v+1; idx[ii+2]=v+3;
-                    idx[ii+3]=v+0; idx[ii+4]=v+3; idx[ii+5]=v+2;
-                }
-                gHaloBar = new T.BufferGeometry();
-                gHaloBar.setAttribute('position', new T.BufferAttribute(pos, 3));
-                gHaloBar.setAttribute('color',    new T.BufferAttribute(col, 3));
-                gHaloBar.setIndex(new T.BufferAttribute(idx, 1));
-            }
-            pHaloBar = pool(noteG, () => new T.Mesh(
-                gHaloBar,
-                new T.MeshBasicMaterial({
-                    vertexColors: true,
-                    transparent: true, opacity: 1.0, depthWrite: false,
-                    blending: T.AdditiveBlending, side: T.DoubleSide, forceSinglePass: true, fog: false,
-                }),
-            ));
-            // Notedetect feedback outline (issue #9): hot magenta-red (0xff0066, hue
-            // ~345°) — distinct from the string red 0xff2828 at hue ~0°. Note rendering
-            // swaps its outline.material between mWhiteOutline / per-string
-            // mHitBright[s] / mMissOutline based on recent notedetect events.
-            mMissOutline = new T.MeshLambertMaterial({ color: 0xff0066, emissive: 0xff0066, emissiveIntensity: 1.2, transparent: true, opacity: 1.0, depthWrite: false });
-            // Transparent placeholder for front (+Z, group 4) and back (-Z, group 5)
-            // of the lateral face-fill material array. Also the default material for
-            // the pNoteEdge pool: pool consumers reassign .material before render, so
-            // the placeholder is never displayed — using an explicitly-invisible
-            // material makes that intent obvious.
-            // BoxGeometry group order: 0=+X, 1=-X, 2=+Y, 3=-Y, 4=+Z(front), 5=-Z(back)
-            mEdgeTransparent = new T.MeshBasicMaterial({ transparent: true, opacity: 0, depthWrite: false });
-            // mMissEdgeArrays: use mMissOutline (same Lambert+emissive material as the gem
-            // border) so the lateral face fill matches the outline colour exactly.
-            mMissEdgeArrays = [mMissOutline, mMissOutline, mMissOutline, mMissOutline, mEdgeTransparent, mEdgeTransparent];
-
-            // Hit: fixed neon spring-green on every string — 0x22ff88 is cyan-shifted
-            // enough to be readable even on the green string (0x30d040). The outline
-            // + lateral faces flash green regardless of which string was hit.
-            mHitBright = activePalette.map(() => new T.MeshLambertMaterial({
-                color: 0x22ff88, emissive: 0x22ff88, emissiveIntensity: 4.0 * glowMul,
-                transparent: true, opacity: 1.0, depthWrite: false,
-            }));
-            mHitBrightArrays = mHitBright.map(m => [m, m, m, m, mEdgeTransparent, mEdgeTransparent]);
-            // Readability (#2 / charrette): the note gems + their outlines punch THROUGH
-            // the distance fog so upcoming notes stay legible as they render in at the
-            // horizon. The board, lane, sustains and background scenery keep their
-            // atmospheric fog — only the note-defining materials are exempted, so the
-            // highway still reads as deep while the notes never dissolve into the haze.
-            [mWhiteOutline, mMissOutline].forEach(m => { if (m) m.fog = false; });
-            [mStr, mGlow, mStrHitOutline, mHitBright].forEach(arr => arr && arr.forEach(m => { if (m) m.fog = false; }));
-            // Outline materials render at a lower renderOrder than the body.
-            // The body is rendered on top with opacity:1 on hit/miss, which
-            // fully covers the outline center — only the fringe that extends
-            // past the body edges (0.2*K on each side) is visible.
-            mSusOutline     = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.3, transparent: true, opacity: 0.75, depthWrite: false });
-            mHitSusOutline  = new T.MeshLambertMaterial({ color: 0x22ff88, emissive: 0x22ff88, emissiveIntensity: 0.8, transparent: true, opacity: 0.45, depthWrite: false });
-            mBeatM = new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.25 });
-            mBeatQ = new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.07 });
-
-            // ── Board ghost: filled rim (ExtrudeGeometry w/ hole) in string colour ──
-            // Matches outline 1.1× vs core 1.0× like drawNote; centre stays empty.
-            // 3 slots per string (up to 3 simultaneous ghost previews, chart-
-            // format style): slot 0 is the "next on string" / chord / arp ghost
-            // (unchanged selection logic), slots 1/2 are independent
-            // "upcoming" lead-note previews. All slots share one geometry —
-            // it's identical (NW/NH/ND-based) regardless of string or slot,
-            // so one ExtrudeGeometry serves all nStr*3 meshes.
-            const _ghostFrameGeo = mkGhostFrameGeometry();
-            projMeshArr = activePalette.map((_, s) => [0, 1, 2].map(() => {
-                const mat = new T.MeshStandardMaterial({
-                    color: activePalette[s],
-                    emissive: activePalette[s],
-                    emissiveIntensity: 0.002,
-                    transparent: true,
-                    opacity: 0.65,
-                    roughness: 1,
-                    depthWrite: false,
-                    depthTest: false,
-                });
-                const m = new T.Mesh(_ghostFrameGeo, mat);
-                m.visible = false;
-                // Board projection ghost frame. depthTest:false above, so
-                // renderOrder alone decides stacking — keep it above the
-                // sus trails (12/13) but below note gems (20/21) so it
-                // stays visible on the fretboard without covering notes.
-                m.renderOrder = 14;
-                noteG.add(m);
-                return m;
-            }));
-
-            // ── Pools ──────────────────────────────────────────────────────
-            pNote = pool(noteG, () => new T.Mesh(gNote, mStr[0]));
-            // Pool default is the always-invisible mEdgeTransparent — every
-            // consumer reassigns .material before render (to a verdict edge
-            // material array), so the placeholder is never displayed.
-            pNoteEdge = pool(noteG, () => new T.Mesh(gNote, mEdgeTransparent));
-            pAccentHalo = pool(noteG, () => new T.Mesh(gNote, mAccentHaloFar[0]));
-            pSus = pool(noteG, () => new T.Mesh(gSus, mSus[0]));
-            pSusOutline = pool(noteG, () => new T.Mesh(gSus, mSusOutline));
-            const mkSlideRibbonGeo = () => {
-                const nVert = 4 * (SLIDE_RIBBON_SAMPLES + 1);
-                const g = new T.BufferGeometry();
-                g.setAttribute('position', new T.Float32BufferAttribute(new Float32Array(nVert * 3), 3));
-                // SLIDE_RIBBON_INDICES_ARR is the plain-Array form (see module-init
-                // comment) shared across pool meshes; setIndex() rewraps it into a
-                // fresh Uint16BufferAttribute per geometry, so the share is safe.
-                g.setIndex(SLIDE_RIBBON_INDICES_ARR);
-                // Static cross-section normals: each ring is an axis-aligned quad,
-                // so vertex normals point radially in the XY plane regardless of
-                // the slide's Z-direction curvature. Pre-fill once and skip the
-                // per-frame computeVertexNormals() pass that previously ran on
-                // every sustained-slide update (Copilot perf finding on PR #215).
-                const SQRT_HALF = Math.SQRT1_2;
-                const normals = new Float32Array(nVert * 3);
-                for (let k = 0; k <= SLIDE_RIBBON_SAMPLES; k++) {
-                    const o = k * 12;
-                    // v0 (-X,-Y), v1 (+X,-Y), v2 (+X,+Y), v3 (-X,+Y)
-                    normals[o]     = -SQRT_HALF; normals[o + 1]  = -SQRT_HALF; normals[o + 2]  = 0;
-                    normals[o + 3] =  SQRT_HALF; normals[o + 4]  = -SQRT_HALF; normals[o + 5]  = 0;
-                    normals[o + 6] =  SQRT_HALF; normals[o + 7]  =  SQRT_HALF; normals[o + 8]  = 0;
-                    normals[o + 9] = -SQRT_HALF; normals[o + 10] =  SQRT_HALF; normals[o + 11] = 0;
-                }
-                g.setAttribute('normal', new T.Float32BufferAttribute(normals, 3));
-                return g;
-            };
-            // Ribbon meshes mutate vertex positions every frame in
-            // slideRibbonUpdatePositions but the mesh itself stays at (0,0,0)
-            // and the geometry's bounding sphere is never recomputed. With
-            // frustum culling on, Three.js tests the (0,0,0)-centred bounds
-            // and culls the ribbon as soon as the camera pans away from world
-            // origin, so slides flicker in/out. Disable culling on these
-            // meshes — the ribbon footprint is small and they're already
-            // gated by t0/t1 reachability before render.
-            pSusRibbon = pool(noteG, () => {
-                const m = new T.Mesh(mkSlideRibbonGeo(), mSus[0]);
-                m.frustumCulled = false;
-                return m;
-            });
-            pSusRibbonOl = pool(noteG, () => {
-                const m = new T.Mesh(mkSlideRibbonGeo(), mSusOutline);
-                m.frustumCulled = false;
-                m.renderOrder = -3;
-                return m;
-            });
-            // One shared material per technique-mesh type. The pool factory
-            // hands out fresh meshes that all reference the same material,
-            // so a dense HO/PO passage doesn't churn N MeshLambertMaterial
-            // allocations and N GPU material switches.
-            // Transparent + no depth write/test so the tap chevron draws in
-            // the transparent pass where drawNote assigns renderOrder 1000.
-            mTapChevron = new T.MeshLambertMaterial({
-                color: 0xd4d4d4,
-                emissive: 0xd4d4d4,
-                emissiveIntensity: 0.9,
-                transparent: true,
-                opacity: 0.85,
-                side: T.DoubleSide, forceSinglePass: true,
-                depthWrite: false,
-                depthTest: false,
-            });
-            pTapChevron = pool(noteG, () => new T.Mesh(gTapChevron, mTapChevron));
-            pLbl  = pool(lblG,  () => new T.Sprite(txtMat('0', '#fff', false, 'technique')));
-            pBeat = pool(beatG, () => new T.Line(gBeat, mBeatQ));
-            pSec  = pool(lblG,  () => new T.Sprite(txtMat('', '#0dd', true, 'section')));
-
-            // Chord sustain length indicator — thin horizontal plane rails.
-            // Unit plane (1×1 in XZ) laid flat; scaled to (railWidth, 1, railLen).
-            // A horizontal plane seen from the camera looking down-forward is
-            // face-on and has real apparent thickness — unlike T.Line (always 1px).
-            // depthTest:false so they never occlude gems; renderOrder 11 places
-            // them above lane dividers (2) and chord fill (10), at the same level
-            // as chord frame edges (11), and BELOW sustain trails (12/13), note
-            // gems (dynamic ≥50), and arp brackets (18). The bloom halo (10) sits
-            // behind the core rail (11). Keeping susrail behind note sus trails
-            // prevents the rail border from covering individual note tails
-            // (sustain/vibrato/tremolo/bend). (Was 14/16 which rendered on top of
-            // 12/13 sus trails, causing the outer border to overlap tails.)
-            gSusRail = new T.PlaneGeometry(1, 1);
-            gSusRail.rotateX(-Math.PI / 2); // lay flat in XZ plane
-            mSusRailBase = new T.MeshBasicMaterial({
-                color: CHORD_BOX_TEAL_HEX,
-                transparent: true, opacity: 0.85,
-                depthTest: false, depthWrite: false,
-                fog: false, side: T.DoubleSide, forceSinglePass: true,
-            });
-            pSusRail = pool(noteG, () => {
-                const m = new T.Mesh(gSusRail, mSusRailBase.clone());
-                m.renderOrder = 5; // below strings (7) so strings render on top
-                return m;
-            });
-
-            // Bloom glow for chord sustain rails — wider plane with a gaussian
-            // falloff texture (bright centre → transparent edges in X direction)
-            // and additive blending, so it brightens whatever is behind it.
-            // renderOrder 4 places it behind the core rail (5).
-            _bloomGaussTex = _makeGaussTex(T);
-            gSusRailBloom = new T.PlaneGeometry(1, 1);
-            gSusRailBloom.rotateX(-Math.PI / 2);
-            mSusRailBloomBase = new T.MeshBasicMaterial({
-                color: CHORD_BOX_TEAL_HEX,
-                map: _bloomGaussTex,
-                transparent: true, opacity: 0.55,
-                blending: T.AdditiveBlending,
-                depthTest: false, depthWrite: false,
-                fog: false, side: T.DoubleSide, forceSinglePass: true,
-            });
-            pSusRailBloom = pool(noteG, () => {
-                const m = new T.Mesh(gSusRailBloom, mSusRailBloomBase.clone());
-                m.renderOrder = 4; // below strings (7) so strings render on top
-                return m;
-            });
-
-            // Rotatable plane pool for technique markers (pm, mt, hm, hp, H/P, bend).
-            // Unlike T.Sprite, a PlaneGeometry mesh accepts rotation.z = approachRot
-            // so markers stay coplanar with the gem as it tilts from vertical to flat.
-            gTechPlane = new T.PlaneGeometry(1, 1);
-            pTechPlane = pool(noteG, () => {
-                const m = new T.Mesh(gTechPlane, new T.MeshBasicMaterial({
-                    transparent: true, depthTest: false, depthWrite: false, side: T.DoubleSide, forceSinglePass: true,
-                }));
-                m.renderOrder = 1000;
-                return m;
-            });
-
-            // ── InstancedMesh temporaries ──────────────────────────────────────
-            _imM4    = new T.Matrix4();
-            _imPos   = new T.Vector3();
-            _imSca   = new T.Vector3();
-            _imQ     = new T.Quaternion();
-            _imAZ    = new T.Vector3(0, 0, 1);
-            _imColor = new T.Color();
-
-            // ── Shared ShaderMaterial templates ───────────────────────────────
-            // Vertex shader used by PM-X and FH-X on individual note gems.
-            // Three.js injects `USE_INSTANCING` + `instanceMatrix` attribute
-            // into the prefix when an InstancedMesh uses a ShaderMaterial.
-            const _imTechVert = [
-                'attribute float instanceAlpha;',
-                'varying float vAlpha;',
-                'varying vec2 vUv;',
-                'void main() {',
-                '    vUv = uv;',
-                '    vAlpha = instanceAlpha;',
-                '    vec4 pos = vec4(position, 1.0);',
-                '    #ifdef USE_INSTANCING',
-                '    pos = instanceMatrix * pos;',
-                '    #endif',
-                '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
-                '}',
-            ].join('\n');
-            const _imTechFrag = [
-                'uniform sampler2D map;',
-                'varying float vAlpha;',
-                'varying vec2 vUv;',
-                'void main() {',
-                '    vec4 t = texture2D(map, vUv);',
-                '    if (t.a * vAlpha < 0.01) discard;',
-                '    gl_FragColor = vec4(t.rgb, t.a * vAlpha);',
-                '}',
-            ].join('\n');
-
-            // ── PM / FH tech marker InstancedMeshes ───────────────────────────
-            // Each IM gets a geometry clone so instanceAlpha is a separate buffer.
-            const _mkTechIM = (spriteMat, alphaArr) => {
-                const geo = gTechPlane.clone();
-                const alphaAttr = new T.InstancedBufferAttribute(alphaArr, 1);
-                alphaAttr.setUsage(T.DynamicDrawUsage);
-                geo.setAttribute('instanceAlpha', alphaAttr);
-                const mat = new T.ShaderMaterial({
-                    uniforms: { map: { value: spriteMat.map } },
-                    vertexShader: _imTechVert,
-                    fragmentShader: _imTechFrag,
-                    transparent: true, depthTest: false, depthWrite: false, side: T.DoubleSide, forceSinglePass: true,
-                });
-                const im = new T.InstancedMesh(geo, mat, IM_TECH_CAP);
-                im.instanceMatrix.setUsage(T.DynamicDrawUsage);
-                im.frustumCulled = false;
-                im.count = 0;
-                noteG.add(im);
-                return { im, geo, mat };
-            };
-            { const r = _mkTechIM(palmMuteXSpriteMat(),    _imPMTechAlphaArr);
-              imPMTech = r.im; _imGPMTech = r.geo; _imPMTechMat = r.mat; imPMTech.renderOrder = 702; }
-            { const r = _mkTechIM(fretHandMuteXSpriteMat(), _imFHTechAlphaArr);
-              imFHTech = r.im; _imGFHTech = r.geo; _imFHTechMat = r.mat; imFHTech.renderOrder = 700; }
-
-            // Dynamic fret number labels (heat-coloured, updated each frame)
-            pFretLbl = pool(lblG, () => new T.Sprite(txtMat('0', '#888', false, 'fretRow')));
-
-            // Highlight lane plane over active fret range. With the anchor-driven
-            // segmented lanes we render up to fret-count × HWY_LANE_TIME_SLICES (96)
-            // pLane meshes per frame, so:
-            //   - geometry is a shared PlaneGeometry(1,1) (was per-mesh, never differed)
-            //   - 2 shared MeshBasicMaterials (odd / even stripe colour) replace the
-            //     per-mesh material clones; the per-frame opacity still travels via
-            //     the materials but is set once outside the inner loop, not per-mesh.
-            gLanePlane = new T.PlaneGeometry(1, 1);
-            mLaneOdd = new T.MeshBasicMaterial({
-                color: HWY_LANE_STRIPE_ODD_HEX, transparent: true, opacity: 0, depthWrite: false,
-            });
-            mLaneEven = new T.MeshBasicMaterial({
-                color: HWY_LANE_STRIPE_EVEN_HEX, transparent: true, opacity: 0, depthWrite: false,
-            });
-            // Tracked for explicit disposal in teardown — these materials may
-            // not be reachable via scene.traverse() if no lane was ever rendered.
-            _ownedSharedMats.push(mLaneOdd, mLaneEven);
-            _ownedSharedGeos.push(gLanePlane);
-            pLane = pool(noteG, () => new T.Mesh(gLanePlane, mLaneOdd));
-
-            gGhostFretPlane = new T.PlaneGeometry(1, 1);
-            _ownedSharedGeos.push(gGhostFretPlane);
-            const mGhostFretLblPh = new T.MeshBasicMaterial({
-                color: 0xffffff, transparent: true, depthTest: false, depthWrite: false,
-            });
-            _ownedSharedMats.push(mGhostFretLblPh);
-            pGhostFretLbl = pool(noteG, () => {
-                const m = new T.Mesh(gGhostFretPlane, mGhostFretLblPh);
-                // Must be above the proj frame (renderOrder=14) and opaque
-                // geometry — same contract as technique labels (renderOrder=1000):
-                // depthTest:false alone is insufficient, renderOrder=1000 needed.
-                m.renderOrder = 1000;
-                m.frustumCulled = false;
-                return m;
-            });
-
-            // Vertical fret dividers within active lane
-            const gLaneDivider = new T.BoxGeometry(0.15 * K, 0.15 * K, 1);
-            mLaneDivider = new T.MeshBasicMaterial({
-                color: 0x46DDE6, transparent: true, opacity: 1.00, fog: false, depthWrite: false,
-            });
-            mLaneDividerArp = new T.MeshBasicMaterial({
-                color: ARPEGGIO_RIM_BLUE_HEX,
-                transparent: true, opacity: 0.08, fog: false, depthWrite: false,
-            });
-            mLaneDividerExt = new T.MeshBasicMaterial({
-                color: 0x364D5F, transparent: true, opacity: 0.4, fog: false, depthWrite: false,
-            });
-            _ownedSharedMats.push(mLaneDivider, mLaneDividerArp, mLaneDividerExt);
-            pLaneDivider = pool(noteG, () => new T.Mesh(gLaneDivider, mLaneDivider));
-
-            // Chord frame palette (frame alpha 128, fill gradient alpha 32; MeshBasic).
-            const chR = CHORD_BOX_TEAL_HEX >> 16 & 255;
-            const chG = CHORD_BOX_TEAL_HEX >> 8 & 255;
-            const chB = CHORD_BOX_TEAL_HEX & 255;
-            const dkR = CHORD_BOX_TEAL_DARK_HEX >> 16 & 255;
-            const dkG = CHORD_BOX_TEAL_DARK_HEX >> 8 & 255;
-            const dkB = CHORD_BOX_TEAL_DARK_HEX & 255;
-            const aFill = Math.round(CHORD_BOX_FILL_GRAD_ALPHA * 255);
-            chordFrameGradTex = new T.DataTexture(
-                new Uint8Array([ chR, chG, chB, aFill, dkR, dkG, dkB, aFill, chR, chG, chB, aFill ]),
-                3, 1, T.RGBAFormat);
-            chordFrameGradTex.magFilter = T.LinearFilter;
-            chordFrameGradTex.minFilter = T.LinearFilter;
-            chordFrameGradTex.wrapS = T.ClampToEdgeWrapping;
-            chordFrameGradTex.wrapT = T.ClampToEdgeWrapping;
-            // DataTexture defaults to linear color space; flag this gradient
-            // as sRGB so the chord-box hex values match other sRGB color textures.
-            chordFrameGradTex.colorSpace = T.SRGBColorSpace;
-            chordFrameGradTex.needsUpdate = true;
-
-            const arR = ARPEGGIO_BOX_BLUE_HEX >> 16 & 255;
-            const arG = ARPEGGIO_BOX_BLUE_HEX >> 8 & 255;
-            const arB = ARPEGGIO_BOX_BLUE_HEX & 255;
-            const arDR = ARPEGGIO_BOX_BLUE_DARK_HEX >> 16 & 255;
-            const arDG = ARPEGGIO_BOX_BLUE_DARK_HEX >> 8 & 255;
-            const arDB = ARPEGGIO_BOX_BLUE_DARK_HEX & 255;
-            chordFrameGradTexArp = new T.DataTexture(
-                new Uint8Array([ arR, arG, arB, aFill, arDR, arDG, arDB, aFill, arR, arG, arB, aFill ]),
-                3, 1, T.RGBAFormat);
-            chordFrameGradTexArp.magFilter = T.LinearFilter;
-            chordFrameGradTexArp.minFilter = T.LinearFilter;
-            chordFrameGradTexArp.wrapS = T.ClampToEdgeWrapping;
-            chordFrameGradTexArp.wrapT = T.ClampToEdgeWrapping;
-            chordFrameGradTexArp.colorSpace = T.SRGBColorSpace;
-            chordFrameGradTexArp.needsUpdate = true;
-
-            pChordFrameFill = pool(noteG, () => new T.Mesh(
-                new T.PlaneGeometry(1, 1),
-                new T.MeshBasicMaterial({
-                    map: chordFrameGradTex,
-                    transparent: true,
-                    opacity: 1,
-                    depthWrite: false,
-                    depthTest: false,
-                    fog: false,
-                    side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-            pChordBox = pool(noteG, () => new T.Mesh(
-                new T.BoxGeometry(1, 1, 1),
-                new T.MeshBasicMaterial({
-                    color: CHORD_BOX_TEAL_HEX,
-                    transparent: true,
-                    opacity: CHORD_BOX_EDGE_ALPHA,
-                    depthWrite: false,
-                    depthTest: false,
-                    fog: false,
-                    side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-
-            // PM strum X fill — 4 corner regions + centre; the 4 arms (L,R,T,B) are left empty.
-            // 16 vertices, 14 triangles.
-            //  0=A(-1,1)  1=TLC(-0.48,1)  2=T(-0.012,0.257)  3=TRC(0.5,1)
-            //  4=BR(1,1)  5=REB(1,0.5)   6=R(0.476,-0.011)  7=RET(1,-0.5)
-            //  8=C(1,-1)  9=BRC(0.48,-1) 10=B(-0.003,-0.276) 11=BLC(-0.48,-1)
-            // 12=D(-1,-1) 13=LET(-1,-0.5) 14=L(-0.494,-0.011) 15=LEB(-1,0.5)
-            {
-                // prettier-ignore
-                const pos = new Float32Array([
-                    -1,      1,      0,  //  0  A
-                    -0.480,  1,      0,  //  1  TLC
-                    -0.012,  0.257,  0,  //  2  T
-                     0.500,  1,      0,  //  3  TRC
-                     1,      1,      0,  //  4  BR
-                     1,      0.5,    0,  //  5  REB
-                     0.476, -0.011,  0,  //  6  R
-                     1,     -0.5,    0,  //  7  RET
-                     1,     -1,      0,  //  8  C
-                     0.480, -1,      0,  //  9  BRC
-                    -0.003, -0.276,  0,  // 10  B
-                    -0.480, -1,      0,  // 11  BLC
-                    -1,     -1,      0,  // 12  D
-                    -1,     -0.5,    0,  // 13  LET
-                    -0.494, -0.011,  0,  // 14  L
-                    -1,      0.5,    0,  // 15  LEB
-                ]);
-                // prettier-ignore
-                const idx = new Uint16Array([
-                    // top-left corner: A,TLC,T,L,LEB
-                     0,  1,  2,
-                     0,  2, 14,
-                     0, 14, 15,
-                    // top-right corner: TRC,BR,REB,R,T
-                     3,  4,  5,
-                     3,  5,  6,
-                     3,  6,  2,
-                    // centre: T,R,B,L
-                     2,  6, 10,
-                     2, 10, 14,
-                    // bottom-right corner: RET,C,BRC,B,R
-                     7,  8,  9,
-                     7,  9, 10,
-                     7, 10,  6,
-                    // bottom-left corner: LET,L,B,BLC,D
-                    13, 14, 10,
-                    13, 10, 11,
-                    13, 11, 12,
-                ]);
-                gPMXFill = new T.BufferGeometry();
-                gPMXFill.setAttribute('position', new T.BufferAttribute(pos, 3));
-                gPMXFill.setIndex(new T.BufferAttribute(idx, 1));
-            }
-            // PM fill — InstancedMesh (black, varying alpha per chord).
-            {
-                const _imFillVert = [
-                    'attribute float instanceAlpha;',
-                    'varying float vAlpha;',
-                    'void main() {',
-                    '    vAlpha = instanceAlpha;',
-                    '    vec4 pos = vec4(position, 1.0);',
-                    '    #ifdef USE_INSTANCING',
-                    '    pos = instanceMatrix * pos;',
-                    '    #endif',
-                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
-                    '}',
-                ].join('\n');
-                const _imFillFrag = [
-                    'varying float vAlpha;',
-                    'void main() {',
-                    '    if (vAlpha <= 0.0) discard;',
-                    '    gl_FragColor = vec4(0.0, 0.0, 0.0, vAlpha);',
-                    '}',
-                ].join('\n');
-                const alphaAttr = new T.InstancedBufferAttribute(_imPMXFillAlphaArr, 1);
-                alphaAttr.setUsage(T.DynamicDrawUsage);
-                gPMXFill.setAttribute('instanceAlpha', alphaAttr);
-                _imPMXFillMat = new T.ShaderMaterial({
-                    vertexShader: _imFillVert, fragmentShader: _imFillFrag,
-                    transparent: true, depthTest: false, depthWrite: false,
-                    fog: false, side: T.DoubleSide, forceSinglePass: true,
-                });
-                imPMXFill = new T.InstancedMesh(gPMXFill, _imPMXFillMat, IM_STRUM_CAP);
-                imPMXFill.instanceMatrix.setUsage(T.DynamicDrawUsage);
-                imPMXFill.frustumCulled = false;
-                imPMXFill.renderOrder = 10.5;
-                imPMXFill.count = 0;
-                noteG.add(imPMXFill);
-            }
-
-            // FH (frethand mute) strum X fill — 5 regions: 4 corner quadrants + centre diamond.
-            // 12 vertices, 10 triangles. L/R wings stop at fx=±0.50 (no solid lateral blocks).
-            //  0=LET(-0.50,+1)  1=TLC(-0.15,+1)  2=T(0,+0.42)   3=TRC(+0.15,+1)
-            //  4=RET(+0.50,+1)  5=REB(+0.50,-1)  6=R(+0.28,0)   7=B(0,-0.42)
-            //  8=BRC(+0.15,-1)  9=BLC(-0.15,-1) 10=LEB(-0.50,-1) 11=L(-0.28,0)
-            {
-                // prettier-ignore
-                const pos = new Float32Array([
-                    -0.50,  1,      0,  //  0  LET
-                    -0.15,  1,      0,  //  1  TLC
-                     0,     0.42,   0,  //  2  T
-                     0.15,  1,      0,  //  3  TRC
-                     0.50,  1,      0,  //  4  RET
-                     0.50, -1,      0,  //  5  REB
-                     0.28,  0,      0,  //  6  R
-                     0,    -0.42,   0,  //  7  B
-                     0.15, -1,      0,  //  8  BRC
-                    -0.15, -1,      0,  //  9  BLC
-                    -0.50, -1,      0,  // 10  LEB
-                    -0.28,  0,      0,  // 11  L
-                ]);
-                // prettier-ignore
-                const idx = new Uint16Array([
-                    // top-left corner: LET,TLC,T,L
-                     0,  1,  2,
-                     0,  2, 11,
-                    // top-right corner: TRC,RET,R,T
-                     3,  4,  6,
-                     3,  6,  2,
-                    // bottom-right corner: REB,R,B,BRC
-                     5,  6,  7,
-                     5,  7,  8,
-                    // bottom-left corner: LEB,L,B,BLC
-                    10, 11,  7,
-                    10,  7,  9,
-                    // centre diamond: L,T,R,B
-                    11,  2,  6,
-                    11,  6,  7,
-                ]);
-                gFHXFill = new T.BufferGeometry();
-                gFHXFill.setAttribute('position', new T.BufferAttribute(pos, 3));
-                gFHXFill.setIndex(new T.BufferAttribute(idx, 1));
-            }
-            // FH fill — InstancedMesh (black, varying alpha per chord).
-            {
-                const _imFillVert = [
-                    'attribute float instanceAlpha;',
-                    'varying float vAlpha;',
-                    'void main() {',
-                    '    vAlpha = instanceAlpha;',
-                    '    vec4 pos = vec4(position, 1.0);',
-                    '    #ifdef USE_INSTANCING',
-                    '    pos = instanceMatrix * pos;',
-                    '    #endif',
-                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
-                    '}',
-                ].join('\n');
-                const _imFillFrag = [
-                    'varying float vAlpha;',
-                    'void main() {',
-                    '    if (vAlpha <= 0.0) discard;',
-                    '    gl_FragColor = vec4(0.0, 0.0, 0.0, vAlpha);',
-                    '}',
-                ].join('\n');
-                const alphaAttr = new T.InstancedBufferAttribute(_imFHXFillAlphaArr, 1);
-                alphaAttr.setUsage(T.DynamicDrawUsage);
-                gFHXFill.setAttribute('instanceAlpha', alphaAttr);
-                _imFHXFillMat = new T.ShaderMaterial({
-                    vertexShader: _imFillVert, fragmentShader: _imFillFrag,
-                    transparent: true, depthTest: false, depthWrite: false,
-                    fog: false, side: T.DoubleSide, forceSinglePass: true,
-                });
-                imFHXFill = new T.InstancedMesh(gFHXFill, _imFHXFillMat, IM_STRUM_CAP);
-                imFHXFill.instanceMatrix.setUsage(T.DynamicDrawUsage);
-                imFHXFill.frustumCulled = false;
-                imFHXFill.renderOrder = 10.5;
-                imFHXFill.count = 0;
-                noteG.add(imFHXFill);
-            }
-
-            // PM X lines — 8 segments baked as thin quads in ±1 normalised space.
-            // Scale the pool mesh by (innerW*0.5, -innerH*0.5, ...) per chord;
-            // the Y-negated scale matches the XLINES convention (fya>0 = below centre).
-            if (!gPMXLines) {
-                const HT = 0.016; // normalised half-thickness ≈ lw/hH for a typical chord
-                // prettier-ignore
-                const XLINES = [
-                    [-1.000, -0.500, -0.494, -0.011],
-                    [-1.000,  0.500, -0.494, -0.011],
-                    [ 1.000, -0.500,  0.476, -0.011],
-                    [ 1.000,  0.500,  0.476, -0.011],
-                    [-0.480,  1.000, -0.012,  0.257],
-                    [ 0.500,  1.000, -0.012,  0.257],
-                    [ 0.480, -1.000,  0.000, -0.276],
-                    [-0.480, -1.000, -0.006, -0.276],
-                ];
-                const pos = new Float32Array(XLINES.length * 4 * 3);
-                const idx = new Uint16Array(XLINES.length * 6);
-                for (let i = 0; i < XLINES.length; i++) {
-                    const [xa, ya, xb, yb] = XLINES[i];
-                    const dx = xb - xa, dy = yb - ya;
-                    const il = 1 / Math.sqrt(dx * dx + dy * dy);
-                    const nx = -dy * il, ny = dx * il;
-                    const vi = i * 12, ii = i * 6, vb = i * 4;
-                    pos[vi+0]=xa+nx*HT; pos[vi+1]=ya+ny*HT; pos[vi+2]=0;
-                    pos[vi+3]=xb+nx*HT; pos[vi+4]=yb+ny*HT; pos[vi+5]=0;
-                    pos[vi+6]=xb-nx*HT; pos[vi+7]=yb-ny*HT; pos[vi+8]=0;
-                    pos[vi+9]=xa-nx*HT; pos[vi+10]=ya-ny*HT; pos[vi+11]=0;
-                    idx[ii+0]=vb;   idx[ii+1]=vb+1; idx[ii+2]=vb+2;
-                    idx[ii+3]=vb;   idx[ii+4]=vb+2; idx[ii+5]=vb+3;
-                }
-                gPMXLines = new T.BufferGeometry();
-                gPMXLines.setAttribute('position', new T.BufferAttribute(pos, 3));
-                gPMXLines.setIndex(new T.BufferAttribute(idx, 1));
-            }
-            // PM lines — InstancedMesh (varying color + alpha per chord).
-            // instanceColor (THREE built-in) carries baseRimHex per instance;
-            // instanceAlpha carries the per-chord opacity.
-            {
-                const _imLinesVert = [
-                    'attribute float instanceAlpha;',
-                    'varying float vAlpha;',
-                    'varying vec3 vColor;',
-                    'void main() {',
-                    '    vAlpha = instanceAlpha;',
-                    '    #ifdef USE_INSTANCING_COLOR',
-                    '    vColor = instanceColor;',
-                    '    #else',
-                    '    vColor = vec3(1.0);',
-                    '    #endif',
-                    '    vec4 pos = vec4(position, 1.0);',
-                    '    #ifdef USE_INSTANCING',
-                    '    pos = instanceMatrix * pos;',
-                    '    #endif',
-                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
-                    '}',
-                ].join('\n');
-                const _imLinesFrag = [
-                    'varying float vAlpha;',
-                    'varying vec3 vColor;',
-                    'void main() {',
-                    '    if (vAlpha <= 0.0) discard;',
-                    '    gl_FragColor = vec4(vColor, vAlpha);',
-                    '}',
-                ].join('\n');
-                const alphaAttr = new T.InstancedBufferAttribute(_imPMXLinesAlphaArr, 1);
-                alphaAttr.setUsage(T.DynamicDrawUsage);
-                gPMXLines.setAttribute('instanceAlpha', alphaAttr);
-                _imPMXLinesMat = new T.ShaderMaterial({
-                    vertexShader: _imLinesVert, fragmentShader: _imLinesFrag,
-                    transparent: true, depthTest: false, depthWrite: false,
-                    fog: false, side: T.DoubleSide, forceSinglePass: true,
-                });
-                imPMXLines = new T.InstancedMesh(gPMXLines, _imPMXLinesMat, IM_STRUM_CAP);
-                imPMXLines.instanceMatrix.setUsage(T.DynamicDrawUsage);
-                imPMXLines.frustumCulled = false;
-                imPMXLines.renderOrder = 11;
-                // Eagerly initialise instanceColor so USE_INSTANCING_COLOR is
-                // defined when the shader is compiled on the first draw.
-                _imColor.set(1, 1, 1);
-                imPMXLines.setColorAt(0, _imColor);
-                imPMXLines.instanceColor.setUsage(T.DynamicDrawUsage);
-                imPMXLines.count = 0;
-                noteG.add(imPMXLines);
-            }
-
-            // FH X lines — same scheme, 8 segments from the FH_XLINES pattern
-            if (!gFHXLines) {
-                const HT = 0.022; // slightly wider — FH wings are shorter, need more visual weight
-                // prettier-ignore
-                const FH_XLINES = [
-                    [-0.50,  1.00, -0.28,  0.00],
-                    [-0.50, -1.00, -0.28,  0.00],
-                    [ 0.50,  1.00,  0.28,  0.00],
-                    [ 0.50, -1.00,  0.28,  0.00],
-                    [-0.15, -1.00,  0.00, -0.42],
-                    [ 0.15, -1.00,  0.00, -0.42],
-                    [ 0.15,  1.00,  0.00,  0.42],
-                    [-0.15,  1.00,  0.00,  0.42],
-                ];
-                const pos = new Float32Array(FH_XLINES.length * 4 * 3);
-                const idx = new Uint16Array(FH_XLINES.length * 6);
-                for (let i = 0; i < FH_XLINES.length; i++) {
-                    const [xa, ya, xb, yb] = FH_XLINES[i];
-                    const dx = xb - xa, dy = yb - ya;
-                    const il = 1 / Math.sqrt(dx * dx + dy * dy);
-                    const nx = -dy * il, ny = dx * il;
-                    const vi = i * 12, ii = i * 6, vb = i * 4;
-                    pos[vi+0]=xa+nx*HT; pos[vi+1]=ya+ny*HT; pos[vi+2]=0;
-                    pos[vi+3]=xb+nx*HT; pos[vi+4]=yb+ny*HT; pos[vi+5]=0;
-                    pos[vi+6]=xb-nx*HT; pos[vi+7]=yb-ny*HT; pos[vi+8]=0;
-                    pos[vi+9]=xa-nx*HT; pos[vi+10]=ya-ny*HT; pos[vi+11]=0;
-                    idx[ii+0]=vb;   idx[ii+1]=vb+1; idx[ii+2]=vb+2;
-                    idx[ii+3]=vb;   idx[ii+4]=vb+2; idx[ii+5]=vb+3;
-                }
-                gFHXLines = new T.BufferGeometry();
-                gFHXLines.setAttribute('position', new T.BufferAttribute(pos, 3));
-                gFHXLines.setIndex(new T.BufferAttribute(idx, 1));
-            }
-            // FH lines — InstancedMesh (varying color + alpha per chord).
-            {
-                const _imLinesVert = [
-                    'attribute float instanceAlpha;',
-                    'varying float vAlpha;',
-                    'varying vec3 vColor;',
-                    'void main() {',
-                    '    vAlpha = instanceAlpha;',
-                    '    #ifdef USE_INSTANCING_COLOR',
-                    '    vColor = instanceColor;',
-                    '    #else',
-                    '    vColor = vec3(1.0);',
-                    '    #endif',
-                    '    vec4 pos = vec4(position, 1.0);',
-                    '    #ifdef USE_INSTANCING',
-                    '    pos = instanceMatrix * pos;',
-                    '    #endif',
-                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
-                    '}',
-                ].join('\n');
-                const _imLinesFrag = [
-                    'varying float vAlpha;',
-                    'varying vec3 vColor;',
-                    'void main() {',
-                    '    if (vAlpha <= 0.0) discard;',
-                    '    gl_FragColor = vec4(vColor, vAlpha);',
-                    '}',
-                ].join('\n');
-                const alphaAttr = new T.InstancedBufferAttribute(_imFHXLinesAlphaArr, 1);
-                alphaAttr.setUsage(T.DynamicDrawUsage);
-                gFHXLines.setAttribute('instanceAlpha', alphaAttr);
-                _imFHXLinesMat = new T.ShaderMaterial({
-                    vertexShader: _imLinesVert, fragmentShader: _imLinesFrag,
-                    transparent: true, depthTest: false, depthWrite: false,
-                    fog: false, side: T.DoubleSide, forceSinglePass: true,
-                });
-                imFHXLines = new T.InstancedMesh(gFHXLines, _imFHXLinesMat, IM_STRUM_CAP);
-                imFHXLines.instanceMatrix.setUsage(T.DynamicDrawUsage);
-                imFHXLines.frustumCulled = false;
-                imFHXLines.renderOrder = 11;
-                _imColor.set(1, 1, 1);
-                imFHXLines.setColorAt(0, _imColor);
-                imFHXLines.instanceColor.setUsage(T.DynamicDrawUsage);
-                imFHXLines.count = 0;
-                noteG.add(imFHXLines);
-            }
-
-            // Pool-based strum-indicator replacements.  The IM approach above uses
-            // a fixed renderOrder per mesh type, which lets far-chord X marks overdraw
-            // gems/frames of nearer chords. Pools give per-chord Z-proportional renderOrder.
-            // Geometries are shared with the (now empty) IMs — MeshBasicMaterial
-            // ignores the instanceAlpha / instanceColor attributes on the geometry.
-            pPMXFill = pool(noteG, () => new T.Mesh(
-                gPMXFill,
-                new T.MeshBasicMaterial({
-                    color: 0x000000, transparent: true, opacity: 1,
-                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-            pFHXFill = pool(noteG, () => new T.Mesh(
-                gFHXFill,
-                new T.MeshBasicMaterial({
-                    color: 0x000000, transparent: true, opacity: 1,
-                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-            pMuteXLines = pool(noteG, () => new T.Mesh(
-                gPMXLines,
-                new T.MeshBasicMaterial({
-                    color: 0xffffff, transparent: true, opacity: 1,
-                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-            pFHXLines = pool(noteG, () => new T.Mesh(
-                gFHXLines,
-                new T.MeshBasicMaterial({
-                    color: 0xffffff, transparent: true, opacity: 1,
-                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
-                }),
-            ));
-
-            pChordLbl   = pool(lblG,  () => new T.Sprite(txtMat('', '#e8d080', true, 'chord').clone()));
-            // Single shared barre material — all pool meshes reference it,
-            // so _applyGlow() can mutate emissiveIntensity once and every
-            // recycled / future-allocated barre mesh picks up the change.
-            mBarre = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.9 * glowMul, transparent: true, depthWrite: false });
-            pBarreLine  = pool(noteG, () => new T.Mesh(new T.BoxGeometry(1, 1, 1), mBarre));
-            // Shared 1×1×1 box geometry — brackets can require many pooled
-            // meshes per frame, so per-mesh BoxGeometry allocation would
-            // duplicate buffers and create unnecessary GPU disposal work.
-            // Disposed once in teardown (alongside the other shared geos).
-            if (!gArpBracket) gArpBracket = new T.BoxGeometry(1, 1, 1);
-            pArpBracket = pool(noteG, () => new T.Mesh(
-                gArpBracket,
-                new T.MeshBasicMaterial({
-                    color: 0xffffff,
-                    transparent: true,
-                    opacity: 1.0,
-                    depthWrite: false,
-                    depthTest: false,
-                    fog: false,
-                }),
-            ));
-
-            // Per-note fret number below note with connector line
-            pNoteFretLabel = pool(lblG, () => {
-                const _nfl = new T.Sprite(txtMat('0', FRET_LABEL_GOLD_HEX, false, 'noteFret').clone());
-                _nfl.material.fog = false;
-                _nfl.material.depthTest = false;
-                return _nfl;
-            });
-            // Teaching marks fg/sd labels (§6.2.2). One pool, two get()s per note
-            // (finger + degree); the texture is swapped per draw via material.map.
-            pTeachMarkLbl = pool(lblG, () => {
-                const _tml = new T.Sprite(txtMat('0', '#7fd1ff', false, 'teachMark').clone());
-                _tml.material.fog = false;
-                _tml.material.depthTest = false;
-                return _tml;
-            });
-            pConnectorLine = pool(noteG, () => new T.Line(
-                new T.BufferGeometry().setFromPoints([new T.Vector3(0, 0, 0), new T.Vector3(0, 1, 0)]),
-                new T.LineBasicMaterial({ color: 0xaaaaaa, transparent: true, opacity: 0.5, depthTest: false }),
-            ));
-            pDropLine = pool(noteG, () => new T.Line(
-                new T.BufferGeometry().setFromPoints([new T.Vector3(0, 0, 0), new T.Vector3(0, 1, 0)]),
-                new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.35 }),
-            ));
-
-            // Fret-column reference markers (visual cue for X-position to fret-number).
-            // Each sprite gets its own clone so the per-frame material.map swap
-            // (dark vs light grey) doesn't poison neighbours sharing the same
-            // cached texture map.
-            // fog:false prevents the scene fog from gradually dimming the sprite
-            // as it enters the far end of the highway — opacity is managed
-            // manually with a short fade-in so the number appears at its
-            // final size the moment it becomes visible rather than seeming to
-            // emerge from a tiny dim spec at the horizon.
-            pFretColMarker = pool(lblG, () => {
-                const _sp = new T.Sprite(txtMat('0', '#666666', false, 'noteFret').clone());
-                // fog=false: prevents scene fog from dimming the sprite as it enters the
-                // far end of the highway.  Opacity is managed by the manual fade-in ramp
-                // so the number appears smoothly instead of emerging as a dim spec.
-                _sp.material.fog = false;
-                return _sp;
-            });
-
-            // ── Pre-warm pools (feedBack#226) ─────────────────────────────
-            // Dense 7/8-string charts can outrun the lazy-grow path in the
-            // first 1-2s of playback, stalling those frames with `new T.Mesh`
-            // allocations *and* growing noteG forever (the pool only hides on
-            // reset). Pay the cost up front instead.
-            //
-            // Trade-off: pre-warming attaches the same meshes to noteG even
-            // on 4/6-string charts that may never use them all. The cost is
-            // paid at boardInit (during the load spinner — wall-clock time
-            // users were already waiting on), so the steady-state win on
-            // playback FPS is worth the init-time scene-graph footprint.
-            // Caps sized for a typical visible-window worst case (NOT the
-            // theoretical max across MAX_RENDER_STRINGS); lazy growth past
-            // the warm cap still works for genuinely dense outliers.
-            const _WARM_NOTE = 48;
-            const _WARM_CHORD = 12;
-            const _WARM_LANE = 32;
-            const _WARM_BEAT = 24;
-            pNote.warm(_WARM_NOTE);
-            pNoteEdge.warm(_WARM_NOTE);
-            pAccentHalo.warm(_WARM_NOTE);
-            pSus.warm(_WARM_NOTE);
-            pSusOutline.warm(_WARM_NOTE);
-            pSusRibbon.warm(_WARM_NOTE / 2);
-            pSusRibbonOl.warm(_WARM_NOTE / 2);
-            pTapChevron.warm(_WARM_CHORD);
-            pLbl.warm(_WARM_NOTE);
-            pSusRail.warm(_WARM_CHORD);
-            pSusRailBloom.warm(_WARM_CHORD);
-            pTechPlane.warm(_WARM_CHORD);
-            pNoteFretLabel.warm(_WARM_NOTE);
-            pTeachMarkLbl.warm(_WARM_NOTE);
-            pChordFrameFill.warm(_WARM_CHORD);
-            pChordBox.warm(_WARM_CHORD);
-            pChordLbl.warm(_WARM_CHORD);
-            pBarreLine.warm(_WARM_CHORD);
-            pArpBracket.warm(_WARM_CHORD);
-            pHaloBar.warm(_WARM_CHORD);
-            pFretLbl.warm(_WARM_LANE);
-            pLane.warm(_WARM_LANE * 2);  // anchor-driven lanes × time slices
-            pLaneDivider.warm(_WARM_LANE);
-            pGhostFretLbl.warm(_WARM_LANE);
-            pFretColMarker.warm(_WARM_LANE);
-            pConnectorLine.warm(_WARM_NOTE / 2);
-            pDropLine.warm(_WARM_NOTE / 2);
-            pBeat.warm(_WARM_BEAT);
-            pSec.warm(8);
-
-            _bgLoadSettings();
-            buildBoard();
-            // Apply the scene color theme now that settings + board exist. Sets
-            // the clear color + fog tint (board plane was themed in buildBoard).
-            // For the default theme this is identical to the hardcoded values
-            // initScene seeded above, so nothing changes for existing users.
-            _applyBgTheme();
-
-            // Background animations (#13). Read settings keyed by this
-            // panel and mount the active style's meshes. Subscribe to
-            // in-app settings changes (settings.html via window.h3dBgSet*)
-            // so they propagate without a reload. Manual localStorage
-            // edits don't fire the pub-sub and require a reload.
-            // Push the freshly-loaded vibrancy/glow values into the
-            // materials. _bgLoadSettings only triggers a palette re-apply
-            // when the palette ID actually changed, so a fresh-init user
-            // on the default palette would otherwise keep the hardcoded
-            // construction-time material values until they touched a
-            // slider.
-            _applyVibrancy();
-            _applyGlow();
-            // inlayLabelsVisible was applied before buildBoard() via _bgLoadSettings.
-            bgGroup = new T.Group();
-            // Note: renderOrder on a Group is a no-op (Three.js Groups
-            // are transforms, not rendered objects, so renderOrder only
-            // affects the actual meshes inside). _bgMountStyle stamps
-            // renderOrder = -1 on every child after build, which IS what
-            // forces background to render before gameplay geometry.
-            // Combined with the deeper-than-note-range placements below,
-            // background never paints over notes.
-            scene.add(bgGroup);
-            _bgMountStyle();
-            _bgListener = (changedKey) => {
-                if (changedKey === 'fretSpacing') {
-                    // _h3dFretUniform + the fretX-derived scalars were already
-                    // updated globally in h3dSetFretSpacing. Rebuild this
-                    // panel's static board geometry (fret wires, lanes, inlays)
-                    // so it re-lays-out for the new spacing; per-frame note
-                    // geometry reads fretX live and needs no rebuild.
-                    if (fretG) buildBoard();
-                    return;
-                }
-                if (changedKey === 'inlayLabelsVisible') {
-                    _bgLoadSettings();
-                    // Flip visibility on the already-built sprites; no
-                    // need to rebuild the board (cheaper, preserves the
-                    // shared materials and avoids palette re-apply churn).
-                    for (const lbl of _inlayLabels) lbl.visible = inlayLabelsVisible;
-                    return;
-                }
-                if (changedKey === 'nutHeadstockVisible') {
-                    _bgLoadSettings();
-                    if (nutHeadstockGroup) nutHeadstockGroup.visible = nutHeadstockVisible;
-                    return;
-                }
-                if (changedKey === 'tuningLabelsVisible') {
-                    _bgLoadSettings();
-                    _lastOpenStringLblSig = '';
-                    if (_tuningLabelSprites.length) _disposeOpenStringPitchSprites();
-                    return;
-                }
-                if (changedKey === 'nutColor' || changedKey === 'headstockColor') {
-                    _bgLoadSettings();
-                    if (fretG) buildBoard();
-                    for (const lbl of _inlayLabels) lbl.visible = inlayLabelsVisible;
-                    return;
-                }
-                if (changedKey === 'reactive' || changedKey === 'showFretOnNote' ||
-                    changedKey === 'fretNumberGhostScope' ||
-                    changedKey === 'cameraSmoothing' || changedKey === 'zoomSmoothing' ||
-                    changedKey === 'tiltSmoothing' || changedKey === 'cameraLockLow' ||
-                    changedKey === 'cameraLockZoom' || changedKey === 'cameraMode' ||
-                    changedKey === 'textSize' ||
-                    changedKey === 'chordDiagramSize' || changedKey === 'chordDiagramPosition' ||
-                    changedKey === 'fretColumnMarkerCadence' ||
-                    changedKey === 'sectionLabelsOnHighway' ||
-                    changedKey === 'sectionHudVisible' ||
-                    changedKey === 'sectionHudPosition' ||
-                    changedKey === 'sectionHudSize' ||
-                    changedKey === 'toneHudVisible' ||
-                    changedKey === 'toneHudPosition' ||
-                    changedKey === 'toneHudSize' ||
-                    changedKey === 'projectionVisible' ||
-                    changedKey === 'slideArrowApproachVisible' ||
-                    changedKey === 'slideArrowNeckVisible' ||
-                    changedKey === 'slideArrowChainPreviewVisible') {
-                    // Flag flips don't need a mesh rebuild — just refresh
-                    // the per-instance state for the next frame to consult.
-                    // Same shape for showFretOnNote (#12), cameraSmoothing
-                    // (#34), the zoom/tilt smoothing follow-ups, and
-                    // cameraLockLow — all read per-frame in update() /
-                    // camUpdate().
-                    _bgLoadSettings();
-                    return;
-                }
-                if (changedKey === 'vibrancy') {
-                    _bgLoadSettings();
-                    _applyVibrancy();
-                    return;
-                }
-                if (changedKey === 'glow') {
-                    _bgLoadSettings();
-                    _applyGlow();
-                    return;
-                }
-                if (changedKey === 'palette') {
-                    // Palette change has three effects:
-                    //  1. _bgLoadSettings -> _applyPaletteToMaterials
-                    //     retints the per-instance shared materials
-                    //     (notes, glows, sustain trails, projection).
-                    //  2. buildBoard rebuilds the fretboard meshes
-                    //     (LineBasicMaterial lane lines + per-string
-                    //     BoxGeometry materials). These are created at
-                    //     build time with palette-baked colors and
-                    //     aren't reachable from _applyPaletteToMaterials.
-                    //  3. lights bg style bakes palette colors into
-                    //     sprite quads at build time, so it needs a
-                    //     full mesh rebuild — fire _bgRebuild when
-                    //     that style is active.
-                    _bgLoadSettings();
-                    if (fretG) buildBoard();
-                    if (bgStyleId === 'lights') _bgRebuild();
-                    return;
-                }
-                if (changedKey === 'bgTheme' || changedKey === 'hwTheme') {
-                    // A scene-color axis changed (background = bgTheme:
-                    // clear+fog; highway = hwTheme: board plane + lane). Recolor
-                    // in place — no mesh rebuild needed (the board plane material
-                    // is mutated via _boardPlaneMat, the lane via mLaneOdd/Even).
-                    // _applyBgTheme reapplies both axes from their own keys, so
-                    // changing one dropdown retints only its half.
-                    _bgLoadSettings();
-                    _applyBgTheme();
-                    return;
-                }
-                if (changedKey === 'customImageDataUrl') {
-                    // Asset bytes changed. Rebuild only when the image
-                    // style is active — otherwise the new bytes will
-                    // pick up next time the user picks `image`.
-                    _bgLoadSettings();
-                    if (bgStyleId === 'image') _bgRebuild();
-                    return;
-                }
-                if (changedKey === 'customImageName') {
-                    // Display-only metadata; no mesh rebuild.
-                    _bgLoadSettings();
-                    return;
-                }
-                if (changedKey === 'customVideoName') {
-                    // Filename change → new <video> source. Rebuild
-                    // only when the video style is currently active;
-                    // otherwise the new bytes pick up next time the
-                    // user picks `video`.
-                    _bgLoadSettings();
-                    if (bgStyleId === 'video') _bgRebuild();
-                    return;
-                }
-                if (changedKey === 'intensity') {
-                    _bgLoadSettings();
-                    // Image style reads s.intensity per frame inside
-                    // update() to scale the drift speed, so a live
-                    // mutation is enough — no need to tear down and
-                    // re-decode the texture for every slider change.
-                    // The procedural styles bake intensity into mesh
-                    // count, opacity, and size at build time, so they
-                    // still need a full rebuild.
-                    if (bgStyleId === 'image' && bgState) {
-                        bgState.intensity = bgIntensity;
-                        return;
-                    }
-                    _bgRebuild();
-                    return;
-                }
-                if (changedKey === 'venueScene') {
-                    _bgRebuild();
-                    return;
-                }
-                if (changedKey === 'venueInstrumentPov') {
-                    if (_bgEffectiveStyleId() === 'venue' && bgState) {
-                        _venueSwapPlateIfNeeded(bgState);
-                    }
-                    return;
-                }
-                if (!changedKey || changedKey === 'style') {
-                    _bgRebuild();
-                }
-            };
-            _bgSubscribe(_bgListener);
-
-            // Notedetect feedback (#9). Listen for hit/miss events on
-            // window. Notedetect dispatches both globally and on its
-            // instanceRoot; the global fire is fine for our case since
-            // each 3dhighway panel just stores any event into its own
-            // queue and renders only the matching note. Listeners are
-            // per-panel so destroy() can cleanly remove them; cost is
-            // a per-event branch + push, negligible vs per-frame work.
-            // Validate every payload field we'll later compare against
-            // chart-data fields (s, f, t). drawNote compares with
-            // Math.abs(m.noteTime - n.t) and trusts the values are
-            // finite, so reject any payload missing one of those
-            // fields here rather than letting bogus data into the
-            // arrays. Prune expired marks on every push so the arrays
-            // settle back to empty when notedetect stops emitting —
-            // drawNote's fast-path short-circuit
-            // (`if (_ndHitMarks.length || _ndMissMarks.length)`) only
-            // works if expired entries don't linger.
-            const _ndNormalizeMark = (d) => {
-                if (!d) return null;
-                const note = d.note || d.chartNote;
-                if (!note) return null;
-                if (!Number.isFinite(note.s) || !Number.isFinite(note.f) || !Number.isFinite(d.noteTime)) return null;
-                const labels = [];
-                if (d.timingState && d.timingState !== 'OK' && Number.isFinite(d.timingError)) {
-                    labels.push({
-                        text: `${d.timingState === 'EARLY' ? '↑' : '↓'} ${d.timingError > 0 ? '+' : ''}${d.timingError}ms`,
-                        color: '#ffb347',
-                    });
-                }
-                if (d.pitchState && d.pitchState !== 'OK' && Number.isFinite(d.pitchError)) {
-                    labels.push({
-                        text: `${d.pitchState === 'SHARP' ? '♯' : '♭'} ${d.pitchError > 0 ? '+' : ''}${d.pitchError}¢`,
-                        color: '#66c7ff',
-                    });
-                }
-                return { s: note.s, f: note.f, noteTime: d.noteTime, labels, timingState: d.timingState || null };
-            };
-            const _ndPushMark = (arr, d) => {
-                const mark = _ndNormalizeMark(d);
-                if (!mark) return arr;
-                const now = performance.now();
-                // Prune expired entries unconditionally. The dedupe path
-                // below can extend expiresAt of any entry (including arr[0]),
-                // so an arr[0] gate is not reliable — it would prevent
-                // pruning entries that expired behind a refreshed front
-                // entry, allowing the array to grow unbounded. These arrays
-                // are tiny (a handful of marks at most), so an unconditional
-                // filter() is negligible and always correct.
-                if (arr.length !== 0) {
-                    const live = arr.filter(m => m.expiresAt > now);
-                    arr.length = 0;
-                    if (live.length) arr.push(...live);
-                }
-                const existing = arr.find(m =>
-                    m.s === mark.s && m.f === mark.f && Math.abs(m.noteTime - mark.noteTime) < _ND_TIME_EPS
-                );
-                if (existing) {
-                    existing.labels = mark.labels.length ? mark.labels : existing.labels;
-                    existing.expiresAt = Math.max(existing.expiresAt, now + _ND_TTL_MS);
-                    return arr;
-                }
-                arr.push({ ...mark, expiresAt: now + _ND_TTL_MS });
-                return arr;
-            };
-            _ndOnHit = (e) => { _ndHitMarks = _ndPushMark(_ndHitMarks, e.detail); };
-            _ndOnMiss = (e) => { _ndMissMarks = _ndPushMark(_ndMissMarks, e.detail); };
-            window.addEventListener('notedetect:hit', _ndOnHit);
-            window.addEventListener('notedetect:miss', _ndOnMiss);
-            if (window.feedBack &&
-                    typeof window.feedBack.on  === 'function' &&
-                    typeof window.feedBack.off === 'function') {
-                _ndOnBusHit  = (e) => { _ndHitMarks  = _ndPushMark(_ndHitMarks,  e.detail); };
-                _ndOnBusMiss = (e) => { _ndMissMarks = _ndPushMark(_ndMissMarks, e.detail); };
-                window.feedBack.on('note:hit', _ndOnBusHit);
-                window.feedBack.on('note:miss', _ndOnBusMiss);
-            }
-
-            // Score FX (notedetect ≥1.13). notedetect dispatches each fx
-            // detail object twice in the same task: first explicitly on
-            // window (unscoped), then as a bubbling CustomEvent from its
-            // per-panel instanceRoot (scoped). Element-targeted copies are
-            // authoritative — accept only the ones whose root lives in this
-            // panel's container. The window copy is DEFERRED a task: by the
-            // time it runs, the element copy (same detail reference) has
-            // either arrived — making the window copy a duplicate to drop —
-            // or it never will (detector root not attached to the DOM), in
-            // which case the window copy is the compat fallback. This keeps
-            // splitscreen panels from rendering each other's FX even for
-            // the first event of a session.
-            _fxResolvePalette();
-            _fxOnFx = (e) => {
-                const d = e && e.detail;
-                if (!d) return;
-                const t = e.target;
-                if (t && t.parentElement) {
-                    _fxElemSeen.add(d);
-                    if (!highwayCanvas || !t.parentElement.contains(highwayCanvas)) return;
-                    _fxHandle(d);
-                    return;
-                }
-                const gen = _fxGen;
-                setTimeout(() => {
-                    if (gen !== _fxGen) return;   // torn down (or re-inited) meanwhile
-                    if (_fxElemSeen.has(d)) return;
-                    _fxHandle(d);
-                }, 0);
-            };
-            window.addEventListener('notedetect:fx', _fxOnFx);
-            if (window.feedBack && typeof window.feedBack.on === 'function'
-                    && typeof window.feedBack.off === 'function') {
-                _fxOnSkin = () => _fxResolvePalette();
-                window.feedBack.on('notedetect:skin', _fxOnSkin);
-            }
-
-            return true;
-        }
-
-        function _bgLoadSettings() {
-            const panelKey = _bgPanelKey(highwayCanvas);
-            bgStyleId = _bgReadSetting(panelKey, 'style');
-            bgIntensity = _bgReadSetting(panelKey, 'intensity');
-            bgReactive = _bgReadSetting(panelKey, 'reactive');
-            // Per-render opt-out (captured from the mount bundle in init): force
-            // the reactive background off for THIS instance, overriding the shared
-            // setting without writing it back. Re-applied here so it sticks across
-            // setting reloads.
-            if (_bgReactiveOptOut) bgReactive = false;
-            if (bgStyleId === 'butterchurn') bgReactive = false; // Butterchurn owns the <audio> tap
-            const newPaletteId = _bgReadSetting(panelKey, 'palette');
-            let newPalette;
-            if (newPaletteId === 'custom') {
-                // Resolve user colors into the stable _customPalette array,
-                // mutated in place so the reference identity is preserved.
-                let stored = null;
-                const raw = _bgReadSetting(panelKey, 'customColors');
-                if (typeof raw === 'string') { try { stored = JSON.parse(raw); } catch (_) { /* corrupt */ } }
-                for (let i = 0; i < _customPalette.length; i++) {
-                    const v = Array.isArray(stored) ? _h3dHexToInt(stored[i]) : null;
-                    _customPalette[i] = (v != null) ? v : PALETTES.default[i];
-                }
-                newPalette = _customPalette;
-            } else {
-                newPalette = PALETTES[newPaletteId] || PALETTES.default;
-            }
-            // Signature guards the in-place custom case: when the user edits a
-            // color the reference stays === activePalette, so compare contents
-            // too to force a retint. _bgPaletteSig caches the applied colors.
-            const newSig = newPalette.join(',');
-            if (newPalette !== activePalette || newSig !== _bgPaletteSig) {
-                activePalette = newPalette;
-                _bgPaletteSig = newSig;
-                _applyPaletteToMaterials();
-            }
-            bgThemeId = _bgReadSetting(panelKey, 'bgTheme');
-            // Highway axis. ONE-TIME BACKWARD-COMPAT BACKFILL: the first time we
-            // load with no stored hwTheme (pre-split installs, or anyone who only
-            // ever touched the old single "Scene colors" control), seed hwTheme
-            // FROM the background pick AND PERSIST it, so an existing 'cathode'
-            // selection looks byte-identical right after the upgrade. Persisting
-            // immediately (rather than re-inheriting on every read) is what keeps
-            // the two axes truly INDEPENDENT thereafter: once hwTheme is stored,
-            // changing the Background dropdown no longer drags the Highway
-            // surface along, and the settings UI's Highway value can never
-            // disagree with what's rendered. Written without _bgEmitChange so the
-            // backfill can't re-enter the change listener.
-            if (_bgHasStored(panelKey, 'hwTheme')) {
-                hwThemeId = _bgReadSetting(panelKey, 'hwTheme');
-            } else {
-                hwThemeId = bgThemeId;
-                _bgMemFallback.hwTheme = String(bgThemeId);
-                try { localStorage.setItem('h3d_bg_hwTheme', String(bgThemeId)); } catch (_) { /* storage blocked — mem fallback still seeds the read */ }
-            }
-            showFretOnNote = _bgReadSetting(panelKey, 'showFretOnNote');
-            fretNumberGhostScope = _bgReadSetting(panelKey, 'fretNumberGhostScope');
-            cameraSmoothing = _bgReadSetting(panelKey, 'cameraSmoothing');
-            // Mirror-at-first-read: zoom + tilt sliders inherit cameraSmoothing
-            // when the user has never explicitly written them. Once the user
-            // moves either slider, the corresponding _bgHasStored() flips
-            // true and the read becomes independent.
-            zoomSmoothing = _bgHasStored(panelKey, 'zoomSmoothing')
-                ? _bgReadSetting(panelKey, 'zoomSmoothing')
-                : cameraSmoothing;
-            tiltSmoothing = _bgHasStored(panelKey, 'tiltSmoothing')
-                ? _bgReadSetting(panelKey, 'tiltSmoothing')
-                : cameraSmoothing;
-            cameraLockLow = _bgReadSetting(panelKey, 'cameraLockLow');
-            cameraLockZoom = _bgReadSetting(panelKey, 'cameraLockZoom');
-            cameraMode = _bgReadSetting(panelKey, 'cameraMode');
-            textSize             = _bgReadSetting(panelKey, 'textSize');
-            vibrancy             = _bgReadSetting(panelKey, 'vibrancy');
-            glowMul              = _bgReadSetting(panelKey, 'glow');
-            _hitFx               = _bgReadSetting(panelKey, 'hitFx');
-            _sparks              = _bgReadSetting(panelKey, 'sparks');
-            _cinematic           = _bgReadSetting(panelKey, 'cinematic');
-            _verdictMarks        = _bgReadSetting(panelKey, 'verdictMarks');
-            _timingFx            = _bgReadSetting(panelKey, 'timingFx');
-            _streakFx            = _bgReadSetting(panelKey, 'streakFx');
-            _bloom               = _bgReadSetting(panelKey, 'bloom');
-            _applyCinematic();
-            fpsVisible           = _bgReadSetting(panelKey, 'fpsVisible');
-            fretDividersVisible  = _bgReadSetting(panelKey, 'fretDividersVisible');
-            chordDiagramVisible  = _bgReadSetting(panelKey, 'chordDiagramVisible');
-            chordDiagramSize     = _bgReadSetting(panelKey, 'chordDiagramSize');
-            chordDiagramPosition = _bgReadSetting(panelKey, 'chordDiagramPosition');
-            fretColumnMarkerCadence = _bgReadSetting(panelKey, 'fretColumnMarkerCadence');
-            inlayLabelsVisible = _bgReadSetting(panelKey, 'inlayLabelsVisible');
-            sectionLabelsOnHighway = _bgReadSetting(panelKey, 'sectionLabelsOnHighway');
-            sectionHudVisible      = _bgReadSetting(panelKey, 'sectionHudVisible');
-            sectionHudPosition     = _bgReadSetting(panelKey, 'sectionHudPosition');
-            sectionHudSize         = _bgReadSetting(panelKey, 'sectionHudSize');
-            toneHudVisible         = _bgReadSetting(panelKey, 'toneHudVisible');
-            toneHudPosition        = _bgReadSetting(panelKey, 'toneHudPosition');
-            toneHudSize            = _bgReadSetting(panelKey, 'toneHudSize');
-            nutHeadstockVisible    = _bgReadSetting(panelKey, 'nutHeadstockVisible');
-            tuningLabelsVisible    = _bgReadSetting(panelKey, 'tuningLabelsVisible');
-            nutColor               = _bgReadSetting(panelKey, 'nutColor');
-            headstockColor         = _bgReadSetting(panelKey, 'headstockColor');
-            projectionVisible      = _bgReadSetting(panelKey, 'projectionVisible');
-            slideArrowApproachVisible = _bgReadSetting(panelKey, 'slideArrowApproachVisible');
-            slideArrowNeckVisible     = _bgReadSetting(panelKey, 'slideArrowNeckVisible');
-            slideArrowChainPreviewVisible = _bgReadSetting(panelKey, 'slideArrowChainPreviewVisible');
-            _vibrancyIdleOp = 0.4  + 0.6  * vibrancy;
-            _vibrancyProjOp = 0.15 + 0.35 * vibrancy;
-            // Custom image asset is a single GLOBAL slot — bytes are
-            // shared across panels (per-panel choice is which style
-            // each panel renders, not which asset). Reading via
-            // _bgReadSetting would let a stray h3d_bg_panel<idx>_*
-            // override silently re-introduce the per-panel asset
-            // duplication this design deliberately avoids (and
-            // h3dBgClearCustomImage wouldn't reach those overrides).
-            // Read globals directly instead.
-            //
-            // Precedence: in-memory fallback BEFORE localStorage. The
-            // setter always populates _bgMemFallback (even when the
-            // localStorage write fails on quota), so the fallback
-            // holds the most-recent staged value. Reading localStorage
-            // first would mean a failed write leaves the renderer
-            // pointed at the previous asset while settings.html shows
-            // a "session-only" warning claiming the new bytes are in
-            // effect — UI and renderer would silently disagree.
-            const memDataUrl = _bgMemFallback.customImageDataUrl;
-            const memName    = _bgMemFallback.customImageName;
-            try {
-                const gDataUrl = (memDataUrl !== undefined) ? memDataUrl : localStorage.getItem('h3d_bg_customImageDataUrl');
-                const gName    = (memName    !== undefined) ? memName    : localStorage.getItem('h3d_bg_customImageName');
-                bgCustomImageDataUrl = (gDataUrl != null) ? gDataUrl : BG_DEFAULTS.customImageDataUrl;
-                bgCustomImageName    = (gName    != null) ? gName    : BG_DEFAULTS.customImageName;
-            } catch (_) {
-                bgCustomImageDataUrl = (memDataUrl !== undefined) ? memDataUrl : BG_DEFAULTS.customImageDataUrl;
-                bgCustomImageName    = (memName    !== undefined) ? memName    : BG_DEFAULTS.customImageName;
-            }
-            // Custom video filename: also a single global slot, same
-            // mem-first precedence as the image keys (a quota-failed
-            // setItem leaves _bgMemFallback ahead of localStorage).
-            const memVideoName = _bgMemFallback.customVideoName;
-            try {
-                const gVideoName = (memVideoName !== undefined) ? memVideoName : localStorage.getItem('h3d_bg_customVideoName');
-                bgCustomVideoName = (gVideoName != null) ? gVideoName : BG_DEFAULTS.customVideoName;
-            } catch (_) {
-                bgCustomVideoName = (memVideoName !== undefined) ? memVideoName : BG_DEFAULTS.customVideoName;
-            }
-        }
-        // Live-swap palette by mutating existing materials in place.
-        // Three.js colors propagate to all sharing meshes on the next
-        // render — no rebuild, no GC. The mGlow material was authored
-        // with .color = white and the per-string color in .emissive
-        // only; we preserve that here so the glow look stays consistent
-        // before/after a palette swap rather than tinting the diffuse
-        // white. Lane lines and drop lines that read
-        // activePalette[s] per frame pick up automatically. Per-string
-        // fretboard materials built inside buildBoard() are independent
-        // and aren't reachable from here — buildBoard re-runs from the
-        // palette listener to regenerate them with the new colors.
-        //
-        // projMeshArr holds filled rim meshes (ExtrudeGeometry frame); centre
-        // is open. Palette + vibrancy mutate each mesh's material like mStr.
-        function _applyPaletteToMaterials() {
-            for (let s = 0; s < activePalette.length; s++) {
-                const c = activePalette[s];
-                if (mStr[s]) {
-                    // Gradient strings (0..5) keep a white base so the per-vertex
-                    // colours in gNoteGrad[s] show pure; only flat strings (6/7)
-                    // take the palette colour. mStr is MeshBasicMaterial (no
-                    // emissive) — guard the legacy emissive retint.
-                    if (s >= 6) mStr[s].color.setHex(c);
-                    if (mStr[s].emissive) mStr[s].emissive.setHex(c);
-                }
-                if (mGlow[s]) mGlow[s].emissive.setHex(c);
-                if (mSus[s]) mSus[s].color.setHex(c);
-                if (mStrHitOutline[s]) {
-                    mStrHitOutline[s].color.setHex(c);
-                    mStrHitOutline[s].emissive.setHex(c);
-                }
-                if (mAccentOutline[s]) {
-                    mAccentOutline[s].color.setHex(c);
-                    mAccentOutline[s].emissive.setHex(c);
-                }
-                if (mAccentCore[s]) mAccentCore[s].emissive.setHex(c);
-                // Verdict materials use fixed colours (0x22ff88 hit, 0xff0066 miss)
-                // that are independent of the string palette — no retint needed.
-                for (const haloArr of [mAccentHaloNear, mAccentHaloMid, mAccentHaloFar]) {
-                    if (haloArr[s]) haloArr[s].color.setHex(c);
-                }
-                if (projMeshArr && projMeshArr[s]) {
-                    for (const pm of projMeshArr[s]) {
-                        if (pm.material) {
-                            pm.material.color.setHex(c);
-                            pm.material.emissive.setHex(c);
-                        }
-                    }
-                }
-            }
-            // Per-string gem bodies (strings 0..5) are a baked per-vertex
-            // gradient (gNoteGrad), not a flat material — recolor them too so a
-            // custom palette reaches the note/sustain/vibrato gem bodies.
-            _recolorGemGradients();
-            // Re-apply vibrancy: mGlow's color is a lerp between white and
-            // the palette colour, so a palette swap must rebuild that
-            // lerp from the new endpoints. Skipped pre-init when mGlow
-            // isn't allocated yet — _applyVibrancy() guards on that.
-            _applyVibrancy();
-        }
-
-        // Recompute the per-vertex gem-gradient colors from the active palette.
-        // Built-in palettes (and unchanged slots of a custom palette) keep the
-        // hand-tuned DEFAULT_GEM_GRADIENTS stops so the stock look is preserved;
-        // a custom slot derives a top-highlight / bottom-shade from its base
-        // color. Mutates the existing 'color' attribute in place (no geometry
-        // churn, pooled note meshes pick it up next frame).
-        function _recolorGemGradients() {
-            if (!T || !gNoteGrad || !gNoteGrad.length) return;
-            const isCustom = (activePalette === _customPalette);
-            const topCol = new T.Color(), botCol = new T.Color(), tmp = new T.Color();
-            const halfH = NH / 2;
-            for (let s = 0; s < gNoteGrad.length; s++) {
-                const g = gNoteGrad[s];
-                if (!g || !g.attributes || !g.attributes.color) continue;
-                const base = activePalette[s];
-                let topHex, botHex;
-                if (isCustom && base !== PALETTES.default[s]) {
-                    // Match the SUBTLE stock gem shading (bottom ≈ 0.78 of a
-                    // near-base top), so a custom gem reads as a flat-ish gem
-                    // in the chosen color rather than a strong gradient.
-                    topHex = _lightenInt(base, 0.05);
-                    botHex = _darkenInt(base, 0.78);
-                } else {
-                    const stops = DEFAULT_GEM_GRADIENTS[s];
-                    if (!stops) continue; // strings 6/7 have no gradient geometry
-                    topHex = stops[0];
-                    botHex = stops[1];
-                }
-                topCol.setHex(topHex);
-                botCol.setHex(botHex);
-                const pos = g.attributes.position;
-                const colAttr = g.attributes.color;
-                for (let i = 0; i < pos.count; i++) {
-                    const t = (pos.getY(i) + halfH) / (2 * halfH); // 0 bottom..1 top
-                    tmp.copy(botCol).lerp(topCol, t);
-                    colAttr.setXYZ(i, tmp.r, tmp.g, tmp.b);
-                }
-                colAttr.needsUpdate = true;
-            }
-        }
-
-        // Vibrancy + glow live-update helpers. Both walk the same
-        // material set _applyPaletteToMaterials walks (plus the static
-        // outline / technique materials) and mutate uniform-backed
-        // properties — colour, opacity, emissiveIntensity. No
-        // material.needsUpdate flag is needed for these; Three.js
-        // re-reads them on the next render call. mGlow.emissiveIntensity
-        // and BASE_GLOW/MAX_GLOW/IDLE_OP are NOT written here — those
-        // are stomped per-frame inside updateStringHighlights() and the
-        // anticipation loop in update(), so they read glowMul /
-        // _vibrancyIdleOp / vibrancy directly each frame instead.
-        function _applyVibrancy() {
-            const t = vibrancy;
-            const idleOp     = 0.4  + 0.6  * t;  // mStr / IDLE_OP source
-            // projIdleOp drives the projMeshArr ghost-frame opacity and is
-            // read by drawNote() as `_vibrancyProjOp`, which layers a
-            // per-frame factor on top.
-            const projIdleOp = 0.15 + 0.35 * t;
-            const susOp      = 0.35 + 0.45 * t;  // mSus
-            const lineGlowOp = 0.15 + 0.35 * t;  // thin Line glow layer behind each string
-            for (let s = 0; s < activePalette.length; s++) {
-                if (mStr[s])  mStr[s].opacity  = idleOp;
-                if (mSus[s])  mSus[s].opacity  = susOp;
-                if (mGlow[s]) {
-                    // Hit-note body lerps from white (current pastel
-                    // look — colour comes through the emissive only)
-                    // toward the palette colour as vibrancy → 1, so at
-                    // vibrancy=1 the white-wash on hit notes goes away.
-                    if (!_paletteColorTmp && T) _paletteColorTmp = new T.Color();
-                    if (_paletteColorTmp) {
-                        mGlow[s].color.setHex(0xffffff).lerp(_paletteColorTmp.setHex(activePalette[s]), t);
-                    }
-                }
-                if (mAccentCore[s]) {
-                    if (!_paletteColorTmp && T) _paletteColorTmp = new T.Color();
-                    if (_paletteColorTmp) {
-                        mAccentCore[s].color.setHex(0xffffff).lerp(_paletteColorTmp.setHex(activePalette[s]), t);
-                    }
-                }
-                if (projMeshArr && projMeshArr[s]) {
-                    for (const pm of projMeshArr[s]) {
-                        if (pm.material) pm.material.opacity = projIdleOp;
-                    }
-                }
-            }
-            // stringLines[s].material.opacity is overwritten by
-            // updateStringHighlights() every frame, so the closed-form
-            // value would be stomped. updateStringHighlights() reads
-            // _vibrancyIdleOp directly instead — keep that in sync.
-            for (let s = 0; s < stringLineGlows.length; s++) {
-                const line = stringLineGlows[s];
-                if (line && line.material) line.material.opacity = lineGlowOp;
-            }
-            _vibrancyIdleOp = idleOp;
-            _vibrancyProjOp = projIdleOp;
-        }
-        function _applyGlow() {
-            const g = glowMul;
-            for (let s = 0; s < activePalette.length; s++) {
-                if (mStr[s])  mStr[s].emissiveIntensity  = 0.002 * g;
-                // mGlow[s].emissiveIntensity is per-frame in update();
-                // see Phase 4 comment block.
-                if (projMeshArr && projMeshArr[s]) {
-                    for (const pm of projMeshArr[s]) {
-                        if (pm.material) pm.material.emissiveIntensity = 0.002 * g;
-                    }
-                }
-                if (mStrHitOutline[s]) mStrHitOutline[s].emissiveIntensity = 1.0 * g;
-                if (mAccentOutline[s]) mAccentOutline[s].emissiveIntensity = ACCENT_RIM_BASE_EMISSIVE * g;
-                // mAccentCore[].emissiveIntensity is per-frame in update()
-                // alongside mGlow (accent fill boost).
-            }
-            if (mWhiteOutline) mWhiteOutline.emissiveIntensity = 0.6 * g;
-            if (mMissOutline)  mMissOutline.emissiveIntensity  = 1.2 * g;
-            for (let s = 0; s < mHitBright.length; s++) {
-                if (mHitBright[s]) mHitBright[s].emissiveIntensity = 4.0 * g;
-            }
-            if (mSusOutline)      mSusOutline.emissiveIntensity      = 0.3 * g;
-            if (mHitSusOutline)   mHitSusOutline.emissiveIntensity   = 0.7 * g;
-            if (mTapChevron)   mTapChevron.emissiveIntensity   = 0.9 * g;
-            if (mBarre)        mBarre.emissiveIntensity        = 0.9 * g;
-            for (let si = 0; si < activePalette.length; si++) {
-                if (mAccentHaloNear[si]) mAccentHaloNear[si].opacity = ACCENT_HALO_OP_NEAR * g;
-                if (mAccentHaloMid[si]) mAccentHaloMid[si].opacity = ACCENT_HALO_OP_MID * g;
-                if (mAccentHaloFar[si]) mAccentHaloFar[si].opacity = ACCENT_HALO_OP_FAR * g;
-            }
-        }
-        function _bgEffectiveStyleId() {
-            return _venueSceneOverride ? 'venue' : bgStyleId;
-        }
-        // The 'butterchurn' bg-style renders a WebGL MilkDrop canvas BEHIND a
-        // transparent highway via the self-contained _bc* controller (top of file),
-        // NOT a Three.js fog-scenery style (its scenery falls back to 'off'). Mount
-        // is idempotent and driven by the bg-style dropdown through _bgMountStyle.
-        function _bcActive() { return bgStyleId === 'butterchurn'; }
-        function _bcSyncMode() {
-            if (_bcActive()) {
-                // Recreate when there's no controller, or the last one died during
-                // async init (lib/WebGL failure) — a dead controller self-cleaned,
-                // so retry here instead of leaving the style permanently broken.
-                if ((!bcCtrl || (bcCtrl.dead && bcCtrl.dead())) && wrap) {
-                    if (bcCtrl) bcCtrl = null;
-                    // audioProvider reuses this instance's shared analyser (the
-                    // fog scenery's #audio / stems tap) so the browser path never
-                    // opens a second createMediaElementSource on #audio.
-                    try { bcCtrl = _bcCreateController(wrap, () => canvasSize(highwayCanvas), () => { try { return _bgGetAnalyser(); } catch (e) { return null; } }); }
-                    catch (e) { console.warn('[3D-Hwy] Butterchurn init failed', e); }
-                }
-                if (ren) ren.setClearColor(0x101820, 0); // transparent so the visualizer shows through
-            } else if (bcCtrl) {
-                try { bcCtrl.destroy(); } catch (e) {}
-                bcCtrl = null;
-                _applyBgTheme(); // restore the opaque themed clear
-            }
-        }
-        function _bgMountStyle() {
-            const effectiveId = _bgEffectiveStyleId();
-            const style = BG_STYLES[effectiveId] || BG_STYLES.off;
-            // Build into a fresh stage group so a partial throw can't
-            // orphan meshes inside bgGroup. On success the stage joins
-            // bgGroup atomically; on failure the stage and everything
-            // in it are disposed and bgState stays null.
-            const stage = new T.Group();
-            let result = null;
-            try {
-                result = style.build(stage, {
-                    intensity: bgIntensity,
-                    palette: activePalette,
-                    customImageDataUrl: bgCustomImageDataUrl,
-                    customVideoName: bgCustomVideoName,
-                    cam: cam,
-                }) || null;
-            } catch (e) {
-                console.error('[3D-Hwy] bg style build failed', effectiveId, e);
-                _bgDisposeGroupTree(stage);
-                bgState = null;
-                bgStage = null;
-                bgMountedStyleId = null;
-                return;
-            }
-            // renderOrder on a Group doesn't propagate to its children
-            // (Three.js sorts by per-object renderOrder, and a Group is a
-            // transform, not a rendered object). Stamp every mesh in the
-            // stage so transparent bg objects always sort behind notes
-            // regardless of their z relative to gameplay geometry.
-            stage.traverse((c) => { c.renderOrder = -1; });
-            bgGroup.add(stage);
-            bgStage = stage;
-            bgState = result;
-            bgMountedStyleId = effectiveId;
-            _bcSyncMode();
-        }
-        function _bgUnmountStyle() {
-            const mountedId = bgMountedStyleId || _bgEffectiveStyleId();
-            const style = BG_STYLES[mountedId] || BG_STYLES.off;
-            try { style.teardown(bgState); } catch (e) { console.error('[3D-Hwy] bg teardown', e); }
-            bgState = null;
-            // Belt + suspenders: even if a style's teardown forgets to
-            // dispose something, the stage tree dispose mops up.
-            if (bgStage) {
-                bgStage.parent?.remove(bgStage);
-                _bgDisposeGroupTree(bgStage);
-                bgStage = null;
-            }
-            bgMountedStyleId = null;
-        }
-        // Recursively dispose geometries / materials attached to an
-        // Object3D tree, then detach. Used as a safety net during
-        // _bgMountStyle failures and on _bgUnmountStyle.
-        //
-        // Deliberately does NOT dispose material.map textures — texture
-        // lifetime belongs to whoever allocated the texture. The
-        // silhouettes style allocates a per-layer CanvasTexture wrapping
-        // the shared _silCanvas bitmap, and disposes those textures in
-        // its own teardown. Disposing them here would double-dispose,
-        // and any future plugin texture sharing across panels (e.g. an
-        // upcoming custom-background feature) would break the same way.
-        // Style teardown owns texture release.
-        function _bgDisposeGroupTree(obj) {
-            if (!obj) return;
-            obj.traverse((child) => {
-                child.geometry?.dispose?.();
-                const mat = child.material;
-                if (mat) {
-                    const mats = Array.isArray(mat) ? mat : [mat];
-                    for (const m of mats) m?.dispose?.();
-                }
-            });
-            obj.parent?.remove(obj);
-        }
-        function _bgRebuild() {
-            if (!bgGroup) return;
-            // Order matters: teardown must run against the (style id,
-            // state) pair that built the meshes, so unmount BEFORE
-            // reloading settings. Reload, then mount with the new id.
-            _bgUnmountStyle();
-            _bgLoadSettings();
-            _bgMountStyle();
-            _bgApplyVenueSceneFog(_venueSceneOverride);
-            // Reset dt accounting so the first frame after a switch
-            // doesn't see a huge "since last update" window — that
-            // would clamp to 0.1 and visibly snap motion / rotation.
-            _bgLastT = 0;
-        }
-        // Venue-only fog/clear/ambient tuning — darker near field, less
-        // washed-out gray haze over the playable highway. Restored when
-        // venue deactivates.
-        function _bgApplyVenueSceneFog(active) {
-            if (!scene || !scene.fog) return;
-            if (active) {
-                scene.fog.color.setHex(0x080c12);
-                scene.fog.near = FOG_START * 0.98;
-                scene.fog.far = FOG_END * 0.98;
-                // Keep the clear transparent while Butterchurn is active so the
-                // venue scene doesn't occlude the visualizer behind the highway.
-                if (ren) ren.setClearColor(0x080c12, _bcActive() ? 0 : 1);
-                if (ambLight) ambLight.intensity = 0.68;
-            } else {
-                // Restore the user's scene-color theme (clear + fog) rather than
-                // the old hardcoded gray, so deactivating venue doesn't wipe a
-                // chosen background theme. _applyBgTheme reads the current theme.
-                scene.fog.near = FOG_START * 0.8;
-                scene.fog.far = FOG_END * 1.2;
-                if (ambLight) ambLight.intensity = 0.85;
-                _applyBgTheme();
-            }
-        }
-
-        // Apply BOTH scene-color axes, each from its own setting key:
-        //   • BACKGROUND (bgThemeId): the WebGL clear color + the distance-fog
-        //     tint. Skipped while the venue scene is active (venue owns those —
-        //     see _bgApplyVenueSceneFog).
-        //   • HIGHWAY (hwThemeId): the fretboard/highway-surface plane + the lit
-        //     highway lane strip (the bright quad under the gems) + its dimmer
-        //     alternating row. Always themed; venue doesn't touch them.
-        // The two axes are independent, so picking a different id in each mixes
-        // freely. Safe to call any time; called from initScene, buildBoard, and
-        // the scene-theme listener (so a live switch of EITHER dropdown retints
-        // only its half immediately).
-        //
-        // The lane fields are OPTIONAL on a highway theme: one that omits `lane`
-        // / `laneDim` falls back to the stock lit/dim lane hexes, so every
-        // existing/neutral highway theme stays byte-identical (default blue lane
-        // unchanged). Only colored highway themes opt into a coordinated lane.
-        function _applyBgTheme() {
-            // --- Background axis: clear + fog ---
-            const bg = _bgBackgroundColors(bgThemeId);
-            if (!_venueSceneOverride) {
-                if (scene && scene.fog) scene.fog.color.setHex(bg.fog);
-                if (ren) ren.setClearColor(bg.clear, _bcActive() ? 0 : 1);
-            }
-            // --- Highway axis: board plane + lane ---
-            const hw = _bgHighwayColors(hwThemeId);
-            if (_boardPlaneMat) _boardPlaneMat.color.setHex(hw.board);
-            // Lit lane strip + its dimmer alternating row. Fall back to the
-            // hardcoded stock lane colors when the highway theme omits them.
-            const laneLit = (typeof hw.lane === 'number') ? hw.lane : HWY_LANE_STRIPE_ODD_HEX;
-            const laneDim = (typeof hw.laneDim === 'number') ? hw.laneDim : HWY_LANE_STRIPE_EVEN_HEX;
-            if (mLaneOdd) mLaneOdd.color.setHex(laneLit);
-            if (mLaneEven) mLaneEven.color.setHex(laneDim);
-            // Keep the (otherwise vestigial) lane target color in sync with the
-            // lit lane so any future lane-blend consumer reads the themed value.
-            if (_laneTargetColor) _laneTargetColor.setHex(laneLit);
-            else _laneTargetColor = new T.Color(laneLit);
-        }
-
-        /* ── Fretboard (static geometry) ────────────────────────────────── */
-        function _h3dHexOrDefault(hexStr, defHex) {
-            const d = defHex || BG_DEFAULTS.nutColor;
-            const s = (typeof hexStr === 'string' && /^#[0-9a-fA-F]{6}$/.test(hexStr.trim()))
-                ? hexStr.trim().toLowerCase()
-                : d;
-            return parseInt(s.slice(1), 16);
-        }
-        // Cinematic lighting (#2): darken ambient so emissive gems have a dark
-        // surround to pop against; strengthen the key light for modelling.
-        // Toggle via the 'cinematic' setting so it's directly comparable.
-        function _applyCinematic() {
-            if (!ambLight || !dirLight) return;
-            ambLight.intensity = _cinematic ? 0.45 : 0.85;
-            dirLight.intensity = _cinematic ? 1.15 : 0.8;
-        }
-        // #5 early/late: tint the hit feedback by timing — on-time green, early cyan,
-        // late amber. Falls back to green when timing is unknown (pure-provider path).
-        function _timingHex(ts) {
-            if (!_timingFx || !ts || ts === 'OK') return 0x22ff88;
-            if (ts === 'EARLY') return 0x35d6ff;
-            if (ts === 'LATE')  return 0xffb84d;
-            return 0x22ff88;
-        }
-        function _sparkBurst(x, y, z, hex, count) {
-            if (!_sparkPts || count <= 0) return;
-            const r = ((hex >> 16) & 255) / 255, g = ((hex >> 8) & 255) / 255, b = (hex & 255) / 255;
-            let made = 0;
-            for (let i = 0; i < _SPARK_N && made < count; i++) {
-                if (_sparkLife[i] > 0) continue;
-                const j = i * 3, ang = Math.random() * Math.PI * 2, sp = (5 + Math.random() * 12) * K;
-                _sparkPos[j] = x; _sparkPos[j + 1] = y; _sparkPos[j + 2] = z;
-                _sparkVel[j] = Math.cos(ang) * sp; _sparkVel[j + 1] = (12 + Math.random() * 24) * K; _sparkVel[j + 2] = Math.sin(ang) * sp * 0.55;
-                _sparkCol[j] = r; _sparkCol[j + 1] = g; _sparkCol[j + 2] = b;
-                _sparkLife[i] = 0.30 + Math.random() * 0.16; made++;
-            }
-        }
-        function _sparkUpdate(dt) {
-            if (!_sparkPts) return;
-            const grav = 55 * K; let any = false;
-            for (let i = 0; i < _SPARK_N; i++) {
-                if (_sparkLife[i] <= 0) continue;
-                const j = i * 3;
-                _sparkLife[i] -= dt;
-                if (_sparkLife[i] <= 0) { _sparkCol[j] = _sparkCol[j + 1] = _sparkCol[j + 2] = 0; continue; }
-                any = true;
-                _sparkVel[j + 1] -= grav * dt;
-                _sparkPos[j] += _sparkVel[j] * dt; _sparkPos[j + 1] += _sparkVel[j + 1] * dt; _sparkPos[j + 2] += _sparkVel[j + 2] * dt;
-                const fade = 1 - Math.min(1, dt * 3.2);
-                _sparkCol[j] *= fade; _sparkCol[j + 1] *= fade; _sparkCol[j + 2] *= fade;
-            }
-            _sparkPts.geometry.attributes.position.needsUpdate = true;
-            _sparkPts.geometry.attributes.color.needsUpdate = true;
-            _sparkPts.visible = any;
-        }
-        // #4 Bloom: lazy-load the vendored postprocessing addons and build an
-        // EffectComposer (RenderPass -> UnrealBloomPass -> OutputPass/ACES). Returns
-        // the composer once ready, or null (caller falls back to a direct render).
-        function _bloomEnsure() {
-            if (_composer) return _composer;
-            if (_bloomLoad || !ren || !scene || !cam) return null;
-            const A = '/static/vendor/three/addons/';
-            _bloomLoad = Promise.all([
-                import(A + 'postprocessing/EffectComposer.js'),
-                import(A + 'postprocessing/RenderPass.js'),
-                import(A + 'postprocessing/UnrealBloomPass.js'),
-                import(A + 'postprocessing/OutputPass.js'),
-            ]).then(([EC, RP, UB, OP]) => {
-                try {
-                    const sz = canvasSize(highwayCanvas) || { w: 1280, h: 720 };
-                    const w = Math.max(2, sz.w | 0), h = Math.max(2, sz.h | 0);
-                    // Multisampled (WebGL2 MSAA) HalfFloat target so anti-aliasing
-                    // survives the bloom path — EffectComposer's default target has no
-                    // `samples`, which is why bloom-on looked jagged (worst on non-Retina
-                    // DPR1 displays that have no supersampling cushion).
-                    const _bloomRT = new T.WebGLRenderTarget(w, h, { type: T.HalfFloatType, samples: 4 });
-                    const comp = new EC.EffectComposer(ren, _bloomRT);
-                    comp.addPass(new RP.RenderPass(scene, cam));
-                    _bloomPass = new UB.UnrealBloomPass(new T.Vector2(w, h), 0.65, 0.5, 0.82); // strength, radius, threshold (high → only emissive blooms)
-                    comp.addPass(_bloomPass);
-                    comp.addPass(new OP.OutputPass());
-                    comp.setSize(w, h);
-                    _bloomW = w; _bloomH = h; _composer = comp;
-                } catch (e) { console.warn('[3D-Hwy] bloom init failed', e); _composer = null; }
-            }).catch((e) => console.warn('[3D-Hwy] bloom modules failed', e));
-            return null;
-        }
-        function buildBoard() {
-            // Dispose before clearing (traverse: nut/headstock may live in a Group).
-            while (fretG.children.length) {
-                const child = fretG.children[0];
-                child.traverse((o) => {
-                    if (o instanceof T.Sprite) return;
-                    // fretTubeGeo is shared across all fret meshes — disposing it
-                    // per-mesh here would fire one redundant dispose event per
-                    // fret. Skip it; it's disposed exactly once below.
-                    if (o.geometry !== fretTubeGeo) o.geometry?.dispose?.();
-                    const mat = o.material;
-                    if (mat) {
-                        const mats = Array.isArray(mat) ? mat : [mat];
-                        for (const m of mats) m?.dispose?.();
-                    }
-                });
-                fretG.remove(child);
-            }
-            stringLines = [];
-            stringLineGlows = [];
-            // Fret wire materials were already disposed by the child.traverse()
-            // above (each is attached 1:1 to a fret mesh) — just clear the
-            // tracking array. The shared fretTubeGeo was skipped by that
-            // traverse, so dispose it exactly once here.
-            fretWireMats = [];
-            fretTubeGeo?.dispose?.();
-            fretTubeGeo = null;
-
-            const board = boardSpanX();
-            const bw = board.width + 4 * K;
-
-            // Fretboard plane — spans exactly from hit line (Z=0) to the note
-            // spawn horizon (-AHEAD * TS), so the far edge aligns with AHEAD.
-            const blAhead = TS * AHEAD;
-            const pg = new T.PlaneGeometry(bw, blAhead);
-            // Board (highway-surface) color comes from the active HIGHWAY scene
-            // theme (default theme = the original 0x08080e). Kept on
-            // _boardPlaneMat so _applyBgTheme can recolor it live without
-            // rebuilding the board.
-            const pm = new T.MeshLambertMaterial({ color: _bgHighwayColors(hwThemeId).board, transparent: true, opacity: 0.6 });
-            _boardPlaneMat = pm;
-            const p = new T.Mesh(pg, pm);
-            p.rotation.x = -Math.PI / 2;
-            p.position.set(board.center, S_BASE - NH / 2 - 2 * K, -blAhead / 2);
-            fretG.add(p);
-
-            // Thin Line strings (glow layer). Retained in stringLineGlows[]
-            // so vibrancy slider changes can mutate opacity in place
-            // without rebuilding the board geometry.
-            // Nut lateral layout (matches headstock block below): playing strings start at the
-            // fretboard-facing edge so they never project through nut/headstock.
-            const mir = _leftyCached ? -1 : 1;
-            const nutLenX = 1.55 * K;
-            const nutXC = -0.78 * K * mir;
-            const xHeadLeft = -6.85 * K * mir;
-            const nutRearX = nutXC - nutLenX * 0.5;
-            const nutFrontX = nutXC + nutLenX * 0.5;
-            const nutJoinX = nutFrontX + 0.03 * K;
-            const bridgeTipX = xFret(NFRETS) + 2 * K * mir;
-            boardStringStartX = Math.min(nutJoinX, bridgeTipX);
-            boardTuningLabelX = (nutRearX + xHeadLeft) * 0.5 - 0.15 * K * mir;
-            const stringEndX = Math.max(nutJoinX, bridgeTipX);
-            const strSpan = Math.max(stringEndX - boardStringStartX, 1.5 * K);
-
-            const lineGlowOp = 0.15 + 0.35 * vibrancy;
-            for (let s = 0; s < nStr; s++) {
-                const pts = [new T.Vector3(boardStringStartX, sY(s), 0), new T.Vector3(stringEndX, sY(s), 0)];
-                const g = new T.BufferGeometry().setFromPoints(pts);
-                const line = new T.Line(g, new T.LineBasicMaterial({ color: activePalette[s], transparent: true, opacity: lineGlowOp }));
-                line.renderOrder = 7; // above sus rails (4/5), below chord fill (10)
-                fretG.add(line);
-                stringLineGlows.push(line);
-            }
-
-            // BoxGeometry strings — emissive glow driven by updateStringHighlights()
-            for (let s = 0; s < nStr; s++) {
-                const g = new T.BoxGeometry(strSpan, STR_THICK, STR_THICK);
-                // Each string gets its own material instance so emissiveIntensity is per-string
-                // (and per-frame opacity is set by updateStringHighlights via _vibrancyIdleOp)
-                const mat = new T.MeshStandardMaterial({
-                    color: activePalette[s], emissive: activePalette[s],
-                    emissiveIntensity: 0.002,
-                    transparent: true, opacity: _vibrancyIdleOp, roughness: 1,
-                });
-                const mesh = new T.Mesh(g, mat);
-                mesh.renderOrder = renderOrderForLayerAtZ(0, 'BOARD_STRING');
-                mesh.position.set(boardStringStartX + strSpan * 0.5, sY(s), 0);
-                fretG.add(mesh);
-                stringLines.push(mesh);
-            }
-
-            // Guitar nut + headstock — grouped so visibility + colors are user-tunable.
-            {
-                nutHeadstockGroup = new T.Group();
-                const yTopN = Math.max(sY(0), sY(nStr - 1));
-                const yBottomN = Math.min(sY(0), sY(nStr - 1));
-                const yMidN = (yTopN + yBottomN) / 2;
-                const spanY = Math.abs(yTopN - yBottomN) + S_GAP * 1.05;
-
-                const nutD = 0.95 * K;
-                const nutZc = -0.62 * K;
-                const nutH = spanY * 1.06;
-                const nutHalfH = nutH * 0.5;
-
-                const zBack = -1.38 * K;
-                const zJoint = -0.58 * K;
-
-                const nutInt = _h3dHexOrDefault(nutColor, BG_DEFAULTS.nutColor);
-                const hsInt = _h3dHexOrDefault(headstockColor, BG_DEFAULTS.headstockColor);
-                const nutBase = new T.Color(nutInt);
-                const nutHi = nutBase.clone().lerp(new T.Color(0xffffff), 0.14);
-                const nutGro = nutBase.clone().multiplyScalar(0.72);
-                const hsBase = new T.Color(hsInt);
-                const hsDarkC = hsBase.clone().multiplyScalar(0.76);
-
-                const mapleMat = new T.MeshStandardMaterial({
-                    color: hsBase, roughness: 0.55, metalness: 0.02,
-                });
-                const mapleDark = new T.MeshStandardMaterial({
-                    color: hsDarkC, roughness: 0.62, metalness: 0.02,
-                });
-
-                const coreLen = Math.max(Math.abs(nutRearX - xHeadLeft), 2 * K);
-                const coreCX = (nutRearX + xHeadLeft) * 0.5;
-                const headCoreD = 1.05 * K;
-                const headCore = new T.Mesh(
-                    new T.BoxGeometry(coreLen, spanY * 1.12, headCoreD),
-                    mapleDark,
-                );
-                headCore.position.set(coreCX, yMidN, zBack - headCoreD * 0.35);
-                nutHeadstockGroup.add(headCore);
-
-                const xs = 14;
-                const ys = 12;
-                const yLo = yMidN - spanY * 0.58;
-                const yHi = yMidN + spanY * 0.58;
-                const posR = new Float32Array((xs + 1) * (ys + 1) * 3);
-                const idxR = [];
-                let ri = 0;
-                for (let j = 0; j <= ys; j++) {
-                    const v = j / ys;
-                    const wy = yLo + v * (yHi - yLo);
-                    const yArc = 1 - Math.abs((wy - yMidN) / (spanY * 0.55 + 1e-6));
-                    const yArcCl = Math.max(0, Math.min(1, yArc));
-                    for (let i = 0; i <= xs; i++) {
-                        const u = i / xs;
-                        const wx = xHeadLeft + u * (nutRearX - xHeadLeft);
-                        const smooth = Math.sin(u * Math.PI * 0.5);
-                        let wz = zBack + (zJoint - zBack) * smooth;
-                        wz += 0.14 * K * yArcCl * yArcCl;
-                        posR[ri++] = wx;
-                        posR[ri++] = wy;
-                        posR[ri++] = wz;
-                    }
-                }
-                const row = xs + 1;
-                for (let j = 0; j < ys; j++) {
-                    for (let i = 0; i < xs; i++) {
-                        const a = j * row + i;
-                        const b = a + row;
-                        idxR.push(a, b, a + 1, b, b + 1, a + 1);
-                    }
-                }
-                const rampGeo = new T.BufferGeometry();
-                rampGeo.setAttribute('position', new T.BufferAttribute(posR, 3));
-                rampGeo.setIndex(idxR);
-                rampGeo.computeVertexNormals();
-                nutHeadstockGroup.add(new T.Mesh(rampGeo, mapleMat));
-
-                const boneMat = new T.MeshStandardMaterial({
-                    color: nutBase, roughness: 0.38, metalness: 0.02,
-                });
-                const boneTop = new T.MeshStandardMaterial({
-                    color: nutHi, roughness: 0.32, metalness: 0.02,
-                });
-                const grooveMat = new T.MeshStandardMaterial({
-                    color: nutGro, roughness: 0.85, metalness: 0,
-                });
-
-                const nutBody = new T.Mesh(
-                    new T.BoxGeometry(nutLenX, nutH, nutD),
-                    boneMat,
-                );
-                nutBody.position.set(nutXC, yMidN, nutZc);
-                nutHeadstockGroup.add(nutBody);
-
-                const crownR = nutLenX * 0.52;
-                const crownSeg = new T.CylinderGeometry(
-                    crownR, crownR, nutLenX * 0.92, 20, 1, true,
-                    Math.PI * 0.08, Math.PI * 0.42,
-                );
-                const crown = new T.Mesh(crownSeg, boneTop);
-                crown.rotation.z = Math.PI * 0.5;
-                crown.position.set(
-                    nutXC,
-                    yMidN + nutHalfH - 0.02 * K,
-                    nutZc + nutD * 0.22,
-                );
-                nutHeadstockGroup.add(crown);
-
-                const slotDrop = 0.11 * K;
-                const slotHalfW = STR_THICK * 1.15;
-                const slotZ = nutZc + nutD * 0.12;
-                for (let st = 0; st < nStr; st++) {
-                    const gr = new T.Mesh(
-                        new T.BoxGeometry(slotHalfW * 2, slotDrop, nutD * 0.42),
-                        grooveMat,
-                    );
-                    gr.position.set(nutXC, sY(st), slotZ);
-                    nutHeadstockGroup.add(gr);
-                }
-                nutHeadstockGroup.visible = nutHeadstockVisible;
-                fretG.add(nutHeadstockGroup);
-            }
-
-            // Fret wires — bowed metal TubeGeometry (backported from
-            // highway_babylon). Board-string and fret-wire layers live in
-            // RENDER_ORDER_LAYER_STACK so the fretboard draws above note
-            // symbols and below fret labels.
-            // Tube (not T.Line): WebGL ignores linewidth > 1px on almost all
-            // platforms, so Line objects always render as hairlines. The tube
-            // bows in Z (middle strings pushed away from camera) so the row of
-            // frets reads as wrapping a cylindrical neck — see FRET_BOW_DZ.
-            // MeshStandardMaterial (vs the old flat MeshBasic): the scene's
-            // ambient+directional light glints across the rounded surface for a
-            // polished-steel look; the per-frame gold albedo (in-anchor) then
-            // reads as brass. depthTest:false: string BoxGeometry (MeshStandard,
-            // depthWrite:true) writes depth at Z=+STR_THICK/2; wires near Z=0
-            // would fail the depth test at string pixels despite higher layer.
-            // Colors are updated each frame by the fretWireMats loop in update(),
-            // which drives every wire to one of two tiers: FRET_WIRE_IDLE_* by
-            // default, FRET_WIRE_ACTIVE_* inside the anchor lane. The material is
-            // created at the idle tier so frame 0 (before update() first runs)
-            // already matches.
-            const yTop = Math.max(sY(0), sY(nStr - 1));
-            const yBottom = Math.min(sY(0), sY(nStr - 1));
-            const wireH = (yTop + S_GAP * 0.3) - (yBottom - S_GAP * 0.3);
-            const wireMidY = (yTop + yBottom) / 2;
-            // Single shared geometry centered at x=0, local Y -half..+half,
-            // bowed in Z by FRET_BOW_DZ * [0,0.6,1,0.6,0]. Reused by every fret
-            // (only mesh position differs). Symmetric in Y → invert/lefty-safe.
-            const yHalf = wireH * 0.5;
-            const zMults = [0, 0.6, 1, 0.6, 0];
-            const tubePath = zMults.map((zm, i) => new T.Vector3(
-                0,
-                -yHalf + (wireH * i) / (zMults.length - 1),
-                FRET_BOW_DZ * zm,
-            ));
-            const tubeCurve = new T.CatmullRomCurve3(tubePath);
-            fretTubeGeo = new T.TubeGeometry(
-                tubeCurve, FRET_TUBE_SEG, FRET_TUBE_RADIUS, FRET_TUBE_RADIAL, false,
-            );
-            for (let f = 0; f <= NFRETS; f++) {
-                const x = xFret(f);
-                const mat = new T.MeshStandardMaterial({
-                    color: FRET_WIRE_IDLE_HEX, metalness: FRET_METALNESS, roughness: FRET_ROUGHNESS,
-                    emissive: FRET_EMISSIVE,
-                    // depthWrite:false (matches other transparent overlays here):
-                    // a transparent fret must not write depth or it can occlude
-                    // later-drawn transparent elements despite depthTest:false.
-                    transparent: true, opacity: FRET_WIRE_IDLE_OP, depthTest: false, depthWrite: false,
-                });
-                const fw = new T.Mesh(fretTubeGeo, mat);
-                fw.position.set(x, wireMidY, 0);
-                fw.renderOrder = renderOrderForLayerAtZ(0, 'BOARD_FRET_WIRE');
-                fretG.add(fw);
-                fretWireMats[f] = mat;
-            }
-
-            // Fret dots — flat circles (CircleGeometry) lying in the XY plane and
-            // facing +Z so they always appear as perfect circles from the camera.
-            // depthWrite:false so they don't steal the depth buffer from the
-            // transparent string meshes. Slight negative Z recessed under the
-            // string plane. Radius 10% below the former 1.5*K dots.
-            const dotRZ = (1.5 * K * 0.9);
-            const dg = new T.CircleGeometry(dotRZ, 64);
-            const dm = new T.MeshBasicMaterial({
-                color: 0x556677,
-                transparent: true,
-                opacity: 1,
-                depthWrite: false,
-            });
-            const dotZBack = -STR_THICK * 0.85;
-            const my = (sY(0) + sY(nStr - 1)) / 2;
-            const addDot = (x, y) => {
-                const d = new T.Mesh(dg, dm);
-                d.position.set(x, y, dotZBack);
-                // Above the dynamic lane (1) and its dividers (2) so the
-                // translucent blue lane no longer paints over and hides the
-                // inlay; still well below strings / wires / notes,
-                // so those keep drawing on top of the inlay.
-                d.renderOrder = 3;
-                fretG.add(d);
-            };
-            for (const f of DOTS) {
-                const cx = xFretMid(f);
-                if (DDOTS.has(f)) {
-                    addDot(cx, my - S_GAP * 0.7);
-                    addDot(cx, my + S_GAP * 0.7);
-                } else {
-                    addDot(cx, my);
-                }
-            }
-
-            // Fret inlay number labels — sprites sitting just behind the hit line
-            // (Z = -K) so camera-distance sorting in the transparent pass puts
-            // them before notes at Z = 0, letting notes paint on top.
-            // Materials are cloned from the txtMat cache with depthWrite:false so
-            // the sprites don't write stale depth values that would clip incoming
-            // notes (which arrive from large negative Z). Clones are tracked in
-            // _inlayMats for explicit disposal on rebuild and destroy().
-            // Scale uses (0.5 + textSize) directly — _textSizeMul is stale here
-            // (only refreshed at the top of update()); update() rescales live.
-            for (const m of _inlayMats) m.dispose();
-            _inlayMats = [];
-            _inlayLabels = [];
-            for (const f of INLAY_LABEL_FRETS) {
-                const mat = txtMat(f, '#7abfcc', false, 'fretRow').clone();
-                mat.depthWrite = false;
-                mat.opacity = 0.55;
-                const lbl = new T.Sprite(mat);
-                const scale = 5.5 * (0.5 + textSize) * fretLabelScaleForFret(f);
-                lbl.scale.set(scale * K, scale * K, 1);
-                lbl.position.set(xFretMid(f), yTop - S_GAP * 0.4, -K);
-                lbl.visible = inlayLabelsVisible;
-                fretG.add(lbl);
-                _inlayLabels.push(lbl);
-                _inlayMats.push(mat);
-            }
-        }
-
-        /* ── String glow (called each frame) ────────────────────────────── */
-        function updateStringHighlights(noteState) {
-            // Glow slider scales both the idle floor and anticipation peak,
-            // so glowMul=0 fully silences the per-string emissive pulse.
-            // Vibrancy controls the idle opacity floor — anticipation
-            // still rides on top regardless of vibrancy so play-feedback
-            // through the opacity channel survives even at glowMul=0.
-            //
-            // Folded with the post-noteState mGlow / mAccentCore writes
-            // (was a separate `for (s = 0; s < nStr)` loop in update()),
-            // so the per-string scratch arrays stay hot in L1 across all
-            // material writes for a given string.
-            const BASE_GLOW = 0.02 * glowMul;
-            const MAX_GLOW  = 3.5  * glowMul;
-            const IDLE_OP   = _vibrancyIdleOp;
-            const g = glowMul;
-            const venueGemMul = _venueSceneOverride ? VENUE_GEM_EMISSIVE_MUL : 1;
-
-            for (let s = 0; s < nStr; s++) {
-                const mesh = stringLines[s];
-                if (mesh) {
-                    const intensity = Math.max(
-                        noteState.stringSustain[s] ? 1 : 0,
-                        noteState.stringAnticipation[s] || 0,
-                    );
-                    mesh.material.emissiveIntensity = BASE_GLOW + intensity * MAX_GLOW;
-                    mesh.material.opacity = IDLE_OP + intensity * (1 - IDLE_OP);
-                    mesh.scale.set(1, 1 + intensity * 0.3, 1 + intensity * 0.3);
-                }
-                // Hit-note emissive — same write pattern as the standalone
-                // loop that previously lived at update()'s post-call site.
-                // The glow slider scales it here since this assignment
-                // stomps anything _applyGlow() set statically.
-                const bg = noteState.strGlow[s] * g;
-                if (mGlow[s]) mGlow[s].emissiveIntensity = bg * venueGemMul;
-                if (mAccentCore[s]) {
-                    mAccentCore[s].emissiveIntensity =
-                        (bg + noteState.accentFillBoost[s] * g) * venueGemMul;
-                }
-            }
-        }
-
-        /* ── Lookahead fret bounds + smooth camera ───────────────────────── */
-        // End time of the lookahead window = start of the measure that is
-        // CAM_LOOKAHEAD_MEASURES measures ahead of the current one. Uses the
-        // _measureStarts cache (times of beats with measure !== -1). With no
-        // beats it falls back to CAM_LOOKAHEAD_SEC seconds. Past the last known
-        // measure it extrapolates using the average measure duration.
-        function lookaheadEndTime(now) {
-            const ms = _measureStarts;
-            if (!ms || ms.length === 0) return now + CAM_LOOKAHEAD_SEC;
-            // Binary search: lo = first index with ms[lo] > now.
-            let lo = 0, hi = ms.length;
-            while (lo < hi) { const mid = (lo + hi) >> 1; if (ms[mid] <= now) lo = mid + 1; else hi = mid; }
-            const curIdx = lo - 1;                       // current measure (-1 if before the first)
-            const targetIdx = curIdx + CAM_LOOKAHEAD_MEASURES;
-            if (targetIdx >= 0 && targetIdx < ms.length) return ms[targetIdx];
-            // Past the last measure: extrapolate using the average measure duration.
-            if (ms.length >= 2) {
-                const avg = (ms[ms.length - 1] - ms[0]) / (ms.length - 1);
-                if (avg > 0) return ms[ms.length - 1] + (targetIdx - (ms.length - 1)) * avg;
-            }
-            return now + CAM_LOOKAHEAD_SEC;
-        }
-
-        function lookaheadComputeFretBounds(now, anchors, notes, chords) {
-            const tEnd = lookaheadEndTime(now);
-            let minF = 99;
-            let maxF = 0;
-            let any = false;
-            if (anchors && anchors.length) {
-                for (let tt = now; tt <= tEnd + 1e-9; tt += 0.125) {
-                    const a = getChartAnchorAt(anchors, tt);
-                    if (!a) continue;
-                    let fStart = Math.round(Number(a.fret));
-                    if (!Number.isFinite(fStart) || fStart < 1) fStart = 1;
-                    let w = Number(a.width);
-                    if (!Number.isFinite(w)) w = 4;
-                    w = Math.max(1, Math.round(w));
-                    const fHi = Math.min(NFRETS, fStart + w - 1);
-                    minF = Math.min(minF, fStart);
-                    maxF = Math.max(maxF, fHi);
-                    any = true;
-                }
-            }
-            const consider = f => {
-                if (!(f > 0)) return;
-                minF = Math.min(minF, f);
-                maxF = Math.max(maxF, f);
-                any = true;
-            };
-            if (notes) {
-                let i = lowerBoundT(notes, now);
-                for (; i < notes.length; i++) {
-                    const n = notes[i];
-                    if (n.t > tEnd) break;
-                    if (!validString(n.s)) continue;
-                    consider(n.f);
-                }
-            }
-            if (chords) {
-                let i = lowerBoundT(chords, now);
-                for (; i < chords.length; i++) {
-                    const ch = chords[i];
-                    if (ch.t > tEnd) break;
-                    if (!ch.notes) continue;
-                    for (const cn of ch.notes) {
-                        if (!validString(cn.s)) continue;
-                        consider(cn.f);
-                    }
-                }
-            }
-            if (!any || minF > maxF) return null;
-            return { minF, maxF };
-        }
-
-        function lookaheadTargetWorldX(minF, maxF) {
-            const wb = CAM_FRET_EDGE_BLEND;
-            const middle = (xFretMid(minF) + xFretMid(maxF)) * 0.5;
-            const weighted = 0.6 * xFret(0) + 0.4 * xFret(NFRETS);
-            return middle * (1 - wb) + weighted * wb;
-        }
-
-        function lookaheadSmoothCamStep(dtSec, tgtXWorld, tgtSpanInt) {
-            const d = Math.min(0.2, Math.max(1e-4, dtSec));
-            const fs = 1 - Math.pow(1 - CAM_FOCUS_BLEND_RATE, d);
-            _lookaheadCamX = tgtXWorld * fs + _lookaheadCamX * (1 - fs);
-            _lookaheadFretSpan = tgtSpanInt * fs + _lookaheadFretSpan * (1 - fs);
-        }
-
-        /* ── Camera target helper ────────────────────────────────────────── */
-        // Compute and apply tgtX + tgtDist from note-window-accumulated data.
-        // Used by BOTH the snap pre-pass (before drawNote() calls, skipDistHyst=true)
-        // and the main per-frame camera-target block (skipDistHyst=false) so the
-        // two paths can never drift out of sync.
-        //
-        // wX/wSum        recency-weighted fret-position centroid accumulator
-        // distMin/Max    min/max fret seen in the camera targeting window
-        // distGot        true iff at least one fretted note was in the window
-        // camHystF       X-axis hysteresis factor (from cameraSmoothing)
-        // camDistHystF   dist hysteresis factor (from zoomSmoothing)
-        // skipDistHyst   true on the snap/first-data frame — no previous tgtDist
-        //                state exists, so bypass the dead-zone gate
-        //
-        // Side-effects: updates tgtX, tgtDist, prevLowFretBonus.
-        // Returns: computed lockActive flag (caller is responsible for setting
-        //          prevLockActive from the returned value).
-        function _applyNoteCamTargets(wX, wSum, distMin, distMax, distGot,
-                                      camHystF, camDistHystF, skipDistHyst) {
-            const lockActive = cameraLockLow && (!distGot || distMax <= 12);
-            if (lockActive) {
-                // Locked view: frets 0-12 fit in frame, with the peak
-                // low-fret bonus baked in so nut chords stay framed.
-                // Both halves derive from the same helpers as the
-                // dynamic branch so future tuning of the base zoom
-                // curve or low-fret pullback can't desync them.
-                const lockedBaseU  = camBaseDistU(12);
-                const lockedBonusU = camLowFretPullbackU(1);
-                // cameraLockZoom slider 0..1 blends between MIN (closest)
-                // and MAX (furthest). Default 0.5 maps to ~1.0× so existing
-                // users see the same locked view as before this slider.
-                const lockZoomMul  = CAM_LOCK_ZOOM_MIN +
-                    (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
-                tgtX             = xFretMid(CAM_LOCK_CENTER_FRET);
-                tgtDist          = (lockedBaseU + lockedBonusU) * K * lockZoomMul;
-                prevLowFretBonus = lockedBonusU;
-            } else if (distGot) {
-                // Base zoom scales by fret count (distMax - distMin).
-                const baseDistU     = camBaseDistU(distMax - distMin);
-                // Low-fret pullback: world-X distance between frets is
-                // logarithmic, so a 2-fret span at the nut takes much
-                // more horizontal screen than the same span at fret 12.
-                // The base term scales by *fret count*, not world-X
-                // span, so low-fret clusters were under-allotted camera
-                // distance and clipped at the left edge (e.g. F power
-                // chord at fret 1 partially off-screen). Add a tapered
-                // bonus that kicks in below fret 5 and peaks at fret 1
-                // (≈16 extra fret-span units, i.e. 16*K world-units of
-                // distance), without affecting mid/high neck framing.
-                const lowFretBonusU = camLowFretPullbackU(distMin);
-                if (skipDistHyst) {
-                    // First data frame — no previous tgtDist state; apply
-                    // directly without the hysteresis dead-zone check.
-                    tgtDist = (baseDistU + lowFretBonusU) * K;
-                } else {
-                    // tgtDist scales at (3 * K) per fret-span unit, so the
-                    // hysteresis threshold (a fret-span dead zone) converts
-                    // to tgtDist-space by multiplying by 3 * K — NOT by
-                    // FRET_WIDTH_MID, which is X-axis world-units-per-fret
-                    // and a different unit (would over-tighten the gate by
-                    // ~4x at SCALE = 2.25).
-                    //
-                    // Hysteresis is applied to the BASE portion only. The
-                    // lowFretBonus changes by 4 fret-span units per integer
-                    // fret near the nut, which sits below the default-
-                    // cameraSmoothing (cs=0.5) dead zone of ~8.25 fret-span
-                    // units (= 2.75 * 3) and would otherwise be suppressed
-                    // for fret 2 → 1 / 3 → 1 transitions — exactly the
-                    // corrections this bonus exists to provide. So gate the
-                    // base, then always reflect bonus changes on top by
-                    // tracking the last-committed bonus contribution
-                    // (prevLowFretBonus) and adjusting tgtDist for its
-                    // delta whether or not the base hysteresis fires.
-                    //
-                    // First frame after a lock release bypasses the gate
-                    // entirely so a >12 fret note that disengaged the lock
-                    // is guaranteed to widen the view. Without this, a
-                    // small span jump (12→13 frets) at default settings
-                    // can sit inside the dead zone and the camera fails
-                    // to follow the high note that just opened the lock.
-                    const candidateBase = baseDistU * K;
-                    const baseTgt       = tgtDist - prevLowFretBonus * K;
-                    const justUnlocked  = prevLockActive;
-                    if (justUnlocked || Math.abs(candidateBase - baseTgt) > camDistHystF * 3 * K) {
-                        tgtDist = (baseDistU + lowFretBonusU) * K;
-                    } else if (lowFretBonusU !== prevLowFretBonus) {
-                        tgtDist = baseTgt + lowFretBonusU * K;
-                    }
-                }
-                prevLowFretBonus = lowFretBonusU;
-            }
-            // X-axis: recency-weighted centroid with a hysteresis dead zone
-            // so small cluster shifts don't trigger visible pan motion.
-            if (!lockActive && wSum > 0) {
-                const candidateX = wX / wSum;
-                if (Math.abs(candidateX - tgtX) > camHystF * FRET_WIDTH_MID) tgtX = candidateX;
-            }
-            return lockActive;
-        }
-
-        /** Tolerate RS/sloppak boolean-ish ``true`` / ``1`` forms. */
-        function truthyChartFlag(v) {
-            if (v === true || v === 1) return true;
-            if (v === '1') return true;
-            return typeof v === 'string' && v.toLowerCase() === 'true';
-        }
-
-        /** RS / sloppak `hd` (highDensity); tolerate occasional string forms. */
-        function chordWireHighDensity(ch) {
-            return truthyChartFlag(ch && ch.hd);
-        }
-
-        /**
-         * Per spec, `displayName` is the UI label for a chord template
-         * (defaulting to `name` when the chart didn't set it). Always go
-         * through this helper so name vs. displayName drift can't surface
-         * the wrong label or break displayName-based dedupe heuristics.
-         */
-        function chordTemplateLabel(tmpl) {
-            if (!tmpl) return '';
-            const d = tmpl.displayName;
-            if (typeof d === 'string' && d.length > 0) return d;
-            const n = tmpl.name;
-            return typeof n === 'string' ? n : '';
-        }
-
-        /**
-         * Arpeggio styling is driven by authored metadata, not by post-hoc
-         * note-stream inference. Prefer explicit hand-shape flags and fall back
-         * to template markers when present.
-         */
-        function chordTemplateMarkedArpeggio(cid, chordTemplates) {
-            if (cid == null || !chordTemplates) return false;
-            const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
-            if (!tmpl) return false;
-            if (truthyChartFlag(tmpl.arp) || truthyChartFlag(tmpl.arpeggio)) return true;
-            const displayName = typeof tmpl.displayName === 'string' ? tmpl.displayName.toLowerCase() : '';
-            if (displayName.includes('-arp')) return true;
-            const name = typeof tmpl.name === 'string' ? tmpl.name.toLowerCase() : '';
-            return name.endsWith('(arp)') || name.includes(' arpeggio');
-        }
-
-        function handShapeMarkedArpeggio(hs, chordTemplates) {
-            if (!hs) return false;
-            if (truthyChartFlag(hs.arp) || truthyChartFlag(hs.arpeggio)) return true;
-            return chordTemplateMarkedArpeggio(hsChordIdNorm(hs), chordTemplates);
-        }
-
-        /**
-         * Matching hand-shape metadata for a chord onset. ``explicit`` follows
-         * authored arpeggio markers only; note inference is handled separately
-         * by the callers that still need it for non-visual behavior.
-         *
-         * Cached per chord: result depends only on (ch, hss, chordTemplates),
-         * all chart-static for the lifetime of an arrangement. The cache is
-         * swapped on (hss, templates) ref change so an arrangement switch
-         * cannot resurrect stale entries. Empty-input case bypasses the cache
-         * — it returns a fresh sentinel anyway and isn't hot enough to share.
-         */
-        const _HINT_NONE = Object.freeze({ explicit: false, covered: false, hs: null });
-        let _hintCache = new WeakMap();
-        let _hintCacheHsRef = null;
-        let _hintCacheTplRef = null;
-        function chordHandShapeArpeggioHint(ch, hss, chordTemplates) {
-            if (!hss || hss.length === 0) return _HINT_NONE;
-            if (_hintCacheHsRef !== hss || _hintCacheTplRef !== chordTemplates) {
-                _hintCache = new WeakMap();
-                _hintCacheHsRef = hss;
-                _hintCacheTplRef = chordTemplates;
-            }
-            const cached = _hintCache.get(ch);
-            if (cached !== undefined) return cached;
-            const t = ch.t;
-            const cid = ch.id;
-            let result = _HINT_NONE;
-            for (let i = 0; i < hss.length; i++) {
-                const hs = hss[i];
-                const tLo = hsStart(hs);
-                const tHi = hsEnd(hs);
-                if (Number.isNaN(tLo) || Number.isNaN(tHi)) continue;
-                if (t + 1e-4 < tLo || t > tHi + 1e-4) continue;
-                const hsCid = hsChordIdNorm(hs);
-                if (hsCid !== cid && Number(hsCid) !== Number(cid)) continue;
-                const explicit = handShapeMarkedArpeggio(hs, chordTemplates);
-                result = { explicit, covered: true, hs };
-                break;
-            }
-            _hintCache.set(ch, result);
-            return result;
-        }
-
-        /** Build ``ch.notes`` from ``chordTemplates[cid].frets`` (-1 omitted). */
-        function chordNotesFromTemplate(cid, templates) {
-            if (templates == null || cid == null) return [];
-            const tmpl = templates[cid] ?? templates[Number(cid)];
-            if (!tmpl || !Array.isArray(tmpl.frets)) return [];
-            const out = [];
-            for (let si = 0; si < tmpl.frets.length; si++) {
-                const f = tmpl.frets[si];
-                if (f >= 0 && validString(si)) out.push({ s: si, f, sus: 0 });
-            }
-            return out;
-        }
-
-        /**
-         * Chart-format fingerpicking passages often have ``<handShape>`` + per-string
-         * ``<note>`` rows but **no** ``<chord>`` events. The 3D chord frame / arp
-         * styling only runs over ``bundle.chords``, so synthesize minimal chord
-         * rows at each hand-shape onset when the chart omits them.
-         */
-        function mergeHandShapeSynthChords(realChords, handShapes, chordTemplates) {
-            if (!handShapes || handShapes.length === 0) return realChords;
-            const reals = realChords && realChords.length ? realChords : [];
-            const synth = [];
-            const seenSynth = new Set();
-            const tol = 0.028;
-            /**
-             * Suppress a synth chord box when a real chord with the **same trimmed
-             * display name** played within this window — Custom songs commonly authors
-             * several ``<chordTemplate>`` rows that share a display name (with
-             * trailing-whitespace IDs) for fingering variants. The follow-up
-             * hand-shape with no chord row is a fingering hint, not a new strum
-             * (e.g. Jackson 5 "I Want You Back" ~0:27 — Fm7 cid=18 strum followed
-             * by Fm7 cid=19 hand-shape, which earlier produced a stacked second
-             * "Fm7" label and an extra chord frame).
-             */
-            const SAME_NAME_RUN_S = 0.5;
-            const trimmedTemplateName = (cid) => {
-                if (cid == null || !chordTemplates) return '';
-                const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
-                // custom songs commonly authors several <chordTemplate> rows that share
-                // a displayName for fingering variants; the suppression
-                // heuristic in the surrounding code dedupes on the *label*,
-                // not the underlying name, so go through chordTemplateLabel.
-                return chordTemplateLabel(tmpl).trim();
-            };
-            outer: for (let i = 0; i < handShapes.length; i++) {
-                const hs = handShapes[i];
-                const cid = hs.chord_id != null ? hs.chord_id : hs.chordId;
-                const st = hs.start_time != null ? hs.start_time : hs.startTime;
-                if (cid == null || st == null || Number.isNaN(Number(st))) continue;
-                const key = `${cid}|${Number(st).toFixed(3)}`;
-                if (seenSynth.has(key)) continue;
-                seenSynth.add(key);
-                const myName = trimmedTemplateName(cid);
-                for (let j = 0; j < reals.length; j++) {
-                    const ch = reals[j];
-                    const rid = ch.id;
-                    const sameId = rid === cid || Number(rid) === Number(cid);
-                    if (sameId && Math.abs(ch.t - st) <= tol) continue outer;
-                    // A real strum at the same onset already represents this
-                    // chord — never synthesize a phantom on top of it. The
-                    // id/name checks alone miss hand-shapes whose template
-                    // differs from (or shares no name with) the coincident real
-                    // chord — e.g. an edited chart that left a stale hand-shape
-                    // template pointing at the pre-edit shape, which then drew a
-                    // spurious second power chord beside the real one.
-                    if (Math.abs(ch.t - st) <= tol) continue outer;
-                    if (!sameId && myName !== '') {
-                        const otherName = trimmedTemplateName(rid);
-                        if (otherName === myName
-                            && st > ch.t
-                            && st - ch.t <= SAME_NAME_RUN_S) {
-                            continue outer;
-                        }
-                    }
-                }
-                const notes = chordNotesFromTemplate(cid, chordTemplates);
-                if (notes.length === 0) continue;
-                const et = hs.end_time != null ? hs.end_time : hs.endTime;
-                synth.push({
-                    t: st,
-                    id: cid,
-                    // `hd` is the chart-format `highDensity` wire field (gallops /
-                    // repeated strums), not an arpeggio carrier — arpeggio
-                    // intent is read directly from the hand-shape via
-                    // chordHandShapeArpeggioHint() downstream. Keep `hd` false
-                    // so chordWireHighDensity() / label-suppression behave the
-                    // same as for any other non-gallop chord row.
-                    hd: false,
-                    notes,
-                    /** Hand-shape fill-in (no authored chord row) — skip note-stream arp frame. */
-                    h3dSynth: true,
-                    /** Hand-shape end time — used to draw the shape-sustain border for non-arp cases. */
-                    h3dSynthEnd: et != null ? Number(et) : null,
-                });
-            }
-            if (synth.length === 0) return reals;
-            const merged = reals.concat(synth);
-            merged.sort((a, b) => {
-                const dt = a.t - b.t;
-                if (Math.abs(dt) > 1e-6) return dt;
-                const ia = Number(a.id);
-                const ib = Number(b.id);
-                return (ia - ib) || 0;
-            });
-            return merged;
-        }
-
-        /**
-         * Merge chart-format ``chordTemplates[id].frets`` with live ``chordNote`` rows.
-         * Cached via WeakMap on the chord object — chord data never changes after
-         * chart load, so the Map is computed once and reused every frame.
-         * The init-time callers (fillArpeggioGhostInferFlags) pass ephemeral `fakeCh`
-         * objects that are never seen again, so they bypass the cache naturally.
-         */
-        let _chordShapeCache = new WeakMap();
-        // Reset the validString()/nStr-dependent chord caches. Called when nStr
-        // changes so a string count discovered after the first frame (e.g. a
-        // 7-string chart whose stringCount arrives in song_info) doesn't leave
-        // string-6+ notes filtered out of cached chord shapes/signatures.
-        function _resetStringDependentCaches() {
-            _filterValidNotesCache = new WeakMap();
-            _chordSigCache = new WeakMap();
-            _chordShapeCache = new WeakMap();
-            // mergeHandShapeSynthChords() is nStr-dependent too: its synth
-            // notes come from chordNotesFromTemplate() -> validString(). The
-            // merge result is memoised by input identity (not nStr), so force a
-            // recompute or string-6+ template notes stay dropped from synth
-            // chords after the count grows.
-            _mergeCacheResult = null;
-        }
-        function mergeChordShape(ch, chordNotes, templates) {
-            if (_chordShapeCache.has(ch)) return _chordShapeCache.get(ch);
-            const shape = new Map();
-            const tid = ch && ch.id != null ? ch.id : null;
-            const tmpl = (tid != null && templates)
-                ? (templates[tid] ?? templates[Number(tid)])
-                : null;
-            if (tmpl && Array.isArray(tmpl.frets)) {
-                for (let si = 0; si < tmpl.frets.length; si++) {
-                    if (!validString(si)) continue;
-                    const f = tmpl.frets[si];
-                    if (f >= 0) shape.set(si, f);
-                }
-            }
-            for (let i = 0; i < chordNotes.length; i++) {
-                const cn = chordNotes[i];
-                if (!validString(cn.s)) continue;
-                if (cn.f < 0) shape.delete(cn.s);
-                else shape.set(cn.s, cn.f);
-            }
-            _chordShapeCache.set(ch, shape);
-            return shape;
-        }
-
-        function hitTimesQualifyArpeggioSpread(hitTimes) {
-            if (hitTimes.length < 2) return false;
-            hitTimes.sort((a, b) => a - b);
-            const spread = hitTimes[hitTimes.length - 1] - hitTimes[0];
-            if (spread >= 0.03) return true;
-            return hitTimes.length >= 4 && spread >= 0.016;
-        }
-
-        /** RS XML / IPC payloads use snake_case or camelCase field names. */
-        function hsStart(hs) {
-            if (!hs) return NaN;
-            const v = hs.start_time != null ? hs.start_time : hs.startTime;
-            if (v == null) return NaN;
-            const n = Number(v);
-            return Number.isNaN(n) ? NaN : n;
-        }
-        function hsEnd(hs) {
-            if (!hs) return NaN;
-            const v = hs.end_time != null ? hs.end_time : hs.endTime;
-            if (v == null) return NaN;
-            const n = Number(v);
-            return Number.isNaN(n) ? NaN : n;
-        }
-        function hsChordIdNorm(hs) {
-            if (!hs) return null;
-            const v = hs.chord_id != null ? hs.chord_id : hs.chordId;
-            return v == null ? null : v;
-        }
-
-        /** ``<handShape>`` chart duration in seconds (snake_case or camelCase XML). */
-        function handShapeChartSpanSec(hs) {
-            const a = hsStart(hs), b = hsEnd(hs);
-            if (Number.isNaN(a) || Number.isNaN(b)) return 0;
-            return Math.max(0, b - a);
-        }
-
-        /**
-         * When ``hd`` is missing/false, detect arpeggio from the **note** stream
-         * using the **full voicing** (template ∪ chord notes). RS often stores the
-         * plucks only in ``notes[]``, not as duplicate chord rows.
-         *
-         * @param {{ tLo: number, tHi: number } | null} [timeWin]
-         *        When set (e.g. from ``<handShape>`` span), scan staggered picks
-         *        across the whole held-shape window — RS often omits ``arp`` and ``hd``.
-         */
-        // Cached per chord: result depends on (ch, shape, notesArr) and an
-        // optional timeWin which itself is a function of the chord's matching
-        // <handShape>. Both inputs are chart-static, so the cache invalidates
-        // on (notesArr, hss) ref change — `hss` is threaded in purely as the
-        // invalidation key for the chord-loop caller, which passes a stable
-        // `ch` (reused across frames) and a timeWin that is null until
-        // bundle.handShapes arrives over the WS; without the hss check the
-        // null-timeWin result would stick once handShapes loaded late. shape
-        // comes from mergeChordShape(ch) which is also chart-static, so it
-        // doesn't enter the invalidation key directly. The cache deliberately
-        // stores boolean results; a sentinel distinguishes "not computed"
-        // from "false".
-        let _arpInferCache = new WeakMap();
-        let _arpInferCacheNotesRef = null;
-        let _arpInferCacheHssRef = null;
-        function inferArpeggioFromNotePattern(ch, shape, notesArr, timeWin, hss = null) {
-            if (!notesArr || notesArr.length === 0 || shape.size < 2) return false;
-            if (_arpInferCacheNotesRef !== notesArr || _arpInferCacheHssRef !== hss) {
-                _arpInferCache = new WeakMap();
-                _arpInferCacheNotesRef = notesArr;
-                _arpInferCacheHssRef = hss;
-            }
-            const cached = _arpInferCache.get(ch);
-            if (cached !== undefined) return cached;
-            const result = _inferArpeggioFromNotePatternUncached(ch, shape, notesArr, timeWin);
-            _arpInferCache.set(ch, result);
-            return result;
-        }
-        function _inferArpeggioFromNotePatternUncached(ch, shape, notesArr, timeWin) {
-            const tHi = timeWin ? timeWin.tHi : ch.t + 2.35;
-            const tLo = timeWin ? timeWin.tLo : ch.t - 0.28;
-            let i2 = lowerBoundT(notesArr, tLo - 0.02);
-            const hitTimes = [];
-            const hitStrings = new Set();
-            for (; i2 < notesArr.length; i2++) {
-                const n = notesArr[i2];
-                if (n.t > tHi) break;
-                if (n.t < tLo) continue;
-                if (!validString(n.s)) continue;
-                const ef = shape.get(n.s);
-                if (ef === undefined || ef !== n.f) continue;
-                hitTimes.push(n.t);
-                hitStrings.add(n.s);
-            }
-            if (!hitTimesQualifyArpeggioSpread(hitTimes)) return false;
-            // A genuine arpeggio SWEEPS across the held shape, so its standalone
-            // notes land on MULTIPLE strings of the shape. When every matching
-            // hit is on a single string, this is a repeated single-string run
-            // (e.g. a palm-muted gallop hammering the chord's root) that happens
-            // to share one string/fret with the chord — NOT an arpeggio. Inferring
-            // one here deferred the chord's gems and made the power chord render as
-            // just that one repeated note (bar 25 of starlight). Require ≥2 strings.
-            if (hitStrings.size < 2) return false;
-            // Strumming/gallop rejection — far more hits than the shape has
-            // strings means the chord's notes are being re-struck repeatedly
-            // (a riff/gallop reusing both power-chord notes), not swept once as
-            // an arpeggio. This guard used to live inside `if (timeWin)`, so it
-            // was skipped for charts with no hand-shapes (timeWin null) — which
-            // let dense two-string gallops over a power chord infer a bogus
-            // arpeggio and defer the chord's gems (bar 88 of starlight: a
-            // (s5:4,s6:2) chord whose root+fifth recur ~16x over 2 s). Apply it
-            // with the actual window span whether or not a hand-shape is present.
-            const winSpan = timeWin ? (timeWin.tHi - timeWin.tLo) : (tHi - tLo);
-            if (winSpan > ARP_INFER_MULTI_STRUM_WIN_MIN_S
-                && hitTimes.length > shape.size + ARP_INFER_MULTI_STRUM_HIT_SLACK) {
-                return false;
-            }
-            if (timeWin) {
-                if (winSpan < 0.70 && hitTimes.length < 4) {
-                    const spread = hitTimes[hitTimes.length - 1] - hitTimes[0];
-                    if (spread < ARP_INFER_STRUM_VS_ARP_SPREAD_MIN_S) return false;
-                }
-                // Reject when too few staggered hits for a genuine sweep across
-                // the held shape — see ARP_INFER_MIN_HITS_VS_SHAPE_CAP.
-                const minHits = Math.min(shape.size, ARP_INFER_MIN_HITS_VS_SHAPE_CAP);
-                if (hitTimes.length < minHits) return false;
-            }
-            return true;
-        }
-
-        /**
-         * True when standalone note rows already cover every string/fret in the
-         * arpeggio shape, so drawing the chord gems too would duplicate the same
-         * authored passage.
-         */
-        // Cached per chord: result depends on (ch, shape, notesArr) — chart-
-        // static; the cache invalidates on notesArr ref change. The same
-        // ``ch`` may be queried multiple times per frame from the chord
-        // render loop (deferChordGems / _deferFallback / suppressSynthChord),
-        // so survival across frames is also useful.
-        let _arpCoverCache = new WeakMap();
-        let _arpCoverCacheNotesRef = null;
-        function chordShapeCoveredByStandaloneNotes(ch, shape, notesArr, timeWin) {
-            if (!notesArr || notesArr.length === 0 || !shape || shape.size === 0) return false;
-            if (_arpCoverCacheNotesRef !== notesArr) {
-                _arpCoverCache = new WeakMap();
-                _arpCoverCacheNotesRef = notesArr;
-            }
-            const cached = _arpCoverCache.get(ch);
-            if (cached !== undefined) return cached;
-            const tLo = (timeWin ? timeWin.tLo : ch.t - ARP_FRAME_ONSET_PAD_S) - NEXT_ON_STRING_T_EPS;
-            const tHi = (timeWin ? timeWin.tHi : ch.t + ARP_FRAME_ONSET_CLUSTER_S) + NEXT_ON_STRING_T_EPS;
-            let i2 = lowerBoundT(notesArr, tLo);
-            const matchedStrings = new Set();
-            let result = false;
-            for (; i2 < notesArr.length; i2++) {
-                const n = notesArr[i2];
-                if (n.t > tHi) break;
-                if (!validString(n.s) || matchedStrings.has(n.s)) continue;
-                const ef = shape.get(n.s);
-                if (ef === undefined || ef !== n.f) continue;
-                matchedStrings.add(n.s);
-                if (matchedStrings.size >= shape.size) { result = true; break; }
-            }
-            _arpCoverCache.set(ch, result);
-            return result;
-        }
-
-        /**
-         * Notes in an inferred arpeggio passage are charted in ``notes[]`` with
-         * staggered times; treat them like chord-cluster notes for chart-format-style
-         * board-ghost fret digits (``fromChord`` + template column).
-         */
-        function arpeggioChordIdForNote(n, handShapes, chordTemplates, notesArr) {
-            if (!handShapes || handShapes.length === 0 || !notesArr || notesArr.length === 0) return null;
-            if (!validString(n.s)) return null;
-            for (let i = 0; i < handShapes.length; i++) {
-                const hs = handShapes[i];
-                const hsLo = hsStart(hs);
-                const hsHi = hsEnd(hs);
-                if (Number.isNaN(hsLo) || Number.isNaN(hsHi)) continue;
-                if (n.t + 1e-4 < hsLo || n.t > hsHi + 1e-4) continue;
-                const cid = hsChordIdNorm(hs);
-                if (cid == null) continue;
-                const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
-                if (!tmpl || !Array.isArray(tmpl.frets)) continue;
-                const tf = tmpl.frets[n.s];
-                if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
-                const synthNotes = chordNotesFromTemplate(cid, chordTemplates);
-                if (synthNotes.length === 0) continue;
-                const fakeCh = { t: hsLo, id: cid, notes: synthNotes };
-                const shape = mergeChordShape(fakeCh, synthNotes, chordTemplates);
-                const tw = { tLo: hsLo - 0.06, tHi: hsHi + 0.06 };
-                if (handShapeChartSpanSec(hs) < ARP_INFER_MIN_HAND_SHAPE_SPAN_S) continue;
-                if (inferArpeggioFromNotePattern(fakeCh, shape, notesArr, tw, handShapes)) return cid;
-            }
-            return null;
-        }
-
-        /**
-         * Per-frame warmup: ``inferArpeggioFromNotePattern`` depends only on
-         * ``handShape × chart``, not on the candidate note — the old path
-         * recomputed it for every visible note (O(notecount × hs × notescan)).
-         * Fill ``outFlags[i]`` with the boolean once per ``handShapes[i]``.
-         */
-        function fillArpeggioGhostInferFlags(handShapes, chordTemplates, notesArr, outFlags, outSynthOnsetSet = null) {
-            for (let i = 0; i < handShapes.length; i++) {
-                let infer = false;
-                const hs = handShapes[i];
-                if (handShapeChartSpanSec(hs) < ARP_INFER_MIN_HAND_SHAPE_SPAN_S) {
-                    outFlags[i] = false;
-                    continue;
-                }
-                const cid = hsChordIdNorm(hs);
-                if (cid != null && notesArr.length > 0) {
-                    const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
-                    if (tmpl && Array.isArray(tmpl.frets)) {
-                        const synthNotes = chordNotesFromTemplate(cid, chordTemplates);
-                        if (synthNotes.length > 0) {
-                            const hsLo = hsStart(hs);
-                            const hsHi = hsEnd(hs);
-                            const fakeCh = { t: hsLo, id: cid, notes: synthNotes };
-                            const shape = mergeChordShape(fakeCh, synthNotes, chordTemplates);
-                            const tw = { tLo: hsLo - 0.06, tHi: hsHi + 0.06 };
-                            infer = inferArpeggioFromNotePattern(fakeCh, shape, notesArr, tw, handShapes);
-                            // Chord-hold gate: inferArpeggioFromNotePattern can fire true
-                            // when open-string notes coincidentally match the template's
-                            // open positions but only a SINGLE fretted (f>0) string is
-                            // actually played at the handshape onset. Treat that as a
-                            // chord hold (not an arpeggio) — clear the arp flag, no
-                            // brackets. The original implementation also intended to
-                            // record a synthetic sustain extending to hsEnd for the
-                            // onset note, but that read-side was never wired up; the
-                            // visual decay-before-handshape-end is benign.
-                            if (infer) {
-                                let _frettedCount = 0;
-                                let _onsetNote = null;
-                                const _fSeen = new Set();
-                                let _ci = lowerBoundT(notesArr, tw.tLo - 0.02);
-                                for (; _ci < notesArr.length; _ci++) {
-                                    const _cn = notesArr[_ci];
-                                    if (_cn.t > tw.tHi + 0.02) break;
-                                    if (_cn.t < tw.tLo) continue;
-                                    if (!validString(_cn.s)) continue;
-                                    if (shape.get(_cn.s) !== _cn.f) continue;
-                                    if (_cn.f > 0 && !_fSeen.has(_cn.s)) {
-                                        _frettedCount++;
-                                        _fSeen.add(_cn.s);
-                                        if (_onsetNote === null) _onsetNote = _cn;
-                                    }
-                                }
-                                if (_frettedCount <= 1 && _onsetNote !== null) {
-                                    outFlags[i] = false;
-                                    continue; // chord hold handled — skip onset-match and outFlags assignment
-                                }
-                            }
-                            // Non-arp template inferred as arpeggio: suppress brackets.
-                            // Only explicit arp-marked templates (arp:true / displayName "-arp")
-                            // should show [ ] / < > bracket markers.
-                            if (infer && outSynthOnsetSet != null
-                                && !handShapeMarkedArpeggio(hs, chordTemplates)) {
-                                outSynthOnsetSet.add(hsLo);
-                            }
-                            // Also treat as arp ghost when the hs generated a suppressed
-                            // synth chord: any standalone note in the onset window matches
-                            // any shape string. Handles patterns where inferArpeggioFromNotePattern
-                            // returns false (e.g. repeated arpeggio across a long hs span
-                            // triggers the multi-strum rejection), but the player still
-                            // needs the "hold this shape" ghost fret numbers on the board.
-                            if (!infer) {
-                                const _oLo = hsLo - ARP_FRAME_ONSET_PAD_S;
-                                const _oHi = hsLo + ARP_FRAME_ONSET_CLUSTER_S;
-                                let _oi = lowerBoundT(notesArr, _oLo - 0.02);
-                                for (; _oi < notesArr.length; _oi++) {
-                                    const _on = notesArr[_oi];
-                                    if (_on.t > _oHi) break;
-                                    if (_on.t < _oLo) continue;
-                                    if (shape.get(_on.s) === _on.f) {
-                                        infer = true;
-                                        // Only suppress brackets when the handshape is NOT an
-                                        // explicit arpeggio (arp:true template / displayName "-arp").
-                                        // Genuine arp handshapes reached via onset-match still need
-                                        // the [ ] bracket markers — only non-arp synth chords are
-                                        // "false positives" that should hide the brackets.
-                                        if (outSynthOnsetSet != null
-                                            && !handShapeMarkedArpeggio(hs, chordTemplates)) {
-                                            outSynthOnsetSet.add(hsLo);
-                                        }
-                                        break;
-                                    }
-                                }
-                            }
-                        }
-                    }
-                }
-                outFlags[i] = infer;
-            }
-        }
-
-        // Chart-static WeakMap cache: note object → chord-id (or null sentinel).
-        // The result depends only on the note's (t, s, f) and the chart's handShapes
-        // + chordTemplates, which never change after load. Keyed by note object so
-        // switching songs/arrangements drops the entries with the old array.
-        const _ARP_CID_NULL = Object.freeze({});
-        const _arpCidCache = new WeakMap();
-        function arpeggioChordIdForNoteWithInferCache(n, handShapes, chordTemplates, notesArr, hsInferFlags) {
-            const cached = _arpCidCache.get(n);
-            if (cached !== undefined) return cached === _ARP_CID_NULL ? null : cached;
-            let result = null;
-            if (!handShapes || handShapes.length === 0 || !notesArr || notesArr.length === 0 || !hsInferFlags) {
-                result = arpeggioChordIdForNote(n, handShapes, chordTemplates, notesArr);
-            } else if (validString(n.s)) {
-                for (let i = 0; i < handShapes.length; i++) {
-                    if (!hsInferFlags[i]) continue;
-                    const hs = handShapes[i];
-                    const hsLo = hsStart(hs);
-                    const hsHi = hsEnd(hs);
-                    if (Number.isNaN(hsLo) || Number.isNaN(hsHi)) continue;
-                    if (n.t + 1e-4 < hsLo || n.t > hsHi + 1e-4) continue;
-                    const cid = hsChordIdNorm(hs);
-                    if (cid == null) continue;
-                    const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
-                    if (!tmpl || !Array.isArray(tmpl.frets)) continue;
-                    const tf = tmpl.frets[n.s];
-                    if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
-                    result = cid;
-                    break;
-                }
-            }
-            _arpCidCache.set(n, result === null ? _ARP_CID_NULL : result);
-            return result;
-        }
-
-        /** Returns {start, end} chart-time bounds of the arpeggio handshape that contains
-         *  this note, or null when not found.  Uses hsInferFlags to skip ruled-out
-         *  handshapes; falls back to a full scan when hsInferFlags is null. */
-        // WeakMap cache — arpHsBoundsForNote result is chart-static (note, handShapes,
-        // and hsInferFlags never change after chart load). Each renderer instance has
-        // its own WeakMap, so splitscreen panels don't interfere.
-        // Sentinel: _ARP_BOUNDS_NULL = {} distinguishes "no matching hs" from "uncached".
-        const _ARP_BOUNDS_NULL = Object.freeze({});
-        const _arpBoundsCache = new WeakMap();
-        function arpHsBoundsForNote(n, handShapes, hsInferFlags) {
-            if (!handShapes || handShapes.length === 0) return null;
-            const cached = _arpBoundsCache.get(n);
-            if (cached !== undefined) return cached === _ARP_BOUNDS_NULL ? null : cached;
-            let result = null;
-            for (let i = 0; i < handShapes.length; i++) {
-                if (hsInferFlags && !hsInferFlags[i]) continue;
-                const hs = handShapes[i];
-                const lo = hsStart(hs);
-                const hi = hsEnd(hs);
-                if (Number.isNaN(lo) || Number.isNaN(hi)) continue;
-                if (n.t + 1e-4 < lo || n.t > hi + 1e-4) continue;
-                result = { start: lo, end: hi };
-                break;
-            }
-            _arpBoundsCache.set(n, result === null ? _ARP_BOUNDS_NULL : result);
-            return result;
-        }
-
-        function handShapeIsArpeggioForLaneRail(hs, chordTemplates) {
-            return handShapeMarkedArpeggio(hs, chordTemplates);
-        }
-
-        /**
-         * Chart-time window for purple rails: hand-shape span clipped to matching
-         * ``chords[].t`` and template notes in the passage — same times that drive
-         * the 3D arpeggio frame (``ch.t`` + note stream), avoiding rails that start
-         * before the box or end before the last arpeggiated note.
-         */
-        function effectiveArpRailChartBoundsForHandShape(hs, chords, chordTemplates, notesArr) {
-            let shapeLo = hsStart(hs);
-            const _hsEndOrig = hsEnd(hs);
-            let shapeHi = _hsEndOrig;
-            const cid = hsChordIdNorm(hs);
-            if (Number.isNaN(shapeLo) || Number.isNaN(shapeHi)) {
-                return { shapeLo: 1e9, shapeHi: -1e9 };
-            }
-            if (notesArr && notesArr.length > 0 && chordTemplates && cid != null) {
-                const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
-                if (tmpl && Array.isArray(tmpl.frets)) {
-                    let tFirst = null;
-                    let tLast = null;
-                    for (let i = 0; i < notesArr.length; i++) {
-                        const n = notesArr[i];
-                        if (n.t + 1e-4 < shapeLo - 0.18 || n.t > shapeHi + 0.45) continue;
-                        if (!validString(n.s)) continue;
-                        const tf = tmpl.frets[n.s];
-                        if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
-                        if (tFirst === null || n.t < tFirst) tFirst = n.t;
-                        if (tLast === null || n.t > tLast) tLast = n.t;
-                    }
-                    if (tFirst != null) shapeLo = Math.max(shapeLo, tFirst);
-                    if (tLast != null) shapeHi = Math.max(shapeHi, tLast);
-                }
-            }
-            if (chords && chords.length && cid != null) {
-                let tMinC = null;
-                let tMaxC = null;
-                for (let j = 0; j < chords.length; j++) {
-                    const ch = chords[j];
-                    if (ch.id !== cid && Number(ch.id) !== Number(cid)) continue;
-                    if (ch.t + 1e-4 < shapeLo || ch.t > shapeHi + 0.28) continue;
-                    if (tMinC === null || ch.t < tMinC) tMinC = ch.t;
-                    if (tMaxC === null || ch.t > tMaxC) tMaxC = ch.t;
-                }
-                if (tMinC != null) shapeLo = Math.max(shapeLo, tMinC);
-                if (tMaxC != null) shapeHi = Math.max(shapeHi, tMaxC);
-            }
-            shapeLo -= ARP_HWY_RAIL_START_LEAD_S;
-            // Only extend past the handshape end when notes/chords genuinely reach
-            // beyond it — otherwise the tail would make the rail visually larger
-            // than the actual handshape duration (e.g. 0.38 s / 1.3 s ≈ 29% extra).
-            if (shapeHi > _hsEndOrig) shapeHi += ARP_HWY_RAIL_END_TAIL_S;
-            return { shapeLo, shapeHi };
-        }
-
-        /** Cache the authored arpeggio marker per hand shape. */
-        function fillLaneRailHandShapeFlags(handShapes, chordTemplates, outFlags) {
-            const nHs = handShapes.length;
-            for (let i = 0; i < nHs; i++) {
-                outFlags[i] = handShapeIsArpeggioForLaneRail(handShapes[i], chordTemplates);
-            }
-        }
-
-        function fillArpeggioRailShapeBoundsCaches(
-            handShapes, chords, chordTemplates, notesArr, laneRailFlags, loOut, hiOut,
-        ) {
-            const nHs = handShapes.length;
-            for (let i = 0; i < nHs; i++) {
-                if (!laneRailFlags[i]) continue;
-                const b = effectiveArpRailChartBoundsForHandShape(
-                    handShapes[i], chords, chordTemplates, notesArr,
-                );
-                loOut[i] = b.shapeLo;
-                hiOut[i] = b.shapeHi;
-            }
-        }
-
-        /** ``[tChartLo,tChartHi]`` chart times that a lane slice covers (see module ``BEHIND`` / approach ``dt``). */
-        function arpeggioLaneOuterRailChartIntervalOverlaps(
-            tChartLo,
-            tChartHi,
-            handShapes,
-            boundLo,
-            boundHi,
-            laneRailFlags,
-        ) {
-            if (!handShapes || handShapes.length === 0) return false;
-            if (!laneRailFlags) return false;
-            if (tChartHi < tChartLo) {
-                const s = tChartLo;
-                tChartLo = tChartHi;
-                tChartHi = s;
-            }
-            for (let i = 0; i < handShapes.length; i++) {
-                if (!laneRailFlags[i]) continue;
-                const shapeLo = boundLo[i];
-                const shapeHi = boundHi[i];
-                if (tChartHi < shapeLo - 1e-4 || tChartLo > shapeHi + 1e-4) continue;
-                return true;
-            }
-            return false;
-        }
-
-        function arpeggioLaneOuterRailLaneSlice(
-            dt0, dt1, nowClock,
-            handShapes, boundLo, boundHi, laneRailFlags,
-        ) {
-            const tLo = nowClock + Math.min(dt0, dt1) - BEHIND;
-            const tHi = nowClock + Math.max(dt0, dt1) - BEHIND;
-            return arpeggioLaneOuterRailChartIntervalOverlaps(
-                tLo, tHi, handShapes, boundLo, boundHi, laneRailFlags,
-            );
-        }
-
-        /**
-         * True when **chart time** ``chartT`` falls inside an arpeggio hand-shape.
-         * Uses a short end tail only — no ``CHORD_HWY_LINGER_S`` — so purple lane
-         * rails match visible highway slices and do not leak after shapes end.
-         */
-        function arpeggioLaneOuterRailAtChartTime(
-            chartT, handShapes, boundLo, boundHi, laneRailFlags,
-        ) {
-            return arpeggioLaneOuterRailChartIntervalOverlaps(
-                chartT, chartT, handShapes, boundLo, boundHi, laneRailFlags,
-            );
-        }
-
-        /**
-         * Same ``chordAccent ? ft *= 1.22`` as the 3D arpeggio chord rim so lane
-         * rails match an accented frame when the active hand shape links to a
-         * chord row that carries ``.ac`` notes.
-         */
-        function arpeggioLaneDividerFrameAccentMul(nowT, handShapes, chords, boundLo, boundHi, laneRailFlags) {
-            if (!handShapes || handShapes.length === 0 || !chords || chords.length === 0) return 1;
-            if (!laneRailFlags) return 1;
-            for (let i = 0; i < handShapes.length; i++) {
-                if (!laneRailFlags[i]) continue;
-                const shapeLo = boundLo[i];
-                const shapeHi = boundHi[i];
-                if (nowT + 1e-4 < shapeLo || nowT > shapeHi + 1e-4) continue;
-
-                const cid = hsChordIdNorm(handShapes[i]);
-                if (cid == null) return 1;
-                for (let j = 0; j < chords.length; j++) {
-                    const ch = chords[j];
-                    if (ch.id !== cid && Number(ch.id) !== Number(cid)) continue;
-                    if (Math.abs(ch.t - hsStart(handShapes[i])) > 0.12) continue;
-                    const chordNotes = ch.notes ? filterValidNotes(ch.notes) : [];
-                    if (chordNotes.some(cn => cn.ac)) return 1.22;
-                    return 1;
-                }
-                return 1;
-            }
-            return 1;
-        }
-
-        /** World-scale XY for purple lane rails = arpeggio ``ftSide`` / ``gLaneDivider`` edge (0.15×K). */
-        function arpeggioLaneDividerXYScaleMatchFrameRim(accentMul = 1) {
-            const yA = sY(0), yB = sY(nStr - 1);
-            const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
-            const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
-            const fullChordBoxH = yMaxF - yMinF;
-            let ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
-            if (accentMul !== 1 && accentMul > 0) ft *= accentMul;
-            const ftSide = ft * 1.55;
-            return ftSide / (0.15 * K);
-        }
-
-        /* ── Fret-label measure-skip rule ───────────────────────────────── */
-        // For each (note_time, fret) pair across standalone notes and chord
-        // notes, determine which ones are allowed to display their fret
-        // indicator number. Rule: per fret (regardless of string), show the
-        // number only on the first note in a given measure; suppress it for
-        // the immediately following measure; then allow it again (current
-        // measure + 2).
-        // Key scheme: Math.round(t * 25) * 100 + fret  (40 ms time buckets).
-        // Using a coarse time-bucket (not exact time) ensures that a synthetic
-        // chord template whose .t differs from the corresponding standalone
-        // arpeggio note by a few ms still resolves to the same key.
-        // Only standalone notes (notesArr) populate the set; regular chord notes
-        // never show labels, and synthetic chord notes share frets/onsets with
-        // their arpeggio counterparts, so the same keys are found at lookup time.
-        // Returns a Set of numeric keys (Math.round(t*25)*100 + fret).
-        function _buildFretLabelSet(notesArr, _chordsArr, beatsArr) {
-            const events = [];
-            if (notesArr) {
-                for (let _i = 0; _i < notesArr.length; _i++) {
-                    const _n = notesArr[_i];
-                    if (_n.f > 0) events.push({ t: _n.t, f: _n.f });
-                }
-            }
-            // Chord events intentionally excluded: regular chord notes don't show
-            // fret labels; synthetic chord notes share frets with arpeggio note-stream
-            // notes already captured above, so no separate chord processing needed.
-            events.sort((a, b) => a.t - b.t);
-            const beats = beatsArr || [];
-            let beatIdx = 0;
-            let currentMeasure = 0;
-            const nextShowMeasure = new Map(); // fret → next measure where label is allowed
-            const allowed = new Set();
-            for (let _ei = 0; _ei < events.length; _ei++) {
-                const { t, f } = events[_ei];
-                // Advance beats pointer: find the current measure for time t.
-                while (beatIdx < beats.length && beats[beatIdx].time <= t + 1e-4) {
-                    if (beats[beatIdx].measure >= 0) currentMeasure = beats[beatIdx].measure;
-                    beatIdx++;
-                }
-                const nextM = nextShowMeasure.get(f) ?? 0;
-                if (currentMeasure >= nextM) {
-                    // Time-bucket key: 40 ms groups absorb timing jitter while
-                    // still distinguishing notes at different positions in the measure.
-                    allowed.add(Math.round(t * 25) * 100 + f);
-                    // Suppress this fret for the next measure; re-allow at +2.
-                    nextShowMeasure.set(f, currentMeasure + 2);
-                }
-            }
-            return allowed;
-        }
-
-        // Smoothed playback clock for this frame. Called once per frame at the
-        // top of update(); camUpdate() reads the stored _frameNow afterward so
-        // notes and camera share one clock. See the _clk* state block above.
-        function smoothNow(bundle) {
-            const raw = bundle.currentTime;
-            const p = performance.now();
-            // Host pause signal (feedBack core's bundle.isPlaying): when the
-            // chart clock isn't advancing (paused / stalled / mid-seek), don't
-            // extrapolate forward against a frozen audio sample — that creeps
-            // the highway ahead by up to the interp cap and then snaps back
-            // when dt finally crosses 0.1. Re-anchor to raw so the next
-            // playing frame resumes from a clean segment. `=== false` so
-            // downlevel hosts (isPlaying undefined) fall through to the
-            // staleness-based cap below, preserving prior behavior there.
-            if (bundle.isPlaying === false) {
-                _clkAudioT = raw;
-                _clkPerf = p;
-                _clkRate = 1;
-                return (_frameNow = raw);
-            }
-            if (raw !== _clkAudioT) {
-                // New audio sample — re-anchor and refine the rate estimate.
-                if (!Number.isNaN(_clkPerf)) {
-                    const dP = (p - _clkPerf) / 1000;
-                    if (dP > 0.001 && dP < 0.5) {
-                        const r = (raw - _clkAudioT) / dP;
-                        _clkRate = (r > 0.05 && r < 5) ? r : 1; // seek/loop → reset
-                    } else if (dP >= 0.5) {
-                        _clkRate = 1; // long gap (paused / tab inactive)
-                    }
-                }
-                _clkAudioT = raw;
-                _clkPerf = p;
-                return (_frameNow = raw);
-            }
-            // Same audio sample as last call — interpolate forward, capped so a
-            // stalled main thread or paused audio can't run the clock away.
-            const dt = (p - _clkPerf) / 1000;
-            if (dt <= 0 || dt > 0.1) return (_frameNow = raw);
-            return (_frameNow = _clkAudioT + _clkRate * dt);
-        }
-
-        /* ── Per-frame rendering ─────────────────────────────────────────── */
-        // ── GPU pre-warm (perf: first-appearance hitches) ─────────────────
-        // Three.js compiles a material's shader program and uploads a
-        // texture the first frame the owning object renders — profiled as
-        // mid-song frame spikes (getParameters / texSubImage2D). Pay those
-        // costs during init (load spinner) instead:
-        //   _prewarmStatic()      — ren.compile() over the fully-built scene
-        //                           + deterministic label textures (fret
-        //                           numbers in every per-frame style/colour
-        //                           combo).
-        //   _prewarmChart(bundle) — chart-dependent labels (chord template
-        //                           names, section names); needs the ready
-        //                           bundle, so it runs once from the first
-        //                           draw() after each init.
-        // txtMat() rasterises into the unbounded cache these draws hit
-        // anyway; ren.initTexture() forces the GPU upload now.
-        // Swap a pooled label sprite's cached texture WITHOUT recompiling.
-        // Setting material.needsUpdate bumps material.version, which forces
-        // Three.js through getParameters/getProgramCacheKey on the next
-        // render. Swapping one non-null texture for another does NOT change
-        // the compiled program (the USE_MAP define is unchanged); only a
-        // null <-> non-null transition does, and pooled label sprites are
-        // constructed with a non-null map, so in practice this never
-        // recompiles. (Note: the DOMINANT getParameters churn turned out to
-        // be Three's transparent-DoubleSide two-pass path — see the
-        // forceSinglePass comment in _spriteMat2MeshMat — this helper
-        // removes the label-swap contribution on top of that.)
-        function _setLabelMap(sprite, srcMat) {
-            const m = sprite.material;
-            if (m.map === srcMat.map) return;
-            const nullnessChanged = (m.map == null) !== (srcMat.map == null);
-            m.map = srcMat.map;
-            if (nullnessChanged) m.needsUpdate = true;
-        }
-
-        let _chartPrewarmed = false;
-        function _prewarmTex(mat) {
-            if (mat && mat.map && ren) ren.initTexture(mat.map);
-        }
-        function _prewarmStatic() {
-            // MAINTENANCE NOTE: this list must cover every deterministic
-            // (chart-independent) material/texture the per-frame paths can
-            // request lazily. Adding a new label style or sprite factory to
-            // drawNote()/update() without warming it here silently
-            // reintroduces a first-appearance texSubImage2D/compile spike
-            // mid-song. Chart-dependent labels (chord names, section names)
-            // live in _prewarmChart.
-            try {
-                if (ren && scene && cam) ren.compile(scene, cam);
-            } catch (e) { console.warn('[3D-Hwy] prewarm compile:', e); }
-            try {
-                // Fret-number labels in the per-frame style/colour combos.
-                for (let f = 0; f <= NFRETS; f++) {
-                    _prewarmTex(txtMat(f, FRET_LABEL_GOLD_HEX, false, 'noteFret'));
-                    _prewarmTex(txtMat(f, FRET_LABEL_GOLD_HEX, false, 'fretRow'));
-                    _prewarmTex(txtMat(f, FRET_LABEL_IDLE_HEX, false, 'fretRow'));
-                    _prewarmTex(txtMat(f, '#ffffff', false, 'ghostFret'));
-                }
-                // Teaching marks (drawNote _drawTeachMark): finger hints
-                // T/1-4 (teachFg) and scale degrees 0-11 (teachSd).
-                _prewarmTex(txtMat('T', '#7fd1ff', false, 'teachFg'));
-                for (let i = 1; i <= 4; i++) _prewarmTex(txtMat(String(i), '#7fd1ff', false, 'teachFg'));
-                for (let i = 0; i <= 11; i++) _prewarmTex(txtMat(String(i), '#ffcc66', false, 'teachSd'));
-                // Technique sprite factories (own caches, keyed by packed
-                // number): PM/FH mute X, hammer/pull triangles, bend
-                // chevron stacks, slide direction arrows — per string
-                // colour of the active palette.
-                _prewarmTex(palmMuteXSpriteMat());
-                _prewarmTex(fretHandMuteXSpriteMat());
-                const _nWarm = Math.min(
-                    Math.max(nStr, 6),
-                    (activePalette && activePalette.length) || 0);
-                for (let s = 0; s < _nWarm; s++) {
-                    const hex = activePalette[s] || 0xffffff;
-                    _prewarmTex(triMat(true, hex));
-                    _prewarmTex(triMat(false, hex));
-                    for (let st = 1; st <= 4; st++) _prewarmTex(bendChevronMat(st, hex));
-                    const arrowHex = darkenHex(hex, 0.55);
-                    _prewarmTex(slideArrowMat(true, arrowHex));
-                    _prewarmTex(slideArrowMat(false, arrowHex));
-                }
-            } catch (e) { console.warn('[3D-Hwy] prewarm labels:', e); }
-        }
-        function _prewarmChart(bundle) {
-            try {
-                const tpls = bundle && bundle.chordTemplates;
-                if (Array.isArray(tpls)) {
-                    for (const tpl of tpls) {
-                        if (tpl && tpl.name) _prewarmTex(txtMat(tpl.name, '#e8d080', true, 'chord'));
-                    }
-                }
-                const secs = bundle && bundle.sections;
-                if (Array.isArray(secs)) {
-                    for (const s of secs) {
-                        if (s && s.name) _prewarmTex(txtMat(s.name, '#00cccc', true, 'section'));
-                    }
-                }
-            } catch (e) { console.warn('[3D-Hwy] prewarm chart labels:', e); }
-        }
-
-        function update(bundle) {
-            pbBeg(0);
-            // [verdict glow] Apply the level-driven verdict brightness captured
-            // last frame (1-frame lag is imperceptible), then reset for this
-            // frame's capture in the gem path below. vg = 1 when no provider
-            // alpha was seen (legacy event path / note_detect off), leaving the
-            // authored 4.0/0.7 × glowMul brightness from _applyGlow() untouched.
-            // Only the verdict-only materials (mHitBright + its face-fill arrays,
-            // and the hit sustain outline) are scaled — never mStrHitOutline,
-            // which is the default rim for every fretted note.
-            {
-                const vg = _ndVerdictSawAlpha ? _ndVerdictMaxAlpha : 1;
-                const venueGemMul = _venueSceneOverride ? VENUE_GEM_EMISSIVE_MUL : 1;
-                for (let s = 0; s < mHitBright.length; s++) {
-                    if (mHitBright[s]) mHitBright[s].emissiveIntensity = 4.0 * glowMul * vg * venueGemMul;
-                }
-                if (mHitSusOutline) mHitSusOutline.emissiveIntensity = 0.7 * glowMul * vg * venueGemMul;
-                _ndVerdictMaxAlpha = 0;
-                _ndVerdictSawAlpha = false;
-            }
-            // Lean sustain rendering is the default (see declaration above):
-            // the trail/ribbon outline always draws; only the additive rail
-            // bloom halo is dropped. The full look (with bloom) is an opt-out.
-            // localStorage.getItem is a synchronous storage read — polled at
-            // ~1 Hz instead of every frame; the console flag still takes
-            // effect live (within a second).
-            if ((_leanSusPollCounter++ % 60) === 0) {
-                try {
-                    _leanSus = localStorage.getItem('h3d_full_sus') !== '1';
-                } catch (_) { _leanSus = true; }
-            }
-            // Materialize the text-size multiplier from the user's slider.
-            // textSize ∈ [0,1]; _textSizeMul ∈ [0.5, 1.5] with 0.5 ↦ 1.0×
-            // so default behaviour matches what the renderer did pre-slider.
-            _textSizeMul = 0.5 + textSize;
-            // Rescale inlay labels to track the live text-size slider.
-            // buildBoard() sets an initial scale using (0.5 + textSize) but
-            // _textSizeMul is only authoritative from here onward.
-            // Guard: only update when the multiplier actually changed.
-            if (_textSizeMul !== _textSizeMulApplied) {
-                _textSizeMulApplied = _textSizeMul;
-                for (let i = 0; i < _inlayLabels.length; i++) {
-                    const f = INLAY_LABEL_FRETS[i];
-                    const s = 5.5 * _textSizeMul * K * fretLabelScaleForFret(f);
-                    _inlayLabels[i].scale.set(s, s, 1);
-                }
-            }
-            _syncOpenStringPitchLabels(bundle);
-
-            pNote.reset(); pNoteEdge.reset(); pSus.reset(); pSusOutline.reset(); pSusRibbon.reset(); pSusRibbonOl.reset(); pTapChevron.reset(); pAccentHalo.reset(); pLbl.reset();
-            pBeat.reset(); pSec.reset();
-            if (projMeshArr) for (const arr of projMeshArr) for (const m of arr) m.visible = false;
-            pFretLbl.reset(); pLane.reset(); pLaneDivider.reset();
-            if (pGhostFretLbl) pGhostFretLbl.reset();
-            _scrGhostUpcomingCount.fill(0, 0, nStr);
-            pChordBox.reset(); pChordFrameFill.reset(); pChordLbl.reset(); pBarreLine.reset(); pArpBracket.reset(); pHaloBar.reset();
-            _imPMTechCount = _imFHTechCount = 0;
-            _imPMXFillCount = _imPMXLinesCount = _imFHXFillCount = _imFHXLinesCount = 0;
-            if (pPMXFill) pPMXFill.reset();
-            if (pFHXFill) pFHXFill.reset();
-            if (pMuteXLines) pMuteXLines.reset();
-            if (pFHXLines) pFHXLines.reset();
-            pNoteFretLabel.reset(); pConnectorLine.reset(); pDropLine.reset();
-            pTeachMarkLbl.reset();
-            pFretColMarker.reset(); pSusRail.reset(); pSusRailBloom.reset(); pTechPlane.reset();
-            // Clear per-frame queues in-place (avoid reallocating the array object).
-            _ndLabels.length = 0;
-            let hwyLaneArpOuterDividers = false;
-
-            // Prune expired notedetect marks once per frame instead of
-            // once per drawNote call (issue #9 perf nit). drawNote then
-            // only does the bounded (s, f, t) match — no per-note
-            // performance.now() / filter() needed. No arr[0] gate: the
-            // dedupe path can refresh any entry's expiresAt, so gating on
-            // arr[0] would silently skip expired entries behind it.
-            _ndFrameNowMs = performance.now();
-            // In-place prune — avoids allocating a new array every frame.
-            // Marks are tiny (0–5 entries typically), so a backwards splice
-            // loop is cheap and keeps the existing array object alive.
-            if (_ndHitMarks.length) {
-                for (let _pi = _ndHitMarks.length - 1; _pi >= 0; _pi--) {
-                    if (_ndHitMarks[_pi].expiresAt <= _ndFrameNowMs) _ndHitMarks.splice(_pi, 1);
-                }
-            }
-            if (_ndMissMarks.length) {
-                for (let _pi = _ndMissMarks.length - 1; _pi >= 0; _pi--) {
-                    if (_ndMissMarks[_pi].expiresAt <= _ndFrameNowMs) _ndMissMarks.splice(_pi, 1);
-                }
-            }
-            // feedBack#254 — capture core's per-note judgment provider for
-            // this frame's drawNote() calls (held-sustain glow + lit gems).
-            // bundle.getNoteState is ALWAYS present (the core stub returns
-            // null when no provider is registered), so its existence isn't
-            // a "detect mode active" signal on its own.
-            // bundle.getNoteStateProvider exposes the registered provider
-            // (or null) directly — drive cull-window / chord-rim-floor
-            // extensions off that so they don't activate in non-detect
-            // mode. Downlevel hosts without getNoteStateProvider fall
-            // back to the existence check, matching pre-PR behavior on
-            // those builds.
-            _ndGetNoteState = (bundle && typeof bundle.getNoteState === 'function') ? bundle.getNoteState : null;
-            _ndHasProvider = (bundle && typeof bundle.getNoteStateProvider === 'function')
-                ? bundle.getNoteStateProvider() != null
-                : !!_ndGetNoteState;
-
-            const now = smoothNow(bundle);
-            const t0 = now - BEHIND;
-            const t1 = now + AHEAD;
-            // With a verdict provider attached, keep notes and chord frames
-            // in the outer loop past BEHIND so async verdicts (~0.4 s late)
-            // still land while drawable; per-note / per-frame culling is
-            // tightened back below.
-            const ndVerdictT0 = _ndHasProvider
-                ? now - Math.max(BEHIND, NOTEDETECT_GEM_VERDICT_WINDOW)
-                : t0;
-            // Prune _chordVerdicts latches whose chord has fully scrolled
-            // past the loop's verdict-window cull. Forward playback never
-            // re-encounters a chord, so without this prune the map would
-            // grow unbounded for the rest of the song (each chord onset
-            // contributes one entry, ~hundreds for a typical song).
-            // verdictKey is now an integer encoded by _encodeChordVerdictKey
-            // — time component sits in the upper bits, so a direct
-            // ``k < pruneBeforeKey`` test prunes correctly without
-            // parseFloat / String.slice on every entry.
-            //
-            // Backward seek (now < lastNow): every latched entry's
-            // chord time is now ahead of `now`, the forward-only check
-            // below would skip them all and the map would grow on every
-            // loop. Clear wholesale — the chord-loop's `chDt > 0` eviction
-            // re-creates entries as chords re-enter the pre-hit window.
-            //
-            // Forward playback: iterate every entry. An earlier `break`
-            // optimization assumed Map insertion order tracked chord
-            // time, but entries are inserted when a verdict OBSERVATION
-            // lands — so a later chord whose verdict arrived first could
-            // sit before an earlier chord whose verdict was still
-            // pending, and breaking on the first in-window entry would
-            // leave the now-older later-inserted entries un-pruned. Full
-            // scan is O(n) but n is bounded (chord count in the song,
-            // ~hundreds) so the per-frame cost is microseconds.
-            if (_ndHasProvider && _chordVerdictsLastNow !== null && now < _chordVerdictsLastNow - 0.25) {
-                // Backward seek — wipe all verdict latches so notes re-judge
-                // from scratch regardless of whether chords were present.
-                _chordVerdicts.clear();
-                _susVerdictLatch.clear();
-                // Score-pop dedup too: a practice loop / rewind re-judges
-                // the same popKeys, and the wall-time TTL alone would
-                // suppress their fresh "+N" pops for up to 4 s.
-                _fxSeen.clear();
-            }
-            if (_ndHasProvider && _chordVerdicts.size > 0) {
-                if (_chordVerdictsLastNow !== null && now < _chordVerdictsLastNow - 0.25) {
-                    // already cleared above
-                } else {
-                    const pruneBefore = ndVerdictT0 - 0.5; // safety margin
-                    const pruneBeforeKey = Math.round(pruneBefore * _CV_KEY_TIME_MUL) * _CV_KEY_TIME_SLOT;
-                    for (const k of _chordVerdicts.keys()) {
-                        if (k < pruneBeforeKey) _chordVerdicts.delete(k);
-                    }
-                }
-            }
-            _chordVerdictsLastNow = now;
-
-            const notes = bundle.notes;
-            // Skip the merge when inputs are identity-equal to the last
-            // frame's; mergeHandShapeSynthChords is chart-static.
-            let chords;
-            if (_mergeCacheResult !== null
-                && _mergeCacheChordsRef === bundle.chords
-                && _mergeCacheHsRef === bundle.handShapes
-                && _mergeCacheTplRef === bundle.chordTemplates) {
-                chords = _mergeCacheResult;
-            } else {
-                chords = mergeHandShapeSynthChords(
-                    bundle.chords,
-                    bundle.handShapes,
-                    bundle.chordTemplates,
-                );
-                _mergeCacheResult = chords;
-                _mergeCacheChordsRef = bundle.chords;
-                _mergeCacheHsRef = bundle.handShapes;
-                _mergeCacheTplRef = bundle.chordTemplates;
-            }
-
-            let arpGhostHsInfer = null;
-            const hsForArpGhost = bundle.handShapes;
-            if (hsForArpGhost && hsForArpGhost.length && notes && notes.length) {
-                const nHs = hsForArpGhost.length;
-                while (_arpGhostHsInferScratch.length < nHs) _arpGhostHsInferScratch.push(false);
-                // fillArpeggioGhostInferFlags is chart-static — skip if
-                // the input refs match the previous frame's.
-                if (_arpGhostInferRefHs !== hsForArpGhost
-                    || _arpGhostInferRefNotes !== notes
-                    || _arpGhostInferRefTpl !== bundle.chordTemplates) {
-                    _arpSynthOnsetHsSet.clear();
-                    fillArpeggioGhostInferFlags(hsForArpGhost, bundle.chordTemplates, notes, _arpGhostHsInferScratch, _arpSynthOnsetHsSet);
-                    _arpGhostInferRefHs = hsForArpGhost;
-                    _arpGhostInferRefNotes = notes;
-                    _arpGhostInferRefTpl = bundle.chordTemplates;
-                }
-                arpGhostHsInfer = _arpGhostHsInferScratch;
-            }
-
-            // ── Arpeggio-persist pre-pass ─────────────────────────────────
-            // Notes in active arpeggio handshapes must keep rendering their
-            // fretboard ghost + brackets until arpBounds.end, even after
-            // their onset+sustain exits the normal back-window (t0 = now-0.5s).
-            // Build a Set of "t_s" keys so the notes loop can skip the normal
-            // window check for these notes.
-            // Reuse hoisted Set — clear instead of reallocating every frame.
-            _scrArpPersistKeys.clear();
-            const _arpPersistKeys = _scrArpPersistKeys;
-            if (arpGhostHsInfer && bundle.handShapes && notes) {
-                for (let _hi = 0; _hi < bundle.handShapes.length; _hi++) {
-                    if (!arpGhostHsInfer[_hi]) continue;
-                    const _hs = bundle.handShapes[_hi];
-                    const _lo = hsStart(_hs), _hi2 = hsEnd(_hs);
-                    if (Number.isNaN(_lo) || Number.isNaN(_hi2)) continue;
-                    if (now > _hi2 + 0.05) continue; // arpeggio already ended
-                    // Only persist notes that have already exited the normal back-window
-                    // (onset+sustain < t0). Notes still in the window enter the loop via
-                    // the normal check; future notes are gated by the t1 check below.
-                    const _nLo = lowerBoundT(notes, _lo - 0.01);
-                    for (let _ni = _nLo; _ni < notes.length; _ni++) {
-                        const _n = notes[_ni];
-                        if (_n.t > _hi2 + 0.05) break;
-                        if (_n.t + (_n.sus || 0) < t0) {
-                            _arpPersistKeys.add(_noteKey(_n.t, _n.s));
-                        }
-                    }
-                }
-            }
-
-            // ── Slide-target gem-suppression pre-pass (chart-static) ──────
-            // Detects notes in bundle.notes that are the slide/link destination
-            // of a preceding note. The gem (outline+core) is suppressed via
-            // skipBody=true, but the sustain/slide trail still renders because
-            // the trail block is now outside the !skipBody gate in drawNote().
-            //
-            // NOTE: an authored `linkNext` flag is NOT present in bundle.notes —
-            // note_to_wire() in lib/song.py emits only t, s, f, sus, sl, slu,
-            // bn, ho, po, hm, hp, pm, mt, vb, tr, ac, tp. So this is an
-            // intentional timing/fret heuristic, not a link-flag lookup.
-            //
-            // Two source patterns (source has sus > 0):
-            //   Case 1 — source has sl/slu: destination.f === source's slide target
-            //   Case 2 — same fret (hold), destination has sl/slu (hold→slide)
-            //
-            // Sources can be single notes OR chord notes (bundle.chords).
-            if (notes !== _slideTargetNotesRef || bundle.chords !== _slideTargetChordsRef) {
-                _slideTargetSet = null;
-                if (notes && notes.length) {
-                    const stSet = new Set();
-                    const checkSrc = (srcT, srcS, srcF, srcSus, srcSl) => {
-                        if (!(srcSus > 0)) return;
-                        const endT = srcT + srcSus;
-                        // Reuse the renderer's shared next-on-string tolerance
-                        // rather than a separate hardcoded literal.
-                        const EPS = NEXT_ON_STRING_T_EPS;
-                        let lo = 0, hi = notes.length;
-                        while (lo < hi) { const m = (lo + hi) >> 1; if (notes[m].t < endT - EPS) lo = m + 1; else hi = m; }
-                        for (let j = lo; j < notes.length; j++) {
-                            const q = notes[j];
-                            if (q.t > endT + EPS) break;
-                            if (q.s !== srcS || q.t <= srcT || Math.abs(q.t - endT) >= EPS) continue;
-                            const qSl = (Number.isFinite(q.sl) && q.sl >= 0) ? q.sl
-                                      : (Number.isFinite(q.slu) && q.slu >= 0) ? q.slu : -1;
-                            if (srcSl >= 0 && q.f === srcSl) { stSet.add(_noteKey(q.t, q.s)); break; } // case 1
-                            if (q.f === srcF && qSl >= 0)    { stSet.add(_noteKey(q.t, q.s)); break; } // case 2
-                        }
-                    };
-                    for (let i = 0; i < notes.length; i++) {
-                        const p = notes[i];
-                        checkSrc(p.t, p.s, p.f, p.sus,
-                            (Number.isFinite(p.sl) && p.sl >= 0) ? p.sl : (Number.isFinite(p.slu) && p.slu >= 0) ? p.slu : -1);
-                    }
-                    const rc = bundle.chords;
-                    if (rc && rc.length) {
-                        for (let ci = 0; ci < rc.length; ci++) {
-                            const ch = rc[ci]; if (!ch.notes) continue;
-                            for (let ni = 0; ni < ch.notes.length; ni++) {
-                                const cn = ch.notes[ni];
-                                checkSrc(ch.t, cn.s, cn.f, cn.sus,
-                                    (Number.isFinite(cn.sl) && cn.sl >= 0) ? cn.sl : (Number.isFinite(cn.slu) && cn.slu >= 0) ? cn.slu : -1);
-                            }
-                        }
-                    }
-                    if (stSet.size > 0) _slideTargetSet = stSet;
-                }
-                _slideTargetNotesRef = notes;
-                _slideTargetChordsRef = bundle.chords;
-            }
-
-            /** Arpeggio lane purple rails — authored-marker cache + bounds cache. */
-            let laneRailArpHsFlags = null;
-            let laneRailBoundLo = null;
-            let laneRailBoundHi = null;
-            const hsLaneRail = bundle.handShapes;
-            const notesArrForRails = notes || [];
-            if (hsLaneRail && hsLaneRail.length) {
-                const nHsL = hsLaneRail.length;
-                while (_arpLaneRailHsScratch.length < nHsL) _arpLaneRailHsScratch.push(false);
-                while (_arpRailBoundLoScratch.length < nHsL) {
-                    _arpRailBoundLoScratch.push(0);
-                    _arpRailBoundHiScratch.push(0);
-                }
-                // Authored-marker flags depend only on (handShapes, templates).
-                if (_laneRailFlagsRefHs !== hsLaneRail
-                    || _laneRailFlagsRefTpl !== bundle.chordTemplates) {
-                    fillLaneRailHandShapeFlags(hsLaneRail, bundle.chordTemplates, _arpLaneRailHsScratch);
-                    _laneRailFlagsRefHs = hsLaneRail;
-                    _laneRailFlagsRefTpl = bundle.chordTemplates;
-                }
-                // Bounds cache depends on (handShapes, chords, templates, notes).
-                if (_laneRailBoundsRefHs !== hsLaneRail
-                    || _laneRailBoundsRefChords !== chords
-                    || _laneRailBoundsRefTpl !== bundle.chordTemplates
-                    || _laneRailBoundsRefNotes !== notesArrForRails) {
-                    fillArpeggioRailShapeBoundsCaches(
-                        hsLaneRail,
-                        chords ?? [],
-                        bundle.chordTemplates,
-                        notesArrForRails,
-                        _arpLaneRailHsScratch,
-                        _arpRailBoundLoScratch,
-                        _arpRailBoundHiScratch,
-                    );
-                    _laneRailBoundsRefHs = hsLaneRail;
-                    _laneRailBoundsRefChords = chords;
-                    _laneRailBoundsRefTpl = bundle.chordTemplates;
-                    _laneRailBoundsRefNotes = notesArrForRails;
-                }
-                laneRailArpHsFlags = _arpLaneRailHsScratch;
-                laneRailBoundLo = _arpRailBoundLoScratch;
-                laneRailBoundHi = _arpRailBoundHiScratch;
-            }
-            const beats = bundle.beats;
-            // Rebuild the fret-label visibility set whenever the chart changes.
-            if (notes !== _fretLabelNotesRef) {
-                _fretLabelAllowed = _buildFretLabelSet(notes, chords, beats);
-                _fretLabelNotesRef = notes;
-            }
-            // Rebuild the measure-start time cache whenever beats change. Only
-            // beats that begin a measure carry measure >= 0; intra-measure beats
-            // (measure === -1) are skipped. Drives the lookahead window.
-            if (beats !== _measureStartsRef) {
-                _measureStartsRef = beats;
-                const _ms = [];
-                if (beats) {
-                    for (let _bi = 0; _bi < beats.length; _bi++) {
-                        const _b = beats[_bi];
-                        if (_b && Number.isFinite(_b.measure) && _b.measure >= 0) _ms.push(_b.time);
-                    }
-                }
-                _measureStarts = _ms;
-            }
-            const sections = bundle.sections;
-            const anchors = bundle.anchors;
-
-            // ── Fret wire anchor highlight ─────────────────────────────────
-            // Default all wires to gray; wires inside the active anchor range
-            // turn gold to match the dynamic highway lane boundary exactly.
-            // Uses laneBoundsFromAnchor() — the same helper the lane uses —
-            // so the gold fret wires on the board align with the lane edges:
-            //   dMin = fret - 1,  dMax = fret + width - 1
-            // e.g. { fret:3, width:4 } → dMin=2, dMax=6 → wires 2,3,4,5,6 gold.
-            if (fretWireMats.length) {
-                const _fwBounds = anchors && anchors.length
-                    ? anchorLaneBoundsAt(anchors, now) : null;
-                const _fwMin = _fwBounds ? _fwBounds.dMin : -1;
-                const _fwMax = _fwBounds ? _fwBounds.dMax : -1;
-                for (let _f = 0; _f <= NFRETS; _f++) {
-                    const _m = fretWireMats[_f];
-                    if (!_m) continue;
-                    if (_fwMin >= 0 && _f >= _fwMin && _f <= _fwMax) {
-                        _m.color.setHex(FRET_WIRE_ACTIVE_HEX);
-                        _m.opacity = FRET_WIRE_ACTIVE_OP;
-                    } else {
-                        _m.color.setHex(FRET_WIRE_IDLE_HEX);
-                        _m.opacity = FRET_WIRE_IDLE_OP;
-                    }
-                    // Baseline emissive every frame: the hit-flash pass below
-                    // lerps these toward FRET_WIRE_HIT_* in place, so they must
-                    // be re-seeded or a flash would never fade back out.
-                    _m.emissive.setHex(FRET_EMISSIVE);
-                    _m.emissiveIntensity = 1;
-                }
-            }
-
-            const lookaheadBoundsNow = (cameraMode === 'lookahead')
-                ? lookaheadComputeFretBounds(now, anchors, notes, chords)
-                : null;
-
-            // Open-string note width: same outer span as chord frame (anchor + padX,
-            // or default 4-fret window when chart has no anchor at t).
-            const padChordOpenX = NW * 0.4;
-            const openNoteLaneBoxW = chartTime => {
-                const chAncB = anchorLaneBoundsAt(anchors, chartTime);
-                if (chAncB) {
-                    const xl = fretX(chAncB.dMin);
-                    const xr = fretX(chAncB.dMax);
-                    if (xr > xl) return (xr - xl) + padChordOpenX * 2;
-                }
-                const spanF = 4;
-                const fMinCh = 1;
-                const fMaxCh = fMinCh + spanF - 1;
-                const xl = fretX(fMinCh - 1);
-                const xr = fretX(Math.max(fMaxCh, fMinCh + 2));
-                if (xr > xl) return (xr - xl) + padChordOpenX * 2;
-                return 40 * K;
-            };
-
-            // ── Frame state ───────────────────────────────────────────────
-            // Reuse hoisted scratch arrays — reset only the live [0..nStr) /
-            // [0..NFRETS] range instead of allocating new arrays every frame.
-            _scrStringSustain.fill(false, 0, nStr);
-            _scrStringAnticipation.fill(0, 0, nStr);
-            _scrFretHeat.fill(0);           // always NFRETS+1, cheap flat fill
-            _fwHitIn.fill(0);               // this frame's confirmed-hit frets
-            _fwChordAcc.clear();
-            _scrStrGlow.fill(0.5, 0, nStr);
-            _scrAccentFillBoost.fill(0, 0, nStr);
-            const noteState = {
-                stringSustain:    _scrStringSustain,
-                stringAnticipation: _scrStringAnticipation,
-                fretHeat:         _scrFretHeat,
-                strGlow:          _scrStrGlow,
-                /** Per-string extra drive for `.ac` gem fill only (`mAccentCore`). */
-                accentFillBoost:  _scrAccentFillBoost,
-            };
-
-            pbBeg(1);
-            // Compute sustain / anticipation / fret heat / per-string glow.
-            // Use lowerBoundT to skip notes far in the past (>30s sustain is
-            // unrealistic); break once notes are >2s ahead (nothing beyond
-            // contributes to fretHeat/anticipation/strGlow).
-            if (notes) {
-                const _fsLo = lowerBoundT(notes, now - 30);
-                for (let _ni = _fsLo; _ni < notes.length; _ni++) {
-                    const n = notes[_ni];
-                    if (!validString(n.s)) continue;
-                    const dt = n.t - now;
-                    if (dt > 2.0) break;
-                    const susEnd = n.t + (n.sus || 0);
-                    if (dt > 0 && dt < 0.6)
-                        noteState.stringAnticipation[n.s] = Math.max(noteState.stringAnticipation[n.s], 1 - dt / 0.6);
-                    if (n.f > 0) {
-                        if (now >= n.t && now <= susEnd) noteState.fretHeat[n.f] = 1;
-                        else if (n.t > now) noteState.fretHeat[n.f] = Math.max(noteState.fretHeat[n.f], Math.max(0, 1 - dt / 2));
-                    }
-                    if (now >= n.t && now <= susEnd) noteState.stringSustain[n.s] = true;
-                    const sustained = dt < 0 && (n.sus || 0) > 0 && now <= susEnd;
-                    const hitDist = Math.abs(dt);
-                    if (hitDist < 0.15 || sustained) {
-                        const hitFade = sustained ? 0.7 : (1 - hitDist / 0.15);
-                        noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], 1.0 + hitFade * 1.5);
-                    }
-                }
-            }
-            if (chords) {
-                // Skip chords further than 30s in the past (covers any sustained chord).
-                const _cfsLo = lowerBoundT(chords, now - 30);
-                for (let _cni = _cfsLo; _cni < chords.length; _cni++) {
-                    const ch = chords[_cni];
-                    if (!ch.notes) continue;
-                    const dt = ch.t - now;
-                    if (dt > 2.0) break;
-                    const chordNotes = filterValidNotes(ch.notes);
-                    if (chordNotes.length === 0) continue;
-                    let maxSus = 0;
-                    for (const n of chordNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
-                    const susEnd = ch.t + maxSus;
-                    for (const cn of chordNotes) {
-                        if (dt > 0 && dt < 0.6)
-                            noteState.stringAnticipation[cn.s] = Math.max(noteState.stringAnticipation[cn.s], 1 - dt / 0.6);
-                        if (cn.f > 0) {
-                            if (now >= ch.t && now <= susEnd) { noteState.fretHeat[cn.f] = 1; continue; }
-                            if (ch.t > now) noteState.fretHeat[cn.f] = Math.max(noteState.fretHeat[cn.f], Math.max(0, 1 - dt / 2));
-                        }
-                    }
-                    if (now >= ch.t && now <= susEnd)
-                        for (const cn of chordNotes) noteState.stringSustain[cn.s] = true;
-                    const sustained = dt < 0 && maxSus > 0 && now <= susEnd;
-                    const hitDist = Math.abs(dt);
-                    if (hitDist < 0.15 || sustained) {
-                        const hitFade = sustained ? 0.7 : (1 - hitDist / 0.15);
-                        for (const cn of chordNotes) {
-                            noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], 1.0 + hitFade * 1.5);
-                        }
-                    }
-                }
-            }
-
-            pbEnd(1);
-            pbBeg(2);
-            // ── Next-note-by-string lookahead (for anticipation projection) ──
-            // Ghost projection window is 0.6s; fretLastActiveTime needs +2s.
-            // Use lowerBoundT to skip past notes and break at +2s.
-            _scrNextNoteByString.fill(null, 0, nStr);
-            const nextNoteByString = _scrNextNoteByString;
-            if (notes) {
-                const _nnLo = lowerBoundT(notes, now);
-                for (let _ni = _nnLo; _ni < notes.length; _ni++) {
-                    const n = notes[_ni];
-                    if (n.t > now + 2) break;
-                    if (!validString(n.s)) continue;
-                    if (!nextNoteByString[n.s] || n.t < nextNoteByString[n.s].t) nextNoteByString[n.s] = n;
-                    if (n.f > 0) fretLastActiveTime[n.f] = now;
-                }
-            }
-            if (chords) {
-                // Time-sorted: lowerBoundT skips past historical chords in O(log N)
-                // instead of walking the entire prefix every frame.
-                const _ncLo = lowerBoundT(chords, now);
-                for (let _ci = _ncLo; _ci < chords.length; _ci++) {
-                    const ch = chords[_ci];
-                    if (ch.t > now + 2) break;
-                    if (!ch.notes || ch.t <= now) continue;
-                    for (const cn of ch.notes) {
-                        if (!validString(cn.s)) continue;
-                        if (!nextNoteByString[cn.s] || ch.t < nextNoteByString[cn.s].t) {
-                            // Reuse per-string scratch object — avoids `{ ...cn, t }` spread allocation.
-                            const _sd = _scrNextNoteByStringData[cn.s];
-                            Object.assign(_sd, cn);
-                            _sd.t = ch.t;
-                            nextNoteByString[cn.s] = _sd;
-                        }
-                        if (cn.f > 0) fretLastActiveTime[cn.f] = now;
-                    }
-                }
-            }
-
-            _drawNextByString = nextNoteByString;
-            _drawChordTemplates = bundle.chordTemplates ?? null;
-            _drawAnchors = anchors ?? null;
-            _drawTeachingMarks = !!bundle.teachingMarksVisible;
-            // Default on: only an explicit false (older bundles omit the flag) hides fg.
-            _showFingerHints = bundle.fingerHintsVisible !== false;
-
-            // ── Recent-past event per string (for _nextAnyT deadline) ─────
-            // Once a note/chord passes `now` it leaves _drawNextByString,
-            // resetting _nextAnyT and letting old gems linger too long.
-            // Scan back at least CHORD_HWY_LINGER_S so the deadline logic
-            // can see every event that lands inside any active linger
-            // window (chord frame linger and gem linger both cap at
-            // CHORD_HWY_LINGER_S — a tighter scan would miss events in
-            // (now - CHORD_HWY_LINGER_S, now - 0.6) and let the frame
-            // linger past the next event).
-            {
-                // Hoisted scratch — avoids `new Array(nStr).fill(...)` every frame.
-                const _recArr = _scrRecentByString;
-                for (let i = 0; i < nStr; i++) _recArr[i] = -Infinity;
-                if (notes) {
-                    let _ri = lowerBoundT(notes, now);
-                    for (let i = _ri - 1; i >= 0; i--) {
-                        const n = notes[i];
-                        if (n.t < now - CHORD_HWY_LINGER_S) break;
-                        if (validString(n.s) && n.t > _recArr[n.s]) _recArr[n.s] = n.t;
-                    }
-                }
-                if (chords) {
-                    // Time-sorted: start at the last chord ≤ now instead of
-                    // chords.length-1 (which walks past every future chord
-                    // when `now` is early in the song).
-                    //
-                    // lowerBoundT returns the first index with t >= now. If
-                    // chords share the same timestamp, walk forward through
-                    // the t===now run to the LAST one (so all duplicates at
-                    // `now` are included — the original `if (ch.t > now)
-                    // continue` scan-from-end included them all). When no
-                    // chord is exactly at `now`, start one slot back.
-                    const _ncHi = lowerBoundT(chords, now);
-                    let _ci = _ncHi;
-                    if (_ci < chords.length && chords[_ci].t === now) {
-                        while (_ci + 1 < chords.length && chords[_ci + 1].t === now) _ci++;
-                    } else {
-                        _ci -= 1;
-                    }
-                    for (; _ci >= 0; _ci--) {
-                        const ch = chords[_ci];
-                        if (ch.t < now - CHORD_HWY_LINGER_S) break;
-                        if (!ch.notes) continue;
-                        for (const cn of ch.notes) {
-                            if (validString(cn.s) && ch.t > _recArr[cn.s]) _recArr[cn.s] = ch.t;
-                        }
-                    }
-                }
-                _drawRecentByString = _recArr;
-            }
-
-            // ── Sorted union of next/recent event times ──────────────────
-            // Populate the scalar scratch used by _firstEventTimeGreaterThan
-            // — at most 2 * nStr finite values, then sorted ascending.
-            // Float64Array.subarray returns a view, so .sort() runs in place
-            // over the live prefix without copying or allocating.
-            // Pulls directly from _drawNextByString / _drawRecentByString
-            // (closure-scoped, populated just above) so we're independent of
-            // the recent-event prepass's inner-block ``_recArr`` alias.
-            _scrEventTimesLen = 0;
-            for (let s = 0; s < nStr; s++) {
-                const nf = _drawNextByString[s];
-                if (nf) {
-                    const tn = nf.t;
-                    if (Number.isFinite(tn)) _scrEventTimes[_scrEventTimesLen++] = tn;
-                }
-                const rt = _drawRecentByString[s];
-                if (Number.isFinite(rt)) _scrEventTimes[_scrEventTimesLen++] = rt;
-            }
-            if (_scrEventTimesLen > 1) {
-                _scrEventTimes.subarray(0, _scrEventTimesLen).sort();
-            }
-
-            // ── Ghost preview gap prepass ──────────────────────────────────
-            // For each note/chord in the upcoming 0.65s window, record the
-            // onset time of its immediate predecessor on the same string.
-            // drawNote() uses this to shrink the ghost preview window from
-            // the fixed 0.6s down to min(0.6, gap) so in dense passages the
-            // fret label doesn't float 0.6s ahead with no gem in sight.
-            //
-            // Two-pointer merge over time-sorted notes + chords so the
-            // predecessor is correct even when notes and chords interleave.
-            // Map with numeric key avoids per-frame string allocation;
-            // key = Math.round(t*1e4)*10 + s (unique for notes > 0.1 ms apart).
-            // Buffer is hoisted (_scrGhostPrevBuf) and cleared at the top of
-            // the prepass; per-string predecessor tracker likewise (_scrGhostLastT).
-            _scrGhostPrevBuf.clear();
-            const _ghostPrevBuf = _scrGhostPrevBuf;
-            {
-                for (let _i = 0; _i < nStr; _i++) _scrGhostLastT[_i] = -Infinity;
-                const _gLastT = _scrGhostLastT;
-                let _gni = notes ? lowerBoundT(notes, now - 1) : 0;
-                let _gci = 0;
-                if (chords) while (_gci < chords.length && chords[_gci].t < now - 1) _gci++;
-                while (true) {
-                    const nt = (notes && _gni < notes.length) ? notes[_gni].t : Infinity;
-                    const ct = (chords && _gci < chords.length) ? chords[_gci].t : Infinity;
-                    const minT = nt <= ct ? nt : ct;
-                    if (minT > now + 0.65 || minT === Infinity) break;
-                    if (nt <= ct) {
-                        const n = notes[_gni++];
-                        if (validString(n.s)) {
-                            _ghostPrevBuf.set(Math.round(n.t * 1e4) * 10 + n.s, _gLastT[n.s]);
-                            _gLastT[n.s] = n.t;
-                        }
-                    } else {
-                        const ch = chords[_gci++];
-                        if (ch.notes) for (const cn of ch.notes) {
-                            if (validString(cn.s)) {
-                                _ghostPrevBuf.set(Math.round(ch.t * 1e4) * 10 + cn.s, _gLastT[cn.s]);
-                                _gLastT[cn.s] = ch.t;
-                            }
-                        }
-                    }
-                }
-            }
-
-            // Ramp strGlow while the board ghost is visible so the flying note
-            // core + rim read as one solid string-coloured shape with proj.
-            // Window is (0, PROJ_WIN_MERGE=0.6s) — use lowerBoundT + break.
-            const PROJ_WIN_MERGE = 0.6;
-            if (notes) {
-                const _sgLo = lowerBoundT(notes, now);
-                for (let _ni = _sgLo; _ni < notes.length; _ni++) {
-                    const n = notes[_ni];
-                    if (!validString(n.s) || n.f <= 0) continue;
-                    const dt = n.t - now;
-                    if (dt >= PROJ_WIN_MERGE) break;
-                    const nn = nextNoteByString[n.s];
-                    if (!nn || Math.abs(nn.t - n.t) > NEXT_ON_STRING_T_EPS) continue;
-                    const blend = 1 - dt / PROJ_WIN_MERGE;
-                    noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], 1.0 + blend * 1.2);
-                }
-            }
-            if (chords) {
-                const _projLo = lowerBoundT(chords, now);
-                for (let _pci = _projLo; _pci < chords.length; _pci++) {
-                    const ch = chords[_pci];
-                    if (!ch.notes || ch.t <= now) continue;
-                    const dt = ch.t - now;
-                    if (dt >= PROJ_WIN_MERGE) break;
-                    const chordNotes = filterValidNotes(ch.notes);
-                    for (const cn of chordNotes) {
-                        if (cn.f <= 0) continue;
-                        const nn = nextNoteByString[cn.s];
-                        if (!nn || Math.abs(nn.t - ch.t) > NEXT_ON_STRING_T_EPS) continue;
-                        const blend = 1 - dt / PROJ_WIN_MERGE;
-                        noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], 1.0 + blend * 1.2);
-                    }
-                }
-            }
-
-            // Accent: brighter note body (`mGlow` in drawNote) instead of the old '>' sprite.
-            // Notes are sorted — break once past the AHEAD window.
-            if (notes) {
-                const _acLo = lowerBoundT(notes, now - AHEAD);
-                for (let _ni = _acLo; _ni < notes.length; _ni++) {
-                    const n = notes[_ni];
-                    if (!validString(n.s) || !n.ac) continue;
-                    const dt = n.t - now;
-                    if (dt > AHEAD) break;
-                    const susEnd = n.t + (n.sus || 0);
-                    const hasSus = (n.sus || 0) > 0;
-                    if (dt < -ACCENT_NOTE_LINGER_EPS && (!hasSus || now > susEnd)) continue;
-                    noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], ACCENT_NOTE_STR_GLOW);
-                    noteState.accentFillBoost[n.s] = Math.max(
-                        noteState.accentFillBoost[n.s],
-                        ACCENT_NOTE_FILL_BOOST,
-                    );
-                }
-            }
-            if (chords) {
-                const _acChordLo = lowerBoundT(chords, now - 30);
-                for (let _aci = _acChordLo; _aci < chords.length; _aci++) {
-                    const ch = chords[_aci];
-                    if (!ch.notes) continue;
-                    const dt = ch.t - now;
-                    if (dt > AHEAD) break;
-                    const chordNotes = filterValidNotes(ch.notes);
-                    if (!chordNotes.length) continue;
-                    let maxSus = 0;
-                    for (const x of chordNotes) if ((x.sus || 0) > maxSus) maxSus = x.sus;
-                    const susEnd = ch.t + maxSus;
-                    const hasChordSus = maxSus > 0;
-                    if (dt < -ACCENT_NOTE_LINGER_EPS && (!hasChordSus || now > susEnd)) continue;
-                    for (const cn of chordNotes) {
-                        if (!validString(cn.s) || !cn.ac) continue;
-                        noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], ACCENT_NOTE_STR_GLOW);
-                        noteState.accentFillBoost[cn.s] = Math.max(
-                            noteState.accentFillBoost[cn.s],
-                            ACCENT_NOTE_FILL_BOOST,
-                        );
-                    }
-                }
-            }
-
-            pbEnd(2);
-            pbBeg(3);
-            // mGlow / mAccentCore emissive writes are folded into
-            // updateStringHighlights() — same per-string scratch reads,
-            // one pass.
-            updateStringHighlights(noteState);
-            pbEnd(3);
-
-            // Active frets (notes in cooldown window) + highway intensity
-            _scrActiveFrets.clear();
-            const activeFrets = _scrActiveFrets;
-            let highwayIntensity = 0;
-            for (let f = 1; f <= NFRETS; f++) {
-                if (now - fretLastActiveTime[f] < FRET_COOLDOWN) activeFrets.add(f);
-            }
-
-            // Camera targeting — steady mode (#34): recency-weighted centroid +
-            // hysteresis over [camT0, camT1]. In lookahead mode, see
-            // lookaheadBoundsNow + lookaheadSmoothCamStep().
-            let cs = 0;
-            let camAhead = CAM_TGT_AHEAD_C;
-            let camTau = CAM_TGT_TAU_C;
-            let camHystF = CAM_TGT_HYST_C;
-            let camT0 = now - CAM_TGT_BEHIND;
-            let camT1 = now + camAhead;
-            let camWX = 0, camWSum = 0;
-            let camDistMin = 99, camDistMax = 0, camDistGot = false;
-            const camDistHystF = CAM_DIST_HYST_T + (CAM_DIST_HYST_C - CAM_DIST_HYST_T) * zoomSmoothing;
-            if (!(cameraMode === 'lookahead')) {
-                cs = cameraSmoothing;
-                camAhead = CAM_TGT_AHEAD_T + (CAM_TGT_AHEAD_C - CAM_TGT_AHEAD_T) * cs;
-                camTau = CAM_TGT_TAU_T + (CAM_TGT_TAU_C - CAM_TGT_TAU_T) * cs;
-                camHystF = CAM_TGT_HYST_T + (CAM_TGT_HYST_C - CAM_TGT_HYST_T) * cs;
-                camT0 = now - CAM_TGT_BEHIND;
-                camT1 = now + camAhead;
-            }
-
-            // Classic path (#34): tgtDist hysteresis tracks fret span over the
-            // narrowed [camT0, camT1]; lookahead mode uses lookaheadBoundsNow + span smoothing.
-            //
-            // Sustain extension: the outer loop keeps notes/chords
-            // whose sustain still rings into the visible window —
-            // n.t + (n.sus || 0) >= t0 for notes, ch.t + maxSus >= t0
-            // for chords — via the continue-filters below at the top
-            // of the single-note and chord branches. camT0 is narrower
-            // than t0, so an onset can age past camT0 while still
-            // being on screen and audible. Mirror that past-side
-            // allowance here so a held low-fret chord keeps
-            // contributing to both camDist (zoom) and camWX (X
-            // target); otherwise the camera dollies/pans away
-            // mid-sustain, re-clipping the very chord the low-fret
-            // pullback was added to keep on screen. The future side
-            // (camT1) is left alone so the #34 invariant (distant
-            // high-fret onsets don't pre-pull the camera) still holds.
-
-            // ── Song-change detection ─────────────────────────────────────────
-            // reconnect() (used for arrangement switches and splitscreen song
-            // changes) does not call renderer.destroy/init, so _camSnapped and
-            // _camPreScanned would persist into the new song and the snap pre-pass
-            // would never fire again.  Detect the change by comparing the current
-            // song+arrangement identity against the last-seen key, and reset the
-            // camera snap state (and the camera position itself) whenever it flips.
-            {
-                const si = bundle.songInfo;
-                // bundle.songInfo has no filename field (the WS song_info message
-                // never includes it).  Use window.feedBack.currentSong.filename
-                // — set by highway.js from the WS URL — combined with the
-                // arrangement index as a reliable per-song-arrangement key.
-                const currentSong = window.feedBack && window.feedBack.currentSong;
-                const key = currentSong ? currentSong.filename + '\0' + (si ? (si.arrangement_index ?? '') : '') : null;
-                if (key !== null && key !== _songKey) {
-                    _songKey = key;
-                    _camSnapped = false;
-                    _camPreScanned = false;
-                    tgtX = curX = xFretMid(CAM_LOCK_CENTER_FRET);
-                    tgtDist = curDist = CAM_DIST_BASE;
-                    prevLowFretBonus = 0;
-                    prevLockActive = false;
-                    _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
-                    _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
-                    _lookaheadCamPrevNow = null;
-                    _lookaheadLowBonusU = 0;
-                    _lookaheadHiNeckLatch = false;
-                    // Drop the previous song's measure-start cache. Otherwise
-                    // lookaheadEndTime() would size the lookahead window off the
-                    // old measure grid (with the new song's now reset to ~0 this
-                    // yields a wrong/huge tEnd) until the new beats arrive and
-                    // rebuild it — the resulting huge fret span over-zooms the
-                    // first-data snap and stays latched. Clearing it falls back
-                    // to the seconds window for this frame; the rebuild repopulates
-                    // it next frame once bundle.beats is the new array.
-                    _measureStarts = []; _measureStartsRef = null;
-                    // Drop the clock anchor so the new song's currentTime
-                    // re-anchors cleanly instead of measuring a bogus rate
-                    // across the seek-to-0 discontinuity.
-                    _clkAudioT = NaN; _clkPerf = NaN; _clkRate = 1;
-                }
-            }
-
-            // ── Camera pre-pass (first-data snap) ────────────────────────────
-            // Before any drawNote() call, iterate notes/chords to accumulate
-            // the camera targeting data for THIS frame.  If this is the first
-            // frame where fretted notes appear in the targeting window, snap
-            // curX/curDist directly to the computed targets so open-string note
-            // placement (which reads curX) and the camera are consistent on the
-            // snap frame.  After the snap _camSnapped is true and this block
-            // becomes a permanent no-op.  Open-string notes (f === 0) do not
-            // contribute to preWX/preWSum and therefore do not trigger the snap.
-            if (!_camSnapped) {
-                // One-time full-chart scan (runs exactly once when both bundle.notes
-                // and bundle.chords are available).  If no fretted note exists
-                // anywhere in either array the snap can never fire, so we disable
-                // the per-frame pre-pass immediately to avoid permanent overhead.
-                // Both arrays are checked because some arrangements have fretted
-                // notes only inside chords (chord-only charts, keys arrangements).
-                if (!_camPreScanned && notes && chords) {
-                    _camPreScanned = true;
-                    const hasFrettedNote  = notes.some(n => n.f > 0 && validString(n.s));
-                    const hasFrettedChord = chords.some(
-                        ch => ch.notes && ch.notes.some(cn => cn.f > 0 && validString(cn.s)));
-                    if (!hasFrettedNote && !hasFrettedChord) _camSnapped = true;
-                }
-                if (!_camSnapped) {
-                    if (cameraMode === 'lookahead') {
-                        const bd = lookaheadBoundsNow;
-                        if (bd) {
-                            _lookaheadCamX = lookaheadTargetWorldX(bd.minF, bd.maxF);
-                            _lookaheadFretSpan = Math.max(1, bd.maxF - bd.minF + 1);
-                            const lockSnapEl = cameraLockLow && bd.maxF <= 12;
-                            if (lockSnapEl) {
-                                const lockedBaseU = camBaseDistU(12);
-                                const lockedBonusU = camLowFretPullbackU(1);
-                                const lockZoomMul = CAM_LOCK_ZOOM_MIN +
-                                    (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
-                                tgtX = xFretMid(CAM_LOCK_CENTER_FRET);
-                                tgtDist = (lockedBaseU + lockedBonusU) * K * lockZoomMul;
-                                prevLowFretBonus = lockedBonusU;
-                                _lookaheadLowBonusU = lockedBonusU;
-                            } else {
-                                const baseDU = camBaseDistU(_lookaheadFretSpan);
-                                const lowBU = camLowFretPullbackU(bd.minF);
-                                tgtDist = (baseDU + lowBU) * K;
-                                prevLowFretBonus = lowBU;
-                                _lookaheadLowBonusU = lowBU;
-                                tgtX = _lookaheadCamX;
-                            }
-                            curX = tgtX;
-                            curDist = tgtDist;
-                            _camSnapped = true;
-                            _lookaheadCamPrevNow = now;
-                        }
-                    } else {
-                    let preWX = 0, preWSum = 0, preDistMin = 99, preDistMax = 0, preDistGot = false;
-                    if (notes) {
-                        for (const n of notes) {
-                            // bundle.notes is time-sorted: skip fully-expired sustains,
-                            // break once the onset is beyond the camera window.
-                            if (n.t + (n.sus || 0) < camT0) continue;
-                            if (n.t > camT1) break;
-                            if (!validString(n.s)) continue;
-                            const nInWin  = n.f > 0 && n.t >= camT0;
-                            const nSusNow = n.f > 0 && n.t < camT0 && n.t + (n.sus || 0) >= now;
-                            if (nInWin || nSusNow) {
-                                const w = Math.exp(-Math.abs(n.t - now) / camTau);
-                                preWX += xFretMid(n.f) * w; preWSum += w;
-                                if (n.f < preDistMin) preDistMin = n.f;
-                                if (n.f > preDistMax) preDistMax = n.f;
-                                preDistGot = true;
-                            }
-                        }
-                    }
-                    if (chords) {
-                        for (const ch of chords) {
-                            if (!ch.notes) continue;
-                            // bundle.chords is time-sorted: break once onset is beyond window.
-                            if (ch.t > camT1) break;
-                            const chNotes = filterValidNotes(ch.notes);
-                            if (!chNotes.length) continue;
-                            let maxSus = 0;
-                            for (const n of chNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
-                            if (ch.t + maxSus < camT0) continue; // fully expired
-                            const chOnsetInWin = ch.t >= camT0;
-                            const chSusNow     = ch.t < camT0 && ch.t + maxSus >= now;
-                            if (!chOnsetInWin && !chSusNow) continue;
-                            const chW = Math.exp(-Math.abs(ch.t - now) / camTau);
-                            for (const cn of chNotes) {
-                                const cnOk = chOnsetInWin || (chSusNow && ch.t + (cn.sus || 0) >= now);
-                                if (cn.f > 0 && cnOk) {
-                                    preWX += xFretMid(cn.f) * chW; preWSum += chW;
-                                    if (cn.f < preDistMin) preDistMin = cn.f;
-                                    if (cn.f > preDistMax) preDistMax = cn.f;
-                                    preDistGot = true;
-                                }
-                            }
-                        }
-                    }
-                    if (preWSum > 0) {
-                        _applyNoteCamTargets(preWX, preWSum, preDistMin, preDistMax, preDistGot,
-                                             camHystF, camDistHystF, /* skipDistHyst= */ true);
-                        curX    = tgtX;
-                        curDist = tgtDist;
-                        _camSnapped = true;
-                    }
-                    } // end steady-mode pre-pass branch
-                } // end !_camSnapped (post-prescan guard)
-            }
-
-            pbBeg(4);
-            // ── Single notes ──────────────────────────────────────────────
-            // Reset the per-frame fret-label dedup set so stacked labels from
-            // multiple strings at the same onset/fret (arpeggio, synth chord) don't repeat.
-            _frameLabeledKeys.clear();
-            // Tracks which (chordId → Set<stringIndex>) pairs already had
-            // brackets drawn by the note-stream loop, so the chord loop can
-            // skip duplicate bracket draws for the same string.
-            // Hoisted Map — clear (rather than reallocate) so the per-frame
-            // chord-bracket dedupe doesn't churn GC in dense arpeggio passages.
-            // (The inner Sets stored as values lose their Map reference on
-            // .clear() and get GC'd along with the keys; only the outer Map
-            // is reused.)
-            _scrNoteStreamBracketStrings.clear();
-            const _noteStreamBracketStrings = _scrNoteStreamBracketStrings;
-            _scrLastFretForString.fill(undefined, 0, nStr);
-            const lastFretForString = _scrLastFretForString;
-            if (notes) {
-                // Start 30s before now — conservative enough to include any arpeggio
-                // persist window while skipping the bulk of old notes in long songs.
-                // The arpPersistKeys check below guards the rare notes that are even
-                // older and still visible (only possible for unrealistically long HS).
-                const _noteRenderLo = lowerBoundT(notes, now - 30);
-                for (let _ni = _noteRenderLo; _ni < notes.length; _ni++) {
-                    const n = notes[_ni];
-                    if (n.f > 0 && n.t > now && n.t < now + 2) activeFrets.add(n.f);
-                    if (n.t > now) {
-                        const dt = n.t - now;
-                        if (dt < AHEAD) highwayIntensity = Math.max(highwayIntensity, 1 - dt / AHEAD);
-                    }
-                    // Far-future notes are always skipped — arpGhostActive
-                    // timing handles when the ghost appears for upcoming arp notes.
-                    // Notes are time-sorted so everything beyond t1 can be skipped entirely.
-                    if (n.t > t1) break;
-                    // Past-window arp notes are exempted from the back-window skip
-                    // so their fretboard ghost + brackets persist until arpBounds.end.
-                    // ndVerdictT0 extends the window when a note-detect provider is
-                    // attached so async verdicts still land while drawable.
-                    const _inArpPersist = _arpPersistKeys.has(_noteKey(n.t, n.s));
-                    if (!_inArpPersist && n.t + (n.sus || 0) < ndVerdictT0) continue;
-                    if (!validString(n.s)) continue;
-                    // Suppress the gem for linkNext slide-target notes (skipBody=true).
-                    // The sustain/slide trail still renders because it now lives outside
-                    // the !skipBody gate in drawNote().
-                    const _isSlideTgt = !!(_slideTargetSet && _slideTargetSet.has(_noteKey(n.t, n.s)));
-                    // Always show the fret label — suppressing it for repeated frets on the same
-                    // string caused the label to be invisible throughout the note's flight and
-                    // only appear moments before being played (when the previous note's linger
-                    // window expired).  Each note now owns its label for its full flight.
-                    const skipLabel = false;
-                    let singleOpenX;
-                    if (n.f === 0) {
-                        const ab = anchorLaneBoundsAt(anchors, n.t);
-                        if (ab) singleOpenX = (xFret(ab.dMin) + xFret(ab.dMax)) / 2;
-                    }
-                    const singleOpenLaneW = n.f === 0 ? openNoteLaneBoxW(n.t) : undefined;
-                    const arGhostCid = arpeggioChordIdForNoteWithInferCache(
-                        n,
-                        bundle.handShapes,
-                        bundle.chordTemplates,
-                        notes,
-                        arpGhostHsInfer,
-                    );
-                    const _arpBoundsForNote = arGhostCid != null
-                        ? arpHsBoundsForNote(n, bundle.handShapes, arpGhostHsInfer)
-                        : null;
-                    drawNote(
-                        n,
-                        now,
-                        singleOpenX,
-                        skipLabel,
-                        _isSlideTgt,
-                        GHOST_HOLD_AFTER_ONSET,
-                        singleOpenLaneW,
-                        arGhostCid != null,
-                        arGhostCid,
-                        arGhostCid != null,
-                        _arpBoundsForNote,
-                        _ghostPrevBuf.get(Math.round(n.t * 1e4) * 10 + n.s) ?? -Infinity,
-                        _arpBoundsForNote !== null, // showDropLine: white line for arp note-stream notes
-                    );
-                    if (arGhostCid != null) {
-                        const _arpBounds = _arpBoundsForNote;
-                        if (_arpBounds) {
-                            // Synth-onset-match handshapes show ghost fret numbers but not [ ] brackets.
-                            if (!_arpSynthOnsetHsSet.has(_arpBounds.start)) {
-                                // Open-string bracket X: always use the anchor at the
-                                // handshape START time (not n.t, not now) so the bracket
-                                // position stays fixed throughout the arpeggio even when
-                                // the chart anchor changes mid-pattern.
-                                const _arpBrktAncB = n.f === 0
-                                    ? anchorLaneBoundsAt(anchors, _arpBounds.start)
-                                    : null;
-                                const _bx = n.f === 0
-                                    ? (_arpBrktAncB
-                                        ? (xFret(_arpBrktAncB.dMin) + xFret(_arpBrktAncB.dMax)) / 2
-                                        : (singleOpenX !== undefined ? singleOpenX : curX))
-                                    : xFretMid(n.f);
-                                const _openHalfW = (() => {
-                                    if (n.f !== 0) return null;
-                                    if (_arpBrktAncB) {
-                                        const _xl = xFret(_arpBrktAncB.dMin), _xr = xFret(_arpBrktAncB.dMax);
-                                        if (_xr > _xl) return Math.max(0.22, (_xr - _xl + NW * 0.4 * 2) * 0.96 / (40 * K)) * 20 * K;
-                                    }
-                                    return singleOpenLaneW != null ? Math.max(0.22, singleOpenLaneW * 0.96 / (40 * K)) * 20 * K : null;
-                                })();
-                                drawArpBrackets(_bx, sY(n.s), _arpBounds.start - now, _arpBounds.end, now, n.s, n.f === 0, _openHalfW);
-                                // Record that this (chordId:occurrenceStart, string) pair has brackets
-                                // so the chord loop doesn't draw a second set on the same string.
-                                // Key includes the arp occurrence start time so two separate arp
-                                // sequences sharing the same chord template ID don't suppress each other.
-                                const _nsbKey = arGhostCid + ':' + _arpBoundsForNote.start;
-                                let _nsbSet = _noteStreamBracketStrings.get(_nsbKey);
-                                if (!_nsbSet) { _nsbSet = new Set(); _noteStreamBracketStrings.set(_nsbKey, _nsbSet); }
-                                _nsbSet.add(n.s);
-                            }
-                        }
-                    }
-                    lastFretForString[n.s] = n.f;
-                    // Onset in window OR started before the window but
-                    // still sustaining right now. Gate sustain carry-over
-                    // against the current frame time so camera framing
-                    // releases as soon as the sustain is no longer
-                    // rendered on screen.
-                    if (!(cameraMode === 'lookahead')) {
-                    const nInWin = n.t >= camT0 && n.t <= camT1;
-                    const nSusActive = n.t < camT0 && n.t + (n.sus || 0) >= now;
-                    if (n.f > 0 && (nInWin || nSusActive)) {
-                        // Symmetric decay around now: previously this
-                        // clamped n.t - now at 0, giving every past-
-                        // onset note weight 1. That was a tolerable
-                        // approximation when the past window was 0.2 s
-                        // (camT0), but the sustain extension widens
-                        // the past side to seconds for held notes — a
-                        // 2-second-old ringing sustain would otherwise
-                        // pin camWX as strongly as a fresh note and
-                        // stale-out the framing for the current
-                        // phrase. Math.abs lets old sustains decay on
-                        // the same time-constant as future notes,
-                        // matching each mode's intent: twitchy
-                        // (camTau=0.35 s) drops a 0.2 s-old note's
-                        // weight to ~0.56 (consistent with "react to
-                        // recent only"), calm (camTau=0.9 s) to ~0.80
-                        // (consistent with "average a wider window").
-                        // Weight is still 1 at onset.
-                        const w = Math.exp(-Math.abs(n.t - now) / camTau);
-                        camWX   += xFretMid(n.f) * w;
-                        camWSum += w;
-                        if (n.f < camDistMin) camDistMin = n.f;
-                        if (n.f > camDistMax) camDistMax = n.f;
-                        camDistGot = true;
-                    }
-                    }
-                }
-            }
-
-            pbEnd(4);
-            pbBeg(5);
-            // ── Chords ────────────────────────────────────────────────────
-            if (chords) {
-                // Single-pass shape-run tracking: the previous pre-loop scanned
-                // every chord (and re-allocated chordShapeSignature() per chord)
-                // each frame, even though the render loop already iterates the
-                // full array. We compute runSig inline once per chord and reuse
-                // it for both first-in-run detection and isRepeat below.
-                // SHAPE_RUN_GAP_S also resets the run when the time gap from
-                // the previous chord exceeds the same 0.5 s window used for
-                // isRepeat — a chord shape that re-appears after a real
-                // musical gap should re-show its label, not be treated as a
-                // continuing run from many bars ago.
-                const SHAPE_RUN_GAP_S = 0.5;
-                let runSigPrev = null;
-                let prevAnyChordTime = -Infinity;
-                let prevChordSig = null;
-                let prevChordTime = -1;
-
-                // Skip past chords that are too old to render. The per-chord filter
-                // (ch.t + _chFilterSus >= ndVerdictT0) passes the earliest chord when
-                // ch.t >= ndVerdictT0 - AHEAD (worst case: _chFilterSus = AHEAD for a
-                // chord with no explicit sustain). Binary search avoids iterating
-                // hundreds of past chords every frame in dense PM/FH sections.
-                const _chordsLoIdx = lowerBoundT(chords, ndVerdictT0 - AHEAD);
-                // Prime shape-run tracking from the chord immediately before the window
-                // so isRepeat and firstInShapeRun are correct on the first visible chord.
-                if (_chordsLoIdx > 0) {
-                    const _pc = chords[_chordsLoIdx - 1];
-                    if (_pc && _pc.notes) {
-                        const _ps = chordShapeSignature(_pc);
-                        if (_ps !== null) {
-                            runSigPrev = _ps;
-                            prevAnyChordTime = _pc.t;
-                            prevChordSig = _ps;
-                            prevChordTime = _pc.t;
-                        }
-                    }
-                }
-
-                for (let ci = _chordsLoIdx; ci < chords.length; ci++) {
-                    const ch = chords[ci];
-                    // Chords are time-sorted — everything beyond t1 is outside the
-                    // visible window and contributes nothing (activeFrets needs t<now+2,
-                    // highwayIntensity needs dt<AHEAD, both < t1).
-                    if (ch.t > t1) break;
-                    const runSig = chordShapeSignature(ch);
-                    let firstInShapeRun;
-                    if (runSig === null) {
-                        firstInShapeRun = true;
-                    } else {
-                        const gap = ch.t - prevAnyChordTime;
-                        firstInShapeRun = (runSig !== runSigPrev) || gap > SHAPE_RUN_GAP_S;
-                        runSigPrev = runSig;
-                        // Only valid chords update the run-gap clock — an entry
-                        // whose runSig is null (no notes / unusable chordId)
-                        // shouldn't make the next real chord look like a tiny
-                        // gap and silently fall into a "still in the run" state.
-                        prevAnyChordTime = ch.t;
-                    }
-                    if (!ch.notes) continue;
-                    // Filter chord notes to in-range strings once. All
-                    // chord-level aggregations (maxSus, repeat-chord
-                    // signature, open-string centroid, frame-box bounds,
-                    // active-fret highlights, camera-window dist) read
-                    // from chordNotes so a clamped 9th-string note can't,
-                    // for instance, extend the chord's linger beyond its
-                    // visible sustain.
-                    const chordNotes = filterValidNotes(ch.notes);
-                    if (chordNotes.length === 0) continue;
-                    const chShape = mergeChordShape(ch, chordNotes, bundle.chordTemplates);
-
-                    if (ch.t > now) {
-                        const dt = ch.t - now;
-                        if (dt < AHEAD) highwayIntensity = Math.max(highwayIntensity, 1 - dt / AHEAD);
-                    }
-                    if (ch.t > now && ch.t < now + 2)
-                        for (const cn of chordNotes) { if (cn.f > 0) activeFrets.add(cn.f); }
-
-                    let maxSus = 0;
-                    for (const n of chordNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
-                    // When maxSus=0 (no explicit sustain on chord notes, including
-                    // all h3dSynth chords) use AHEAD as the filter window so the
-                    // chord stays in the loop long enough for a handshape-derived
-                    // sustain rail to finish drawing. The rail itself gates on
-                    // _dtSusEnd>0, so chords with no actual sustain produce no
-                    // visual artifact despite staying in the loop longer.
-                    // ndVerdictT0 extends the window when a note-detect provider is
-                    // attached so async verdicts still land while drawable.
-                    const _chFilterSus = maxSus > 0 ? maxSus : AHEAD;
-                    if (ch.t + _chFilterSus < ndVerdictT0) continue;
-                    if (ch.t > t1) break;
-
-                    // Repeat-chord detection (consecutive same shape, short gap).
-                    // Reuses runSig computed at loop entry — same signature as the
-                    // dedicated chordShapeSignature() call we used to make twice.
-                    // Synthetic chords (h3dSynth — injected at handshape onsets by
-                    // mergeHandShapeSynthChords) are never real strums, so they must
-                    // not update prevChordSig/prevChordTime. Without this guard a
-                    // real chord whose handshape generates a synth onset at the
-                    // handshape start_time (e.g. a slide-in where the real strum
-                    // falls mid-handshape, > 28 ms after the onset) would see the
-                    // synth as its "previous chord" and be falsely flagged isRepeat.
-                    const isRepeat = runSig !== null && prevChordSig === runSig && Math.abs(ch.t - prevChordTime) < 0.5;
-                    if (!ch.h3dSynth) {
-                        prevChordSig = runSig;
-                        prevChordTime = ch.t;
-                    }
-
-                    // Anchor selection for chord frame + open-string X + sustain rails:
-                    // • Upcoming (chDtEarly > 0): onset time — frame previews the correct
-                    //   neck region before the chord hits the line.
-                    // • Past, actively sustaining (now < ch.t + maxSus): onset time — frame
-                    //   stays at the frets where the chord was struck. Using `now` here
-                    //   causes the frame to jump to whichever anchor is active at `now`,
-                    //   which may be a different/wider region and makes the sustain box
-                    //   appear in the wrong fret zone ("invading" adjacent anchors).
-                    // • Past, linger-only (sustain expired or chord had no sustain): `now`
-                    //   — brief fade-out frame tracks the current lane position so it
-                    //   doesn't visibly drift while the lane has already transitioned.
-                    const chDtEarly = ch.t - now;
-                    const _chAnchorT = chDtEarly > 0 ? ch.t
-                        : (maxSus > 0 && now < ch.t + maxSus) ? ch.t
-                        : now;
-                    const chAncB = anchorLaneBoundsAt(anchors, _chAnchorT);
-                    // Open-string X: chart <anchor> lane centre when present (not curX /
-                    // fretted centroid), matching highway span.
-                    let chordCX = curX;
-                    if (chAncB) chordCX = (xFret(chAncB.dMin) + xFret(chAncB.dMax)) / 2;
-                    else {
-                        let cxL = Infinity, cxR = -Infinity, fretted = 0;
-                        for (const cn of chordNotes) {
-                            if (cn.f > 0) {
-                                const fx = xFretMid(cn.f);
-                                if (fx < cxL) cxL = fx;
-                                if (fx > cxR) cxR = fx;
-                                fretted++;
-                            }
-                        }
-                        if (fretted > 0) chordCX = (cxL + cxR) / 2;
-                    }
-
-                    // Horizontals for chord frame + open-string mesh width. With anchors,
-                    // span matches HWY lane columns (wire dMin..dMax); no extra pad.
-                    let chordFrameXL = null, chordFrameXR = null, chordOpenBoxW = null;
-                    let chordFrameAnchorMatched = false;
-                    if (chShape.size > 1) {
-                        let fMinCh = 99, fMaxCh = 0, anyFretted = false;
-                        for (const [, f] of chShape) {
-                            if (f > 0) {
-                                anyFretted = true;
-                                fMinCh = Math.min(fMinCh, f);
-                                fMaxCh = Math.max(fMaxCh, f);
-                            }
-                        }
-                        // Prefer the anchor span so chord frames and arpeggio
-                        // frames align with the highway lane window — BUT only
-                        // when the chord's fretted notes actually fall within
-                        // the anchor range. If the anchor at this chord's time
-                        // doesn't cover the chord's frets (e.g. a chord at frets
-                        // 2–4 with an anchor locked to frets 5–8), the framebox
-                        // would clip the very gems it's supposed to contain, so
-                        // fall back to chord-fret-based bounds instead.
-                        const anchorCoversChordFrets = chAncB && anyFretted
-                            ? (fMinCh >= chAncB.dMin && fMaxCh <= chAncB.dMax)
-                            : true; // all-open chord: anchor centre is fine
-                        if (chAncB && anchorCoversChordFrets) {
-                            chordFrameXL = xFret(chAncB.dMin);
-                            chordFrameXR = xFret(chAncB.dMax);
-                            chordFrameAnchorMatched = true;
-                        } else if (anyFretted) {
-                            chordFrameXL = xFret(fMinCh - 1);
-                            chordFrameXR = xFret(Math.max(fMaxCh, fMinCh + 2));
-                        } else {
-                            const wNut = openNoteLaneBoxW(ch.t);
-                            chordFrameXL = chordCX - wNut * 0.5;
-                            chordFrameXR = chordCX + wNut * 0.5;
-                        }
-                        if (chordFrameXL != null && chordFrameXR != null) {
-                            const span = Math.abs(chordFrameXR - chordFrameXL);
-                            if (span > 1e-8) {
-                                // Anchor-driven lane stripes span [dMin..dMax] wire-to-wire with
-                                // no horizontal pad — match that ONLY when the frame is actually
-                                // following the anchor (all-open chord, fallback path). The
-                                // fretted-span path always pads so the frame breathes around
-                                // the outermost fretted notes; without the pad it sat exactly
-                                // on the fret lines and looked clipped.
-                                if (chordFrameAnchorMatched) chordOpenBoxW = span;
-                                else {
-                                    const padX = NW * 0.4;
-                                    chordOpenBoxW = span + padX * 2;
-                                }
-                            }
-                        }
-                    }
-
-                    const laneWForOpenStrings = (chordOpenBoxW != null && chordOpenBoxW > 1e-8)
-                        ? chordOpenBoxW
-                        : openNoteLaneBoxW(ch.t);
-
-                    const hsHintFrame = chordHandShapeArpeggioHint(ch, bundle.handShapes, bundle.chordTemplates);
-                    const hsTimeWinFrame = hsHintFrame.hs
-                        ? { tLo: hsStart(hsHintFrame.hs) - 0.06, tHi: hsEnd(hsHintFrame.hs) + 0.06 }
-                        : null;
-                    // chordShapeCoveredByStandaloneNotes is now cached per
-                    // chord (see _arpCoverCache), so a direct call from the
-                    // deferChordGems short-circuit chain is both lazy
-                    // (skipped for branches that don't need it) AND O(1)
-                    // when re-hit later in the same frame. The previous
-                    // per-chord IIFE memo is therefore redundant — drop it
-                    // to avoid the per-chord closure allocation in dense
-                    // PM/FH passages.
-                    const inferredArpPattern = (!hsHintFrame.hs
-                        || handShapeChartSpanSec(hsHintFrame.hs) >= ARP_INFER_MIN_HAND_SHAPE_SPAN_S)
-                        && inferArpeggioFromNotePattern(
-                            ch, chShape, notes, hsTimeWinFrame, bundle.handShapes);
-                    // Only suppress the chord gems when standalone notes really
-                    // cover the arpeggio shape; otherwise explicit/synth hand
-                    // shapes can produce an empty lavender frame with no notes
-                    // inside (e.g. template-marked `-arp` chord rows).
-                    // Lazy wrapper so the note-stream scan is skipped when
-                    // neither branch needs it (short-circuit evaluation).
-                    const noteStreamCoversArpShape = () => chordShapeCoveredByStandaloneNotes(ch, chShape, notes);
-                    const deferChordGems = (ch.h3dSynth && noteStreamCoversArpShape())
-                        || inferredArpPattern
-                        || (hsHintFrame.explicit && hsHintFrame.covered && noteStreamCoversArpShape());
-                    /**
-                     * Lavender chord frame + purple highway rails: authored
-                     * arpeggio metadata only. RS ``highDensity`` marks gallops /
-                     * repeated strums on the same voicing (e.g. Frantic ~2:46) —
-                     * not arpeggio; keep ``hd`` for sustain-ribbon width via
-                     * ``chordSusTrailMatchArpFrame``.
-                     *
-                     * Only the chord that INITIATES the handshape span gets
-                     * the lavender treatment — subsequent strums of the same
-                     * voicing within the same handshape window are repeats and
-                     * render as ordinary chord frames. Proximity to
-                     * hsStart() (≤ 100 ms) identifies the initiating chord
-                     * regardless of how wide the span is.
-                     */
-                    const _hsStartT = hsHintFrame.hs ? hsStart(hsHintFrame.hs) : NaN;
-                    const chordHighwayLavenderArpVisual = hsHintFrame.explicit
-                        && !isNaN(_hsStartT) && Math.abs(ch.t - _hsStartT) <= 0.1;
-                    const chordSusTrailMatchArpFrame = chordWireHighDensity(ch)
-                        || chordHighwayLavenderArpVisual;
-
-                    // Onset in window OR chord started before the window
-                    // but is still sustaining right now. Gate sustain
-                    // carry-over against the current frame time so camera
-                    // framing releases as soon as the chord is no longer
-                    // rendered on screen.
-                    const chOnsetInWin = ch.t >= camT0 && ch.t <= camT1;
-                    const chSusActive  = ch.t < camT0 && ch.t + maxSus >= now;
-                    const chWindowed   = chOnsetInWin || chSusActive;
-                    // Symmetric decay — see matching comment in the
-                    // single-note branch. The chord-wide chW uses
-                    // ch.t (not per-note onset) since chord notes
-                    // share a strum time.
-                    const chW          = chWindowed ? Math.exp(-Math.abs(ch.t - now) / camTau) : 0;
-                    // Next-chord tail: same voicing (``highDensity`` gallop) keeps full linger + optional
-                    // fade suppression inside [hold−fade, hold]; a voicing change clips the tail to the
-                    // chart gap so D5→D#5 (~185 ms) does not stack two cyan frames (Frantic ~2:47).
-                    let cjNext = null;
-                    for (let j = ci + 1; j < chords.length; j++) {
-                        const cj = chords[j];
-                        if (!cj?.notes) continue;
-                        if (filterValidNotes(cj.notes).length === 0) continue;
-                        cjNext = cj;
-                        break;
-                    }
-                    // Nearest following event (chord OR single note) — used by
-                    // chordTailMul so the framebox vanishes the moment any next
-                    // event is played, not just when the next chord arrives.
-                    // Pull from the same sorted scalar scratch used by drawNote
-                    // — the per-string Math.min walk became O(log N) over the
-                    // shared 2*nStr buffer.
-                    const _chFirstEventAfter = _firstEventTimeGreaterThan(ch.t + 1e-6);
-                    const _chNextEventT = cjNext != null
-                        ? Math.min(cjNext.t, _chFirstEventAfter)
-                        : _chFirstEventAfter;
-                    let chordTailHoldS = CHORD_HWY_LINGER_S;
-                    let chordNextSoon = false;
-                    if (cjNext && cjNext.t > ch.t + 1e-6) {
-                        // Clip the hold tail to the gap for both same-voicing (repeat)
-                        // and different-voicing chords. The chordTailMul instant-cut
-                        // check handles the precise zero at onset; the clipped holdS
-                        // prevents the outer gate and hwyPostHitTailFadeMul from
-                        // lingering past that point.
-                        chordTailHoldS = Math.min(CHORD_HWY_LINGER_S, Math.max(cjNext.t - ch.t, 1e-3));
-                    }
-                    // feedBack#254 — engine verdicts land ~0.4 s after the
-                    // chord crosses; on a fast different-voicing sequence
-                    // the clip above can shrink the rim's draw life below
-                    // that, so the green/red latch is set but the rim isn't
-                    // drawn anymore. When a verdict provider is attached,
-                    // floor the hold at NOTEDETECT_GEM_VERDICT_WINDOW so
-                    // the tinted rim is actually visible.
-                    //
-                    // This deliberately overrides the "voicing-change clip
-                    // prevents two stacked cyan frames" behavior documented
-                    // above (the D5→D#5 / Frantic ~2:47 case): the post-hit
-                    // z clamp (Math.min(0, dZ(chDt)) below) pins extended
-                    // frames at z=0, so the two frames do overlap in plane
-                    // — they're distinguished by their now-tinted rim
-                    // colors (green/red verdict vs teal default) rather
-                    // than perspective depth. In detect mode that's the
-                    // right trade: verdict visibility beats the cleaner
-                    // approach silhouette. Without detect mode the
-                    // original clip still applies.
-                    if (_ndHasProvider && chordTailHoldS < NOTEDETECT_GEM_VERDICT_WINDOW) {
-                        chordTailHoldS = NOTEDETECT_GEM_VERDICT_WINDOW;
-                    }
-                    const chordTailFadeS = Math.min(CHORD_HWY_FADE_S, chordTailHoldS);
-
-                    // ── Approaching-arpeggio first-note identification ──────────────────
-                    // When an authored arpeggio chord frame is still approaching (not yet
-                    // at the hit line), only the first note to be played is shown as a gem.
-                    // All others are suppressed until chDtEarly <= 0 so the frame doesn't
-                    // flood the player's view with simultaneous gems before they arrive.
-                    // The first note is the earliest match in the note stream within the
-                    // handshape window. If no note-stream note matches the chord shape
-                    // within the handshape (i.e. there is no sequential arpeggio pattern),
-                    // _arpApproachFirstNote stays null and ALL chord gems are shown — this
-                    // handles chords that are played simultaneously even when tagged as arp.
-                    let _arpApproachFirstNote = null;
-                    if (chordHighwayLavenderArpVisual && !deferChordGems
-                        && chDtEarly > 0 && hsHintFrame.hs) {
-                        const _aHsLo = hsStart(hsHintFrame.hs);
-                        const _aHsHi = hsEnd(hsHintFrame.hs);
-                        let _aFirstT = Infinity;
-                        const _aNLo = lowerBoundT(notes, _aHsLo - 0.08);
-                        for (let _ani = _aNLo; _ani < notes.length; _ani++) {
-                            const _an = notes[_ani];
-                            if (_an.t > _aHsHi + 0.08) break;
-                            if (!validString(_an.s)) continue;
-                            for (const _acn of chordNotes) {
-                                if (_acn.s === _an.s && _acn.f === _an.f && _an.t < _aFirstT) {
-                                    _aFirstT = _an.t;
-                                    _arpApproachFirstNote = _acn;
-                                    break;
-                                }
-                            }
-                        }
-                        // No fallback to chordNotes[0]: if the note stream has no sequential
-                        // notes matching this shape, the chord is played simultaneously and
-                        // all gems must be shown.
-                    }
-
-                    // ── Deferred-arpeggio gem fallback ─────────────────────────────────
-                    // When gems are deferred to the note stream (deferChordGems=true) but
-                    // no individual note matching the chord shape falls within the chord's
-                    // onset cluster window, the frame box has no gems at its Z position.
-                    // Show all chord gems as a preview so the frame box isn't empty.
-                    // Uses the same onset window as chordShapeCoveredByStandaloneNotes so
-                    // the fallback deactivates precisely when the stream truly covers the
-                    // onset. Inlined (not an IIFE) to skip the per-chord closure allocation.
-                    let _deferFallback = false;
-                    if (deferChordGems && chDtEarly > 0) {
-                        _deferFallback = true;
-                        const _fLo = ch.t - ARP_FRAME_ONSET_PAD_S;
-                        const _fHi = ch.t + ARP_FRAME_ONSET_CLUSTER_S;
-                        let _fi = lowerBoundT(notes, _fLo - 0.02);
-                        for (; _fi < notes.length; _fi++) {
-                            const _fn = notes[_fi];
-                            if (_fn.t > _fHi) break;
-                            if (_fn.t < _fLo) continue;
-                            const _fef = chShape.get(_fn.s);
-                            if (_fef !== undefined && _fef === _fn.f) { _deferFallback = false; break; }
-                        }
-                    }
-
-                    // Suppress gems AND frame for hand-shape-synthesized chords whose
-                    // notes are already rendered individually via the note stream. Showing
-                    // chord gems or a framebox for a synth chord that duplicates the note
-                    // stream looks like phantom notes/chords. Check: any standalone note
-                    // matching any shape string in the onset window → player is already
-                    // guided by the note stream. Weaker than chordShapeCoveredByStandaloneNotes
-                    // (all strings covered) to handle patterns where one shape string only
-                    // appears well after the onset cluster (e.g. Walk intro, string 5 at
-                    // +0.7 s outside the 0.26 s window). Inlined for the same reason as
-                    // _deferFallback above.
-                    let suppressSynthChord = false;
-                    if (ch.h3dSynth && notes && chShape.size > 0) {
-                        const _sLo = ch.t - ARP_FRAME_ONSET_PAD_S;
-                        const _sHi = ch.t + ARP_FRAME_ONSET_CLUSTER_S;
-                        let _si = lowerBoundT(notes, _sLo - 0.02);
-                        for (; _si < notes.length; _si++) {
-                            const _sn = notes[_si];
-                            if (_sn.t > _sHi) break;
-                            if (_sn.t < _sLo) continue;
-                            if (chShape.get(_sn.s) === _sn.f) { suppressSynthChord = true; break; }
-                        }
-                    }
-
-                    // suppressSynthChord: skip gems + frame but still call drawNote with
-                    // skipBody=true so the board projection (fret ghost on fretboard) renders
-                    // for all shape strings — shows the hand position like a chord would.
-                    // chordLinksSlide: true when any chord note has a direct sl/slu marker,
-                    // OR when the chord's sustain connects (via case-2 linkNext) to a note
-                    // in bundle.notes that has a slide.  Repeated chords matching either
-                    // condition are treated as normal chords so the player sees the gem.
-                    let chordLinksSlide = chordNotes.some(cn =>
-                        (Number.isFinite(cn.sl) && cn.sl >= 0) ||
-                        (Number.isFinite(cn.slu) && cn.slu >= 0));
-                    if (!chordLinksSlide && isRepeat && maxSus > 0 && notes) {
-                        const _EPS = NEXT_ON_STRING_T_EPS;
-                        outer: for (const cn of chordNotes) {
-                            if (!(cn.sus > 0)) continue;
-                            const _endT = ch.t + cn.sus;
-                            let _ji = lowerBoundT(notes, _endT - _EPS);
-                            for (; _ji < notes.length; _ji++) {
-                                const _q = notes[_ji];
-                                if (_q.t > _endT + _EPS) break;
-                                if (_q.s !== cn.s || Math.abs(_q.t - _endT) >= _EPS) continue;
-                                if ((Number.isFinite(_q.sl) && _q.sl >= 0) ||
-                                    (Number.isFinite(_q.slu) && _q.slu >= 0)) {
-                                    chordLinksSlide = true; break outer;
-                                }
-                            }
-                        }
-                    }
-                    if (!deferChordGems || _deferFallback || suppressSynthChord) {
-                        for (const cn of chordNotes) {
-                            // Suppress non-first gems while an authored arpeggio frame
-                            // approaches — but not for the deferred fallback path, where
-                            // all chord gems serve as the only visual preview.
-                            // _arpApproachFirstNote is null when no sequential note-stream
-                            // pattern was found, so simultaneous chords are unaffected.
-                            // suppressSynthChord: show all shape strings for the projection.
-                            if (!_deferFallback && !suppressSynthChord && _arpApproachFirstNote !== null && cn !== _arpApproachFirstNote) continue;
-                            // Only suppress labels on repeated chord shapes (not on first-in-run);
-                            // removed the lastFretForString check — same fix as single notes above.
-                            const skipLabel = !firstInShapeRun;
-                            // Reuse _scrChordNote scratch instead of `{ ...cn }` spread
-                            // (avoids per-chord-note object allocation every frame).
-                            Object.assign(_scrChordNote, cn);
-                            _scrChordNote.t   = ch.t;
-                            _scrChordNote.sus = cn.sus || 0;
-                            // `fhm` is omit-when-false in the wire format (unlike `mt`/`pm`
-                            // which are always emitted). Before 5913129, chord-level
-                            // fretHandMute was folded into `mt` (always-emitted), so
-                            // Object.assign would overwrite any stale value. After that
-                            // commit fhm is its own field — absent on non-muted notes —
-                            // so Object.assign leaves a stale `true` from a previous
-                            // muted chord note untouched. Reset it explicitly here.
-                            _scrChordNote.fhm = cn.fhm || false;
-                            // Same stale-scratch hazard for the bend shape:
-                            // `bnv`/`bt` are omit-when-default on the wire, so a
-                            // chord note without them would otherwise inherit the
-                            // previous note's curve (and bendSemisAtTime would
-                            // apply the wrong contour). Reset explicitly.
-                            _scrChordNote.bnv = Array.isArray(cn.bnv) ? cn.bnv : undefined;
-                            _scrChordNote.bt  = cn.bt || 0;
-                            // Same stale-scratch hazard for the teaching marks
-                            // (§6.2.2): fg/sd are omit-when-default on the wire,
-                            // so a chord note without them must reset to -1 or it
-                            // inherits the previous note's finger/degree label.
-                            _scrChordNote.fg  = Number.isInteger(cn.fg) ? cn.fg : -1;
-                            _scrChordNote.sd  = Number.isInteger(cn.sd) ? cn.sd : -1;
-                            drawNote(
-                                _scrChordNote,
-                                now,
-                                cn.f === 0 ? chordCX : undefined,
-                                skipLabel,
-                                (isRepeat && !chordLinksSlide) || suppressSynthChord,
-                                chordTailHoldS,
-                                cn.f === 0 ? laneWForOpenStrings : undefined,
-                                true,
-                                ch.id,
-                                chordSusTrailMatchArpFrame,
-                                null,
-                                _ghostPrevBuf.get(Math.round(ch.t * 1e4) * 10 + cn.s) ?? -Infinity,
-                                chordHighwayLavenderArpVisual || suppressSynthChord || chordWireHighDensity(ch),
-                            );
-                            lastFretForString[cn.s] = cn.f;
-                            // gate by THIS note's own sustain against the
-                            // current render time — drawNote has already
-                            // dropped short-sustain notes whose ringing has
-                            // ended, so they should not keep pulling the
-                            // camera frame wider than the notes actually
-                            // still on screen (chord-wide maxSus would
-                            // over-pullback for mixed-sustain chords).
-                            if (!(cameraMode === 'lookahead')) {
-                            const cnSustainOk = chOnsetInWin || (chSusActive && ch.t + (cn.sus || 0) >= now);
-                            if (cn.f > 0 && cnSustainOk) {
-                                camWX += xFretMid(cn.f) * chW;
-                                camWSum += chW;
-                                if (cn.f < camDistMin) camDistMin = cn.f;
-                                if (cn.f > camDistMax) camDistMax = cn.f;
-                                camDistGot = true;
-                            }
-                            }
-                        }
-                    }
-
-                    // ── Arpeggio note brackets [ ] ────────────────────────
-                    // Drawn only for explicitly authored arpeggio frames
-                    // (chordHighwayLavenderArpVisual = explicit handshape arp mark).
-                    // Covers both paths: gems shown directly from the chord
-                    // (!deferChordGems) and the deferred-fallback preview path
-                    // (_deferFallback). The inferred-arpeggio path (inferredArpPattern
-                    // only, no explicit mark) intentionally does NOT draw brackets —
-                    // the inference heuristic can false-positive on fast strummed
-                    // chords, and brackets on non-arp chords confuse players.
-                    // Note-stream arpeggios draw their own brackets in the notes[]
-                    // loop above (for notes already in AHEAD). The chord loop covers
-                    // any strings whose notes haven't entered AHEAD yet — _nsBrackets
-                    // prevents duplicates for strings already handled by notes[].
-                    if (chordHighwayLavenderArpVisual) {
-                        const _arpBracketDt = ch.t - now;
-                        if (_arpBracketDt < AHEAD) {
-                            const _arpEnd = (hsHintFrame.hs && !isNaN(hsEnd(hsHintFrame.hs)))
-                                ? hsEnd(hsHintFrame.hs)
-                                : ch.t + maxSus + CHORD_HWY_LINGER_S;
-                            // The notes[] loop already drew brackets for any note-stream
-                            // note that entered AHEAD, recording (chordId:occurrenceStart → strings)
-                            // in _noteStreamBracketStrings. Use the same composite key (template id +
-                            // handshape start time) so two arp occurrences sharing a chord template
-                            // ID are treated as distinct occurrences — not one suppressing the other.
-                            const _nsBracketsKey = ch.id + ':' + _hsStartT;
-                            const _nsBrackets = _noteStreamBracketStrings.get(_nsBracketsKey);
-                            // Open-string bracket X: anchor at handshape start so
-                            // position stays fixed even when chordCX drifts with now.
-                            const _arpChBrktAncB = !isNaN(_hsStartT)
-                                ? anchorLaneBoundsAt(anchors, _hsStartT)
-                                : null;
-                            const _arpChBrktOpenX = _arpChBrktAncB
-                                ? (xFret(_arpChBrktAncB.dMin) + xFret(_arpChBrktAncB.dMax)) / 2
-                                : (chordCX ?? curX);
-                            const _arpChBrktOpenW = (() => {
-                                if (_arpChBrktAncB) {
-                                    const _xl = xFret(_arpChBrktAncB.dMin), _xr = xFret(_arpChBrktAncB.dMax);
-                                    if (_xr > _xl) return _xr - _xl + NW * 0.4 * 2;
-                                }
-                                return laneWForOpenStrings;
-                            })();
-                            for (const cn of chordNotes) {
-                                if (!validString(cn.s)) continue;
-                                if (_nsBrackets && _nsBrackets.has(cn.s)) continue;
-                                const _bx = cn.f === 0
-                                    ? _arpChBrktOpenX
-                                    : xFretMid(cn.f);
-                                const _openHalfW = (cn.f === 0 && _arpChBrktOpenW != null)
-                                    ? Math.max(0.22, _arpChBrktOpenW * 0.96 / (40 * K)) * 20 * K
-                                    : null;
-                                drawArpBrackets(_bx, sY(cn.s), _arpBracketDt, _arpEnd, now, cn.s, cn.f === 0, _openHalfW);
-                            }
-                        }
-                    }
-
-                    // Chord frame-box: rim bars + interior fill gradient.
-                    const chDt = chDtEarly; // already computed above for anchor selection
-                    const chordTailMul = (() => {
-                        // When a next event (chord OR single note) has already crossed
-                        // the hit line, hide this frame immediately — no fadeout overlap
-                        // when another event is already playing.
-                        if (chDt < 0 && _chNextEventT < Infinity && now >= _chNextEventT) {
-                            return 0;
-                        }
-                        return hwyPostHitTailFadeMul(chDt, chordTailHoldS, chordNextSoon, chordTailFadeS);
-                    })();
-                    if (chShape.size > 1 && chDt > -chordTailHoldS && chDt < AHEAD && chordOpenBoxW != null
-                        && (!suppressSynthChord || chordTemplateMarkedArpeggio(ch.id, bundle.chordTemplates))
-                    ) {
-                        const z = Math.min(0, dZ(chDt));
-                        const width = chordOpenBoxW;
-                        const xLeft = chordFrameXL;
-                        const xRight = chordFrameXR;
-                        const cx = (xLeft + xRight) * 0.5;
-                        const yA = sY(0), yB = sY(nStr - 1);
-                        const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
-                        const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
-                        const fullChordBoxH = yMaxF - yMinF;
-                        let height = fullChordBoxH;
-                        if (isRepeat) height *= 0.5;
-                        // Repeat frames use half height but anchor at yMinF (board
-                        // level) rather than centering in the string range. With the
-                        // camera tilted downward, a centered half-height frame puts
-                        // its bottom bar mid-strings — far above the board — causing
-                        // perspective-induced apparent X-misalignment with the lane
-                        // tiles (which sit at board level). Anchoring at yMinF keeps
-                        // the bottom bar near the board so both frame and lane tile
-                        // edges share the same projected screen X.
-                        const yBot = yMinF;
-                        const yTop = yMinF + height;
-                        const cY = (yBot + yTop) * 0.5;
-                        const fade = Math.max(0, 1 - chDt / AHEAD);
-                        const chordAccent = chordNotes.some(cn => cn.ac);
-
-                        // Rim thickness from full vertical span — repeat halves inner height only,
-                        // not bar thickness vs first chord — see CHORD_FRAME_RIM_* tuning.
-                        let ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
-                        if (chordAccent) ft *= 1.22;
-                        // Lavender frame: authored arpeggio marker only.
-                        // RS ``highDensity`` is kept out — it tags gallops & repeated
-                        // strums (Frantic ~2:46), not arpeggio.
-                        const isArpeggioFrame = chordHighwayLavenderArpVisual;
-                        const ftSide = isArpeggioFrame ? ft * 1.55 : ft;
-                        let rimHex = isArpeggioFrame ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
-                        // Capture the neutral frame color before any verdict overwrite.
-                        // Used for the mute X lines so hit/miss feedback only shows on
-                        // the outer borders of the framebox, not inside the X pattern.
-                        const baseRimHex = rimHex;
-                        // feedBack#254 — once the chord crosses the hit
-                        // line, tint the teal frame by the note-state
-                        // provider verdict: green on a clean grab, red on a
-                        // miss. The verdict is async (the engine verifier
-                        // reports ~0.4 s after the line), so the frame stays
-                        // teal while the verdict is still pending — it must
-                        // not flash red before the verdict lands. The green/
-                        // red verdict is latched in _chordVerdicts so it
-                        // can't flicker as constituent glows decay.
-                        // Only engages when a scorer is attached. Arpeggio
-                        // frames keep their blue identity.
-                        // Per-occurrence key — ch.id is the template id
-                        // (reused across same-shape chord occurrences) so
-                        // composing it with ch.t gives one entry per
-                        // physical onset in the chart.
-                        const verdictKey = _encodeChordVerdictKey(ch);
-                        // Evict any stale latch the next time the chord
-                        // re-enters the pre-hit window (rewinds, section
-                        // loops, full restarts). Bounds Map growth too.
-                        if (chDt > 0 && _chordVerdicts.has(verdictKey)) {
-                            _chordVerdicts.delete(verdictKey);
-                        }
-                        // The verdict scan no longer skips authored-handshape
-                        // frames — power chords sometimes carry an explicit
-                        // handshape (RS authoring quirk), which previously
-                        // dropped them into the `isArpeggioFrame` path and
-                        // left them lavender-blue regardless of hit/miss.
-                        // A true arpeggio (handshape over a real sweeping
-                        // note run) is unaffected: its constituents are
-                        // standalone notes judged at their own times, so the
-                        // scan's query at `ch.t` finds nothing for them and
-                        // the frame keeps its lavender default.
-                        if (chDt <= 0 && _ndHasProvider && !isArpeggioFrame) {
-                            const latched = _chordVerdicts.get(verdictKey);
-                            if (latched === 'green') {
-                                rimHex = CHORD_BOX_HIT_BRIGHT_HEX;
-                            } else if (latched === 'red') {
-                                rimHex = CHORD_BOX_MISS_DARK_HEX;
-                            } else if (latched === 'unmatched') {
-                                // The first scan past the verdict window
-                                // came up empty (no constituent ever had a
-                                // state — most often a true arpeggio frame
-                                // whose actual notes are judged at their
-                                // own times, not at ch.t). Skip the
-                                // per-frame provider scan and keep the
-                                // frame's default identity (lavender for
-                                // arpeggios, teal for chords). See the
-                                // unmatched-latch below.
-                            } else {
-                                // Latch both green AND red:
-                                //   - any constituent 'miss' → red latched.
-                                //     One decisive miss verdict means the
-                                //     chord can't be all-hit; without
-                                //     latching, the rim would fall back to
-                                //     teal once noteStateFor's miss-wash
-                                //     window (~0.6 s TTL) expires and the
-                                //     state returns null again.
-                                //   - all hit/active → green latched.
-                                //   - else (no miss yet, some constituents
-                                //     still null) → keep teal default. A
-                                //     partial state must not flash red on
-                                //     a chord whose verdicts arrive
-                                //     incrementally.
-                                let allHit = chordNotes.length > 0;
-                                let anyMiss = false;
-                                let anyState = false;  // true if any constituent had a non-null state this scan
-                                for (const cn of chordNotes) {
-                                    let cs = null;
-                                    try { cs = _ndGetNoteState(cn, ch.t); } catch (e) { cs = null; }
-                                    const st = (cs && typeof cs === 'object') ? cs.state : cs;
-                                    if (st === 'hit' || st === 'active') {
-                                        anyState = true;
-                                    } else if (st === 'miss') {
-                                        // First miss decides the chord — no
-                                        // point querying the rest of the
-                                        // constituents this frame; the rim
-                                        // is about to be red-latched below.
-                                        // Short-circuits provider calls in
-                                        // chord-dense passages.
-                                        allHit = false;
-                                        anyMiss = true;
-                                        anyState = true;
-                                        break;
-                                    } else {
-                                        // null — undecided yet
-                                        allHit = false;
-                                    }
-                                }
-                                if (anyMiss) {
-                                    _chordVerdicts.set(verdictKey, 'red');
-                                    rimHex = CHORD_BOX_MISS_DARK_HEX;
-                                } else if (allHit) {
-                                    _chordVerdicts.set(verdictKey, 'green');
-                                    rimHex = CHORD_BOX_HIT_BRIGHT_HEX;
-                                } else if (chDt < -_ND_UNMATCHED_LATCH_AFTER && !anyState) {
-                                    // The engine verdict typically lands
-                                    // ~0.4 s after the chord crosses the
-                                    // line, so after the
-                                    // _ND_UNMATCHED_LATCH_AFTER threshold
-                                    // we've already waited well past the
-                                    // verdict-arrival window. If no
-                                    // constituent ever returned a non-
-                                    // null state by then, there's no
-                                    // verdict coming for this chord
-                                    // (true arpeggio frames: their actual
-                                    // notes are judged at their own
-                                    // times, never at ch.t — the scan
-                                    // at ch.t finds nothing forever).
-                                    //
-                                    // Latch 'unmatched' so subsequent
-                                    // frames skip the provider scan
-                                    // entirely. The threshold must be
-                                    // INSIDE the chord frame's visible
-                                    // draw window — `chordTailHoldS` is
-                                    // floored to NOTEDETECT_GEM_VERDICT_
-                                    // WINDOW (0.75 s) in detect mode, so
-                                    // chord frames stop drawing at
-                                    // `chDt < -0.75`; a latch threshold
-                                    // at `-NOTEDETECT_GEM_VERDICT_WINDOW`
-                                    // (i.e. exactly -0.75) is unreachable
-                                    // because the draw gate kicks the
-                                    // frame out of the loop first. Place
-                                    // the threshold ~0.55 s past line so
-                                    // it fires for ~0.2 s of the remaining
-                                    // visible window — enough frames to
-                                    // catch and skip future re-scans.
-                                    //
-                                    // The !anyState guard keeps the
-                                    // partial-resolve case (one cn 'hit',
-                                    // another still null) scanning until
-                                    // anyMiss / allHit commits it.
-                                    _chordVerdicts.set(verdictKey, 'unmatched');
-                                }
-                                // else: no verdict yet → leave teal default
-                            }
-                        }
-
-                        if (chDt > 0) { // framebox only on highway, not on the fretboard
-                        const repDim = isRepeat ? 0.78 : 1;
-                        const edgeOp = fade * chordTailMul;
-                        const thickZ = Math.max(CHORD_FRAME_RIM_Z_MIN * K, ft * CHORD_FRAME_RIM_Z_SCAL);
-                        // Per-depth layer stack: chord frames, gems, technique markers,
-                        // and fret labels all derive from RENDER_ORDER_LAYER_STACK so new layers
-                        // have one vocabulary instead of ad hoc arithmetic at call sites.
-                        // Sub-increments of 0.0001 for intra-chord ordering; safe for any
-                        // chord gap >= 0.001 s.
-                        const chordFrameRenderOrder = renderOrderForLayerAtZ(z, 'CHORD_FRAME');
-                        const drawFrameBox = (px, py, sx, sy, ord, hex = rimHex, op = edgeOp) => {
-                            const b = pChordBox.get();
-                            b.renderOrder = ord;
-                            b.material.color.setHex(hex);
-                            b.position.set(px, py, z);
-                            b.scale.set(sx, sy, thickZ);
-                            b.rotation.set(0, 0, 0);
-                            b.material.opacity = op;
-                        };
-                        const sideHex = isArpeggioFrame ? rimHex : 0x163137;
-
-                        const innerW = Math.max(width - 2 * ftSide, width * 0.45);
-                        const innerH = Math.max(height - 2 * ft, height * 0.3);
-                        const fill = pChordFrameFill.get();
-                        fill.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_FILL');
-                        fill.rotation.set(0, 0, 0);
-                        fill.position.set(cx, cY, z - 0.004 * K);
-                        fill.scale.set(innerW, innerH, 1);
-                        fill.material.opacity = fade * repDim * chordTailMul;
-                        // Swapping `map` between two non-null gradient textures
-                        // doesn't change shader-defining state, so no needsUpdate
-                        // — that flag would otherwise force a recompile per frame.
-                        fill.material.map = isArpeggioFrame ? chordFrameGradTexArp : chordFrameGradTex;
-                        fill.material.color.setRGB(1, 1, 1);
-
-                        const withTopFrame = !isRepeat;
-                        // Non-repeat tapers the upper side bars + draws a thin top bar;
-                        // hoisted out so ySideHi can match the actual top-bar thickness
-                        // (using ft would leave a visible gap between the thin top bar
-                        // and the side bars meeting it).
-                        const ftThin = ftSide * 0.22;
-
-                        const ySideLo = yBot + ft;
-                        const ySideHi = withTopFrame ? yTop - ftThin : yTop - ft * 0.15;
-                        const sideH = Math.max(ySideHi - ySideLo, ft * 1.25);
-                        const sideCy = ySideLo + sideH * 0.5;
-
-                        // Bottom bar: thin teal (like top bar) + dark corners on top.
-                        {
-                            const botCW = Math.min(sideH * (isRepeat ? 0.5 : 0.25), width * 0.4);
-                            drawFrameBox(cx, yBot + ftThin * 0.5, width, ftThin, chordFrameRenderOrder);
-                            drawFrameBox(cx + width * 0.5 - botCW * 0.5, yBot + ft * 0.5, botCW, ft, chordFrameRenderOrder + 0.0001, sideHex);
-                            drawFrameBox(cx - width * 0.5 + botCW * 0.5, yBot + ft * 0.5, botCW, ft, chordFrameRenderOrder + 0.0002, sideHex);
-                        }
-
-                        if (isRepeat) {
-                            // Lower 30%: thick dark segment
-                            const repLoH = sideH * 0.3;
-                            const repLoCy = ySideLo + repLoH * 0.5;
-                            drawFrameBox(cx - width * 0.5 + ftSide * 0.5, repLoCy, ftSide, repLoH, chordFrameRenderOrder + 0.0001, sideHex);
-                            drawFrameBox(cx + width * 0.5 - ftSide * 0.5, repLoCy, ftSide, repLoH, chordFrameRenderOrder + 0.0001, sideHex);
-                            // Upper 70%: thin teal segment (same style as non-repeat upper)
-                            const repHiH = sideH - repLoH;
-                            const repHiCy = ySideLo + repLoH + repHiH * 0.5;
-                            drawFrameBox(cx - width * 0.5 + ftThin * 0.5, repHiCy, ftThin, repHiH, chordFrameRenderOrder + 0.0001);
-                            drawFrameBox(cx + width * 0.5 - ftThin * 0.5, repHiCy, ftThin, repHiH, chordFrameRenderOrder + 0.0001);
-                        } else {
-                            // Non-repeat: thick sides up to repeat-frame height, then taper to thin above.
-                            const threshY = yBot + fullChordBoxH * 0.5; // top of what a repeat frame would be
-
-                            // Lower thick segment (ySideLo → threshY)
-                            const loSideH = Math.max(Math.min(threshY, ySideHi) - ySideLo, 0);
-                            if (loSideH > 0) {
-                                const loCy = ySideLo + loSideH * 0.5;
-                                drawFrameBox(cx - width * 0.5 + ftSide * 0.5, loCy, ftSide, loSideH, chordFrameRenderOrder + 0.0001, sideHex);
-                                drawFrameBox(cx + width * 0.5 - ftSide * 0.5, loCy, ftSide, loSideH, chordFrameRenderOrder + 0.0001, sideHex);
-                            }
-
-                            // Upper thin segment (threshY → ySideHi)
-                            const hiSideH = Math.max(ySideHi - threshY, 0);
-                            if (hiSideH > 0) {
-                                const hiCy = threshY + hiSideH * 0.5;
-                                drawFrameBox(cx - width * 0.5 + ftThin * 0.5, hiCy, ftThin, hiSideH, chordFrameRenderOrder + 0.0001);
-                                drawFrameBox(cx + width * 0.5 - ftThin * 0.5, hiCy, ftThin, hiSideH, chordFrameRenderOrder + 0.0001);
-                            }
-
-                            // Top bar: thin
-                            drawFrameBox(cx, yTop - ftThin * 0.5, width, ftThin, chordFrameRenderOrder);
-                        }
-
-                        // Accent bloom on frame edges: 4 additive shells with
-                        // Gaussian-style falloff. Each border expands only in its
-                        // perpendicular axis so bloom never leaves the frame boundary:
-                        //   horizontal bars (top/bottom) → expand Y only
-                        //   vertical bars (left/right)   → expand X only
-                        if (chordAccent && pHaloBar) {
-                            // Bloom only on the teal (thin) parts of the frame — the dark
-                            // "#163137" L-corners are deliberately left without bloom so they
-                            // remain visibly dark (same appearance as non-accent chords).
-                            const haloHex = isArpeggioFrame ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
-                            const EXPAND_MAX = 1.45;
-                            const dynamicOp = fade * chordTailMul;
-                            const drawHaloBar = (px, py, scaleX, scaleY, rotZ) => {
-                                const b = pHaloBar.get();
-                                b.material.color.setHex(haloHex);
-                                b.material.opacity = dynamicOp;
-                                b.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_EDGE_GLOW');
-                                b.position.set(px, py, z - 0.001 * K);
-                                b.scale.set(scaleX, scaleY * EXPAND_MAX * 0.5, thickZ * 2.0);
-                                b.rotation.set(0, 0, rotZ);
-                            };
-                            // Bottom: center-only bloom (skip dark corner areas)
-                            const _bCW = Math.min(sideH * (isRepeat ? 0.5 : 0.25), width * 0.4);
-                            const centerBotW = width - 2 * _bCW;
-                            if (centerBotW > 0)
-                                drawHaloBar(cx, yBot + ft * 0.5, centerBotW * 0.5, ft, 0);
-                            // Top bar
-                            if (withTopFrame)
-                                drawHaloBar(cx, yTop - ftThin * 0.5, width * 0.5, ftThin, 0);
-                            // Lateral: bloom only on the upper thin-teal segment (skip dark lower segment)
-                            if (isRepeat) {
-                                const repLoH = sideH * 0.3;
-                                const repHiH = sideH - repLoH;
-                                if (repHiH > 0) {
-                                    const repHiCy = ySideLo + repLoH + repHiH * 0.5;
-                                    drawHaloBar(cx - width * 0.5 + ftSide * 0.5, repHiCy, repHiH * 0.5, ftSide, Math.PI * 0.5);
-                                    drawHaloBar(cx + width * 0.5 - ftSide * 0.5, repHiCy, repHiH * 0.5, ftSide, Math.PI * 0.5);
-                                }
-                            } else {
-                                const threshY = yBot + fullChordBoxH * 0.5;
-                                const hiSideH = Math.max(ySideHi - threshY, 0);
-                                if (hiSideH > 0) {
-                                    const hiCy = threshY + hiSideH * 0.5;
-                                    drawHaloBar(cx - width * 0.5 + ftSide * 0.5, hiCy, hiSideH * 0.5, ftSide, Math.PI * 0.5);
-                                    drawHaloBar(cx + width * 0.5 - ftSide * 0.5, hiCy, hiSideH * 0.5, ftSide, Math.PI * 0.5);
-                                }
-                            }
-                        }
-                        const chordName = chordTemplateLabel(bundle.chordTemplates?.[ch.id]);
-                        if (chordName && firstInShapeRun && !chordWireHighDensity(ch)) {
-                            const lblW = 28 * K, lblH = 9 * K;
-                            const lbl = pChordLbl.get();
-                            const mat = txtMat(chordName, '#e8d080', true, 'chord');
-                            _setLabelMap(lbl, mat);
-                            lbl.material.opacity = Math.min(1, 0.3 + fade * 0.7) * chordTailMul;
-                            // Gold chord name: slight +X shift from flush-left so it sits farther right.
-                            const lblWS = lblW * _textSizeMul;
-                            const lblHS = lblH * _textSizeMul;
-                            const frameLeft = cx - width / 2;
-                            const nameShiftX = NW * 0.94;
-                            const nameVertTuck = NH * 0.02;
-                            lbl.position.set(
-                                frameLeft - lblWS / 2 + nameShiftX,
-                                yMaxF + lblHS / 2 - nameVertTuck,
-                                z);
-                            lbl.scale.set(lblWS, lblHS, 1);
-                        }
-
-                        // Harmony annotations (§6.3.1 / §6.6) — the chord's
-                        // function (fn.rn Roman numeral) and template voicing,
-                        // stacked above the chord name. Gated by the
-                        // teaching-marks opt-in (mirrors the 2D overlay). Display
-                        // only — never grading.
-                        if (_drawTeachingMarks && firstInShapeRun && !chordWireHighDensity(ch)) {
-                            const _tmpl = bundle.chordTemplates?.[ch.id];
-                            const _h = chordHarmonyLabels(ch.fn, _tmpl?.voicing, _tmpl?.caged, _tmpl?.guideTones);
-                            if (_h.rn || _h.voicing || _h.caged || _h.guideTones) {
-                                const hlW = 24 * K * _textSizeMul;
-                                const hlH = 9 * K * _textSizeMul;
-                                const frameLeft = cx - width / 2;
-                                const baseX = frameLeft - hlW / 2 + NW * 0.94;
-                                const opacity = Math.min(1, 0.3 + fade * 0.7) * chordTailMul;
-                                // Start one chord-name-height above the name and
-                                // stack upward so labels never overlap the gems.
-                                let hy = yMaxF + hlH * 1.6;
-                                const _drawHarmony = (text, colorHex) => {
-                                    if (!text) return;
-                                    const s = pChordLbl.get();
-                                    const m = txtMat(text, colorHex, true, 'chord');
-                                    _setLabelMap(s, m);
-                                    s.material.opacity = opacity;
-                                    s.position.set(baseX, hy, z);
-                                    s.scale.set(hlW, hlH, 1);
-                                    hy += hlH;
-                                };
-                                _drawHarmony(_h.rn, '#ffcc66');         // sd teaching color
-                                _drawHarmony(_h.voicing, '#7fd1ff');    // fg teaching color
-                                _drawHarmony(_h.caged, '#a0ffa0');      // CAGED shape teaching color
-                                _drawHarmony(_h.guideTones, '#d0a0ff'); // guide-tone teaching color
-                            }
-                        }
-
-                        // Shape-based barre detection for the 3D indicator.
-                        // Drives off chord notes alone — independent of label
-                        // availability, so charts whose chordTemplates lack a
-                        // .name still show the barre line.
-                        // Matches drawChordDiagram PATH A + PATH B so the highway
-                        // line and overlay bracket always agree on the same shapes:
-                        //   PATH A: 2+ adjacent strings at the minimum fret.
-                        //   PATH B: outer-edge full-span barre (e.g. B major x24442)
-                        //           where the two outer strings are at the minimum fret,
-                        //           every intermediate string is fretted (f>0), and no
-                        //           intermediate string also sits at the minimum fret.
-                        // Scattered voicings like "1 3 1 3 1 0" (strings 0,2,4 at
-                        // fret 1 but no two adjacent, and string 2 sits at min fret)
-                        // correctly produce no indicator.
-                        {
-                            let bFret = Infinity;
-                            for (const [, f] of chShape) {
-                                if (f > 0) bFret = Math.min(bFret, f);
-                            }
-                            // Collect strings at minimum fret into scratch array (no allocation)
-                            _scrAtMinFretLen = 0;
-                            if (bFret < Infinity) {
-                                for (const [s, f] of chShape) {
-                                    if (f === bFret) _scrAtMinFretArr[_scrAtMinFretLen++] = s;
-                                }
-                                // insertion sort — array is ≤8 elements
-                                for (let _ii = 1; _ii < _scrAtMinFretLen; _ii++) {
-                                    const _v = _scrAtMinFretArr[_ii];
-                                    let _jj = _ii - 1;
-                                    while (_jj >= 0 && _scrAtMinFretArr[_jj] > _v) {
-                                        _scrAtMinFretArr[_jj + 1] = _scrAtMinFretArr[_jj]; _jj--;
-                                    }
-                                    _scrAtMinFretArr[_jj + 1] = _v;
-                                }
-                            }
-                            // Inline longestConsecutiveRun (no array allocation)
-                            let _barreRunStart = -1, _barreRunLen = 0;
-                            {
-                                let _curStart = -1, _curLen = 0;
-                                for (let _ri = 0; _ri < _scrAtMinFretLen; _ri++) {
-                                    const _rv = _scrAtMinFretArr[_ri];
-                                    if (_curLen === 0 || _rv === _scrAtMinFretArr[_ri - 1] + 1) {
-                                        if (_curLen === 0) _curStart = _rv;
-                                        _curLen++;
-                                    } else {
-                                        if (_curLen > _barreRunLen) { _barreRunLen = _curLen; _barreRunStart = _curStart; }
-                                        _curStart = _rv; _curLen = 1;
-                                    }
-                                }
-                                if (_curLen > _barreRunLen) { _barreRunLen = _curLen; _barreRunStart = _curStart; }
-                            }
-                            let is3dBarre    = _barreRunLen >= 2;   // PATH A
-                            let barreMinStr3d = is3dBarre ? _barreRunStart : -1;
-                            let barreMaxStr3d = is3dBarre ? _barreRunStart + _barreRunLen - 1 : -1;
-
-                            // PATH B: outer-edge full-span barre
-                            const MIN_BARRE_SPAN_3D = Math.min(nStr - 1, 4);
-                            if (_scrAtMinFretLen >= 2) {
-                                const minS = _scrAtMinFretArr[0];
-                                const maxS = _scrAtMinFretArr[_scrAtMinFretLen - 1];
-                                if (maxS - minS >= MIN_BARRE_SPAN_3D) {
-                                    // chShape is already a Map<s, f> — query it directly
-                                    // instead of building a transient Set<s> every frame.
-                                    let allFretted = true;
-                                    for (let si = minS; si <= maxS; si++) {
-                                        if (!chShape.has(si) || chShape.get(si) <= 0) { allFretted = false; break; }
-                                    }
-                                    if (allFretted) {
-                                        if (is3dBarre) {
-                                            // PATH A fired: extend to full outer span.
-                                            barreMinStr3d = minS; barreMaxStr3d = maxS;
-                                        } else {
-                                            // PATH A did not fire: only draw if no inner
-                                            // string also sits at the minimum fret.
-                                            let innerAtMinFret = false;
-                                            for (let _ai = 1; _ai < _scrAtMinFretLen - 1; _ai++) {
-                                                const _as = _scrAtMinFretArr[_ai];
-                                                if (_as > minS && _as < maxS) { innerAtMinFret = true; break; }
-                                            }
-                                            if (!innerAtMinFret) {
-                                                is3dBarre = true;
-                                                barreMinStr3d = minS; barreMaxStr3d = maxS;
-                                            }
-                                        }
-                                    }
-                                }
-                            }
-
-                            if (is3dBarre && chDt <= 0) {
-                                const bx = xFretMid(bFret);
-                                const yTop = Math.max(sY(barreMinStr3d), sY(barreMaxStr3d));
-                                const yBot = Math.min(sY(barreMinStr3d), sY(barreMaxStr3d));
-                                const lineH = yTop - yBot;
-                                const bl = pBarreLine.get();
-                                bl.position.set(bx, (yTop + yBot) / 2, 0.05 * K);
-                                bl.scale.set(0.5 * K, lineH, 0.5 * K);
-                                bl.material.opacity = 0.8 * chordTailMul;
-                            }
-                        }
-
-                        // ── Chord fret numbers at the base of the highway ───────────────
-                        // Show fret number per unique fretted position for non-repeated
-                        // chords so the player can read the shape at a glance.
-                        if (!isRepeat) {
-                            const _chFretLblAlpha = Math.min(1.0, (AHEAD - chDt) / 0.35) * chordTailMul;
-                            const _seenChordFrets = new Set();
-                            for (const [, f] of chShape) {
-                                if (f <= 0 || _seenChordFrets.has(f)) continue;
-                                _seenChordFrets.add(f);
-                                const lbl = pNoteFretLabel.get();
-                                const mat = txtMat(f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
-                                _setLabelMap(lbl, mat);
-                                lbl.position.set(xFretMid(f), yMinF, z);
-                                lbl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_FRET_LABEL');
-                                const _flS = 7.0 * K * (1 + 0.4 * chDt / AHEAD) * _textSizeMul * fretLabelScaleForFret(f);
-                                lbl.scale.set(_flS, _flS, 1);
-                                lbl.material.opacity = _chFretLblAlpha;
-                            }
-                        }
-
-                        // ── Palm-mute strum indicator — pool (fill + lines) ──────────────
-                        // Per-chord Z-proportional renderOrder: muted fill/lines and
-                        // frame edges all use the named layer offsets above.
-                        if (isRepeat && chordNotes.some(cn => cn.pm)) {
-                            if (pPMXFill) {
-                                const xf = pPMXFill.get();
-                                xf.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_FILL');
-                                xf.material.opacity = edgeOp * CHORD_BOX_EDGE_ALPHA;
-                                xf.position.set(cx, cY, z - 0.0045 * K);
-                                xf.scale.set(innerW * 0.5, -innerH * 0.5, 1);
-                                xf.rotation.set(0, 0, 0);
-                            }
-                            if (pMuteXLines) {
-                                const xl = pMuteXLines.get();
-                                xl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_LINE');
-                                xl.material.opacity = edgeOp * 0.85;
-                                xl.material.color.setHex(baseRimHex);
-                                xl.position.set(cx, cY, z - 0.005 * K);
-                                xl.scale.set(innerW * 0.5, -innerH * 0.5, thickZ * 0.5);
-                                xl.rotation.set(0, 0, 0);
-                            }
-                        }
-
-                        // ── Frethand-mute strum indicator — pool (fill + lines) ───────────
-                        if (isRepeat && chordNotes.some(cn => cn.mt || cn.fhm)) {
-                            if (pFHXFill) {
-                                const xf = pFHXFill.get();
-                                xf.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_FILL');
-                                xf.material.opacity = edgeOp * CHORD_BOX_EDGE_ALPHA;
-                                xf.position.set(cx, cY, z - 0.0045 * K);
-                                xf.scale.set(innerW * 0.5, -innerH * 0.5, 1);
-                                xf.rotation.set(0, 0, 0);
-                            }
-                            if (pFHXLines) {
-                                const xl = pFHXLines.get();
-                                xl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_LINE');
-                                xl.material.opacity = edgeOp * 0.85;
-                                xl.material.color.setHex(baseRimHex);
-                                xl.position.set(cx, cY, z - 0.005 * K);
-                                xl.scale.set(innerW * 0.5, -innerH * 0.5, thickZ * 0.5);
-                                xl.rotation.set(0, 0, 0);
-                            }
-                        }
-
-                        } // end if (chDt > 0) — framebox + PM/FH mute only on highway
-
-                    }
-
-                    // ── Chord sustain length indicator — 3D plane rails ─────────────
-                    // Left + right rail as plane meshes (PlaneGeometry +
-                    // MeshBasicMaterial) in the WebGL scene so they respect
-                    // renderOrder (16) and never occlude note gems (20/21).
-                    // isRepeat chords also draw their rail: each repeat shows a
-                    // segment from its own onset to the next chord's onset (or the
-                    // handshape end, whichever is shorter), chaining together to
-                    // cover the full handshape duration visually.
-                    if (chShape.size > 1 && chordOpenBoxW != null && chDt < AHEAD) {
-                        // Cap handshape-derived sustain at the gap to the next chord.
-                        // Each chord (including repeats) only extends to the next
-                        // chord's onset, so the rail never lingers past the anchor
-                        // region of the current chord.
-                        const _nextChordGap = (ci + 1 < chords.length)
-                            ? chords[ci + 1].t - ch.t
-                            : Infinity;
-                        // Use the time remaining in the handshape from this chord's
-                        // onset (hsEnd - ch.t), NOT the full handshape span. When
-                        // multiple chords share the same handshape window (e.g. A5
-                        // at 63.527 and again at 64.137 both fall inside the same
-                        // handshape start=63.527 end=64.239), each chord after the
-                        // first starts mid-handshape. Using the full span (0.712s)
-                        // for the mid-handshape chord gives a rail that extends
-                        // 0.611s — far past the handshape end — causing the
-                        // "elongated border" that visually swallows subsequent
-                        // single notes. Clamping to (hsEnd - ch.t) gives 0.102s,
-                        // which correctly terminates at the handshape boundary.
-                        const _hsSus = (maxSus === 0 && !deferChordGems && hsHintFrame && hsHintFrame.hs)
-                            ? Math.min(Math.max(0, hsEnd(hsHintFrame.hs) - ch.t), _nextChordGap)
-                            : 0;
-                        // "Chord hold": suppressed non-arp synth chord where deferChordGems
-                        // zeroed _hsSus. Use h3dSynthEnd (= handshape end_time) instead.
-                        const _synthSus = (suppressSynthChord && ch.h3dSynth
-                            && !chordTemplateMarkedArpeggio(ch.id, bundle.chordTemplates)
-                            && ch.h3dSynthEnd != null)
-                            ? Math.max(0, ch.h3dSynthEnd - ch.t)
-                            : 0;
-                        const _rawSus = maxSus > 0 ? maxSus : Math.max(_hsSus, _synthSus);
-                        // Apply the 0.4 s visual-minimum only to chords with an
-                        // explicit note sustain (maxSus > 0). Handshape-derived
-                        // sustain (_hsSus, already capped at _nextChordGap) must
-                        // not be inflated — that would undo the gallop cap and
-                        // cause the rail to reappear at the old anchor position.
-                        const _effSus = maxSus > 0
-                            ? Math.max(_rawSus, 0.4)
-                            : _rawSus;
-                        const _dtSusEnd  = chDt + _effSus;
-                        if (_dtSusEnd > 0) {
-                            // Clip the rail at the next anchor boundary so it doesn't
-                            // extend into a different fret zone. The lane (pLane) slices
-                            // correctly per-anchor; a single-segment rail at fixed X would
-                            // visually "invade" the neighbouring region when anchors change
-                            // within the sustain window.
-                            let _dtSusEndRail = _dtSusEnd;
-                            if (anchors && anchors.length) {
-                                const _susAbsT = chDt > 0 ? ch.t : now;
-                                if (getChartAnchorAt(anchors, _susAbsT) !==
-                                    getChartAnchorAt(anchors, now + _dtSusEnd)) {
-                                    // Binary search: first anchor starting strictly after _susAbsT.
-                                    let _lo = 0, _hi = anchors.length;
-                                    while (_lo < _hi) {
-                                        const _mid = (_lo + _hi) >>> 1;
-                                        if (anchors[_mid].time <= _susAbsT) _lo = _mid + 1;
-                                        else _hi = _mid;
-                                    }
-                                    if (_lo < anchors.length)
-                                        _dtSusEndRail = anchors[_lo].time - now;
-                                }
-                            }
-                            const _zNear = chDt > 0 ? dZ(chDt) : 0;
-                            const _zFar  = dZ(Math.min(_dtSusEndRail, AHEAD));
-                            const _railLen = _zNear - _zFar;
-                            if (_railLen > 0.001) {
-                                const _yA   = sY(0), _yB = sY(nStr - 1);
-                                const _yBot = Math.min(_yA, _yB) - S_GAP * 0.8;
-                                const _fadeAhead = chDt > 0 ? Math.max(0, 1 - chDt / AHEAD) : 1;
-                                const _fadeSus   = Math.min(1, _dtSusEnd / 0.25);
-                                const _op  = _fadeAhead * _fadeSus * 0.9;
-                                const _hex = chordHighwayLavenderArpVisual ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
-                                const _railW = 1.875 * K; // visual width of each rail strip
-                                const _zMid  = _zNear - _railLen * 0.5; // centre in Z
-                                for (const [_rx, _inDir] of [[chordFrameXL, -1], [chordFrameXR, 1]]) {
-                                    const _rxIn = _rx + _inDir * _railW * 0.5;
-                                    // Core rail
-                                    const rl = pSusRail.get();
-                                    rl.material.color.setHex(_hex);
-                                    rl.material.opacity = _op;
-                                    rl.position.set(_rxIn, _yBot, _zMid);
-                                    rl.scale.set(_railW, 1, _railLen);
-                                    // Bloom glow — wider gaussian plane, additive blending
-                                    if (!_leanSus) {
-                                        const bl = pSusRailBloom.get();
-                                        bl.material.color.setHex(_hex);
-                                        bl.material.opacity = _op * 0.8;
-                                        bl.position.set(_rxIn, _yBot + 0.001, _zMid);
-                                        bl.scale.set(3 * K, 1, _railLen);
-                                    }
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-
-            // Fret span of the dynamic highway lane (wire dMin .. dMax). Reused
-            // so fret-column measure markers stay inside the same horizontal
-            // band as the blue track — previously markers used every inlay
-            // fret and stuck out past the lane whenever the camera narrowed.
-            let hwyLaneFretClipMin = null, hwyLaneFretClipMax = null;
-
-            const handShapesRails = bundle.handShapes;
-            hwyLaneArpOuterDividers = !!(handShapesRails && handShapesRails.length && laneRailArpHsFlags
-                && arpeggioLaneOuterRailAtChartTime(
-                    now, handShapesRails, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
-                ));
-            const arpLaneRimAccentMul = hwyLaneArpOuterDividers && laneRailArpHsFlags && handShapesRails
-                ? arpeggioLaneDividerFrameAccentMul(
-                    now, handShapesRails, chords, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
-                )
-                : 1;
-            const arpLaneS = hwyLaneArpOuterDividers
-                ? arpeggioLaneDividerXYScaleMatchFrameRim(arpLaneRimAccentMul)
-                : 1;
-
-            // ── Fret-wire hit flash (apply) ───────────────────────────────
-            // Runs here, after the note + chord draw loops, so it sees this
-            // frame's verdicts (_fwHitIn) rather than the previous frame's —
-            // the base tier loop that seeds color/opacity/emissive sits far
-            // above, before any note has been drawn.
-            //
-            // _fwHitGlow decays exponentially in CHART time, so the tail is
-            // frame-rate independent and honours playback speed. Seeking
-            // backward resets it — otherwise a flash from a hit we jumped away
-            // from would linger on the wire.
-            if (fretWireMats.length && _fwHitColor) {
-                // Resolve accumulated chord hits: a chord's flash frames the
-                // LANE, not its own shape. The lit lane strip spans the anchor's
-                // width (min ~4 frets), which can run a fret past the chord's
-                // outermost fret — and a bracket one wire INSIDE the lit lane
-                // reads as misaligned. So a chord lights the anchor lane's edge
-                // wires: the exact wires the lane strip spans, and the same pair
-                // open strings already use. The shape's own outer pair (wire
-                // behind the lowest fret, wire at the highest) survives only as
-                // the fallback for charts with no anchors.
-                for (const _fwE of _fwChordAcc.values()) {
-                    const _fwA = Math.max(_fwE.a, _fwE.openA);
-                    if (_fwA <= 0) continue;
-                    let _w0 = -1, _w1 = -1;
-                    const _fwB = anchorLaneBoundsAt(_drawAnchors, _fwE.t);
-                    if (_fwB) {
-                        _w0 = _fwB.dMin;
-                        _w1 = _fwB.dMax;
-                    } else if (_fwE.maxF >= _fwE.minF) {
-                        _w0 = Math.max(0, _fwE.minF - 1);
-                        _w1 = Math.min(NFRETS, _fwE.maxF);
-                    }
-                    if (_w0 < 0) continue; // all-open chord on an anchor-less chart
-                    if (_fwA > _fwHitIn[_w0]) _fwHitIn[_w0] = _fwA;
-                    if (_fwA > _fwHitIn[_w1]) _fwHitIn[_w1] = _fwA;
-                }
-
-                const _fwDt = now - _fwHitPrevTime;
-                if (!(_fwDt >= 0) || _fwDt > 1) _fwHitGlow.fill(0); // first frame, seek, or long stall
-                const _fwDecay = (_fwDt > 0 && _fwDt <= 1)
-                    ? Math.exp(-_fwDt / FRET_WIRE_HIT_DECAY)
-                    : 0;
-                _fwHitPrevTime = now;
-                // Decay EVERY wire's glow state, but flash only the OUTERMOST
-                // pair of lit wires. Fast passages overlap their decay tails, so
-                // without this a run of consecutive notes lights a picket fence
-                // of wires at once; collapsing to the outer pair keeps the whole
-                // lit span reading as ONE bracket — the same rule chords already
-                // follow, applied across everything currently glowing. Interior
-                // wires keep decaying invisibly (the base tier loop re-seeds
-                // their materials each frame), so the bracket tightens naturally
-                // as outer tails expire.
-                let _fwLo = -1, _fwHi = -1;
-                for (let _f = 0; _f <= NFRETS; _f++) {
-                    const _g = Math.max(_fwHitIn[_f], _fwHitGlow[_f] * _fwDecay);
-                    _fwHitGlow[_f] = _g;
-                    if (_g < 0.004) continue;   // below perceptible
-                    if (_fwLo < 0) _fwLo = _f;
-                    _fwHi = _f;
-                }
-                for (let _i = 0; _i < 2; _i++) {
-                    const _f = _i === 0 ? _fwLo : _fwHi;
-                    if (_f < 0) break;                       // nothing lit
-                    if (_i === 1 && _f === _fwLo) break;     // single wire lit
-                    const _g = _fwHitGlow[_f];
-                    const _m = fretWireMats[_f];
-                    if (!_m) continue;
-                    _m.color.lerp(_fwHitColor, _g);
-                    _m.emissive.lerp(_fwHitEmissive, _g);
-                    _m.emissiveIntensity = 1 + (FRET_WIRE_HIT_INTENSITY - 1) * _g;
-                    _m.opacity += (FRET_WIRE_HIT_OP - _m.opacity) * _g;
-                }
-            }
-
-            // ── Dynamic highway lane ──────────────────────────────────────
-            // Chart <anchor> tags drive the lane whenever they exist — do not
-            // require nearby notes (activeFrets) or camera-driven activity.
-            const hasChartAnchors = anchors && anchors.length;
-            if (hasChartAnchors || activeFrets.size > 0) {
-                // Lane tint: one translucent quad per playable fret column, exact
-                // wire→wire span (no horizontal pad) — see HWY_LANE_STRIPE_*.
-                const boardY = S_BASE - NH / 2 - 2 * K;
-
-                if (hasChartAnchors) {
-                    const nearB = laneBoundsFromAnchor(getChartAnchorAt(anchors, now));
-                    if (nearB) {
-                        hwyLaneFretClipMin = nearB.dMin;
-                        hwyLaneFretClipMax = nearB.dMax;
-                    }
-
-                    // Span the full (AHEAD + BEHIND) window so the lane's far edge
-                    // lands at dZ(AHEAD) = -AHEAD*TS, aligned with the note horizon.
-                    // Using just AHEAD here made the far edge stop at -TS*(AHEAD-BEHIND),
-                    // leaving the last BEHIND seconds of notes without a lane underneath.
-                    const sliceDt = (AHEAD + BEHIND) / HWY_LANE_TIME_SLICES;
-                    // Single-pass build-and-merge into the parallel-array
-                    // scratch buffers. Consecutive slices that resolve to the
-                    // same anchor bounds collapse into one segment by extending
-                    // its z1; otherwise a new entry appends. No per-frame array
-                    // or {b,z0,z1} object allocations.
-                    _laneSegLen = 0;
-                    for (let k = 0; k < HWY_LANE_TIME_SLICES; k++) {
-                        const dt0 = k * sliceDt;
-                        const dt1 = (k + 1) * sliceDt;
-                        const tC = now + (dt0 + dt1) * 0.5 - BEHIND;
-                        const b = laneBoundsFromAnchor(getChartAnchorAt(anchors, tC));
-                        if (!b) continue;
-                        // The lane STOPS AT THE HIT LINE (z = 0) — issue #991. The
-                        // slice window starts BEHIND seconds in the past, so the
-                        // first slices map to positive z, i.e. past the hit line
-                        // toward the player. Nothing is ever drawn there: notes and
-                        // chord frames clamp to Math.min(0, dZ(dt)), so that strip
-                        // is lane with nothing on it. Clamp the NEAR edge only —
-                        // the far edge stays at dZ(AHEAD+BEHIND)+TS*BEHIND = -AHEAD*TS,
-                        // aligned with the note horizon, exactly as before.
-                        const z0 = Math.min(0, dZ(dt0) + TS * BEHIND);
-                        const z1 = Math.min(0, dZ(dt1) + TS * BEHIND);
-                        // Slice lies entirely past the hit line -> zero length, nothing
-                        // to draw. Skip before the arp probe so it costs nothing.
-                        if (z0 === z1) continue;
-                        const arpSlice = (laneRailArpHsFlags && handShapesRails && handShapesRails.length)
-                            ? arpeggioLaneOuterRailLaneSlice(
-                                dt0, dt1, now,
-                                handShapesRails, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
-                            )
-                            : false;
-                        if (_laneSegLen > 0
-                            && _laneSegDMin[_laneSegLen - 1] === b.dMin
-                            && _laneSegDMax[_laneSegLen - 1] === b.dMax
-                            && arpSlice === _laneSegArp[_laneSegLen - 1]) {
-                            _laneSegZ1[_laneSegLen - 1] = z1;
-                            _laneSegTHi[_laneSegLen - 1] = tC;
-                        } else if (_laneSegLen > 0
-                            && _laneSegDMin[_laneSegLen - 1] === b.dMin
-                            && _laneSegDMax[_laneSegLen - 1] === b.dMax
-                            && arpSlice !== _laneSegArp[_laneSegLen - 1]) {
-                            _laneSegDMin[_laneSegLen] = b.dMin;
-                            _laneSegDMax[_laneSegLen] = b.dMax;
-                            _laneSegZ0[_laneSegLen] = z0;
-                            _laneSegZ1[_laneSegLen] = z1;
-                            _laneSegTLo[_laneSegLen] = tC;
-                            _laneSegTHi[_laneSegLen] = tC;
-                            _laneSegArp[_laneSegLen] = arpSlice;
-                            _laneSegLen++;
-                        } else {
-                            _laneSegDMin[_laneSegLen] = b.dMin;
-                            _laneSegDMax[_laneSegLen] = b.dMax;
-                            _laneSegZ0[_laneSegLen] = z0;
-                            _laneSegZ1[_laneSegLen] = z1;
-                            _laneSegTLo[_laneSegLen] = tC;
-                            _laneSegTHi[_laneSegLen] = tC;
-                            _laneSegArp[_laneSegLen] = arpSlice;
-                            _laneSegLen++;
-                        }
-                    }
-                    {
-                        const laneOp = (HWY_LANE_STRIPE_OP_BASE + highwayIntensity * HWY_LANE_STRIPE_OP_INT)
-                            * (_venueSceneOverride ? VENUE_LANE_OP_BOOST : 1);
-                        // 2 shared materials (odd/even); opacity travels via the
-                        // material so set it once per frame, not per mesh.
-                        mLaneOdd.opacity = laneOp;
-                        mLaneEven.opacity = laneOp;
-                        for (let s = 0; s < _laneSegLen; s++) {
-                            const segZ0 = _laneSegZ0[s];
-                            const segZ1 = _laneSegZ1[s];
-                            const stripLen = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
-                            const zc = (segZ0 + segZ1) * 0.5;
-                            const fLow = _laneSegDMin[s] + 1;
-                            const fHi = _laneSegDMax[s];
-                            for (let f = fLow; f <= fHi; f++) {
-                                const xl = xFret(f - 1), xr = xFret(f);
-                                const laneW = Math.abs(xr - xl);
-                                const lane = pLane.get();
-                                lane.position.set((xl + xr) * 0.5, boardY + 0.02 * K, zc);
-                                lane.rotation.x = -Math.PI / 2;
-                                lane.scale.set(laneW, stripLen, 1);
-                                const odd = ((f - fLow) & 1) === 0;
-                                lane.material = odd ? mLaneOdd : mLaneEven;
-                                lane.renderOrder = 1;
-                            }
-                        }
-                    }
-
-                    {
-                        const yPos = boardY + 0.03 * K;
-                        const divOpArp = Math.min(0.92, 0.16 + highwayIntensity * 0.42);
-                        if (mLaneDividerArp) {
-                            mLaneDividerArp.opacity = divOpArp;
-                        }
-
-                        for (let s = 0; s < _laneSegLen; s++) {
-                            const segZ0 = _laneSegZ0[s];
-                            const segZ1 = _laneSegZ1[s];
-                            const dz = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
-                            const zMid = (segZ0 + segZ1) * 0.5;
-                            const dMinSeg = _laneSegDMin[s];
-                            const dMaxSeg = _laneSegDMax[s];
-                            const fDiv0 = Math.floor(dMinSeg);
-                            const fDiv1 = Math.ceil(dMaxSeg);
-                            for (let f = fDiv0; f <= fDiv1; f++) {
-                                if (_laneSegArp[s] && (f === fDiv0 || f === fDiv1)) continue;
-                                const div = pLaneDivider.get();
-                                div.position.set(xFret(f), yPos, zMid);
-                                div.material = mLaneDivider;
-                                div.scale.set(1, 1, dz);
-                                div.renderOrder = 2;
-                            }
-                        }
-                        for (let s = 0; s < _laneSegLen; s++) {
-                            if (!_laneSegArp[s]) continue;
-                            const dMinSeg = _laneSegDMin[s];
-                            const dMaxSeg = _laneSegDMax[s];
-                            const fL = Math.floor(dMinSeg);
-                            const fR = Math.ceil(dMaxSeg);
-                            const segZ0 = _laneSegZ0[s];
-                            const segZ1 = _laneSegZ1[s];
-                            const arpRailLen = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
-                            const zArpMid = (segZ0 + segZ1) * 0.5;
-                            const tMidSeg = (_laneSegTLo[s] + _laneSegTHi[s]) * 0.5;
-                            const arpMulSeg = (laneRailArpHsFlags && handShapesRails && handShapesRails.length)
-                                ? arpeggioLaneDividerFrameAccentMul(
-                                    tMidSeg, handShapesRails, chords,
-                                    laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
-                                )
-                                : 1;
-                            const arpSSeg = arpeggioLaneDividerXYScaleMatchFrameRim(arpMulSeg);
-                            for (const xf of [fL, fR]) {
-                                const div = pLaneDivider.get();
-                                div.position.set(xFret(xf), yPos, zArpMid);
-                                div.material = mLaneDividerArp;
-                                div.scale.set(arpSSeg, arpSSeg, arpRailLen);
-                                div.renderOrder = 2;
-                            }
-                        }
-                    }
-                } else {
-                    let dMin, dMax;
-                    let divMin, divMax;
-                    let minF = 99, maxF = 0;
-                    activeFrets.forEach(f => { if (f > 0) { minF = Math.min(minF, f); maxF = Math.max(maxF, f); } });
-                    dMin = minF - 1;
-                    dMax = maxF;
-                    const HWY_LANE_SPAN = 4;
-                    let span = dMax - dMin;
-                    if (span > HWY_LANE_SPAN) {
-                        dMin = Math.round((dMin + dMax - HWY_LANE_SPAN) / 2);
-                        dMax = dMin + HWY_LANE_SPAN;
-                        if (dMax > NFRETS) {
-                            dMax = NFRETS;
-                            dMin = dMax - HWY_LANE_SPAN;
-                        }
-                        if (dMin < 0) {
-                            dMin = 0;
-                            dMax = HWY_LANE_SPAN;
-                        }
-                    } else if (span < HWY_LANE_SPAN) {
-                        const need = HWY_LANE_SPAN - span;
-                        dMax = Math.min(NFRETS, dMax + need);
-                        if (dMax - dMin < HWY_LANE_SPAN) {
-                            dMin = Math.max(0, dMin - (HWY_LANE_SPAN - (dMax - dMin)));
-                        }
-                    }
-                    if (dMax < dMin) dMax = dMin;
-                    hwyLaneFretClipMin = dMin;
-                    hwyLaneFretClipMax = dMax;
-                    divMin = dMin;
-                    divMax = dMax;
-
-                    // Far edge at -AHEAD*TS (the note horizon), near edge at the
-                    // hit line (z = 0) — the lane does not run past it toward the
-                    // player, where nothing is ever drawn (#991). Spanning
-                    // AHEAD+BEHIND and shifting by +TS*BEHIND put the near edge at
-                    // +TS*BEHIND; spanning AHEAD alone keeps the same far edge.
-                    const laneLen = TS * AHEAD;
-                    const zLane = -laneLen / 2;
-                    const laneOp = (HWY_LANE_STRIPE_OP_BASE + highwayIntensity * HWY_LANE_STRIPE_OP_INT)
-                        * (_venueSceneOverride ? VENUE_LANE_OP_BOOST : 1);
-                    mLaneOdd.opacity = laneOp;
-                    mLaneEven.opacity = laneOp;
-                    const fLow = dMin + 1;
-                    const fHi = dMax;
-                    for (let f = fLow; f <= fHi; f++) {
-                        const xl = xFret(f - 1), xr = xFret(f);
-                        const laneWStrip = Math.abs(xr - xl);
-                        const lane = pLane.get();
-                        lane.position.set((xl + xr) / 2, boardY + 0.02 * K, zLane);
-                        lane.rotation.x = -Math.PI / 2;
-                        lane.scale.set(laneWStrip, laneLen, 1);
-                        const odd = ((f - fLow) & 1) === 0;
-                        lane.material = odd ? mLaneOdd : mLaneEven;
-                        lane.renderOrder = 1;
-                    }
-
-                    if (highwayIntensity > 0.05) {
-                        // Matches the lane above: ends at the hit line (#991).
-                        const divLen = TS * AHEAD;
-                        const yPos = boardY + 0.03 * K;
-                        const divOp2 = 0.02 + highwayIntensity * 0.1;
-                        const divOpArp2 = Math.min(0.92, 0.16 + highwayIntensity * 0.42);
-                        if (mLaneDivider && mLaneDividerArp) {
-                            mLaneDivider.opacity = divOp2;
-                            mLaneDividerArp.opacity = divOpArp2;
-                        }
-                        const fDivA = Math.floor(divMin);
-                        const fDivB = Math.ceil(divMax);
-                        for (let f = fDivA; f <= fDivB; f++) {
-                            if (hwyLaneArpOuterDividers && (f === fDivA || f === fDivB)) continue;
-                            const div = pLaneDivider.get();
-                            div.position.set(xFret(f), yPos, -divLen * 0.5);
-                            div.material = mLaneDivider;
-                            div.scale.set(1, 1, divLen);
-                            div.renderOrder = 2;
-                        }
-                        if (hwyLaneArpOuterDividers) {
-                            for (const xf of [fDivA, fDivB]) {
-                                const div = pLaneDivider.get();
-                                div.position.set(xFret(xf), yPos, zLane);
-                                div.material = mLaneDividerArp;
-                                div.scale.set(arpLaneS, arpLaneS, laneLen);
-                                div.renderOrder = 2;
-                            }
-                        }
-                    }
-                }
-
-                // ── Fret boundary extension lines ─────────────────────────
-                if (mLaneDividerExt && fretDividersVisible) {
-                    // Same hit-line stop as the lane (#991) — otherwise these lines
-                    // would be the only floor geometry still running past it.
-                    const extLaneLen = TS * AHEAD;
-                    const extZMid = -extLaneLen / 2;
-                    const extYPos = boardY + 0.03 * K;
-                    mLaneDividerExt.opacity = Math.max(0.3, 0.3 + highwayIntensity * 0.15);
-                    for (let f = 0; f <= NFRETS; f++) {
-                        const div = pLaneDivider.get();
-                        div.position.set(xFret(f), extYPos, extZMid);
-                        div.material = mLaneDividerExt;
-                        div.scale.set(1, 1, extLaneLen);
-                        div.renderOrder = 2;
-                    }
-                }
-            }
-
-            // ── Dynamic fret number row (heat-coloured) ───────────────────
-            // Two-part fix for issue #35:
-            //  1. renderOrder = 1000 forces these sprites to the end of
-            //     the transparent queue so they always paint on top of
-            //     notes, sustain trails, lane plane, etc. depthTest is
-            //     already disabled by txtMat(), but `depthTest: false`
-            //     only exempts the sprite from depth comparison — it
-            //     doesn't pin draw order. Without an explicit
-            //     renderOrder, a note rendered after the label in the
-            //     transparent pass would still overdraw it. Match the
-            //     pattern already used for lane and dividers.
-            //  2. Y-offset bumped from S_GAP * 0.6 to S_GAP * 1.4 so the
-            //     label band sits clearly below the lowest string in
-            //     screen space, even at the largest active scale
-            //     (intensity-driven, up to ~5.7 * K vertical extent).
-            //     This buys a real visual gap between notes-on-the-
-            //     lowest-string and the row, on top of the renderOrder
-            //     guarantee — labels never share screen with what's
-            //     happening on the playing strings just above them.
-            {
-                const yBottom = Math.min(sY(0), sY(nStr - 1));
-                // anchorSpan: [f0, f1] = [anchor.fret, anchor.fret + width - 1]
-                // e.g. { fret:3, width:4 } → f0=3, f1=6 → frets 3,4,5,6 gold.
-                const anchorSpan = anchorPlayedFretSpanAt(anchors, now);
-                for (let f = 1; f <= NFRETS; f++) {
-                    const isInAnchor = anchorSpan
-                        && f >= anchorSpan.f0 && f <= anchorSpan.f1;
-                    const isMainFret = DOTS.includes(f);
-                    // Rule 1: show gray label only on main frets (dot positions).
-                    // Rule 2: show gold label on any fret inside the anchor range.
-                    // Non-main frets outside the anchor range are hidden entirely.
-                    if (!isInAnchor && !isMainFret) continue;
-                    const lb = pFretLbl.get();
-                    lb.material = txtMat(f,
-                        isInAnchor ? FRET_LABEL_GOLD_HEX : FRET_LABEL_IDLE_HEX,
-                        false, 'fretRow');
-                    lb.position.set(xFretMid(f), yBottom - S_GAP * 1.4, 0.5 * K);
-                    lb.material.opacity = isInAnchor ? 1.0 : 0.55;
-                    const scale = 5.95 * _textSizeMul * fretLabelScaleForFret(f);
-                    lb.scale.set(scale * K, scale * K, 1);
-                    lb.renderOrder = 1000;
-                }
-            }
-
-            // ── Beat lines ────────────────────────────────────────────────
-            if (beats) {
-                const board = boardSpanX();
-                const bw2 = board.width + 4 * K;
-                let lastM = -1;
-                for (const b of beats) {
-                    const meas = b.measure !== lastM; lastM = b.measure;
-                    if (b.time < t0 || b.time > t1) continue;
-                    const bl2 = pBeat.get();
-                    bl2.material = meas ? mBeatM : mBeatQ;
-                    bl2.scale.set(bw2, 1, 1);
-                    bl2.position.set(board.min - 2 * K, S_BASE - NH / 2 - 1.5 * K, dZ(b.time - now));
-                }
-            }
-
-            // ── Section labels ────────────────────────────────────────────
-            // Gated on sectionLabelsOnHighway (advanced setting, default off).
-            // The HUD card (drawSectionHud, called from the lyricsCtx block in
-            // draw()) is the primary surface for section info; the on-highway
-            // sprites are kept as an opt-in for users who want the in-scene cue.
-            if (sections && sectionLabelsOnHighway) {
-                const labelY = Math.max(sY(0), sY(nStr - 1)) + 8 * K;
-                for (const s of sections) {
-                    if (s.time < t0 || s.time > t1) continue;
-                    const sp = pSec.get();
-                    sp.material = txtMat(s.name, '#00cccc', true, 'section');
-                    sp.scale.set(20 * K * _textSizeMul, 5 * K * _textSizeMul, 1);
-                    sp.position.set(xFret(12), labelY, dZ(s.time - now));
-                }
-            }
-
-            // ── Fret-column reference markers ─────────────────────────────
-            // Every Nth measure, spawn a row of fret-number sprites on the
-            // board floor that scroll toward the hit line and vanish at Z=0.
-            // With a chart <anchor>, which frets appear follows the inlay
-            // cadence (DOTS) centred on the snapped anchor fret (~2 positions
-            // back and ~3 forward in that list, e.g. anchor 7 → 3,5,7,9,12,15).
-            // Without anchors, all DOTS positions are candidates; octave + lane
-            // clipping apply. With <anchor>, the cadence row ignores both so
-            // frets before/after the lane still show as reference. Light grey
-            // when that fret is in the active set, dark grey otherwise.
-            //
-            // Per-wave gate cache: hasLow/hasHigh/fretList snapshotted at first
-            // sight of a wave so the render decision stays stable through
-            // the wave's full flight. Without this, activeFrets shifting
-            // mid-song would drop markers mid-flight (user-reported bug:
-            // "numbers disappear before they get all the way towards me").
-            if (beats && fretColumnMarkerCadence > 0) {
-                // Prune stale wave cache entries (wave already past now).
-                if (_fretMarkerWaveCache.size > 0) {
-                    for (const k of _fretMarkerWaveCache.keys()) {
-                        if (k < now) _fretMarkerWaveCache.delete(k);
-                    }
-                }
-                const minStringY = Math.min(sY(0), sY(nStr - 1));
-                const labelY = minStringY - S_GAP * 0.8;
-                for (const b of beats) {
-                    // Non-downbeats are encoded as measure=-1; only actual
-                    // measure starts (measure >= 0) can spawn marker waves.
-                    if (b.measure < 0) continue;
-                    if (b.time < 0 || b.time > t1) continue;
-                    if (b.time <= now) continue;
-                    if ((b.measure | 0) % fretColumnMarkerCadence !== 0) continue;
-
-                    // Snapshot the active-range gate at first sight of this
-                    // wave. We scan notes/chords in a 2s window starting at
-                    // b.time rather than activeFrets, because activeFrets only
-                    // covers now+2s and waves first become visible up to
-                    // AHEAD (3s) ahead — using activeFrets would cache
-                    // {hasLow:false, hasHigh:false} for far waves and suppress
-                    // the entire row for its full flight.
-                    let cached = _fretMarkerWaveCache.get(b.time);
-                    if (!cached) {
-                        let hasLow = false, hasHigh = false;
-                        const wT0 = b.time, wT1 = b.time + 2;
-                        // notes and chords are time-sorted; binary-search to the
-                        // first entry >= wT0, then break once past wT1 to avoid
-                        // O(song_length) work per newly-seen wave.
-                        if (notes) {
-                            const startI = lowerBoundT(notes, wT0);
-                            for (let i = startI; i < notes.length; i++) {
-                                const n = notes[i];
-                                if (n.t > wT1) break;
-                                if (!validString(n.s) || n.f <= 0) continue;
-                                if (n.f <= 12) hasLow = true; else hasHigh = true;
-                                if (hasLow && hasHigh) break;
-                            }
-                        }
-                        if ((!hasLow || !hasHigh) && chords) {
-                            const startI = lowerBoundT(chords, wT0);
-                            outer: for (let i = startI; i < chords.length; i++) {
-                                const ch = chords[i];
-                                if (ch.t > wT1) break outer;
-                                if (!ch.notes) continue;
-                                for (const cn of ch.notes) {
-                                    if (!validString(cn.s) || cn.f <= 0) continue;
-                                    if (cn.f <= 12) hasLow = true; else hasHigh = true;
-                                    if (hasLow && hasHigh) break outer;
-                                }
-                            }
-                        }
-                        const anc = anchors && anchors.length ? getChartAnchorAt(anchors, b.time) : null;
-                        const anchorFret = anc != null ? Number(anc.fret) : NaN;
-                        const anchorKeyed = Number.isFinite(anchorFret) && anchorFret >= 0;
-                        const fretList = anchorKeyed
-                            ? fretColumnMarkersForAnchor(anchorFret, DOTS)
-                            : DOTS.slice();
-                        cached = { hasLow, hasHigh, fretList, anchorKeyed };
-                        _fretMarkerWaveCache.set(b.time, cached);
-                    }
-                    if (!cached.hasLow && !cached.hasHigh && !cached.anchorKeyed) continue;
-
-                    const dt = b.time - now;
-                    // Fade in over 0.35 s from the maximum lookahead distance so
-                    // the label appears at its correct final size the moment it
-                    // becomes visible, rather than gradually emerging as a tiny
-                    // dim spec through scene fog (fog is disabled on the sprite
-                    // material; this manual ramp replaces it).
-                    const _colFadeIn = Math.min(1.0, (AHEAD - dt) / 0.35);
-                    if (_colFadeIn <= 0) continue;
-
-                    const z = dZ(dt);
-                    // Sprite scale matches the per-note connector fret label
-                    // (drawNote → pNoteFretLabel) so cadence markers read the
-                    // same size at a given Z — no extra world-scale boost.
-                    const clipMin = hwyLaneFretClipMin;
-                    const clipMax = hwyLaneFretClipMax;
-                    const fretList = cached.fretList || DOTS;
-                    const anchorKeyedRow = !!cached.anchorKeyed;
-                    for (const f of fretList) {
-                        let show;
-                        if (anchorKeyedRow) {
-                            show = true;
-                        } else {
-                            if (f === 12) show = cached.hasLow || cached.hasHigh;
-                            else if (f < 12) show = cached.hasLow;
-                            else show = cached.hasHigh;
-                        }
-                        if (!show) continue;
-                        if (!anchorKeyedRow && clipMin != null && (f <= clipMin || f > clipMax)) continue;
-                        // Fixed colour — avoids mid-flight colour flips caused by
-                        // activeFrets only covering now+2s while waves appear at
-                        // AHEAD (3s), which made each marker start dark then
-                        // suddenly jump to light when its note entered the 2s window.
-                        const color = '#888888';
-                        const sp = pFretColMarker.get();
-                        const m = txtMat(f, color, false, 'noteFret');
-                        _setLabelMap(sp, m);
-                        sp.material.opacity = 0.85 * _colFadeIn;
-                        sp.position.set(xFretMid(f), labelY, z);
-                        // Z-proportional: sits between chord frame and note gem
-                        // at the same depth, so chord frames never overdraw the
-                        // marker and the marker never overdraws gems.
-                        sp.renderOrder = renderOrderForLayerAtZ(z, 'FRET_COLUMN');
-                        // Scale grows linearly from 2× at max lookahead to 1× at hit line,
-                        // combined with natural perspective attenuation the label starts
-                        // visibly larger and converges to the row-label size at z=0.
-                        const sz = 7.0 * K * (1 + 0.4 * dt / AHEAD) * _textSizeMul * fretLabelScaleForFret(f);
-                        sp.scale.set(sz, sz, 1);
-                    }
-
-                }
-            }
-
-            // ── Camera target ─────────────────────────────────────────────
-            let lockActive;
-            if (!(cameraMode === 'lookahead')) {
-                lockActive = _applyNoteCamTargets(
-                    camWX, camWSum, camDistMin, camDistMax, camDistGot,
-                    camHystF, camDistHystF, /* skipDistHyst= */ false);
-                prevLockActive = lockActive;
-            } else {
-                const lookaheadMaxF = lookaheadBoundsNow ? lookaheadBoundsNow.maxF : 0;
-                const lookaheadHasBounds = lookaheadBoundsNow != null;
-
-                let dtSec = 1 / 120;
-                if (_lookaheadCamPrevNow !== null) {
-                    const rawDt = _frameNow - _lookaheadCamPrevNow;
-                    if (rawDt > -1 && rawDt < 2) dtSec = Math.min(0.2, Math.max(1 / 960, rawDt));
-                }
-                _lookaheadCamPrevNow = _frameNow;
-                const dBlend = Math.min(0.2, Math.max(1e-4, dtSec));
-                const lowBlendFs = 1 - Math.pow(1 - CAM_FOCUS_BLEND_RATE, dBlend);
-
-                if (!lookaheadHasBounds || lookaheadMaxF <= LOOKAHEAD_LOCK_ENGAGE_MAXF)
-                    _lookaheadHiNeckLatch = false;
-                else if (lookaheadMaxF >= LOOKAHEAD_LOCK_RELEASE_MAXF)
-                    _lookaheadHiNeckLatch = true;
-
-                const lookaheadLockLowEligible = cameraLockLow
-                    && (!lookaheadHasBounds
-                        || (!_lookaheadHiNeckLatch && lookaheadMaxF <= 12));
-
-                let rawLowBU;
-                if (lookaheadLockLowEligible) {
-                    rawLowBU = camLowFretPullbackU(1);
-                } else if (lookaheadBoundsNow) {
-                    rawLowBU = camLowFretPullbackU(lookaheadBoundsNow.minF);
-                } else {
-                    rawLowBU = camLowFretPullbackU(CAM_LOCK_CENTER_FRET);
-                }
-                _lookaheadLowBonusU = rawLowBU * lowBlendFs + _lookaheadLowBonusU * (1 - lowBlendFs);
-
-                if (lookaheadLockLowEligible) {
-                    const lockedBaseU = camBaseDistU(12);
-                    const lockZoomMul = CAM_LOCK_ZOOM_MIN +
-                        (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
-                    lookaheadSmoothCamStep(dtSec, xFretMid(CAM_LOCK_CENTER_FRET), 12);
-                    tgtX = _lookaheadCamX;
-                    tgtDist = (lockedBaseU + _lookaheadLowBonusU) * K * lockZoomMul;
-                    prevLowFretBonus = _lookaheadLowBonusU;
-                    lockActive = true;
-                } else {
-                    if (lookaheadBoundsNow) {
-                        const tgtWX = lookaheadTargetWorldX(
-                            lookaheadBoundsNow.minF, lookaheadBoundsNow.maxF);
-                        const tgtSpanInt = Math.max(
-                            1, lookaheadBoundsNow.maxF - lookaheadBoundsNow.minF + 1);
-                        lookaheadSmoothCamStep(dtSec, tgtWX, tgtSpanInt);
-                        tgtDist = (camBaseDistU(_lookaheadFretSpan) + _lookaheadLowBonusU) * K;
-                        prevLowFretBonus = _lookaheadLowBonusU;
-                    } else {
-                        lookaheadSmoothCamStep(dtSec, _lookaheadCamX, _lookaheadFretSpan);
-                        tgtDist = (camBaseDistU(_lookaheadFretSpan) + _lookaheadLowBonusU) * K;
-                        prevLowFretBonus = _lookaheadLowBonusU;
-                    }
-                    tgtX = _lookaheadCamX;
-                    lockActive = false;
-                }
-                prevLockActive = lockActive;
-            }
-
-            // ── Chord diagram: track chord, drive entrance + crossfade animations ─
-            {
-                let newChord = null;
-                if (chords) {
-                    // Only chords in (now - DIAG_LINGER_S, now] — use binary search
-                    // to skip past old chords, break once we pass `now`.
-                    const _dlo = lowerBoundT(chords, now - DIAG_LINGER_S);
-                    for (let _di = _dlo; _di < chords.length; _di++) {
-                        const ch = chords[_di];
-                        const chDt = ch.t - now;
-                        if (chDt > 0) break;
-                        if (!ch.notes) continue;
-                        const tmpl = bundle.chordTemplates?.[ch.id];
-                        const lbl = chordTemplateLabel(tmpl);
-                        // Last valid chord (highest t ≤ now) naturally wins since array is sorted.
-                        if (lbl && tmpl?.frets) {
-                            newChord = { name: lbl, frets: tmpl.frets, t: ch.t, t0: ch.t, chDt, nStr };
-                        }
-                    }
-                }
-
-                // Include frets in the key so two templates sharing a display name but
-                // differing in fingering each trigger a fresh crossfade/entrance.
-                const newKey = newChord ? newChord.name + '|' + newChord.frets.join(',') : null;
-                if (newKey !== _diagLastKey) {
-                    if (_diagChord && newKey !== null) {
-                        // Recompute outgoing alpha from stored event time rather than the
-                        // stale per-frame chDt; after dropped frames or seeks this prevents
-                        // the overlay jumping to a stale brightness before the crossfade.
-                        const freshChDt = _diagChord.t !== undefined ? _diagChord.t - now : _diagChord.chDt;
-                        const prevOpacity = Math.max(0, Math.min(1, 1 + freshChDt / DIAG_LINGER_S));
-                        // Only crossfade when the outgoing chord is actually visible at now.
-                        // freshChDt > 0 means the old chord is in the future (backward seek
-                        // crossed the chord boundary).  In that case _diagChord is stale, so
-                        // recompute the outgoing diagram from the chart — find the most recent
-                        // named chord that ends just before newChord.t and use it as _diagPrev
-                        // so that seeking into a historical chord transition fades correctly
-                        // rather than snapping straight to the new chord.
-                        if (freshChDt <= 0 && prevOpacity > 0) {
-                            // Use the string count the outgoing chord was captured with, not the
-                            // current nStr — an arrangement switch during a 150 ms crossfade
-                            // must not remap the outgoing diagram onto the new layout.
-                            _diagPrev = { name: _diagChord.name, frets: _diagChord.frets, nStr: _diagChord.nStr ?? nStr, t: _diagChord.t0 ?? _diagChord.t ?? now };
-                            _diagPrevStartOpacity = prevOpacity;
-                            _diagPrevOpacity = prevOpacity;
-                            _diagPrevStartT = now;
-                            // entranceT for the outgoing diagram is computed live from _diagPrev.t
-                            // each frame (see draw path), so it rewinds correctly on backward seeks
-                            // within the crossfade window — no separate snapped state needed here.
-                        } else if (freshChDt > 0) {
-                            // Backward seek: _diagChord is now in the future.
-                            // Look up the chart chord immediately before newChord.t to provide
-                            // the correct historical outgoing diagram for the crossfade.
-                            let histPrev = null;
-                            if (chords && newChord) {
-                                // Find the most recent named chord before newChord.t.
-                                // Chords are sorted ascending, so all matches are before
-                                // lowerBoundT(chords, newChord.t); iterate in order and
-                                // take the last valid one.
-                                const _hpHi = lowerBoundT(chords, newChord.t);
-                                for (let _hpi = 0; _hpi < _hpHi; _hpi++) {
-                                    const ch = chords[_hpi];
-                                    if (!ch.notes) continue;
-                                    const tmpl = bundle.chordTemplates?.[ch.id];
-                                    const lbl = chordTemplateLabel(tmpl);
-                                    if (lbl && tmpl?.frets) {
-                                        histPrev = { name: lbl, frets: tmpl.frets, t: ch.t, t0: ch.t, nStr };
-                                    }
-                                }
-                            }
-                            // Only start a crossfade if we are still within DIAG_CROSSFADE_S of
-                            // newChord.t; seeking further into the chord skips the crossfade.
-                            // Also skip if histPrev was no longer visible when newChord started
-                            // (gap longer than DIAG_LINGER_S), so only genuinely adjacent chord
-                            // transitions produce a crossfade — not seeks to just after any new
-                            // chord that happens to have an older chord somewhere earlier in the song.
-                            const elapsed = newChord ? now - newChord.t : Infinity;
-                            const histPrevVisible = histPrev && (newChord.t - histPrev.t) < DIAG_LINGER_S;
-                            if (histPrevVisible && elapsed >= 0 && elapsed < DIAG_CROSSFADE_S) {
-                                // Start at the linger opacity the outgoing chord would have had at
-                                // newChord.t during forward playback, not always 1.  This prevents
-                                // a chord that was mostly faded from appearing brighter on a seek.
-                                const histStartOpacity = Math.max(0, Math.min(1,
-                                    1 - (newChord.t - histPrev.t) / DIAG_LINGER_S));
-                                _diagPrev = histPrev;
-                                _diagPrevStartOpacity = histStartOpacity;
-                                _diagPrevOpacity = Math.max(0, histStartOpacity * (1 - elapsed / DIAG_CROSSFADE_S));
-                                _diagPrevStartT = newChord.t;
-                            } else {
-                                _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
-                                _diagPrevStartT = null;
-                            }
-                        } else {
-                            // prevOpacity <= 0: old chord already fully faded, no crossfade needed.
-                            _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
-                            _diagPrevStartT = null;
-                        }
-                    } else {
-                        _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
-                        _diagPrevStartT = null;
-                    }
-                    _diagLastKey = newKey;
-                    // Only update _diagChord when the chord key actually changes so that a
-                    // lingering chord's original nStr is preserved on subsequent frames.
-                    // (newChord is rebuilt every frame with the live nStr; unconditionally
-                    // assigning here would stomp the captured nStr if the arrangement switches
-                    // while the same chord is still in its linger window.)
-                    _diagChord = newChord;
-                } else if (newKey !== null && newChord && _diagChord) {
-                    // Same chord re-seen. Update linger expiry (t) when the event time changes.
-                    // Forward restrum (newChord.t > _diagChord.t): extend the linger window
-                    // but preserve t0 so the entrance animation is NOT replayed — avoids the
-                    // overlay jumping back to its 0.85× scale on every strum of the same chord.
-                    // Backward seek to earlier occurrence (newChord.t < _diagChord.t): update
-                    // both t and t0 to restart the entrance animation from the earlier position.
-                    if (newChord.t !== _diagChord.t) {
-                        _diagChord = newChord.t < _diagChord.t
-                            ? { ..._diagChord, t: newChord.t, t0: newChord.t }  // backward seek
-                            : { ..._diagChord, t: newChord.t };                 // forward restrum
-                    }
-                }
-
-                // Guard for backward seeks within the same chord (same key, no branch above).
-                // If _diagPrevStartT is in the future relative to now, the crossfade was set up
-                // during a later playback position that has since been seeked past. Clear it so
-                // the stale outgoing diagram does not stay fully visible at the seek target.
-                if (_diagPrev && _diagPrevStartT !== null && _diagPrevStartT > now) {
-                    _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
-                    _diagPrevStartT = null;
-                }
-
-                // Entrance: derived from t0 (the original appearance time, not updated on
-                // forward restrums) so repeated hits of the same chord do not replay the
-                // 0.85→1.0 scale animation. On backward seeks t0 is updated alongside t,
-                // so the animation still rewinds correctly to the earlier position.
-                const _entranceAnchor = _diagChord && (_diagChord.t0 ?? _diagChord.t);
-                _diagEntranceT = (_diagChord && _entranceAnchor !== undefined)
-                    ? Math.min(1.0, Math.max(0, (now - _entranceAnchor) / DIAG_ENTRANCE_S))
-                    : 1.0;
-
-                // Crossfade: derived from absolute start time so backward seeks within the
-                // crossfade window correctly rewind the fade. _diagPrev is kept alive (at
-                // opacity 0) until the next key change rather than destroyed here, so that a
-                // backward seek that re-enters the crossfade window can recompute a positive
-                // opacity. Seeks before _diagPrevStartT are handled by the guard above.
-                if (_diagPrev && _diagPrevStartT !== null) {
-                    const fadedT = Math.max(0, now - _diagPrevStartT);
-                    _diagPrevOpacity = Math.max(0, _diagPrevStartOpacity * (1 - fadedT / DIAG_CROSSFADE_S));
-                }
-            }
-            // ── Finalise InstancedMesh batches ────────────────────────────────
-            // Flush all 6 IMs: set visible instance count and mark buffers dirty.
-            // Must run after all drawNote() / chord-loop writes are done.
-            if (imPMTech) {
-                imPMTech.count = _imPMTechCount;
-                if (_imPMTechCount > 0) {
-                    imPMTech.instanceMatrix.needsUpdate = true;
-                    imPMTech.geometry.getAttribute('instanceAlpha').needsUpdate = true;
-                }
-            }
-            if (imFHTech) {
-                imFHTech.count = _imFHTechCount;
-                if (_imFHTechCount > 0) {
-                    imFHTech.instanceMatrix.needsUpdate = true;
-                    imFHTech.geometry.getAttribute('instanceAlpha').needsUpdate = true;
-                }
-            }
-            // These IMs are kept alive but always empty (count=0) — rendering
-            // is now handled by the pPMXFill / pMuteXLines / pFHXFill / pFHXLines
-            // pools which support per-chord Z-proportional renderOrder.
-            if (imPMXFill)  imPMXFill.count  = 0;
-            if (imPMXLines) imPMXLines.count = 0;
-            if (imFHXFill)  imFHXFill.count  = 0;
-            if (imFHXLines) imFHXLines.count = 0;
-
-            pbEnd(5);
-            pbEnd(0);
-            pbReportTick();
-        }
-
-        /**
-         * Indexed sustain ribbon (~SLIDE_RIBBON_SAMPLES longitudinal slices)
-         * for slides, bends, vibrato and tremolo — smooth contour vs stacked
-         * BoxGeometry segments.
-         */
-        function slideRibbonUpdatePositions(geom, strandBaseX, tw, th, y, sliceDur, susStart, now, n, slideSt) {
-            const pa = geom.attributes.position.array;
-            const S = SLIDE_RIBBON_SAMPLES;
-            // slideOffsetWorldX is defined at module scope so it returns a
-            // right-handed delta (built from non-lefty fretMid). strandBaseX is
-            // already lefty-mirrored via xFretMid at the call site, so the
-            // delta needs the same sign flip to keep the slide tracking the
-            // mirrored fretboard direction.
-            const dirMul = _leftyCached ? -1 : 1;
-            let v = 0;
-            for (let k = 0; k <= S; k++) {
-                const Tk = susStart + (k / S) * sliceDur;
-                const zk = dZ(Tk - now);
-                const xc = strandBaseX
-                    + dirMul * slideOffsetWorldX(n, Tk, slideSt)
-                    + tremoloOffsetWorldX(n, Tk, tw);
-                const yc = y + techniqueYOffsetWorld(n, Tk);
-                pa[v++] = xc - tw * 0.5; pa[v++] = yc - th * 0.5; pa[v++] = zk;
-                pa[v++] = xc + tw * 0.5; pa[v++] = yc - th * 0.5; pa[v++] = zk;
-                pa[v++] = xc + tw * 0.5; pa[v++] = yc + th * 0.5; pa[v++] = zk;
-                pa[v++] = xc - tw * 0.5; pa[v++] = yc + th * 0.5; pa[v++] = zk;
-            }
-            geom.attributes.position.needsUpdate = true;
-            // Normals are pre-baked at geometry creation (see mkSlideRibbonGeo);
-            // axis-aligned cross-section means they don't need per-frame recompute.
-        }
-
-        function noteHasVibrato(n) {
-            return !!(n && (n.vb || n.vibrato));
-        }
-
-        function bendVisualDirY(stringIdx) {
-            if (!Number.isFinite(stringIdx) || nStr <= 1) return 1;
-            const visualIdx = _invertedCached ? stringIdx : (nStr - 1 - stringIdx);
-            return visualIdx >= (nStr - 1) * 0.5 ? -1 : 1;
-        }
-
-        // Teaching marks (§6.2.2) — display only, never grading. Pure label
-        // helpers, mirroring static/highway.js so the two highways agree;
-        // node-tested via tests/js/highway_teaching_marks.test.js.
-        function teachingFingerLabel(fg) {
-            // fret-hand finger: '' when unset/out of range; 0 -> 'T' (thumb),
-            // 1..4 -> '1'..'4'.
-            if (!Number.isInteger(fg) || fg < 0 || fg > 4) return '';
-            return fg === 0 ? 'T' : String(fg);
-        }
-        function teachingDegreeLabel(sd) {
-            // scale degree: chromatic 0..11 above the active key tonic; '' when
-            // unset/out of range.
-            if (!Number.isInteger(sd) || sd < 0 || sd > 11) return '';
-            return String(sd);
-        }
-        /** Harmony annotations (§6.3.1 / §6.6): display labels for a chord's
-         * function (instance `fn.rn` Roman numeral) and template `voicing`,
-         * `caged` shape, and `guideTones`. '' for each when absent/malformed;
-         * `caged`/`guideTones` come back pre-formatted ("CAGED: E" / "gt 4,10").
-         * Pure; shared with the 2D highway and node-tested. Display only — never
-         * grading. */
-        function chordHarmonyLabels(fn, voicing, caged, guideTones) {
-            const rn = (fn && typeof fn.rn === 'string') ? fn.rn.trim() : '';
-            const vc = (typeof voicing === 'string') ? voicing.trim() : '';
-            const cg = (typeof caged === 'string' && /^[CAGED]$/.test(caged.trim()))
-                ? 'CAGED: ' + caged.trim() : '';
-            const gt = Array.isArray(guideTones)
-                ? guideTones.filter(n => Number.isInteger(n) && n >= 0 && n <= 11) : [];
-            return { rn, voicing: vc, caged: cg, guideTones: gt.length ? 'gt ' + gt.join(',') : '' };
-        }
-
-        function bnvSampleAt(bnv, t) {
-            // Linear interpolation of a bend curve [{t, v}] (§6.2.1; t is
-            // seconds from the note onset) at elapsed time t. Clamps to the
-            // endpoints; returns 0 for an empty/invalid curve.
-            if (!Array.isArray(bnv) || bnv.length === 0) return 0;
-            if (t <= bnv[0].t) return bnv[0].v;
-            const last = bnv[bnv.length - 1];
-            if (t >= last.t) return last.v;
-            for (let i = 1; i < bnv.length; i++) {
-                const a = bnv[i - 1], b = bnv[i];
-                if (t <= b.t) {
-                    const span = b.t - a.t;
-                    return span > 0 ? a.v + (b.v - a.v) * ((t - a.t) / span) : b.v;
-                }
-            }
-            return last.v;
-        }
-
-        function bendSemisAtTime(n, chartTime) {
-            if (!(n?.sus > 0)) return 0;
-            // When the note carries an authoritative bend curve (§6.2.1),
-            // sample its real shape at the elapsed time so the gem's Y gesture
-            // and sustain ribbon follow the actual bend (pre-bend, round-trip,
-            // release, …). Negative samples clamp to 0 (upward-only Y offset).
-            if (Array.isArray(n.bnv) && n.bnv.length) {
-                return Math.max(0, bnvSampleAt(n.bnv, chartTime - n.t));
-            }
-            const bn = Number(n?.bn) || 0;
-            if (!(bn > 0)) return 0;
-            const p = Math.max(0, Math.min(1, (chartTime - n.t) / Math.max(n.sus, 1e-6)));
-            // Fallback: synthesize rise → hold → release from the scalar peak.
-            // Ramp up over the first ~35 %, hold, then release over the last
-            // ~30 % — the bend gesture rather than a monotone climb. Drives both
-            // the sustain ribbon's Y contour and the gem's techniqueYNow offset.
-            const RISE = BEND_ENV_RISE_FRAC, REL = BEND_ENV_RELEASE_FRAC;
-            let env;
-            if (p < RISE) env = p / RISE;
-            else if (p < 1 - REL) env = 1;
-            else env = (1 - p) / REL;
-            return bn * Math.max(0, Math.min(1, env));
-        }
-
-        function vibratoSemisAtTime(n, chartTime) {
-            if (!noteHasVibrato(n) || !(n?.sus > 0)) return 0;
-            const elapsed = Math.max(0, chartTime - n.t);
-            return Math.sin(elapsed * Math.PI / VIBRATO_HALF_WAVE_S);
-        }
-
-        function techniqueYOffsetWorld(n, chartTime) {
-            if (!(n?.sus > 0)) return 0;
-            const bendSemi = bendSemisAtTime(n, chartTime);
-            const vibratoSemi = vibratoSemisAtTime(n, chartTime);
-            if (bendSemi === 0 && vibratoSemi === 0) return 0;
-            return bendVisualDirY(n.s) * BEND_HALFSTEP_WORLD_Y * (bendSemi + vibratoSemi);
-        }
-
-        function tremoloOffsetWorldX(n, chartTime, trailW) {
-            if (!(n?.tr) || !(n?.sus > 0)) return 0;
-            const elapsed = Math.max(0, chartTime - n.t);
-            const phase = (elapsed % TREMOLO_BUMP_S) / TREMOLO_BUMP_S;
-            const tri = (Math.abs(phase - 0.5) - 0.25) * 3;
-            return trailW * 0.5 * tri;
-        }
-
-        /* ── Note renderer ───────────────────────────────────────────────── */
-        // Chart-format <chordTemplates> frets: -1 = unused, 0 = open, n>0 = fret.
-        // Ghost digit for chord notes uses the template row when present so it
-        // matches the XML diagram, not a divergent chordNote.f if any.
-        function _templateFretForChordGhost(chordId, stringIdx, noteFret) {
-            if (chordId == null) return noteFret;
-            // Coerce: some upstream paths (e.g. hs.chord_id from sloppaks)
-            // hand us string ids like "12". Cf. `templates[cid] ?? templates[Number(cid)]`
-            // earlier in this file.
-            const cid = typeof chordId === 'number' ? chordId : Number(chordId);
-            if (!Number.isFinite(cid)) return noteFret;
-            const fr = _drawChordTemplates?.[cid]?.frets;
-            if (!Array.isArray(fr) || stringIdx < 0 || stringIdx >= fr.length) return noteFret;
-            const tf = fr[stringIdx];
-            if (typeof tf !== 'number' || tf < 0) return noteFret;
-            return tf;
-        }
-        // Chart-format-style ghost digit: finger position (1=index … 4=pinky) from
-        // the chord template.  Returns null when no finger data is available
-        // (GP imports emit all -1; open strings have finger 0 which we skip too
-        // since "0" is already shown via the open-string note path).
-        function _templateFingerForChordGhost(chordId, stringIdx) {
-            if (chordId == null) return null;
-            const cid = typeof chordId === 'number' ? chordId : Number(chordId);
-            if (!Number.isFinite(cid)) return null;
-            const fi = _drawChordTemplates?.[cid]?.fingers;
-            if (!Array.isArray(fi) || stringIdx < 0 || stringIdx >= fi.length) return null;
-            const tf = fi[stringIdx];
-            // -1 = unused / no data (GP imports); 0 = open string (skip — gem path handles it)
-            if (typeof tf !== 'number' || tf <= 0) return null;
-            return tf; // 1–4
-        }
-        /**
-         * Renders one board-ghost fret digit onto a pooled label mesh, flat
-         * in the board XY plane at (x, y, 0) — a Mesh (not a Sprite
-         * billboard) so perspective + projRim match the 3D ghost frame.
-         * Shared by drawNote()'s Primary ghost slot (chord/arp-aware caller
-         * resolves fretDisplay/alpha/fretForScale itself) and its Upcoming
-         * slots (always plain lead notes, where those collapse to
-         * n.f/projFactor/n.f).
-         */
-        function drawGhostFretLabel(x, y, projRim, fretDisplay, alpha, growScale, fretForScale) {
-            const lb = pGhostFretLbl.get();
-            const sprMat = txtMat(fretDisplay, '#ffffff', false, 'ghostFret');
-            const baseGhostMat = _meshMatForGhostFretDigit(sprMat);
-            let instMat = lb.userData.h3dGhostFretLblInstMat;
-            if (!instMat || instMat.map !== baseGhostMat.map) {
-                if (instMat) {
-                    try { instMat.dispose(); } catch (_) { /* idempotent */ }
-                }
-                instMat = baseGhostMat.clone();
-                instMat.transparent = true;
-                instMat.needsUpdate = true;
-                lb.userData.h3dGhostFretLblInstMat = instMat;
-            }
-            instMat.opacity = alpha;
-            instMat.depthTest = false;
-            lb.material = instMat;
-            lb.renderOrder = 1000;
-            const ghostOuterL = Math.max(NW * 1.1, NH * 1.1);
-            const ghostLblS = 0.7 * ghostOuterL * _textSizeMul * fretLabelScaleForFret(fretForScale);
-            const ghostLblScaled = ghostLblS * growScale;
-            lb.scale.set(ghostLblScaled, ghostLblScaled, 1);
-            // Z=0 matches the projection frame plane exactly — avoids parallax
-            // horizontal drift that appears when the camera is offset from the
-            // fret centre (camera sits at curX+20*K and looks toward curX, so
-            // any positive-Z offset on this label projects leftward vs the frame).
-            lb.position.set(x, y, 0);
-            lb.rotation.set(0, 0, projRim);
-        }
-
-        // skipLabel: don't draw per-note connector label (repeated fret)
-        // skipBody:  don't draw the 3D note mesh (repeat chord — still shows projection)
-        // showDropLine: draw a white vertical drop line from note to below board (arpeggio / synth chord notes)
-        function drawNote(n, now, openX, skipLabel, skipBody, linger = 0.10, openChordBoxWidth, fromChord = false, chordId, susTrailMatchArpFrame = false, arpBounds = null, prevOnsetT = -Infinity, showDropLine = false) {
-            const s = n.s;
-            // Belt + suspenders: callers already gate via validString(),
-            // but drawNote is also entered through { ...cn } chord-note
-            // spreads, so re-check here before indexing material arrays.
-            if (!validString(s)) return;
-            const nxFrame = _drawNextByString && _drawNextByString[s];
-            const dt = n.t - now;
-            const ghostHold = fromChord ? linger : GHOST_HOLD_AFTER_ONSET;
-            const nextTAligned = nxFrame != null && Math.abs(nxFrame.t - n.t) < NEXT_ON_STRING_T_EPS;
-            const ghostPastHold = dt <= 0 && dt > -ghostHold
-                && (nxFrame == null || nxFrame.t > n.t - 1e-6);
-            const isNextOnString = nextTAligned || ghostPastHold;
-            const y = sY(s);
-            const susEnd = n.t + (n.sus || 0);
-            const hasSus = n.sus > 0;
-            // Nearest event time across ALL strings strictly after this note —
-            // sourced from the sorted union of next/recent event times built
-            // once per frame in update() (see _scrEventTimes). _drawRecentByString
-            // is folded in so that once an event passes `now` (and leaves
-            // _drawNextByString) the deadline still holds: without this the
-            // next future event would reset _nextAnyT and old gems would
-            // linger after the new chord/note is already playing.
-            const _nextAnyT = _firstEventTimeGreaterThan(n.t + 1e-6);
-            // Deadline: absolute time after which the gem is culled.
-            //   Sustain long (sus >= linger): die immediately at susEnd — no tail.
-            //   Sustain short (sus < linger):  tail = linger - sus after susEnd,
-            //     capped by gap to next note (any string) so the gem disappears
-            //     when the next note arrives if it comes before the tail runs out.
-            //   No sustain: linger from onset, same gap-cap rule.
-            let _lingerDeadline;
-            if (hasSus) {
-                const extraLinger = Math.max(0, linger - (n.sus || 0));
-                // _nextAnyT cap only applies to the post-sustain linger tail.
-                // For long sustains (extraLinger = 0) the deadline is exactly
-                // susEnd — notes on other strings must not cut the held sustain
-                // short, which would hide the gem and trail mid-play.
-                _lingerDeadline = extraLinger > 0
-                    ? Math.min(susEnd + extraLinger, _nextAnyT)
-                    : susEnd;
-            } else {
-                const _gap = _nextAnyT - n.t;
-                _lingerDeadline = n.t + (_gap < linger ? _gap : linger);
-            }
-            const _overLinger = now > _lingerDeadline;
-            // For arp-persisted notes past their time: bypass the early exit so
-            // the board projection (fretboard ghost + fret labels) keeps rendering
-            // until arpBounds.end. The gem/sustain blocks are gated by arpGhostOnlyMode.
-            const arpGhostShouldRun = arpBounds != null
-                && (arpBounds.start - now) < 0.6   // same as PROJ_WIN
-                && now <= arpBounds.end + 0.05;
-            const arpGhostOnlyMode = arpGhostShouldRun
-                && _overLinger && (!hasSus || now > susEnd);
-            // Smart cull: keep the gem alive only if a note-state verdict is
-            // available to display. Probe result cached in _ndProbed/_ndProbedState
-            // so the later getNoteState query reuses it (avoids two provider calls).
-            // arpGhostShouldRun takes precedence — arp ghosts stay alive
-            // regardless of verdict state so their board projections persist.
-            let _ndProbed = false;
-            let _ndProbedState = null;
-            if (_overLinger && (!hasSus || now > susEnd) && !arpGhostShouldRun) {
-                // Prune the sustain-verdict latch before any cull-path return.
-                // The matching delete inside the sustain-render block (line ~9262)
-                // only runs when the note isn't culled — without this prune, a
-                // sustained note that crosses susEnd on the same frame as
-                // _overLinger goes true would leak its latch entry until a
-                // teardown/seek clears the Map. !hasSus notes never wrote to
-                // the latch, so Map.delete is a harmless no-op there.
-                if (hasSus) _susVerdictLatch.delete(Math.round(n.t * 1e4) * 10 + n.s);
-                if (!_ndHasProvider || dt < -NOTEDETECT_GEM_VERDICT_WINDOW) return;
-                let _ndProbe = null;
-                try { _ndProbe = _ndGetNoteState(n, n.t); } catch (e) { _ndProbe = null; }
-                _ndProbed = true;
-                _ndProbedState = _ndProbe;
-                const _probeSt = (_ndProbe && typeof _ndProbe === 'object') ? _ndProbe.state : _ndProbe;
-                if (_probeSt !== 'hit' && _probeSt !== 'active' && _probeSt !== 'miss') return;
-            }
-
-            const sustained = dt < 0 && hasSus && now <= susEnd;
-            const hitDist = Math.abs(dt);
-            const hit = hitDist < 0.15 || sustained || (_ndHasProvider && dt < 0);
-            const hitFade = sustained ? 0.7 : (hitDist < 0.15 ? 1 - hitDist / 0.15 : 0);
-            // skipBody (slide-target gem suppression) only applies to this
-            // note's own pre-hit approach — it exists so the destination's
-            // approaching gem doesn't duplicate the source note's gem, which
-            // is already sliding toward this fret. Once this note is hit,
-            // its gem must render normally so a chained slide (this note
-            // sliding on to a further fret) keeps following.
-            const effSkipBody = skipBody && dt > 0;
-            const hasTechniqueVibrato = noteHasVibrato(n);
-            const techniqueYNow = sustained ? techniqueYOffsetWorld(n, now) : 0;
-            const noteZ = sustained ? 0 : Math.min(0, dZ(dt));
-            // Per-note Z-based renderOrder: far notes get a low value (render
-            // first, get overdrawn by close geometry), close notes get a high
-            // value (render last, appear on top). RENDER_ORDER_LAYER_STACK decides
-            // the local stack for outline, core, technique symbols, and fret labels.
-            const xBase = n.f === 0 ? (openX !== undefined ? openX : curX) : xFretMid(n.f);
-            // Slide-in-progress: glide the gem (and everything anchored to it —
-            // outline, core, halo, technique markers) from its starting fret
-            // toward the slide's end fret over the sustain, the same way
-            // techniqueYOffsetWorld already offsets the gem in Y for bends.
-            const slideSt = slideTrailEnd(n);
-            // Once hit, keep gliding (and then holding at the end fret) for
-            // as long as the gem stays on screen — not just while `sustained`
-            // (now <= susEnd). Otherwise, during the brief extra moment a
-            // short note lingers after its sustain ends (see _lingerDeadline/
-            // extraLinger above), `sustained` flips false and the gem would
-            // snap back to its starting fret. slideOffsetWorldX's `p` clamps
-            // to 1 once now > susEnd, so this naturally holds at the slide's
-            // end position during that tail.
-            const slideXNow = (dt < 0 && hasSus && slideSt)
-                ? (_leftyCached ? -1 : 1) * slideOffsetWorldX(n, now, slideSt)
-                : 0;
-            const x = xBase + slideXNow;
-            const isHarm = n.hm || n.hp;
-
-            // Open chord notes: wide default mesh is capped to chord frame width.
-            const OPEN_NOTE_WORLD_W = 40 * K;
-            let openWScale = 1;
-            if (n.f === 0 && openChordBoxWidth != null && openChordBoxWidth > 1e-8) {
-                openWScale = Math.max(0.22, (openChordBoxWidth * 0.96) / OPEN_NOTE_WORLD_W);
-            }
-
-            // Hoisted so both !skipBody blocks (gem and technique labels) and
-            // the unconditional sustain trail all share one declaration.
-            // For skipBody=true (slide targets), defaults are safe no-ops.
-            const openSlabThickMul = n.f === 0 ? 1.5 : 1;
-            const approachRot = n.f > 0 ? Math.max(0, Math.min(1, dt / AHEAD)) * Math.PI / 2 : 0;
-            // Ghost preview window: capped to the gap from the previous note
-            // on this string so dense passages don't show the preview 0.6 s
-            // ahead with no visible gem. Minimum 0.05 s so the ghost isn't
-            // completely suppressed even in very tight passages.
-            const _rawGap = n.t - prevOnsetT;
-            const effectiveProjWin = _rawGap > 0 ? Math.min(0.6, Math.max(0.05, _rawGap)) : 0.6;
-            const projFactorG = Math.max(0, Math.min(1, 1 - Math.max(dt, 0) / effectiveProjWin));
-            const inGhostWin = n.f > 0 && isNextOnString && dt > -ghostHold && dt < effectiveProjWin && projFactorG > 0.001;
-            // feedBack#254 — query the provider once per note, before both !skipBody
-            // blocks, so _showHit can be a const and _ndGood is available for the
-            // sustain trail (which renders even when skipBody=true for slide targets).
-            let _ndGood = false;    // true when provider confirms hit/active
-            let _hitPunch = 1;      // #3 per-gem scale-punch on a fresh hit
-            let _ndState = null;    // 'hit'|'active'|'miss'|null; null → fall back to proximity heuristic
-            let _ndCs = null;       // raw provider response — truthy when provider returned a verdict
-            let _ndCsIsObj = false; // typeof _ndCs === 'object'
-            let _ndFaceMat = null;  // [mat×4, transparent×2] array for lateral face fill, or null
-            if (_ndGetNoteState) {
-                // Reuse the smart-cull probe result if we already called
-                // _ndGetNoteState for this gem above; otherwise probe now.
-                let _raw = null;
-                if (_ndProbed) {
-                    _raw = _ndProbedState;
-                } else {
-                    try { _raw = _ndGetNoteState(n, n.t); } catch (e) { _raw = null; }
-                }
-                if (_raw) {
-                    _ndCsIsObj = typeof _raw === 'object';
-                    const _st = _ndCsIsObj ? _raw.state : _raw;
-                    if (_st === 'miss') {
-                        _ndState = 'miss';
-                        _ndCs = _raw;
-                    } else if (_st === 'hit' || _st === 'active') {
-                        _ndState = _st;
-                        _ndGood = true;
-                        _ndCs = _raw;
-                    }
-                }
-            }
-
-            // [verdict glow] feed the provider alpha into the per-frame max so
-            // update()'s top scales the verdict-glow brightness by live level
-            // (note_detect returns alpha = live input level for held sustains,
-            // and a time-fade for fresh strikes). Only object responses carry an
-            // alpha; the latch/legacy string responses leave brightness at full.
-            if (_ndGood && _ndCsIsObj && _ndCs && typeof _ndCs.alpha === 'number') {
-                _ndVerdictSawAlpha = true;
-                if (_ndCs.alpha > _ndVerdictMaxAlpha) _ndVerdictMaxAlpha = _ndCs.alpha;
-            }
-
-            // ── Sustain verdict latch ────────────────────────────────────
-            // note_detect's hitGlowDuration (~0.5 s) and the legacy mark
-            // TTL (500 ms) both expire before a long chart sustain ends.
-            // For any sustained note, latch the verdict from EITHER source
-            // (provider _ndState OR legacy _ndHitMarks / _ndMissMarks) and
-            // re-inject it so hit/miss color persists for the full hold.
-            // Works with both the modern provider path and the legacy event
-            // path — vibrato and other long-sustain notes benefit equally.
-            if (hasSus) {
-                const _sk = Math.round(n.t * 1e4) * 10 + n.s;
-                // Resolve current verdict: provider takes priority, then
-                // fall back to scanning the legacy mark arrays so a hit or
-                // miss event that arrived this frame can seed the latch.
-                let _lv_cur = _ndState;
-                let _lv_good = _ndGood;
-                if (!_lv_cur) {
-                    for (let _mi = 0; _mi < _ndHitMarks.length; _mi++) {
-                        const _mm = _ndHitMarks[_mi];
-                        if (_mm.s === n.s && _mm.f === n.f && Math.abs(_mm.noteTime - n.t) < _ND_TIME_EPS) {
-                            _lv_cur = 'hit'; _lv_good = true; break;
-                        }
-                    }
-                    if (!_lv_cur) {
-                        for (let _mi = 0; _mi < _ndMissMarks.length; _mi++) {
-                            const _mm = _ndMissMarks[_mi];
-                            if (_mm.s === n.s && _mm.f === n.f && Math.abs(_mm.noteTime - n.t) < _ND_TIME_EPS) {
-                                _lv_cur = 'miss'; _lv_good = false; break;
-                            }
-                        }
-                    }
-                }
-                if (_lv_cur) {
-                    // Fresh verdict (provider or legacy mark) — save to latch.
-                    // Distinguish a *live* provider hit (note_detect tags its
-                    // ring-tracking 'active' responses with live:true) from a
-                    // legacy/brief one: a live hit must NOT be re-injected once
-                    // the provider goes silent (that kept muted sustains lit),
-                    // whereas the legacy event path still needs the latch to
-                    // bridge its ~0.5 s mark TTL across a long hold.
-                    const _live = _ndCsIsObj && _ndCs && _ndCs.live === true;
-                    _susVerdictLatch.set(_sk, _lv_good ? (_live ? 'hit-live' : 'hit') : 'miss');
-                    // If the verdict came from a legacy mark (provider was
-                    // silent — _ndState was null before the scan), propagate
-                    // it to _ndState/_ndGood/_ndCs now so the sustain trail
-                    // picks up the same colour this frame instead of waiting
-                    // until the mark expires and the latch re-injects it.
-                    if (!_ndState) {
-                        if (_lv_good) {
-                            _ndState = 'active'; _ndGood = true;
-                            _ndCs = 'active'; _ndCsIsObj = false;
-                        } else {
-                            _ndState = 'miss';
-                            _ndCs = 'miss'; _ndCsIsObj = false;
-                        }
-                    }
-                } else if (dt < 0 && now < susEnd) {
-                    // No current verdict — reuse latch if available.
-                    // dt < 0 guards against coloring notes that haven't
-                    // crossed the hit line yet (approaching notes must never
-                    // inherit a latch from a previous play-through).
-                    const _lv = _susVerdictLatch.get(_sk);
-                    if (_lv === 'hit') {
-                        // Legacy/brief provider or event-path hit: bridge the
-                        // gap across the hold (the mark/glow TTL expires before a
-                        // long chart sustain ends).
-                        _ndState = 'active'; _ndGood = true;
-                        _ndCs = 'active'; _ndCsIsObj = false;
-                    } else if (_lv === 'hit-live') {
-                        // Live provider is authoritative for the active glow: it
-                        // returns 'active' only while the string is actually
-                        // ringing, and null once muted / decayed. Don't re-inject
-                        // a stale 'active' (that kept a muted sustain lit) — leave
-                        // the gem un-lit when the provider is silent; a re-strike
-                        // relights it via the provider on the next frame.
-                    } else if (_lv === 'miss') {
-                        _ndState = 'miss';
-                        _ndCs = 'miss'; _ndCsIsObj = false;
-                    }
-                }
-                if (now >= susEnd) _susVerdictLatch.delete(_sk);
-            }
-
-            const _showHit = (_ndState === 'miss') ? false
-                : (_ndState ? _ndGood
-                : (hit || (n.f > 0 && inGhostWin)));
-
-            // ── Fret-wire hit flash ───────────────────────────────────────
-            // A confirmed note lights the wires that bracket it:
-            //   single, fretted (f > 0) → the wire behind it (f-1) and the wire
-            //           it's pressed against (f).
-            //   open (f = 0)  → the OUTER wires of the anchor lane. An open
-            //           string has no fret of its own, and its gem is drawn as a
-            //           wide slab spanning the lane (see xBase /
-            //           openNoteLaneBoxW), so the lane's edge wires are exactly
-            //           what the slab sits between — the same relationship a
-            //           fretted note has to its own two wires.
-            //   chord   → only the OUTERMOST wires of the whole shape, not every
-            //           wire it spans. drawNote() is the chord loop's per-note
-            //           call, so it can't see the span from here: chord hits
-            //           accumulate into _fwChordAcc and the flash pass resolves
-            //           min/max fret → outer wires once the loop has finished.
-            // Gated on _ndGood, not _showHit: only a scorer's verdict counts,
-            // never the proximity heuristic that merely means "near the line".
-            if (_ndGood) {
-                const _fwA = (_ndCsIsObj && _ndCs && typeof _ndCs.alpha === 'number')
-                    ? Math.max(0, Math.min(1, _ndCs.alpha))
-                    : 1;
-                if (fromChord) {
-                    // ch.id can be absent (pitfall #8) — fall back to the chord's
-                    // time, which is what n.t already carries for a chord note.
-                    const _fwK = (chordId !== undefined && chordId !== null) ? chordId : `t${n.t}`;
-                    let _fwE = _fwChordAcc.get(_fwK);
-                    if (!_fwE) {
-                        _fwE = { minF: Infinity, maxF: -Infinity, a: 0, openA: 0, t: n.t };
-                        _fwChordAcc.set(_fwK, _fwE);
-                    }
-                    if (n.f > 0 && n.f <= NFRETS) {
-                        if (_fwA > _fwE.a) _fwE.a = _fwA;
-                        if (n.f < _fwE.minF) _fwE.minF = n.f;
-                        if (n.f > _fwE.maxF) _fwE.maxF = n.f;
-                    } else if (n.f === 0 && _fwA > _fwE.openA) {
-                        _fwE.openA = _fwA;   // open strings in the chord → lane edges
-                    }
-                } else if (n.f > 0 && n.f <= NFRETS) {
-                    if (_fwA > _fwHitIn[n.f - 1]) _fwHitIn[n.f - 1] = _fwA;
-                    if (_fwA > _fwHitIn[n.f]) _fwHitIn[n.f] = _fwA;
-                } else if (n.f === 0) {
-                    // Sampled at the note's own time, matching how the open
-                    // slab's width is derived (openNoteLaneBoxW(n.t)) — so the
-                    // flashed wires are the ones the slab is actually drawn
-                    // between, even if the lane has since moved.
-                    const _fwB = anchorLaneBoundsAt(_drawAnchors, n.t);
-                    if (_fwB) {
-                        if (_fwA > _fwHitIn[_fwB.dMin]) _fwHitIn[_fwB.dMin] = _fwA;
-                        if (_fwA > _fwHitIn[_fwB.dMax]) _fwHitIn[_fwB.dMax] = _fwA;
-                    }
-                }
-            }
-
-            if (!effSkipBody && !arpGhostOnlyMode && !_overLinger) {
-
-                // ── Outline (slightly larger, bright emissive) ────────────
-                // Notedetect feedback (#9): if a recent hit/miss event
-                // matches this note's (s, f, t), swap the outline tint.
-                // Linear scan over a small bounded array — typical
-                // queues are 0-5 entries, expired marks pruned by the
-                // listener. Hit takes precedence over miss so the user
-                // sees the more positive feedback if both happen
-                // (shouldn't, but cheap guard).
-                let _ndOutline = (n.f > 0 && mStrHitOutline[s]) ? mStrHitOutline[s] : mWhiteOutline;
-                // update() prunes expired marks once per frame and
-                // caches performance.now() in _ndFrameNowMs so the hot
-                // path here just does the bounded match — no extra
-                // now() / filter() per note. After update()'s prune,
-                // every entry in the arrays has expiresAt > _ndFrameNowMs,
-                // so we don't re-validate inside the loop.
-                let _ndMatchedMark = null;
-                let _ndHadHitMark = false;
-                if (_ndHitMarks.length) {
-                    for (let i = 0; i < _ndHitMarks.length; i++) {
-                        const m = _ndHitMarks[i];
-                        if (m.s === n.s && m.f === n.f && Math.abs(m.noteTime - n.t) < _ND_TIME_EPS) {
-                            _ndOutline = mHitBright[s] ?? mGlow[s]; _ndFaceMat = mHitBrightArrays[s] ?? null; _ndMatchedMark = m; _ndHadHitMark = true; break;
-                        }
-                    }
-                }
-                if (!_ndHadHitMark && _ndMissMarks.length) {
-                    for (let i = 0; i < _ndMissMarks.length; i++) {
-                        const m = _ndMissMarks[i];
-                        if (m.s === n.s && m.f === n.f && Math.abs(m.noteTime - n.t) < _ND_TIME_EPS) {
-                            _ndOutline = mMissOutline; _ndFaceMat = mMissEdgeArrays; _ndMatchedMark = m; break;
-                        }
-                    }
-                }
-                if (_ndMatchedMark && _ndMatchedMark.labels && _ndMatchedMark.labels.length) {
-                    _ndLabels.push({
-                        x,
-                        y: y + NH * 1.7,
-                        z: noteZ + 0.02,
-                        labels: _ndMatchedMark.labels,
-                    });
-                }
-                // (approachRot / PROJ_WIN_G / projFactorG / inGhostWin hoisted above)
-
-                const rimXY = n.ac ? ACCENT_RIM_XY_SCALE_MUL : 1;
-                const rimZ = n.ac ? ACCENT_RIM_Z_SCALE_MUL : 1;
-
-                // feedBack#254 — apply outline + lateral face-fill overrides from provider verdict.
-                // hit/active → green outline (mHitBright[s]) + green lateral faces;
-                // miss → magenta-red outline (mMissOutline) + dark lateral faces; front/back stay transparent.
-                if (_ndCs) {
-                    const _vAlpha = (_ndCsIsObj && typeof _ndCs.alpha === 'number') ? _ndCs.alpha : 1;
-                    if (_ndState === 'miss') {
-                        _ndOutline = mMissOutline;
-                        _ndFaceMat = mMissEdgeArrays;
-                        _streakHits = 0;            // #7 break the streak (heat eases down)
-                        if (_verdictMarks) _ndLabels.push({ x, y: y + NH * 1.7, z: noteZ + 0.02, labels: [{ text: '✗', color: '#ff5a7a' }] });  // #6
-                    } else if (_ndGood) {
-                        _ndOutline = mHitBright[s] ?? mGlow[s];
-                        _ndFaceMat = mHitBrightArrays[s] ?? null;
-                        _hitPunch = 1 + 0.22 * _hitFx * _vAlpha;   // #3 scale-punch (biggest at strike, eases)
-                        if (_verdictMarks) { const _tc = _timingHex(_ndMatchedMark && _ndMatchedMark.timingState); _ndLabels.push({ x, y: y + NH * 1.7, z: noteZ + 0.02, labels: [{ text: '✓', color: '#' + _tc.toString(16).padStart(6, '0') }] }); }  // #6 + #5
-                        if (_sparks && _hitFx > 0 && _vAlpha > 0.5) {
-                            const _spk = s + '|' + n.f + '|' + n.t.toFixed(2);
-                            if (!(_sparkSeen.get(_spk) > now)) {
-                                _sparkSeen.set(_spk, now + 1.0);
-                                if (_sparkSeen.size > 600) _sparkSeen.clear();
-                                _streakHits++;
-                                const _heatMul = _streakFx ? (1 + 0.85 * _streakHeat) : 1;   // #7 escalate
-                                _sparkBurst(x, y, noteZ, _timingHex(_ndMatchedMark && _ndMatchedMark.timingState), Math.round((4 + 7 * _hitFx) * _heatMul));
-                            }
-                        }
-                    }
-                }
-
-                // Score pop: the first frame a gem's verdict carries points
-                // (notedetect ≥1.13 object verdicts), float a "+N" above it.
-                // popKey dedupes — chord members all hand back the chord-
-                // level key, so a chord pops once, not once per gem; the
-                // _fxSeen TTL also stops a sustain's long-lived verdict from
-                // re-popping every frame.
-                if (_ndGood && _ndCsIsObj
-                        && _ndCs.points !== undefined && _ndCs.popKey != null) {
-                    _fxSpawnPop(_ndCs.popKey, _ndCs.points, _ndCs.mult,
-                        x, y + NH * 2.2, noteZ + 0.02);
-                }
-
-                // Accent: soft neon outer glow (reference: diffused halo fading out).
-                // Three additive shells drawn behind outline/core; colour = string hue.
-                // Suppressed on a provider miss verdict — a bright accent halo
-                // around a missed gem muddies the dark-core-plus-red-rim fail
-                // signal, matching the same miss-over-accent priority the
-                // gem core material applies below.
-                if (n.ac && _ndState !== 'miss' && mAccentHaloNear[s]) {
-                    const rZ = approachRot;
-                    const accentShells = _accentShellsByString[s];
-                    for (let hi = 0; hi < accentShells.length; hi++) {
-                        const sh = accentShells[hi];
-                        const glow = pAccentHalo.get();
-                        glow.material = sh.mat;
-                        glow.rotation.z = rZ;
-                        glow.position.set(x, y + techniqueYNow, noteZ - sh.zK * K);
-                        if (n.f === 0) {
-                            // Inside a chord/arpeggio frame: bloom only vertically so the
-                            // halo doesn't burst past the chord box edges horizontally.
-                            // Outside a frame: modest horizontal cap (1.4×) so it doesn't
-                            // overflow into adjacent lane visuals.
-                            const openIxy = fromChord ? 1.0 : Math.min(sh.ixy, 1.4);
-                            const slabPuff = Math.max(1.4, sh.ixy);
-                            glow.scale.set(
-                                (40 * K / NW) * rimXY * openIxy * openWScale,
-                                0.1 * openSlabThickMul * slabPuff,
-                                0.6 * rimZ * sh.iz,
-                            );
-                        } else {
-                            glow.scale.set(rimXY * sh.ixy, rimXY * sh.ixy, 2.5 * rimZ * sh.iz);
-                        }
-                    }
-                }
-                const outline = pNote.get();
-                // Verdict beats accent on the outline so hit/miss feedback isn't
-                // hidden by mAccentOutline. Mirrors the same miss-over-accent
-                // priority the accent halo guard above already applies.
-                const _ndVerdict = (_ndCs && (_ndState === 'miss' || _ndGood))
-                    || !!_ndMatchedMark;
-                outline.material = (n.ac && !_ndVerdict) ? mAccentOutline[s] : _ndOutline;
-                // outline + core share the pNote pool, so set geometry explicitly
-                // each frame (a recycled mesh may carry a gradient geometry from a
-                // prior core use). Outline always uses the plain box.
-                outline.geometry = gNote;
-                outline.renderOrder = renderOrderForLayerAtZ(noteZ, 'NOTE_OUTLINE');
-                outline.position.set(x, y + techniqueYNow, noteZ);
-                outline.rotation.z = approachRot;
-                const ndRim = 1.1;
-                if (n.f === 0) {
-                    outline.scale.set(
-                        (35 * K / NW) * ndRim * rimXY * openWScale,
-                        0.1 * ndRim * openSlabThickMul,
-                        0.6 * ndRim * rimZ,
-                    );
-                } else {
-                    outline.scale.set(ndRim * rimXY, ndRim * rimXY, 2.8 * rimZ);
-                }
-
-                // ── Lateral face fill (top / bottom / left / right only) ─────
-                // Material array: groups 0-3 (±X ±Y) get the verdict colour;
-                // groups 4-5 (+Z front / -Z back) are transparent so the large
-                // front face shows only the core body's string colour beneath.
-                if (_ndFaceMat) {
-                    const edges = pNoteEdge.get();
-                    edges.material = _ndFaceMat;
-                    edges.renderOrder = renderOrderForLayerAtZ(noteZ, 'TECHNIQUE_MARKER');
-                    edges.position.set(x, y + techniqueYNow, noteZ + 0.001);
-                    edges.rotation.z = approachRot;
-                    if (n.f === 0) {
-                        edges.scale.set(
-                            (40 * K / NW) * rimXY * openWScale * 1.02,
-                            0.1 * openSlabThickMul * 1.02,
-                            0.6 * rimZ * 1.02,
-                        );
-                    } else {
-                        edges.scale.set(rimXY * 1.02, rimXY * 1.02, 2.5 * rimZ * 1.02);
-                    }
-                }
-
-                // ── Core (filled note body) ───────────────────────────────
-                const core = pNote.get();
-                // Body always keeps the string colour. Verdict feedback is
-                // carried by the outline shell and lateral face fill.
-                core.material = n.ac ? mAccentCore[s] : mStr[s];
-                // Gradient gem body for strings 0..5; flat box otherwise.
-                core.geometry = (!n.ac && gNoteGrad[s]) ? gNoteGrad[s] : gNote;
-                core.renderOrder = renderOrderForLayerAtZ(noteZ, 'NOTE_CORE');
-                core.position.set(x, y + techniqueYNow, noteZ + 0.001);
-                core.rotation.z = approachRot;
-                if (n.f === 0) {
-                    core.scale.set(
-                        (40 * K / NW) * rimXY * openWScale,
-                        0.1 * openSlabThickMul,
-                        0.6 * rimZ,
-                    );
-                } else {
-                    core.scale.set(rimXY, rimXY, 2.5 * rimZ);
-                }
-                if (_hitPunch !== 1) core.scale.multiplyScalar(_hitPunch);   // #3 hit scale-punch
-                // Fret digits on fretted (n.f > 0) flying notes deliberately
-                // omitted: the showFretOnNote setting and its UI helper text
-                // promise digits on the fretboard ghost only, never on the
-                // gems coming down the highway. The ghost path is at
-                // pGhostFretLbl below.
-            } // end gem block — technique labels reopen !skipBody below
-
-            // ── Sustain trail ─────────────────────────────────────────────
-            // Rendered for ALL notes with sustain, including skipBody=true
-            // slide-target notes (e.g. linkNext hold→slide: gem suppressed,
-            // slide trail stays visible as the continuation of the sustain).
-            // _ndGetNoteState is queried for every note (skipBody slide
-            // targets included), so the trail picks bright mGlow[s] when the
-            // provider confirms hit/active and dim mSus[s] otherwise — a
-            // slide-target trail is not forced dim.
-            // Chord-member open strings (fromChord && f === 0) skip the
-            // sustain trail entirely — fretted constituents already carry
-            // the chord's sustains; an extra ribbon under the wide open
-            // body looked like clutter. The note BODY still draws above.
-            if (hasSus && !_overLinger && !(fromChord && n.f === 0)) {
-                    const susStart = Math.max(n.t, now);
-                    const remSus = susEnd - susStart;
-                    if (remSus > 0.01) {
-                        const sliceDur = Math.min(remSus, AHEAD);
-                        let tw = NW * 0.85 * (n.f === 0 ? openWScale : 1);
-                        let th = NH * 0.12 * (n.f === 0 ? openWScale : 1) * openSlabThickMul;
-                        if (susTrailMatchArpFrame) {
-                            const yA = sY(0), yB = sY(nStr - 1);
-                            const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
-                            const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
-                            const fullChordBoxH = yMaxF - yMinF;
-                            const ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
-                            const ftSide = ft * 1.55;
-                            if (n.f > 0) {
-                                th = ftSide;
-                            } else {
-                                th = Math.max(th, ftSide * openSlabThickMul);
-                            }
-                            tw = Math.max(tw, ftSide * 1.05);
-                        }
-                        // Standalone open strings get two parallel trails
-                        // offset along X — visually echoes the wide flat
-                        // open-note body. Fretted notes keep the
-                        // single-trail path. Offsets are scaled by
-                        // `openWScale` (the same body-width scale
-                        // computed at line 7367) so the trails stay
-                        // underneath the body's edges no matter how wide
-                        // the anchor lane is. Chord-member open strings
-                        // can't reach here (guarded at the `hasSus`
-                        // check above).
-                        //
-                        // openTrailOff is always > 0 because openWScale
-                        // is clamped >= 0.22 at line 7368 (or defaults
-                        // to 1 when there's no openChordBoxWidth), so
-                        // openTrailOff >= NW * 3 * 0.22 = 3.3 * K.
-                        // No degenerate-small-offset fallback needed.
-                        const offsets = (n.f === 0)
-                            ? [-(NW * 3 * openWScale), NW * 3 * openWScale]
-                            : SINGLE_SUS_OFFSETS;
-                        const ribbonSusTrail = !!(
-                            (slideSt && n.f > 0 && (n.sus || 0) > 1e-4)
-                            || (Number(n.bn) > 0)
-                            || (Array.isArray(n.bnv) && n.bnv.length > 0)
-                            || n.tr
-                            || hasTechniqueVibrato
-                        );
-                        // Outline material for the sustain trail border — uses the
-                        // same materials as the gem border so hit/miss colours are
-                        // perceptually identical across gem outline, lateral faces,
-                        // and sustain trail rim.
-                        const _susOlMat = _ndState === 'miss' ? mMissOutline
-                            : _ndGood ? (mHitBright[s] ?? mHitSusOutline)
-                            : mSusOutline;
-                        const emitSusStrip = (xCenter, segLen, zCenter) => {
-                            // Same depth-bucket scheme as chord frames, using the
-                            // ordered sustain-trail layer so same-depth frames win
-                            // while closer trail segments still beat farther frames.
-                            const trailRenderOrder = renderOrderForLayerAtZ(Math.min(0, zCenter), 'SUSTAIN_TRAIL');
-                            for (let i = 0; i < offsets.length; i++) {
-                                const xOff = xCenter + offsets[i];
-                                const trOut = pSusOutline.get();
-                                trOut.material = _susOlMat;
-                                trOut.renderOrder = trailRenderOrder;
-                                trOut.position.set(xOff, y, zCenter);
-                                trOut.scale.set(tw + 0.4 * K, th + 0.4 * K, segLen);
-                                const tr = pSus.get();
-                                tr.material = _ndState ? mGlow[s] : mSus[s];
-                                tr.renderOrder = trailRenderOrder + 0.0005;
-                                tr.position.set(xOff, y, zCenter);
-                                tr.scale.set(tw, th, segLen);
-                            }
-                        };
-                        if (!ribbonSusTrail) {
-                            const len = sliceDur * TS;
-                            const zPos = dZ(susStart - now) - len / 2;
-                            emitSusStrip(x, len, zPos);
-                        } else {
-                            // Same depth-based renderOrder as box trail — ribbon center
-                            // at susStart + sliceDur/2, using TS so it matches dZ().
-                            const _ribDt = Math.max(0, susStart + sliceDur / 2 - now);
-                            const ribbonRenderOrder = renderOrderForLayerAtZ(-_ribDt * TS, 'SUSTAIN_TRAIL');
-                            for (let si = 0; si < offsets.length; si++) {
-                                const strandX = xBase + offsets[si];
-                                const olMesh = pSusRibbonOl.get();
-                                olMesh.renderOrder = ribbonRenderOrder;
-                                olMesh.scale.set(1, 1, 1);
-                                olMesh.rotation.set(0, 0, 0);
-                                olMesh.position.set(0, 0, 0);
-                                olMesh.material = _susOlMat;
-                                slideRibbonUpdatePositions(
-                                    olMesh.geometry, strandX,
-                                    tw + 0.4 * K, th + 0.4 * K,
-                                    y, sliceDur, susStart, now, n, slideSt,
-                                );
-                                const body = pSusRibbon.get();
-                                body.renderOrder = ribbonRenderOrder + 0.0005;
-                                body.scale.set(1, 1, 1);
-                                body.rotation.set(0, 0, 0);
-                                body.position.set(0, 0, 0);
-                                body.material = _ndState ? mGlow[s] : mSus[s];
-                                slideRibbonUpdatePositions(
-                                    body.geometry, strandX, tw, th, y,
-                                    sliceDur, susStart, now, n, slideSt,
-                                );
-                            }
-                        }
-                    }
-            }
-
-            // Shared by both slide-arrow blocks so the neck-preview arrow
-            // below can match the on-note arrow's size once the note
-            // arrives (the technique-labels block further down also reads
-            // this for its own label scaling).
-            const LBL_MULT = 1.6;
-            // Fade-in window for the neck-preview slide arrow below.
-            const GHOST_UPCOMING_WIN = 0.6;
-
-            // ── Slide direction arrow (neck preview) ─────────────────────
-            // A standalone preview of the same arrow, sitting flat on
-            // the neck (Z=0) at the note's resting fret. Full size from
-            // the moment it appears (matches the on-note arrow's size at
-            // dt=0) — just a linear fade-in over the same GHOST_UPCOMING_WIN
-            // window the board-projection ghost note uses, so the two
-            // previews feel like part of the same effect. No grow effect:
-            // tried and found too hard to see. Stops at dt <= 0, handing
-            // off to the on-note arrow.
-            //
-            // Placed outside the !effSkipBody block (unlike the on-note
-            // arrow above) so a note whose own gem is suppressed because
-            // it's the destination of a previous slide (skipBody) can
-            // still preview ITS OWN outgoing slide ahead of time — i.e.
-            // multi-leg/chained slides — when slideArrowChainPreviewVisible
-            // is on. For a normal note (skipBody === false) this behaves
-            // exactly as before.
-            if (slideArrowNeckVisible && dt > 0 && slideSt && validString(s) && !arpGhostOnlyMode && !_overLinger
-                && (!skipBody || slideArrowChainPreviewVisible)) {
-                const slideDirN = Math.sign(fretMid(slideSt.endFret) - fretMid(n.f)) * (_leftyCached ? -1 : 1);
-                if (slideDirN !== 0) {
-                    const neckAlpha = Math.max(0, Math.min(1, 1 - dt / GHOST_UPCOMING_WIN));
-                    if (neckAlpha > 0.001) {
-                        const arrowHexN = darkenHex(activePalette[s], 0.55);
-                        const arrowSmN = slideArrowMat(slideDirN > 0, arrowHexN);
-                        const arrowN = pTechPlane.get();
-                        arrowN.material = _spriteMat2MeshMat(arrowN, arrowSmN);
-                        const arrowScaleN = NH * 1.1 * LBL_MULT * _textSizeMul;
-                        arrowN.scale.set(arrowScaleN, arrowScaleN, 1);
-                        arrowN.position.set(x + slideDirN * NW * 1.15, y, 0);
-                        arrowN.rotation.z = 0;
-                        arrowN.renderOrder = renderOrderForLayerAtZ(0, 'TECHNIQUE_MARKER');
-                        arrowN.material.opacity = neckAlpha;
-                    }
-                }
-            }
-
-            if (!effSkipBody && !arpGhostOnlyMode && !_overLinger) {
-                // ── Technique labels ──────────────────────────────────────
-                // Label scale = base × LBL_MULT × distFactor (LBL_MULT
-                // declared above, shared with the neck-preview slide arrow).
-                // distFactor compensates for perspective shrink so a
-                // label far from the camera (note approaching at dt≈AHEAD)
-                // doesn't collapse to a single dim pixel. LBL_MULT bumps
-                // every base scale uniformly. Issues #21-25 track proper
-                // visual upgrades (3D arrows, ribbons, glows); this is
-                // the cheap legibility win in the meantime.
-                //
-                // Offsets scale with sLbl too. The labels grow in world
-                // units to compensate for perspective; if the offsets
-                // didn't grow, stacked labels would overlap each other
-                // and the first label would overlap the note at the
-                // AHEAD edge. In screen space the offset stays roughly
-                // constant — labels appear anchored to the note even
-                // though the world-space distance grows.
-                const distFactor = 1 + Math.max(0, Math.min(1, dt / AHEAD)) * 1.5;
-                // Fold the user's text-size multiplier into sLbl so technique
-                // labels (bend, H/P/T arrows, tremolo) plus on-body markers
-                // such as palm mute and the pinch-harmonic icon.
-                // all scale alongside the rest (`ac` accent → brighter body via mGlow).
-                const sLbl = LBL_MULT * distFactor * _textSizeMul;
-                // txtMat(..., 'technique') disables depthTest; without a high
-                // renderOrder the transparent note core (mStr) can still paint
-                // afterward and hide H/P/T, PM X, bends, etc. Same contract as
-                // fret-row labels (issue #35, CLAUDE pitfall #7 corollary).
-                const techniqueMarkerRenderOrder = renderOrderForLayerAtZ(noteZ, 'TECHNIQUE_MARKER');
-                let yo = y + techniqueYNow + NH * 0.8 * sLbl;
-                const specialMarkerScale = n.f === 0
-                    ? NH * 1.5 * sLbl * openWScale
-                    : NH * 1.5 * sLbl;
-                // ── Slide direction arrow (on the note/gem) ─────────────────
-                // A small ›/‹ chevron beside the note pointing toward the
-                // slide's destination fret. Visible for the note's whole
-                // time on screen — approaching (rides the incoming note at
-                // noteZ+K) and sustained (rides the gem as it glides via
-                // slideXNow, Edit A) — at a constant full opacity, no
-                // fade or grow.
-                if (slideArrowApproachVisible && slideSt && validString(s)) {
-                    const slideDir = Math.sign(fretMid(slideSt.endFret) - fretMid(n.f)) * (_leftyCached ? -1 : 1);
-                    if (slideDir !== 0) {
-                        const arrowHex = darkenHex(activePalette[s], 0.55);
-                        const arrowSm = slideArrowMat(slideDir > 0, arrowHex);
-                        const arrow = pTechPlane.get();
-                        arrow.material = _spriteMat2MeshMat(arrow, arrowSm);
-                        const arrowScale = NH * 1.1 * sLbl;
-                        arrow.scale.set(arrowScale, arrowScale, 1);
-                        arrow.position.set(x + slideDir * NW * 1.15, y + techniqueYNow, noteZ + K);
-                        // No rotation, ever — notes themselves rotate in
-                        // (approachRot) as they approach, but that would
-                        // tilt the ›/‹ chevron and make its left/right
-                        // direction ambiguous. Always flat.
-                        arrow.rotation.z = 0;
-                        arrow.renderOrder = techniqueMarkerRenderOrder;
-                        arrow.material.opacity = 1;
-                    }
-                }
-                // Derive the peak from bn OR the bnv curve: a note may carry an
-                // authoritative curve with bn left at 0 (bn SHOULD be the peak
-                // whenever bnv exists — this is the robustness fallback).
-                const _bnvPeak = (Array.isArray(n.bnv) && n.bnv.length)
-                    ? n.bnv.reduce((m, p) => Math.max(m, Number(p.v) || 0), 0) : 0;
-                const _bendPeak = Math.max(Number(n.bn) || 0, _bnvPeak);
-                if (_bendPeak > 0) {
-                    // Bend chevron stack — PlaneGeometry mesh so it tilts with
-                    // the gem (approachRot). Fixed world size so it perspective-
-                    // shrinks naturally without distFactor compensation.
-                    const steps = Math.max(1, Math.min(4, Math.round(_bendPeak)));
-                    const bendSm = bendChevronMat(steps, activePalette[s] || 0xffffff);
-                    const l = pTechPlane.get();
-                    l.material = _spriteMat2MeshMat(l, bendSm);
-                    const cs = NH * 2.4;
-                    l.scale.set(cs, cs, 1);
-                    l.position.set(x, y + techniqueYNow + NH * 1.1, noteZ + K);
-                    l.rotation.z = approachRot;
-                    l.renderOrder = techniqueMarkerRenderOrder;
-                    // Reserve stack space above the chevron.
-                    yo = Math.max(yo, y + techniqueYNow + NH * 2.5);
-                }
-                if (n.ho || n.po || n.tp) {
-                    if (n.ho || n.po) {
-                        // Hammer-on / pull-off: ▲/▼ triangle — PlaneGeometry mesh
-                        // so it tilts with the gem instead of billboarding.
-                        const triSm = triMat(!!n.po, activePalette[s] || 0xffffff);
-                        const tri = pTechPlane.get();
-                        tri.material = _spriteMat2MeshMat(tri, triSm);
-                        tri.scale.set(NH * 1.8, NH * 1.60, 1);
-                        tri.position.set(x, y + techniqueYNow, noteZ + K);
-                        tri.rotation.z = approachRot;
-                        tri.renderOrder = techniqueMarkerRenderOrder;
-                        // Reserve stack space above the triangle for stacked labels.
-                        yo = Math.max(yo, y + techniqueYNow + NH * 1.0);
-                    } else {
-                        const chevron = pTapChevron.get();
-                        const chevronScale = NH * 0.8 * sLbl;
-                        chevron.position.set(x, y + techniqueYNow, noteZ + 1.1 * K);
-                        chevron.rotation.z = approachRot;
-                        chevron.scale.set(chevronScale, chevronScale, 1);
-                        chevron.renderOrder = techniqueMarkerRenderOrder;
-                    }
-                }
-                // Tremolo label ('~~~') removed — trail shape already conveys it visually.
-                if (n.pm || n.mt || n.fhm) {
-                    // Muted notes: pool-based plane with per-note Z-proportional
-                    // renderOrder (techniqueMarkerRenderOrder). The previous InstancedMesh
-                    // approach used a fixed renderOrder (702/700), which made PM/FH markers from
-                    // far notes overdraw chord frames and gems of nearer chords.
-                    // PM = black X / white border; FH/MT = inverse.
-                    const _fhm = !!(n.mt || n.fhm);
-                    const _pmSprite = _fhm ? fretHandMuteXSpriteMat() : palmMuteXSpriteMat();
-                    const _pmMark = pTechPlane.get();
-                    _pmMark.material = _spriteMat2MeshMat(_pmMark, _pmSprite);
-                    _pmMark.material.opacity = _showHit ? 1.0 : 0.8;
-                    // Arms cover 62.5% of canvas → scale 1/0.625 = 1.60.
-                    const _sx = n.f === 0 ? NW * 1.60 * openWScale : NW * 1.60;
-                    _pmMark.scale.set(_sx, NH * 1.60, 1);
-                    _pmMark.position.set(x, y + techniqueYNow, noteZ + K);
-                    _pmMark.rotation.z = approachRot;
-                    _pmMark.renderOrder = techniqueMarkerRenderOrder;
-                }
-                // hm / hp — PlaneGeometry overlay sized like the palm-mute X,
-                // so the symbol only appears on the front face and matches
-                // the palm-mute marker proportions.
-                if (n.hm || n.hp) {
-                    const harmSprite = n.hm ? naturalHarmonicMat() : pinchHarmonicMat(activePalette[s]);
-                    const harmMark = pTechPlane.get();
-                    harmMark.material = _spriteMat2MeshMat(harmMark, harmSprite);
-                    harmMark.material.opacity = _showHit ? 1.0 : 0.85;
-                    const harmScaleX = n.f === 0 ? NW * 1.90 * openWScale : NW * 1.90;
-                    harmMark.scale.set(harmScaleX, NH * 2.0, 1);
-                    harmMark.position.set(x, y + techniqueYNow, noteZ + K);
-                    harmMark.rotation.z = approachRot;
-                    harmMark.renderOrder = techniqueMarkerRenderOrder;
-                }
-
-                // ── Per-note fret connector label ─────────────────────────
-                if (n.f > 0 && !skipLabel) {
-                    const minStringY = Math.min(sY(0), sY(nStr - 1));
-                    const labelY = minStringY - S_GAP * 0.8;
-                    // Fade in over 0.35s at the far end; stay at full opacity until
-                    // the note hits (dt = 0).  No pre-hit fade-out — removing it
-                    // eliminates the "label disappears before the note arrives" artifact.
-                    const alpha = dt >= 0 ? Math.min(1.0, (AHEAD - dt) / 0.35) : 0;
-                    // Arpeggio notes use the arpeggio fret-label layer at the same
-                    // depth so they stay above non-arp connector lines of the same chord.
-                    const _isArpNote = arpBounds !== null;
-
-                    // String-coloured connector line — standalone notes only.
-                    // Arpeggio and chord notes already have a drop line to the board.
-                    if (!fromChord) {
-                        const line = pConnectorLine.get();
-                        line.position.set(x, labelY, noteZ);
-                        // Half-length (50% shorter), anchored at the fret-label end.
-                        line.scale.set(1, (y - labelY) * 0.5, 1);
-                        // Tint the line with the incoming note's string colour.
-                        // mStr is white for gradient strings, so use the canonical
-                        // flat palette colour instead of the material's .color.
-                        if (activePalette[s] != null) line.material.color.setHex(activePalette[s]);
-                        line.renderOrder = renderOrderForLayerAtZ(noteZ,
-                            _isArpNote
-                                ? 'ARP_CONNECTOR_LINE'
-                                : 'CONNECTOR_LINE'
-                        );
-                        line.material.opacity = alpha * 0.8;
-                    }
-
-                    // Regular chord notes (fromChord=true, arpBounds=null) never show
-                    // fret labels — only standalone notes and arpeggio note-stream notes
-                    // (fromChord=true with arpBounds!=null) show labels.
-                    // Key uses 40 ms buckets (same formula as _buildFretLabelSet) so
-                    // the lookup matches exactly, even if the note's time drifts ±20 ms.
-                    // Frame-dedup prevents multiple strings at the same onset/fret from
-                    // stacking duplicate labels.
-                    const _flFrameKey = Math.round(n.t * 25) * 100 + n.f;
-                    const _showNum = (!fromChord || arpBounds !== null)
-                        && _fretLabelAllowed.has(_flFrameKey)
-                        && !_frameLabeledKeys.has(_flFrameKey);
-                    if (_showNum) {
-                        _frameLabeledKeys.add(_flFrameKey);
-                        const fretLabel  = pNoteFretLabel.get();
-                        const cachedMat  = txtMat(n.f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
-                        _setLabelMap(fretLabel, cachedMat);
-                        fretLabel.position.set(x, labelY, noteZ);
-                        fretLabel.renderOrder = renderOrderForLayerAtZ(noteZ,
-                            _isArpNote
-                                ? 'ARP_NOTE_FRET_LABEL'
-                                : 'NOTE_FRET_LABEL'
-                        );
-                        // Same scale ramp as fret column markers: 2× base at max lookahead,
-                        // converging to 1× at hit line.  Final size matches row labels.
-                        const flS = 7.0 * K * (1 + 0.4 * Math.max(0, dt) / AHEAD) * _textSizeMul * fretLabelScaleForFret(n.f);
-                        fretLabel.scale.set(flS, flS, 1);
-                        fretLabel.material.opacity = alpha;
-                    }
-
-                    // Teaching marks (§6.2.2) — display only, never grading. The
-                    // fret-hand finger (fg) renders by default to the right of the
-                    // fret label (hideable via the finger-hints toggle); the scale
-                    // degree (sd) is opt-in (mirrors the 2D `teachingMarksVisible`
-                    // toggle) and renders to the left.
-                    if (alpha > 0 && n.f > 0) {
-                        const _tmS = 5.0 * K * _textSizeMul * fretLabelScaleForFret(n.f);
-                        const _drawTeachMark = (text, colorHex, dx, cacheKey) => {
-                            if (!text) return;
-                            const spr = pTeachMarkLbl.get();
-                            const m = txtMat(text, colorHex, false, cacheKey);
-                            _setLabelMap(spr, m);
-                            spr.position.set(x + dx, labelY, noteZ);
-                            spr.renderOrder = renderOrderForLayerAtZ(noteZ,
-                                _isArpNote ? 'ARP_NOTE_FRET_LABEL' : 'NOTE_FRET_LABEL');
-                            spr.scale.set(_tmS, _tmS, 1);
-                            spr.material.opacity = alpha;
-                        };
-                        if (_showFingerHints) {
-                            _drawTeachMark(teachingFingerLabel(n.fg), '#7fd1ff', NW * 0.95, 'teachFg');
-                        }
-                        if (_drawTeachingMarks) {
-                            _drawTeachMark(teachingDegreeLabel(n.sd), '#ffcc66', -NW * 0.95, 'teachSd');
-                        }
-                    }
-                }
-            }
-
-            // ── Fret number for synthetic chord notes rendered with skipBody=true ──
-            // suppressSynthChord paths skip the !skipBody block entirely, so their
-            // fret label never fires from inside it. Handle them here, outside the
-            // gate. Applies the same measure-based + frame-dedup rules so that if
-            // the corresponding standalone arpeggio note already showed a label this
-            // frame, we don't duplicate it.
-            if (skipBody && fromChord && !skipLabel && n.f > 0 && dt >= 0) {
-                const _fl2FrameKey = Math.round(n.t * 25) * 100 + n.f;
-                if (_fretLabelAllowed.has(_fl2FrameKey)
-                    && !_frameLabeledKeys.has(_fl2FrameKey)) {
-                    _frameLabeledKeys.add(_fl2FrameKey);
-                    const _minStrY2 = Math.min(sY(0), sY(nStr - 1));
-                    const _labelY2  = _minStrY2 - S_GAP * 0.8;
-                    const _alpha2   = Math.min(1.0, (AHEAD - dt) / 0.35);
-                    const _isArp2   = arpBounds !== null;
-                    const fl2 = pNoteFretLabel.get();
-                    const cm2 = txtMat(n.f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
-                    _setLabelMap(fl2, cm2);
-                    fl2.position.set(x, _labelY2, noteZ);
-                    fl2.renderOrder = renderOrderForLayerAtZ(noteZ,
-                        _isArp2
-                            ? 'ARP_NOTE_FRET_LABEL'
-                            : 'NOTE_FRET_LABEL'
-                    );
-                    const _flS2 = 7.0 * K * (1 + 0.4 * dt / AHEAD) * _textSizeMul * fretLabelScaleForFret(n.f);
-                    fl2.scale.set(_flS2, _flS2, 1);
-                    fl2.material.opacity = _alpha2;
-                }
-            }
-
-            // ── Drop line for chord / arpeggio notes ──────────────────────────
-            // Styled to match the standalone single-note connector: tinted with
-            // the incoming note's string colour and 50% length (anchored at the
-            // fret-label end), instead of a full-height white line to the board.
-            const _wantDropLine = pDropLine && n.f > 0 && dt >= 0 && fromChord && showDropLine && !skipBody;
-            if (_wantDropLine) {
-                const _minStrY = Math.min(sY(0), sY(nStr - 1));
-                const _dropY = _minStrY - S_GAP * 0.8;
-                const _alpha = Math.min(1.0, (AHEAD - dt) / 0.35);
-                const dl = pDropLine.get();
-                dl.position.set(x, _dropY, noteZ);
-                // Half-length, anchored at the label end (matches single notes).
-                dl.scale.set(1, (y - _dropY) * 0.5, 1);
-                // String-colour tint (palette is canonical; mStr is white for
-                // gradient strings).
-                if (activePalette[s] != null) dl.material.color.setHex(activePalette[s]);
-                dl.renderOrder = renderOrderForLayerAtZ(noteZ, 'CONNECTOR_LINE');
-                dl.material.depthTest = false;
-                dl.material.opacity = _alpha * 0.8;
-            }
-
-            // ── Board ghost: filled rim at Z=0 (up to 3 slots/string) ────
-            // Lead notes (!fromChord, so !arpGhostActive too — see arpBounds
-            // below) use a fixed GHOST_UPCOMING_WIN pre-impact ramp instead
-            // of the gap-capped effectiveProjWin, so fast same-string runs
-            // don't pop in at full size right before impact. Chords/arps
-            // keep effectiveProjWin exactly as before — effectiveProjWin /
-            // projFactorG / inGhostWin (computed above, for the separate gem
-            // pre-glow) are untouched. Arp ghosts always use the full 0.6 s
-            // window — their timing is authored, not gap-driven.
-            const _PROJ_WIN_ARP = 0.6;
-            const ghostWin = fromChord ? effectiveProjWin : GHOST_UPCOMING_WIN;
-            const projFactor = Math.max(0, Math.min(1, 1 - Math.max(dt, 0) / ghostWin));
-            // isBlocked suppresses the pre-impact ghost in a note's last 150ms
-            // so it doesn't peek out from under the incoming note body. Scoped
-            // to chord notes only (#843): for plain lead notes this previously
-            // suppressed the board-ghost frame for every sustained note's last
-            // 150ms, making it vanish right before impact and reappear during
-            // the post-hit linger ("ghosts disappearing" in dense runs). Also
-            // excludes slide notes (`!slideSt`, #862/#257): a sliding gem
-            // glides off the start fret via slideXNow, so the body no longer
-            // covers the ghost and the slide's own ghost preview should show.
-            // Gate on dt > 0 so the post-hit linger (dt ≤ 0) keeps the ghost.
-            const isBlocked = fromChord && dt > 0 && dt < 0.15 && n.sus > 0 && !slideSt;
-
-            // For arpeggio notes: ALL notes show their ghost simultaneously
-            // the moment the FIRST note enters _PROJ_WIN_ARP — exactly when
-            // isNextOnString would reveal the first note's ghost on its own.
-            // Using arpBounds.start as the shared reference makes every note
-            // in the arpeggio fade in together, keyed off that single anchor.
-            const arpDtToStart = arpBounds != null ? arpBounds.start - now : Infinity;
-            const arpProjFactor = Math.max(0, Math.min(1, 1 - Math.max(arpDtToStart, 0) / _PROJ_WIN_ARP));
-            const arpGhostActive = arpBounds != null
-                && arpDtToStart < _PROJ_WIN_ARP
-                && now <= arpBounds.end + 0.05;
-            // Ghost stays at final "on the board" orientation — not the
-            // incoming approachRot sweep — so it nests with the note at
-            // impact. projRim/projScale/bodyDim are pure functions of
-            // effSkipBody/_vibrancyProjOp; hoisted here so both the Primary
-            // ghost (below) and the Upcoming-slot ghosts (sibling block
-            // further down) can use them.
-            const projRim = 0; // harmonic gems now land horizontal (no diamond offset)
-            // _vibrancyProjOp (0.15..0.5) is the vibrancy-scaled idle floor;
-            // scale the whole opacity by (_vibrancyProjOp / 0.15) so the slider
-            // affects the projection the same way it affects note bodies.
-            const projScale = _vibrancyProjOp / 0.15;
-            // effSkipBody (= skipBody && dt > 0, #862): a slide-destination note
-            // whose own gem is suppressed pre-hit isn't dimmed once it's hit.
-            const bodyDim = effSkipBody ? 0.38 : 1;
-            if (n.f > 0 && projectionVisible && (
-                (!_overLinger && isNextOnString && dt > -ghostHold && dt < ghostWin && projFactor > 0.001 && !isBlocked)
-                || arpGhostActive
-            )) {
-                const proj = projMeshArr[s][0];
-                // Arp ghost: uniform opacity keyed off arpBounds.start so all
-                // notes fade in/out together regardless of individual dt values.
-                let arpGhostAlpha = 1;
-                if (arpGhostActive) {
-                    const remainingP = arpBounds.end - now;
-                    const fadeOutP = remainingP < 0.25 ? Math.max(0, remainingP / 0.25) : 1;
-                    arpGhostAlpha = Math.min(arpProjFactor, fadeOutP);
-                }
-                // Chart-format-style ghost: a single 0→1 progress value drives both the
-                // fade-in (opacity/emissive, below) and the grow-from-small scale
-                // on the frame mesh and fret-digit label. Reuses the existing
-                // per-path progress signals — arp ghosts use arpGhostAlpha
-                // (already 0→1, incl. fade-out tail), non-arp ghosts use
-                // projFactor (0→1 across ghostWin).
-                const ghostProgress = arpGhostActive ? arpGhostAlpha : projFactor;
-                const projGrowScale = PROJ_GROW_MIN + (1 - PROJ_GROW_MIN) * ghostProgress;
-                const rimSolid = arpGhostActive
-                    ? 0.75 * arpGhostAlpha
-                    : projFactor * 0.94;
-                proj.material.opacity = Math.min(0.96,
-                    projScale * rimSolid * (0.5 + 0.5 * glowMul) * bodyDim);
-                proj.material.emissiveIntensity = arpGhostActive
-                    ? 0.35 * arpGhostAlpha * glowMul * bodyDim
-                    : projFactor * 0.55 * glowMul * bodyDim;
-                proj.position.set(x, y, 0);
-                proj.scale.set(projGrowScale, projGrowScale, projGrowScale);
-                proj.rotation.z = projRim;
-                proj.visible = true;
-
-                const ghostFretOk = showFretOnNote && (
-                    arpGhostActive ||
-                    fretNumberGhostScope === 'all' ||
-                    (fretNumberGhostScope === 'chords' && fromChord)
-                );
-                if (ghostFretOk && pGhostFretLbl) {
-                    // chord-hand style → show finger number (1–4) from the chord
-                    // template; fall back to fret number when no finger data exists
-                    // (GP imports, open strings, non-chord notes).
-                    const ghostFretDisplay = fromChord && fretNumberGhostScope === 'chords'
-                        ? (_templateFingerForChordGhost(chordId, n.s) ?? _templateFretForChordGhost(chordId, n.s, n.f))
-                        : fromChord
-                            ? _templateFretForChordGhost(chordId, n.s, n.f)
-                            : n.f;
-                    let ghostFretLblAlpha = 1;
-                    if (arpGhostActive) {
-                        // Reuse arpGhostAlpha — already encodes fade-in (keyed
-                        // off arpBounds.start via arpProjFactor) + fade-out.
-                        ghostFretLblAlpha = arpGhostAlpha;
-                    } else if (ghostPastHold) {
-                        const nextSoon = nxFrame != null && nxFrame.t > n.t + 1e-6
-                            && (nxFrame.t - now) <= GHOST_FRET_LBL_FADE_S;
-                        const ghostFadeS = Math.min(GHOST_FRET_LBL_FADE_S, ghostHold);
-                        ghostFretLblAlpha = hwyPostHitTailFadeMul(dt, ghostHold, nextSoon, ghostFadeS);
-                    } else {
-                        // Pre-impact approach: fade the digit in alongside the
-                        // frame (projFactor), instead of popping in at full alpha.
-                        ghostFretLblAlpha = projFactor;
-                    }
-                    const _ghostFretForScale = fromChord && fretNumberGhostScope === 'chords'
-                        ? n.f
-                        : ghostFretDisplay;
-                    drawGhostFretLabel(x, y, projRim, ghostFretDisplay, ghostFretLblAlpha, projGrowScale, _ghostFretForScale);
-                }
-            }
-
-            // ── Upcoming board ghosts (slots 1/2): up to 2 additional,
-            // independent pre-impact previews per string for plain lead
-            // notes, chart-format-style. Primary (slot 0, above) already shows the
-            // very next note on this string; this sibling block shows the
-            // 1-2 notes after that, each on its own mesh with its own
-            // fixed-GHOST_UPCOMING_WIN ramp — fixes fast same-string runs
-            // where every note after the first had almost no ramp time
-            // (capped at the gap to the *previous* note on that string).
-            // !nextTAligned excludes exactly the note Primary is already
-            // showing, so a note is never drawn in two slots at once.
-            if (n.f > 0 && projectionVisible && !fromChord && !nextTAligned
-                && dt > 0 && dt < GHOST_UPCOMING_WIN) {
-                const slotIdx = 1 + _scrGhostUpcomingCount[s];
-                if (slotIdx <= 2) {
-                    _scrGhostUpcomingCount[s]++;
-                    // Same formula as Primary's projFactor for !fromChord
-                    // notes (ghostWin === GHOST_UPCOMING_WIN there too) —
-                    // keeps the size/brightness curve continuous as a note's
-                    // rank improves frame-to-frame (slot 2 → 1 → 0).
-                    const upcomingProgress = projFactor;
-                    const proj = projMeshArr[s][slotIdx];
-                    const rimSolid = upcomingProgress * 0.94;
-                    proj.material.opacity = Math.min(0.96,
-                        projScale * rimSolid * (0.5 + 0.5 * glowMul) * bodyDim);
-                    proj.material.emissiveIntensity = upcomingProgress * 0.55 * glowMul * bodyDim;
-                    const growScale = PROJ_GROW_MIN + (1 - PROJ_GROW_MIN) * upcomingProgress;
-                    proj.position.set(x, y, 0);
-                    proj.scale.set(growScale, growScale, growScale);
-                    proj.rotation.z = projRim;
-                    proj.visible = true;
-
-                    if (showFretOnNote && fretNumberGhostScope === 'all' && pGhostFretLbl) {
-                        drawGhostFretLabel(x, y, projRim, n.f, upcomingProgress, growScale, n.f);
-                    }
-                }
-            }
-        }
-
-        /**
-         * Draw  [ GEM ]  bracket pair for an arpeggio note.
-         *
-         * While the note is approaching (bracketDt > 0) the brackets travel at the
-         * same Z as the gem.  Once the note hits the line (bracketDt <= 0) the
-         * brackets sit at Z = 0 (the fretboard plane) and persist until arpEnd.
-         * They fade in with approach and fade out in the last 0.25 s of the arpeggio.
-         *
-         * Fretted notes: `[ ]` — 3 BoxGeometry bars per side (vertical + 2 caps).
-         * Open strings:  `< >` — 2 diagonal arms per side, tips at note edges.
-         *
-         * openHalfW (optional) — half-width of the open note body; when supplied,
-         * the < > tips are placed at the actual edges of the note rather than a
-         * fixed offset.
-         */
-        function drawArpBrackets(x, y, bracketDt, arpEnd, now, s, isOpen = false, openHalfW = null) {
-            if (bracketDt >= AHEAD) return;
-            if (bracketDt < 0 && now > arpEnd + 0.05) return;
-            if (!pArpBracket) return;
-
-            let alpha;
-            if (bracketDt > 0) {
-                // Match the chord frame box visibility: full opacity throughout the
-                // entire AHEAD window so brackets appear the moment the frame enters
-                // view, not after a slow linear fade from alpha≈0 at 3 s out.
-                alpha = 1;
-            } else {
-                const remaining = arpEnd - now;
-                alpha = remaining > 0.25 ? 1 : Math.max(0, remaining / 0.25);
-            }
-            if (alpha < 0.01) return;
-
-            const bracketZ = bracketDt > 0 ? Math.min(0, dZ(bracketDt)) : 0;
-            const col = activePalette[s % activePalette.length];
-            const barThick = NW * 0.09;
-            const bracketH = NH * 1.05;
-            const capLen   = NW * 0.42;
-            const xOff     = (isOpen && openHalfW != null) ? openHalfW : NW * 0.95;
-            const zOff     = 0.006 * K;
-            const ord      = 18;
-
-            if (isOpen) {
-                // < > chevron — 2 diagonal arms per side.
-                // Arm goes from tip outward; angle from positive-X axis via atan2.
-                const armLen = Math.sqrt(capLen * capLen + (bracketH * 0.5) * (bracketH * 0.5));
-                const ang    = Math.atan2(bracketH * 0.5, capLen); // upper-right arm angle
-
-                const diagBar = (px, py, rz) => {
-                    const b = pArpBracket.get();
-                    b.material.color.setHex(col);
-                    b.material.opacity = alpha;
-                    b.renderOrder = ord;
-                    b.position.set(px, py, bracketZ + zOff);
-                    b.rotation.set(0, 0, rz);
-                    b.scale.set(armLen, barThick, barThick);
-                };
-
-                // < tip at (x - xOff), arms open to the right
-                diagBar(x - xOff + capLen * 0.5, y + bracketH * 0.25,  ang);
-                diagBar(x - xOff + capLen * 0.5, y - bracketH * 0.25, -ang);
-
-                // > tip at (x + xOff), arms open to the left
-                diagBar(x + xOff - capLen * 0.5, y + bracketH * 0.25,  Math.PI - ang);
-                diagBar(x + xOff - capLen * 0.5, y - bracketH * 0.25, -Math.PI + ang);
-            } else {
-                const bar = (px, py, sw, sh) => {
-                    const b = pArpBracket.get();
-                    b.material.color.setHex(col);
-                    b.material.opacity = alpha;
-                    b.renderOrder = ord;
-                    b.position.set(px, py, bracketZ + zOff);
-                    b.rotation.set(0, 0, 0);
-                    b.scale.set(sw, sh, barThick);
-                };
-
-                // Left bracket  [  – vertical bar then caps opening to the right
-                bar(x - xOff,                     y,                  barThick, bracketH);
-                bar(x - xOff + capLen * 0.5, y + bracketH * 0.5, capLen,   barThick);
-                bar(x - xOff + capLen * 0.5, y - bracketH * 0.5, capLen,   barThick);
-
-                // Right bracket  ]  – vertical bar then caps opening to the left
-                bar(x + xOff,                     y,                  barThick, bracketH);
-                bar(x + xOff - capLen * 0.5, y + bracketH * 0.5, capLen,   barThick);
-                bar(x + xOff - capLen * 0.5, y - bracketH * 0.5, capLen,   barThick);
-            }
-        }
-
-        function drawNotedetectLabels(ctx, W, H) {
-            if (!_ndLabels.length || !cam || !_probe) return;
-            ctx.save();
-            ctx.font = 'bold 12px sans-serif';
-            ctx.textAlign = 'center';
-            ctx.textBaseline = 'middle';
-            for (const item of _ndLabels) {
-                _probe.set(item.x, item.y, item.z);
-                _probe.project(cam);
-                if (_probe.z < -1 || _probe.z > 1) continue;
-                const sx = (_probe.x * 0.5 + 0.5) * W;
-                const sy = (-_probe.y * 0.5 + 0.5) * H;
-                for (let i = 0; i < item.labels.length; i++) {
-                    const label = item.labels[i];
-                    const y = sy + (i - (item.labels.length - 1) / 2) * 15;
-                    ctx.lineWidth = 4;
-                    ctx.strokeStyle = 'rgba(0,0,0,0.8)';
-                    ctx.strokeText(label.text, sx, y);
-                    ctx.fillStyle = label.color;
-                    ctx.fillText(label.text, sx, y);
-                }
-            }
-            ctx.restore();
-        }
-
-        // Score FX overlay pass — "+N" pops rising off their gems, milestone
-        // particle bursts / multiplier ring-pulses / streak-break flickers
-        // anchored on the strike line. Same overlay layer + projection
-        // pattern as drawNotedetectLabels; costs one early-out when nothing
-        // is active.
-        function drawScoreFx(ctx, W, H) {
-            if (!cam || !_probe) return;
-            const nowMs = _ndFrameNowMs || performance.now();
-            // TTL-prune the pop dedup keys (bounded: only notes hit in the
-            // last few seconds).
-            if (_fxSeen.size) {
-                for (const [k, exp] of _fxSeen) {
-                    if (exp <= nowMs) _fxSeen.delete(k);
-                }
-            }
-            let anyPop = false;
-            for (let i = 0; i < _fxPops.length; i++) {
-                if (_fxPops[i].active) { anyPop = true; break; }
-            }
-            let anyBurst = false;
-            for (let i = 0; i < _fxBursts.length; i++) {
-                if (_fxBursts[i].active) { anyBurst = true; break; }
-            }
-            const ringAge = nowMs - _fxRingMs;
-            const breakAge = nowMs - _fxBreakMs;
-            if (!anyPop && !anyBurst && ringAge >= 600 && breakAge >= 350) return;
-
-            const pal = _fxPalette;
-            ctx.save();
-
-            // Streak-break flicker: brief red wash over the whole panel.
-            if (breakAge < 350) {
-                const a = 0.10 * (1 - breakAge / 350);
-                ctx.fillStyle = pal.miss;
-                ctx.globalAlpha = a;
-                ctx.fillRect(0, 0, W, H);
-                ctx.globalAlpha = 1;
-            }
-
-            // Strike-line center in screen px — anchor for bursts + pulses.
-            let cx = W / 2, cy = H * 0.72, centerOk = false;
-            {
-                const fretMidY = (sY(0) + sY(nStr - 1)) / 2;
-                _probe.set(curX, fretMidY, 0);
-                _probe.project(cam);
-                if (_probe.z >= -1 && _probe.z <= 1) {
-                    cx = (_probe.x * 0.5 + 0.5) * W;
-                    cy = (-_probe.y * 0.5 + 0.5) * H;
-                    centerOk = true;
-                }
-            }
-
-            // Multiplier ring-pulse: one expanding ring on tier-up; the ×4
-            // tier pulses in the secondary accent like the HUD badge.
-            if (centerOk && ringAge < 600) {
-                const t = ringAge / 600;
-                const ease = 1 - Math.pow(1 - t, 2);
-                ctx.beginPath();
-                ctx.arc(cx, cy, 20 + ease * Math.min(W, H) * 0.28, 0, Math.PI * 2);
-                ctx.strokeStyle = _fxRingMult >= 4 ? pal.accent2 : pal.accent;
-                ctx.globalAlpha = 0.6 * (1 - t);
-                ctx.lineWidth = 3;
-                ctx.stroke();
-                ctx.globalAlpha = 1;
-            }
-
-            // Milestone bursts.
-            if (anyBurst && centerOk) {
-                for (let i = 0; i < _fxBursts.length; i++) {
-                    const b = _fxBursts[i];
-                    if (!b.active) continue;
-                    const age = nowMs - b.bornMs;
-                    if (age >= _FX_BURST_LIFE_MS) { b.active = false; continue; }
-                    const t = age / _FX_BURST_LIFE_MS;
-                    ctx.globalAlpha = 1 - t;
-                    for (let j = 0; j < _FX_BURST_N; j++) {
-                        b.px[j] += b.vx[j];
-                        b.py[j] += b.vy[j];
-                        b.vy[j] += 0.08;
-                        ctx.fillStyle = (j & 1) ? pal.accent : pal.accent2;
-                        ctx.fillRect(cx + b.px[j] - 2, cy + b.py[j] - 2, 4, 4);
-                    }
-                    ctx.globalAlpha = 1;
-                }
-            }
-
-            // "+N" pops: rise off the gem and fade over the back half.
-            if (anyPop) {
-                ctx.textAlign = 'center';
-                ctx.textBaseline = 'middle';
-                for (let i = 0; i < _fxPops.length; i++) {
-                    const p = _fxPops[i];
-                    if (!p.active) continue;
-                    const age = nowMs - p.bornMs;
-                    if (age >= _FX_POP_LIFE_MS) { p.active = false; continue; }
-                    _probe.set(p.x, p.y, p.z);
-                    _probe.project(cam);
-                    if (_probe.z < -1 || _probe.z > 1) continue;
-                    const t = age / _FX_POP_LIFE_MS;
-                    const sx = (_probe.x * 0.5 + 0.5) * W;
-                    const sy2 = (-_probe.y * 0.5 + 0.5) * H - t * 30;
-                    ctx.globalAlpha = t < 0.4 ? 1 : 1 - (t - 0.4) / 0.6;
-                    ctx.font = `bold ${13 + (p.mult - 1) * 2}px '${pal.font}', sans-serif`;
-                    ctx.lineWidth = 4;
-                    ctx.strokeStyle = 'rgba(0,0,0,0.8)';
-                    ctx.strokeText(p.text, sx, sy2);
-                    ctx.fillStyle = pal.accent;
-                    ctx.fillText(p.text, sx, sy2);
-                }
-                ctx.globalAlpha = 1;
-            }
-
-            ctx.restore();
-        }
-
-        // Horizontal-FOV-hold ("Hor+"). Returns the vertical fov (deg) the
-        // camera should use for the given pane aspect. With the bridge off (or
-        // absent), or at/under the start aspect, it returns the base vertical
-        // fov unchanged — an exact no-op, so normal panes render identically to
-        // before. Past the start aspect it lowers the vertical fov to keep the
-        // horizontal cone ~constant, so the neck fills an ultra-wide pane
-        // instead of collapsing into a central sliver. Pure + finite-guarded.
-        function effectiveVfov(aspect, tune) {
-            const base = (tune && Number.isFinite(tune.baseVfov)) ? tune.baseVfov : BASE_VFOV;
-            if (!tune || !tune.enabled || !Number.isFinite(aspect) || aspect <= 0) return base;
-            const start = (Number.isFinite(tune.startAspect) && tune.startAspect > 0)
-                ? tune.startAspect : HORPLUS_START_ASPECT;
-            if (aspect <= start) return base;
-            const floor = Number.isFinite(tune.minVfovDeg) ? tune.minVfovDeg : HORPLUS_MIN_VFOV;
-            const DEG = Math.PI / 180;
-            // Held horizontal fov: explicit hfovDeg if given, else the horizontal
-            // cone the base vertical fov produces at the start aspect.
-            const hfov = (Number.isFinite(tune.hfovDeg) && tune.hfovDeg > 0)
-                ? tune.hfovDeg * DEG
-                : 2 * Math.atan(Math.tan(base * DEG / 2) * start);
-            // Vertical fov that reproduces that horizontal cone at this aspect.
-            let vfov = 2 * Math.atan(Math.tan(hfov / 2) / aspect) / DEG;
-            const blend = Number.isFinite(tune.blend) ? Math.max(0, Math.min(1, tune.blend)) : 1;
-            vfov = base + (vfov - base) * blend;            // 0 = base, 1 = full Hor+
-            if (!Number.isFinite(vfov)) return base;
-            return Math.max(floor, Math.min(base, vfov));
-        }
-
-        /* ── Camera smooth lerp ──────────────────────────────────────────── */
-        function camUpdate(bundle) {
-            const bpm = computeBPM(bundle.beats, bundle.currentTime);
-            const lerp = CAM_LERP_BASE * Math.max(bpm, 60) / 120;
-
-            // ── Horizontal-FOV-hold + optional wide-pane pose nudges ──
-            // Driven by window.__h3dAspectTune (default off → exact no-op).
-            // _resolveTuneFor(paneKey) returns the shared base with THIS pane's
-            // overrides (if any) laid on top, so a single split pane can be framed
-            // independently. The base is seeded from defaults + localStorage on
-            // first read, so a persisted tuning session applies on load without
-            // opening the panel. Every field is finite-coerced. When disabled (or
-            // splitOnly and not in a split) the tune is treated as null, so
-            // effectiveVfov returns the base vertical fov and cam.fov is restored
-            // to it. The fov write is guarded on an actual change so a steady pane
-            // costs nothing.
-            const _paneKey = _aspectPaneKey(
-                bundle && bundle.songInfo && bundle.songInfo.arrangement, _paneUid);
-            // Only feed the Target-picker registry while the tuner is open (same
-            // gate as the readout). Closed → nothing is registered, so the registry
-            // can't grow for users who never open the panel; the key is still
-            // resolved below so any saved overrides keep applying.
-            if (window.__h3dAspectPanelOpen) _aspectRegisterPane(_paneKey);
-            const _aspTune = _resolveTuneFor(_paneKey);
-            const _aspActive = !!(_aspTune && _aspTune.enabled
-                && !(_aspTune.splitOnly && !_ssActive()));
-            const _tune = _aspActive ? _aspTune : null;
-            const _vfov = effectiveVfov(_paneAspect, _tune);
-            if (Number.isFinite(_vfov) && Math.abs(_vfov - cam.fov) > 1e-4) {
-                cam.fov = _vfov;
-                cam.updateProjectionMatrix();
-            }
-            // Publish a per-pane live readout for the tuner panel (only while it's
-            // open, so the steady path stays allocation-free). Keyed by pane so
-            // the panel can show the reading for whichever target is selected.
-            if (window.__h3dAspectPanelOpen) {
-                const _ro = window.__h3dAspectReadout || (window.__h3dAspectReadout = {});
-                const _slot = _ro[_paneKey] || (_ro[_paneKey] = {});
-                _slot.aspect = _paneAspect; _slot.vfov = _vfov;
-                _ro.__last = _paneKey;
-            }
-            // Optional pose nudges (height / dolly / pitch) to chase a low-flat
-            // wide-pane look if fov alone isn't enough. Gated to wide panes and
-            // suppressed while the Camera Director owns the view (it wins).
-            const _startAspect = (_tune && Number.isFinite(_tune.startAspect) && _tune.startAspect > 0)
-                ? _tune.startAspect : HORPLUS_START_ASPECT;
-            // Resolve the Camera Director bridge once (per-panel under splitscreen,
-            // else global). Used both for the wide-pane gate and the transforms below.
-            const _freeCam = _freeCamFor(highwayCanvas);
-            const _dirActive = !!(_freeCam && _freeCam.enabled);
-            const _wide = !!(_tune && _paneAspect > _startAspect) && !_dirActive;
-            const _poseHMul = (_wide && Number.isFinite(_tune.heightMul)) ? _tune.heightMul : 1;
-            const _poseDMul = (_wide && Number.isFinite(_tune.distMul)) ? _tune.distMul : 1;
-            const _poseLookYAdd = (_wide && Number.isFinite(_tune.pitchAdd)) ? _tune.pitchAdd * K : 0;
-            const _poseLookZMul = (_wide && Number.isFinite(_tune.lookDepthMul) && _tune.lookDepthMul > 0)
-                ? _tune.lookDepthMul : 1;
-
-            curX += (tgtX - curX) * lerp;
-            // The fret-row fit guard (end of camUpdate) may dolly the camera back
-            // via _fretRowFitBoost; the span-driven tgtDist still owns zooming IN.
-            curDist += (tgtDist * _fretRowFitBoost - curDist) * lerp;
-            const dist = curDist * aspectScale;
-            const h = CAM_H_BASE * (dist / CAM_DIST_BASE);
-
-            // Zoom-interpolated framing multipliers: tight (NEAR) -> lower/closer;
-            // wide (FAR, fret 1<->20) -> higher/pulled back.
-            const _zt = Math.max(0, Math.min(1,
-                (dist - CAM_FRAME_DIST_NEAR) / (CAM_FRAME_DIST_FAR - CAM_FRAME_DIST_NEAR)));
-            const _hMul = CAM_FRAME_H_NEAR + (CAM_FRAME_H_FAR - CAM_FRAME_H_NEAR) * _zt;
-            const _dMul = CAM_FRAME_D_NEAR + (CAM_FRAME_D_FAR - CAM_FRAME_D_NEAR) * _zt;
-            const shoulderOffset = (_leftyCached ? -1 : 1) * 10 * K;
-            let _camX = curX + shoulderOffset, _camY = h * _hMul, _camZ = dist * _dMul;
-            // Optional wide-pane pose nudges (default identity → no-op).
-            if (_poseHMul !== 1) _camY *= _poseHMul;
-            if (_poseDMul !== 1) _camZ *= _poseDMul;
-            // ── Free-camera user tweaks (orbit / height / zoom / pan) ──
-            // Driven by the Camera Director plugin via the camera bridge:
-            // window.__h3dCamCtlPanels[panelIndexFor(canvas)] when split (this
-            // panel's own camera), falling back to the global window.__h3dCamCtl.
-            // Layered ON TOP of the auto-framing so note tracking still works.
-            // The bridge is read once into _freeCam and reused for both the
-            // position and the look-at transforms; every field is coerced to a
-            // finite number before use so a malformed object can never feed NaN
-            // into cam.position / cam.lookAt.
-            // _freeCam resolved above via _freeCamFor(highwayCanvas): the
-            // per-panel __h3dCamCtlPanels entry, else global __h3dCamCtl, else null.
-            const _lookAtZ = -FOCUS_D * 0.35 * _poseLookZMul;
-            if (_freeCam && _freeCam.enabled) {
-                const _distMul = Number.isFinite(_freeCam.distMul) ? _freeCam.distMul : 1;
-                const _heightMul = Number.isFinite(_freeCam.heightMul) ? _freeCam.heightMul : 1;
-                const _yaw = Number.isFinite(_freeCam.yaw) ? _freeCam.yaw : 0;
-                const _tx = curX, _ty = curLookY, _tz = _lookAtZ; // look target
-                let _vx = _camX - _tx, _vy = _camY - _ty, _vz = _camZ - _tz;
-                _vx *= _distMul; _vy *= _distMul; _vz *= _distMul; // zoom (dolly)
-                _vy *= _heightMul;                                 // height
-                const _cy = Math.cos(_yaw), _sy = Math.sin(_yaw);  // orbit around Y
-                const _rx = _vx * _cy - _vz * _sy, _rz = _vx * _sy + _vz * _cy;
-                _camX = _tx + _rx; _camY = _ty + _vy; _camZ = _tz + _rz;
-            }
-            cam.position.set(_camX, _camY, _camZ);
-
-            // Self-correcting look-at Y: project the fretboard's near-edge centre
-            // to NDC space. If it drifts toward the frame edge, nudge tgtLookY
-            // toward the fretboard centre so the camera tilts to re-frame it.
-            // This lets the camera adapt to any panel aspect ratio automatically.
-            const fretMidY = (sY(0) + sY(nStr - 1)) / 2;
-            _probe.set(curX, fretMidY, 0);                  // play-line fretboard centre
-            cam.lookAt(curX, curLookY + _poseLookYAdd, _lookAtZ);    // tentative look — needed for project()
-            cam.updateMatrixWorld();
-            _probe.project(cam);                             // _probe.y → NDC in [-1, 1]
-
-            // Keep fretboard centre in the lower third of the screen (NDC ≈ -0.35).
-            // The deadband width and correction strength are both blended
-            // between Twitchy and Calm bounds by the user's tiltSmoothing
-            // setting — twitchy = re-frame aggressively (narrow band, strong
-            // nudge); calm = let small drift ride (wide band, weak nudge).
-            const DESIRED_NDC_Y = -0.35;
-            const tiltBand   = CAM_TILT_BAND_T + (CAM_TILT_BAND_C - CAM_TILT_BAND_T) * tiltSmoothing;
-            const tiltStr    = CAM_TILT_STR_T  + (CAM_TILT_STR_C  - CAM_TILT_STR_T)  * tiltSmoothing;
-            if (_probe.y < DESIRED_NDC_Y - tiltBand || _probe.y > DESIRED_NDC_Y + tiltBand) {
-                // _probe.y too low → fretboard near bottom → tgtLookY decreases → camera tilts down → fretboard rises
-                // _probe.y too high → fretboard near top  → tgtLookY increases → camera tilts up   → fretboard drops
-                const correction = (DESIRED_NDC_Y - _probe.y) * fretMidY * tiltStr;
-                tgtLookY = Math.max(-fretMidY, Math.min(fretMidY, tgtLookY - correction));
-            }
-            curLookY += (tgtLookY - curLookY) * lerp;
-
-            // Final look-at with the corrected Y (overrides the tentative one above).
-            // User tilt (pitch) + pan offsets layer on top when the free-cam is
-            // enabled; each is coerced to a finite number to avoid a NaN look-at.
-            if (_freeCam && _freeCam.enabled) {
-                const _panX = Number.isFinite(_freeCam.panX) ? _freeCam.panX : 0;
-                const _panY = Number.isFinite(_freeCam.panY) ? _freeCam.panY : 0;
-                const _pitch = Number.isFinite(_freeCam.pitch) ? _freeCam.pitch : 0;
-                cam.lookAt(curX + _panX * K, curLookY + (_pitch + _panY) * K, _lookAtZ);
-            } else {
-                cam.lookAt(curX, curLookY + _poseLookYAdd, _lookAtZ);
-            }
-
-            // ── Fret-row fit guard ────────────────────────────────────────────
-            // Project the fret-number-row band (just below the lowest string, at
-            // the play line) with the final camera. If it sits below the safe
-            // bottom line, dolly back (raise _fretRowFitBoost → applied to the
-            // curDist lerp target next frame) until it clears; relax lazily once
-            // there's comfortable headroom. Asymmetric + deadbanded so it
-            // converges without hunting, and capped so the zoom can't pop. It
-            // cooperates with the tilt loop above rather than fighting it: pulling
-            // back shrinks the scene, the tilt loop keeps the board centre anchored
-            // at DESIRED_NDC_Y, so only the row's bottom headroom changes. Skipped
-            // while the free-cam (Camera Director) owns the view.
-            if (_freeCam && _freeCam.enabled) {
-                if (_fretRowFitBoost !== 1) _fretRowFitBoost = 1;
-            } else {
-                cam.updateMatrixWorld();
-                const _rowY = Math.min(sY(0), sY(nStr - 1)) - S_GAP * 1.4;
-                _probe.set(curX, _rowY, 0.5 * K);
-                _probe.project(cam);                              // _probe.y → NDC; < -1 = off the bottom
-                const _rowNdcY = _probe.y;
-                if (_rowNdcY < FRET_ROW_FIT_NDC_MIN) {
-                    // Row below the safe line → pull back promptly, proportional to
-                    // the deficit so it converges in a few frames without overshoot.
-                    const _need = FRET_ROW_FIT_NDC_MIN - _rowNdcY;
-                    _fretRowFitBoost = Math.min(FRET_ROW_FIT_BOOST_MAX,
-                        _fretRowFitBoost + Math.min(0.05, _need * 0.4));
-                } else if (_rowNdcY > FRET_ROW_FIT_NDC_MIN + FRET_ROW_FIT_DEADBAND
-                           && _fretRowFitBoost > 1) {
-                    // Comfortable headroom → relax the dolly back toward normal, lazily.
-                    _fretRowFitBoost = Math.max(1, _fretRowFitBoost - 0.01);
-                }
-            }
-        }
-
-        /* ── Resize helper ───────────────────────────────────────────────── */
-        function applySize(w, h) {
-            if (!ren || !cam || !wrap) return;
-            if (!Number.isFinite(w) || !Number.isFinite(h) || w <= 0 || h <= 0) return;
-            const baseDPR = _ssActive() ? Math.min(devicePixelRatio, 1.25) : Math.min(devicePixelRatio, 2);
-            ren.setPixelRatio(_renderScale * baseDPR);
-            ren.setSize(w, h);
-            // Pin the overlay to #highway's exact box so it fully covers the
-            // canvas. The wrap is anchored to top:0/left:0/right:0 of its
-            // offset parent, which only lines up with #highway when the
-            // canvas sits at the parent's origin. The v3 player can place
-            // chrome above the canvas, shifting the wrap up so its lower edge
-            // falls short of #highway — leaving a strip of the canvas exposed
-            // (the reported gap, where the previous renderer's frame showed
-            // through). The wrap is a sibling of highwayCanvas, so they share
-            // an offset parent; tracking the canvas's box keeps the overlay
-            // flush in single-player and splitscreen alike.
-            //
-            // Derive the box from the SAME getBoundingClientRect measurements
-            // that drive ren.setSize(w, h) — NOT integer offsetTop/Width — so
-            // the overlay matches the renderer exactly. Under browser zoom or
-            // fractional flex layouts the canvas lands on sub-pixel bounds;
-            // offsetWidth/Top round to whole pixels and would leave the wrap up
-            // to 1px short of (or shifted from) the canvas, reopening the
-            // exposed edge strip. Position is taken relative to the containing
-            // block's padding edge (clientTop/Left strip the parent's border),
-            // which is what `top`/`left` resolve against for the absolutely
-            // positioned wrap. Guarded on a laid-out canvas (offsetWidth/Height
-            // > 0); otherwise fall back to the static top:0/left:0/right:0.
-            if (highwayCanvas && highwayCanvas.offsetWidth > 0 && highwayCanvas.offsetHeight > 0) {
-                const _pinParent = wrap.offsetParent || highwayCanvas.parentNode;
-                const _cr = highwayCanvas.getBoundingClientRect();
-                const _pr = _pinParent ? _pinParent.getBoundingClientRect() : { top: 0, left: 0 };
-                const _pbTop = _pinParent ? _pinParent.clientTop : 0;
-                const _pbLeft = _pinParent ? _pinParent.clientLeft : 0;
-                wrap.style.top = (_cr.top - _pr.top - _pbTop) + 'px';
-                wrap.style.left = (_cr.left - _pr.left - _pbLeft) + 'px';
-                wrap.style.right = 'auto';
-                wrap.style.width = _cr.width + 'px';
-                wrap.style.height = _cr.height + 'px';
-                _wrapPinned = true;
-            } else {
-                // Canvas not laid out (e.g. init ran before #highway had a real
-                // box, or a panel hide/show where canvasSize() falls back to the
-                // parent panel). Reset to the static anchor — if we had pinned
-                // before, the old top/left/right:auto/width would otherwise stay
-                // and the wrap would reappear at a stale horizontal position on
-                // the next show. Leave _wrapPinned false so the rAF loop re-pins
-                // once the canvas materializes again.
-                wrap.style.top = '0';
-                wrap.style.left = '0';
-                wrap.style.right = '0';
-                wrap.style.width = 'auto';
-                wrap.style.height = h + 'px';
-                _wrapPinned = false;
-            }
-            if (lyricsCanvas) { lyricsCanvas.width = w; lyricsCanvas.height = h; }
-            _diagRenderCache.clear();
-            cam.aspect = w / h;
-            cam.updateProjectionMatrix();
-            aspectScale = Math.max(1, REF_ASPECT / Math.max(cam.aspect, 0.5));
-            // Cache the pane aspect for the horizontal-FOV-hold in camUpdate.
-            // cam.fov itself is owned by camUpdate (not set here) so live
-            // __h3dAspectTune edits apply every frame without a resize.
-            _paneAspect = cam.aspect;
-            _appliedW = w; _appliedH = h;
-        }
-
-        /* ── Teardown ────────────────────────────────────────────────────── */
-        function teardown() {
-            // Background animations (#13). Drop the listener first so any
-            // mid-teardown settings change doesn't try to rebuild a torn-
-            // down scene; then dispose the active style's resources.
-            if (_bgListener) { _bgUnsubscribe(_bgListener); _bgListener = null; }
-            // WebGL context-loss listeners (bound in initScene on ren.domElement).
-            // Remove before ren is disposed below so a torn-down instance can't
-            // keep firing them; reset the flag so a reused instance starts clean.
-            if (ren && ren.domElement) {
-                if (_onCtxLost) { try { ren.domElement.removeEventListener('webglcontextlost', _onCtxLost, false); } catch (e) {} }
-                if (_onCtxRestored) { try { ren.domElement.removeEventListener('webglcontextrestored', _onCtxRestored, false); } catch (e) {} }
-            }
-            _onCtxLost = _onCtxRestored = null;
-            _ctxLost = false;
-            // Notedetect listeners (issue #9). Remove on destroy so a
-            // panel that stops doesn't keep accumulating marks. Marks
-            // arrays are cleared too — they hold stale chart positions
-            // that next init() may reuse (drawNote keys on (s, f, t)).
-            if (_ndOnHit) { window.removeEventListener('notedetect:hit', _ndOnHit); _ndOnHit = null; }
-            if (_ndOnMiss) { window.removeEventListener('notedetect:miss', _ndOnMiss); _ndOnMiss = null; }
-            if (_fxOnFx) { window.removeEventListener('notedetect:fx', _fxOnFx); _fxOnFx = null; }
-            if (window.feedBack && typeof window.feedBack.off === 'function') {
-                if (_fxOnSkin) { try { window.feedBack.off('notedetect:skin', _fxOnSkin); } catch (e) {} _fxOnSkin = null; }
-                if (_ndOnBusHit)  window.feedBack.off('note:hit', _ndOnBusHit);
-                if (_ndOnBusMiss) window.feedBack.off('note:miss', _ndOnBusMiss);
-                if (_visibilityHandler) {
-                    try { window.feedBack.off('highway:visibility', _visibilityHandler); } catch (e) {}
-                }
-                if (_canvasReplacedHandler) {
-                    try { window.feedBack.off('highway:canvas-replaced', _canvasReplacedHandler); } catch (e) {}
-                }
-            }
-            _ndOnBusHit = _ndOnBusMiss = null;
-            _visibilityHandler = null;
-            _canvasReplacedHandler = null;
-            _ndHitMarks = [];
-            _ndMissMarks = [];
-            _ndLabels = [];
-            for (const p of _fxPops) p.active = false;
-            for (const b of _fxBursts) b.active = false;
-            _fxSeen.clear();
-            _fxGen++;   // invalidate any pending deferred window-copy fallbacks
-            _fxLastFxDetail = null;
-            _fxElemSeen = new WeakSet();
-            _fxRingMs = _fxBreakMs = -1e9;
-            _chordVerdicts = new Map();
-            if (bcCtrl) { try { bcCtrl.destroy(); } catch (e) {} bcCtrl = null; }
-            _bgUnmountStyle();
-            bgGroup = null; _bgLastT = 0;
-            _diagChord = null; _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0; _diagPrevStartT = null;
-            _diagEntranceT = 1.0; _diagLastKey = null; _diagRenderCache.clear();
-
-            if (wrap) { wrap.remove(); wrap = null; }
-            _disposeOpenStringPitchSprites();
-            if (scene) {
-                // Don't dispose material.map textures here. Texture
-                // lifetime belongs to whoever allocated it; the bg
-                // styles' per-layer CanvasTextures (e.g. silhouettes'
-                // wrappers around the shared _silCanvas) are released
-                // in their own teardowns. txtCache textures are
-                // explicitly disposed below; mStr/mGlow/etc. don't have
-                // a .map. Disposing here would either double-free or
-                // yank a still-in-use texture out from under another
-                // mount.
-                scene.traverse((obj) => {
-                    // fretTubeGeo is shared across all fret meshes — dispose it
-                    // exactly once below, not once per mesh here.
-                    if (obj.geometry !== fretTubeGeo) obj.geometry?.dispose?.();
-                    if (obj.material) {
-                        const mats = Array.isArray(obj.material) ? obj.material : [obj.material];
-                        for (const m of mats) m?.dispose?.();
-                    }
-                });
-                // Shared chord-frame fill gradient — not owned by txtCache;
-                // MeshBasicMaterial.dispose() does not release maps.
-                chordFrameGradTex?.dispose?.();
-                chordFrameGradTexArp?.dispose?.();
-            }
-            gNote?.dispose?.(); gSus?.dispose?.(); gBeat?.dispose?.(); gSusRail?.dispose?.(); gTapChevron?.dispose?.();
-            mSusRailBase?.dispose?.(); mSusRailBase = null; gSusRail = null; pSusRail = null;
-            gSusRailBloom?.dispose?.(); mSusRailBloomBase?.dispose?.(); _bloomGaussTex?.dispose?.();
-            gSusRailBloom = null; mSusRailBloomBase = null; _bloomGaussTex = null; pSusRailBloom = null;
-            gTechPlane?.dispose?.(); gTechPlane = null; pTechPlane = null;
-            // InstancedMesh disposal — .dispose() releases instanceMatrix / instanceColor
-            // GPU buffers. Geometry and material are disposed separately below.
-            imPMTech?.dispose?.(); imPMTech = null;
-            imFHTech?.dispose?.(); imFHTech = null;
-            imPMXFill?.dispose?.(); imPMXFill = null;
-            imPMXLines?.dispose?.(); imPMXLines = null;
-            imFHXFill?.dispose?.(); imFHXFill = null;
-            imFHXLines?.dispose?.(); imFHXLines = null;
-            // Geometry clones for PM/FH tech IMs (own instanceAlpha attribute).
-            _imGPMTech?.dispose?.(); _imGPMTech = null;
-            _imGFHTech?.dispose?.(); _imGFHTech = null;
-            // ShaderMaterials for all 6 IMs.
-            _imPMTechMat?.dispose?.();  _imPMTechMat = null;
-            _imFHTechMat?.dispose?.();  _imFHTechMat = null;
-            _imPMXFillMat?.dispose?.(); _imPMXFillMat = null;
-            _imPMXLinesMat?.dispose?.(); _imPMXLinesMat = null;
-            _imFHXFillMat?.dispose?.(); _imFHXFillMat = null;
-            _imFHXLinesMat?.dispose?.(); _imFHXLinesMat = null;
-            _imM4 = _imPos = _imSca = _imQ = _imAZ = _imColor = null;
-            gHaloBar?.dispose?.(); gHaloBar = null;
-            gArpBracket?.dispose?.(); gArpBracket = null;
-            for (const m of mStr) m?.dispose?.();
-            for (const m of mGlow) m?.dispose?.();
-            for (const m of mSus) m?.dispose?.();
-            for (const m of mStrHitOutline) m?.dispose?.();
-            for (const m of mAccentOutline) m?.dispose?.();
-            for (const m of mAccentCore) m?.dispose?.();
-            for (const m of mAccentHaloNear) m?.dispose?.();
-            for (const m of mAccentHaloMid) m?.dispose?.();
-            for (const m of mAccentHaloFar) m?.dispose?.();
-            mBeatM?.dispose?.(); mBeatQ?.dispose?.();
-            // Notedetect outline materials (#9). May not be reachable
-            // via scene.traverse if no event ever fired (never attached
-            // to a mesh), so dispose explicitly.
-            mMissOutline?.dispose?.();
-            mHitSusOutline?.dispose?.();
-            mEdgeTransparent?.dispose?.(); mEdgeTransparent = null;
-            for (const m of mHitBright) m?.dispose?.(); mHitBright = []; mHitBrightArrays = [];
-            for (const k in txtCache) {
-                const tm = txtCache[k];
-                tm.userData.h3dGhostFretMeshMat?.dispose?.();
-                tm.userData.h3dGhostFretMeshMat = null;
-                tm.userData.h3dTechMeshMat?.dispose?.();
-                tm.userData.h3dTechMeshMat = null;
-                tm.map?.dispose();
-                tm.dispose();
-            }
-            // Technique-marker sprite materials (triMat / bendChevronMat) —
-            // own numeric-keyed cache, not reachable via txtCache.
-            for (const tm of _techMatCache.values()) {
-                tm.map?.dispose();
-                tm.dispose();
-            }
-            _techMatCache.clear();
-            // Dispose per-sprite cloned materials (e.g. pmMark._pmMat).
-            // These aren't reachable via scene.traverse once the sprite
-            // gets reassigned a different material, so the array tracks
-            // them at allocation time.
-            for (const m of _ownedClonedMats) m?.dispose?.();
-            _ownedClonedMats.length = 0;
-            // Per-mesh technique-marker clones (from _spriteMat2MeshMat).
-            // The Set tracks the live clone for each pool mesh; dispose all
-            // on teardown so no GPU material leaks between init() cycles.
-            for (const m of _techMeshMatClones) m?.dispose?.();
-            _techMeshMatClones.clear();
-            // Shared pool-factory materials/geometries (mLaneOdd/Even, etc.) —
-            // see _ownedSharedMats comment near the declaration. Dispose is
-            // idempotent so the scene.traverse() pass above won't double-free.
-            for (const m of _ownedSharedMats) m?.dispose?.();
-            _ownedSharedMats.length = 0;
-            for (const g of _ownedSharedGeos) g?.dispose?.();
-            _ownedSharedGeos.length = 0;
-            txtCache = {};
-            if (_sparkPts) { try { _sparkPts.geometry.dispose(); _sparkPts.material.dispose(); } catch (e) {} _sparkPts = null; }
-            if (_composer) { try { _composer.dispose(); if (_bloomPass && _bloomPass.dispose) _bloomPass.dispose(); } catch (e) {} _composer = null; _bloomPass = null; }
-            if (ren) { ren.dispose(); ren = null; }
-            scene = cam = noteG = beatG = lblG = fretG = tuningLblG = null;
-            ambLight = dirLight = null;
-            mStr = []; mGlow = []; mSus = []; mStrHitOutline = []; mAccentOutline = []; mAccentCore = []; mAccentHaloNear = []; mAccentHaloMid = []; mAccentHaloFar = []; _accentShellsByString = []; mWhiteOutline = mSusOutline = null; mMissOutline = null; mHitSusOutline = null; stringLines = []; stringLineGlows = []; _boardPlaneMat = null; fretWireMats = []; fretTubeGeo?.dispose?.(); fretTubeGeo = null;
-            for (const m of _inlayMats) m?.dispose?.(); _inlayMats = []; _inlayLabels = [];
-            // mTapChevron: dispose explicitly — if no tap marker ever
-            // spawned a pooled mesh, the scene.traverse() pass above never
-            // reaches this material.
-            mTapChevron?.dispose?.();
-            mTapChevron = null;
-            // mBarre is a shared material that all pBarreLine pool meshes
-            // reference. If no barre chord ever appears, the pool factory
-            // is never called, so no mesh carries mBarre into the scene
-            // and scene.traverse() will miss it. Dispose explicitly here
-            // to avoid leaking the GPU resource across panel lifecycles.
-            // Three.js dispose() is idempotent, so calling it before or
-            // after scene.traverse() is safe in both the instantiated and
-            // uninstantiated cases.
-            mBarre?.dispose?.(); mBarre = null;
-            _paletteColorTmp = null;
-            lyricsCanvas = lyricsCtx = null;
-            projMeshArr = null;
-            _probe = null;
-            _drawNextByString = null; _drawRecentByString = null;
-            _susVerdictLatch.clear();
-            _drawChordTemplates = null;
-            _drawAnchors = null;
-            _laneTargetColor = null;
-            _fwHitColor = _fwHitEmissive = null;
-            _fwHitGlow.fill(0);
-            _fwChordAcc.clear();
-            _fwHitPrevTime = -Infinity;
-            _renderScale = 1;
-            mBeatM = mBeatQ = null;
-            pNote = pNoteEdge = pSus = pSusOutline = pSusRibbon = pSusRibbonOl = pLbl = pBeat = pSec = null;
-            pFretLbl = pLane = pLaneDivider = pGhostFretLbl = pChordBox = pChordFrameFill = pChordLbl = pBarreLine = pArpBracket = pNoteFretLabel = pConnectorLine = pDropLine = pTapChevron = pAccentHalo = pHaloBar = pPMXFill = pFHXFill = pMuteXLines = pFHXLines = pTeachMarkLbl = null;
-            if (gPMXFill) { gPMXFill.dispose(); gPMXFill = null; }
-            if (gFHXFill) { gFHXFill.dispose(); gFHXFill = null; }
-            if (gPMXLines) { gPMXLines.dispose(); gPMXLines = null; }
-            if (gFHXLines) { gFHXLines.dispose(); gFHXLines = null; }
-            mLaneOdd = mLaneEven = mLaneDivider = mLaneDividerArp = gLanePlane = gGhostFretPlane = null;
-            chordFrameGradTex = chordFrameGradTexArp = null;
-            pFretColMarker = null;
-            _fretMarkerWaveCache.clear();
-            gNote = gSus = gBeat = gTapChevron = null;
-            tgtX = curX = xFretMid(CAM_LOCK_CENTER_FRET); tgtDist = curDist = CAM_DIST_BASE; tgtLookY = curLookY = 0; _fretRowFitBoost = 1; nStr = NSTR; _oobStringWarned = false;
-            _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
-            _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
-            _lookaheadCamPrevNow = null;
-            _lookaheadLowBonusU = 0;
-            _lookaheadHiNeckLatch = false;
-            _measureStarts = []; _measureStartsRef = null;
-            _clkAudioT = NaN; _clkPerf = NaN; _clkRate = 1; _frameNow = 0;
-            prevLowFretBonus = 0;
-            prevLockActive = false;
-            _camSnapped = false;
-            _camPreScanned = false;
-            _songKey = null;
-            _slideTargetSet = null;
-            _slideTargetNotesRef = null;
-            _slideTargetChordsRef = null;
-        }
-
-        function canvasSize(canvas) {
-            if (canvas) {
-                // If the canvas has zero bounds (hidden via any mechanism — inline style,
-                // CSS class, or hidden ancestor) fall back to the parent container
-                // (the splitscreen panelDiv) which is always visible and correctly sized.
-                const rect = canvas.getBoundingClientRect();
-                const target = (rect.width === 0 || rect.height === 0) && canvas.parentNode ? canvas.parentNode : canvas;
-                const sz = target === canvas ? rect : target.getBoundingClientRect();
-                if (sz.width > 0 && sz.height > 0) return { w: sz.width, h: sz.height };
-            }
-            // Reserve the full bottom area: #player-footer wraps the Section
-            // Practice bar + #player-controls. Fall back to #player-controls.
-            const ch = (document.getElementById('player-footer')
-                || document.getElementById('player-controls'))?.offsetHeight || 50;
-            return { w: innerWidth, h: innerHeight - ch };
-        }
-
-        /* ── setRenderer contract ────────────────────────────────────────── */
-        return {
-            // Tells highway.js this renderer needs a webgl2-capable canvas.
-            // Browsers lock a <canvas> to the first context type acquired,
-            // so when this renderer is installed mid-session highway.js
-            // replaces the underlying <canvas> element so getContext('webgl2')
-            // can succeed (see static/highway.js _replaceCanvas).
-            contextType: 'webgl2',
-            init(canvas, bundle) {
-                _unsubscribeFocus();
-                if (wrap || ren) {
-                    teardown();
-                }
-                _destroyed = _isReady = false;
-                _isFocused = true;
-                if (!_paneUid) _paneUid = ++_aspectPaneCounter;   // fallback pane id (no-arrangement panes)
-                _registerTunerShortcut();   // session-global tuner shortcut (self-guarded)
-                const myToken = ++_initToken;
-                highwayCanvas = canvas;
-                _invertedCached = !!(bundle && bundle.inverted);
-                _leftyCached = !!(bundle && bundle.lefty);
-                _renderScale = (bundle && bundle.renderScale) || 1;
-                // Per-render background opt-out. A plugin borrowing the highway as
-                // a visualization can set bundle.bgReactive === false to suppress
-                // the audio-reactive background for THIS instance only — without
-                // writing the shared h3d_bg_* settings (which would also change the
-                // host's own highway). Motivation: the reactive bg taps the core
-                // <audio> element, and when another consumer already holds it the
-                // setup throws + the cleanup AudioContext.close() is an audible
-                // click — which a borrower that never taps <audio> (e.g. a
-                // contained-playback practice plugin) inherits for no benefit.
-                // Default behavior is unchanged when the field is absent.
-                _bgReactiveOptOut = !!(bundle && bundle.bgReactive === false);
-
-                if (_ssActive()) {
-                    window.feedBackSplitscreen.onFocusChange(_onFocusChange);
-                    _focusSubscribed = true;
-                }
-
-                // Async-ready contract (feedBack#36 readyPromise). Resolves
-                // when Three.js loaded + scene initialised (_isReady = true).
-                // Rejects on any async failure so highway.js can revert.
-                let _resolveReady, _rejectReady;
-                this.readyPromise = new Promise((res, rej) => {
-                    _resolveReady = res;
-                    _rejectReady = rej;
-                });
-                // Shared rejection for superseded init cycles (destroy() or a
-                // newer init() started before this one completed). highway.js
-                // ignores the rejection when the renderer is no longer active.
-                const _rejectSuperseded = () => _rejectReady(new Error('superseded'));
-
-                loadThree().then(() => {
-                    if (_destroyed || _initToken !== myToken) {
-                        _rejectSuperseded();
-                        return;
-                    }
-                    try {
-                        nStr = resolveStringCount(bundle);
-                        _invertedForBoard = _invertedCached;
-                        _leftyForBoard = _leftyCached;
-                        if (!initScene()) { _unsubscribeFocus(); _rejectReady(new Error('initScene failed')); return; }
-                        // Pre-compile shaders + upload deterministic label
-                        // textures while the load spinner is still up; the
-                        // chart-dependent half runs on first draw() (bundle
-                        // arrays are only guaranteed populated post-ready).
-                        _prewarmStatic();
-                        _chartPrewarmed = false;
-                        const sz = canvasSize(highwayCanvas);
-                        // Mark ready before RAF so any resize(w,h) calls that arrive
-                        // in the meantime (e.g. from sizeCanvases()) are applied directly.
-                        _isReady = true;
-                        _resolveReady();
-                        _updateFocusState();
-                        if (sz.w > 0 && sz.h > 0) {
-                            applySize(sz.w, sz.h);
-                        } else {
-                            // Panel container not yet laid out (sizeCanvases() runs after
-                            // initPanel() in the setup sequence). Retry each frame until
-                            // the panelDiv has real dimensions.
-                            (function retrySize() {
-                                if (_destroyed || !_isReady) return;
-                                const s = canvasSize(highwayCanvas);
-                                if (s.w > 0 && s.h > 0) applySize(s.w, s.h);
-                                else requestAnimationFrame(retrySize);
-                            })();
-                        }
-                    } catch (e) {
-                        console.error('[3D-Hwy] init .then() threw:', e);
-                        _isReady = false;
-                        _unsubscribeFocus(); teardown();
-                        _rejectReady(e);
-                    }
-                }).catch(e => {
-                    if (_initToken !== myToken || _destroyed) {
-                        _rejectSuperseded();
-                        return;
-                    }
-                    console.error('[3D-Hwy] Three.js unavailable:', e);
-                    _unsubscribeFocus();
-                    _rejectReady(e);
-                });
-            },
-
-            // The host throttles paused frames to ~10 fps, on the assumption
-            // that a paused chart is a static picture and re-rendering it is
-            // pure waste (highway-constants._PAUSED_FRAME_INTERVAL_MS).
-            //
-            // That stopped being true when the venue landed. The venue backdrop
-            // is a PLAYING VIDEO and the crowd reacts on its own clock, and they
-            // are drawn into this same canvas as the highway — so throttling the
-            // highway throttled the whole room. Pausing the song dropped the
-            // venue, the crowd and the stage to 10 fps.
-            //
-            // Two independent sources of motion, and BOTH must keep their frames:
-            //
-            //  • a crowd video rolling on its own clock (career venue pack), and
-            //  • the venue scene's own fake-depth motion — the backdrop breathes,
-            //    the haze drifts, warmth pulses, the shimmer moves. That is
-            //    Math.sin(t) in the draw loop (see _venueApplyFakeDepthMotion),
-            //    so it only moves while we are actually given frames, and it runs
-            //    with NO pack at all.
-            //
-            // The throttle fires whenever the CHART CLOCK is stalled — which is
-            // not just a pause. A count-in and the credits/author overlay stall it
-            // exactly the same way, so the venue was stuttering there too.
-            //
-            // With no venue at all (plain 3D highway) the paused scene really is a
-            // still picture: motion mode reads 'off', we claim nothing, and the
-            // throttle still saves the GPU as #654 intended.
-            needsContinuousFrames() {
-                if (!_isReady || _ctxLost) return false;
-                for (const v of _venueCrowdVideos) {
-                    if (v && !v.paused && !v.ended && v.readyState >= 2) return true;
-                }
-                // 'off' also covers prefers-reduced-motion and "no venue scene".
-                try { return _venueEffectiveMotionMode() !== 'off'; } catch (_) { return false; }
-            },
-
-            draw(bundle) {
-                if (!_isReady) return;
-                if (_ctxLost) return;   // GPU context lost (alt-tab / reset) — skip until restored
-                if (!_chartPrewarmed) {
-                    _chartPrewarmed = true;
-                    _prewarmChart(bundle);
-                }
-                _invertedCached = !!bundle.inverted;
-                _leftyCached = !!bundle.lefty;
-                const newNStr = resolveStringCount(bundle);
-                const newScale = bundle.renderScale || 1;
-                const leftyChanged = _leftyCached !== _leftyForBoard;
-                if (_invertedCached !== _invertedForBoard || leftyChanged || newNStr !== nStr) {
-                    if (newNStr !== nStr) {
-                        _oobStringWarned = false;
-                        // Drop chord caches computed under the old string count
-                        // so extended-range notes (string 6+) aren't left
-                        // filtered out of cached shapes.
-                        _resetStringDependentCaches();
-                    }
-                    if (leftyChanged) {
-                        curX = -curX;
-                        tgtX = -tgtX;
-                        _lookaheadCamX = -_lookaheadCamX;
-                    }
-                    nStr = newNStr;
-                    buildBoard();
-                    _invertedForBoard = _invertedCached;
-                    _leftyForBoard = _leftyCached;
-                }
-                if (newScale !== _renderScale) {
-                    _renderScale = newScale;
-                    const s = canvasSize(highwayCanvas);
-                    if (s.w > 0 && s.h > 0) applySize(s.w, s.h);
-                }
-                // Keep the render matched to the highway canvas's real box.
-                // Two independent drifts to catch each frame:
-                //  1. Backing store (canvas.width/height) changed out from under
-                //     us — e.g. the splitscreen hw.resize override resizes the
-                //     element but never calls renderer.resize(). Also re-sizes
-                //     the lyrics overlay canvas via applySize().
-                //  2. The CSS box (canvasSize()) drifted while the backing store
-                //     held. #highway is flex:1, so its rendered height changes as
-                //     the player layout settles right after a song opens — with
-                //     no backing-store change and no window 'resize' event, so the
-                //     check above never fires. Without this the camera stays framed
-                //     for the pre-settle (too-tall) size and crops the near strings
-                //     / fret numbers until the user un/re-maximizes the window.
-                if (highwayCanvas) {
-                    // Backing-store drift (branch 1) is detected with cheap
-                    // property reads every frame. The CSS-box checks (branches
-                    // 2/3) need canvasSize() → getBoundingClientRect(), a
-                    // forced layout read — profiled at ~1.2% of throttled
-                    // main-thread time when run per frame. Throttle the box
-                    // read to every 10th frame (plus whenever the backing
-                    // store changed or the wrap isn't pinned yet): the layout
-                    // settle it exists to catch plays out over hundreds of ms
-                    // right after a song opens, so a ~166 ms detection cadence
-                    // loses nothing visible.
-                    const _bsChanged = highwayCanvas.width !== _lastHwW
-                        || highwayCanvas.height !== _lastHwH;
-                    _boxCheckCountdown = (_boxCheckCountdown + 1) % 10;
-                    if (_bsChanged || !_wrapPinned || _boxCheckCountdown === 0) {
-                        const box = canvasSize(highwayCanvas);
-                        if (_bsChanged) {
-                            _lastHwW = highwayCanvas.width;
-                            _lastHwH = highwayCanvas.height;
-                            if (box.w > 0 && box.h > 0) applySize(box.w, box.h);
-                        } else if (box.w > 0 && box.h > 0 &&
-                                (Math.abs(box.w - _appliedW) > 1 || Math.abs(box.h - _appliedH) > 1)) {
-                            applySize(box.w, box.h);
-                        } else if (!_wrapPinned && box.w > 0 && box.h > 0 &&
-                                highwayCanvas.offsetWidth > 0 && highwayCanvas.offsetHeight > 0) {
-                            //  3. The overlay pin couldn't be applied at init because
-                            //     #highway had no layout yet (offsetWidth/Height === 0),
-                            //     so applySize() only set the wrap height. The canvas has
-                            //     now laid out but to the same logical size, so neither
-                            //     drift branch above fires — re-run applySize to pin the
-                            //     wrap to the canvas box now that its offsets are real.
-                            //     Otherwise the overlay stays at top:0;left:0;right:0 and
-                            //     a strip of #highway is exposed on first load / split.
-                            applySize(box.w, box.h);
-                        }
-                    }
-                }
-                update(bundle);
-                camUpdate(bundle);
-
-                // Background animations (#13). Compute frame dt once,
-                // read audio bands when reactivity is on, delegate to
-                // the active style's update().
-                if (bgGroup && _bgEffectiveStyleId() !== 'off') {
-                    const nowMs = performance.now();
-                    const dt = _bgLastT === 0 ? 1 / 60 : Math.min(0.1, (nowMs - _bgLastT) / 1000);
-                    _bgLastT = nowMs;
-                    const bands = bgReactive ? _bgReadBands() : BG_ZERO_BANDS;
-                    const style = BG_STYLES[_bgEffectiveStyleId()];
-                    if (style && bgState) {
-                        try { style.update(bgState, bands, dt, nowMs / 1000); }
-                        catch (e) { console.error('[3D-Hwy] bg update threw', _bgEffectiveStyleId(), e); }
-                    }
-                }
-
-                // Browser: the shared analyser can change between songs (a sloppak
-                // stems swap replaces it, often on a new context) — or may not have
-                // existed when the controller mounted. Keep the visualizer bound to
-                // the LIVE analyser by comparing against what the controller
-                // actually bound (boundAnalyser()), not a separately-tracked guess:
-                // cheap reconnect when it's the same context, full controller
-                // rebuild when the context changed (cross-context connectAudio is
-                // impossible). Only act once the viz is ready (ready()), so we
-                // don't thrash a controller that's still loading async. Done before
-                // the render block so a rebuild this frame just skips one bc frame
-                // (bcCtrl goes null) without affecting the highway's own render.
-                if (bcCtrl && !_bcIsDesktop() && bcCtrl.ready && bcCtrl.ready()) {
-                    let a = null;
-                    try { a = _bgGetAnalyser(); } catch (e) { a = null; }
-                    const an = a && a.analyser;
-                    const bound = bcCtrl.boundAnalyser ? bcCtrl.boundAnalyser() : null;
-                    if (an && an !== bound) {
-                        if (!(bcCtrl.reconnectAudio && bcCtrl.reconnectAudio(a))) {
-                            // Context changed (or reconnect failed) — rebuild via the
-                            // proven destroy/create paths so the new context binds.
-                            try { bcCtrl.destroy(); } catch (e) {}
-                            bcCtrl = null;
-                            _bcSyncMode();
-                        }
-                    }
-                }
-                if (bcCtrl) {
-                    const cfg = _bcLoadSettings();
-                    const _ct = bundle.currentTime || 0;
-                    if (cfg.chartAccents) {
-                        if (_ct < _chartPrevT - 0.08 || _ct - _chartPrevT > 1.0) {
-                            _bcBeatIdx = _bcFfIdx(bundle.beats, _ct, 'time');
-                            _bcNoteIdx = _bcFfIdx(bundle.notes, _ct, 't');
-                            _bcChordIdx = _bcFfIdx(bundle.chords, _ct, 't');
-                        }
-                        const _beats = bundle.beats || [];
-                        while (_bcBeatIdx < _beats.length && _beats[_bcBeatIdx].time <= _ct) {
-                            const strong = _beats[_bcBeatIdx].measure !== undefined && _beats[_bcBeatIdx].measure !== -1;
-                            _chartEnv = Math.max(_chartEnv, strong ? 1.0 : 0.6);
-                            _bcBeatIdx++;
-                        }
-                        const _notes = bundle.notes || [];
-                        let _tintS = -1;
-                        while (_bcNoteIdx < _notes.length && _notes[_bcNoteIdx].t <= _ct) {
-                            _chartEnv = Math.max(_chartEnv, 0.6);
-                            _tintS = _notes[_bcNoteIdx].s;
-                            _bcNoteIdx++;
-                        }
-                        const _chords = bundle.chords || [];
-                        while (_bcChordIdx < _chords.length && _chords[_bcChordIdx].t <= _ct) {
-                            _chartEnv = Math.max(_chartEnv, 0.95);
-                            _bcChordIdx++;
-                        }
-                        if (_tintS >= 0 && activePalette && activePalette.length) {
-                            _bcTintTarget = activePalette[((_tintS % activePalette.length) + activePalette.length) % activePalette.length];
-                        }
-                        _chartPrevT = _ct;
-                        _chartEnv *= 0.86;
-                        bcCtrl.chart(_chartEnv * (cfg.chartStrength != null ? cfg.chartStrength : 1));
-                    } else {
-                        bcCtrl.chart(0);
-                    }
-                    if (cfg.colorTint && _bcTintTarget != null) {
-                        const tr = (_bcTintTarget >> 16) & 255, tg = (_bcTintTarget >> 8) & 255, tb = _bcTintTarget & 255;
-                        _tintR += (tr - _tintR) * 0.06; _tintG += (tg - _tintG) * 0.06; _tintB += (tb - _tintB) * 0.06;
-                        bcCtrl.tint((Math.round(_tintR) << 16) | (Math.round(_tintG) << 8) | Math.round(_tintB), cfg.tintStrength != null ? cfg.tintStrength : 0.65);
-                    } else {
-                        bcCtrl.tint(null, 0);
-                    }
-                    bcCtrl.render();
-                }
-                {
-                    const _jNow = performance.now();
-                    const _jdt = _juiceLastT === 0 ? 1 / 60 : Math.min(0.05, (_jNow - _juiceLastT) / 1000);
-                    _juiceLastT = _jNow;
-                    _sparkUpdate(_jdt);
-                    _streakHeat += (Math.min(1, _streakHits / 16) - _streakHeat) * 0.08;   // #7 ease heat
-                }
-                {
-                    const comp = (_bloom && !_ssActive()) ? _bloomEnsure() : null;
-                    if (comp) {
-                        const bsz = canvasSize(highwayCanvas);
-                        if (bsz && bsz.w > 0 && bsz.h > 0 && (bsz.w !== _bloomW || bsz.h !== _bloomH)) {
-                            comp.setSize(bsz.w | 0, bsz.h | 0); _bloomW = bsz.w | 0; _bloomH = bsz.h | 0;
-                        }
-                        if (ren.toneMapping !== T.ACESFilmicToneMapping) ren.toneMapping = T.ACESFilmicToneMapping;
-                        pbBeg(6); comp.render(); pbEnd(6);
-                    } else {
-                        if (ren.toneMapping !== T.NoToneMapping) ren.toneMapping = T.NoToneMapping;
-                        pbBeg(6); ren.render(scene, cam); pbEnd(6);
-                    }
-                }
-                if (lyricsCtx && lyricsCanvas) {
-                    lyricsCtx.clearRect(0, 0, lyricsCanvas.width, lyricsCanvas.height);
-                    // Capture the actual lyrics-banner bottom so overlay cards
-                    // step down past every wrapped row, not just a 2-row estimate.
-                    let lyricsBottom = 0;
-                    if (bundle.lyricsVisible && bundle.lyrics?.length) {
-                        lyricsBottom = drawLyrics(bundle.lyrics, bundle.currentTime, lyricsCtx, lyricsCanvas.width, lyricsCanvas.height) || 0;
-                    }
-                    drawNotedetectLabels(lyricsCtx, lyricsCanvas.width, lyricsCanvas.height);
-                    drawScoreFx(lyricsCtx, lyricsCanvas.width, lyricsCanvas.height);
-
-                    // Corner-stacking: overlays drawn first claim the topmost slot;
-                    // later overlays are pushed down by the accumulated height + gap.
-                    // Draw order (top → bottom per corner):
-                    //   1. FPS counter  — always first
-                    //   2. Section HUD
-                    //   3. Tone HUD
-                    //   4. Chord diagram — always last
-                    const STACK_GAP = 8;
-                    const cornerStack = { tl: 0, tr: 0, bl: 0, br: 0 };
-                    const stackPush = (pos, h) => {
-                        if (pos in cornerStack && h > 0) cornerStack[pos] += h + STACK_GAP;
-                    };
-
-                    // 1. FPS counter (always top-right, always topmost).
-                    // EMA update runs unconditionally so the smoothed value is accurate
-                    // even when fpsVisible is off.
-                    const _fpsNowMs = performance.now();
-                    if (_fpsLastT > 0) {
-                        const dt = _fpsNowMs - _fpsLastT;
-                        if (dt > 0) {
-                            const inst = 1000 / dt;
-                            _fpsEma = _fpsEma === 0 ? inst : _fpsEma + (inst - _fpsEma) * (1 / 30);
-                        }
-                    }
-                    _fpsLastT = _fpsNowMs;
-                    if (fpsVisible) {
-                        if (_fpsNowMs - _fpsLastSampleT > 250) {
-                            _fpsDisplay = _fpsEma;
-                            _fpsLastSampleT = _fpsNowMs;
-                        }
-                        const W = lyricsCanvas.width;
-                        const H = lyricsCanvas.height;
-                        const txt = _fpsDisplay.toFixed(1) + ' fps';
-                        lyricsCtx.save();
-                        lyricsCtx.font = 'bold 14px ui-monospace, Menlo, Consolas, monospace';
-                        lyricsCtx.textAlign = 'right';
-                        lyricsCtx.textBaseline = 'top';
-                        const _fpsPadX = 8, _fpsPadY = 4;
-                        const _fpsMetrics = lyricsCtx.measureText(txt);
-                        const _fpsBoxW = Math.ceil(_fpsMetrics.width) + _fpsPadX * 2;
-                        const _fpsBoxH = 14 + _fpsPadY * 2;
-                        const _fpsE = 8;
-                        // Keep it top-right but below the v3 Up Next pill / live HUD
-                        // (whichever is showing) so the readout is never occluded.
-                        const _fpsBaseY = Math.round(Math.max(
-                            _fpsE + H * 0.06,
-                            lyricsBottom + _fpsE,
-                            _v3TopRightChromeBottom() + _fpsE,
-                        ));
-                        const _fpsX = W - 8 - _fpsBoxW;
-                        const _fpsY = _fpsBaseY + cornerStack['tr'];
-                        lyricsCtx.fillStyle = 'rgba(0,0,0,0.55)';
-                        lyricsCtx.fillRect(_fpsX, _fpsY, _fpsBoxW, _fpsBoxH);
-                        lyricsCtx.fillStyle = _fpsDisplay >= 55 ? '#7fff9a'
-                            : _fpsDisplay >= 30 ? '#ffe84d' : '#ff6b6b';
-                        lyricsCtx.fillText(txt, _fpsX + _fpsBoxW - _fpsPadX, _fpsY + _fpsPadY);
-                        lyricsCtx.restore();
-                        stackPush('tr', _fpsBoxH);
-                    }
-
-                    // 2. Section HUD.
-                    if (sectionHudVisible && bundle.sections && bundle.sections.length) {
-                        const secH = drawSectionHud(lyricsCtx, {
-                            sections: bundle.sections,
-                            currentTime: bundle.currentTime,
-                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
-                            position: sectionHudPosition,
-                            sizeSlider: sectionHudSize,
-                            lyricsBottom,
-                            stackOffset: cornerStack[sectionHudPosition] || 0,
-                        });
-                        stackPush(sectionHudPosition, secH);
-                    }
-
-                    // 3. Tone HUD.
-                    if (toneHudVisible && (bundle.toneChanges?.length || bundle.toneBase)) {
-                        const toneH = drawToneHud(lyricsCtx, {
-                            toneChanges: bundle.toneChanges,
-                            toneBase: bundle.toneBase,
-                            currentTime: bundle.currentTime,
-                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
-                            position: toneHudPosition,
-                            sizeSlider: toneHudSize,
-                            lyricsBottom,
-                            stackOffset: cornerStack[toneHudPosition] || 0,
-                        });
-                        stackPush(toneHudPosition, toneH);
-                    }
-
-                    // 4. Chord diagram — always last (bottommost in the stack).
-                    // Draw outgoing first so the incoming diagram renders on top,
-                    // making the entrance scale-in animation visible during crossfades.
-                    // The outgoing (prev) diagram uses the same corner slot — it is
-                    // fading out while the incoming one fades in, so they share the
-                    // same stack position and don't double-count the height.
-                    if (chordDiagramVisible && _diagPrev && _diagPrevOpacity > 0) {
-                        _drawDiagramCached(lyricsCtx, {
-                            name: _diagPrev.name, frets: _diagPrev.frets,
-                            opacity: _diagPrevOpacity,
-                            entranceT: (_diagPrev.t !== undefined)
-                                ? Math.min(1.0, Math.max(0, (bundle.currentTime - _diagPrev.t) / DIAG_ENTRANCE_S))
-                                : 1.0,
-                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
-                            inverted: _invertedCached,
-                            sizeSlider: chordDiagramSize, position: chordDiagramPosition,
-                            nStr: _diagPrev.nStr ?? nStr,
-                            lyricsBottom,
-                            stackOffset: cornerStack[chordDiagramPosition] || 0,
-                        });
-                        // Don't push here — outgoing and incoming share the same slot.
-                    }
-                    if (chordDiagramVisible && _diagChord) {
-                        const diagH = _drawDiagramCached(lyricsCtx, {
-                            name: _diagChord.name, frets: _diagChord.frets,
-                            opacity: Math.max(0, 1 + (_diagChord.t - bundle.currentTime) / DIAG_LINGER_S),
-                            entranceT: _diagEntranceT,
-                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
-                            inverted: _invertedCached,
-                            sizeSlider: chordDiagramSize, position: chordDiagramPosition,
-                            nStr: _diagChord.nStr ?? nStr,
-                            lyricsBottom,
-                            stackOffset: cornerStack[chordDiagramPosition] || 0,
-                        });
-                        stackPush(chordDiagramPosition, diagH);
-                    }
-                }
-                // Draw-hook compatibility: fire hooks registered via
-                // window.highway.addDrawHook() on our 2D overlay canvas
-                // so overlay plugins (fretboard, chord-label HUDs, etc.)
-                // continue to render when the 3D renderer is active.
-                // The hooks expect a 2D context — lyricsCtx is exactly
-                // that, positioned above the WebGL surface.
-                if (lyricsCtx && lyricsCanvas &&
-                        window.highway &&
-                        typeof window.highway.fireDrawHooks === 'function') {
-                    window.highway.fireDrawHooks(
-                        lyricsCtx, lyricsCanvas.width, lyricsCanvas.height
-                    );
-                }
-            },
-
-            resize(w, h) {
-                if (!_isReady) return;
-                const s = canvasSize(highwayCanvas);
-                applySize(s.w > 0 ? s.w : w, s.h > 0 ? s.h : h);
-            },
-
-            destroy() {
-                _destroyed = true; _isReady = false; _diagChord = null; _diagPrev = null; _diagLastKey = null; _diagRenderCache.clear();
-                _lastHwW = 0; _lastHwH = 0;
-                _appliedW = 0; _appliedH = 0;
-                _paneAspect = 0;
-                if (cam && cam.fov !== BASE_VFOV) { cam.fov = BASE_VFOV; cam.updateProjectionMatrix(); }
-                _wrapPinned = false;
-                _unsubscribeFocus(); teardown();
-                highwayCanvas = null;
-            },
-        };
-    }
-
-    window.feedBackViz_highway_3d = createFactory;
-    // Per-panel control descriptors (splitscreen). The palette selector was
-    // removed — per-string colors are set via the core "Highway String Colors"
-    // UI, which drives both highways by named string.
-    window.feedBackViz_highway_3d.panelControls = [
-        {
-            key: 'cameraSmoothing',
-            label: 'Camera smoothing (X-pan)',
-            type: 'range',
-            min: 0,
-            max: 1,
-            step: 0.05,
-            default: BG_DEFAULTS.cameraSmoothing,
-        },
-        {
-            key: 'cameraLockLow',
-            label: 'Lock camera at frets 1-12',
-            type: 'toggle',
-            default: BG_DEFAULTS.cameraLockLow,
-        },
-        {
-            key: 'cameraLockZoom',
-            label: 'Locked zoom (In ↔ Out)',
-            type: 'range',
-            min: 0,
-            max: 1,
-            step: 0.05,
-            default: BG_DEFAULTS.cameraLockZoom,
-        },
-    ];
-    // Static metadata exposed on the factory:
-    //   panelControls      - optional, host-readable descriptors for a
-    //                        curated per-panel control surface. Renderer
-    //                        values still flow through _bgLoadSettings().
-    //   contextType        - required canvas context type. highway.js
-    //                        replaces the <canvas> element when the
-    //                        requested type differs from the current one,
-    //                        so this renderer can be installed mid-session
-    //                        even if the canvas was previously bound to 2D.
-    //   matchesArrangement - Auto-mode predicate. When the picker is on
-    //                        "Auto", core installs the first registered
-    //                        viz whose predicate returns truthy on the
-    //                        current song_info. Lead/Rhythm/Bass/Guitar
-    //                        arrangements route here; Keys arrangements
-    //                        are matched by the piano plugin instead.
-    //                        _canRun3D() in app.js still gates Auto from
-    //                        picking us on machines without WebGL2.
-    window.feedBackViz_highway_3d.contextType = 'webgl2';
-    window.feedBackViz_highway_3d.__test = {
-        getAnalyserForBridgeTest: _bgGetAnalyser,
-        readBandsForBridgeTest: _bgReadBands,
-        resetAnalyserBridgeForTest() { _bgBridgeKeys.clear(); _bgAudio = null; _bgAudioCore = null; _bgAudioFailedAt = 0; },
-    };
-    // Canonical guitar arrangement names (server.py: _ALLOWED_ARRANGEMENT_NAMES)
-    // are Lead / Rhythm / Bass / Combo. `guitar` is included as a safety
-    // net for sources that use a generic name (older imports, third-party
-    // sloppaks). Word boundaries (\b) keep us from accidentally matching
-    // arrangements that merely contain these as substrings (e.g. a
-    // "BasslineKeys" arrangement would otherwise match `bass`).
-    window.feedBackViz_highway_3d.matchesArrangement = function (songInfo) {
-        const arr = (songInfo && songInfo.arrangement) || '';
-        return /\b(?:lead|rhythm|bass|combo|guitar)\b/i.test(arr);
-    };
-
-    // No imperative register() call needed: feedBack#272 introduced the
-    // consolidated tour menu, which discovers this plugin's tour automatically
-    // via /api/plugins (has_tour:true from plugin.json's tour field) and
-    // gates relevance on whether highway_3d is the active viz. A register()
-    // call with only injectTriggerInto was a no-op anyway since the new menu
-    // owns trigger placement; for buildSteps / onStart / onComplete / a
-    // custom screens override, register() is still the right hook.
-
-})();
+// 3D Highway visualization plugin — Three.js note highway.
+// Visual layer from joel's prototype (vibrant palette, glowing strings,
+// fret heat, dynamic lane, chord frame-boxes, per-note connector labels,
+// board projection, outline+core note meshes) adapted into the
+// feedBackViz setRenderer contract (feedBack#36) so it works in the
+// main player and per-panel in splitscreen without any architectural
+// changes.
+
+(function () {
+    'use strict';
+
+    /* ======================================================================
+     *  Constants
+     * ====================================================================== */
+
+    // Three.js is vendored under static/vendor/three/ in core (pinned r170 —
+    // see static/vendor/three/VERSION). The bundled plugin loads from the
+    // same origin to avoid the first-launch CDN round-trip and to pin the
+    // version against breakages from upstream Three.js drift.
+    const THREE_URL = '/static/vendor/three/three.module.min.js';
+    const THREE_CDN = 'https://cdn.jsdelivr.net/npm/three@0.170.0/build/three.module.min.js';
+
+    /* ── Butterchurn audio-reactive background ──────────────────────────
+     * Mounts a Butterchurn (WebGL MilkDrop) canvas BEHIND the transparent
+     * 3D highway. On desktop it's driven by the guitar/mic input (the song
+     * audio lives in JUCE, not the webview <audio>); in a browser it taps
+     * the song <audio> directly.
+     * ──────────────────────────────────────────────────────────────────── */
+    const BC_VENDOR = '/api/plugins/highway_3d/assets/vendor/';
+    const BC_FRAME = 1024;
+    const BC_WORKLET = '/api/plugins/highway_3d/assets/viz-worklet.js';
+    const _bcMeters = { gtr: 0, song: 0 }; // live levels shown in the panel readout
+    const BC_BTN = 'background:rgba(255,255,255,.09);color:#cfe3ff;border:1px solid rgba(255,255,255,.16);border-radius:5px;padding:3px 8px;cursor:pointer;font:12px system-ui';
+    let _bcLoading = null;
+    function _bcLoadLib() {
+        if (_bcLoading) return _bcLoading;
+        _bcLoading = new Promise((resolve, reject) => {
+            const add = (url, next) => {
+                const s = document.createElement('script');
+                s.src = url; s.async = true;
+                s.onload = next; s.onerror = () => reject(new Error('load ' + url));
+                document.head.appendChild(s);
+            };
+            add(BC_VENDOR + 'butterchurn.min.js', () =>
+                add(BC_VENDOR + 'butterchurnPresets.min.js', resolve));
+        });
+        // Don't cache a rejected promise: a transient load failure (network
+        // hiccup, blocked request) must not permanently disable the feature for
+        // the session. Clearing _bcLoading lets the next mount retry the load.
+        _bcLoading.catch(() => { _bcLoading = null; });
+        return _bcLoading;
+    }
+    function _bcResolve() { let b = window.butterchurn; if (b && b.default) b = b.default; return b; }
+    function _bcPresets() { let p = window.butterchurnPresets; if (p && p.default) p = p.default; return p; }
+    function _bcIsDesktop() {
+        const d = window.feedBackDesktop || window.slopsmithDesktop;
+        return !!(d && d.isDesktop && d.audio && typeof d.audio.getRawAudioFrame === 'function');
+    }
+    // Fast-forward an index to the first entry after time `ct` (used on seek/loop).
+    // Position at the first entry whose time is >= ct (strict <), so an event
+    // landing exactly on the seek/loop target time is still fired by the update
+    // walkers (which consume `<= ct`) instead of being skipped past here.
+    function _bcFfIdx(arr, ct, key) { if (!arr) return 0; let i = 0; while (i < arr.length && (arr[i][key] || 0) < ct) i++; return i; }
+    // Force-free a canvas's WebGL context so the GPU resources are released
+    // immediately instead of lingering until GC — repeated Butterchurn
+    // mount/unmount cycles otherwise pile up live contexts toward the browser cap.
+    function _bcReleaseCanvasGL(canvas) {
+        if (!canvas || typeof canvas.getContext !== 'function') return;
+        let gl = null;
+        try { gl = canvas.getContext('webgl2') || canvas.getContext('webgl'); } catch (e) { gl = null; }
+        if (!gl || typeof gl.getExtension !== 'function') return;
+        try { const lose = gl.getExtension('WEBGL_lose_context'); if (lose) lose.loseContext(); } catch (e) {}
+    }
+
+    // Desktop: bridge GUITAR input PCM + SONG output level into a Web Audio node
+    // Butterchurn can tap. Guitar gives spectral texture from your playing; the
+    // song's output meter (getLevels) injects an energy pulse so the visuals also
+    // react to the backing track (JUCE plays it — there's no song PCM to FFT).
+    function _bcGuitarFeed(actx, onReady) {
+        const latest = new Float32Array(BC_FRAME);
+        let polling = true, songLevel = 0, chartLevel = 0;
+        let node = null, sp = null, silent = null;
+        const api = (window.feedBackDesktop || window.slopsmithDesktop).audio;
+        const gainNow = () => (_bcLoadSettings().guitarGain) || 6;
+
+        // Keep the source node processing (silently — JUCE already monitors the
+        // guitar), and hand it to Butterchurn via the onReady callback.
+        function attach(srcNode) {
+            silent = actx.createGain(); silent.gain.value = 0;
+            srcNode.connect(silent); silent.connect(actx.destination);
+            try { if (onReady) onReady(srcNode); } catch (e) {}
+        }
+        // Fallback for contexts without AudioWorklet support.
+        function useScriptProcessor() {
+            let phase = 0, phase2 = 0;
+            const TWO_PI = Math.PI * 2;
+            const oscStep = TWO_PI * (90 / actx.sampleRate);
+            const oscStep2 = TWO_PI * (520 / actx.sampleRate);
+            sp = actx.createScriptProcessor(BC_FRAME, 1, 1);
+            sp.onaudioprocess = (e) => {
+                const out = e.outputBuffer.getChannelData(0);
+                const n = Math.min(out.length, latest.length);
+                const lvl = songLevel, clvl = chartLevel, gg = gainNow();
+                for (let i = 0; i < out.length; i++) {
+                    const g = (i < n ? latest[i] : 0) * gg;
+                    const song = lvl * (0.7 * Math.sin(phase) + 0.3 * (Math.random() * 2 - 1)) * 1.4;
+                    const chart = clvl * (0.5 * Math.sin(phase2) + 0.5 * (Math.random() * 2 - 1)) * 1.5;
+                    phase += oscStep; if (phase > TWO_PI) phase -= TWO_PI;
+                    phase2 += oscStep2; if (phase2 > TWO_PI) phase2 -= TWO_PI;
+                    const v = g + song + chart;
+                    out[i] = v > 1 ? 1 : (v < -1 ? -1 : v);
+                }
+            };
+            attach(sp);
+            console.log('[viz3d] audio feed: ScriptProcessor (fallback)');
+        }
+
+        // Preferred path: AudioWorklet (runs off the main thread).
+        if (actx.audioWorklet && typeof actx.audioWorklet.addModule === 'function' && typeof AudioWorkletNode === 'function') {
+            actx.audioWorklet.addModule(BC_WORKLET).then(() => {
+                if (!polling || sp) return;
+                node = new AudioWorkletNode(actx, 'viz-feed', { numberOfInputs: 0, numberOfOutputs: 1, outputChannelCount: [1] });
+                attach(node);
+                console.log('[viz3d] audio feed: AudioWorklet');
+            }).catch((e) => {
+                console.warn('[viz3d] AudioWorklet unavailable, using ScriptProcessor:', e && e.message);
+                if (polling && !sp && !node) useScriptProcessor();
+            });
+        } else {
+            useScriptProcessor();
+        }
+
+        // Guitar PCM poll → waveform + level meter (+ pushed to the worklet).
+        (function pcmLoop() {
+            if (!polling) return;
+            Promise.resolve(api.getRawAudioFrame(BC_FRAME)).then((f) => {
+                if (f && f.length) {
+                    if (f.length >= BC_FRAME) latest.set(f.subarray(0, BC_FRAME));
+                    else { latest.fill(0); latest.set(f); }
+                    let s = 0; for (let i = 0; i < BC_FRAME; i++) s += latest[i] * latest[i];
+                    _bcMeters.gtr = Math.sqrt(s / BC_FRAME) * gainNow();
+                    if (node) node.port.postMessage({ frame: latest.slice(0), song: songLevel, chart: chartLevel, gain: gainNow() });
+                }
+            }).catch(() => {}).then(() => { if (polling) setTimeout(pcmLoop, 16); });
+        })();
+        // Song output meter poll → music energy pulse.
+        (function levelLoop() {
+            if (!polling) return;
+            Promise.resolve(api.getLevels && api.getLevels()).then((L) => {
+                if (L && typeof L.outputLevel === 'number') {
+                    songLevel = Math.min(1, L.outputLevel * ((_bcLoadSettings().songGain) || 1.8));
+                    _bcMeters.song = songLevel;
+                    if (node) node.port.postMessage({ song: songLevel, chart: chartLevel, gain: gainNow() });
+                }
+            }).catch(() => {}).then(() => { if (polling) setTimeout(levelLoop, 40); });
+        })();
+
+        return {
+            setChart(v) { chartLevel = v; },
+            stop() {
+                polling = false;
+                try { if (sp) { sp.disconnect(); sp.onaudioprocess = null; } } catch (e) {}
+                try { if (node) node.disconnect(); } catch (e) {}
+                try { if (silent) silent.disconnect(); } catch (e) {}
+            }
+        };
+    }
+    // Browser audio is sourced by REUSING the highway's own shared analyser
+    // (the same #audio / stems side-chain tap the fog scenery uses), passed in
+    // as `audioProvider` to _bcCreateController. We deliberately do NOT open a
+    // second createMediaElementSource on #audio here: it can only be called
+    // once per element (a second tap throws InvalidStateError and permanently
+    // disables the other consumer), it would route the song through a fresh,
+    // possibly-suspended context and mute playback, and it would miss the stems
+    // side-chain that sloppaks expose at window.feedBack.stems.getAnalyser().
+    /* ── Controls + readability (localStorage-backed, global config) ───── */
+    const BC_LS = 'viz3d_settings';
+    const BC_DEFAULTS = { enabled: true, opacity: 1.0, laneDim: true, laneDimStrength: 0.45, chartAccents: true, colorTint: true, chartStrength: 1.0, tintStrength: 0.65, guitarGain: 6, songGain: 1.8, cyclePool: 'all', hold: false };
+    let _bcSettings = null;
+    function _bcLoadSettings() {
+        if (_bcSettings) return _bcSettings;
+        let saved = {};
+        try { saved = JSON.parse(localStorage.getItem(BC_LS) || '{}'); } catch (e) {}
+        _bcSettings = Object.assign({}, BC_DEFAULTS, saved);
+        return _bcSettings;
+    }
+    function _bcSaveSettings() { try { localStorage.setItem(BC_LS, JSON.stringify(_bcSettings)); } catch (e) {} }
+    const _bcControllers = new Set();
+    function _bcApplyAll() { _bcControllers.forEach((c) => { try { c.applySettings(); } catch (e) {} }); }
+    // Live-apply hook for the plugin's settings.html. The visualizer's on/off +
+    // slider controls now live in the standard settings panel (settings.html),
+    // which persists them into the BC_LS blob and then calls this so a mounted
+    // highway re-reads and applies them immediately. Defined on window at module
+    // scope so it's available regardless of whether a highway is mounted yet;
+    // settings.html guards the call with `?.` for the not-yet-loaded case.
+    window.h3dBcApplySettings = function () {
+        _bcSettings = null;        // drop the cache so the next read reloads from localStorage
+        _bcLoadSettings();
+        _bcApplyAll();
+        try { _bcUpdatePanelPreset(); } catch (e) {}
+    };
+
+    // Preset curation: favorites / bans (persisted globally) + the "primary"
+    // controller the panel's preset buttons drive.
+    // Seeded once on first run (reputation-based starter set; user can edit freely).
+    const BC_DEFAULT_FAVORITES = [
+        'Flexi, martin + geiss - dedicated to the sherwin maxawow',
+        'Geiss - Reaction Diffusion 2',
+        'Geiss - Spiral Artifact',
+        'Flexi + Martin - cascading decay swing',
+        'Flexi - mindblob [shiny mix]',
+        'Geiss - Cauldron - painterly 2 (saturation remix)',
+        'Zylot - Paint Spill (Music Reactive Paint Mix)',
+        'Flexi - predator-prey-spirals',
+        'Rovastar + Loadus + Geiss - FractalDrop (Triple Mix)',
+        'Flexi, fishbrain, Geiss + Martin - tokamak witchery',
+    ];
+    const BC_DEFAULT_BANS = [
+        'martin - mucus cervix',
+        'Goody - The Wild Vort',
+        'martin - extreme heat',
+        'Unchained - Rewop',
+        'high-altitude basket unraveling - singh grooves nitrogen argon nz+',
+        '$$$ Royal - Mashup (197)',
+        '$$$ Royal - Mashup (431)',
+        'suksma - uninitialized variabowl (hydroponic chronic)',
+        'shifter - dark tides bdrv mix 2',
+        '_Mig_049',
+    ];
+    const _bcFavorites = new Set();
+    const _bcBanned = new Set();
+    let _bcListsLoaded = false;
+    function _bcLoadLists() {
+        if (_bcListsLoaded) return; _bcListsLoaded = true;
+        try { (JSON.parse(localStorage.getItem('viz3d_favorites') || '[]') || []).forEach((n) => _bcFavorites.add(n)); } catch (e) {}
+        try { (JSON.parse(localStorage.getItem('viz3d_banned') || '[]') || []).forEach((n) => _bcBanned.add(n)); } catch (e) {}
+        let seeded = false;
+        try { seeded = !!localStorage.getItem('viz3d_seeded'); } catch (e) {}
+        if (!seeded) {
+            BC_DEFAULT_FAVORITES.forEach((n) => _bcFavorites.add(n));
+            BC_DEFAULT_BANS.forEach((n) => _bcBanned.add(n));
+            try { localStorage.setItem('viz3d_seeded', '1'); } catch (e) {}
+            _bcSaveLists();
+        }
+    }
+    function _bcSaveLists() {
+        try { localStorage.setItem('viz3d_favorites', JSON.stringify([..._bcFavorites])); } catch (e) {}
+        try { localStorage.setItem('viz3d_banned', JSON.stringify([..._bcBanned])); } catch (e) {}
+    }
+    // Re-add the bundled defaults anytime (merges; a default-fav un-bans, a default-ban un-favs).
+    function _bcRestoreDefaults() {
+        BC_DEFAULT_FAVORITES.forEach((n) => { _bcBanned.delete(n); _bcFavorites.add(n); });
+        BC_DEFAULT_BANS.forEach((n) => { _bcFavorites.delete(n); _bcBanned.add(n); });
+        try { localStorage.setItem('viz3d_seeded', '1'); } catch (e) {}
+        _bcSaveLists(); _bcUpdatePanelPreset(); _bcRenderList();
+    }
+    let _bcPrimary = null;
+    let _bcPane = null, _bcListEl = null, _bcFilterEl = null, _bcPaneOpen = false, _bcCollapsed = false;
+
+    function _bcStatusMark(name) {
+        return _bcFavorites.has(name) ? '★ ' : (_bcBanned.has(name) ? '🚫 ' : '');
+    }
+    function _bcSetHold(v) {
+        const s = _bcLoadSettings();
+        s.hold = !!v; _bcSaveSettings();
+        const b = _bcPanel && _bcPanel.querySelector('#vz-hold');
+        if (b) b.textContent = s.hold ? '▶ Resume' : '⏸ Hold';
+    }
+    // Drives both panels off the right edge. Order when both open (L→R):
+    //   visualizer panel → preset pane → window edge. Pane lives off-screen by
+    //   default; opening it shoves the panel LEFT to make room.
+    function _bcLayout() {
+        if (_bcPanel) {
+            let tx = 0;
+            if (_bcCollapsed) tx = 210;        // tuck the whole panel off the right edge
+            else if (_bcPaneOpen) tx = -248;   // slide panel LEFT to make room for the pane
+            _bcPanel.style.transform = 'translateX(' + tx + 'px) translateY(-50%)';
+        }
+        if (_bcPane) {
+            _bcPane.style.transform = (_bcPaneOpen && !_bcCollapsed) ? 'translateX(0) translateY(-50%)' : 'translateX(calc(100% + 16px)) translateY(-50%)';
+        }
+    }
+    function _bcSetPane(open) {
+        _bcPaneOpen = !!open && !_bcCollapsed;
+        const b = _bcPanel && _bcPanel.querySelector('#vz-listbtn');
+        if (b) b.textContent = _bcPaneOpen ? '>>' : '<<';
+        if (_bcPaneOpen) _bcRenderList();
+        _bcLayout();
+    }
+    function _bcRenderList() {
+        if (!_bcListEl) return;
+        const ctrl = _bcPrimary;
+        const keys = (ctrl && ctrl.keys) ? ctrl.keys : [];
+        const filt = ((_bcFilterEl && _bcFilterEl.value) || '').toLowerCase();
+        const cur = ctrl && ctrl.curName;
+        const frag = document.createDocumentFragment();
+        for (let i = 0; i < keys.length; i++) {
+            const name = keys[i];
+            if (filt && name.toLowerCase().indexOf(filt) === -1) continue;
+            const row = document.createElement('div');
+            row.textContent = _bcStatusMark(name) + name;
+            row.title = name;
+            row.style.cssText = 'padding:3px 7px;border-radius:4px;cursor:pointer;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;font-size:11px;' +
+                (name === cur ? 'background:rgba(110,160,255,.28);' : '') + (_bcBanned.has(name) ? 'opacity:.55;' : '');
+            row.addEventListener('click', () => {
+                if (!_bcPrimary) return;
+                _bcPrimary.loadByName(name, 1.0);
+                _bcSetHold(true); // picked from the list → sit on it
+            });
+            frag.appendChild(row);
+        }
+        _bcListEl.innerHTML = '';
+        _bcListEl.appendChild(frag);
+    }
+    function _bcUpdatePanelPreset() {
+        if (!_bcPanel) return;
+        const name = _bcPrimary ? (_bcPrimary.curName || null) : null;
+        const nameEl = _bcPanel.querySelector('#vz-pname');
+        const favBtn = _bcPanel.querySelector('#vz-fav');
+        const banBtn = _bcPanel.querySelector('#vz-ban');
+        const cntEl = _bcPanel.querySelector('#vz-pcount');
+        if (nameEl) { nameEl.textContent = (name ? _bcStatusMark(name) : '') + (name || '—'); nameEl.title = name ? (name + ' — click for full list') : ''; }
+        if (favBtn) favBtn.textContent = (name && _bcFavorites.has(name)) ? '★ Favorited' : '☆ Favorite';
+        if (banBtn) banBtn.textContent = (name && _bcBanned.has(name)) ? '🚫 Banned' : '🚫 Ban';
+        if (cntEl) cntEl.textContent = '★ ' + _bcFavorites.size + '   🚫 ' + _bcBanned.size;
+        if (_bcPaneOpen) _bcRenderList();
+    }
+
+    let _bcPanel = null, _bcPanelKeyBound = false;
+    function _bcEnsurePanel(host) {
+        if (_bcPanel && _bcPanel.isConnected) {
+            // Singleton panel: follow the active highway. If it's still parented
+            // to a different wrap (e.g. another mounted highway instance such as
+            // Virtuoso's embedded one), move it — and the pane — to this wrap so
+            // it appears on whichever highway is currently on-screen.
+            if (host && _bcPanel.parentNode !== host) {
+                host.appendChild(_bcPanel);
+                if (_bcPane) host.appendChild(_bcPane);
+            }
+            return _bcPanel;
+        }
+        const s = _bcLoadSettings();
+        const p = document.createElement('div');
+        p.id = 'viz3d-panel';
+        p.style.cssText = 'position:absolute;top:50%;right:10px;z-index:100000;pointer-events:auto;font:12px/1.45 system-ui,sans-serif;' +
+            'color:#cfe3ff;background:rgba(8,10,20,0.82);padding:9px 11px;border-radius:8px;width:186px;' +
+            'box-shadow:0 2px 12px rgba(0,0,0,0.5);user-select:none;transition:transform 0.28s ease;';
+        p.innerHTML =
+            '<div style="display:flex;align-items:center;justify-content:space-between;margin-bottom:7px"><span style="font-weight:600">🌀 Visualizer</span><button id="vz-listbtn" title="Show / hide full preset list" style="' + BC_BTN + ';padding:1px 7px">&lt;&lt;</button></div>' +
+            // On/off + opacity/dim/chart/tint/gain controls now live in the
+            // plugin's Settings panel (settings.html). This in-canvas panel is
+            // only the LIVE preset browser (pick / favorite / ban / cycle).
+            '<div style="opacity:.55;font-size:11px;margin:2px 0 6px">Background &amp; reactivity options are in Settings ▸ 3D Highway.</div>' +
+            '<div style="display:flex;align-items:center;gap:6px;margin:4px 0">' +
+              '<button id="vz-prev" style="' + BC_BTN + '">◀</button>' +
+              '<div id="vz-pname" style="flex:1;text-align:center;font-size:11px;opacity:.9;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;cursor:pointer" title="">—</div>' +
+              '<button id="vz-next" style="' + BC_BTN + '">▶</button>' +
+            '</div>' +
+            '<div style="display:flex;gap:6px;margin:4px 0">' +
+              '<button id="vz-fav" style="' + BC_BTN + ';flex:1">♡ Favorite</button>' +
+              '<button id="vz-ban" style="' + BC_BTN + ';flex:1">🚫 Ban</button>' +
+            '</div>' +
+            '<div style="display:flex;gap:6px;align-items:flex-end;margin:6px 0">' +
+              '<label style="flex:1">Cycle <select id="vz-cyc" style="width:100%;background:#11141f;color:#cfe3ff;border:1px solid rgba(255,255,255,.15);border-radius:5px;padding:3px"><option value="all">All</option><option value="favorites">Favorites</option><option value="bans">Bans</option></select></label>' +
+              '<button id="vz-hold" style="' + BC_BTN + '">⏸ Hold</button>' +
+            '</div>' +
+            '<div style="margin:5px 0 4px;font-size:11px;opacity:.75"><span id="vz-pcount">★ 0   🚫 0</span></div>' +
+            '<div id="vz-meter" style="opacity:.65;margin-top:6px;font:11px/1.3 monospace">gtr —  ·  song —</div>' +
+            '<div style="opacity:.45;margin-top:4px;font-size:11px">` or ‹‹ to hide</div>';
+        (host || document.body).appendChild(p);
+
+        // Slide handle (<< / >>) so the panel can tuck off the right edge and stop
+        // covering the Now / Up-Next labels.
+        const tab = document.createElement('button');
+        tab.textContent = '>>';
+        tab.title = 'Hide / show controls';
+        tab.style.cssText = 'position:absolute;top:6px;left:-23px;width:23px;height:28px;border:none;cursor:pointer;' +
+            'background:rgba(8,10,20,0.82);color:#cfe3ff;border-radius:7px 0 0 7px;font:12px/1 monospace;padding:0;';
+        p.appendChild(tab);
+        tab.addEventListener('click', () => {
+            _bcCollapsed = !_bcCollapsed;
+            if (_bcCollapsed) _bcPaneOpen = false; // collapsing the panel hides the pane too
+            tab.textContent = _bcCollapsed ? '<<' : '>>';
+            const lb = p.querySelector('#vz-listbtn'); if (lb) lb.textContent = _bcPaneOpen ? '>>' : '<<';
+            _bcLayout();
+        });
+
+        // Sliding preset-list pane (sits to the LEFT of the control panel)
+        const pane = document.createElement('div');
+        pane.id = 'viz3d-listpane';
+        pane.style.cssText = 'position:absolute;top:50%;right:10px;z-index:99999;pointer-events:auto;width:236px;max-height:74vh;display:flex;flex-direction:column;' +
+            'background:rgba(8,10,20,0.93);border-radius:8px;box-shadow:0 2px 14px rgba(0,0,0,0.55);color:#cfe3ff;' +
+            'font:12px system-ui,sans-serif;overflow:hidden;transform:translateX(calc(100% + 16px)) translateY(-50%);transition:transform 0.28s ease;';
+        pane.innerHTML =
+            '<div style="display:flex;align-items:center;justify-content:space-between;padding:7px 9px 7px 10px;font-weight:600;border-bottom:1px solid rgba(255,255,255,.1)"><span>Presets</span><button id="vz-defaults" title="Restore the bundled default favorites + bans" style="' + BC_BTN + ';font-weight:400">↺ defaults</button></div>' +
+            '<input id="vz-filter" placeholder="filter…" spellcheck="false" style="margin:8px 9px 6px;padding:4px 7px;background:#11141f;color:#cfe3ff;border:1px solid rgba(255,255,255,.15);border-radius:5px;outline:none">' +
+            '<div id="vz-list" style="overflow-y:auto;padding:0 4px 8px"></div>';
+        (host || document.body).appendChild(pane);
+        _bcPane = pane;
+        _bcListEl = pane.querySelector('#vz-list');
+        _bcFilterEl = pane.querySelector('#vz-filter');
+        _bcFilterEl.addEventListener('input', _bcRenderList);
+        pane.querySelector('#vz-defaults').addEventListener('click', _bcRestoreDefaults);
+
+        const q = (id) => p.querySelector(id);
+        _bcPanel = p;
+
+        // Preset curation wiring (favorites / bans / cycle / reset)
+        _bcLoadLists();
+        const cyc = q('#vz-cyc');
+        cyc.value = s.cyclePool || 'all';
+        // Read fresh: settings.html writes can replace _bcSettings, so the `s`
+        // captured at panel creation may be stale by the time this fires.
+        cyc.addEventListener('change', () => { _bcLoadSettings().cyclePool = cyc.value; _bcSaveSettings(); });
+        _bcSetHold(!!s.hold); // sync the Hold button label to the saved state
+        q('#vz-hold').addEventListener('click', () => _bcSetHold(!_bcLoadSettings().hold));
+        q('#vz-listbtn').addEventListener('click', () => _bcSetPane(!_bcPaneOpen));
+        q('#vz-pname').addEventListener('click', () => _bcSetPane(!_bcPaneOpen));
+        q('#vz-prev').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.step(-1); });
+        q('#vz-next').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.step(1); });
+        q('#vz-fav').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.toggleFav(); });
+        q('#vz-ban').addEventListener('click', () => { if (_bcPrimary) _bcPrimary.banCur(); });
+        _bcSetPane(false); // start collapsed; sets the list-button label
+        _bcUpdatePanelPreset();
+
+        // Live level readout — proves the song (not just guitar) is driving things.
+        // Self-stops when the panel is removed (_bcPanel !== p).
+        (function meterLoop() {
+            if (_bcPanel !== p) return;
+            const m = p.querySelector('#vz-meter');
+            if (m) m.textContent = 'gtr ' + _bcMeters.gtr.toFixed(2) + '  ·  song ' + _bcMeters.song.toFixed(2);
+            setTimeout(meterLoop, 150);
+        })();
+
+        if (!_bcPanelKeyBound) {
+            _bcPanelKeyBound = true;
+            window.addEventListener('keydown', (e) => {
+                if (e.key !== '`' || e.metaKey || e.ctrlKey || !_bcPanel) return;
+                const tag = (e.target && e.target.tagName) || '';
+                if (tag === 'INPUT' || tag === 'TEXTAREA') return;
+                const reveal = _bcPanel.style.display === 'none';
+                _bcPanel.style.display = reveal ? '' : 'none';
+                if (_bcPane) _bcPane.style.display = reveal ? '' : 'none';
+            });
+        }
+        return _bcPanel;
+    }
+
+    // Create a Butterchurn background controller bound to a wrap element.
+    function _bcCreateController(wrap, sizeProvider, audioProvider) {
+        const ctrl = { viz: null, actx: null, guitar: null, map: null, keys: [], cycle: 0, dead: false, lastW: -1, lastH: -1, canvas: null, backdrop: null, scrim: null, tint: null, wrap: wrap };
+        // Layered DOM in the wrap, all BEHIND the transparent 3D highway:
+        //   backdrop(z-4 dark) → bc canvas(z-3) → tint(z-2 instrument color) → scrim(z-1 lane dim)
+        const mkLayer = (cls, css) => { const d = document.createElement('div'); d.className = cls; d.style.cssText = css; wrap.appendChild(d); return d; };
+        const backdrop = mkLayer('viz3d-backdrop', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-4;background:#070710;pointer-events:none;');
+        const canvas = document.createElement('canvas');
+        canvas.className = 'viz3d-bc';
+        canvas.style.cssText = 'position:absolute;top:0;left:0;z-index:-3;pointer-events:none;';
+        wrap.appendChild(canvas);
+        const tint = mkLayer('viz3d-tint', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-2;pointer-events:none;mix-blend-mode:overlay;background:transparent;');
+        const scrim = mkLayer('viz3d-scrim', 'position:absolute;top:0;left:0;right:0;bottom:0;z-index:-1;pointer-events:none;');
+        ctrl.canvas = canvas; ctrl.backdrop = backdrop; ctrl.scrim = scrim; ctrl.tint = tint;
+
+        ctrl.applySettings = function () {
+            const s = _bcLoadSettings();
+            canvas.style.display = s.enabled ? '' : 'none';
+            canvas.style.opacity = String(s.enabled ? s.opacity : 0);
+            if (s.laneDim) {
+                const a = Math.max(0, Math.min(1, s.laneDimStrength)).toFixed(3);
+                scrim.style.display = '';
+                scrim.style.background = 'linear-gradient(to right, rgba(0,0,0,0) 0%, rgba(0,0,0,' + a +
+                    ') 30%, rgba(0,0,0,' + a + ') 70%, rgba(0,0,0,0) 100%)';
+            } else {
+                scrim.style.display = 'none';
+            }
+        };
+
+        // ── Preset curation (favorites / bans / cycle mode) ──
+        ctrl.curName = null; ctrl.lastManual = 0;
+        ctrl.allList = () => (ctrl.keys || []).filter((k) => !_bcBanned.has(k));
+        ctrl.pool = () => {
+            const mode = _bcLoadSettings().cyclePool || 'all';
+            if (mode === 'bans') return (ctrl.keys || []).filter((k) => _bcBanned.has(k));
+            if (mode === 'favorites') {
+                const f = (ctrl.keys || []).filter((k) => _bcFavorites.has(k) && !_bcBanned.has(k));
+                if (f.length) return f;
+            }
+            return ctrl.allList();
+        };
+        ctrl.browseArr = () => ctrl.keys || []; // ◀▶ and the list pane walk the full preset list
+        ctrl.loadByName = (name, blend) => {
+            if (!ctrl.viz || !name || !ctrl.map || !ctrl.map[name]) return;
+            try { ctrl.viz.loadPreset(ctrl.map[name], blend || 0); ctrl.curName = name; } catch (e) {}
+            _bcUpdatePanelPreset();
+        };
+        ctrl.autoTick = () => {
+            if (ctrl.dead || _bcLoadSettings().hold) return;
+            if (performance.now() - ctrl.lastManual < 8000) return;
+            const pool = ctrl.pool();
+            if (!pool.length) return;
+            let name = pool[(Math.random() * pool.length) | 0];
+            if (pool.length > 1 && name === ctrl.curName) name = pool[(pool.indexOf(name) + 1) % pool.length];
+            ctrl.loadByName(name, 2.7);
+        };
+        ctrl.step = (dir) => {
+            const list = ctrl.browseArr();
+            if (!list.length) return;
+            let i = list.indexOf(ctrl.curName); if (i < 0) i = (dir > 0 ? -1 : 0);
+            i = (i + dir + list.length) % list.length;
+            ctrl.lastManual = performance.now();
+            ctrl.loadByName(list[i], 1.5);
+        };
+        ctrl.toggleFav = () => {
+            if (!ctrl.curName) return;
+            if (_bcFavorites.has(ctrl.curName)) _bcFavorites.delete(ctrl.curName);
+            else { _bcFavorites.add(ctrl.curName); _bcBanned.delete(ctrl.curName); }
+            _bcSaveLists(); _bcUpdatePanelPreset();
+        };
+        ctrl.banCur = () => {
+            if (!ctrl.curName) return;
+            if (_bcBanned.has(ctrl.curName)) {           // un-ban (two-way) — stay on it
+                _bcBanned.delete(ctrl.curName);
+                _bcSaveLists(); _bcUpdatePanelPreset();
+            } else {                                     // ban + advance off it
+                _bcBanned.add(ctrl.curName); _bcFavorites.delete(ctrl.curName);
+                _bcSaveLists(); ctrl.step(1);
+            }
+        };
+        _bcPrimary = ctrl;
+
+        _bcControllers.add(ctrl);
+        _bcEnsurePanel(wrap);
+        ctrl.applySettings();
+
+        _bcLoadLib().then(() => {
+            if (ctrl.dead) return;
+            const bc = _bcResolve();
+            if (!bc || typeof bc.createVisualizer !== 'function') { console.warn('[viz3d] Butterchurn global missing'); return; }
+            const Ctx = window.AudioContext || window.webkitAudioContext;
+            const sz = (sizeProvider && sizeProvider()) || { w: 1280, h: 720 };
+            // Browser (Docker/web app): REUSE the highway's existing shared
+            // analyser (the fog scenery's #audio / stems tap) via audioProvider,
+            // and build Butterchurn on that SAME AudioContext so connectAudio()
+            // doesn't fail cross-context. Desktop uses its own context fed by the
+            // guitar/mic input. `ownsActx` tracks whether WE created the context
+            // (so destroy() closes only contexts we own, never the shared one).
+            const fogAudio = _bcIsDesktop() ? null : (audioProvider ? audioProvider() : null);
+            ctrl.ownsActx = !(fogAudio && fogAudio.ctx);
+            ctrl.actx = (fogAudio && fogAudio.ctx) || new Ctx();
+            if (ctrl.actx.state === 'suspended' && ctrl.actx.resume) ctrl.actx.resume().catch(() => {});
+            // Seed the DRAWING BUFFER (canvas.width/height) to the device-pixel
+            // render size and report that SAME size to Butterchurn. Its on-screen
+            // pass viewports to the reported size but never sizes the output canvas
+            // itself — leaving the buffer at the 300x150 default blits the whole
+            // visualizer into a corner that CSS then stretches across the highway.
+            // pixelRatio:1 because DPR is now folded into the reported size, so
+            // buffer == viewport == internal texsize (no double-counting).
+            const _bcRatio0 = Math.min(window.devicePixelRatio || 1, 1.5);
+            const _bcW0 = Math.max(1, Math.round((sz.w || 1280) * _bcRatio0));
+            const _bcH0 = Math.max(1, Math.round((sz.h || 720) * _bcRatio0));
+            canvas.width = _bcW0; canvas.height = _bcH0;
+            ctrl.viz = bc.createVisualizer(ctrl.actx, canvas, {
+                width: _bcW0, height: _bcH0,
+                pixelRatio: 1, textureRatio: 1,
+            });
+            if (_bcIsDesktop()) {
+                try {
+                    ctrl.guitar = _bcGuitarFeed(ctrl.actx, (srcNode) => { try { if (ctrl.viz) ctrl.viz.connectAudio(srcNode); } catch (e) {} });
+                    console.log('[viz3d] bg: feeding GUITAR input into Butterchurn');
+                } catch (e) { console.warn('[viz3d] guitar feed failed', e); }
+            } else if (fogAudio && fogAudio.analyser) {
+                // The shared AnalyserNode is a passthrough — connecting it onward
+                // to Butterchurn's internal analyser doesn't disturb the fog's reads.
+                try { ctrl.viz.connectAudio(fogAudio.analyser); console.log('[viz3d] browser: Butterchurn tapping shared analyser (' + (fogAudio.source || 'core') + ')'); }
+                catch (e) { console.warn('[viz3d] shared-analyser connect failed', e); }
+            }
+            _bcLoadLists();
+            const presets = _bcPresets();
+            if (presets && typeof presets.getPresets === 'function') { ctrl.map = presets.getPresets(); ctrl.keys = Object.keys(ctrl.map); }
+            const pool0 = ctrl.pool();
+            ctrl.loadByName(pool0.length ? pool0[(Math.random() * pool0.length) | 0] : (ctrl.keys[0] || null), 0.0);
+            ctrl.cycle = setInterval(() => ctrl.autoTick(), 30000);
+            ctrl.connectedAnalyser = (fogAudio && fogAudio.analyser) || null;
+            console.log('[viz3d] Butterchurn ready, presets:', ctrl.keys.length);
+        }).catch((e) => {
+            // Async init failed (lib load, WebGL/context creation, etc.). Clean up
+            // the half-mounted controller so we don't leak an owned AudioContext /
+            // DOM layers, and mark it dead so _bcSyncMode can retry on a later
+            // mount instead of seeing a live-looking but non-functional bcCtrl.
+            console.error('[viz3d] Butterchurn load/init failed', e);
+            try { _bcReleaseCanvasGL(ctrl.canvas); } catch (_) {}
+            try { if (ctrl.guitar) { ctrl.guitar.stop(); ctrl.guitar = null; } } catch (_) {}
+            try { [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => { if (el && el.parentNode) el.parentNode.removeChild(el); }); } catch (_) {}
+            if (ctrl.ownsActx && ctrl.actx && typeof ctrl.actx.close === 'function') { try { ctrl.actx.close(); } catch (_) {} }
+            ctrl.actx = null; ctrl.viz = null; ctrl.dead = true;
+            _bcControllers.delete(ctrl);
+        });
+        // Size the Butterchurn output: set the canvas DRAWING BUFFER to the
+        // device-pixel render size AND report that same size, so buffer ==
+        // on-screen viewport == full fill. Butterchurn never sizes the output
+        // canvas itself; the previous code set only CSS size, leaving the buffer
+        // at the 300x150 default -> the viz showed a stretched lower-left corner
+        // (worse the larger the panel). Ratio reuses the highway's DPR budget.
+        function _bcApplySize(cssW, cssH) {
+            if (!(cssW > 0 && cssH > 0)) return;
+            ctrl.lastW = cssW; ctrl.lastH = cssH;
+            const ratio = Math.min(window.devicePixelRatio || 1, 1.5);
+            const bw = Math.max(1, Math.round(cssW * ratio)), bh = Math.max(1, Math.round(cssH * ratio));
+            if (canvas.width !== bw) canvas.width = bw;
+            if (canvas.height !== bh) canvas.height = bh;
+            const wpx = cssW + 'px', hpx = cssH + 'px';
+            // Confine ALL layers to exactly the highway-canvas rect so the opaque
+            // backdrop can't bleed over the transport bar above the highway.
+            [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => {
+                if (el) { el.style.width = wpx; el.style.height = hpx; el.style.right = 'auto'; el.style.bottom = 'auto'; }
+            });
+            if (ctrl.viz && ctrl.viz.setRendererSize) { try { ctrl.viz.setRendererSize(bw, bh); } catch (e) {} }
+        }
+        return {
+            applySettings() { ctrl.applySettings(); },
+            dead() { return ctrl.dead; },
+            ready() { return !!ctrl.viz; },
+            boundAnalyser() { return ctrl.connectedAnalyser || null; },
+            audioCtx() { return ctrl.actx; },
+            // Re-bind audio when the shared analyser changes (e.g. a stems song
+            // swap replaces the analyser). Same context → cheap reconnect; the
+            // caller handles a context change with a full rebuild (cross-context
+            // connectAudio is impossible — the visualizer is bound to one ctx).
+            reconnectAudio(a) {
+                if (!a || !a.analyser || !ctrl.viz) return false;
+                if (a.analyser === ctrl.connectedAnalyser) return true;
+                if (a.ctx && a.ctx !== ctrl.actx) return false; // needs rebuild
+                try { ctrl.viz.connectAudio(a.analyser); ctrl.connectedAnalyser = a.analyser; return true; } catch (e) { return false; }
+            },
+            chart(v) { if (ctrl.guitar && ctrl.guitar.setChart) ctrl.guitar.setChart(v); },
+            tint(hex, alpha) {
+                if (!ctrl.tint) return;
+                if (hex == null) { ctrl.tint.style.background = 'transparent'; return; }
+                const r = (hex >> 16) & 255, g = (hex >> 8) & 255, b = hex & 255;
+                ctrl.tint.style.background = 'rgba(' + r + ',' + g + ',' + b + ',' + (alpha || 0).toFixed(3) + ')';
+            },
+            render() {
+                const s = _bcLoadSettings();
+                if (!ctrl.viz || !s.enabled) return; // skip GPU work when the bg is off
+                const sz = sizeProvider && sizeProvider();
+                if (sz && sz.w > 0 && sz.h > 0 && (sz.w !== ctrl.lastW || sz.h !== ctrl.lastH)) {
+                    _bcApplySize(sz.w, sz.h);
+                }
+                try { ctrl.viz.render(); } catch (e) {}
+            },
+            resize(w, h) { _bcApplySize(w, h); },
+            destroy() {
+                ctrl.dead = true;
+                _bcControllers.delete(ctrl);
+                if (_bcPrimary === ctrl) { _bcPrimary = _bcControllers.values().next().value || null; _bcUpdatePanelPreset(); }
+                if (ctrl.cycle) { clearInterval(ctrl.cycle); ctrl.cycle = 0; }
+                if (ctrl.guitar) { ctrl.guitar.stop(); ctrl.guitar = null; }
+                // Release the Butterchurn WebGL context deterministically (don't
+                // wait for GC) so repeated mounts/toggles can't exhaust the
+                // browser's WebGL context cap (~16). Do it before removing the
+                // canvas from the DOM.
+                _bcReleaseCanvasGL(ctrl.canvas);
+                [ctrl.canvas, ctrl.backdrop, ctrl.scrim, ctrl.tint].forEach((el) => { if (el && el.parentNode) el.parentNode.removeChild(el); });
+                ctrl.viz = null; ctrl.connectedAnalyser = null;
+                // Close the AudioContext only if we own it (desktop, or the
+                // browser fallback). The browser path normally reuses the
+                // highway's shared context, which the fog system owns — never
+                // close that. Without this, desktop leaks a new AudioContext per
+                // mount and hits the browser's ~6-context cap after a few toggles.
+                if (ctrl.ownsActx && ctrl.actx && typeof ctrl.actx.close === 'function') {
+                    try { ctrl.actx.close(); } catch (e) {}
+                }
+                ctrl.actx = null;
+                if (_bcControllers.size === 0) {
+                    if (_bcPanel && _bcPanel.parentNode) _bcPanel.parentNode.removeChild(_bcPanel);
+                    if (_bcPane && _bcPane.parentNode) _bcPane.parentNode.removeChild(_bcPane);
+                    _bcPanel = null; _bcPane = null; _bcListEl = null; _bcFilterEl = null; _bcPaneOpen = false;
+                } else if (_bcPrimary && _bcPrimary.wrap) {
+                    // Splitscreen: a controller other than this one is still
+                    // alive. The singleton panel was parented to THIS (now
+                    // destroyed) wrap, so re-home it onto the surviving primary's
+                    // wrap — otherwise the panel is orphaned on the dead wrap and
+                    // the surviving highway is left with no visualizer controls
+                    // (_bcEnsurePanel only runs at controller creation). It moves
+                    // the existing panel+pane when connected, or rebuilds them on
+                    // the survivor if this wrap was already detached.
+                    try { _bcEnsurePanel(_bcPrimary.wrap); _bcUpdatePanelPreset(); } catch (e) {}
+                }
+            },
+        };
+    }
+
+    // Selectable per-string color palettes (issue #10). Each palette has
+    // 8 entries to match MAX_RENDER_STRINGS so 6/7/8-string arrangements
+    // all index safely. Default is the canonical chart-format classic
+    // mapping (low E=red, A=yellow, D=blue, G=orange, B=green,
+    // high E=purple); Neon pushes saturation harder; Pastel desaturates
+    // for long-session comfort; Colorblind (high contrast) is derived from
+    // the chart format's built-in colorblind-mode palette, but this preset
+    // intentionally keeps some entries tuned for feedBack rather than
+    // reproducing every original hex value verbatim. The chart-format base
+    // values came from community reverse-engineering of the original chart
+    // files; do not treat the tuned values below as the exact original
+    // palette.
+    // In feedBack's index convention s=0 is the low E (thickest) and
+    // s=5 is the high E (thinnest), matching the chart format's native string
+    // indexing. Per-index ordering is preserved across all palettes so
+    // switching between them never reassigns a string to a different
+    // colour family. Indices 6/7 are supplementary slots used for
+    // 7/8-string arrangements.
+    // NOTE: settings.html mirrors these arrays in its hydration script
+    // for the palette-preview swatches — keep them in sync.
+    const PALETTES = {
+        default: [
+            0xe61f26, 0xecd234, 0x1096e6, 0xf18313,
+            0x3fc413, 0xb518d9, 0xff6bd5, 0x6bffe6,
+        ],
+        neon: [
+            0xff0030, 0xffe800, 0x0080ff, 0xff8030,
+            0x40ff50, 0xb050ff, 0xff40d0, 0x40ffd0,
+        ],
+        pastel: [
+            0xe89aa0, 0xefdf90, 0x9adfee, 0xefb898,
+            0xa6e0a8, 0xc4a6e0, 0xe0a6c8, 0xa6e0d8,
+        ],
+        colorblind_hc: [
+            0xa42424, 0xa3f300, 0x19abfc, 0xda7e41,
+            0x30d0a0, 0x7648a7, 0xff6bd5, 0x6bffe6,
+        ],
+    };
+    const PALETTE_IDS = Object.keys(PALETTES);
+    // User-defined per-string colors (core "Highway String Colors" theming).
+    // Persisted as a JSON hex array under the bg setting key 'customColors';
+    // when the active palette id is 'custom' the renderer resolves this into
+    // numeric hex, falling back to the default palette per missing index.
+    // Mutated in place by _resolveCustomPalette so the reference stays stable.
+    let _customPalette = PALETTES.default.slice();
+    function _h3dHexToInt(hex) {
+        if (typeof hex !== 'string') return null;
+        const t = hex.trim().replace(/^#/, '');
+        const full = t.length === 3 ? t[0] + t[0] + t[1] + t[1] + t[2] + t[2] : t;
+        if (!/^[0-9a-fA-F]{6}$/.test(full)) return null;
+        return parseInt(full, 16);
+    }
+    // Numeric (0xRRGGBB) darken/lighten — used to derive the gem-gradient
+    // top-highlight / bottom-shade stops from a custom per-string base color
+    // so the note bodies follow the custom palette (mirrors the 2D highway's
+    // dim/bright derivation). factor 0..1 keeps that fraction of each channel;
+    // lighten mixes t toward white.
+    function _clampByteI(n) { return n < 0 ? 0 : (n > 255 ? 255 : Math.round(n)); }
+    function _darkenInt(hex, factor) {
+        const r = (hex >> 16) & 0xff, g = (hex >> 8) & 0xff, b = hex & 0xff;
+        return (_clampByteI(r * factor) << 16) | (_clampByteI(g * factor) << 8) | _clampByteI(b * factor);
+    }
+    function _lightenInt(hex, t) {
+        const r = (hex >> 16) & 0xff, g = (hex >> 8) & 0xff, b = hex & 0xff;
+        return (_clampByteI(r + (255 - r) * t) << 16) | (_clampByteI(g + (255 - g) * t) << 8) | _clampByteI(b + (255 - b) * t);
+    }
+    // Default per-string gem gradient stops [topHighlight, bottomShade] —
+    // sampled from the original colour PNGs. Used verbatim for the built-in
+    // palettes (and for unchanged slots of a custom palette) so the stock look
+    // is byte-for-byte preserved; custom slots derive their stops from the
+    // chosen base color via _lightenInt/_darkenInt. Strings 6/7 have no entry
+    // and fall back to flat gNote.
+    const DEFAULT_GEM_GRADIENTS = [
+        [0xec0816, 0xbd0400], // 0 red
+        [0xefd20b, 0xceaa00], // 1 yellow
+        [0x0b93e9, 0x0e69b2], // 2 blue
+        [0xf77b0b, 0xdb5808], // 3 orange
+        [0x37c40b, 0x139305], // 4 green
+        [0xaf10db, 0x8907af], // 5 violet
+    ];
+    // Default palette at module scope so out-of-IIFE consumers (e.g. the
+    // out-of-range warning's reference to "palette size") still have a
+    // canonical length to compare against.
+    const S_COL = PALETTES.default;
+
+    const SCALE = 2.25;
+    const K = SCALE / 300;
+    // Horizontal stretch factor for fret X positions.  Increasing this widens
+    // the lane (frets, board plane, strings, notes, lane strip) without
+    // affecting K-based vertical dimensions (string gap, note height, camera).
+    const FRET_SCALE = SCALE * 1.1;
+
+    const NFRETS = 24;
+    const NSTR = 6;
+    /**
+     * Pure 12-semitone spacing compresses toward the bridge; multiply each
+     * segment **above** this fret by the factor so high positions stay
+     * slightly more playable/readable in 3D.
+     */
+    const FRET_SPACING_STRETCH_ABOVE12 = 1.1;
+    const FRET_SPACING_ANCHOR_F = 12;
+    // Per-string materials and projection meshes are built via S_COL.map(),
+    // so the renderer can only address strings 0..S_COL.length-1. Using a
+    // higher count would index undefined into mGlow/mStr/mSus/projMeshArr.
+    // Extend S_COL above to support more strings.
+    const MAX_RENDER_STRINGS = S_COL.length;
+
+    // Resolve the string count for the active arrangement. Prefer
+    // bundle.stringCount (exposed by feedBack core since #93 — derived
+    // from notes/chords/tuning, so it works for 5-string bass, 7- and
+    // 8-string guitar, etc.). Fall back to arrangement-name detection
+    // for older feedBack cores that don't emit the field. Clamp to the
+    // palette size so a malformed bundle or a 12-string chart doesn't
+    // index past the per-string material arrays.
+    function resolveStringCount(bundle) {
+        const sc = bundle && bundle.stringCount;
+        if (Number.isFinite(sc) && sc >= 1) {
+            return Math.min(Math.trunc(sc), MAX_RENDER_STRINGS);
+        }
+        return /bass/i.test(bundle?.songInfo?.arrangement || '') ? 4 : NSTR;
+    }
+
+    /** Chart-format tuning entries are semitone offsets from instrument standard. */
+    const _NOTE_NAMES_SHARP = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
+
+    // Open-string MIDI (thick → thin), matched to RS string index 0 low.
+    const _BASE_OPEN_MIDI_BASS4 = Object.freeze([28, 33, 38, 43]);
+    const _BASE_OPEN_MIDI_BASS5 = Object.freeze([23, 28, 33, 38, 43]);
+    const _BASE_OPEN_MIDI_GUITAR6 = Object.freeze([40, 45, 50, 55, 59, 64]);
+    const _BASE_OPEN_MIDI_GUITAR7 = Object.freeze([35, 40, 45, 50, 55, 59, 64]);
+    // F#/B/E standard extension — low string is a fifth below RS 7‑string low B.
+    const _BASE_OPEN_MIDI_GUITAR8 = Object.freeze([28, 35, 40, 45, 50, 55, 59, 64]);
+
+    function _baseOpenStringMidis(sc, arrangement) {
+        const isBass = /bass/i.test(arrangement || '');
+        if (sc === 4 && isBass) return _BASE_OPEN_MIDI_BASS4.slice();
+        if (sc === 4) return _BASE_OPEN_MIDI_GUITAR6.slice(0, 4);
+        if (sc === 5 && isBass) return _BASE_OPEN_MIDI_BASS5.slice();
+        if (sc === 5) return _BASE_OPEN_MIDI_GUITAR6.slice(0, 5);
+        if (sc === 7) return _BASE_OPEN_MIDI_GUITAR7.slice();
+        if (sc === 8) return _BASE_OPEN_MIDI_GUITAR8.slice();
+        if (Number.isFinite(sc) && sc > 8) {
+            const out = Array.from(_BASE_OPEN_MIDI_GUITAR8);
+            let last = out[out.length - 1];
+            while (out.length < sc) {
+                last += 5;
+                out.push(last);
+            }
+            return out.slice(0, sc);
+        }
+        const g6 = _BASE_OPEN_MIDI_GUITAR6.slice();
+        if (Number.isFinite(sc) && sc < 6 && sc >= 1) return g6.slice(0, sc);
+        return g6;
+    }
+
+    function _midiToPitchLabel(midi) {
+        const m = Math.round(midi);
+        const octave = Math.floor(m / 12) - 1;
+        const n = _NOTE_NAMES_SHARP[(m % 12 + 12) % 12];
+        return n + octave;
+    }
+
+    /**
+     * @param {number} nEffective string count clamped like nStr / resolveStringCount
+     * @param {Record<string, unknown>} songInfo WS song_info blob (subset)
+     */
+    function _openStringPitchLabelsForTuning(bundle, songInfo, nEffective) {
+        const n = Number.isFinite(nEffective) ? Math.min(Math.max(1, Math.trunc(nEffective)), MAX_RENDER_STRINGS) : resolveStringCount(bundle);
+        let tuning = (songInfo && songInfo.tuning) || bundle.tuning;
+        let cap = songInfo && songInfo.capo;
+        cap = Number.isFinite(cap) ? cap : (Number.isFinite(bundle.capo) ? bundle.capo : 0);
+        if (!Array.isArray(tuning)) tuning = [];
+
+        const base = _baseOpenStringMidis(n, songInfo?.arrangement);
+        const labels = [];
+        for (let s = 0; s < n; s++) {
+            const offRaw = tuning[s];
+            const off = Number.isFinite(offRaw) ? offRaw : 0;
+            const midi = (base[s] !== undefined ? base[s] : 40) + off + cap;
+            labels.push(_midiToPitchLabel(midi));
+        }
+        return labels;
+    }
+
+    const STR_THICK = 0.25 * K;
+
+    // Fret wires — bowed metal tubes (backported from highway_babylon's
+    // "hit-zone fret bars"). All frets share one bowed TubeGeometry whose
+    // middle (the middle strings) pushes away from the camera so the row of
+    // frets reads as wrapping a cylindrical neck — chart-format depth cue.
+    // Negative Z = away from camera (into the highway). All tunable.
+    const FRET_BOW_DZ = -1.2 * K;        // middle-of-span Z offset
+    const FRET_TUBE_RADIUS = STR_THICK * 0.75; // slightly thicker than a string
+    const FRET_TUBE_SEG = 12;            // tubular segments along the curve
+    // Radial segments (cross-section). 8 rather than 6: at FRET_TUBE_RADIUS the
+    // hexagonal facets of a 6-segment tube are visible along the top highlight.
+    // One shared geometry for all frets, so the extra segments are ~free.
+    const FRET_TUBE_RADIAL = 8;
+    // metalness kept moderate, NOT ~1.0: MeshStandardMaterial is PBR and the
+    // scene has no envMap, so a full-metal fret would reflect black and render
+    // dark (the nut/headstock use metalness 0.02 for the same reason). At ~0.4
+    // the lit albedo body survives while the directional light still throws a
+    // glossy specular streak across the rounded tube. The dim emissive floor
+    // keeps frets from going muddy far down the (fogged) neck.
+    const FRET_METALNESS = 0.4;          // lit steel / brass when gold
+    const FRET_ROUGHNESS = 0.3;
+    const FRET_EMISSIVE = 0x12141a;      // cool dim floor, never fully black
+
+    // Fret-wire tiers. Wires inside the active anchor lane (the frets the player
+    // is actually reading) sit bright; everything outside recedes. Kept far
+    // apart on purpose — a narrow gap reads as noise rather than as a focus cue.
+    const FRET_WIRE_ACTIVE_HEX = 0xD8A636; // gold; numeric twin of FRET_LABEL_GOLD_HEX
+    const FRET_WIRE_ACTIVE_OP = 0.9;
+    const FRET_WIRE_IDLE_HEX = 0x4A4A60;
+    const FRET_WIRE_IDLE_OP = 0.28;
+
+    // Hit flash: when a scorer (feedBack#254) confirms a note, the two wires
+    // bracketing its fret (f-1 and f) flash bright. Emissive is boosted as well
+    // as albedo — a MeshStandard fret with no envMap barely brightens from
+    // albedo alone, so without the emissive lift the "flash" reads as a shrug.
+    const FRET_WIRE_HIT_HEX = 0xFFFFFF;      // blown out to white at full flash
+    const FRET_WIRE_HIT_EMISSIVE = 0xFFE9B0; // hot warm-white glow
+    const FRET_WIRE_HIT_OP = 1.0;
+    // Emissive multiplier at full flash (baseline is 1). Pushing emissive past
+    // 1.0 is what actually makes the wire read as a light source rather than a
+    // brightly-lit object — the color alone saturates and stops there.
+    const FRET_WIRE_HIT_INTENSITY = 4.2;
+    // Seconds for a flash to fall to ~1/e once the provider stops reporting.
+    // The provider already fades its own `alpha` on a struck note; this tail
+    // just keeps the hand-off from popping, and smooths the frame-to-frame
+    // jitter of a held sustain (whose alpha tracks live input level).
+    const FRET_WIRE_HIT_DECAY = 0.32;
+
+    const S_BASE = 3 * K;
+    const S_GAP = 4 * K;
+
+    const AHEAD = 3.0;
+    const BEHIND = 0.5;
+    // How long a note/chord-frame stays renderable past the hit line while a
+    // note-state provider (feedBack#254) is attached. The provider's
+    // hit/miss verdict is asynchronous — the engine-side verifier reports it
+    // ~0.35-0.5 s after the line — so the default ~50 ms note linger /
+    // ~0.48 s chord linger lapses before the tint can apply. Drives both
+    // the outer-loop cull (ndVerdictT0) and the smart drawNote cull below.
+    const NOTEDETECT_GEM_VERDICT_WINDOW = 0.75;
+    // chDt threshold past the hit line at which the chord-frame scan
+    // gives up on an arpeggio-style frame whose constituents never come
+    // in. Must be < NOTEDETECT_GEM_VERDICT_WINDOW (the rim's draw life
+    // in detect mode); placing it at 0.55 s leaves ~0.2 s of the visible
+    // window for the latch to fire and skip subsequent scans.
+    const _ND_UNMATCHED_LATCH_AFTER = 0.55;
+    // Sample approach offsets dt in [0, AHEAD] into strips. Lane quads use
+    // z = dZ(dt) + TS*BEHIND = TS*(BEHIND - dt), while notes use z = dZ(n.t-now).
+    // So note hit line (z=0) aligns with dt=BEHIND, not dt=0. Chart time at
+    // lane parameter dt is now + dt - BEHIND (same z as a note at that time).
+    // Each strip’s <anchor> uses that chart time so the blue lane doesn’t
+    // switch ~BEHIND seconds before the XML <anchor time="…"/>.
+    const HWY_LANE_TIME_SLICES = 96;
+    /** Odd columns (1st/3rd/…) darker teal; even columns brighter blue. */
+    const HWY_LANE_STRIPE_ODD_HEX  = 0x103B5C;
+    const HWY_LANE_STRIPE_EVEN_HEX = 0x08283C;
+    /** Lane quad alpha: base + highwayIntensity * scale (readable on dark floor). */
+    const HWY_LANE_STRIPE_OP_BASE = 1.0;
+    const HWY_LANE_STRIPE_OP_INT  = 0;
+    /** Venue mode: slight near-lane contrast boost (visual only). */
+    const VENUE_LANE_OP_BOOST = 1.1;
+    /** Venue mode: gem emissive pop (~12%, visual only). */
+    const VENUE_GEM_EMISSIVE_MUL = 1.12;
+    /** Venue steady-state haze coefficient — kept low for raster bg plate. */
+    const VENUE_HAZE_STEADY = 0.008;
+    /** Venue backdrop pushed slightly farther for parallax depth. */
+    const VENUE_BACKDROP_DISTANCE_MUL = 1.06;
+    /** Note travel speed. */
+    const TS = 230 * K;
+
+    const RENDER_ORDER_LAYER_STACK = Object.freeze([
+        'CHORD_FILL',
+        'CHORD_STRUM_FILL',
+        'CHORD_STRUM_LINE',
+        'SUSTAIN_TRAIL',
+        'CHORD_FRAME',
+        'CHORD_EDGE_GLOW',
+        'CONNECTOR_LINE',
+        'FRET_COLUMN',
+        'ARP_CONNECTOR_LINE',
+        'NOTE_OUTLINE',
+        'NOTE_CORE',
+        'TECHNIQUE_MARKER',
+        'BOARD_STRING',
+        'BOARD_FRET_WIRE',
+        'NOTE_FRET_LABEL',
+        'ARP_NOTE_FRET_LABEL',
+        'CHORD_FRET_LABEL',
+    ]);
+    const RENDER_ORDER_LAYER_INDEX = Object.freeze(RENDER_ORDER_LAYER_STACK.reduce(
+        (indexByLayer, layerName, layerIndex) => {
+            indexByLayer[layerName] = layerIndex;
+            return indexByLayer;
+        },
+        Object.create(null)
+    ));
+
+    const RENDER_ORDER_AT_Z_ZERO = 700;
+    const RENDER_ORDER_FAR_CLAMP = 50;
+
+    /**
+     * Computes renderOrder from world depth plus a named layer.
+     * Closer objects receive larger values and paint over farther objects; the
+     * layer stack breaks ties at the same depth, keeping labels above note gems.
+     *
+     * The layer index is added as a sub-unit fraction (< 1) so the integer
+     * depth bucket STRICTLY dominates: a farther object can never outrank a
+     * nearer one merely because it sits on a higher layer. Adding the raw index
+     * (0..N-1) directly would let the ~N-wide layer span leak across depth
+     * buckets and re-introduce far-over-near bleed for notes within ~N draw
+     * units of each other. Fraction granularity (1/N ≈ 0.06) stays well above
+     * the 0.0001 intra-element sub-increments used at some call sites.
+     */
+    function renderOrderForLayerAtZ(worldZ, layerName) {
+        const layerIndex = RENDER_ORDER_LAYER_INDEX[layerName];
+        if (layerIndex === undefined) throw new Error(`Unknown 3D highway depth layer: ${layerName}`);
+        const depthRenderOrder = Math.max(
+            RENDER_ORDER_FAR_CLAMP,
+            Math.round(RENDER_ORDER_AT_Z_ZERO + worldZ / K)
+        );
+        return depthRenderOrder + layerIndex / RENDER_ORDER_LAYER_STACK.length;
+    }
+
+    /** Match `nextNoteByString` onset to this note (float + chart rounding; avoids ghost / glow flicker). */
+    const NEXT_ON_STRING_T_EPS = 0.06;
+    /** Fixed pre-impact ramp window for lead-note board ghosts (Primary + Upcoming slots). */
+    const GHOST_UPCOMING_WIN = 0.6;
+    /** Ghost starts at this fraction of full size/brightness and grows to 1.0 as it approaches. */
+    const PROJ_GROW_MIN = 0.45;
+    /**
+     * 3D highway post-strum tail — chord frame + ghost fret digit share the same
+     * hold and fade so timing stays consistent.
+     */
+    const CHORD_HWY_LINGER_S = 0.75;
+    /** Linear fade at end of `CHORD_HWY_LINGER_S` (applies to chord UI and board ghost numbers). */
+    const CHORD_HWY_FADE_S = 0.32;
+    const GHOST_HOLD_AFTER_ONSET = CHORD_HWY_LINGER_S;
+    const GHOST_FRET_LBL_FADE_S = CHORD_HWY_FADE_S;
+    /** Purple lane rails: extend past last matched chord/note so Z reaches frame end. */
+    const ARP_HWY_RAIL_END_TAIL_S = 0.38;
+    /** Keep 0 — chord/note-based ``shapeLo`` already aligns to the visible frame. */
+    const ARP_HWY_RAIL_START_LEAD_S = 0;
+    /** Drives emissive (`mGlow` / accent fill) for notes with `.ac`; matches drawNote `linger` cutoff (0.05). */
+    const ACCENT_NOTE_STR_GLOW = 3.55;
+    const ACCENT_NOTE_LINGER_EPS = 0.05;
+    /** Extra emissive layered on accent-only body material (`mAccentCore`), after `strGlow * glowMul`. */
+    const ACCENT_NOTE_FILL_BOOST = 2.55;
+    /** Accent rim draws brighter than normal string-coloured outlines (`mStrHitOutline`). */
+    const ACCENT_RIM_BASE_EMISSIVE = 3.45;
+    /** Outline / core scale bump vs normal gems (accent reads slightly larger). */
+    const ACCENT_RIM_XY_SCALE_MUL = 1.09;
+    const ACCENT_RIM_Z_SCALE_MUL = 1.06;
+    // Soft neon-style outer bloom (AdditiveBlending) — layered shells behind outline/core.
+    const ACCENT_HALO_OP_NEAR = 0.68;
+    const ACCENT_HALO_OP_MID = 0.42;
+    const ACCENT_HALO_OP_FAR = 0.24;
+    const ACCENT_HALO_XY_INNER = 1.36;
+    const ACCENT_HALO_XY_MID = 1.82;
+    const ACCENT_HALO_XY_OUTER = 2.32;
+    const ACCENT_HALO_Z_INNER = 1.05;
+    const ACCENT_HALO_Z_MID = 1.12;
+    const ACCENT_HALO_Z_OUTER = 1.22;
+
+    /**
+     * Post-hit tail fade shared by ghost fret digits and 3D chord UI: full
+     * opacity until (holdS − fadeS) after onset, then linear fade over fadeS;
+     * canceled when `nextSoon` — for ghosts: next note within `fadeS` of `now`;
+     * for chord frame: next chord onset lies in chart time [hold − fade, hold]
+     * after the current chord (so fade does not run into a same-window handoff).
+     * @param {number} dt chart time minus now (negative once struck)
+     * @param {number} fadeS linear fade duration (default: GHOST_FRET_LBL_FADE_S)
+     */
+    function hwyPostHitTailFadeMul(dt, holdS, nextSoon, fadeS = GHOST_FRET_LBL_FADE_S) {
+        if (nextSoon || dt >= 0) return 1;
+        const gone = -dt;
+        if (gone >= holdS) return 0;
+        const fS = Math.min(Math.max(fadeS, 1e-6), holdS);
+        const fadeStartT = Math.max(0, holdS - fS);
+        if (gone < fadeStartT) return 1;
+        return Math.max(0, 1 - (gone - fadeStartT) / fS);
+    }
+
+    // Shorter, flatter notes (joel style)
+    const NW = 5 * K, NH = 3 * K, ND = 0.25 * K;
+    // Sustain-trail X offset for fretted notes. Module-scoped + frozen
+    // so the hot path's `offsets.length` loop sees a stable singleton
+    // reference. The standalone-open-string path builds a fresh pair
+    // each call because its offset magnitude depends on the per-note
+    // `openWScale` (set in drawNote at line 7367 from the open-string
+    // body's lane width), so a module-scoped constant can't capture
+    // it; the allocation is the same one the prior code did via
+    // `const baseOff = NW * 3 * openWScale` plus the inline `[-, +]`
+    // literal in the chord-member branch — just consolidated.
+    const SINGLE_SUS_OFFSETS = Object.freeze([0]);
+    const BEND_HALFSTEP_WORLD_Y = S_GAP * 0.8;
+    const VIBRATO_HALF_WAVE_S = 0.08;
+    // Bend ribbon envelope: fraction of the sustain spent ramping up to
+    // the bent pitch, and releasing back down (rest is the held plateau).
+    const BEND_ENV_RISE_FRAC = 0.35;
+    const BEND_ENV_RELEASE_FRAC = 0.30;
+    const TREMOLO_BUMP_S = 0.06;
+
+    /** Longitudinal samples for sustain-technique prism (indexed BufferGeometry). */
+    const SLIDE_RIBBON_SAMPLES = 96;
+    /** Pre-built index buffer: `SLIDE_RIBBON_SAMPLES` × 8 tris × 3 verts. */
+    const SLIDE_RIBBON_INDICES = (() => {
+        const S = SLIDE_RIBBON_SAMPLES;
+        const idx = new Uint16Array(S * 24);
+        let o = 0;
+        for (let k = 0; k < S; k++) {
+            const b = k * 4;
+            const nx = (k + 1) * 4;
+            // Bottom (-Y outward)
+            idx[o++] = b; idx[o++] = b + 1; idx[o++] = nx + 1;
+            idx[o++] = b; idx[o++] = nx + 1; idx[o++] = nx;
+            // Top (+Y outward)
+            idx[o++] = b + 3; idx[o++] = nx + 3; idx[o++] = nx + 2;
+            idx[o++] = b + 3; idx[o++] = nx + 2; idx[o++] = b + 2;
+            // Left (-X outward)
+            idx[o++] = b; idx[o++] = nx; idx[o++] = nx + 3;
+            idx[o++] = b; idx[o++] = nx + 3; idx[o++] = b + 3;
+            // Right (+X outward)
+            idx[o++] = b + 1; idx[o++] = b + 2; idx[o++] = nx + 2;
+            idx[o++] = b + 1; idx[o++] = nx + 2; idx[o++] = nx + 1;
+        }
+        return idx;
+    })();
+    // Three r170's setIndex() only wraps plain Arrays into Uint16BufferAttribute;
+    // typed-array input gets assigned raw onto .index, which trips WebGL's
+    // byteLength check. Convert once at module init so each pooled geometry
+    // reuses the same Array reference instead of allocating per mesh.
+    const SLIDE_RIBBON_INDICES_ARR = Array.from(SLIDE_RIBBON_INDICES);
+    const N_RAD = 1.5 * K;
+    const SW = 2 * K, SH = 1.5 * K;
+
+    const CAM_H_BASE = 190 * K;
+    const CAM_DIST_BASE = 240 * K;
+    const REF_ASPECT = 16 / 9;
+    const FOCUS_D = 600 * K;
+    const CAM_LERP_BASE = 0.02;
+
+    // Base vertical field of view (deg). THREE's PerspectiveCamera fov is the
+    // VERTICAL angle; horizontal follows from the aspect ratio. At a normal
+    // ~16:9 pane this gives a ~102° horizontal cone. On an ultra-wide pane
+    // (top/bottom 2-player split → full-width/half-height → ~32:9) that
+    // horizontal cone balloons past 130° and squeezes the fixed-width neck into
+    // a central sliver. The optional horizontal-FOV-hold path below counters
+    // that by lowering the effective vertical fov as the pane widens.
+    const BASE_VFOV = 70;
+    // Horizontal-FOV-hold ("Hor+") defaults. At/under HORPLUS_START_ASPECT the
+    // effective vertical fov equals BASE_VFOV (exact no-op); past it the
+    // vertical fov drops to keep the horizontal cone ~constant so the neck
+    // fills a wide pane. HORPLUS_MIN_VFOV floors the result on pathological
+    // aspects. Engaged only via the window.__h3dAspectTune bridge (default off).
+    const HORPLUS_START_ASPECT = 16 / 9;
+    const HORPLUS_MIN_VFOV = 28;
+
+    // Zoom-dependent framing — height (h*) and depth (dist*) multipliers
+    // applied to cam.position. Interpolated by `dist`:
+    //   NEAR = tight view (nut position, span<=4 -> dist~=93*K): lower/closer.
+    //   FAR  = wide view (midpoint fret 1<->20 -> dist~=141*K): higher/pulled back
+    //          to fit the whole neck.
+    // Outside this range the values clamp at the endpoints.
+    const CAM_FRAME_DIST_NEAR = 93 * K;
+    const CAM_FRAME_DIST_FAR  = 141 * K;
+    const CAM_FRAME_H_NEAR = 0.75;
+    const CAM_FRAME_H_FAR  = 1.00;
+    const CAM_FRAME_D_NEAR = 0.575;
+    const CAM_FRAME_D_FAR  = 0.60;
+    // Fret-row fit guard. The heat-coloured fret-number row is a band drawn
+    // BELOW the board (at sY(lowest) - S_GAP*1.4). The lower-third framing
+    // anchors the board CENTRE, not that row, so a tight zoom on a centred span
+    // (worst mid-neck — fine pushed to either end of the neck) drops the row off
+    // the bottom edge. Tilt can't add vertical room there (it would only trade a
+    // bottom clip for a top clip), so camUpdate dollies the camera back just
+    // enough to bring the row back into frame — auto-sized, capped, hysteretic.
+    const FRET_ROW_FIT_NDC_MIN   = -0.86;  // keep the row anchor at/above this NDC y (>-1 = on screen)
+    const FRET_ROW_FIT_DEADBAND  = 0.06;   // headroom past the min before the dolly relaxes (anti-hunt)
+    const FRET_ROW_FIT_BOOST_MAX = 1.6;    // cap the pull-back so the zoom can't pop (never dolly back > +60%)
+
+    // Camera-X targeting (issue #34). The visible AHEAD = 4.0 s window is
+    // far too coarse for picking where the camera should sit — a single
+    // 17th-fret bend 2.5 s away yanks tgtX several frets even though the
+    // immediate playing area hasn't moved. These constants are bounds for
+    // a smoothing dial (0 = twitchy, 1 = calm); the runtime lerps between
+    // the pair using the user's `cameraSmoothing` setting.
+    const CAM_TGT_BEHIND   = 0.2;   // s behind hit line for X targeting
+    const CAM_TGT_AHEAD_T  = 2.0;   // s — twitchy: longer lookahead (more reactive)
+    const CAM_TGT_AHEAD_C  = 0.7;   // s — calm: shorter lookahead (ignore distant outliers)
+    const CAM_TGT_TAU_T    = 0.35;  // s — twitchy: short recency time-constant
+    const CAM_TGT_TAU_C    = 0.9;   // s — calm: longer time-constant (averages more)
+    const CAM_TGT_HYST_T   = 0.25;  // frets — twitchy: tiny dead zone
+    const CAM_TGT_HYST_C   = 5.0;   // frets — calm: ~5-fret dead zone, wide
+                                    // enough to swallow chord-to-chord
+                                    // alternations across a 6-fret span
+                                    // (e.g. Am ↔ D in first position).
+
+    // Zoom (tgtDist) damping. Controlled by its own `zoomSmoothing` setting
+    // so X-pan and zoom-pull-back can be tuned independently. New users
+    // (and existing users who never wrote zoomSmoothing) inherit
+    // cameraSmoothing's value on first read, so default behaviour is
+    // unchanged from when zoom + X shared a single slider.
+    const CAM_DIST_HYST_T  = 0.5;   // fret-span — twitchy: minimal dead zone
+    const CAM_DIST_HYST_C  = 5.0;   // fret-span — calm: 5-fret span change required
+
+    // Vertical-tilt damping. Drives the tgtLookY self-correction loop in
+    // camUpdate(): how far the fretboard's NDC Y can drift from
+    // DESIRED_NDC_Y before we nudge the camera, and how strongly each
+    // nudge corrects. Twitchy = narrow band + strong correction (re-frame
+    // aggressively); calm = wide band + weak correction (let small drift
+    // ride). Driven by `tiltSmoothing`, mirrors cameraSmoothing on first
+    // read like zoomSmoothing does.
+    // Bounds chosen so the midpoint (tiltSmoothing=0.5) reproduces the
+    // pre-PR hardcoded behaviour (band=0.15, str=0.5). Without that, a
+    // fresh install would silently change the vertical-tilt feel even
+    // though the PR description promises "default behaviour unchanged."
+    const CAM_TILT_BAND_T  = 0.05;  // NDC — twitchy: narrow tolerance
+    const CAM_TILT_BAND_C  = 0.25;  // NDC — calm: wide tolerance, fewer corrections
+    const CAM_TILT_STR_T   = 0.8;   // multiplier — twitchy: strong nudge per correction
+    const CAM_TILT_STR_C   = 0.2;   // multiplier — calm: weak nudge per correction
+
+    // Lock-low zoom range. The cameraLockZoom slider (0..1) blends between
+    // these two multipliers and scales the locked tgtDist. Defaults pick
+    // 1.0× at slider=0.5 so the previous locked view is the midpoint.
+    const CAM_LOCK_ZOOM_MIN = 0.55;  // slider=0 — closest, biggest fretboard
+    const CAM_LOCK_ZOOM_MAX = 1.45;  // slider=1 — furthest
+    const CAM_LOCK_CENTER_FRET = 6;  // default camera X center (first-position midpoint)
+
+    // ── 3D preview: lookahead fret bounds + smoothed focal X / span ─────────
+    /** User-selectable via `cameraMode`. Legacy `classic` in storage maps to `steady`. */
+    const CAMERA_MODE_IDS = ['steady', 'lookahead'];
+    const CAM_LOOKAHEAD_SEC = 3.0;       // fallback when no beats/measures are available
+    const CAM_LOOKAHEAD_MEASURES = 9;    // lookahead window = N measures ahead
+    const CAM_FOCUS_BLEND_RATE = 0.7;
+    const CAM_FRET_EDGE_BLEND = 0.1;
+    const DEFAULT_LOOKAHEAD_FRET_SPAN = 4;
+    /** Schmitt: avoid lock↔dynamic flicker when lookahead maxF jitters at the 12th fret. */
+    const LOOKAHEAD_LOCK_RELEASE_MAXF = 13;
+    const LOOKAHEAD_LOCK_ENGAGE_MAXF = 10;
+    // Note: we deliberately do NOT scale the camUpdate lerp speed with
+    // cameraSmoothing. Smoothing widens the hysteresis dead zones so the
+    // camera stays put through small/repetitive shifts; but when a shift
+    // *does* clear the gate (a real jump to a far fret), we want the slide
+    // to be snappy, not lethargic. The dead zone gates "should we move?",
+    // the BPM-scaled lerp answers "how fast" — keeping those orthogonal
+    // gives the right feel.
+
+    const FOG_START = 200 * K;
+    const FOG_END = 670 * K;
+
+    const DOTS = [3, 5, 7, 9, 12, 15, 17, 19, 21, 24];
+    const DDOTS = new Set([12, 24]);
+    const INLAY_LABEL_FRETS = [3, 5, 7, 9, 12, 15, 17, 19, 22, 24]; // 22 not 21: intentional display choice
+
+    // Fret-column reference markers: floor-aligned fret-number sprites
+    // that scroll toward the hit line every Nth measure. When the chart
+    // has <anchor>, the row uses the inlay cadence (DOTS) around the
+    // anchor fret: two marker positions before and three after the
+    // snapped cadence cell (e.g. anchor fret 7 → 3,5,7,9,12,15).
+    const FRET_COL_MARKER_ANCHOR_BACK = 2;
+    const FRET_COL_MARKER_ANCHOR_FWD = 3;
+
+    /**
+     * @param {number} anchorFret Chart anchor `.fret` (world start fret).
+     * @param {number[]} [cadence] Ascending frets (e.g. DOTS).
+     * @returns {number[]}
+     */
+    function fretColumnMarkersForAnchor(anchorFret, cadence = DOTS) {
+        const f0 = Math.round(Number(anchorFret));
+        if (!Number.isFinite(f0) || cadence.length === 0) return cadence.slice();
+        let iBest = 0;
+        let dBest = Infinity;
+        for (let i = 0; i < cadence.length; i++) {
+            const d = Math.abs(cadence[i] - f0);
+            if (d < dBest || (d === dBest && cadence[i] < cadence[iBest])) {
+                dBest = d;
+                iBest = i;
+            }
+        }
+        const i0 = Math.max(0, iBest - FRET_COL_MARKER_ANCHOR_BACK);
+        const i1 = Math.min(cadence.length, iBest + FRET_COL_MARKER_ANCHOR_FWD + 1);
+        return cadence.slice(i0, i1);
+    }
+
+    // Fast integer key for (t, s) pairs — avoids per-frame string allocation in
+    // hot-path Set lookups. Encodes chart time in 0.1 ms steps (sufficient for
+    // chart-format note precision) combined with the string index.
+    // t range 0–600 s → 0–6,000,000; * 10 + s(0–7) = max 60,000,007 < 2^53 ✓.
+    // The |0 truncates to int32 but the outer multiply stays in float64, so the
+    // key is always a safe JS integer for songs ≤ 214,748 s (well above any song).
+    function _noteKey(t, s) { return ((t * 10000 + 0.5) | 0) * 10 + s; }
+
+    // Binary lower-bound: returns the first index i in arr where arr[i].t >= t.
+    // Assumes arr is sorted ascending by .t (bundle.notes / bundle.chords always are).
+    // Byte-identical to core's bundle.lowerBoundT — kept as a local because this
+    // plugin must run on downlevel hosts whose bundles don't carry the helper
+    // (it's called from ~30 sites incl. top-level helpers that don't receive a
+    // bundle). New code that already holds a bundle should prefer
+    // bundle.lowerBoundT / bundle.lowerBoundTime.
+    function lowerBoundT(arr, t) {
+        let lo = 0, hi = arr.length;
+        while (lo < hi) {
+            const mid = (lo + hi) >>> 1;
+            if (arr[mid].t < t) lo = mid + 1;
+            else hi = mid;
+        }
+        return lo;
+    }
+
+    // Last arrangement <anchor> at or before chart time `t` (sorted by .time).
+    // Mirrors static/highway.js getAnchorAt — until t reaches the first anchor’s
+    // time, the first anchor still defines fret/width.
+    // Binary search: this is called inside per-frame loops (lane slicing,
+    // lookahead sampling, marker spawning), so the linear scan was O(samples *
+    // numAnchors) on dense charts.
+    function getChartAnchorAt(anchorArr, t) {
+        if (!anchorArr || !anchorArr.length) return null;
+        let lo = 0, hi = anchorArr.length;
+        while (lo < hi) {
+            const mid = (lo + hi) >>> 1;
+            if (anchorArr[mid].time <= t) lo = mid + 1;
+            else hi = mid;
+        }
+        return lo === 0 ? anchorArr[0] : anchorArr[lo - 1];
+    }
+
+    /** @returns {{ dMin: number, dMax: number } | null} */
+    function laneBoundsFromAnchor(anc) {
+        if (!anc) return null;
+        let fStart = Math.round(Number(anc.fret));
+        // Match anchorPlayedFretInclusiveSpan(): fret 0 (and below) clamps
+        // to 1, otherwise the lane span ends up one fret narrower than the
+        // played-fret span / label highlighting on charts that emit
+        // <anchor fret="0" width="N">.
+        if (!Number.isFinite(fStart) || fStart < 1) fStart = 1;
+        let w = Number(anc.width);
+        if (!Number.isFinite(w)) w = 4;
+        w = Math.max(1, Math.round(w));
+        const fLast = Math.min(NFRETS, fStart + w - 1);
+        const dMin = Math.max(0, fStart - 1);
+        const dMax = Math.min(NFRETS, fLast);
+        return { dMin, dMax };
+    }
+
+    /** Same horizontal span as the dynamic highway lane: anchor at chart time `t`. */
+    function anchorLaneBoundsAt(anchorArr, t) {
+        if (!anchorArr || !anchorArr.length) return null;
+        return laneBoundsFromAnchor(getChartAnchorAt(anchorArr, t));
+    }
+
+    /**
+     * Inclusive chart-fret indices for the playing window (anchor `fret` + `width`),
+     * e.g. fret=5 width=4 → 5..8. Unlike {@link laneBoundsFromAnchor}'s `dMin`/`dMax`
+     * (diagram wire span), these are the labels shown on gems / row numbers.
+     * @returns {{ f0: number, f1: number } | null}
+     */
+    function anchorPlayedFretInclusiveSpan(anc) {
+        if (!anc) return null;
+        let f0 = Math.round(Number(anc.fret));
+        if (!Number.isFinite(f0) || f0 < 1) f0 = 1;
+        let w = Number(anc.width);
+        if (!Number.isFinite(w)) w = 4;
+        w = Math.max(1, Math.round(w));
+        const f1 = Math.min(NFRETS, f0 + w - 1);
+        return { f0, f1 };
+    }
+
+    function anchorPlayedFretSpanAt(anchorArr, t) {
+        if (!anchorArr || !anchorArr.length) return null;
+        return anchorPlayedFretInclusiveSpan(getChartAnchorAt(anchorArr, t));
+    }
+
+    const FRET_COOLDOWN = 0.5; // seconds a lane fret stays active after last note
+
+    const DIAG_LINGER_S    = 0.55;
+    const DIAG_ENTRANCE_S  = 0.20;
+    const DIAG_CROSSFADE_S = 0.15;
+    const DIAG_SIZE_MIN    = 0.08;
+    const DIAG_SIZE_MAX    = 0.16;
+    const DIAG_CELL_MAX    = 34;
+    // 'bl' and 'br' removed — diagram is top-only. Legacy localStorage values
+    // that contain 'bl'/'br' will fall back to BG_DEFAULTS.chordDiagramPosition
+    // via _bgCoerce (which rejects values not in this list).
+    const CHORD_DIAG_POSITION_IDS = ['tl', 'tr'];
+
+    /** Default chord-box rim / fill gradient (teal family). */
+    const CHORD_BOX_TEAL_HEX = 0x00d2d5;
+    const CHORD_BOX_TEAL_DARK_HEX = 0x003c3d;
+    /** Frame edge quads: premultiplied-ish alpha match (~128/255). */
+    const CHORD_BOX_EDGE_ALPHA = 128 / 255;
+    /** Interior gradient strip alpha on both stops (~32/255). */
+    const CHORD_BOX_FILL_GRAD_ALPHA = 32 / 255;
+    /** Arpeggio interior wash; dedicated gradient tex so teal map doesn’t dominate. */
+    const ARPEGGIO_BOX_BLUE_HEX = 0x454BB6;
+    const ARPEGGIO_BOX_BLUE_DARK_HEX = 0x2D3190;
+    /** Arpeggio rim accent and lane tint. */
+    const ARPEGGIO_RIM_BLUE_HEX = 0x454BB6;
+    /** Post-hit chord-frame rim tints driven by the note-state provider
+     *  (feedBack#254). Applied only to the teal frame during the linger
+     *  fade (chDt <= 0) when a scorer is attached.
+     *  Matches the gem hit/miss colours so chord frame and note body
+     *  give a consistent signal:
+     *    hit  → neon spring-green 0x22ff88 (same as mHitBright).
+     *    miss → hot magenta-red 0xff0066 (same as mMissOutline). */
+    const CHORD_BOX_HIT_BRIGHT_HEX  = 0x22ff88;
+    const CHORD_BOX_MISS_DARK_HEX   = 0xff0066;
+
+    /** Fret-number label tints — gold on approaching/active notes, muted blue when idle. */
+    const FRET_LABEL_GOLD_HEX = '#D8A636';
+    const FRET_LABEL_IDLE_HEX = '#9ab8cc';
+
+    /** 3D chord-box rim bars (thin on all chords, including repeats in a sequence). */
+    const CHORD_FRAME_RIM_MIN = 0.055;       // × K — floor thickness
+    const CHORD_FRAME_RIM_FRAC_H = 0.028;    // × fullChordBoxH
+    const CHORD_FRAME_RIM_Z_MIN = 0.048;      // × K — depth squash
+    const CHORD_FRAME_RIM_Z_SCAL = 0.68;     // thickZ scales with ft
+    /**
+     * Highway arpeggio frame uses ``inferArpeggioFromNotePattern`` only inside this
+     * window around ``ch.t``. Hand-shape spans can cover many seconds and several
+     * separate strums of the same voicing; a full-span scan mis-detects arpeggio
+     * from beats that belong to different chord rows.
+     */
+    const ARP_FRAME_ONSET_PAD_S = 0.06;
+    const ARP_FRAME_ONSET_CLUSTER_S = 0.26;
+    /**
+     * The chart format encodes fast alternating power chords (e.g. D5/D#5 gallops) as
+     * very short ``<handShape>`` rows (~0.05–0.2 s). Note-stream arpeggio
+     * inference must not treat strum spread across strings as arpeggio there —
+     * it false-triggers lavender highway rails / frames (see Frantic ~2:36).
+     */
+    const ARP_INFER_MIN_HAND_SHAPE_SPAN_S = 0.21;
+    /**
+     * In a **short** chart window, chord strums (same voicing, strings picked
+     * within ~30–45 ms) barely exceed this total spread; real arpeggios in that
+     * window are usually slower across strings OR have 4+ plucks.
+     */
+    const ARP_INFER_STRUM_VS_ARP_SPREAD_MIN_S = 0.047;
+    /**
+     * If more than ``shape.size + ARP_INFER_MULTI_STRUM_HIT_SLACKS`` matching picks
+     * sit inside a non-trivial hand-shape window, the chart is almost certainly
+     * **repeated strums** of the same chord (or gallops), not one arpeggio sweep.
+     */
+    const ARP_INFER_MULTI_STRUM_HIT_SLACK = 2;
+    /** ``timeWin`` span above which we apply the multi-strum hit-count cap. */
+    const ARP_INFER_MULTI_STRUM_WIN_MIN_S = 0.26;
+    /**
+     * Minimum staggered hits inside a hand-shape window for note-stream arpeggio
+     * inference. A genuine arpeggio sweeps several strings of the held shape;
+     * a 2-note melodic motif inside a multi-string ``<handShape>`` (e.g. Jackson 5
+     * "I Want You Back" ~0:27 — Fm7 transition fingering with two plucks on
+     * strings 4–5) earlier registered as arpeggio and produced a stray lavender
+     * chord frame + purple lane outer dividers. Cap at ``min(shape.size, 3)``
+     * so 2-string voicings still infer normally and 3+ string templates need
+     * a real sweep.
+     */
+    const ARP_INFER_MIN_HITS_VS_SHAPE_CAP = 3;
+
+    /* ======================================================================
+     *  Pure helpers
+     * ====================================================================== */
+
+    // Logarithmic spacing — mirrors real guitar fret geometry (12th root of 2).
+    const _fretXLog = f => {
+        if (f <= 0) return 0;
+        const raw = FRET_SCALE - FRET_SCALE / Math.pow(2, f / 12);
+        if (f <= FRET_SPACING_ANCHOR_F) return raw;
+        const rawAnchor = FRET_SCALE - FRET_SCALE / Math.pow(2, FRET_SPACING_ANCHOR_F / 12);
+        return rawAnchor + (raw - rawAnchor) * FRET_SPACING_STRETCH_ABOVE12;
+    };
+    // Uniform spacing — same column width per fret (chart-format style).
+    // Total board width equals the logarithmic NFRETS position for consistency.
+    const _fretXUniStep = _fretXLog(NFRETS) / NFRETS;
+    const _fretXUni = f => f <= 0 ? 0 : f * _fretXUniStep;
+
+    let _h3dFretUniform = true;
+    try { _h3dFretUniform = localStorage.getItem('highway_3d.fretSpacing') !== 'logarithmic'; } catch (_) {}
+    const fretX = f => _h3dFretUniform ? _fretXUni(f) : _fretXLog(f);
+
+    window.h3dSetFretSpacing = mode => {
+        // Validate against the two supported modes before persisting so an
+        // unexpected input can't leave an invalid value in localStorage
+        // (mirrors h3dBgSetFretNumberGhostScope's allowlist guard). No-op
+        // when the stored mode is already what was requested.
+        const m = mode === 'logarithmic' ? 'logarithmic' : 'uniform';
+        try {
+            if (localStorage.getItem('highway_3d.fretSpacing') === m) return;
+            localStorage.setItem('highway_3d.fretSpacing', m);
+        } catch (_) {}
+        // Apply live rather than reloading the page — a full page reload
+        // reboots the SPA to the home screen (index.html's `.screen.active`),
+        // ejecting the user from Settings. Rebind the module-scope flag so
+        // panels mounted later this session pick up the new mode, recompute
+        // the fretX-derived scalars, then broadcast a change so every mounted
+        // panel rebuilds its board. Same live-update path as every other
+        // 3D-highway setting.
+        _h3dFretUniform = (m !== 'logarithmic');
+        _recomputeFretSpacingDerived();
+        _bgEmitChange('fretSpacing');
+    };
+
+    const fretMid = f => (f <= 0 ? -2 * K : (fretX(f - 1) + fretX(f)) / 2);
+    /** World-space width of fret column (wires f−1 .. f); used to scale row markers past ~12. */
+    function fretColumnWorldW(f) {
+        const fi = Math.round(Number(f));
+        if (!Number.isFinite(fi) || fi <= 0) return Math.abs(fretX(1) - fretX(0));
+        const lo = Math.min(NFRETS, Math.max(1, fi));
+        return Math.abs(fretX(lo) - fretX(lo - 1));
+    }
+    /** Reference column (~mid board): prior fixed K-based sprites matched this neighborhood. */
+    const FRET_LABEL_SCALE_REF_FRET = 5;
+    // `let` (not `const`): recomputed by _recomputeFretSpacingDerived when the
+    // user flips Uniform/Logarithmic at runtime so label scaling tracks the
+    // new geometry without a page reload.
+    let _fretLabelScaleRefW = Math.max(1e-8, fretColumnWorldW(FRET_LABEL_SCALE_REF_FRET));
+    function fretLabelScaleForFret(f) {
+        const w = fretColumnWorldW(f);
+        const m = w / _fretLabelScaleRefW;
+        return Math.max(0.32, Math.min(1.45, m));
+    }
+    const dZ = dt => -dt * TS;
+
+    /**
+     * Pitched slide uses `sl`, unpitched uses `slu` (slide-to vs unpitched slide fields).
+     * Prefer `sl` when both are present — matches RS wire.
+     * @returns {{ endFret: number, unpitched: boolean } | null}
+     */
+    function slideTrailEnd(n) {
+        const sl = n.sl;
+        const slu = n.slu;
+        if (Number.isFinite(sl) && sl >= 0) {
+            return { endFret: sl | 0, unpitched: false };
+        }
+        if (Number.isFinite(slu) && slu >= 0) {
+            return { endFret: slu | 0, unpitched: true };
+        }
+        return null;
+    }
+
+    /**
+     * Lateral slide offset along the fretboard during sustain — easing
+     * mirrors the pitched/unpitched slide offset convention above.
+     * @param {{ endFret: number, unpitched: boolean } | null} [st_] from slideTrailEnd
+     */
+    function slideOffsetWorldX(n, chartTime, st_) {
+        const st = st_ || slideTrailEnd(n);
+        if (!st || n.f <= 0 || !(n.sus > 0)) return 0;
+        const denom = Math.max(n.sus, 1e-6);
+        const p = Math.max(0, Math.min(1, (chartTime - n.t) / denom));
+        const startX = fretMid(n.f);
+        const endX = fretMid(st.endFret);
+        const w = st.unpitched
+            ? 1 - Math.sin((1 - p) * Math.PI / 2)
+            : Math.pow(Math.sin(p * Math.PI / 2), 3);
+        return (endX - startX) * w;
+    }
+
+    // Camera tgtDist building blocks. Both the dynamic (camera-follow)
+    // and locked (frets 1-12) branches compose tgtDist from these, so
+    // any future tuning of the base zoom curve or low-fret pullback
+    // lands in both branches without drift.
+    //   span    — camDistMax - camDistMin in fret-span units
+    //   minFret — lowest fretted note in the camera window (or 1 for
+    //             the locked branch, which assumes nut chords)
+    const camBaseDistU = span => 65 + Math.max(span, 4) * 3;
+    const camLowFretPullbackU = minFret => Math.max(0, 5 - minFret) * 4;
+
+    // World-units-per-fret near mid-neck. Used by the camera-X hysteresis
+    // gate (issue #34) to convert a fret-equivalent dead zone into world
+    // units. Pure function of SCALE — hoist out of update()'s hot path.
+    // `let` (not `const`): recomputed alongside _fretLabelScaleRefW when the
+    // fret-spacing mode flips at runtime — see _recomputeFretSpacingDerived.
+    let FRET_WIDTH_MID = fretX(7) - fretX(6);
+
+    // Recompute the fretX-derived scalars baked at module init. Called from
+    // h3dSetFretSpacing after _h3dFretUniform flips so label scaling and the
+    // camera hysteresis threshold track the newly chosen spacing — the live
+    // alternative to the old location.reload(), which ejected the user from
+    // Settings back to the home screen.
+    function _recomputeFretSpacingDerived() {
+        _fretLabelScaleRefW = Math.max(1e-8, fretColumnWorldW(FRET_LABEL_SCALE_REF_FRET));
+        FRET_WIDTH_MID = fretX(7) - fretX(6);
+    }
+
+    function computeBPM(beats, t) {
+        if (!beats || beats.length < 2) return 120;
+        let lo = 0, hi = beats.length;
+        while (lo < hi) {
+            const mid = (lo + hi) >> 1;
+            if (beats[mid].time < t) lo = mid + 1; else hi = mid;
+        }
+        let closest = lo;
+        if (lo === beats.length) closest = beats.length - 1;
+        else if (lo > 0 && Math.abs(beats[lo - 1].time - t) < Math.abs(beats[lo].time - t)) closest = lo - 1;
+        const start = Math.max(0, closest - 2);
+        const end = Math.min(beats.length - 1, closest + 2);
+        let sum = 0, count = 0;
+        for (let i = start; i < end; i++) {
+            const dt = beats[i + 1].time - beats[i].time;
+            if (dt > 0) { sum += dt; count++; }
+        }
+        return count > 0 && sum > 0 ? 60 / (sum / count) : 120;
+    }
+
+    // Build a horizontal gaussian DataTexture for the sustain-rail bloom effect.
+    // Returns a W×1 RGBA texture where alpha follows exp(-0.5*(u−0.5)²/σ²),
+    // peaking at 1.0 in the centre. With the default σ=0.28 the edges retain
+    // ~0.20 alpha (not fully transparent) — a deliberately soft, wide falloff
+    // so the additive bloom fades gradually rather than cutting off sharply.
+    // Power-of-two width keeps WebGL mipmapping happy.
+    function _makeGaussTex(ThreeLib, w = 128, sigma = 0.28) {
+        const data = new Uint8Array(w * 4);
+        for (let i = 0; i < w; i++) {
+            const u = i / (w - 1);
+            const d = (u - 0.5) / sigma;
+            const v = Math.exp(-0.5 * d * d);
+            const a = Math.round(v * 255);
+            data[i * 4]     = 255;
+            data[i * 4 + 1] = 255;
+            data[i * 4 + 2] = 255;
+            data[i * 4 + 3] = a;
+        }
+        const tex = new ThreeLib.DataTexture(data, w, 1, ThreeLib.RGBAFormat);
+        // LinearFilter on both axes so the bloom plane interpolates smoothly
+        // when scaled — the default NearestFilter causes visible banding.
+        tex.magFilter = ThreeLib.LinearFilter;
+        tex.minFilter = ThreeLib.LinearFilter;
+        tex.needsUpdate = true;
+        return tex;
+    }
+
+    /* ======================================================================
+     *  Three.js module — lazily loaded, memoized
+     * ====================================================================== */
+
+    let T = null;
+    let threeLoadPromise = null;
+    function loadThree() {
+        if (!threeLoadPromise) {
+            threeLoadPromise = import(THREE_URL)
+                .then(mod => { T = mod; return mod; })
+                .catch(() => import(THREE_CDN)
+                    .then(mod => { T = mod; return mod; })
+                    .catch(e => {
+                        console.error('[3D-Hwy] Three.js load failed:', e);
+                        threeLoadPromise = null;
+                        throw e;
+                    }));
+        }
+        return threeLoadPromise;
+    }
+
+    /* ======================================================================
+     *  Splitscreen helpers
+     * ====================================================================== */
+
+    function _ssActive() {
+        const ss = window.feedBackSplitscreen;
+        if (!ss || typeof ss.isActive !== 'function' || !ss.isActive()) return false;
+        return typeof ss.isCanvasFocused === 'function'
+            && typeof ss.onFocusChange === 'function'
+            && typeof ss.offFocusChange === 'function';
+    }
+
+    function _ssIsCanvasFocused(highwayCanvas) {
+        const ss = window.feedBackSplitscreen;
+        if (!_ssActive()) return true;
+        return !!(ss && typeof ss.isCanvasFocused === 'function' &&
+            ss.isCanvasFocused(highwayCanvas));
+    }
+
+    // Shortcut for the wide-pane framing tuner. Opens/closes the floating panel
+    // (the A/B on/off and the per-pane target live inside it now). Registered
+    // once per session via a module-level guard (it drives shared module state,
+    // so per-instance registration would stack duplicate handlers and cancel
+    // itself out); it's a harmless debug control, so it is never unregistered.
+    // No-ops where the core shortcut API isn't present (older core / borrowed
+    // contexts).
+    let _tunerShortcutRegistered = false;
+    function _registerTunerShortcut() {
+        if (_tunerShortcutRegistered) return;
+        if (typeof window.registerShortcut !== 'function') return;
+        _tunerShortcutRegistered = true;
+        try {
+            window.registerShortcut({
+                key: 'A',   // uppercase e.key → produced with Shift held (Shift+A)
+                description: '3D Highway: open/close wide-pane framing tuner (Shift+A)',
+                scope: 'player',
+                handler: () => {
+                    // Open/close the live tuner panel. The A/B on/off and the
+                    // per-pane target now live in the panel itself, so the
+                    // shortcut is just a dismiss/reveal.
+                    _toggleAspectPanel();
+                },
+            });
+        } catch (e) {
+            _tunerShortcutRegistered = false;   // allow a later retry if it threw
+        }
+    }
+
+    // ── Wide-pane framing: live tuner bridge + panel ──────────────────────────
+    // window.__h3dAspectTune is the single source of truth the renderer reads
+    // each frame (see effectiveVfov + camUpdate). The defaults reproduce the
+    // current framing exactly (enabled:false). Values persist to localStorage so
+    // a tuning session survives reloads; the floating panel (Shift+A) writes the
+    // same object live. All of this is a debug aid — none of it runs unless the
+    // user opts in.
+    // Versioned key: the first iteration shipped a broken default (enabled:true,
+    // baseVfov:30) and may have persisted it. Bumping the key ignores that stale
+    // state so the corrected default-off config actually takes effect.
+    const _ASPECT_LS = 'h3d_aspect_tune2';
+    // Working defaults. Default OFF, so out of the box this is an exact no-op —
+    // every pane renders byte-for-byte as before (effectiveVfov returns
+    // BASE_VFOV and the pose nudges gate off). The config is also coherent when
+    // a tester turns it ON via Shift+A: baseVfov == BASE_VFOV so normal ~16:9
+    // panes (single-player, most 2x2) stay at 70° even enabled, and only panes
+    // wider than startAspect (2.25) engage the Hor+ hold; blend:1 makes that
+    // hold actually take effect; minVfovDeg (28) sits below baseVfov so the floor
+    // is a real floor. The pose nudges are the in-progress wide-pane look a
+    // tester sees once enabled. localStorage overrides all of this per machine.
+    const _ASPECT_DEFAULTS = {
+        enabled: false, baseVfov: BASE_VFOV, startAspect: 2.25, hfovDeg: null,
+        blend: 1, minVfovDeg: HORPLUS_MIN_VFOV, splitOnly: false,
+        heightMul: 0.30, distMul: 0.95, pitchAdd: -1.5, lookDepthMul: 1,
+    };
+    // Slider specs (numeric fields). Checkboxes (enabled/splitOnly) + the hfov
+    // override are handled separately in the panel builder. Ranges are wide on
+    // purpose — this is a tuning aid, the no-op default sits mid-range.
+    const _ASPECT_FIELDS = [
+        { k: 'baseVfov',     label: 'Base vFOV°',   min: 18,  max: 90,  step: 1 },
+        { k: 'startAspect',  label: 'Start aspect', min: 1.0, max: 4.0, step: 0.05 },
+        { k: 'blend',        label: 'Blend',        min: 0,   max: 1,   step: 0.05 },
+        { k: 'minVfovDeg',   label: 'Min vFOV°',    min: 10,  max: 60,  step: 1 },
+        { k: 'heightMul',    label: 'Height ×',     min: 0.1, max: 2.5, step: 0.05 },
+        { k: 'distMul',      label: 'Dolly ×',      min: 0.2, max: 3.0, step: 0.05 },
+        { k: 'pitchAdd',     label: 'Pitch +',      min: -40, max: 40,  step: 0.5 },
+        // Aims the camera further down the neck (>1) or pulls the aim back (<1).
+        // This is the lever that flattens the mid-distance "hump" toward a
+        // straight gradual recede.
+        { k: 'lookDepthMul', label: 'Look depth',   min: 0.2, max: 3.0, step: 0.05 },
+    ];
+    let _aspectPanelEl = null;        // the floating panel root (built once)
+    let _aspectPanelRO = null;        // readout <div>
+    let _aspectPanelRAF = 0;          // readout poll handle
+    let _aspectTargetSel = null;      // the "Target" <select>
+    let _aspectTgtRow = null;         // the Target row (hidden when only one pane)
+    let _aspectHfovCb = null;         // hfov-override checkbox (synced explicitly)
+    let _aspectHfovSl = null;         // hfov-override slider
+    // Which pane the panel edits. '' = all panes (writes the shared base object);
+    // a pane key ('arr:<name>' or the fallback 'pane:<uid>') writes that pane's
+    // sparse override, so one split pane can be framed independently.
+    let _aspectEditTarget = '';
+    // Bumped when the SET of live panes changes (add/prune) so the panel rebuilds
+    // the Target dropdown — never on a per-frame label re-report, which would
+    // flicker the <select>.
+    let _aspectPanesDirty = true;
+    // Monotonic counter for the per-instance fallback key (when a pane has no
+    // arrangement name to key by).
+    let _aspectPaneCounter = 0;
+    function _aspectNowMs() {
+        try { if (performance && performance.now) return performance.now(); } catch (e) {}
+        try { return Date.now(); } catch (e) { return 0; }   // keep pruning functional
+    }
+    // Pane key: prefer the arrangement name ('arr:Bass') so a pane's framing is
+    // stable across songs AND distinct between split panes, with no dependency on
+    // the external splitscreen panel index (which isn't always available). Fall
+    // back to a per-instance id ('pane:3') when there's no arrangement.
+    function _aspectPaneKey(arrangement, uid) {
+        const a = (typeof arrangement === 'string') ? arrangement.trim() : '';
+        return a ? ('arr:' + a) : ('pane:' + uid);
+    }
+    // Human label derived from the key.
+    function _aspectPaneLabel(paneKey) {
+        if (paneKey.slice(0, 4) === 'arr:') return paneKey.slice(4);
+        if (paneKey.slice(0, 5) === 'pane:') return 'Pane ' + paneKey.slice(5);
+        return paneKey;
+    }
+
+    // Get-or-create the shared bridge object, seeded from defaults + localStorage.
+    // May carry a sparse `__panels` map of per-pane overrides.
+    function _aspectTune() {
+        let t = window.__h3dAspectTune;
+        if (!t || typeof t !== 'object') {
+            t = Object.assign({}, _ASPECT_DEFAULTS);
+            try {
+                const raw = localStorage.getItem(_ASPECT_LS);
+                if (raw) Object.assign(t, JSON.parse(raw));
+            } catch (e) {}
+            window.__h3dAspectTune = t;
+        }
+        return t;
+    }
+    // Bumped on every tune mutation (all writes funnel through _aspectPersist) so
+    // the per-pane resolve cache below can invalidate cheaply.
+    let _aspectRev = 0;
+    function _aspectPersist() {
+        _aspectRev++;
+        try {
+            const t = _aspectTune(), out = {};
+            Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = t[k]; });
+            // Persist per-pane overrides keyed by arrangement ('arr:*') only, so a
+            // pane's framing carries across songs. Instance-id fallback keys
+            // ('pane:*') are session-only — persisting them would leak a new key
+            // every reload.
+            if (t.__panels) {
+                const p = {}; let any = false;
+                Object.keys(t.__panels).forEach((k) => {
+                    if (k.slice(0, 4) === 'arr:') { p[k] = t.__panels[k]; any = true; }
+                });
+                if (any) out.__panels = p;
+            }
+            localStorage.setItem(_ASPECT_LS, JSON.stringify(out));
+        } catch (e) {}
+    }
+
+    // Resolve the effective tune for a pane: the shared base, with that pane's
+    // override keys (if any) laid on top. Called every frame per renderer, so the
+    // merged object is memoized per pane and only rebuilt when the tune mutates
+    // (_aspectRev changes). Panes with no override return the base directly (no
+    // allocation).
+    const _aspectResolveCache = new Map();   // paneKey -> { rev, obj }
+    function _resolveTuneFor(paneKey) {
+        const base = _aspectTune();
+        const ov = base.__panels && base.__panels[paneKey];
+        if (!ov) return base;
+        const c = _aspectResolveCache.get(paneKey);
+        if (c && c.rev === _aspectRev) return c.obj;
+        const out = {};
+        Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = (k in ov) ? ov[k] : base[k]; });
+        _aspectResolveCache.set(paneKey, { rev: _aspectRev, obj: out });
+        return out;
+    }
+    // Record a live pane so the Target dropdown can list it. Called every frame
+    // by each renderer with its pane key. `seen` is refreshed each call for
+    // pruning; the dropdown is only marked dirty when a pane is newly added — not
+    // on every re-report, which would flicker the <select>.
+    function _aspectRegisterPane(paneKey) {
+        const reg = window.__h3dAspectPanes || (window.__h3dAspectPanes = {});
+        const label = _aspectPaneLabel(paneKey);
+        let e = reg[paneKey];
+        if (!e) { e = reg[paneKey] = { label, seen: 0 }; _aspectPanesDirty = true; }
+        else if (e.label !== label) { e.label = label; _aspectPanesDirty = true; }
+        e.seen = _aspectNowMs();
+    }
+    // Drop panes not reported recently (song change, split teardown, pane close).
+    function _aspectPrunePanes() {
+        const reg = window.__h3dAspectPanes;
+        if (!reg) return;
+        const now = _aspectNowMs();
+        const ro = window.__h3dAspectReadout;
+        Object.keys(reg).forEach((k) => {
+            if (now - (reg[k].seen || 0) > 1500) {
+                delete reg[k];
+                // Prune the matching readout slot so it can't grow unbounded as
+                // songs/arrangements churn, and drop a dangling __last pointer.
+                if (ro) { delete ro[k]; if (ro.__last === k) delete ro.__last; }
+                _aspectPanesDirty = true;
+            }
+        });
+    }
+
+    // True while _syncAspectPanel is programmatically refreshing controls, so the
+    // synthetic 'input' events it dispatches to update labels don't write back
+    // into the tune (which would populate a full override for every field and
+    // spam localStorage). Real user input runs with this false.
+    let _aspectSyncing = false;
+    // Read/write against the current edit target ('' → base, else pane override).
+    function _aspectReadVal(k) {
+        const base = _aspectTune();
+        if (!_aspectEditTarget) return base[k];
+        const ov = base.__panels && base.__panels[_aspectEditTarget];
+        return (ov && (k in ov)) ? ov[k] : base[k];
+    }
+    function _aspectWriteVal(k, v) {
+        const base = _aspectTune();
+        if (!_aspectEditTarget) { base[k] = v; }
+        else {
+            const m = base.__panels || (base.__panels = {});
+            (m[_aspectEditTarget] || (m[_aspectEditTarget] = {}))[k] = v;
+        }
+        _aspectPersist();
+    }
+    // Clear a field: for the base target set the explicit auto value (null); for a
+    // pane target delete the override key so the pane re-inherits the base value
+    // (and drop the pane's override object once it's empty).
+    function _aspectClearVal(k) {
+        const base = _aspectTune();
+        if (!_aspectEditTarget) { base[k] = null; }
+        else {
+            const m = base.__panels, ov = m && m[_aspectEditTarget];
+            if (ov) { delete ov[k]; if (!Object.keys(ov).length) delete m[_aspectEditTarget]; }
+        }
+        _aspectPersist();
+    }
+
+    // (Re)build the Target dropdown from the live pane registry, preserving the
+    // current selection when it's still valid.
+    function _aspectBuildTargets() {
+        if (!_aspectTargetSel) return;
+        // Don't yank a dropdown the user is actively interacting with — leave it
+        // dirty and rebuild on a later tick once it's no longer focused.
+        if (document.activeElement === _aspectTargetSel) return;
+        const reg = window.__h3dAspectPanes || {};
+        const keys = Object.keys(reg).sort();
+        _aspectTargetSel.innerHTML = '';
+        const all = document.createElement('option');
+        all.value = ''; all.textContent = keys.length > 1 ? 'All panes' : 'All';
+        _aspectTargetSel.appendChild(all);
+        keys.forEach((pk) => {
+            const o = document.createElement('option');
+            o.value = pk; o.textContent = reg[pk].label;
+            _aspectTargetSel.appendChild(o);
+        });
+        // Force the edit target back to "All" when the Target row is hidden
+        // (single pane) or the selected pane is gone — otherwise a stale pane
+        // target would silently route edits into a hidden (and persistent
+        // arr:*) override in single-player.
+        if (keys.length <= 1 || (_aspectEditTarget && !reg[_aspectEditTarget])) {
+            _aspectEditTarget = '';
+        }
+        _aspectTargetSel.value = _aspectEditTarget;
+        // The Target row only matters with more than one pane (a split). With a
+        // single pane there's nothing to disambiguate, so hide it.
+        if (_aspectTgtRow) _aspectTgtRow.style.display = keys.length > 1 ? '' : 'none';
+        _aspectPanesDirty = false;
+    }
+
+    function _ensureAspectPanel() {
+        if (_aspectPanelEl || typeof document === 'undefined') return;
+        const wrap = document.createElement('div');
+        wrap.id = 'h3d-aspect-tuner';
+        wrap.style.cssText = [
+            'position:fixed', 'top:64px', 'right:12px', 'z-index:99999',
+            'width:236px', 'padding:10px 12px', 'border-radius:8px',
+            'background:rgba(12,18,28,0.92)', 'border:1px solid rgba(120,150,200,0.35)',
+            'box-shadow:0 6px 24px rgba(0,0,0,0.5)', 'color:#cfe0f5',
+            'font:11px/1.35 system-ui,sans-serif', 'user-select:none',
+            'pointer-events:auto',
+        ].join(';');
+
+        // Header: title + close (×). Close hides the panel; the feature keeps
+        // whatever enabled state it had — this is a dismiss, not an A/B toggle.
+        const hdr = document.createElement('div');
+        hdr.style.cssText = 'display:flex;align-items:center;justify-content:space-between;margin-bottom:6px;';
+        const title = document.createElement('div');
+        title.textContent = 'Wide-pane framing';
+        title.style.cssText = 'font-weight:700;color:#e8c040;';
+        const close = document.createElement('button');
+        close.type = 'button';                 // never submit if nested in a <form>
+        close.textContent = '×';
+        close.title = 'Close (Shift+A)';
+        close.setAttribute('aria-label', 'Close');
+        close.style.cssText = 'border:none;background:transparent;color:#cfe0f5;font-size:17px;line-height:1;cursor:pointer;padding:0 2px;';
+        close.addEventListener('click', () => _setAspectPanelVisible(false));
+        hdr.appendChild(title); hdr.appendChild(close); wrap.appendChild(hdr);
+
+        // Target selector — which pane the controls below edit.
+        const tgtRow = document.createElement('div'); tgtRow.style.cssText = 'margin:2px 0 7px;';
+        _aspectTgtRow = tgtRow;
+        const tgtLab = document.createElement('div');
+        tgtLab.textContent = 'Target'; tgtLab.style.cssText = 'color:#9fb0c8;margin-bottom:2px;';
+        _aspectTargetSel = document.createElement('select');
+        _aspectTargetSel.setAttribute('aria-label', 'Target pane');
+        _aspectTargetSel.style.cssText = 'width:100%;background:rgba(30,44,66,0.9);color:#cfe0f5;border:1px solid rgba(120,150,200,0.4);border-radius:4px;padding:3px;';
+        _aspectTargetSel.addEventListener('change', () => {
+            _aspectEditTarget = _aspectTargetSel.value; _syncAspectPanel();
+        });
+        tgtRow.appendChild(tgtLab); tgtRow.appendChild(_aspectTargetSel); wrap.appendChild(tgtRow);
+        _aspectBuildTargets();
+
+        // enabled + splitOnly checkboxes (per-target)
+        [['enabled', 'Enabled'], ['splitOnly', 'Split panes only']].forEach(([k, lbl]) => {
+            const row = document.createElement('label');
+            row.style.cssText = 'display:flex;align-items:center;gap:6px;margin:2px 0;cursor:pointer;';
+            const cb = document.createElement('input');
+            cb.type = 'checkbox'; cb.checked = !!_aspectReadVal(k); cb.dataset.k = k;
+            cb.addEventListener('change', () => { _aspectWriteVal(k, cb.checked); });
+            const span = document.createElement('span'); span.textContent = lbl;
+            row.appendChild(cb); row.appendChild(span); wrap.appendChild(row);
+        });
+
+        // numeric sliders (per-target)
+        _ASPECT_FIELDS.forEach((f) => {
+            const row = document.createElement('div');
+            row.style.cssText = 'margin:5px 0;';
+            const head = document.createElement('div');
+            head.style.cssText = 'display:flex;justify-content:space-between;';
+            const lab = document.createElement('span'); lab.textContent = f.label;
+            const val = document.createElement('span');
+            val.style.cssText = 'color:#8fb6ff;font-variant-numeric:tabular-nums;';
+            head.appendChild(lab); head.appendChild(val); row.appendChild(head);
+            const sl = document.createElement('input');
+            sl.type = 'range'; sl.min = f.min; sl.max = f.max; sl.step = f.step;
+            const rv = _aspectReadVal(f.k);
+            sl.value = Number.isFinite(rv) ? rv : _ASPECT_DEFAULTS[f.k];
+            sl.dataset.k = f.k;
+            sl.style.cssText = 'width:100%;';
+            const show = () => { val.textContent = (+sl.value).toFixed(f.step < 1 ? 2 : 0); };
+            show();
+            sl.addEventListener('input', () => {
+                show();                                   // label always refreshes
+                if (!_aspectSyncing) _aspectWriteVal(f.k, parseFloat(sl.value));
+            });
+            row.appendChild(sl); wrap.appendChild(row);
+        });
+
+        // hfov override (checkbox enables a slider; off → hfovDeg=null = auto)
+        {
+            const row = document.createElement('div'); row.style.cssText = 'margin:5px 0;';
+            const head = document.createElement('label');
+            head.style.cssText = 'display:flex;align-items:center;gap:6px;cursor:pointer;';
+            const cb = document.createElement('input');
+            cb.type = 'checkbox'; cb.checked = Number.isFinite(_aspectReadVal('hfovDeg'));
+            const lbl = document.createElement('span'); lbl.textContent = 'Override held hFOV°';
+            head.appendChild(cb); head.appendChild(lbl); row.appendChild(head);
+            const sl = document.createElement('input');
+            sl.type = 'range'; sl.min = 40; sl.max = 160; sl.step = 1;
+            const hv = _aspectReadVal('hfovDeg');
+            sl.value = Number.isFinite(hv) ? hv : 102;
+            sl.disabled = !cb.checked;
+            sl.style.cssText = 'width:100%;';
+            cb.addEventListener('change', () => {
+                if (_aspectSyncing) return;
+                sl.disabled = !cb.checked;
+                if (cb.checked) _aspectWriteVal('hfovDeg', parseFloat(sl.value));
+                else _aspectClearVal('hfovDeg');   // base → auto (null); pane → re-inherit base
+            });
+            sl.addEventListener('input', () => {
+                if (!_aspectSyncing && cb.checked) _aspectWriteVal('hfovDeg', parseFloat(sl.value));
+            });
+            row.appendChild(sl); wrap.appendChild(row);
+            _aspectHfovCb = cb; _aspectHfovSl = sl;
+        }
+
+        // live readout
+        _aspectPanelRO = document.createElement('div');
+        _aspectPanelRO.style.cssText = 'margin-top:6px;padding-top:6px;border-top:1px solid rgba(120,150,200,0.25);color:#9fb;font-variant-numeric:tabular-nums;';
+        _aspectPanelRO.textContent = 'aspect — · vFOV —';
+        wrap.appendChild(_aspectPanelRO);
+
+        // buttons
+        const btnRow = document.createElement('div');
+        btnRow.style.cssText = 'display:flex;gap:6px;margin-top:8px;';
+        const mkBtn = (txt, fn) => {
+            const b = document.createElement('button');
+            b.type = 'button';                 // never submit if nested in a <form>
+            b.textContent = txt;
+            b.style.cssText = 'flex:1;padding:4px 0;border-radius:5px;border:1px solid rgba(120,150,200,0.4);background:rgba(40,60,90,0.6);color:#cfe0f5;cursor:pointer;font:11px system-ui;';
+            b.addEventListener('click', fn);
+            return b;
+        };
+        // Reset: for "All" restores the shared defaults exactly; for a pane
+        // clears that pane's override so it inherits the shared base again. Panel
+        // visibility is independent (Shift+A / ×), so Reset doesn't force it open.
+        btnRow.appendChild(mkBtn('Reset', () => {
+            const base = _aspectTune();
+            if (!_aspectEditTarget) {
+                Object.keys(_ASPECT_DEFAULTS).forEach((k) => { base[k] = _ASPECT_DEFAULTS[k]; });
+            } else if (base.__panels) {
+                delete base.__panels[_aspectEditTarget];
+            }
+            _aspectPersist(); _syncAspectPanel();
+        }));
+        // Copy: the resolved values for the current target, as JSON.
+        btnRow.appendChild(mkBtn('Copy', () => {
+            const r = _aspectEditTarget ? _resolveTuneFor(_aspectEditTarget) : _aspectTune();
+            const out = {};
+            Object.keys(_ASPECT_DEFAULTS).forEach((k) => { out[k] = r[k]; });
+            const json = JSON.stringify(out, null, 2);
+            try { console.log('[h3d] wide-pane framing values (' + (_aspectEditTarget || 'all') + '):\n' + json); } catch (e) {}
+            try { if (navigator.clipboard) navigator.clipboard.writeText(json); } catch (e) {}
+        }));
+        wrap.appendChild(btnRow);
+
+        document.body.appendChild(wrap);
+        _aspectPanelEl = wrap;
+        _aspectPanelEl.style.display = 'none';
+    }
+
+    // Push the current target's values back into the panel controls (after Reset,
+    // a target switch, or an external edit). Cheap; only runs on demand.
+    function _syncAspectPanel() {
+        if (!_aspectPanelEl) return;
+        _aspectBuildTargets();
+        // Guard so the synthetic 'input' events below only refresh labels and
+        // don't write the read-back values into the target (which would turn a
+        // sparse pane override into a full one and spam localStorage).
+        _aspectSyncing = true;
+        try {
+            _aspectPanelEl.querySelectorAll('input[type=checkbox][data-k]').forEach((cb) => {
+                cb.checked = !!_aspectReadVal(cb.dataset.k);
+            });
+            _aspectPanelEl.querySelectorAll('input[type=range][data-k]').forEach((sl) => {
+                const v = _aspectReadVal(sl.dataset.k);
+                if (Number.isFinite(v)) sl.value = v;
+                sl.dispatchEvent(new Event('input'));   // refresh the value label only
+            });
+            if (_aspectHfovCb) {
+                const hv = _aspectReadVal('hfovDeg');
+                _aspectHfovCb.checked = Number.isFinite(hv);
+                _aspectHfovSl.disabled = !_aspectHfovCb.checked;
+                if (Number.isFinite(hv)) _aspectHfovSl.value = hv;
+            }
+        } finally {
+            _aspectSyncing = false;
+        }
+    }
+
+    function _setAspectPanelVisible(on) {
+        _ensureAspectPanel();
+        if (!_aspectPanelEl) return;
+        _aspectPanelEl.style.display = on ? 'block' : 'none';
+        window.__h3dAspectPanelOpen = !!on;        // gates the per-frame readout publish
+        // Prune before the first build so panes from a prior song/split don't
+        // flash in the dropdown until the first RAF tick.
+        if (on) { _aspectPrunePanes(); _aspectBuildTargets(); }
+        if (on && !_aspectPanelRAF) {
+            const tick = () => {
+                if (!window.__h3dAspectPanelOpen) { _aspectPanelRAF = 0; return; }
+                _aspectPrunePanes();
+                if (_aspectPanesDirty) _aspectBuildTargets();
+                const ro = window.__h3dAspectReadout;
+                if (_aspectPanelRO && ro) {
+                    const key = _aspectEditTarget || ro.__last;
+                    const e = key && ro[key];
+                    if (e && Number.isFinite(e.aspect)) {
+                        _aspectPanelRO.textContent =
+                            'aspect ' + e.aspect.toFixed(2) + ' · vFOV ' + e.vfov.toFixed(1) + '°';
+                    }
+                }
+                _aspectPanelRAF = requestAnimationFrame(tick);
+            };
+            _aspectPanelRAF = requestAnimationFrame(tick);
+        }
+    }
+    // Toggle the panel open/closed (the Shift+A dismiss/reveal).
+    function _toggleAspectPanel() {
+        _ensureAspectPanel();
+        const open = !(_aspectPanelEl && _aspectPanelEl.style.display !== 'none');
+        _setAspectPanelVisible(open);
+        if (open) _syncAspectPanel();
+    }
+
+    /* ======================================================================
+     *  Background animations (issue #13)
+     *
+     *  Audio-reactive ambient scenery in the fog band beyond the highway.
+     *  Module-level singletons share an AudioContext + AnalyserNode tap on
+     *  the feedBack core <audio id="audio"> element across all panel
+     *  instances; per-panel settings live in localStorage with a global
+     *  fallback so settings.html drives a single default while per-panel
+     *  overrides (h3d_bg_panel<idx>_*) can be set for splitscreen layouts.
+     *
+     *  Caveat: createMediaElementSource() can only be called once per
+     *  element. 3dhighway owns that source for now; future plugins
+     *  needing an analyser will have to share through a core API.
+     * ====================================================================== */
+
+    // Returned from _bgReadBands when reactive=false or analyser
+    // unavailable; shared so the per-frame non-reactive path doesn't
+    // allocate. Declared up-front because _bgBandsCache initializes to
+    // it during the same IIFE execution pass.
+    const BG_ZERO_BANDS = Object.freeze({ bass: 0, mid: 0, treble: 0 });
+
+    // Module-level AudioContext singleton. Intentionally never torn
+    // down: createMediaElementSource(<audio>) is irrevocable — once
+    // called, the element's audio is permanently routed through this
+    // context for the page's lifetime. Closing the context would
+    // silence playback. The leak (one AudioContext + one AnalyserNode,
+    // a few KB) is the cost of having a plugin tap audio at all.
+    let _bgAudio = null;
+    // The core (#audio-tap) cache is held separately from the stems cache so
+    // we can switch back to it without re-calling createMediaElementSource on
+    // #audio — that call is one-shot per element, and a second one throws
+    // InvalidStateError (which would then be marked permanent and disable
+    // reactivity forever on legacy songs after any sloppak detour).
+    let _bgAudioCore = null;
+    let _bgAudioFailedAt = 0;  // performance.now() of last failure, 0 = never
+    const _BG_AUDIO_RETRY_MS = 1000;
+    // _bgReadBands sums bins 0..7 (bass), 8..39 (mid), 40..127 (treble),
+    // so the frequency buffer must hold at least 128 bins regardless of
+    // the source analyser's fftSize.
+    const BG_FREQ_BINS = 128;
+    const _bgBridgeKeys = new Map();
+    function _bgRecordAudioBridge(bridgeId, legacySurface, outcome = 'handled', reason = '', status = 'used') {
+        const key = `${outcome}:${status}:${reason}`;
+        if (_bgBridgeKeys.get(bridgeId) === key) return;
+        _bgBridgeKeys.set(bridgeId, key);
+        const session = window.feedBack && window.feedBack.audioSession;
+        if (!session || typeof session.recordBridgeHit !== 'function') return;
+        try {
+            session.recordBridgeHit({
+                domain: 'audio-mix',
+                bridgeId,
+                legacySurface,
+                participantId: 'highway_3d',
+                outcome,
+                status,
+                reason,
+            });
+        } catch (_) { /* diagnostics are best-effort */ }
+    }
+
+    function _bgGetAnalyser() {
+        // Prefer the stems plugin's side-chain analyser when a sloppak is
+        // loaded. As of feedBack-plugin-stems 0.5.0 (sample-locked playback)
+        // the #audio element is a silent virtual transport on sloppaks, so
+        // tapping it sees only silence; the stems mix is exposed at
+        // window.feedBack.stems.getAnalyser() instead. The stems plugin
+        // creates and destroys that AnalyserNode per song, so we re-check
+        // each call and key the cache on its identity — when the node
+        // changes (song switch), the cache is replaced automatically.
+        const stemsApi = window.feedBack && window.feedBack.stems;
+        const stemsAnalyser = (stemsApi && typeof stemsApi.getAnalyser === 'function')
+            ? stemsApi.getAnalyser() : null;
+        if (stemsAnalyser) {
+            if (!_bgAudio || _bgAudio.source !== 'stems' || _bgAudio.analyser !== stemsAnalyser) {
+                // Adopt the live stems analyser. Do NOT close its context — it's
+                // shared with stem playback and the stems plugin owns its
+                // lifecycle. No play-event resume hooks either; the stems
+                // plugin manages context resume itself.
+                _bgAudio = {
+                    ctx: stemsAnalyser.context,
+                    analyser: stemsAnalyser,
+                    // _bgReadBands reads bins 0..127 unconditionally. Always
+                    // allocate at least 128 bytes so a smaller analyser (e.g.
+                    // fftSize < 256) can't leave undefined values in the loop.
+                    freq: new Uint8Array(Math.max(BG_FREQ_BINS, stemsAnalyser.frequencyBinCount)),
+                    source: 'stems',
+                };
+                _bgRecordAudioBridge('audio-mix.analyser', 'window.feedBack.stems.getAnalyser', 'handled', '', 'stems');
+            }
+            return _bgAudio;
+        }
+        // No sloppak active — drop a stale stems-sourced cache, restoring the
+        // core-tap cache if we'd already built one. Without this, the next
+        // step would try to createMediaElementSource(#audio) a second time
+        // (one-shot per element) and throw InvalidStateError — disabling
+        // reactivity for the rest of the page lifetime.
+        if (_bgAudio && _bgAudio.source === 'stems') _bgAudio = _bgAudioCore;
+
+        if (_bgAudio && !_bgAudio.failed) return _bgAudio;
+        if (_bgAudio && _bgAudio.failed) {
+            // Distinguish permanent failures from transient ones.
+            // InvalidStateError on createMediaElementSource means the
+            // <audio> element is already tapped by another consumer —
+            // there's no recovering from that without a page reload, so
+            // don't retry. Transient failures (NotAllowedError before
+            // first user gesture, etc.) get a once-per-second retry so
+            // reactivity recovers once the blocking condition clears.
+            if (_bgAudio.permanent) return null;
+            if (performance.now() - _bgAudioFailedAt < _BG_AUDIO_RETRY_MS) return null;
+        }
+        const audio = document.getElementById('audio');
+        if (!audio) return null;
+        // Shared tap: createMediaElementSource is one-shot per element, so
+        // the FIRST visualizer to tap #audio publishes it at
+        // window.__feedBackAudioTap and every later one (this plugin, the
+        // drum/keys 3D highways) adopts it instead of throwing
+        // InvalidStateError when visualizers are switched or mixed in
+        // splitscreen.
+        const sharedTap = window.__feedBackAudioTap;
+        if (sharedTap && sharedTap.analyser && sharedTap.mediaEl === audio) {
+            _bgAudio = {
+                ctx: sharedTap.ctx,
+                analyser: sharedTap.analyser,
+                freq: new Uint8Array(Math.max(BG_FREQ_BINS, sharedTap.analyser.frequencyBinCount)),
+                source: 'core',
+            };
+            _bgAudioCore = _bgAudio;
+            _bgRecordAudioBridge('audio-mix.analyser', 'shared #audio analyser tap', 'handled', '', 'core');
+            return _bgAudio;
+        }
+        // Hoist ctx out of the try so we can close() it if a later step
+        // throws (e.g. createMediaElementSource on an element that
+        // already has a source node). Otherwise the AudioContext leaks.
+        let ctx = null;
+        try {
+            const Ctx = window.AudioContext || window.webkitAudioContext;
+            if (!Ctx) throw new Error('Web Audio API not available');
+            ctx = new Ctx();
+            const source = ctx.createMediaElementSource(audio);
+            const analyser = ctx.createAnalyser();
+            analyser.fftSize = 256;
+            source.connect(analyser);
+            analyser.connect(ctx.destination);
+            _bgAudio = { ctx, analyser, freq: new Uint8Array(Math.max(BG_FREQ_BINS, analyser.frequencyBinCount)), source: 'core' };
+            try { window.__feedBackAudioTap = { ctx, analyser, mediaEl: audio }; } catch (_) {}
+            _bgRecordAudioBridge('audio-mix.analyser', 'HTMLAudioElement analyser tap', 'handled', '', 'core');
+            // Remember the core analyser so a later stems-then-back-to-core
+            // transition can re-use it instead of re-tapping #audio (which
+            // would throw InvalidStateError on the one-shot per element).
+            _bgAudioCore = _bgAudio;
+            // Browsers with autoplay restrictions hand back a suspended
+            // AudioContext; createMediaElementSource then routes the
+            // <audio> through that suspended graph and playback goes
+            // silent (and the analyser reads zeros) until we resume.
+            // Try once now (fine if the page already had a user gesture)
+            // and again on every play event so the first successful
+            // user-initiated play unblocks the graph.
+            const resume = () => {
+                if (ctx.state === 'suspended' && typeof ctx.resume === 'function') {
+                    ctx.resume().catch(() => { /* no gesture yet, retry on next play */ });
+                }
+            };
+            resume();
+            audio.addEventListener('play', resume);
+            return _bgAudio;
+        } catch (e) {
+            if (ctx && typeof ctx.close === 'function') {
+                try { ctx.close(); } catch (_) { /* close errors during failure path are noise */ }
+            }
+            console.warn('[3D-Hwy] failed to set up audio analyser:', e);
+            const permanent = !!(e && e.name === 'InvalidStateError');
+            _bgRecordAudioBridge('audio-mix.analyser', 'HTMLAudioElement analyser tap', 'failed', e && e.message ? e.message : String(e), permanent ? 'permanent-failure' : 'transient-failure');
+            _bgAudio = { failed: true, permanent };
+            _bgAudioFailedAt = performance.now();
+            return null;
+        }
+    }
+
+    // Bands cache: in splitscreen, every panel asks for bands per frame.
+    // The analyser is shared, so the answer is identical — cache for a
+    // few ms so 4-up splitscreen pays one getByteFrequencyData + one sum
+    // pass per frame instead of four.
+    const _BG_BANDS_CACHE_MS = 5;
+    let _bgBandsLastT = -Infinity;
+    // Mutable cache reused across reads — refreshing in place keeps the
+    // per-frame allocation count at zero. Style.update() uses the bands
+    // synchronously within the same frame so the live-mutation contract
+    // is safe.
+    const _bgBandsCache = { bass: 0, mid: 0, treble: 0 };
+    function _bgReadBands() {
+        const a = _bgGetAnalyser();
+        if (!a) return BG_ZERO_BANDS;
+        const t = performance.now();
+        if (t - _bgBandsLastT < _BG_BANDS_CACHE_MS) return _bgBandsCache;
+        _bgBandsLastT = t;
+        a.analyser.getByteFrequencyData(a.freq);
+        let bass = 0, mid = 0, treble = 0;
+        for (let i = 0; i < 8; i++) bass += a.freq[i];
+        for (let i = 8; i < 40; i++) mid += a.freq[i];
+        for (let i = 40; i < 128; i++) treble += a.freq[i];
+        _bgBandsCache.bass = bass / (8 * 255);
+        _bgBandsCache.mid = mid / (32 * 255);
+        _bgBandsCache.treble = treble / (88 * 255);
+        return _bgBandsCache;
+    }
+
+    const BG_DEFAULTS = { style: 'particles', intensity: 0.5, reactive: true, palette: 'default', bgTheme: 'default', hwTheme: 'default', showFretOnNote: true, fretNumberGhostScope: 'chords', cameraSmoothing: 0.5, zoomSmoothing: 0.5, tiltSmoothing: 0.5, cameraLockLow: false, cameraLockZoom: 0.5, cameraMode: 'lookahead', nutHeadstockVisible: true, tuningLabelsVisible: true, nutColor: '#f5f3f0', headstockColor: '#d4b48a', textSize: 0.5, vibrancy: 0.85, glow: 0.25, customImageDataUrl: '', customImageName: '', customVideoName: '', chordDiagramVisible: true, chordDiagramSize: 0.5, chordDiagramPosition: 'tl', fretColumnMarkerCadence: 1, projectionVisible: true, inlayLabelsVisible: false, sectionLabelsOnHighway: false, sectionHudVisible: false, sectionHudPosition: 'tr', sectionHudSize: 0.5, toneHudVisible: false, toneHudPosition: 'tl', toneHudSize: 0.5, fpsVisible: false, fretDividersVisible: true, slideArrowApproachVisible: true, slideArrowNeckVisible: true, slideArrowChainPreviewVisible: true, hitFx: 0.7, sparks: true, cinematic: true, verdictMarks: true, timingFx: true, streakFx: true, bloom: true };
+    // User-selectable, persistable bg styles — must mirror settings.html's
+    // VALID_STYLES. 'venue' is deliberately NOT here: it is an internal effective
+    // style reached only via _venueSceneOverride (the viz-picker Venue flow), so
+    // _bgCoerce must reject a stored h3d_bg_style='venue' — otherwise venue could
+    // mount outside that flow and settings.html (which can't represent 'venue')
+    // would be unable to switch back. BG_STYLES still has a 'venue' renderer entry.
+    const BG_STYLE_IDS = ['off', 'particles', 'silhouettes', 'lights', 'geometric', 'butterchurn', 'image', 'video'];
+    // Scene color themes — TWO INDEPENDENT AXES sharing one palette family.
+    // The combined `BG_THEMES` table below is the single source of truth; each
+    // entry carries the colors for BOTH axes, but the two axes are selected and
+    // applied SEPARATELY (two dropdowns, two settings keys):
+    //   • BACKGROUND axis (setting key `bgTheme`) owns:
+    //       clear — WebGL clear color (the empty background behind everything)
+    //       fog   — distance fog tint (kept === clear so the horizon dissolves
+    //               cleanly instead of showing a seam)
+    //   • HIGHWAY axis (setting key `hwTheme`) owns:
+    //       board   — the fretboard / highway-surface plane color
+    //       lane    — the lit highway lane strip under the gems (optional)
+    //       laneDim — the lane's dimmer alternating row (optional)
+    // Because both axes read from the SAME id-set (the keys of this table), ANY
+    // background id can mix with ANY highway id (e.g. Deep Focus background +
+    // Cathode Green highway); picking the SAME id in both gives the original
+    // "matched" combined look. _bgBackgroundColors()/_bgHighwayColors() below
+    // are the per-axis accessors; both fall back to 'default' for unknown ids.
+    // 'default' reproduces the original look byte-for-byte on BOTH axes, so
+    // existing users (and anyone who never touches either setting) see no
+    // change. A migration in _bgLoadSettings() makes an existing single-`bgTheme`
+    // pick drive BOTH axes until the user diverges them, so upgrades are
+    // visually identical too. All themes keep the board very dark and the
+    // background dark so the bright per-string note gems, lane, and labels
+    // retain contrast. NOTE: settings.html mirrors these ids in its
+    // VALID_BG_THEMES set (shared by both dropdowns) — keep them in sync.
+    // Optional `lane` / `laneDim` fields retint the lit highway lane strip + its
+    // dimmer alternating row. A theme that omits them falls back to the stock
+    // blue lane (HWY_LANE_STRIPE_ODD_HEX / _EVEN_HEX); only 'default' relies on
+    // that fallback (so its output stays byte-identical). Every other theme sets
+    // its own lane so the Highway axis is visibly distinct entry-to-entry — the
+    // near-black neutral boards alone aren't separable, so the lane carries it.
+    // See _applyBgTheme().
+    const BG_THEMES = {
+        default:    { clear: 0x101820, fog: 0x101820, board: 0x08080e },
+        // Cool navy surface + a brighter pure-blue lane, so it reads distinct
+        // from 'default' (neutral board + stock teal-blue lane) on the Highway axis.
+        midnight:   { clear: 0x0a0e1a, fog: 0x0a0e1a, board: 0x080d1c, lane: 0x244fae, laneDim: 0x122a5e },
+        // Lighter NEUTRAL-grey surface + a steel-grey lane — the only mid-dark
+        // neutral board, so the surface itself is visibly different from the
+        // near-black neutrals around it (board kept dark enough for gem contrast).
+        charcoal:   { clear: 0x16181c, fog: 0x16181c, board: 0x141417, lane: 0x525a66, laneDim: 0x282d34 },
+        deeppurple: { clear: 0x140a1e, fog: 0x140a1e, board: 0x0b0610, lane: 0x3a1f6e, laneDim: 0x1f1040 },
+        forest:     { clear: 0x0a1614, fog: 0x0a1614, board: 0x06100c, lane: 0x15602a, laneDim: 0x0a3318 },
+        // Warm dark neutral (espresso/umber) — the first non-cool scene.
+        warmslate:  { clear: 0x1c130b, fog: 0x1c130b, board: 0x0e0805, lane: 0x5e3a12, laneDim: 0x341f0a },
+        // Recessive near-black neutral (a hair above #000000, ~zero chroma) —
+        // maximizes gem-vs-board contrast; a clean stage/stream look. Purest-dark
+        // board + a clean steel-cyan lane (brighter/cooler than 'default's muted
+        // teal-blue) so the Highway axis reads clearly distinct from default.
+        deepfocus:  { clear: 0x0c0c0d, fog: 0x0c0c0d, board: 0x060606, lane: 0x2f7fa0, laneDim: 0x163c4e },
+        // Calm dark teal — blue-dominant so it reads distinct from the navy
+        // 'midnight' and the green 'forest'.
+        deepsea:    { clear: 0x06222b, fog: 0x06222b, board: 0x03141a, lane: 0x0e5a63, laneDim: 0x063338 },
+        // Retro CRT glow — a warm AMBER phosphor cast (the classic amber
+        // terminal). Amber rather than green so a phosphor board can't crush
+        // green/teal gems, and so it stays clearly distinct from 'forest' and
+        // 'deepsea'. Board stays very dark / low-chroma to keep gems popping.
+        cathode:    { clear: 0x140b03, fog: 0x140b03, board: 0x0c0702, lane: 0x6e4a0e, laneDim: 0x3a2806 },
+        // Retro CRT GREEN phosphor — leaned more saturated / cyan-green than
+        // 'forest' so it reads as a terminal, not woodland (dRGB 35 vs forest,
+        // 32 vs deepsea). Phosphor-green board + green lane. Verified to keep
+        // green/teal gems legible (green-on-green floor CR ~2.2).
+        cathodegreen: { clear: 0x07301a, fog: 0x07301a, board: 0x031a0c, lane: 0x0e6e2a, laneDim: 0x073a18 },
+        // Warm hearth — the first warm-RED scene, pairs with the Ember/Sunrise
+        // strings. Deep red, pushed away from the amber 'cathode'/'warmslate'
+        // (dRGB ~26 from cathode). Ember-red lane.
+        hearth:     { clear: 0x280806, fog: 0x280806, board: 0x1a0606, lane: 0x7a2410, laneDim: 0x3f1409 },
+    };
+    const BG_THEME_IDS = Object.keys(BG_THEMES);
+    // Shared lookup for the combined entry (both axes are keyed by the same id
+    // set, so a single id list / coerce check validates either axis).
+    function _bgThemeColors(id) { return BG_THEMES[id] || BG_THEMES.default; }
+    // Per-axis accessors. Background reads clear/fog; highway reads
+    // board/lane/laneDim. They alias the same table — splitting at read-time
+    // keeps one source of truth while letting the two dropdowns pick freely.
+    function _bgBackgroundColors(id) { return _bgThemeColors(id); }
+    function _bgHighwayColors(id) { return _bgThemeColors(id); }
+    const VENUE_SCENE_ASSET_BASE = '/static/assets/venue/themes/small-club/';
+    const VENUE_BG_PLATE_PNG = 'bg-plate.png';
+    const VENUE_BG_PLATE_WEBP = 'bg-plate.webp';
+    const VENUE_INSTRUMENT_PLATES = {
+        guitar: { webp: 'guitar-pov-bg.webp', png: 'guitar-pov-bg.png' },
+        bass: { webp: 'bass-pov-bg.webp', png: 'bass-pov-bg.png' },
+        drums: { webp: 'drums-pov-bg.webp', png: 'drums-pov-bg.png' },
+        piano: { webp: 'piano-pov-bg.webp', png: 'piano-pov-bg.png' },
+        vocals: { webp: 'vocals-pov-bg.webp', png: 'vocals-pov-bg.png' },
+    };
+    let _venueSceneOverride = false;
+    let _venueMoodState = 'idle';
+    let _venueInstrumentPov = 'guitar';
+    let _venueMotionMode = 'subtle';
+    let _venuePlateUrl = '';
+    let _venueSceneAssetsLoaded = false;
+    let _venueSceneLoadFailed = false;
+    const _venueTextureCache = new Map();
+    // Crowd video layers (career mode). venue-crowd.js owns the <video>
+    // elements and the crossfade timing; the renderer only maps them onto
+    // two planes in front of the static plate. _venueCrowdRev bumps on any
+    // element (re)assignment so update() knows to rebind textures.
+    const _venueCrowdVideos = [null, null];
+    let _venueCrowdMix = 0;
+    let _venueCrowdRev = 0;
+
+    function _bgVenueMoodCoeffs(state) {
+        const s = String(state || 'idle').toLowerCase();
+        if (s === 'fire' || s === 'strong') {
+            return { light: 1.0, crowd: 0, haze: 0.012, warmth: 1.02 };
+        }
+        if (s === 'recovery' || s === 'smoke') {
+            return { light: 0.55, crowd: 0, haze: 0.032, warmth: 0.94 };
+        }
+        return { light: 0.72, crowd: 0, haze: VENUE_HAZE_STEADY, warmth: 0.96 };
+    }
+
+    function _venueResolvePovFromInput(input) {
+        if (typeof window !== 'undefined' && window.v3VenueInstrumentPov &&
+            typeof window.v3VenueInstrumentPov.resolveVenueInstrumentPov === 'function') {
+            return window.v3VenueInstrumentPov.resolveVenueInstrumentPov(input);
+        }
+        const s = String(input == null ? '' : input).trim().toLowerCase();
+        if (!s) return 'guitar';
+        if (/\b(drums?)\b/.test(s)) return 'drums';
+        if (/\b(bass)\b/.test(s)) return 'bass';
+        if (/\b(piano|keys|keyboard)\b/.test(s)) return 'piano';
+        if (/\b(karaoke|vocal|vocals|lyric|lyrics|sing|singing)\b/.test(s)) return 'vocals';
+        if (/\b(lead|rhythm|guitar|combo)\b/.test(s)) return 'guitar';
+        return 'guitar';
+    }
+
+    function _venueMotionProfile(mode) {
+        if (typeof window !== 'undefined' && window.v3VenueMoodFx &&
+            typeof window.v3VenueMoodFx.venueMotionProfile === 'function') {
+            return window.v3VenueMoodFx.venueMotionProfile(mode);
+        }
+        const m = String(mode || 'subtle').toLowerCase();
+        if (m === 'off') {
+            return { breathe: 0, parallax: 0, hazeDrift: 0, warmthPulse: 0, shimmer: 0 };
+        }
+        if (m === 'full') {
+            return { breathe: 0.014, parallax: 0.010, hazeDrift: 0.020, warmthPulse: 0.028, shimmer: 0.10 };
+        }
+        return { breathe: 0.005, parallax: 0.004, hazeDrift: 0.007, warmthPulse: 0.010, shimmer: 0.04 };
+    }
+
+    function _venuePrefersReducedMotion() {
+        if (typeof window !== 'undefined' && window.v3VenueMoodFx &&
+            typeof window.v3VenueMoodFx.prefersReducedMotion === 'function') {
+            return window.v3VenueMoodFx.prefersReducedMotion();
+        }
+        return false;
+    }
+
+    function _venueEffectiveMotionMode() {
+        if (!_venueSceneOverride) return 'off';
+        if (_venuePrefersReducedMotion()) return 'off';
+        return _venueMotionMode;
+    }
+
+    function _venueApplyFakeDepthMotion(s, coeffs, t) {
+        const motion = _venueMotionProfile(_venueEffectiveMotionMode());
+        if (!motion.breathe && !motion.parallax && !motion.hazeDrift && !motion.warmthPulse) {
+            if (s.haze && s.haze.mesh) {
+                s.haze.mesh.position.set(s.haze.baseX, s.haze.baseY, s.haze.baseZ);
+            }
+            return motion;
+        }
+        const breath = Math.sin(t * 0.38);
+        const parallax = Math.sin(t * 0.21);
+        const shimmer = Math.sin(t * 0.55);
+        if (s.backdrop && s.backdrop.loaded && s.backdrop.mesh) {
+            const mesh = s.backdrop.mesh;
+            const vh = s.backdrop.lastVisibleHeight || 1;
+            const vw = s.backdrop.lastVisibleWidth || vh;
+            const offX = parallax * motion.parallax * vh;
+            const offY = breath * motion.breathe * vh * 0.35;
+            mesh.position.x += offX;
+            mesh.position.y += offY;
+            const scaleMul = 1 + breath * motion.breathe * 2.5;
+            mesh.scale.set(vw * scaleMul, vh * scaleMul, 1);
+            if (s.backdrop.mat) {
+                const warm = coeffs.warmth;
+                const warmPulse = 1 + shimmer * motion.warmthPulse;
+                s.backdrop.mat.color.setRGB(
+                    warm * warmPulse,
+                    warm * 0.98 * warmPulse,
+                    warm * 0.95 * (1 + shimmer * motion.warmthPulse * 0.6),
+                );
+            }
+        } else if (s.backdrop && s.backdrop.mat) {
+            const warm = coeffs.warmth;
+            s.backdrop.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
+        }
+        if (s.haze && s.haze.mesh) {
+            const driftX = Math.sin(t * 0.18) * motion.hazeDrift * 8 * K;
+            const driftY = Math.cos(t * 0.14) * motion.hazeDrift * 4 * K;
+            s.haze.mesh.position.set(
+                s.haze.baseX + driftX,
+                s.haze.baseY + driftY,
+                s.haze.baseZ,
+            );
+            if (s.haze.mat) {
+                const baseOp = (s.haze.baseOp || VENUE_HAZE_STEADY) * (coeffs.haze / VENUE_HAZE_STEADY);
+                s.haze.mat.opacity = baseOp * (1 + shimmer * motion.shimmer * 0.12);
+            }
+        }
+        return motion;
+    }
+
+    function _venuePlateUrlChain(pov) {
+        const plate = VENUE_INSTRUMENT_PLATES[pov] || VENUE_INSTRUMENT_PLATES.guitar;
+        const base = VENUE_SCENE_ASSET_BASE;
+        return [
+            base + plate.webp,
+            base + plate.png,
+            base + VENUE_BG_PLATE_WEBP,
+            base + VENUE_BG_PLATE_PNG,
+        ];
+    }
+
+    function _venueLoadCachedTexture(loader, url, onSuccess, onFail) {
+        const cached = _venueTextureCache.get(url);
+        if (cached) {
+            onSuccess(cached, url);
+            return;
+        }
+        loader.load(
+            url,
+            (tex) => {
+                _venueTextureCache.set(url, tex);
+                onSuccess(tex, url);
+            },
+            undefined,
+            onFail,
+        );
+    }
+
+    function _venueApplyPlateTexture(backdrop, tex, url) {
+        backdrop.tex = tex;
+        backdrop.plateUrl = url;
+        _venuePlateUrl = url;
+        backdrop.mat.map = tex;
+        backdrop.mat.needsUpdate = true;
+        if (backdrop.applyCoverCrop) backdrop.applyCoverCrop();
+        backdrop.loaded = true;
+        backdrop.mesh.visible = true;
+    }
+
+    function _venueLoadPlateForPov(loader, pov, backdrop, onSuccess, onFail) {
+        const chain = _venuePlateUrlChain(pov);
+        let idx = 0;
+        function tryNext() {
+            if (idx >= chain.length) {
+                onFail();
+                return;
+            }
+            const url = chain[idx++];
+            _venueLoadCachedTexture(loader, url, (tex, loadedUrl) => {
+                _venueApplyPlateTexture(backdrop, tex, loadedUrl);
+                onSuccess(tex, loadedUrl);
+            }, tryNext);
+        }
+        tryNext();
+    }
+
+    function _venueSwapPlateIfNeeded(s) {
+        if (!s || s.failed || s.plateLoading || !s.loader || !s.backdrop) return;
+        const pov = _venueInstrumentPov;
+        if (s.instrumentPov === pov && s.backdrop.loaded) return;
+        s.plateLoading = true;
+        _venueLoadPlateForPov(
+            s.loader,
+            pov,
+            s.backdrop,
+            () => {
+                s.instrumentPov = pov;
+                s.plateLoading = false;
+                s.loaded = true;
+                _venueSceneAssetsLoaded = true;
+                _venueSceneLoadFailed = false;
+                // The POV may have changed while this load was in flight (the
+                // plateLoading latch made concurrent swaps no-op). Re-sync to the
+                // current target so the backdrop isn't stranded on a stale plate.
+                if (_venueInstrumentPov !== pov) _venueSwapPlateIfNeeded(s);
+            },
+            () => {
+                s.plateLoading = false;
+                if (s.backdrop.loaded) return;
+                s.failed = true;
+                _venueSceneLoadFailed = true;
+                _venueSceneAssetsLoaded = false;
+                console.warn('[venue-scene] failed to load venue bg plate for pov ' + pov);
+                _venueSceneOverride = false;
+                _bgEmitChange('venueScene');
+                try {
+                    if (typeof window !== 'undefined' && window.v3VenueScene3d &&
+                        typeof window.v3VenueScene3d.onAssetsFailed === 'function') {
+                        window.v3VenueScene3d.onAssetsFailed('failed to load venue bg plate');
+                    }
+                } catch (_) { /* visual-only */ }
+            },
+        );
+    }
+    const FRET_NUMBER_GHOST_SCOPE_IDS = ['chords', 'all'];
+
+    /**
+     * localStorage panel key for per-panel background settings ('main' or
+     * 'panel<index>'). Defensive on the splitscreen global-name rename in flight,
+     * and throw-safe on panelIndexFor — same as _freeCamFor — so a misbehaving
+     * splitscreen build can't take down background-settings resolution. Only a
+     * non-negative integer index yields a 'panel<N>' key; anything else (null,
+     * NaN, negative, non-integer) falls back to 'main' so a bad index can never
+     * mint a bogus "panelNaN"-style key.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @returns {string} 'main' or 'panel<index>'
+     */
+    function _bgPanelKey(canvas) {
+        const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
+        let idx = null;
+        if (ss && typeof ss.panelIndexFor === 'function') {
+            try { idx = ss.panelIndexFor(canvas); } catch (e) { idx = null; }
+        }
+        return (Number.isInteger(idx) && idx >= 0) ? 'panel' + idx : 'main';
+    }
+
+    /**
+     * Camera Director bridge resolver. Prefers THIS panel's per-panel camera under
+     * splitscreen (window.__h3dCamCtlPanels[panelIndex]) and falls back to the
+     * single global (window.__h3dCamCtl); returns null when Camera Director is
+     * absent → 100% stock framing. Defensive on the splitscreen global-name rename
+     * in flight (feedBackSplitscreen vs slopsmithSplitscreen); throw-safe on
+     * panelIndexFor. Mirrors the panel resolution in _bgPanelKey.
+     * @param {HTMLCanvasElement} canvas this renderer's highway canvas
+     * @returns {object|null} the resolved free-camera bridge, or null
+     */
+    function _freeCamFor(canvas) {
+        const map = window.__h3dCamCtlPanels;
+        if (map) {
+            const ss = window.feedBackSplitscreen || window.slopsmithSplitscreen;
+            if (ss && typeof ss.panelIndexFor === 'function') {
+                try {
+                    const i = ss.panelIndexFor(canvas);
+                    // Only a non-negative integer indexes the map (same hardening
+                    // as _bgPanelKey) — a non-int / negative / string index must not
+                    // resolve an unintended/inherited property; fall through then.
+                    if (Number.isInteger(i) && i >= 0 && map[i]) return map[i];
+                } catch (e) { /* ignore */ }
+            }
+        }
+        return window.__h3dCamCtl || null;
+    }
+    // In-memory fallback for when localStorage is blocked (private mode,
+    // sandboxed iframes, some test runners). _bgWriteGlobal stages the
+    // value here unconditionally, so it always reflects the most recent
+    // in-session intent — _bgReadSetting prefers it over the global
+    // localStorage slot to avoid serving a stale persisted value when
+    // a write failed silently (quota exceeded, etc.). Per-panel
+    // localStorage overrides still win because they're an explicit
+    // per-instance opt-out and shouldn't be shadowed by a global edit.
+    const _bgMemFallback = Object.create(null);
+    function _bgReadSetting(panelKey, key) {
+        let panelVal = null;
+        let globalVal = null;
+        try {
+            // 'palette' + 'customColors' are GLOBAL-only: the per-panel palette
+            // control was removed in favour of the global "Highway String Colors"
+            // UI, so a panel must never be shadowed by a stale per-panel override
+            // (h3d_bg_panel<idx>_palette / _customColors). Neither is a
+            // BG_DEFAULTS key, so per-panel scoping never applied to them.
+            if (key !== 'palette' && key !== 'customColors') {
+                panelVal = localStorage.getItem('h3d_bg_' + panelKey + '_' + key);
+            }
+            globalVal = localStorage.getItem('h3d_bg_' + key);
+        } catch (_) { /* storage blocked — both stay null */ }
+        if (panelVal !== null && panelVal !== undefined) return _bgCoerce(key, panelVal);
+        // Prefer the in-memory staged value over the persisted global slot.
+        // _bgWriteGlobal always writes to _bgMemFallback first, so the
+        // memory value is at least as fresh as the persisted one.
+        if (key in _bgMemFallback) return _bgCoerce(key, _bgMemFallback[key]);
+        if (globalVal !== null && globalVal !== undefined) return _bgCoerce(key, globalVal);
+        return BG_DEFAULTS[key];
+    }
+    // Shared "stored string -> bool" coercion for every boolean
+    // setting. Mirrors settings.html's coerceBool so the renderer and
+    // the UI hydration always agree on what a corrupted/unknown value
+    // means (fall back to default rather than silently flipping to
+    // false). Add new boolean keys to BG_DEFAULTS and they pick this
+    // up via the dispatch below.
+    const _BG_BOOL_KEYS = new Set(['reactive', 'showFretOnNote', 'cameraLockLow', 'inlayLabelsVisible', 'sectionLabelsOnHighway', 'sectionHudVisible', 'nutHeadstockVisible', 'tuningLabelsVisible', 'projectionVisible', 'chordDiagramVisible', 'fpsVisible', 'toneHudVisible', 'fretDividersVisible', 'slideArrowApproachVisible', 'slideArrowNeckVisible', 'slideArrowChainPreviewVisible', 'sparks', 'cinematic', 'verdictMarks', 'timingFx', 'streakFx', 'bloom']);
+    function _bgCoerceBool(val, fallback) {
+        if (val === 'true' || val === '1') return true;
+        if (val === 'false' || val === '0') return false;
+        return fallback;
+    }
+    // Settings stored as 0..1 floats. cameraSmoothing controls X-pan
+    // hysteresis; zoomSmoothing the zoom dead zone; tiltSmoothing the
+    // vertical-tilt deadband + correction strength. All three slider-
+    // shaped settings share the same parse + clamp behaviour.
+    const _BG_FLOAT_KEYS = new Set(['intensity', 'cameraSmoothing', 'zoomSmoothing', 'tiltSmoothing', 'cameraLockZoom', 'textSize', 'vibrancy', 'glow', 'chordDiagramSize', 'sectionHudSize', 'toneHudSize', 'hitFx']);
+    function _bgCoerce(key, val) {
+        if (_BG_FLOAT_KEYS.has(key)) {
+            const n = parseFloat(val);
+            return Number.isFinite(n) ? Math.max(0, Math.min(1, n)) : BG_DEFAULTS[key];
+        }
+        if (_BG_BOOL_KEYS.has(key)) return _bgCoerceBool(val, BG_DEFAULTS[key]);
+        if (key === 'style') return BG_STYLE_IDS.includes(val) ? val : BG_DEFAULTS.style;
+        if (key === 'palette') return (PALETTE_IDS.includes(val) || val === 'custom') ? val : BG_DEFAULTS.palette;
+        if (key === 'bgTheme') return BG_THEME_IDS.includes(val) ? val : BG_DEFAULTS.bgTheme;
+        // Highway axis shares the same id-set as the background axis.
+        if (key === 'hwTheme') return BG_THEME_IDS.includes(val) ? val : BG_DEFAULTS.hwTheme;
+        if (key === 'chordDiagramPosition')
+            return CHORD_DIAG_POSITION_IDS.includes(val) ? val : BG_DEFAULTS.chordDiagramPosition;
+        if (key === 'sectionHudPosition')
+            return ['tl', 'tr', 'bl', 'br'].includes(val) ? val : BG_DEFAULTS.sectionHudPosition;
+        if (key === 'toneHudPosition')
+            return ['tl', 'tr', 'bl', 'br'].includes(val) ? val : BG_DEFAULTS.toneHudPosition;
+        if (key === 'cameraMode') {
+            if (val === 'classic') val = 'steady';
+            return CAMERA_MODE_IDS.includes(val) ? val : BG_DEFAULTS.cameraMode;
+        }
+        if (key === 'fretNumberGhostScope')
+            return FRET_NUMBER_GHOST_SCOPE_IDS.includes(val) ? val : BG_DEFAULTS.fretNumberGhostScope;
+        if (key === 'nutColor' || key === 'headstockColor') {
+            if (typeof val !== 'string') return BG_DEFAULTS[key];
+            const t = val.trim();
+            if (/^#[0-9a-fA-F]{6}$/.test(t)) return t.toLowerCase();
+            return BG_DEFAULTS[key];
+        }
+        if (key === 'fretColumnMarkerCadence') {
+            const n = parseInt(val, 10);
+            if (!Number.isFinite(n)) return BG_DEFAULTS.fretColumnMarkerCadence;
+            return Math.max(0, Math.min(16, n));
+        }
+        return val;
+    }
+
+    // Mirror-at-first-read fallback: returns true if the user has ever
+    // explicitly written `key` (per-panel, in-memory, or global). When
+    // false, callers should treat the value as "unset" — useful for
+    // zoomSmoothing / tiltSmoothing which inherit cameraSmoothing's
+    // value the first time they're read so existing users who calmed
+    // the camera don't lose calmness on the new axes by default.
+    function _bgHasStored(panelKey, key) {
+        try {
+            if (localStorage.getItem('h3d_bg_' + panelKey + '_' + key) != null) return true;
+        } catch (_) {}
+        if (key in _bgMemFallback) return true;
+        try {
+            if (localStorage.getItem('h3d_bg_' + key) != null) return true;
+        } catch (_) {}
+        return false;
+    }
+    function _bgWriteGlobal(key, val) {
+        const s = String(val);
+        // Stage in memory FIRST so _bgReadSetting's "memory beats global
+        // localStorage" precedence has a true freshness guarantee even
+        // if localStorage.setItem throws partway through. Without this
+        // ordering, a quota exception thrown after the persisted slot
+        // was already mutated would leave a stale value in localStorage
+        // that's newer than _bgMemFallback.
+        _bgMemFallback[key] = s;
+        try { localStorage.setItem('h3d_bg_' + key, s); } catch (_) { /* storage blocked */ }
+        _bgEmitChange(key);
+    }
+
+    // Pub-sub so settings.html can update live across all panel instances.
+    const _bgListeners = new Set();
+    function _bgSubscribe(fn) { _bgListeners.add(fn); }
+    function _bgUnsubscribe(fn) { _bgListeners.delete(fn); }
+    function _bgEmitChange(key) {
+        for (const fn of _bgListeners) {
+            try { fn(key); } catch (e) { console.error('[3D-Hwy] bg listener threw', e); }
+        }
+    }
+
+    // Settings.html setters — global keys; per-panel overrides via direct
+    // localStorage edits today, runtime UI in a follow-up.
+    window.h3dBgSetStyle = (v) => _bgWriteGlobal('style', v);
+    window.h3dBgSetIntensity = (v) => _bgWriteGlobal('intensity', v);
+    window.h3dBgSetReactive = (v) => _bgWriteGlobal('reactive', !!v);
+    window.h3dBgSetPalette = (v) => _bgWriteGlobal('palette', v);
+    // BACKGROUND scene-color axis (clear + fog only). Validated against
+    // BG_THEME_IDS in _bgCoerce; the listener re-applies clear/fog live and
+    // independently of the highway axis.
+    window.h3dBgSetBgTheme = (v) => {
+        const s = String(v);
+        _bgWriteGlobal('bgTheme', BG_THEME_IDS.includes(s) ? s : BG_DEFAULTS.bgTheme);
+    };
+    // HIGHWAY scene-color axis (board + lane + laneDim). Same id-set as the
+    // background axis, so any highway can mix with any background. The listener
+    // re-applies the board plane + lane live and independently.
+    window.h3dBgSetHwTheme = (v) => {
+        const s = String(v);
+        _bgWriteGlobal('hwTheme', BG_THEME_IDS.includes(s) ? s : BG_DEFAULTS.hwTheme);
+    };
+    // Apply a user-defined per-string color set (core theming UI). `hexArray`
+    // is up to 8 hex strings; invalid/missing entries fall back to the default
+    // palette per index. Writes the colors, then flips the palette to 'custom'
+    // — the palette listener retints all materials + rebuilds the board live.
+    // Pass null/[] then h3dBgSetPalette('default') to revert.
+    window.h3dBgSetStringColors = (hexArray) => {
+        const arr = Array.isArray(hexArray) ? hexArray : [];
+        const norm = [];
+        for (let i = 0; i < MAX_RENDER_STRINGS; i++) {
+            const n = _h3dHexToInt(arr[i]);
+            norm[i] = (n != null) ? '#' + n.toString(16).padStart(6, '0') : null;
+        }
+        _bgWriteGlobal('customColors', JSON.stringify(norm));
+        _bgWriteGlobal('palette', 'custom');
+    };
+    window.h3dBgSetShowFretOnNote = (v) => _bgWriteGlobal('showFretOnNote', !!v);
+    window.h3dBgSetFretNumberGhostScope = (v) => {
+        const s = String(v);
+        _bgWriteGlobal('fretNumberGhostScope', FRET_NUMBER_GHOST_SCOPE_IDS.includes(s) ? s : BG_DEFAULTS.fretNumberGhostScope);
+    };
+    window.h3dBgSetCameraSmoothing = (v) => _bgWriteGlobal('cameraSmoothing', v);
+    window.h3dBgSetZoomSmoothing = (v) => _bgWriteGlobal('zoomSmoothing', v);
+    window.h3dBgSetTiltSmoothing = (v) => _bgWriteGlobal('tiltSmoothing', v);
+    window.h3dBgSetCameraLockLow = (v) => _bgWriteGlobal('cameraLockLow', !!v);
+    window.h3dBgSetCameraLockZoom = (v) => _bgWriteGlobal('cameraLockZoom', v);
+    window.h3dBgSetCameraMode = (v) => {
+        let s = String(v);
+        if (s === 'classic') s = 'steady';
+        _bgWriteGlobal('cameraMode', s);
+    };
+    window.h3dBgSetNutHeadstockVisible = (v) => _bgWriteGlobal('nutHeadstockVisible', !!v);
+    window.h3dBgSetTuningLabelsVisible = (v) => _bgWriteGlobal('tuningLabelsVisible', !!v);
+    window.h3dBgSetNutColor = (v) => _bgWriteGlobal('nutColor', v);
+    window.h3dBgSetHeadstockColor = (v) => _bgWriteGlobal('headstockColor', v);
+    window.h3dBgSetTextSize = (v) => _bgWriteGlobal('textSize', v);
+    window.h3dBgSetVibrancy = (v) => _bgWriteGlobal('vibrancy', v);
+    window.h3dBgSetGlow     = (v) => _bgWriteGlobal('glow', v);
+    window.h3dBgSetHitFx        = (v) => _bgWriteGlobal('hitFx', v);
+    window.h3dBgSetSparks       = (v) => _bgWriteGlobal('sparks', !!v);
+    window.h3dBgSetCinematic    = (v) => _bgWriteGlobal('cinematic', !!v);
+    window.h3dBgSetVerdictMarks = (v) => _bgWriteGlobal('verdictMarks', !!v);
+    window.h3dBgSetTimingFx     = (v) => _bgWriteGlobal('timingFx', !!v);
+    window.h3dBgSetStreakFx     = (v) => _bgWriteGlobal('streakFx', !!v);
+    window.h3dBgSetBloom        = (v) => _bgWriteGlobal('bloom', !!v);
+    window.h3dBgSetToneHudVisible   = (v) => _bgWriteGlobal('toneHudVisible', !!v);
+    window.h3dBgSetToneHudPosition  = (v) => _bgWriteGlobal('toneHudPosition', v);
+    window.h3dBgSetToneHudSize      = (v) => _bgWriteGlobal('toneHudSize', v);
+    window.h3dBgSetFpsVisible           = (v) => _bgWriteGlobal('fpsVisible', !!v);
+    window.h3dBgSetFretDividersVisible  = (v) => _bgWriteGlobal('fretDividersVisible', !!v);
+    window.h3dBgSetChordDiagramVisible  = (v) => _bgWriteGlobal('chordDiagramVisible', !!v);
+    window.h3dBgSetChordDiagramSize     = (v) => _bgWriteGlobal('chordDiagramSize', v);
+    window.h3dBgSetChordDiagramPosition = (v) => _bgWriteGlobal('chordDiagramPosition', v);
+    window.h3dBgSetFretColumnMarkerCadence = (v) => _bgWriteGlobal('fretColumnMarkerCadence', v);
+    window.h3dBgSetInlayLabelsVisible = (v) => _bgWriteGlobal('inlayLabelsVisible', !!v);
+    window.h3dBgSetSectionLabelsOnHighway = (v) => _bgWriteGlobal('sectionLabelsOnHighway', !!v);
+    window.h3dBgSetSectionHudVisible      = (v) => _bgWriteGlobal('sectionHudVisible', !!v);
+    window.h3dBgSetSectionHudPosition     = (v) => _bgWriteGlobal('sectionHudPosition', v);
+    window.h3dBgSetSectionHudSize         = (v) => _bgWriteGlobal('sectionHudSize', v);
+    window.h3dBgSetProjectionVisible      = (v) => _bgWriteGlobal('projectionVisible', !!v);
+    window.h3dBgSetSlideArrowApproachVisible = (v) => _bgWriteGlobal('slideArrowApproachVisible', !!v);
+    window.h3dBgSetSlideArrowNeckVisible     = (v) => _bgWriteGlobal('slideArrowNeckVisible', !!v);
+    window.h3dBgSetSlideArrowChainPreviewVisible = (v) => _bgWriteGlobal('slideArrowChainPreviewVisible', !!v);
+    // Custom image asset for the 'image' bg style (#19). Composite setter:
+    // writes both the data URL (the bytes that drive the texture) and the
+    // display filename, each emitting a change event. The listener
+    // rebuilds on customImageDataUrl change when the image style is
+    // active; customImageName is display-only and skips rebuild.
+    window.h3dBgSetCustomImage = (asset) => {
+        const a = asset || {};
+        _bgWriteGlobal('customImageDataUrl', a.dataUrl || '');
+        _bgWriteGlobal('customImageName', a.name || '');
+    };
+    window.h3dBgClearCustomImage = () => {
+        _bgWriteGlobal('customImageDataUrl', '');
+        _bgWriteGlobal('customImageName', '');
+    };
+    // Custom video asset for the 'video' bg style (#19 follow-up).
+    // Bytes live on disk under {config_dir}/plugin_uploads/highway_3d/
+    // and are served by routes.py — localStorage only stores the
+    // filename, which the renderer maps to the served URL. Single
+    // global slot; the file picker in settings.html POSTs to the
+    // upload route and then calls this setter with the response name.
+    window.h3dBgSetCustomVideo = (asset) => {
+        _bgWriteGlobal('customVideoName', (asset && asset.name) || '');
+    };
+    window.h3dBgClearCustomVideo = () => _bgWriteGlobal('customVideoName', '');
+    window.h3dVenueSceneSetActive = (on) => {
+        const next = !!on;
+        if (_venueSceneOverride === next) return;
+        _venueSceneOverride = next;
+        if (!next) {
+            _venueSceneAssetsLoaded = false;
+            _venueSceneLoadFailed = false;
+        }
+        _bgEmitChange('venueScene');
+    };
+    window.h3dVenueSceneSetMood = (state) => {
+        _venueMoodState = String(state || 'idle').toLowerCase();
+    };
+    // Crowd video layers (career mode) — see venue-crowd.js. Layer 0/1 are
+    // two coplanar backdrop planes; mix selects between them (0 → layer 0,
+    // 1 → layer 1) so the caller can crossfade loop videos.
+    window.h3dVenueBackdropSetVideo = (layer, videoEl) => {
+        const i = layer ? 1 : 0;
+        const el = videoEl || null;
+        if (_venueCrowdVideos[i] === el) return;
+        _venueCrowdVideos[i] = el;
+        _venueCrowdRev++;
+    };
+    window.h3dVenueBackdropSetMix = (mix) => {
+        const v = Number(mix);
+        _venueCrowdMix = Number.isFinite(v) ? Math.max(0, Math.min(1, v)) : 0;
+    };
+    window.h3dVenueSceneSetInstrumentPov = (input) => {
+        const next = _venueResolvePovFromInput(input);
+        if (_venueInstrumentPov === next) return;
+        _venueInstrumentPov = next;
+        _bgEmitChange('venueInstrumentPov');
+    };
+    window.h3dVenueSceneSetMotionMode = (mode) => {
+        const next = String(mode || 'subtle').toLowerCase();
+        const allowed = { off: 1, subtle: 1, full: 1 };
+        _venueMotionMode = allowed[next] ? next : 'subtle';
+    };
+    window.h3dVenueSceneGetState = () => {
+        const motionMode = _venueEffectiveMotionMode();
+        const motionProfile = _venueMotionProfile(motionMode);
+        return {
+            active: _venueSceneOverride,
+            mood: _venueMoodState,
+            instrumentPov: _venueInstrumentPov,
+            motionMode: _venueMotionMode,
+            motionEffective: motionMode,
+            motionEnabled: motionMode !== 'off',
+            motionIntensity: motionProfile.breathe + motionProfile.parallax + motionProfile.hazeDrift,
+            motionProfile,
+            plateUrl: _venuePlateUrl || null,
+            assetsLoaded: _venueSceneAssetsLoaded,
+            loadFailed: _venueSceneLoadFailed,
+        };
+    };
+    // Back-compat alias for any caller that picked up the original
+    // (inconsistent) name during this PR's review window.
+    window.h3dSetPalette = window.h3dBgSetPalette;
+
+    // Procedural silhouette bitmap, drawn once and shared across panels.
+    // The Canvas2D bitmap is module-level (cheap, CPU-only); each layer
+    // wraps it in its own CanvasTexture so per-layer texture.offset.x
+    // can drive a seam-free scroll without coupling to other layers /
+    // panels (a shared CanvasTexture would synchronize all offsets).
+    let _silCanvas = null;
+    function _bgEnsureSilhouetteCanvas() {
+        if (_silCanvas) return _silCanvas;
+        const c = document.createElement('canvas');
+        c.width = 1024; c.height = 64;
+        const cx = c.getContext('2d');
+        if (!cx) {
+            // Restrictive environments (some sandboxed iframes, headless
+            // tests) can return null. Without a guard, the clearRect/
+            // fillRect calls below would throw TypeError and the silhouette
+            // style would never become available.
+            throw new Error('[3D-Hwy] 2D canvas context unavailable for silhouette texture');
+        }
+        cx.clearRect(0, 0, c.width, c.height);
+        cx.fillStyle = '#000814';
+        let x = 0;
+        while (x < c.width) {
+            const w = 8 + Math.random() * 30;
+            const h = 20 + Math.random() * 40;
+            cx.fillRect(x, c.height - h, w, h);
+            x += w + Math.random() * 10;
+        }
+        _silCanvas = c;
+        return c;
+    }
+
+    // Helpers shared by the asset-driven bg styles (image, video).
+    // Both render a "stage backdrop" plane that's full-bleed: sized
+    // each frame to fill the camera's view frustum at a fixed
+    // distance and positioned to track the camera (so the user's
+    // image/video reads as the entire visible BG, with highway and
+    // notes painting on top via renderOrder).
+    //
+    // Distance is chosen far enough back that no note ever lands
+    // beyond it; depthWrite=false on the plane material plus
+    // renderOrder=-1 means notes still paint on top regardless.
+    const BG_BACKDROP_DISTANCE = FOG_END * 0.95;
+
+    // Module-level scratch vector reused each frame to avoid GC
+    // churn from per-frame Vector3 allocation. Only valid for the
+    // duration of a single update() call.
+    const _bgBackdropTmp = (() => {
+        // Lazily created when T is available (T isn't bound at module
+        // parse time — initScene assigns it inside loadThree().then).
+        // Returning a getter that allocates on first read keeps the
+        // dependency timing clean.
+        let v = null;
+        return () => v || (v = new T.Vector3());
+    })();
+
+    // Frustum-fit a plane mesh: scale a unit PlaneGeometry to exactly
+    // fill the camera's view at the configured distance, then position
+    // it `distance` units in front of the camera and orient it so the
+    // texture faces the camera. Called whenever cam.aspect changes
+    // (resize) and to position-track the camera each frame.
+    function _bgFitBackdropPlane(state) {
+        const cam = state.cam;
+        const d = state.distance;
+        const halfFovRad = cam.fov * Math.PI / 360;
+        const visibleHeight = 2 * Math.tan(halfFovRad) * d;
+        const visibleWidth = visibleHeight * cam.aspect;
+        if (state.lastAspect !== cam.aspect ||
+            state.lastVisibleHeight !== visibleHeight) {
+            state.mesh.scale.set(visibleWidth, visibleHeight, 1);
+            state.lastAspect = cam.aspect;
+            state.lastVisibleHeight = visibleHeight;
+            state.lastVisibleWidth = visibleWidth;
+            // Aspect change shifts the cover-crop ratio; re-apply.
+            if (state.applyCoverCrop) state.applyCoverCrop();
+        }
+        // Track camera each frame: position = cam.position +
+        // cam.forward * distance, orient toward camera.
+        const fwd = cam.getWorldDirection(_bgBackdropTmp());
+        state.mesh.position.copy(cam.position).addScaledVector(fwd, d);
+        state.mesh.lookAt(cam.position);
+    }
+
+    // Cover-crop a texture to the plane aspect: the larger axis fills
+    // the plane (cropped if needed), centered. For wider-than-plane
+    // textures the X offset is left at the centered value but the
+    // image style's drift loop overwrites it per frame; the video
+    // style leaves it centered.
+    function _bgCoverCrop(tex, srcW, srcH, planeAspect) {
+        if (srcW <= 0 || srcH <= 0) return;
+        tex.repeat.set(1, 1);
+        tex.offset.set(0, 0);
+        const srcAspect = srcW / srcH;
+        if (srcAspect > planeAspect) {
+            tex.repeat.x = planeAspect / srcAspect;
+            tex.offset.x = (1 - tex.repeat.x) * 0.5;
+        } else {
+            tex.repeat.y = srcAspect / planeAspect;
+            tex.offset.y = (1 - tex.repeat.y) * 0.5;
+        }
+        tex.needsUpdate = true;
+    }
+
+    // Background-style registry. Each entry returns a per-panel state
+    // object from build() and reads from it in update() / teardown().
+    // T (THREE) is set by the time these are invoked (initScene runs
+    // inside loadThree().then).
+    const BG_STYLES = {
+        off: {
+            build() { return null; },
+            update() {},
+            teardown() {},
+        },
+        particles: {
+            build(scene, settings) {
+                const N = Math.max(20, Math.floor(80 + 200 * settings.intensity));
+                const positions = new Float32Array(N * 3);
+                for (let i = 0; i < N; i++) {
+                    positions[i * 3] = (Math.random() - 0.5) * 800 * K;
+                    positions[i * 3 + 1] = (Math.random() - 0.4) * 80 * K;
+                    // Spawn within the visible fog range. Fog reaches
+                    // its far limit at FOG_END * 1.2 from the camera,
+                    // and cam.position.z is updated each frame in
+                    // camUpdate() (`dist * 0.75`, where dist tracks
+                    // aspectScale). Anything beyond that camera-relative
+                    // distance gets fully fogged out, so the cutoff in
+                    // world z is dynamic — the earlier "push past notes"
+                    // fix placed particles at -FOG_END * (0.95..1.20)
+                    // which sat past fog far at any camera z, making
+                    // them invisible. renderOrder = -1 on the bg stage
+                    // already keeps particles behind notes regardless
+                    // of z, so depth-based separation wasn't needed and
+                    // was actively breaking visibility.
+                    positions[i * 3 + 2] = -FOG_START - Math.random() * (FOG_END - FOG_START) * 0.85;
+                }
+                const geo = new T.BufferGeometry();
+                geo.setAttribute('position', new T.BufferAttribute(positions, 3));
+                const mat = new T.PointsMaterial({
+                    // size 5*K (bumped from 1.5*K). At distance ~700*K
+                    // with sizeAttenuation the prior sprite shrank
+                    // below 2 pixels — practically invisible against
+                    // dark fog. 5*K reads as a small bright dot.
+                    // Build-time opacity is overridden every frame in
+                    // update() — the runtime formula is the source of
+                    // truth.
+                    color: 0xa0c0ff, size: 5 * K, transparent: true,
+                    blending: T.AdditiveBlending, depthWrite: false, sizeAttenuation: true,
+                });
+                const points = new T.Points(geo, mat);
+                scene.add(points);
+                return { points, geo, mat, N };
+            },
+            update(s, bands, dt) {
+                const positions = s.geo.attributes.position.array;
+                const dx = dt * (3 + bands.mid * 12) * K;
+                for (let i = 0; i < s.N; i++) {
+                    positions[i * 3] += dx;
+                    if (positions[i * 3] > 400 * K) positions[i * 3] -= 800 * K;
+                }
+                s.geo.attributes.position.needsUpdate = true;
+                // Bumped opacity floor 0.4 → 0.55 + treble headroom
+                // 0.4 → 0.45 so particles read as visible specks even
+                // when bgReactive is false / treble≈0 (was effectively
+                // 0.4 floor, below noise floor against dark fog).
+                s.mat.opacity = 0.55 + bands.treble * 0.45;
+            },
+            teardown(s) {
+                if (!s) return;
+                s.points.parent?.remove(s.points);
+                s.geo.dispose();
+                s.mat.dispose();
+            },
+        },
+        silhouettes: {
+            build(scene, settings) {
+                const canvas = _bgEnsureSilhouetteCanvas();
+                // Inside the visible fog range. Fog far = FOG_END * 1.2
+                // from the camera, and cam.position.z is dynamic
+                // (camUpdate() sets `dist * 0.75`). renderOrder = -1
+                // on the bg stage handles "behind notes" regardless
+                // of z. Spread the three layers across the back half
+                // of the visible fog band for parallax separation.
+                const depths = [-FOG_END * 0.55, -FOG_END * 0.70, -FOG_END * 0.85];
+                const layers = [];
+                const allocated = [];
+                try {
+                    for (const z of depths) {
+                        // Per-layer CanvasTexture wrapping the shared
+                        // canvas: lets each layer scroll independently
+                        // via texture.offset.x without coupling to its
+                        // siblings or to other panels.
+                        const tex = new T.CanvasTexture(canvas);
+                        tex.wrapS = T.RepeatWrapping;
+                        const geo = new T.PlaneGeometry(800 * K, 50 * K);
+                        const mat = new T.MeshBasicMaterial({
+                            map: tex, transparent: true, opacity: 0.4, depthWrite: false,
+                        });
+                        const mesh = new T.Mesh(geo, mat);
+                        mesh.position.set(0, -10 * K, z);
+                        scene.add(mesh);
+                        // Parallax: nearer layers move more than farther
+                        // ones (perspective). distance = -z; small d ->
+                        // large parallax. Scaled so the nearest sits
+                        // around 0.32 and farthest around 0.18.
+                        const distance = -z;
+                        const parallax = Math.max(0.05, 1 - distance / (FOG_END * 1.4));
+                        const layer = { mesh, geo, mat, tex, z, drift: 0, parallax };
+                        layers.push(layer);
+                        allocated.push(layer);
+                    }
+                    return { layers, intensity: settings.intensity };
+                } catch (e) {
+                    // Build threw partway — clean up any per-layer
+                    // textures we already created. _bgMountStyle's catch
+                    // disposes the stage tree's meshes, but a partial-
+                    // build's CanvasTextures aren't reachable from any
+                    // mesh yet, so this catch owns them.
+                    for (const L of allocated) {
+                        L.tex?.dispose?.();
+                    }
+                    throw e;
+                }
+            },
+            update(s, bands, dt) {
+                // Intensity multiplier: 0 dims to ~50% of base, 1
+                // brightens to ~120%. Below-base values still leave the
+                // silhouettes faintly visible so users know the style
+                // is on; above-base lets the layers read as a real
+                // backdrop on louder passages.
+                const intensityMul = 0.5 + s.intensity * 0.7;
+                for (const L of s.layers) {
+                    // Scroll via texture.offset.x with RepeatWrapping —
+                    // unbounded, no modulus snap. The mesh stays put;
+                    // the texture wraps continuously across the visible
+                    // surface. (offset is in normalized texture space,
+                    // so we keep it small and let the wrap do the job.)
+                    L.drift += dt * (0.05 + bands.mid * 0.15) * L.parallax;
+                    L.mat.map.offset.x = L.drift;
+                    L.mesh.position.y = -10 * K + bands.bass * 4 * K;
+                    L.mat.opacity = (0.25 + 0.5 * L.parallax) * intensityMul;
+                }
+            },
+            teardown(s) {
+                if (!s) return;
+                for (const L of s.layers) {
+                    L.mesh.parent?.remove(L.mesh);
+                    L.geo.dispose();
+                    L.mat.dispose();
+                    L.tex.dispose();
+                }
+            },
+        },
+        lights: {
+            build(scene, settings) {
+                // Lights count scales 6 → 14 over intensity 0 → 1.
+                // _bgCoerce clamps intensity to [0,1] before it reaches
+                // here, so no further clamp is needed.
+                const N = Math.floor(6 + 8 * settings.intensity);
+                const lights = [];
+                // Palette comes from the calling panel's settings so
+                // each splitscreen panel picks its own (issue #10).
+                // Falls back to the default palette if the caller
+                // doesn't supply one (e.g. an older code path).
+                const palette = settings.palette || PALETTES.default;
+                for (let i = 0; i < N; i++) {
+                    const color = palette[i % palette.length];
+                    // 30*K plane reads as a real stage glow at distance.
+                    // Build-time opacity is overridden every frame in
+                    // update() — the runtime formula is the source of
+                    // truth.
+                    const geo = new T.PlaneGeometry(30 * K, 30 * K);
+                    const mat = new T.MeshBasicMaterial({
+                        color, transparent: true,
+                        blending: T.AdditiveBlending, depthWrite: false,
+                    });
+                    const mesh = new T.Mesh(geo, mat);
+                    mesh.position.set(
+                        (Math.random() - 0.5) * 600 * K,
+                        (Math.random() - 0.3) * 80 * K,
+                        // Inside visible fog range; renderOrder = -1
+                        // keeps lights behind notes regardless of z.
+                        -FOG_START - Math.random() * (FOG_END - FOG_START) * 0.85
+                    );
+                    scene.add(mesh);
+                    lights.push({ mesh, geo, mat, baseScale: 1 + Math.random() * 0.5, phase: Math.random() * Math.PI * 2 });
+                }
+                return { lights };
+            },
+            update(s, bands, dt, t) {
+                // Bumped opacity floor 0.35 → 0.55 + treble headroom
+                // 0.3 → 0.4 so lights read as visible stage glows at
+                // distance instead of faint specks (was effectively
+                // 0.35 floor since the build-time bump was overridden
+                // by this formula).
+                for (const L of s.lights) {
+                    const pulse = 1 + bands.bass * 1.5 + Math.sin(t * 1.5 + L.phase) * 0.2;
+                    L.mesh.scale.set(L.baseScale * pulse, L.baseScale * pulse, 1);
+                    L.mat.opacity = 0.55 + bands.treble * 0.4;
+                }
+            },
+            teardown(s) {
+                if (!s) return;
+                for (const L of s.lights) {
+                    L.mesh.parent?.remove(L.mesh);
+                    L.geo.dispose();
+                    L.mat.dispose();
+                }
+            },
+        },
+        geometric: {
+            build(scene, settings) {
+                const meshes = [];
+                // Bumped opacity floor (0.25 → 0.45) + ceiling so the
+                // wireframes read as real shapes instead of barely-
+                // there ghosts at low intensity.
+                const op = 0.45 + 0.25 * settings.intensity;
+                const ico = new T.Mesh(
+                    new T.IcosahedronGeometry(30 * K, 1),
+                    new T.MeshBasicMaterial({ color: 0x6080c0, wireframe: true, transparent: true, opacity: op, depthWrite: false }),
+                );
+                // Inside visible fog range; renderOrder = -1 keeps
+                // wireframes behind notes regardless of z.
+                ico.position.set(-100 * K, 30 * K, -FOG_END * 0.65);
+                scene.add(ico);
+                meshes.push(ico);
+                const torus = new T.Mesh(
+                    new T.TorusGeometry(22 * K, 4 * K, 6, 12),
+                    new T.MeshBasicMaterial({ color: 0xc06080, wireframe: true, transparent: true, opacity: op * 0.9, depthWrite: false }),
+                );
+                torus.position.set(120 * K, 20 * K, -FOG_END * 0.75);
+                scene.add(torus);
+                meshes.push(torus);
+                return { meshes };
+            },
+            update(s, bands, dt) {
+                const speed = 0.2 + bands.mid * 0.4;
+                const pulse = 1 + bands.bass * 0.25;
+                for (const m of s.meshes) {
+                    m.rotation.x += dt * speed * 0.3;
+                    m.rotation.y += dt * speed * 0.4;
+                    m.scale.setScalar(pulse);
+                }
+            },
+            teardown(s) {
+                if (!s) return;
+                for (const m of s.meshes) {
+                    m.parent?.remove(m);
+                    m.geometry.dispose();
+                    m.material.dispose();
+                }
+            },
+        },
+        // Venue visualization — generated small-club raster bg plate
+        // behind the highway. Activated via h3dVenueSceneSetActive(true)
+        // when Visualization = Venue; does not persist as a user bg style.
+        venue: {
+            build(scene, settings) {
+                const coeffs = _bgVenueMoodCoeffs(_venueMoodState);
+                const state = {
+                    backdrop: null,
+                    haze: null,
+                    loader: null,
+                    instrumentPov: _venueInstrumentPov,
+                    plateLoading: false,
+                    pending: 1,
+                    loaded: false,
+                    failed: false,
+                };
+
+                function _venueMarkLoaded() {
+                    state.pending--;
+                    if (state.pending <= 0 && !state.failed) {
+                        state.loaded = true;
+                        _venueSceneAssetsLoaded = true;
+                        _venueSceneLoadFailed = false;
+                        try {
+                            if (typeof window !== 'undefined' && window.v3VenueScene3d &&
+                                typeof window.v3VenueScene3d.onAssetsLoaded === 'function') {
+                                window.v3VenueScene3d.onAssetsLoaded();
+                            }
+                        } catch (_) { /* visual-only */ }
+                    }
+                }
+                function _venueMarkFailed(msg) {
+                    if (state.failed) return;
+                    state.failed = true;
+                    _venueSceneLoadFailed = true;
+                    _venueSceneAssetsLoaded = false;
+                    console.warn('[venue-scene] ' + msg);
+                    _venueSceneOverride = false;
+                    _bgEmitChange('venueScene');
+                    try {
+                        if (typeof window !== 'undefined' && window.v3VenueScene3d &&
+                            typeof window.v3VenueScene3d.onAssetsFailed === 'function') {
+                            window.v3VenueScene3d.onAssetsFailed(msg);
+                        }
+                    } catch (_) { /* visual-only */ }
+                }
+
+                const loader = new T.TextureLoader();
+                state.loader = loader;
+                const backdrop = {
+                    mesh: null, geo: null, mat: null, tex: null,
+                    cam: settings.cam, distance: BG_BACKDROP_DISTANCE * VENUE_BACKDROP_DISTANCE_MUL,
+                    lastAspect: 0, lastVisibleHeight: 0, lastVisibleWidth: 0, loaded: false,
+                };
+                backdrop.geo = new T.PlaneGeometry(1, 1);
+                backdrop.mat = new T.MeshBasicMaterial({
+                    color: 0xffffff, transparent: false, depthWrite: false, fog: false,
+                });
+                backdrop.mesh = new T.Mesh(backdrop.geo, backdrop.mat);
+                backdrop.mesh.visible = false;
+                scene.add(backdrop.mesh);
+                state.backdrop = backdrop;
+                backdrop.applyCoverCrop = function () {
+                    if (!backdrop.tex || !backdrop.tex.image) return;
+                    _bgCoverCrop(
+                        backdrop.tex,
+                        backdrop.tex.image.width || 0,
+                        backdrop.tex.image.height || 0,
+                        backdrop.cam.aspect,
+                    );
+                };
+                _venueLoadPlateForPov(
+                    loader,
+                    _venueInstrumentPov,
+                    backdrop,
+                    () => _venueMarkLoaded(),
+                    () => _venueMarkFailed('failed to load small-club bg plate'),
+                );
+
+                // Crowd video planes (career mode): two crossfading layers
+                // just in front of the static plate (which stays mounted as
+                // the no-pack / load-failure fallback). Textures bind lazily
+                // in update() when venue-crowd.js assigns video elements.
+                state.crowd = { layers: [], rev: -1 };
+                for (let i = 0; i < 2; i++) {
+                    const geo = new T.PlaneGeometry(1, 1);
+                    const mat = new T.MeshBasicMaterial({
+                        color: 0xffffff, transparent: true, opacity: 0,
+                        depthWrite: false, fog: false,
+                    });
+                    const mesh = new T.Mesh(geo, mat);
+                    mesh.visible = false;
+                    // Layer 1 sits nearest so three.js's back-to-front
+                    // transparent sort draws it after layer 0.
+                    const layer = {
+                        mesh, geo, mat, tex: null, videoEl: null,
+                        cam: settings.cam,
+                        distance: BG_BACKDROP_DISTANCE * (i === 0 ? 1.04 : 1.03),
+                        lastAspect: 0, lastVisibleHeight: 0,
+                    };
+                    layer.applyCoverCrop = function () {
+                        if (!layer.videoEl || !layer.tex) return;
+                        _bgCoverCrop(
+                            layer.tex,
+                            layer.videoEl.videoWidth || 0,
+                            layer.videoEl.videoHeight || 0,
+                            layer.cam.aspect,
+                        );
+                    };
+                    scene.add(mesh);
+                    state.crowd.layers.push(layer);
+                }
+
+                const hazeGeo = new T.PlaneGeometry(280 * K, 40 * K);
+                const hazeMat = new T.MeshBasicMaterial({
+                    color: 0x101820, transparent: true, opacity: coeffs.haze,
+                    depthWrite: false, fog: false,
+                });
+                const hazeMesh = new T.Mesh(hazeGeo, hazeMat);
+                hazeMesh.position.set(0, -12 * K, -FOG_END * 0.70);
+                scene.add(hazeMesh);
+                state.haze = {
+                    mesh: hazeMesh, geo: hazeGeo, mat: hazeMat, baseOp: coeffs.haze,
+                    baseX: 0, baseY: -12 * K, baseZ: -FOG_END * 0.70,
+                };
+
+                return state;
+            },
+            update(s, bands, dt, t) {
+                if (!s || s.failed) return;
+                _venueSwapPlateIfNeeded(s);
+                const coeffs = _bgVenueMoodCoeffs(_venueMoodState);
+                if (s.backdrop && s.backdrop.loaded) {
+                    _bgFitBackdropPlane(s.backdrop);
+                }
+                const motion = _venueApplyFakeDepthMotion(s, coeffs, t);
+                if (s.backdrop && s.backdrop.loaded && s.backdrop.mat && !motion.breathe && !motion.warmthPulse) {
+                    const warm = coeffs.warmth;
+                    s.backdrop.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
+                }
+                if (s.haze && s.haze.mat && !motion.hazeDrift && !motion.shimmer) {
+                    s.haze.mat.opacity = (s.haze.baseOp || VENUE_HAZE_STEADY)
+                        * (coeffs.haze / VENUE_HAZE_STEADY);
+                }
+                if (s.crowd) {
+                    // Rebind VideoTextures when venue-crowd.js (re)assigns
+                    // elements. VideoTexture samples the element every frame,
+                    // so a src change on the same element needs no rebind.
+                    if (s.crowd.rev !== _venueCrowdRev) {
+                        s.crowd.rev = _venueCrowdRev;
+                        s.crowd.layers.forEach((layer, i) => {
+                            const el = _venueCrowdVideos[i];
+                            if (layer.videoEl === el) return;
+                            if (layer.tex) { layer.mat.map = null; layer.tex.dispose(); layer.tex = null; }
+                            layer.videoEl = el;
+                            layer.lastAspect = 0; // force refit + recrop
+                            if (el) {
+                                const tex = new T.VideoTexture(el);
+                                tex.colorSpace = T.SRGBColorSpace;
+                                tex.wrapS = T.ClampToEdgeWrapping;
+                                tex.wrapT = T.ClampToEdgeWrapping;
+                                tex.minFilter = T.LinearFilter;
+                                tex.magFilter = T.LinearFilter;
+                                tex.generateMipmaps = false;
+                                layer.tex = tex;
+                                layer.mat.map = tex;
+                            }
+                            layer.mat.needsUpdate = true;
+                        });
+                    }
+                    const warm = coeffs.warmth;
+                    s.crowd.layers.forEach((layer, i) => {
+                        const el = layer.videoEl;
+                        // videoWidth === 0 until metadata lands — showing the
+                        // plane before that paints a black flash over the plate.
+                        const ready = !!el && el.videoWidth > 0;
+                        // venue-crowd.js swaps src on the same element (loop ↔
+                        // stinger); a new intrinsic size needs a fresh
+                        // cover-crop, which _bgFitBackdropPlane only reapplies
+                        // on camera aspect changes.
+                        if (ready && (layer.lastVidW !== el.videoWidth ||
+                                      layer.lastVidH !== el.videoHeight)) {
+                            layer.lastVidW = el.videoWidth;
+                            layer.lastVidH = el.videoHeight;
+                            layer.applyCoverCrop();
+                        }
+                        // Layer 0 (rear) stays fully opaque whenever any of the
+                        // fade involves it: two half-transparent layers would
+                        // let the static plate behind bleed through (~25% at
+                        // mid-fade). The crossfade is therefore layer 1 (front)
+                        // fading over an opaque layer 0 — in both directions.
+                        const opacity = i === 0
+                            ? (_venueCrowdMix < 0.999 ? 1 : 0)
+                            : _venueCrowdMix;
+                        layer.mat.opacity = opacity;
+                        layer.mesh.visible = ready && opacity > 0.01;
+                        if (layer.mesh.visible) {
+                            layer.mat.color.setRGB(warm, warm * 0.98, warm * 0.95);
+                            _bgFitBackdropPlane(layer);
+                        }
+                    });
+                }
+            },
+            teardown(s) {
+                if (!s) return;
+                _venueSceneAssetsLoaded = false;
+                for (const key of ['backdrop', 'haze']) {
+                    const p = s[key];
+                    if (!p) continue;
+                    p.mesh?.parent?.remove(p.mesh);
+                    p.geo?.dispose?.();
+                    if (p.mat) {
+                        p.mat.map = null;
+                        p.mat.dispose?.();
+                    }
+                }
+                // Crowd planes: this style owns the VideoTextures; the
+                // <video> elements belong to venue-crowd.js and survive.
+                if (s.crowd) {
+                    for (const layer of s.crowd.layers) {
+                        layer.mesh?.parent?.remove(layer.mesh);
+                        layer.geo?.dispose?.();
+                        if (layer.mat) {
+                            layer.mat.map = null;
+                            layer.mat.dispose?.();
+                        }
+                        layer.tex?.dispose?.();
+                    }
+                }
+                // Dispose the cached plate textures too — the module-level cache
+                // otherwise keeps every loaded POV plate GPU-resident for the
+                // page lifetime (steady VRAM growth across POV/arrangement swaps).
+                try {
+                    _venueTextureCache.forEach((tex) => { tex?.dispose?.(); });
+                } catch (_) { /* visual-only */ }
+                _venueTextureCache.clear();
+            },
+        },
+        // Custom image backdrop (#19). User uploads a JPG/PNG/WebP
+        // through settings.html; the bytes are persisted as a base64
+        // data URL in localStorage under h3d_bg_customImageDataUrl and
+        // passed in via settings.customImageDataUrl. Renders as a
+        // PlaneGeometry in the silhouette parallax band, "cover" cropped
+        // (via texture.repeat / offset) so non-matching aspects fill
+        // the plane without distortion. Slow horizontal drift on
+        // texture.offset.x for life. When no asset is uploaded, build
+        // returns null and the style is inert (settings.html disables
+        // the picker option in that case).
+        image: {
+            build(scene, settings) {
+                // Upfront validation: only accept the same raster image
+                // formats settings.html lets the user upload (jpeg /
+                // png / webp). Without this, a corrupt localStorage
+                // value (truncated base64, wrong scheme, plain string)
+                // OR an unsupported type (e.g. data:image/svg+xml)
+                // reaches TextureLoader and can fail asynchronously
+                // after the plane has been mounted — a silent black
+                // backdrop with no clear cause. Returning null here
+                // treats invalid bytes the same as "no asset uploaded":
+                // style is inert, the user can clear and re-upload
+                // from settings.html.
+                const dataUrl = (typeof settings.customImageDataUrl === 'string')
+                    ? settings.customImageDataUrl.trim() : '';
+                if (!/^data:image\/(jpeg|png|webp);/i.test(dataUrl)) return null;
+                // Renderer-side encoded-length cap. settings.html
+                // enforces the same limit on upload, but a manually
+                // edited localStorage value (or legacy data from
+                // before the upload guard existed) could still feed
+                // an arbitrarily large data URL into TextureLoader
+                // and burn memory / CPU during decode. Treat overlong
+                // values as "no asset" — style is inert, user can
+                // clear and re-upload from settings.
+                if (dataUrl.length > 2.5 * 1024 * 1024) return null;
+                // Renderer-side decompression-bomb caps. Mirror
+                // settings.html's upload-time guard so a manual
+                // localStorage edit (or legacy data from before that
+                // guard existed) can't sneak a 50000×50000 PNG past
+                // and OOM the GPU on texture upload.
+                const MAX_IMAGE_DIM = 4096;
+                const MAX_IMAGE_PIXELS = 16 * 1024 * 1024;
+                // Full-bleed backdrop: unit plane, scaled per frame in
+                // _bgFitBackdropPlane to fill the camera's view at
+                // BG_BACKDROP_DISTANCE. fog: false so the backdrop
+                // shows in full color; notes drawn on top still pick
+                // up atmospheric fog as before.
+                const state = {
+                    mesh: null, geo: null, mat: null, tex: null,
+                    drift: 0.5, intensity: settings.intensity, loaded: false,
+                    cam: settings.cam, distance: BG_BACKDROP_DISTANCE,
+                    lastAspect: 0, lastVisibleHeight: 0,
+                };
+                // Helper closure for cover-crop refresh — called both
+                // on async decode (initial) and from _bgFitBackdropPlane
+                // when the camera aspect changes (resize).
+                state.applyCoverCrop = function () {
+                    if (!state.tex || !state.tex.image) return;
+                    _bgCoverCrop(
+                        state.tex,
+                        state.tex.image.width  || 0,
+                        state.tex.image.height || 0,
+                        state.cam.aspect,
+                    );
+                };
+                const tex = new T.TextureLoader().load(
+                    dataUrl,
+                    (loaded) => {
+                        // Image dimensions are only known after async decode.
+                        const imgW = loaded.image?.width  || 0;
+                        const imgH = loaded.image?.height || 0;
+                        if (imgW > MAX_IMAGE_DIM || imgH > MAX_IMAGE_DIM || (imgW * imgH) > MAX_IMAGE_PIXELS) {
+                            // Bail before the texture gets uploaded to
+                            // the GPU (Three.js uploads on first render
+                            // of a visible mesh — hiding the mesh here
+                            // skips that). Disposing the texture too,
+                            // belt-and-suspenders, in case anything
+                            // else holds a reference.
+                            console.warn('[3D-Hwy] custom image dimensions too large to render', imgW + 'x' + imgH);
+                            if (state.mesh) state.mesh.visible = false;
+                            loaded.dispose();
+                            return;
+                        }
+                        state.applyCoverCrop();
+                        // Reset drift to the centered triangle-wave
+                        // phase now that repeat.x is final. Without
+                        // this reset, drift accumulated during the
+                        // async decode would phase-shift the initial
+                        // offset by a non-deterministic amount —
+                        // wider images would open at whatever crop
+                        // the elapsed-decode-time happened to land on.
+                        state.drift = 0.5;
+                        state.loaded = true;
+                    },
+                    undefined,
+                    // Async-failure path: the upfront regex catches the
+                    // common "corrupted/truncated bytes" case, but a
+                    // valid-looking data URL can still fail to decode
+                    // (e.g. wrong MIME / unsupported codec). Hide the
+                    // mesh so we don't paint a frozen blank plane on
+                    // top of fog, and log so the failure isn't silent.
+                    (err) => {
+                        console.error('[3D-Hwy] custom image decode failed', err);
+                        if (state.mesh) state.mesh.visible = false;
+                    },
+                );
+                tex.colorSpace = T.SRGBColorSpace;
+                // ClampToEdge on both axes — user uploads are non-
+                // power-of-two in general, and WebGL1 rejects RepeatWrapping
+                // on NPOT textures (renders black or emits GL errors). The
+                // drift logic below uses a triangle-wave so the offset
+                // stays inside [0, 1-repeat] and never needs wrap.
+                tex.wrapS = T.ClampToEdgeWrapping;
+                tex.wrapT = T.ClampToEdgeWrapping;
+                // User uploads aren't power-of-two in general; mipmaps
+                // are noisy for a single static backdrop and burn memory.
+                tex.generateMipmaps = false;
+                tex.minFilter = T.LinearFilter;
+                tex.magFilter = T.LinearFilter;
+                const geo = new T.PlaneGeometry(1, 1);
+                const mat = new T.MeshBasicMaterial({
+                    map: tex, transparent: false, depthWrite: false, fog: false,
+                });
+                const mesh = new T.Mesh(geo, mat);
+                scene.add(mesh);
+                state.mesh = mesh;
+                state.geo  = geo;
+                state.mat  = mat;
+                state.tex  = tex;
+                // Initial fit so the first frame is correctly sized
+                // and positioned, even if update() hasn't run yet.
+                _bgFitBackdropPlane(state);
+                return state;
+            },
+            update(s, bands, dt) {
+                if (!s) return;
+                // Track camera position / aspect every frame. The
+                // helper resizes the plane and refreshes cover-crop
+                // when aspect changes, and re-positions the plane to
+                // stay BG_BACKDROP_DISTANCE in front of the camera.
+                _bgFitBackdropPlane(s);
+                // Skip drift advance until the texture has finished
+                // decoding. Without this guard, drift accumulates
+                // during the async load while repeat.x is still 1
+                // (its default), and once the cover-crop applies the
+                // image opens at a phase-shifted offset whose value
+                // depends on how long the decode took — the
+                // "centered start" intent becomes non-deterministic.
+                if (!s.loaded) return;
+                // Triangle-wave ping-pong drift inside the cropped slack.
+                // ClampToEdge on wrapS means we cannot wrap across the
+                // texture boundary (would render edge pixels stretched);
+                // ping-pong oscillates the visible window between the
+                // image's left and right edges, which gives the same
+                // "alive" feel without the WebGL1 NPOT-Repeat hazard.
+                // Slack is the horizontal margin between the cropped
+                // window and the texture edges; for taller-than-plane
+                // images repeat.x stays 1, slack collapses to 0, and
+                // the offset stays at 0 — the image sits still, which
+                // is correct (it's already filling horizontally).
+                s.drift += dt * 0.02 * s.intensity;
+                const slack = Math.max(0, 1 - s.tex.repeat.x);
+                // Period of 2 drift units ≈ 100 s at intensity = 0.5;
+                // gentle, cinematic. cyc ∈ [0, 2), tri ∈ [0, 1] then back.
+                const cyc = ((s.drift % 2) + 2) % 2;
+                const tri = cyc < 1 ? cyc : 2 - cyc;
+                s.tex.offset.x = tri * slack;
+            },
+            teardown(s) {
+                if (!s) return;
+                s.mesh.parent && s.mesh.parent.remove(s.mesh);
+                s.geo.dispose();
+                s.mat.dispose();
+                // This style owns the texture lifecycle (per the comment
+                // at _bgDisposeGroupTree: tree dispose does NOT touch
+                // material.map textures).
+                s.tex.dispose();
+            },
+        },
+        // Custom video backdrop (#19 follow-up). User uploads a
+        // .mp4/.webm via settings.html; routes.py stores it on disk and
+        // serves a same-origin URL (avoids CORS taint on VideoTexture).
+        // localStorage holds only the filename — bytes live in
+        // {config_dir}/plugin_uploads/highway_3d/. Per-panel video
+        // element so each panel can mount/teardown independently;
+        // browsers cache the video bytes after first fetch so multi-
+        // panel splitscreen pays only the decoder cost, not the
+        // network or disk-read cost.
+        video: {
+            build(scene, settings) {
+                // Lowercase before validation so a manual localStorage
+                // edit like `current.MP4` doesn't pass a case-insensitive
+                // regex check and then 404 against the server, which
+                // only ever produces and serves lowercase
+                // current.<ext> (the upload route lowercases the
+                // extension; routes.py's GET pattern is case-sensitive).
+                const filename = (typeof settings.customVideoName === 'string')
+                    ? settings.customVideoName.trim().toLowerCase() : '';
+                // Strict pattern matches routes.py's deterministic
+                // single-slot naming. Any other shape (corrupt
+                // localStorage, future schema change) → style is
+                // inert, no <video> created, no orphan request to a
+                // 404 endpoint.
+                if (!/^current\.(mp4|webm)$/.test(filename)) return null;
+                const url = '/api/plugins/highway_3d/files/' + filename;
+
+                // Track partial allocations so a throw between any of
+                // them can clean up. _bgMountStyle's failure path
+                // disposes the stage tree but explicitly does NOT
+                // dispose textures (per the comment at
+                // _bgDisposeGroupTree), and the <video> element is
+                // parented to document.body — not the stage — so
+                // neither would be reached without an explicit catch.
+                let videoEl = null, tex = null, geo = null, mat = null, mesh = null;
+                try {
+                    // muted + playsInline + autoplay is the cross-
+                    // browser recipe that bypasses gesture requirements
+                    // (Chrome, Firefox, Safari desktop + mobile).
+                    // preload='auto' lets the first frame land before
+                    // play() is called. src is deliberately NOT set
+                    // yet — we want every piece of state (mesh, tex)
+                    // to exist before the browser can fire
+                    // loadedmetadata or error events on a cached
+                    // resource. The handlers close over state.tex /
+                    // state.mesh; setting src first would create a
+                    // window where a fast cache hit could fire an
+                    // event into half-initialized state.
+                    videoEl = document.createElement('video');
+                    // No crossOrigin attribute: the URL is same-origin
+                    // (/api/plugins/highway_3d/files/…), so VideoTexture
+                    // never sees a tainted canvas. Setting
+                    // `crossOrigin = "anonymous"` would also strip
+                    // cookies from the fetch, which would 401 against
+                    // any cookie-protected feedBack deployment. If
+                    // this ever needs to fetch cross-origin, switch
+                    // to `use-credentials` AND have the server send
+                    // the matching CORS headers.
+                    videoEl.muted = true;
+                    videoEl.playsInline = true;
+                    videoEl.loop = true;
+                    videoEl.autoplay = true;
+                    videoEl.preload = 'auto';
+                    videoEl.style.display = 'none';
+                    document.body.appendChild(videoEl);
+
+                    // Build mesh + texture before registering listeners
+                    // and before setting src. By the time loadedmetadata
+                    // or error can fire, state.tex and state.mesh are
+                    // both populated.
+                    tex = new T.VideoTexture(videoEl);
+                    tex.colorSpace = T.SRGBColorSpace;
+                    tex.wrapS = T.ClampToEdgeWrapping;
+                    tex.wrapT = T.ClampToEdgeWrapping;
+                    tex.minFilter = T.LinearFilter;
+                    tex.magFilter = T.LinearFilter;
+                    tex.generateMipmaps = false;
+                    geo = new T.PlaneGeometry(1, 1);
+                    mat = new T.MeshBasicMaterial({
+                        map: tex, transparent: false, depthWrite: false, fog: false,
+                    });
+                    mesh = new T.Mesh(geo, mat);
+                    scene.add(mesh);
+
+                    // Full-bleed backdrop: scaled and positioned each
+                    // frame in update() via _bgFitBackdropPlane.
+                    // cam + distance + lastAspect / lastVisibleHeight
+                    // power that helper.
+                    const state = {
+                        videoEl, mesh, geo, mat, tex,
+                        cam: settings.cam, distance: BG_BACKDROP_DISTANCE,
+                        lastAspect: 0, lastVisibleHeight: 0,
+                    };
+                    state.applyCoverCrop = function () {
+                        if (!state.videoEl) return;
+                        _bgCoverCrop(
+                            state.tex,
+                            state.videoEl.videoWidth  || 0,
+                            state.videoEl.videoHeight || 0,
+                            state.cam.aspect,
+                        );
+                    };
+
+                    // Cover-crop math runs on loadedmetadata since
+                    // video dimensions aren't known until then.
+                    // _bgFitBackdropPlane will also re-apply when the
+                    // camera aspect changes.
+                    videoEl.addEventListener('loadedmetadata', () => {
+                        state.applyCoverCrop();
+                    });
+                    videoEl.addEventListener('error', () => {
+                        // Fired for: codec unsupported, 404 from
+                        // server, truncated file, etc. Hide the mesh
+                        // so we don't paint a frozen blank plane on
+                        // top of fog.
+                        console.error('[3D-Hwy] custom video load failed', videoEl.error);
+                        state.mesh.visible = false;
+                    });
+
+                    // Set src last — this is what triggers the async
+                    // load. With handlers and state in place, any
+                    // synchronous-feeling event from a cached resource
+                    // is still safely received and handled.
+                    videoEl.src = url;
+
+                    // play() can reject for transient reasons (tab
+                    // backgrounded at mount time, low-power mode,
+                    // brief autoplay-policy timing window) even with
+                    // muted + autoplay set — but the browser retries
+                    // on its own once conditions improve (visibility
+                    // change, foregrounding, gesture). Real load /
+                    // codec failures come through the `error` event
+                    // we registered above and DO hide the mesh. So
+                    // just log here and leave the mesh visible; the
+                    // next ready frame will paint.
+                    videoEl.play().catch((err) => {
+                        console.warn('[3D-Hwy] custom video play() rejected (will retry on visibility/gesture)', err);
+                    });
+                    // Initial fit so the first frame is correctly
+                    // sized and positioned even before update() runs.
+                    _bgFitBackdropPlane(state);
+                    return state;
+                } catch (err) {
+                    // Best-effort cleanup of whatever was allocated
+                    // before the throw. Each step is independently
+                    // guarded so a secondary failure (e.g. dispose
+                    // throwing on an already-disposed object) can't
+                    // mask the original error.
+                    try {
+                        if (videoEl) {
+                            videoEl.pause();
+                            videoEl.removeAttribute('src');
+                            videoEl.load();
+                            if (videoEl.parentNode) videoEl.parentNode.removeChild(videoEl);
+                        }
+                    } catch (_) { /* ignore */ }
+                    try { if (mesh && mesh.parent) mesh.parent.remove(mesh); } catch (_) { /* ignore */ }
+                    try { if (geo) geo.dispose(); } catch (_) { /* ignore */ }
+                    try { if (mat) mat.dispose(); } catch (_) { /* ignore */ }
+                    try { if (tex) tex.dispose(); } catch (_) { /* ignore */ }
+                    throw err;
+                }
+            },
+            update(s) {
+                if (!s) return;
+                // VideoTexture auto-updates from the playing element —
+                // Three.js samples the current frame each render. No
+                // per-frame texture mutation here. Drift on offset.x
+                // is intentionally omitted: the video's own motion is
+                // the "life", drifting the crop on top would feel
+                // busy and compete with playback. The only per-frame
+                // work is keeping the plane camera-locked and resized
+                // when aspect changes (handled inside the helper).
+                _bgFitBackdropPlane(s);
+            },
+            teardown(s) {
+                if (!s) return;
+                if (s.videoEl) {
+                    try { s.videoEl.pause(); } catch (_) {}
+                    s.videoEl.removeAttribute('src');
+                    // load() with no src tells the browser to release
+                    // any decoder/buffer state for this element.
+                    try { s.videoEl.load(); } catch (_) {}
+                    if (s.videoEl.parentNode) s.videoEl.parentNode.removeChild(s.videoEl);
+                }
+                if (s.mesh) s.mesh.parent && s.mesh.parent.remove(s.mesh);
+                if (s.geo) s.geo.dispose();
+                if (s.mat) s.mat.dispose();
+                if (s.tex) s.tex.dispose();
+            },
+        },
+    };
+
+    /* ======================================================================
+     *  Per-instance counter
+     * ====================================================================== */
+
+    let _nextInstanceId = 0;
+
+    /* ======================================================================
+     *  Factory — feedBack#36 setRenderer contract
+     * ====================================================================== */
+
+    function createFactory() {
+        const _instanceId = ++_nextInstanceId;
+
+        // ── Per-instance Three.js state ───────────────────────────────────
+        let scene = null, cam = null, ren = null;
+        let wrap = null;
+        // WebGL context-loss recovery. Switching the active window / alt-tabbing
+        // (especially on Windows) can trigger a GPU context reset; with no
+        // handler the lost context escalates into a render-process crash. The
+        // listeners (bound in initScene on ren.domElement, removed in teardown)
+        // preventDefault the loss so the browser keeps the context restorable,
+        // _ctxLost gates draw() off the dead context, and on restore we reset the
+        // viewport + resume (Three re-uploads scene resources on the next render).
+        let _ctxLost = false;
+        let _onCtxLost = null, _onCtxRestored = null;
+        let bcCtrl = null; // Butterchurn audio-reactive background (the 'butterchurn' bg-style)
+        let _chartEnv = 0, _chartPrevT = -1, _bcBeatIdx = 0, _bcNoteIdx = 0, _bcChordIdx = 0, _bcTintTarget = null;
+        let _tintR = 20, _tintG = 24, _tintB = 40; // smoothed instrument-color tint for the bg
+        // highway:visibility listener (feedBack#246). Hides the .h3d-wrap
+        // overlay when feedBack's canvas is display:none'd (splitscreen
+        // case). Without this, the wrap is a *sibling* of #highway so
+        // hiding #highway leaves the WebGL scene painting full-screen.
+        // Bound in initScene after wrap creation, unbound in destroy().
+        let _visibilityHandler = null;
+        // highway:canvas-replaced listener — keeps highwayCanvas up to
+        // date across context-type swaps (e.g. swapping back to a 2D
+        // viz). The visibility handler's identity gate (event.detail.
+        // canvas === highwayCanvas) would otherwise stop matching
+        // after the swap; this listener follows the documented plugin
+        // contract from CLAUDE.md.
+        let _canvasReplacedHandler = null;
+        let ambLight = null, dirLight = null;
+        let fretG = null, tuningLblG = null, noteG = null, beatG = null, lblG = null;
+        let gNote = null, gSus = null, gBeat = null, gTapChevron = null;
+        // Per-string gradient gem geometries (index 0..5). Built in initScene
+        // from sampled colour PNGs; each carries a per-vertex colour attribute.
+        let gNoteGrad = [];
+        let mStr = [], mGlow = [], mSus = [], mStrHitOutline = [], mAccentOutline = [], mAccentCore = [], mAccentHaloNear = [], mAccentHaloMid = [], mAccentHaloFar = [];
+        // Pre-built accent-halo shell descriptors per string. Populated after
+        // mAccentHaloFar/Mid/Near are materialised; consumed in drawNote()'s
+        // hot path so the inner per-note `accentShells = [...]` array literal
+        // (3 plain-object allocations per accent gem per frame) is replaced
+        // by a stable read. Index 0 = outer, 1 = mid, 2 = near.
+        let _accentShellsByString = [];
+        let mWhiteOutline = null, mSusOutline = null;
+        // Dedicated sustain-trail outline material for the hit verdict.
+        // Drawn at opacity 0.45 — lower than mSusOutline (0.75) so the
+        // bright green emissive doesn't tint the body interior, and the
+        // verdict shows mostly on the outline fringe past the body edges.
+        // Only the hit-side rim ships; the verdict on miss is carried by
+        // mMissOutline (the gem-border material) instead of a dedicated
+        // sustain outline — matches the "outline-only verdict, body retains
+        // string colour" doctrine for the rest of the rendering path.
+        let mHitSusOutline = null;
+        // Shared materials for the legato technique meshes — one per geometry
+        // type, reused across every pooled mesh instance to avoid per-mesh
+        // material allocation in dense HO/PO/tap passages. Allocated in
+        // initScene() alongside the other scene materials and disposed in
+        // teardown.
+        let mTapChevron = null;
+        // Barre indicator material (white vertical line at the barre fret
+        // during chord linger). Promoted from inline pool-factory authoring
+        // to a named module-scope reference so _applyGlow() can mutate
+        // emissiveIntensity in place when the user drags the glow slider.
+        let mBarre = null;
+        // Notedetect feedback outlines (issue #9). Created in initScene
+        // alongside mWhiteOutline; swapped onto the note's outline mesh
+        // when a recent notedetect:hit / :miss event matches the note's
+        // (s, f, t). The miss gem border uses mMissOutline; the hit side
+        // uses per-string mHitBright[s] for the cyan-shifted flash.
+        let mMissOutline = null;
+        // Per-string hit verdict material used for outline + lateral face fill.
+        // Built in initScene() after mGlow. Array share the same material
+        // instances so outline and face fill always match exactly.
+        let mHitBright = [], mHitBrightArrays = [];
+        // Gem-rim hit flash ("just the rims"): per-string materials that flash
+        // in the STRING'S OWN colour with the same intensity treatment as the
+        // fret wires (FRET_WIRE_HIT_INTENSITY ramp, provider-alpha fade). Shared
+        // per string, so the applied intensity is the per-frame MAX alpha across
+        // that string's flashing gems — same compromise mGlow already makes.
+        let mRimFlash = [];
+        const _rimFlashIn = new Float32Array(S_COL.length);
+        // [verdict glow] Per-frame accumulation of the note-state provider's
+        // alpha (note_detect drives this from the live input level for held
+        // sustains, and as a time-fade for fresh strikes). Applied at the top of
+        // update() to scale the verdict-glow materials' emissiveIntensity so the
+        // gem brightness tracks how hard the string is actually ringing. Stays
+        // at "no provider" (vg = 1, unchanged brightness) for the legacy event
+        // path or when note_detect is off.
+        let _ndVerdictMaxAlpha = 0;
+        let _ndVerdictSawAlpha = false;
+        // Magenta-red face fill for miss — see initScene() for construction
+        // (uses mMissOutline ×4 + mEdgeTransparent ×2).
+        let mMissEdgeArrays = null;
+        let mEdgeTransparent = null;
+        let pSusOutline = null, pNoteEdge = null;
+        let projMeshArr = null;
+        let _probe = null;
+        /** Snapshotted in update() for drawNote() ghost / glow (single source vs per-caller isNext). */
+        let _drawNextByString = null;
+        /** Most-recent past event time per string (within 0.6 s back), for _nextAnyT deadline. */
+        let _drawRecentByString = null;
+        /** Snapshotted in update() — drawNote() is a sibling of update(), not nested in its closure. */
+        let _drawChordTemplates = null;
+        /** Ditto — drawNote() needs the anchors to resolve the lane's outer
+         * wires for an open note's hit flash (an open note has no fret of its
+         * own; its slab spans the lane, so the lane edges are what bracket it). */
+        let _drawAnchors = null;
+        /** Teaching marks sd/ch overlay pref (§6.2.2), mirrored from the 2D
+         * highway's `teachingMarksVisible` bundle flag. */
+        let _drawTeachingMarks = false;
+        /** Fret-hand finger (fg) hint pref, mirrored from the 2D highway's
+         * `fingerHintsVisible` bundle flag — default on (shown unless an explicit
+         * false), hideable independently of the sd/ch overlays. */
+        let _showFingerHints = true;
+        let _laneTargetColor = null;
+        let _renderScale = 1;
+        let lyricsCanvas = null, lyricsCtx = null;
+        // FPS counter overlay. EMA-smoothed over ~30 frames so the readout doesn't
+        // jitter every rAF tick. Controlled by the 'fpsVisible' setting (BG_DEFAULTS).
+        // Legacy 'h3d_showFps' localStorage key and window.h3dShowFps are no longer
+        // consulted — use the Settings → 3D Highway — Camera → Show FPS counter checkbox.
+        let _fpsLastT = 0;
+        let _fpsEma = 0;
+        let _fpsDisplay = 0;
+        let _fpsLastSampleT = 0;
+        // The FPS readout is pinned top-right of the highway overlay — the same
+        // corner the v3 player chrome stacks its persistent "Up Next" pill and
+        // live-performance HUD into, on a higher layer that paints over the
+        // canvas. So out of the box the readout sits *behind* that chrome and
+        // can't be read (exactly when you've turned it on to judge perf). Rather
+        // than relocate it (testers look top-right), we drop it just BELOW
+        // whichever of that chrome is showing. Refs are resolved once and cached
+        // — never a per-frame querySelector (see CLAUDE.md "never run DOM queries
+        // on a per-frame path") — and re-resolved only when a node detaches.
+        let _v3HudEls = null;
+        // Returns the bottom edge (in overlay-canvas px, which are 1:1 CSS px on
+        // this overlay) of the lowest visible top-right v3 chrome element, or 0
+        // when none apply (classic v2 UI, or all hidden). Only called while the
+        // FPS readout is actually drawn, so the layout reads cost nothing in the
+        // common (counter-off) case.
+        function _v3TopRightChromeBottom() {
+            if (typeof document === 'undefined' || !highwayCanvas) return 0;
+            // Only the v3 chrome stacks persistent HUD elements over the canvas's
+            // top-right. Gate on the documented detector so this is a strict no-op
+            // in classic v2 (where 'hud-time' also exists but sits elsewhere).
+            if (!(window.feedBack && window.feedBack.uiVersion === 'v3')) return 0;
+            if (!_v3HudEls || _v3HudEls.some((el) => el && !el.isConnected)) {
+                _v3HudEls = ['v3-upnext', 'v3-live-performance-hud', 'hud-time']
+                    .map((id) => document.getElementById(id));
+            }
+            const top = highwayCanvas.getBoundingClientRect().top;
+            let maxBottom = 0;
+            for (const el of _v3HudEls) {
+                // offsetParent === null ⇒ display:none (a `.hidden` pill/HUD) or
+                // not laid out — don't duck under something that isn't shown.
+                if (!el || el.offsetParent === null) continue;
+                const b = el.getBoundingClientRect().bottom - top;
+                if (b > maxBottom) maxBottom = b;
+            }
+            return maxBottom;
+        }
+        let _diagChord            = null;
+        // Chord diagram render cache. Keys: static layout inputs joined as a
+        // string. Values: OffscreenCanvas (or <canvas>) rendered at opacity=1
+        // entranceT=1 — composited each frame via drawImage + globalAlpha.
+        // Cleared on canvas resize (bx/by depend on canvasW/H/lyricsBottom)
+        // and on teardown/destroy.
+        const _diagRenderCache = new Map();
+        // Cap chosen to cover the ~5–6 active chord shapes per phrase while
+        // keeping the cached-OffscreenCanvas footprint bounded (~50 MB per
+        // panel at typical 1920×1080). A structural fix — caching a
+        // tightly-sized box surface instead of the full overlay canvas —
+        // is tracked as a follow-up.
+        const _DIAG_CACHE_MAX  = 6;
+        let pSusRail = null, gSusRail = null, mSusRailBase = null;
+        let pSusRailBloom = null, gSusRailBloom = null, mSusRailBloomBase = null, _bloomGaussTex = null;
+        let pTechPlane = null, gTechPlane = null;
+
+        // ── InstancedMesh for PM/FH X markers ────────────────────────────────
+        // Replaces pTechPlane pool entries for PM and FH mute techniques,
+        // collapsing O(visible-muted-notes) draw calls to 2 per type.
+        // pTechPlane pool is still used for H/P triangles, harmonics and bends.
+        let imPMTech = null, imFHTech = null;
+        let _imGPMTech = null, _imGFHTech = null; // cloned geometries (own instanceAlpha attr)
+        let _imPMTechMat = null, _imFHTechMat = null;
+        const IM_TECH_CAP = 256;
+        const _imPMTechAlphaArr = new Float32Array(IM_TECH_CAP);
+        const _imFHTechAlphaArr = new Float32Array(IM_TECH_CAP);
+        let _imPMTechCount = 0, _imFHTechCount = 0;
+
+        // ── InstancedMesh for chord strum indicators ──────────────────────────
+        // Replaces pPMXFill, pMuteXLines, pFHXFill, pFHXLines pools.
+        // Fixed renderOrder per type — no per-instance sort needed.
+        let imPMXFill = null, imPMXLines = null, imFHXFill = null, imFHXLines = null;
+        let _imPMXFillMat = null, _imPMXLinesMat = null;
+        let _imFHXFillMat = null, _imFHXLinesMat = null;
+        const IM_STRUM_CAP = 64;
+        const _imPMXFillAlphaArr  = new Float32Array(IM_STRUM_CAP);
+        const _imPMXLinesAlphaArr = new Float32Array(IM_STRUM_CAP);
+        const _imFHXFillAlphaArr  = new Float32Array(IM_STRUM_CAP);
+        const _imFHXLinesAlphaArr = new Float32Array(IM_STRUM_CAP);
+        let _imPMXFillCount = 0, _imPMXLinesCount = 0, _imFHXFillCount = 0, _imFHXLinesCount = 0;
+
+        // Temporaries for InstancedMesh matrix composition — allocated once in
+        // initScene() after Three.js loads, reused every frame without allocation.
+        let _imM4 = null, _imPos = null, _imSca = null, _imQ = null, _imAZ = null, _imColor = null;
+
+        let _diagPrev             = null;
+        let _diagPrevOpacity      = 0;
+        let _diagPrevStartOpacity = 0;
+        let _diagPrevStartT       = null;  // bundle.currentTime when crossfade began (drives rewindable fade)
+        let _diagEntranceT        = 1.0;
+        let _diagLastKey          = null;  // chord identity: name + '|' + frets.join(',')
+        // Per-wave cache for fret-column reference markers. Keyed by the
+        // wave's beat timestamp. We snapshot { hasLow, hasHigh, fretList,
+        // anchorKeyed } at first sight of a wave so its render gate stays consistent through the
+        // wave's flight even as activeFrets shifts mid-song. Entries are
+        // pruned each frame once their wave has passed `now`.
+        let _fretMarkerWaveCache = new Map();
+        // Per-frame booleans: handShapes[i] passes inferArpeggioFromNotePattern
+        // once (see fillArpeggioGhostInferFlags) so the note loop skips O(hs×notes)
+        // rescans — ref fillArpeggioGhostInferFlags in update().
+        let _arpGhostHsInferScratch = [];
+        // Handshape start-times where ghost fret numbers show but [ ] brackets are suppressed
+        // (synth-chord onset-match cases — not genuine arpeggios).
+        let _arpSynthOnsetHsSet = new Set();
+        /** Per-frame: ``handShapeIsArpeggioForLaneRail`` baked once — lane slices were O(96 × hs × infer). */
+        let _arpLaneRailHsScratch = [];
+        let _arpRailBoundLoScratch = [];
+        let _arpRailBoundHiScratch = [];
+
+        // ── Cross-frame caches for chart-static derivations ──────────────
+        // The merge + arp-flag fills below depend only on chart-static
+        // input arrays (handShapes / chords / chordTemplates / notes),
+        // not on `now`. The bundle hands us the same array refs every
+        // frame within an arrangement, so we can skip the recompute when
+        // the inputs are identity-equal to the previous frame's. On dense
+        // arrangements this avoids per-frame Set construction, nested
+        // O(hs × notes) scans, and a sort — significant FPS recovery.
+        let _mergeCacheResult = null;
+        let _mergeCacheChordsRef = null;
+        let _mergeCacheHsRef = null;
+        let _mergeCacheTplRef = null;
+
+        // Fret connector-label visibility cache: tracks which (time, fret)
+        // pairs may show their indicator number per the measure-skip rule
+        // (show only the first note with a given fret in a measure; suppress
+        // the same fret for the following measure, then allow it again).
+        let _fretLabelAllowed = new Set();
+        let _fretLabelNotesRef = null;
+        // Cache of measure-start times (beats with measure !== -1), rebuilt when
+        // the beats array changes. Drives the camera lookahead window
+        // (CAM_LOOKAHEAD_MEASURES measures instead of a fixed number of seconds).
+        let _measureStarts = [];
+        let _measureStartsRef = null;
+        // Frame-level dedup: tracks which (40ms-rounded-time, fret) pairs have already
+        // rendered a label this frame so that multiple strings at the same fret/onset
+        // (arpeggio chords, synthetic chords) never produce stacked duplicate labels.
+        const _frameLabeledKeys = new Set();
+
+        let _arpGhostInferRefHs = null;
+        let _arpGhostInferRefNotes = null;
+        let _arpGhostInferRefTpl = null;
+
+        // Slide-target gem suppression. A Set of "t_s" keys for notes in
+        // bundle.notes that are the linkNext destination of a preceding note
+        // (single or chord). The gem is suppressed (skipBody=true) but the
+        // sustain/slide trail still renders so the slide motion stays visible.
+        let _slideTargetSet = null;
+        let _slideTargetNotesRef = null;
+        let _slideTargetChordsRef = null;
+
+        let _laneRailFlagsRefHs = null;
+        let _laneRailFlagsRefTpl = null;
+
+        let _laneRailBoundsRefHs = null;
+        let _laneRailBoundsRefChords = null;
+        let _laneRailBoundsRefTpl = null;
+        let _laneRailBoundsRefNotes = null;
+        let _lastHwW = 0, _lastHwH = 0;
+        // Frame counter for throttling the CSS-box drift check in draw()
+        // (getBoundingClientRect is a forced layout read; see the comment
+        // at the check).
+        let _boxCheckCountdown = 0;
+        // Last logical (CSS px) size handed to applySize(). #highway is a
+        // flex:1 item, so its real rendered box (canvasSize()) can change as
+        // the player layout settles after a song opens WITHOUT the backing
+        // store (canvas.width) changing — which the _lastHwW/H check below
+        // would miss. Tracking the applied logical size lets draw() detect
+        // that CSS-box drift and re-frame, instead of the user having to
+        // un/re-maximize the window.
+        let _appliedW = 0, _appliedH = 0;
+        // Last pane aspect (w/h) handed to the camera, cached so camUpdate can
+        // recompute the horizontal-FOV-hold each frame (and react to live
+        // __h3dAspectTune edits) without waiting for a resize. 0 until first
+        // applySize().
+        let _paneAspect = 0;
+        // Per-instance fallback id for the wide-pane tuner's pane key, used only
+        // when this pane has no arrangement name to key by. Assigned once in
+        // init(); overrides keyed off arrangement persist across songs, this
+        // fallback is session-only.
+        let _paneUid = 0;
+        // True once applySize() has pinned the .h3d-wrap overlay to the
+        // highway canvas's offset box. Stays false while the canvas has no
+        // layout yet (init() can run before #highway has a real box, where
+        // applySize falls back to the parent-panel size and only sets the
+        // wrap height). The rAF loop re-pins once the canvas lays out even
+        // when the logical render size is unchanged — otherwise the overlay
+        // would stay at top:0;left:0;right:0 and expose a strip of #highway.
+        let _wrapPinned = false;
+        let mBeatM = null, mBeatQ = null;
+        let txtCache = {};
+        // Cloned sprite materials cached on individual sprite instances
+        // (e.g. pmMark._pmMat). pLbl pool reuses sprites across labels,
+        // so when a sprite is later assigned a different material the
+        // _pmMat stays referenced on the sprite itself but isn't reached
+        // by the scene.traverse-based dispose. Track them here so
+        // teardown can dispose them explicitly.
+        const _ownedClonedMats = [];
+        // Per-mesh technique-marker clones — keyed by mesh, disposed when
+        // the source sprite's map changes or on teardown. Replaces the old
+        // unbounded push-per-frame approach in _spriteMat2MeshMat.
+        const _techMeshMatClones = new Set();
+        // Shared (non-clone) materials and geometries that pool factories
+        // reference but that aren't guaranteed to be reachable via
+        // scene.traverse() — e.g. mLaneEven is only reached if at least one
+        // even-numbered fret stripe ever spawns. Track them here so teardown
+        // disposes the GPU resource regardless.
+        const _ownedSharedMats = [];
+        const _ownedSharedGeos = [];
+
+        // Background animation state (issue #13). bgGroup is the parent
+        // container for all bg meshes so teardown is one remove + dispose
+        // pass. bgState is the active style's per-panel state object.
+        let bgGroup = null, bgStage = null, bgState = null;
+        let bgMountedStyleId = null;
+        let bgStyleId = 'particles', bgIntensity = 0.5, bgReactive = true;
+        // Active scene color theme (background + highway surface). Read in
+        // _bgLoadSettings, applied by _applyBgTheme (clear + fog + board plane).
+        let bgThemeId = 'default';   // BACKGROUND axis (clear + fog)
+        let hwThemeId = 'default';   // HIGHWAY axis (board + lane + laneDim)
+        // Board (fretboard/highway-surface) plane material — kept so the theme
+        // can recolor it live without rebuilding the board. Set in buildBoard().
+        let _boardPlaneMat = null;
+        // Per-render opt-out for plugins borrowing the highway as a viz: when the
+        // mount bundle sets bgReactive === false, suppress the audio-reactive
+        // background for THIS instance only (no shared h3d_bg_* write). Captured
+        // from the bundle in init(); applied in _bgLoadSettings() so it survives
+        // later setting reloads. See init() for the rationale.
+        let _bgReactiveOptOut = false;
+        // Active palette for this panel (issue #10). Materials and per-
+        // frame color reads inside createFactory all consult this rather
+        // than the module-level S_COL, so a palette swap re-tints the
+        // panel live without touching module-level state.
+        let activePalette = PALETTES.default;
+        // Content signature of the colors last applied to materials; lets
+        // _bgLoadSettings force a retint when the in-place custom palette
+        // changes values without changing array identity.
+        let _bgPaletteSig = '';
+        // Fret digits on the board ghost (hollow preview at Z=0), not on
+        // flying note bodies — see fretNumberGhostScope for chord-hand vs all.
+        let showFretOnNote = false;
+        let fretNumberGhostScope = 'chords';
+        // Camera-X smoothing dial (issue #34). 0 = twitchy (track every
+        // upcoming fret), 1 = calm (ignore small intra-cluster shifts).
+        // Cached here and refreshed via the bg listener to avoid a
+        // per-frame localStorage hit inside update().
+        let cameraSmoothing = 0.5;
+        // Per-axis follow-ups: zoom (tgtDist hysteresis) and vertical-tilt
+        // (tgtLookY NDC self-correction) each get their own dial. Same
+        // 0..1 shape; same caching pattern. Both mirror cameraSmoothing's
+        // value when not explicitly stored, so existing users who only
+        // ever moved the camera-smoothing slider get the same calmness on
+        // the new axes by default.
+        let zoomSmoothing = 0.5;
+        let tiltSmoothing = 0.5;
+        // Camera lock: when true, pin the camera to a fixed wide view of
+        // frets 1-12 unless an upcoming note would otherwise be off-screen.
+        // The lock disengages while any note above fret 12 is in the
+        // lookahead window so the camera can briefly widen to include it,
+        // then re-engages once the high note ages out.
+        let cameraLockLow = false;
+        // Zoom-level for the locked view. Slider 0..1 maps to a multiplier
+        // on the locked tgtDist: 0 → CAM_LOCK_ZOOM_MIN (closest, biggest
+        // fretboard), 0.5 → 1.0× (the default locked view), 1 → CAM_LOCK_ZOOM_MAX
+        // (furthest). Inactive when the lock isn't engaged.
+        let cameraLockZoom = 0.5;
+        /** 'steady' = recency-weighted centroid + hysteresis (#34); 'lookahead' = wide preview window + smooth focal. */
+        let cameraMode = BG_DEFAULTS.cameraMode;
+        // Global text-size multiplier for in-scene text sprites (chord
+        // names, fret labels, section banners, technique markers, etc.).
+        // Slider is 0..1; mapped to a 0.5..1.5× multiplier with 0.5 = 1.0×
+        // (current default behaviour). _textSizeMul is the materialized
+        // multiplier — refreshed once per frame at the top of update()
+        // and consumed by every text-sprite scale.set call inside update
+        // and drawNote.
+        let textSize = 0.5;
+        let _textSizeMul = 1.0;
+        let _textSizeMulApplied = -1;
+        // Visual look dials (issue: pastel/washed-out feel + too-much-glow
+        // complaint). vibrancy raises idle string/note opacity and de-whites
+        // the hit-note body; glow scales every emissive contribution +
+        // projection glow layer opacity. Sliders are 0..1; defaults lean
+        // vivid + minimal-glow to match the requested out-of-box look.
+        // _vibrancyIdleOp / _vibrancyProjOp are cached so
+        // updateStringHighlights() and drawNote() don't recompute the
+        // linear blend every frame.
+        let vibrancy            = BG_DEFAULTS.vibrancy;
+        let glowMul             = BG_DEFAULTS.glow;
+        let _hitFx              = BG_DEFAULTS.hitFx;
+        let _sparks             = BG_DEFAULTS.sparks;
+        let _cinematic          = BG_DEFAULTS.cinematic;
+        let _verdictMarks       = BG_DEFAULTS.verdictMarks;
+        let _timingFx           = BG_DEFAULTS.timingFx;
+        let _streakFx           = BG_DEFAULTS.streakFx;
+        let _bloom              = BG_DEFAULTS.bloom;
+        let _composer = null, _bloomPass = null, _bloomLoad = null, _bloomW = 0, _bloomH = 0;
+        let _sparkPts = null, _sparkPos = null, _sparkCol = null, _sparkVel = null, _sparkLife = null;
+        const _SPARK_N = 256;
+        const _sparkSeen = new Map();     // note-key -> expiry; one burst per hit
+        let _juiceLastT = 0;              // frame-dt clock for the juice layer
+        let _streakHits = 0, _streakHeat = 0;  // #7 consecutive-hit escalation
+        let fpsVisible           = BG_DEFAULTS.fpsVisible;
+        let fretDividersVisible  = BG_DEFAULTS.fretDividersVisible;
+        let chordDiagramVisible  = BG_DEFAULTS.chordDiagramVisible;
+        let chordDiagramSize     = BG_DEFAULTS.chordDiagramSize;
+        let chordDiagramPosition = BG_DEFAULTS.chordDiagramPosition;
+        let fretColumnMarkerCadence = BG_DEFAULTS.fretColumnMarkerCadence;
+        let inlayLabelsVisible = BG_DEFAULTS.inlayLabelsVisible;
+        let sectionLabelsOnHighway = BG_DEFAULTS.sectionLabelsOnHighway;
+        let sectionHudVisible      = BG_DEFAULTS.sectionHudVisible;
+        let sectionHudPosition     = BG_DEFAULTS.sectionHudPosition;
+        let sectionHudSize         = BG_DEFAULTS.sectionHudSize;
+        let toneHudVisible         = BG_DEFAULTS.toneHudVisible;
+        let toneHudPosition        = BG_DEFAULTS.toneHudPosition;
+        let toneHudSize            = BG_DEFAULTS.toneHudSize;
+        let nutHeadstockVisible    = BG_DEFAULTS.nutHeadstockVisible;
+        let tuningLabelsVisible    = BG_DEFAULTS.tuningLabelsVisible;
+        let nutColor               = BG_DEFAULTS.nutColor;
+        let headstockColor         = BG_DEFAULTS.headstockColor;
+        let projectionVisible      = BG_DEFAULTS.projectionVisible;   // board "note preview" ghost on the fretboard
+        let slideArrowApproachVisible = BG_DEFAULTS.slideArrowApproachVisible; // slide-direction arrow riding with the note/gem
+        let slideArrowNeckVisible      = BG_DEFAULTS.slideArrowNeckVisible;    // slide-direction arrow preview on the neck
+        let slideArrowChainPreviewVisible = BG_DEFAULTS.slideArrowChainPreviewVisible; // early neck preview for chained/multi-leg slides
+        let _vibrancyIdleOp = 0.4  + 0.6  * BG_DEFAULTS.vibrancy;
+        let _vibrancyProjOp = 0.15 + 0.35 * BG_DEFAULTS.vibrancy;
+        // Custom image asset (issue #19). Data URL is the bytes that
+        // drive the 'image' bg style's texture; name is display-only
+        // metadata that settings.html shows next to the file picker.
+        let bgCustomImageDataUrl = '';
+        let bgCustomImageName = '';
+        // Custom video asset (issue #19 follow-up). Stores the
+        // server-side filename only; bytes live on disk via routes.py.
+        // The renderer composes the served URL from this filename in
+        // BG_STYLES.video.build.
+        let bgCustomVideoName = '';
+        let _bgListener = null;
+        let _bgLastT = 0;  // ms timestamp for dt
+
+        // Notedetect feedback (issue #9). Per-panel mark queues populated
+        // by two event sources: (a) legacy `notedetect:hit` /
+        // `notedetect:miss` window CustomEvents, and (b) FeedBack
+        // event-bus `note:hit` / `note:miss` events (subscribed in
+        // initScene() when window.feedBack exposes both `on` and `off`).
+        // Both sources feed the same _ndPushMark() helper which dedupes
+        // dual emissions. drawNote looks up its (s, f, t) against these
+        // arrays each frame and swaps the outline material when a match
+        // is current. Marks expire after _ND_TTL_MS so the visual flash
+        // is brief. Marks self-prune unconditionally in the listener and
+        // once per frame in update() to keep the arrays small.
+        const _ND_TTL_MS = 500;
+        const _ND_TIME_EPS = 0.01;
+        let _ndHitMarks = [];
+        let _ndMissMarks = [];
+        let _ndOnHit = null, _ndOnMiss = null;
+        let _ndOnBusHit = null, _ndOnBusMiss = null;
+        let _ndLabels = [];
+        // Per-chord-occurrence verdict latch for the chord-frame rim
+        // tint. Once a chord is observed all-hit/active during its linger
+        // fade we latch 'green' here so subsequent frames can't undo it
+        // as individual constituent glows decay and getNoteState starts
+        // returning null again (which would otherwise flicker the rim
+        // back to red mid-linger). Keyed by `${ch.id}|${ch.t}` — ch.id
+        // alone is the chord *template* id and is reused across every
+        // occurrence of the same shape, so id-only latching would bleed
+        // a single clean grab onto every later occurrence of that chord.
+        // Pre-hit-line invalidation (chDt > 0 path in the rim selection)
+        // evicts a chord's latch the next time it's seen approaching, so
+        // loops/rewinds re-judge from scratch and the Map can't grow
+        // beyond the current pre-hit-line frontier. Also cleared in
+        // destroy().
+        let _chordVerdicts = new Map();
+        // Previous-frame `now` for the chord-verdicts pruner — on a
+        // backward seek the latches behind that time become "future"
+        // entries the forward-only prune can't reach, so we wipe the
+        // map instead of paying an O(n) scan per frame to find them.
+        let _chordVerdictsLastNow = null;
+        // Numeric encoding for the _chordVerdicts key — replaces
+        // ``${ch.id}|${ch.t}`` which allocated a string per chord per
+        // frame in detect mode. Encoded so the key is monotonic in
+        // chord time and the prune sweep can compare keys directly
+        // (no parseFloat / String.slice). The time component sits in
+        // the upper bits; chord-template ids share the lower 1e6 slot
+        // and ch.id == null reserves idSlot 0 (no real chord id can
+        // collide with it because real ids encode as id + 1).
+        // ``time * 1e4`` keeps a 0.1 ms resolution — more than enough
+        // to disambiguate distinct chord onsets — and stays under the
+        // safe-integer limit for any realistic song length.
+        const _CV_KEY_TIME_MUL = 1e4;
+        const _CV_KEY_TIME_SLOT = 1e6;
+        function _encodeChordVerdictKey(ch) {
+            const tSlot = Math.round(ch.t * _CV_KEY_TIME_MUL) * _CV_KEY_TIME_SLOT;
+            const idSlot = ch.id != null ? ((Number(ch.id) | 0) + 1) : 0;
+            return tSlot + idSlot;
+        }
+        // Per-frame timestamp captured by update() and used by its
+        // prune pass for the notedetect mark arrays. drawNote itself
+        // no longer reads it — pruning lives once per frame so
+        // drawNote's hot path is just the bounded (s, f, t) match.
+        let _ndFrameNowMs = 0;
+        // feedBack#254 — core's per-note judgment provider, captured
+        // from `bundle.getNoteState` at the top of each update(). When
+        // present it's authoritative over the event-driven marks above:
+        // 'hit'/'active' → bright string-tinted outline (mGlow[s]) +
+        // bright body + glowing sustain trail + a contained sparkle on
+        // the overlay (a held sustain keeps glowing/sparkling for as
+        // long as it stays 'active'); 'miss' → red outline (mMissOutline)
+        // + suppressed body. null on cores without the API or songs
+        // with no scorer registered. Older note_detect builds that only
+        // emit notedetect:hit/miss events still work via _ndHitMarks.
+        let _ndGetNoteState = null;
+        let _ndHasProvider = false;  // true iff a note-state provider is registered (feedBack#254)
+        // Sustain verdict latch — persists a provider's hit/miss verdict for the
+        // full duration of a sustained note. Once hitGlowDuration expires the
+        // provider stops returning state; the latch re-injects the last verdict
+        // so the green/red color stays alive until susEnd.
+        // Key: Math.round(n.t * 1e4) * 10 + n.s  (matches _ghostPrevBuf scheme)
+        // Value: 'hit' | 'hit-live' | 'miss'  ('hit-live' = a live provider hit,
+        // tagged live:true, which is NOT re-injected once the provider goes
+        // silent — see the live-latch handling in the per-gem loop below).
+        let _susVerdictLatch = new Map();
+
+        // ── Score FX (notedetect game-scoring layer, notedetect ≥1.13) ──
+        // Two channels: (1) per-note "+N" score pops, sourced from the
+        // note-state provider's new { points, mult, popKey } fields at the
+        // moment a gem's verdict lands; (2) session-level bursts/pulses from
+        // the new `notedetect:fx` event (streak milestones, multiplier tier
+        // changes, streak breaks). Everything renders on the 2D overlay
+        // canvas (same layer as drawNotedetectLabels) — no Three.js objects,
+        // no txtMat() cache entries, nothing to dispose. Pools are fixed-
+        // size slot arrays created once per factory instance; when all slots
+        // are busy a new effect is simply dropped.
+        const _FX_POP_LIFE_MS = 700;
+        const _FX_BURST_LIFE_MS = 900;
+        const _FX_BURST_N = 36;
+        const _fxPops = Array.from({ length: 24 }, () => (
+            { active: false, x: 0, y: 0, z: 0, bornMs: 0, text: '', mult: 1 }
+        ));
+        const _fxBursts = Array.from({ length: 4 }, () => ({
+            active: false, bornMs: 0,
+            px: new Float32Array(_FX_BURST_N), py: new Float32Array(_FX_BURST_N),
+            vx: new Float32Array(_FX_BURST_N), vy: new Float32Array(_FX_BURST_N),
+        }));
+        // popKey -> expiry ms. Dedupes pops (chord members share the chord's
+        // popKey; sustains keep returning points for the whole glow window).
+        const _fxSeen = new Map();
+        let _fxOnFx = null;          // notedetect:fx listener (window)
+        let _fxOnSkin = null;        // notedetect:skin bus listener
+        // Generation counter: bumped by teardown() so the deferred window-
+        // copy fallback (a zero-delay task the listener removal can't cancel)
+        // bails instead of re-arming ring/burst state after teardown — or,
+        // worse, leaking a stale event into a subsequent init's fresh state.
+        let _fxGen = 0;
+        let _fxLastFxDetail = null;  // reference dedup: window + instanceRoot dispatches share one detail
+        // Details seen via element-scoped (bubbled) dispatch. A WeakSet, not a
+        // single slot: one judged hit can emit several fx in the same task
+        // (milestone + multiplier tier-up), and the deferred window-copy
+        // fallback for the FIRST must still see that its element copy arrived
+        // after the SECOND overwrote any last-detail slot. GC reclaims
+        // entries once notedetect drops the detail objects.
+        let _fxElemSeen = new WeakSet();
+        let _fxRingMs = -1e9;        // multiplier ring-pulse anchor
+        let _fxRingMult = 1;
+        let _fxBreakMs = -1e9;       // streak-break flicker anchor
+        // Canvas-side palette per notedetect skin (mirrors the accents in
+        // notedetect's assets/plugin.css; fonts are document-loaded by that
+        // stylesheet so the overlay canvas can use the family names).
+        const _FX_PALETTES = {
+            neon:    { accent: '#00f0ff', accent2: '#ff2ec4', miss: '#ff4444', font: 'Orbitron' },
+            esports: { accent: '#e8b43a', accent2: '#f5f5f4', miss: '#f87171', font: 'Rajdhani' },
+            metal:   { accent: '#ffb347', accent2: '#ff6b35', miss: '#ef4444', font: 'Russo One' },
+        };
+        let _fxPalette = _FX_PALETTES.neon;
+        function _fxResolvePalette() {
+            let skin = null;
+            try { skin = localStorage.getItem('feedBack_notedetect_skin'); } catch (e) {}
+            _fxPalette = _FX_PALETTES[skin] || _FX_PALETTES.neon;
+        }
+        function _fxSpawnPop(popKey, points, mult, x, y, z) {
+            if (_fxSeen.has(popKey)) return;
+            const nowMs = _ndFrameNowMs || performance.now();
+            _fxSeen.set(popKey, nowMs + 4000);
+            for (let i = 0; i < _fxPops.length; i++) {
+                const p = _fxPops[i];
+                if (p.active) continue;
+                p.active = true;
+                p.x = x; p.y = y; p.z = z;
+                p.bornMs = nowMs;
+                p.text = '+' + points;
+                p.mult = mult || 1;
+                return;
+            }
+        }
+        function _fxSpawnBurst(nowMs) {
+            for (let i = 0; i < _fxBursts.length; i++) {
+                const b = _fxBursts[i];
+                if (b.active) continue;
+                b.active = true;
+                b.bornMs = nowMs;
+                for (let j = 0; j < _FX_BURST_N; j++) {
+                    const a = (j / _FX_BURST_N) * Math.PI * 2;
+                    const sp = 2 + (j % 5) * 0.8;
+                    b.px[j] = 0; b.py[j] = 0;
+                    b.vx[j] = Math.cos(a) * sp;
+                    b.vy[j] = Math.sin(a) * sp - 1.2;
+                }
+                return;
+            }
+        }
+        function _fxHandle(d) {
+            // Reference dedup — notedetect dispatches the SAME detail object
+            // on window and on its instanceRoot; whichever arrives first wins.
+            if (d === _fxLastFxDetail) return;
+            _fxLastFxDetail = d;
+            const nowMs = performance.now();
+            if (d.fxType === 'milestone') {
+                _fxSpawnBurst(nowMs);
+            } else if (d.fxType === 'multiplier' && d.mult > (d.prevMult || 1)) {
+                _fxRingMs = nowMs;
+                _fxRingMult = d.mult;
+            } else if (d.fxType === 'streakBreak') {
+                _fxBreakMs = nowMs;
+            }
+        }
+
+        // Object pools
+        let pNote, pSus, pLbl, pBeat, pSec;
+        let pFretLbl, pLane, pLaneDivider;
+        // Shared materials/geometry for the lane stripes — see initScene().
+        // Hoisted so draw() can reference them when assigning per-stripe.
+        let mLaneOdd = null, mLaneEven = null, gLanePlane = null;
+        /** Lane fret dividers: default white vs arpeggio frame tint on outer wires only. */
+        let mLaneDivider = null, mLaneDividerArp = null, mLaneDividerExt = null;
+        /** Shared XY plane for ghost fret digits (lies on board like proj, not billboarding). */
+        let gGhostFretPlane = null, pGhostFretLbl = null;
+        // Anchor-driven lane scratch buffers. Per-frame the loop builds up
+        // to HWY_LANE_TIME_SLICES segments, but consecutive slices that share
+        // an anchor (the common case) collapse into the same entry. Held as
+        // four parallel arrays so the per-frame work allocates nothing once
+        // the buffers reach their steady-state size.
+        const _laneSegDMin = [];
+        const _laneSegDMax = [];
+        const _laneSegZ0 = [];
+        const _laneSegZ1 = [];
+        /** Chart-time span per merged lane segment (for per-slice arpeggio rail tint). */
+        const _laneSegTLo = [];
+        const _laneSegTHi = [];
+        const _laneSegArp = [];
+        let _laneSegLen = 0;
+        let pChordBox, pChordFrameFill, pChordLbl, pBarreLine, pArpBracket, pPMXFill, pFHXFill;
+        let gPMXFill = null; // shared geometry for PM X fill — disposed in teardown
+        let gFHXFill = null; // shared geometry for FH X fill — disposed in teardown
+        let gPMXLines = null, pMuteXLines = null; // PM X lines combined geometry (8 segs as quads)
+        let gFHXLines = null, pFHXLines = null;   // FH X lines combined geometry
+        let pNoteFretLabel, pConnectorLine, pDropLine, pTapChevron, pAccentHalo;
+        let pTeachMarkLbl;  // teaching marks fg/sd label sprites (§6.2.2)
+        let pHaloBar = null, gHaloBar = null; // gradient halo bar geometry — replaces per-shell pChordAccentHalo
+        let gArpBracket = null; // shared 1×1×1 box geometry for pArpBracket; built once, disposed in teardown
+        let pSusRibbon = null, pSusRibbonOl = null;
+        let pFretColMarker;
+        /** Horizontal gradient for chord box interior fill. */
+        let chordFrameGradTex = null;
+        /** Lavender gradient for arpeggio box interior (cyan × lavender blend — fades back to cyan). */
+        let chordFrameGradTexArp = null;
+
+        // Dynamic glowing string meshes (BoxGeometry, one per string)
+        let stringLines = [];
+        // Static thin-line glow layer behind each string (one Line per
+        // string). Retained so _applyVibrancy() can mutate opacity in
+        // place — without this the layer stays at its built-in opacity
+        // until the next palette change rebuilds buildBoard().
+        let stringLineGlows = [];
+        // One MeshStandardMaterial per fret wire (index = fret 0..NFRETS).
+        // Updated each frame to gold when inside the active anchor range,
+        // gray otherwise. Reset to [] on every buildBoard() rebuild.
+        let fretWireMats = [];
+        // Shared bowed TubeGeometry for all fret wires (centered at x=0;
+        // each fret mesh only differs by position). Disposed on rebuild +
+        // teardown. See FRET_BOW_DZ constants.
+        let fretTubeGeo = null;
+        /** Nut + headstock 3D subtree; visibility toggled from settings without rebuild. */
+        let nutHeadstockGroup = null;
+        /** Left edge X of drawable string meshes; updated in buildBoard() at nut / fret junction. */
+        let boardStringStartX = fretX(0);
+        /** Open-string label column X — over headstock, left of nut (set in buildBoard()). */
+        let boardTuningLabelX = -4.2 * K;
+        // Fret inlay number label sprites (one per INLAY_LABEL_FRETS entry).
+        // Retained so update() can rescale them live when _textSizeMul changes.
+        let _inlayLabels = [];
+        // Cloned SpriteMaterials for the inlay labels — disposed on rebuild and
+        // destroy() to prevent GPU leaks across palette changes or panel reuse.
+        let _inlayMats = [];
+        // Open-string tuning labels beside the headstock (issue: per-song tuning).
+        let _tuningLabelSprites = [], _tuningLabelMats = [];
+        let _lastOpenStringLblSig = '';
+        // Cheap-key cache for _syncOpenStringPitchLabels: skip the expensive
+        // labels-array + signature-string build when the inputs that actually
+        // change the labels haven't changed reference/value since last frame.
+        let _lastSyncTuningRef = undefined;
+        let _lastSyncBundleTuningRef = undefined;
+        let _lastSyncCapo = NaN;
+        let _lastSyncArrIdx = undefined;
+        let _lastSyncPaletteRef = null;
+        let _lastSyncNStr = -1;
+        let _lastSyncTextSizeMul = NaN;
+        let _lastSyncStartX = NaN;
+        let _lastSyncLabelX = NaN;
+        // Scratch Color used by _applyVibrancy() to avoid allocating a
+        // fresh THREE.Color each time the user drags a slider.
+        // Allocated lazily once Three.js is loaded inside initScene().
+        let _paletteColorTmp = null;
+        // Per-fret last-active timestamp for lane persistence
+        let fretLastActiveTime = new Array(NFRETS + 1).fill(0);
+
+        // Active string count for the current arrangement (resolved each
+        // frame from bundle.stringCount and clamped to MAX_RENDER_STRINGS).
+        let nStr = NSTR;
+        // Set true once a chart with out-of-range s indices has triggered
+        // its warning. Reset only on teardown or when nStr changes (e.g.
+        // arrangement switch from guitar to bass) — same-nStr songs share
+        // the suppression, which is fine for what is purely a developer
+        // aid log.
+        let _oobStringWarned = false;
+
+        // Per-string bounds check used by every loop that indexes a
+        // per-string array (noteState.*, nextNoteByString, lastFretForString,
+        // mStr/mGlow/mSus, ...). Skipping out-of-range s upstream keeps
+        // sparse-array extension out of those arrays AND keeps drawNote's
+        // material lookup safe in one place.
+        function validString(s) {
+            const ok = Number.isInteger(s) && s >= 0 && s < nStr;
+            if (!ok && !_oobStringWarned) {
+                _oobStringWarned = true;
+                let msg = '[3D-Hwy] dropping notes with s out of range [0,' + nStr + ')';
+                if (nStr === S_COL.length) msg += ' (extended-range chart beyond palette size)';
+                console.warn(msg);
+            }
+            return ok;
+        }
+
+        // filter() allocates a new array per chord per frame, even though
+        // the vast majority of charts have no out-of-range strings. Scan
+        // first; only allocate when there's actually something to drop.
+        // The unfiltered array is reused as-is in the common case.
+        //
+        // Result is cached by ``ch.notes`` identity — call sites (chord
+        // render loop, camera pre-pass, strGlow / accent prepasses, cjNext
+        // peek) hit the same chord-notes array many times per frame, and
+        // the array contents are chart-static for the lifetime of the
+        // arrangement. The cache stores either the input array itself
+        // (common case) or the filtered copy, so the identity-preservation
+        // contract callers depend on is unchanged.
+        // NOTE: this cache (and _chordSigCache / _chordShapeCache below) keys on
+        // the notes/chord object but its result depends on validString() →
+        // nStr. If first computed while nStr is still the default 6 (an early
+        // frame before song_info applies stringCount), string-6+ notes get
+        // filtered out and would stay gone forever. The nStr-change handler
+        // resets all three via _resetStringDependentCaches() so extended-range
+        // (7+ string) charts recompute once the real string count arrives.
+        let _filterValidNotesCache = new WeakMap();
+        function filterValidNotes(notes) {
+            const cached = _filterValidNotesCache.get(notes);
+            if (cached !== undefined) return cached;
+            let filtered = notes;
+            for (let i = 0; i < notes.length; i++) {
+                if (!validString(notes[i].s)) {
+                    filtered = notes.filter(cn => validString(cn.s));
+                    break;
+                }
+            }
+            _filterValidNotesCache.set(notes, filtered);
+            return filtered;
+        }
+
+        /**
+         * Normalized fingering signature for chord repeat-run detection, or null.
+         * Cached via WeakMap so the sort+join only runs once per unique chord object
+         * across all frames — chart data never changes after load.
+         */
+        let _chordSigCache = new WeakMap();
+        function chordShapeSignature(ch) {
+            if (!ch?.notes) return null;
+            if (_chordSigCache.has(ch)) return _chordSigCache.get(ch);
+            const chordNotes = filterValidNotes(ch.notes);
+            let sig = null;
+            if (chordNotes.length > 0) {
+                sig = chordNotes.slice().sort((a, b) => a.s - b.s).map(n => `${n.s}:${n.f}`).join('|');
+            }
+            _chordSigCache.set(ch, sig);
+            return sig;
+        }
+
+        // ── Per-frame scratch arrays (hoisted to avoid per-frame allocation) ─────
+        // Sized to MAX_RENDER_STRINGS / NFRETS+1 — always large enough for any
+        // arrangement. We fill only [0..nStr) each frame and reset with .fill().
+        // Holding these at closure scope keeps them in a GC root; the engine can
+        // keep them hot in L1/L2 across frames, and no allocation pressure from
+        // update() itself.
+        const _scrStringSustain      = new Array(MAX_RENDER_STRINGS).fill(false);
+        const _scrStringAnticipation = new Array(MAX_RENDER_STRINGS).fill(0);
+        const _scrFretHeat           = new Array(NFRETS + 1).fill(0);
+        // Fret-wire hit flash. _fwHitIn is per-frame (cleared with the rest of
+        // the frame state, written by drawNote when a provider confirms a note);
+        // _fwHitGlow persists across frames so the flash can decay smoothly
+        // rather than snapping off the frame the provider goes quiet.
+        const _fwHitIn               = new Float32Array(NFRETS + 1);
+        const _fwHitGlow             = new Float32Array(NFRETS + 1);
+        // Per-frame chord accumulator. A chord flashes only the OUTERMOST wires
+        // of its shape, but drawNote() sees one chord note at a time and can't
+        // know the span — so hits accumulate here keyed by chord, and the flash
+        // pass (which runs after every draw loop) resolves min/max into wires.
+        // Typically 0-2 entries: only chords with a confirmed hit land here.
+        const _fwChordAcc            = new Map();
+        let _fwHitPrevTime = -Infinity; // chart time of the last decay step
+        let _fwHitColor = null;         // T.Color scratch (built in initScene)
+        let _fwHitEmissive = null;
+        const _scrStrGlow            = new Array(MAX_RENDER_STRINGS).fill(0.5);
+        const _scrAccentFillBoost    = new Array(MAX_RENDER_STRINGS).fill(0);
+        const _scrNextNoteByString   = new Array(MAX_RENDER_STRINGS).fill(null);
+        const _scrLastFretForString  = new Array(MAX_RENDER_STRINGS).fill(undefined);
+        // Scratch buffer for the recent-past-event prepass (~0.6 s back) — avoids
+        // re-allocating a per-string Array every frame. Re-filled with -Infinity
+        // at the top of each prepass run.
+        const _scrRecentByString     = new Array(MAX_RENDER_STRINGS).fill(-Infinity);
+        // Scratch buffers for the ghost-preview gap prepass — refilled each
+        // frame to avoid the `new Array(nStr)` + `Object.create(null)` churn.
+        // The Map is cleared at the top of the prepass; live entries are
+        // consumed by drawNote() reads later in the same frame.
+        const _scrGhostLastT         = new Array(MAX_RENDER_STRINGS).fill(-Infinity);
+        const _scrGhostPrevBuf       = new Map();
+        // Per-string count of upcoming-ghost slots (1/2) claimed so far this
+        // frame (board ghost — up to 3 simultaneous previews per string).
+        // Reset to 0 each frame alongside the other pool .reset() calls.
+        const _scrGhostUpcomingCount = new Array(MAX_RENDER_STRINGS).fill(0);
+        // Hoisted scratch for the arp-bracket dedupe within a single draw().
+        // Keys are `${chordId}:${occurrenceStart}` strings (cheap to build, low
+        // cardinality per frame); values are Sets of string-indices that have
+        // already drawn brackets in the AHEAD note-stream pass. Cleared at the
+        // top of every chord pass so the Set objects (and the outer Map) are
+        // reused across frames instead of reallocated.
+        const _scrNoteStreamBracketStrings = new Map();
+        // Scratch object reused for chord-note drawNote calls so `{ ...cn, t: ch.t }`
+        // doesn't allocate a new object per chord note per frame.
+        const _scrChordNote = {};
+        // Scratch objects for the nextNoteByString prepass — chord notes need
+        // a merged `{ ...cn, t: ch.t }` object, but spread allocates every frame.
+        // One scratch object per string (max MAX_RENDER_STRINGS) is safe because:
+        // (a) the prepass writes each string's entry at most once per frame,
+        // (b) drawNote() reads nxFrame.t before the next frame's prepass can overwrite.
+        const _scrNextNoteByStringData = Array.from({ length: MAX_RENDER_STRINGS }, () => ({}));
+        // Reusable Set for arpeggio persistence key lookup — cleared each frame
+        // instead of reallocating a new Set.
+        const _scrArpPersistKeys = new Set();
+        // Reusable Set for active-fret cooldown tracking — cleared each frame.
+        const _scrActiveFrets = new Set();
+        // Reusable scratch for barre atMinFretStrings computation — avoids the
+        // [...chShape].filter().map().sort() chain (3 allocations per chord per frame).
+        const _scrAtMinFretArr = new Array(MAX_RENDER_STRINGS).fill(0);
+        let _scrAtMinFretLen = 0;
+        // Sorted scalar view of "next event time per string ∪ recent event
+        // time per string" — populated once per frame in update() after
+        // _drawNextByString and _drawRecentByString are set. drawNote() and
+        // the chord render loop both need "earliest event time strictly
+        // greater than t" to deadline-cap gem visibility; the previous
+        // implementation re-scanned both per-string arrays (2 * nStr
+        // lookups) per note/chord per frame, which is hot in dense
+        // PM/FH/arpeggio passages. With this scratch the same query is
+        // O(log N) over at most 2 * MAX_RENDER_STRINGS = 16 entries via
+        // _firstEventTimeGreaterThan(). Capacity is fixed (Float64Array)
+        // to keep the buffer in stable memory; _scrEventTimesLen tracks
+        // the live prefix.
+        const _scrEventTimes    = new Float64Array(MAX_RENDER_STRINGS * 2);
+        let   _scrEventTimesLen = 0;
+        function _firstEventTimeGreaterThan(t) {
+            let lo = 0, hi = _scrEventTimesLen;
+            while (lo < hi) {
+                const mid = (lo + hi) >>> 1;
+                if (_scrEventTimes[mid] <= t) lo = mid + 1;
+                else hi = mid;
+            }
+            return lo < _scrEventTimesLen ? _scrEventTimes[lo] : Infinity;
+        }
+
+        // Camera state
+        let _leftyCached = false;
+        const xFret = f => (_leftyCached ? -fretX(f) : fretX(f));
+        const xFretMid = f => (_leftyCached ? -fretMid(f) : fretMid(f));
+        const boardSpanX = () => {
+            const x0 = xFret(0);
+            const xN = xFret(NFRETS);
+            return {
+                min: Math.min(x0, xN),
+                max: Math.max(x0, xN),
+                center: (x0 + xN) / 2,
+                width: Math.abs(xN - x0),
+            };
+        };
+
+        let tgtX = xFretMid(CAM_LOCK_CENTER_FRET), curX = xFretMid(CAM_LOCK_CENTER_FRET);
+        let tgtDist = CAM_DIST_BASE, curDist = CAM_DIST_BASE;
+        // Dolly-back multiplier applied to the curDist lerp target by camUpdate's
+        // fret-row fit guard. 1 = no extra pull-back (the common case); rises
+        // toward FRET_ROW_FIT_BOOST_MAX only when a tight, centred zoom would push
+        // the fret-number row past the bottom edge, then relaxes back to 1.
+        let _fretRowFitBoost = 1;
+        // Last committed lowFretBonus contribution baked into tgtDist
+        // (see candidateDist block — bonus is applied on top of the
+        // hysteresis-gated base).
+        let prevLowFretBonus = 0;
+        // Tracks whether the camera lock was active on the previous
+        // frame, so the dynamic branch can bypass zoom hysteresis on
+        // the first frame after a lock release. Without this, a >12
+        // fret note that disengaged the lock could be swallowed by
+        // the dead zone and the camera would fail to widen — a UX
+        // promise of the lock toggle.
+        let prevLockActive = false;
+        let tgtLookY = 0, curLookY = 0;   // lerped look-at Y for self-correcting camera
+        let aspectScale = 1;
+        // _camSnapped / _camPreScanned / _songKey: together they gate the first-data snap.
+        //
+        // On the first update() frame where bundle.notes is available,
+        // _camPreScanned is set and the full notes array is scanned (O(N), once)
+        // to check whether ANY fretted note (f > 0) exists.  If none do (e.g. an
+        // all-open-string bass arrangement), _camSnapped is set to true immediately
+        // so the per-frame pre-pass is disabled for the entire song.
+        //
+        // For charts that do have fretted notes, a lightweight O(window) pre-pass
+        // runs before any drawNote() call on every frame until the first frame
+        // where fretted notes appear in the camera targeting window (preWSum > 0).
+        // At that point curX/curDist are snapped directly to the computed targets,
+        // eliminating the camera swoop for songs with long silent intros.
+        //
+        // Once _camSnapped is true it is never cleared for the current song; the
+        // pre-pass is a permanent no-op thereafter and the camera reverts to
+        // normal lerp-based tracking for the rest of the song.
+        //
+        // _songKey tracks the active song/arrangement so the snap state resets
+        // automatically when the user switches songs or arrangements via
+        // reconnect() (which does not call renderer.destroy/init).
+        let _camSnapped = false;
+        let _camPreScanned = false;
+        let _songKey = null;
+        // Smooth lookahead camera: fused world-X and displayed fret-span.
+        let _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
+        let _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
+        let _lookaheadCamPrevNow = null;
+        let _lookaheadLowBonusU = 0;
+        let _lookaheadHiNeckLatch = false;
+
+        // ── Sub-frame clock smoothing ─────────────────────────────────────
+        // bundle.currentTime is the browser's audio.currentTime, which only
+        // refreshes every ~20–23 ms — coarser than a 60/144 Hz rAF frame. Fed
+        // straight into note Z-positions it makes the whole highway step in
+        // micro-jumps (1–2 static frames, then a jump), most visible as a
+        // "stutter" across a dense wall of repeated chords even when FPS is
+        // steady. smoothNow() interpolates forward with performance.now()
+        // between distinct audio samples (mirroring core highway.js
+        // getTime()), tracking the observed playback rate so the speed slider
+        // stays accurate, and falls back to the raw value on pause / seek /
+        // stall so the scroll never drifts against silent audio.
+        let _clkAudioT = NaN;   // last distinct bundle.currentTime sample
+        let _clkPerf = NaN;     // performance.now() when that sample arrived
+        let _clkRate = 1;       // observed chart-seconds per real-second
+        let _frameNow = 0;      // smoothed time for THIS frame (update → camUpdate)
+
+        // Low-overdraw sustain rendering (DEFAULT since perf profiling on
+        // dense palm-mute / fret-hand-mute passages). Those sections are GPU
+        // fill-bound: the transparent sustain trails/rails stack many blended
+        // fragments. Profiling (pinned A/B loop) showed ren.render() p50 at
+        // ~7.5 ms vs ~5.9 ms with all the sustain extras off. The additive
+        // rail bloom halo (wide gaussian planes, additive blending) is the
+        // single most expensive per-pixel contributor, so the lean default
+        // drops ONLY the bloom. The trail/ribbon white OUTLINE (mSusOutline,
+        // with hit/miss colour) is kept — it's a thin, cheap layer and gives
+        // tails their border, so it's worth the small fill cost. Opt back into
+        // the full look (re-enable the rail bloom) per browser, no rebuild:
+        //   localStorage.h3d_full_sus = '1'   // re-enable rail bloom halo
+        //   delete localStorage.h3d_full_sus  // back to lean default
+        // Polled at ~1 Hz at the top of update() (perf: localStorage reads
+        // are synchronous) so the console flag still takes effect live.
+        // The bloom pool/material/gaussian texture are kept intact
+        // (still pinned by the bloom unit tests and used by the opt-out path).
+        let _leanSus = true;
+        let _leanSusPollCounter = 0;
+
+        // Lifecycle flags
+        let _isReady = false;
+        let _destroyed = false;
+        let _invertedCached = false;
+        let _invertedForBoard = false;
+        let _leftyForBoard = false;
+        let _initToken = 0;
+        let highwayCanvas = null;
+
+        // ── Focus state (splitscreen dim) ─────────────────────────────────
+        let _focusSubscribed = false;
+        let _isFocused = true;
+        const _onFocusChange = () => _updateFocusState();
+
+        function _unsubscribeFocus() {
+            if (!_focusSubscribed) return;
+            const ss = window.feedBackSplitscreen;
+            if (ss && typeof ss.offFocusChange === 'function') ss.offFocusChange(_onFocusChange);
+            _focusSubscribed = false;
+        }
+
+        function _updateFocusState() {
+            if (_destroyed || !_isReady) return;
+            const focused = _ssIsCanvasFocused(highwayCanvas);
+            if (focused === _isFocused) return;
+            _isFocused = focused;
+            if (ambLight) ambLight.intensity = focused ? 0.85 : 0.4;
+            if (dirLight) dirLight.intensity = focused ? 0.8 : 0.35;
+        }
+
+        // ── String-to-Y (respects invert) ─────────────────────────────────
+        const sY = s => S_BASE + (_invertedCached ? s : (nStr - 1 - s)) * S_GAP;
+
+        // ── Text-sprite cache ──────────────────────────────────────────────
+        // ── Text-sprite style presets ─────────────────────────────────────
+        // Each preset describes how a class of label is rasterised.
+        // Tweak per-class look here (font, outline color/width, source
+        // canvas size). `wide` toggles a long aspect ratio for multi-char
+        // labels (chord/section names, "↑1/2", "~~~").
+        //
+        // Knobs:
+        //   font        — full CSS font shorthand (weight + size + family)
+        //   wideFont    — same, used when caller passes wide=true
+        //   srcH        — source-canvas height in px (square; wide=4×).
+        //                 Keep power-of-two so WebGL1 / Three.js retain
+        //                 mipmaps + linear-mip-linear filtering — NPOT
+        //                 textures silently fall back to no-mipmap and
+        //                 shimmer at distance.
+        //   stroke      — outline color (null = no outline)
+        //   strokeW     — outline line-width in source-canvas px
+        //   shadow      — { color, blur, dx, dy } or null
+        const TXT_STYLES = {
+            // The two fret-number sets the user wants to pop hardest.
+            fretRow: {
+                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                srcH: 256, stroke: '#0a1018', strokeW: 18,
+                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
+            },
+            noteFret: {
+                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                srcH: 256, stroke: '#0a1018', strokeW: 18,
+                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
+            },
+            // Ghost-fret labels on the board projection: same weight/size/outline
+            // as noteFret, but uses textAlign='center'; textBaseline='middle'
+            // (the standard branch in txtMat) so the glyph is truly centred on
+            // the PlaneGeometry UV. inkCenterFret's actualBoundingBox path is
+            // intentionally NOT activated for this style — that path was designed
+            // for Sprites and shifts the canvas origin, which causes visible
+            // lower-left drift on Mesh + MeshBasicMaterial (UV-direct mapping).
+            ghostFret: {
+                font:     '900 160px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                wideFont: '900 128px "Arial Black", "Helvetica Neue", Arial, sans-serif',
+                srcH: 256, stroke: '#0a1018', strokeW: 18,
+                shadow: { color: 'rgba(0,0,0,0.7)', blur: 14, dx: 0, dy: 0 },
+            },
+            // Chord names — gold script-style label, lighter outline keeps
+            // the colour readable.
+            chord: {
+                font:     'bold 80px sans-serif',
+                wideFont: 'bold 64px sans-serif',
+                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
+            },
+            // Section banners ("Verse", "Chorus") — same as chord weight.
+            section: {
+                font:     'bold 80px sans-serif',
+                wideFont: 'bold 64px sans-serif',
+                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
+            },
+            // Technique markers (pinch-harmonic icon, PM, AC, H/P/T, etc.).
+            technique: {
+                font:     'bold 80px sans-serif',
+                wideFont: 'bold 64px sans-serif',
+                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
+            },
+            // Open-string "0" label on the note body itself.
+            open: {
+                font:     'bold 80px sans-serif',
+                wideFont: 'bold 64px sans-serif',
+                srcH: 128, stroke: '#0a1018', strokeW: 6, shadow: null,
+            },
+        };
+
+        function txtMat(text, col, wide, style) {
+            const sName = style || 'technique';
+            const k = sName + '|' + (wide ? 'W' : '') + text + '|' + col;
+            if (txtCache[k]) return txtCache[k];
+            const sp = TXT_STYLES[sName] || TXT_STYLES.technique;
+            const h  = sp.srcH;
+            const str = String(text);
+            const font = wide ? sp.wideFont : sp.font;
+
+            let w = wide ? h * 4 : h;
+
+            if (!wide && sName === 'noteFret') {
+                // Wide labels (D#2, Bb3) need a canvas wider than srcH; cap so
+                // glyphs stay centred at (w/2, h/2) without edge clipping.
+                const probe = document.createElement('canvas').getContext('2d');
+                probe.font = font;
+                const tw = probe.measureText(str).width;
+                let pad = 0;
+                if (sp.stroke && sp.strokeW > 0) pad += sp.strokeW * 2;
+                if (sp.shadow) {
+                    pad += Math.abs(sp.shadow.dx) + sp.shadow.blur * 2;
+                }
+                w = Math.min(12 * h, Math.max(h, Math.ceil(tw + pad)));
+            }
+
+            const c  = document.createElement('canvas');
+            c.width = w; c.height = h;
+            const x = c.getContext('2d');
+            x.font = font;
+            // Fret / open-string digits: anchor from actualBoundingBox so the
+            // glyph sits at the true optical centre of the canvas (fixes
+            // sprites looking off-centre inside the board ghost and elsewhere).
+            const inkCenterFret = !wide && (sName === 'noteFret' || sName === 'open');
+            // Ghost fret labels live on a PlaneGeometry Mesh (UV-direct), not a Sprite
+            // billboard.  Sprites tolerate slight canvas off-centering because Three.js
+            // centres them at their world position; a Mesh does not — the digit lands
+            // wherever it sits in UV space.  Use the advance-width centre as the initial
+            // pen position and then correct for any ink asymmetry via actualBoundingBox.
+            const inkCenterGhost = !wide && sName === 'ghostFret';
+            let drawX = w / 2;
+            let drawY = h / 2;
+            if (inkCenterFret) {
+                x.textAlign = 'left';
+                x.textBaseline = 'alphabetic';
+                const m = x.measureText(str);
+                const L = m.actualBoundingBoxLeft;
+                const R = m.actualBoundingBoxRight;
+                const A = m.actualBoundingBoxAscent;
+                const D = m.actualBoundingBoxDescent;
+                if (
+                    L != null && R != null && A != null && D != null &&
+                    Number.isFinite(L) && Number.isFinite(R) &&
+                    Number.isFinite(A) && Number.isFinite(D)
+                ) {
+                    const inkW = R - L;
+                    drawX = (w - inkW) / 2 - L;
+                    drawY = (h + A - D) / 2;
+                    // Tab digits sit visually a hair low vs bbox (stroke/shadow);
+                    // small canvas nudge keeps sprites centred on the board ghost.
+                    if (sName === 'noteFret') drawY -= h * 0.028;
+                } else {
+                    x.textAlign = 'center';
+                    x.textBaseline = 'middle';
+                    drawX = w / 2;
+                    drawY = h / 2;
+                }
+            } else if (inkCenterGhost) {
+                // Alpha-weighted centroid approach on FILL-ONLY ink (no shadow, no
+                // stroke) to find the true ink centre of mass without contamination
+                // from the isotropic shadow blur.  For Arial Black "1" the shadow from
+                // the thin upper-left flag bleeds leftward and cancels part of the
+                // rightward correction when we include it in the scan.  Measuring fill
+                // alone isolates the actual glyph shape.
+                // 1. Draw fill-only (no shadow, no stroke) at (w/2, h/2) on temp canvas.
+                // 2. Compute Σ(px·alpha) / Σ(alpha) → ink centroid.
+                // 3. Shift drawX/drawY so centroid lands exactly at (w/2, h/2).
+                // Max 4 unique digits (1–4) → cache-miss runs at most 4 times ever.
+                x.textAlign = 'center';
+                x.textBaseline = 'middle';
+                try {
+                    const tmpC = document.createElement('canvas');
+                    tmpC.width = w; tmpC.height = h;
+                    const tc = tmpC.getContext('2d');
+                    tc.font = font;
+                    tc.textAlign = 'center';
+                    tc.textBaseline = 'middle';
+                    // Deliberately NO shadow and NO stroke — shadow spreads isotropically
+                    // and muddles the centroid; fill alone gives the cleanest reading.
+                    tc.fillStyle = '#ffffff';
+                    tc.fillText(str, w / 2, h / 2);
+                    const id = tc.getImageData(0, 0, w, h).data;
+                    // Alpha-weighted centroid — heavier ink pixels (thick vertical stem
+                    // of "1") outweigh thin/sparse pixels (diagonal flag), producing the
+                    // correct perceptual centre rather than the geometric bbox midpoint.
+                    let sumX = 0, sumY = 0, sumA = 0;
+                    for (let py = 0; py < h; py++) {
+                        for (let px = 0; px < w; px++) {
+                            const a = id[(py * w + px) * 4 + 3];
+                            if (a > 4) { sumX += px * a; sumY += py * a; sumA += a; }
+                        }
+                    }
+                    if (sumA > 0) {
+                        // shift pen so centroid → canvas centre, then add a small
+                        // extra rightward nudge (8 %) so the vertical stroke of
+                        // narrow digits like "1" sits visually at gem centre rather
+                        // than the advance-width centre (which may be slightly left
+                        // of the dominant ink mass for Arial Black numerals).
+                        drawX = w / 2 + (w / 2 - sumX / sumA) + w * 0.08;
+                        drawY = h / 2 + (h / 2 - sumY / sumA);
+                    }
+                } catch (_) { /* fallback: draw at (w/2, h/2) */ }
+                // x (real canvas) still has textAlign='center'; textBaseline='middle'
+            } else {
+                x.textAlign = 'center';
+                x.textBaseline = 'middle';
+            }
+            if (sp.shadow) {
+                x.shadowColor   = sp.shadow.color;
+                x.shadowBlur    = sp.shadow.blur;
+                x.shadowOffsetX = sp.shadow.dx;
+                x.shadowOffsetY = sp.shadow.dy;
+            }
+            if (sp.stroke && sp.strokeW > 0) {
+                x.lineJoin    = 'round';
+                x.miterLimit  = 2;
+                x.strokeStyle = sp.stroke;
+                x.lineWidth   = sp.strokeW;
+                x.strokeText(str, drawX, drawY);
+            }
+            x.fillStyle = col;
+            x.fillText(str, drawX, drawY);
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c),
+                transparent: true,
+                // depthTest:false means later geometry never *fails* depth
+                // against these sprites, but without depthWrite:false the
+                // sprites still write to the depth buffer (Three.js default
+                // is depthWrite:true even for SpriteMaterial). That can
+                // make subsequent sprites/labels vanish — match the
+                // pattern used by the other sprite materials in this file.
+                depthTest: false,
+                depthWrite: false,
+            });
+            txtCache[k] = mat;
+            return mat;
+        }
+
+        function pinchHarmonicMat(col) {
+            const baseCol = new T.Color(col != null ? col : '#ffd84d');
+            // v5 — compact concentric ellipses:
+            //   1. black outer border  rx=0.430h ry=0.255h
+            //   2. string-color body   rx=0.418h ry=0.232h
+            //   3. black inner ring    rx=0.407h ry=0.218h
+            //   4. string-color inner  rx=0.264h ry=0.218h
+            //   5. black center dot    rx=0.134h ry=0.120h
+            const k = 'technique|pinchHarmonicIcon|rs2014-v5b|' + baseCol.getHexString();
+            if (txtCache[k]) return txtCache[k];
+
+            const h = 512;
+            const c = document.createElement('canvas');
+            c.width = h; c.height = h;
+            const x = c.getContext('2d');
+            const TAU = Math.PI * 2;
+            const colStr = `rgb(${Math.round(baseCol.r * 255)},${Math.round(baseCol.g * 255)},${Math.round(baseCol.b * 255)})`;
+
+            x.clearRect(0, 0, h, h);
+            x.save();
+            x.translate(h / 2, h / 2);
+
+            // Form 1 — black outer border
+            x.fillStyle = '#000000';
+            x.beginPath(); x.ellipse(0, 0, h * 0.430, h * 0.255, 0, 0, TAU); x.fill();
+
+            // Form 2 — string-color main body
+            x.fillStyle = colStr;
+            x.beginPath(); x.ellipse(0, 0, h * 0.418, h * 0.232, 0, 0, TAU); x.fill();
+
+            // Form 3 — black inner ring
+            x.fillStyle = '#000000';
+            x.beginPath(); x.ellipse(0, 0, h * 0.407, h * 0.218, 0, 0, TAU); x.fill();
+
+            // Form 4 — string-color inner spot (narrower)
+            x.fillStyle = colStr;
+            x.beginPath(); x.ellipse(0, 0, h * 0.2637, h * 0.218, 0, 0, TAU); x.fill();
+
+            // Form 5 — black center dot
+            x.fillStyle = '#000000';
+            x.beginPath(); x.ellipse(0, 0, h * 0.134, h * 0.120, 0, 0, TAU); x.fill();
+
+            x.restore();
+
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c),
+                transparent: true,
+                depthTest: false,
+                depthWrite: false,
+            });
+            txtCache[k] = mat;
+            return mat;
+        }
+
+        function naturalHarmonicMat() {
+            const k = 'technique|naturalHarmonicIcon|pink-ring-v3';
+            if (txtCache[k]) return txtCache[k];
+
+            const h = 256;
+            const c = document.createElement('canvas');
+            c.width = h; c.height = h;
+            const x = c.getContext('2d');
+            const cx = h / 2;
+            const cy = h / 2;
+            const TAU = Math.PI * 2;
+
+            x.clearRect(0, 0, h, h);
+
+            const glow = x.createRadialGradient(cx, cy, h * 0.03, cx, cy, h * 0.47);
+            glow.addColorStop(0, 'rgba(255,170,255,0.14)');
+            glow.addColorStop(0.55, 'rgba(0,0,0,0.22)');
+            glow.addColorStop(1, 'rgba(0,0,0,0)');
+            x.fillStyle = glow;
+            x.beginPath();
+            x.arc(cx, cy, h * 0.44, 0, TAU);
+            x.fill();
+
+            x.shadowColor = 'rgba(0,0,0,0.85)';
+            x.shadowBlur = 14;
+            x.fillStyle = 'rgba(255, 255, 255, 0.96)';
+            x.beginPath();
+            x.arc(cx, cy, h * 0.31, 0, TAU);
+            x.fill();
+
+            // Punch out the inner gap so the icon reads as a bright ring.
+            x.shadowBlur = 0;
+            x.globalCompositeOperation = 'destination-out';
+            x.beginPath();
+            x.arc(cx, cy, h * 0.20, 0, TAU);
+            x.fill();
+            x.globalCompositeOperation = 'source-over';
+
+            x.shadowColor = 'rgba(0, 0, 0, 0.7)';
+            x.shadowBlur = 10;
+            x.strokeStyle = 'rgba(255, 255, 255, 0.98)';
+            x.lineWidth = 8;
+            x.beginPath();
+            x.arc(cx, cy, h * 0.255, 0, TAU);
+            x.stroke();
+
+            x.shadowColor = 'rgba(0,0,0,0)';
+            x.fillStyle = 'rgba(255, 255, 255, 0.98)';
+            x.beginPath();
+            x.arc(cx, cy, h * 0.12, 0, TAU);
+            x.fill();
+
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c),
+                transparent: true,
+                depthTest: false,
+                depthWrite: false,
+                opacity: 0.96,
+            });
+            txtCache[k] = mat;
+            return mat;
+        }
+
+        // Only two PM/FH variants exist (palm-mute = black-on-white,
+        // fret-hand mute = white-on-black). drawNote() hits muteXMat per
+        // muted chord-note per frame, so dense PM/FH passages were paying
+        // for a string concat + Map lookup on every call. Hoist both
+        // SpriteMaterial refs and short-circuit before touching the cache.
+        // They're populated lazily on first use; teardown still reaches
+        // them via the shared ``txtCache`` because muteXMat writes there.
+        let _pmXSpriteMat = null;
+        let _fhXSpriteMat = null;
+        function palmMuteXSpriteMat() {
+            return _pmXSpriteMat ?? (_pmXSpriteMat = muteXMat('#000000', '#ffffff'));
+        }
+        function fretHandMuteXSpriteMat() {
+            return _fhXSpriteMat ?? (_fhXSpriteMat = muteXMat('#ffffff', '#000000'));
+        }
+
+        function muteXMat(fillCol, strokeCol) {
+            const k = 'technique|muteX|v2|' + String(fillCol) + '|' + String(strokeCol);
+            if (txtCache[k]) return txtCache[k];
+
+            // lineCap:'square' gives flat tips. For a 45° diagonal the square-cap
+            // corners sit at ±outerW/2 rotated 45° from the endpoint — they land
+            // outside the canvas unless pad ≥ outerW/√2 (the common mistake is
+            // using outerW/2, which is too small). With the correct pad the white
+            // cap is fully inside the canvas and the border is visible at every tip.
+            const h = 512;
+            const outerW = 132, innerW = 114;
+            // pad must satisfy: pad ≥ outerW / Math.SQRT2  (≈ outerW × 0.707)
+            const pad = Math.ceil(outerW / Math.SQRT2) + 2; // 96
+            const c = document.createElement('canvas');
+            c.width = h; c.height = h;
+            const x = c.getContext('2d');
+
+            x.clearRect(0, 0, h, h);
+            x.lineCap = 'square';
+
+            // Draw each diagonal in its own stroke() call — caps of the two
+            // diagonals don't interact, and the white outer is drawn before the
+            // black inner so the border is clean at every edge and tip.
+            x.strokeStyle = strokeCol;
+            x.lineWidth = outerW;
+            x.beginPath(); x.moveTo(pad, pad); x.lineTo(h - pad, h - pad); x.stroke();
+            x.beginPath(); x.moveTo(h - pad, pad); x.lineTo(pad, h - pad); x.stroke();
+
+            x.strokeStyle = fillCol;
+            x.lineWidth = innerW;
+            x.beginPath(); x.moveTo(pad, pad); x.lineTo(h - pad, h - pad); x.stroke();
+            x.beginPath(); x.moveTo(h - pad, pad); x.lineTo(pad, h - pad); x.stroke();
+
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c),
+                transparent: true,
+                depthTest: false,
+                depthWrite: false,
+            });
+            txtCache[k] = mat;
+            return mat;
+        }
+
+        // Technique-marker sprite materials (triangle / chevron). Keyed by a
+        // packed NUMBER, not a string — triMat/bendChevronMat are called from
+        // the drawNote hot path, so a string cache key would allocate per
+        // note per frame. Disposed in teardown. `hex` is a 0xRRGGBB number;
+        // the low nibble of the key tags the variant (0 ▲, 1 ▼, 3-6 chevron
+        // step-count) so triangle and chevron entries can't collide.
+        const _techMatCache = new Map();
+
+        // Hammer-on / pull-off triangle marker: a white ▲ (up) / ▼ (down)
+        // with a thick border in the gem's string colour.
+        function triMat(up, hex) {
+            const h = (hex >>> 0) & 0xffffff;
+            const key = h * 16 + (up ? 0 : 1);
+            const cached = _techMatCache.get(key);
+            if (cached) return cached;
+            const S = 256, m = S * 0.15;
+            const c = document.createElement('canvas');
+            c.width = c.height = S;
+            const g = c.getContext('2d');
+            g.beginPath();
+            if (up) { g.moveTo(S / 2, m); g.lineTo(S - m, S - m); g.lineTo(m, S - m); }
+            else    { g.moveTo(S / 2, S - m); g.lineTo(S - m, m); g.lineTo(m, m); }
+            g.closePath();
+            g.lineJoin = 'round';
+            g.fillStyle = '#ffffff';
+            g.fill();
+            g.lineWidth = S * 0.122;
+            g.strokeStyle = '#' + (hex >>> 0).toString(16).padStart(6, '0');
+            g.stroke();
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c), transparent: true,
+                depthTest: false, depthWrite: false,
+            });
+            _techMatCache.set(key, mat);
+            return mat;
+        }
+
+        // Strength-of-bend chevron stack: `steps` (1-4) chevrons in the gem's
+        // string colour (chart-format bend notation — 1 per half-step).
+        function bendChevronMat(steps, hex) {
+            const h = (hex >>> 0) & 0xffffff;
+            const key = h * 16 + 2 + steps;   // steps 1-4 → low nibble 3-6
+            const cached = _techMatCache.get(key);
+            if (cached) return cached;
+            const S = 256;
+            const c = document.createElement('canvas');
+            c.width = c.height = S;
+            const g = c.getContext('2d');
+            g.strokeStyle = '#' + (hex >>> 0).toString(16).padStart(6, '0');
+            g.lineWidth = S * 0.10;
+            g.lineJoin = g.lineCap = 'round';
+            const padX = S * 0.18;
+            const rowH = S / steps;
+            const amp = Math.min(rowH * 0.55, S * 0.24);
+            for (let i = 0; i < steps; i++) {
+                const cy = (i + 0.5) * rowH;
+                g.beginPath();
+                g.moveTo(padX, cy + amp * 0.5);
+                g.lineTo(S / 2, cy - amp * 0.5);
+                g.lineTo(S - padX, cy + amp * 0.5);
+                g.stroke();
+            }
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c), transparent: true,
+                depthTest: false, depthWrite: false,
+            });
+            _techMatCache.set(key, mat);
+            return mat;
+        }
+
+        // Darken a 0xRRGGBB colour by `factor` (0..1) for the slide-arrow
+        // marker — full string colour is too bright next to the gem.
+        function darkenHex(hex, factor) {
+            const h = (hex >>> 0) & 0xffffff;
+            const r = Math.round(((h >> 16) & 0xff) * factor);
+            const g = Math.round(((h >> 8) & 0xff) * factor);
+            const b = Math.round((h & 0xff) * factor);
+            return (r << 16) | (g << 8) | b;
+        }
+
+        // Slide-direction arrow (›/‹): a filled triangle pointing toward the
+        // slide's destination fret, in the gem's (darkened) string colour.
+        // `hex` here is already the darkened colour — keep its own cache-key
+        // nibble range (8/9) so it can't collide with triMat (0/1) or
+        // bendChevronMat (3-6).
+        function slideArrowMat(pointRight, hex) {
+            const h = (hex >>> 0) & 0xffffff;
+            const key = h * 16 + 8 + (pointRight ? 0 : 1);
+            const cached = _techMatCache.get(key);
+            if (cached) return cached;
+            const S = 256, m = S * 0.18;
+            const c = document.createElement('canvas');
+            c.width = c.height = S;
+            const g = c.getContext('2d');
+            g.beginPath();
+            if (pointRight) { g.moveTo(S - m, S / 2); g.lineTo(m, m); g.lineTo(m, S - m); }
+            else            { g.moveTo(m, S / 2); g.lineTo(S - m, m); g.lineTo(S - m, S - m); }
+            g.closePath();
+            g.fillStyle = '#' + h.toString(16).padStart(6, '0');
+            g.fill();
+            const mat = new T.SpriteMaterial({
+                map: new T.CanvasTexture(c), transparent: true,
+                depthTest: false, depthWrite: false,
+            });
+            _techMatCache.set(key, mat);
+            return mat;
+        }
+
+        function _meshMatForGhostFretDigit(spriteMat) {
+            let mb = spriteMat.userData.h3dGhostFretMeshMat;
+            if (!mb) {
+                mb = new T.MeshBasicMaterial({
+                    map: spriteMat.map,
+                    transparent: true,
+                    depthTest: false,
+                    depthWrite: false,
+                });
+                spriteMat.userData.h3dGhostFretMeshMat = mb;
+            }
+            return mb;
+        }
+
+        /**
+         * Convert any SpriteMaterial to a MeshBasicMaterial that shares its canvas
+         * texture, so technique markers can be applied to a rotatable PlaneGeometry
+         * mesh instead of a billboard Sprite. Cached on userData to avoid allocations.
+         *
+         * The cache is multi-entry: each pTechPlane mesh holds a Map<sm.map,
+         * clone> so a recycled mesh that's used for several techniques
+         * (hammer-on, palm-mute, harmonic, bend...) across frames keeps a
+         * clone for each one rather than disposing-and-recloning on every
+         * switch. With nStr-wide chords containing mixed PM/FH/HO/HP
+         * markers this collapses the per-frame allocation entirely while
+         * still being bounded — the per-mesh Map has at most one entry per
+         * distinct technique × colour the mesh has ever been used for.
+         */
+        function _spriteMat2MeshMat(mesh, sm) {
+            let perMesh = mesh.userData.h3dTechMeshMatCloneByMap;
+            if (perMesh) {
+                const hit = perMesh.get(sm.map);
+                if (hit) return hit;
+            }
+
+            let base = sm.userData.h3dTechMeshMat;
+            if (!base) {
+                base = new T.MeshBasicMaterial({
+                    map: sm.map,
+                    transparent: true,
+                    // depthTest: false — cross-note Z ordering is handled by
+                    // per-note renderOrderForLayerAtZ(...) calls rather than the
+                    // depth buffer. This is necessary because close notes often use
+                    // mGlow (depthWrite:false), so the depth buffer can't reliably
+                    // occlude far markers near the hit line. With per-note renderOrder,
+                    // far labels render first and close note geometry renders last,
+                    // appearing on top without depthTest.
+                    depthTest: false,
+                    depthWrite: false,
+                    // forceSinglePass accompanies EVERY transparent DoubleSide
+                    // material in this file: without it, Three r158+ renders
+                    // each such object in TWO passes (back side then front),
+                    // setting material.needsUpdate on both — which forces a
+                    // full getParameters/program-cache lookup per object per
+                    // frame (profiled at ~4% of throttled main-thread time)
+                    // and doubles the draw calls. The two-pass path exists to
+                    // fix self-occlusion sorting on closed transparent meshes;
+                    // all our DoubleSide materials are flat unlit quads
+                    // (labels, rails, frames, lanes) where it buys nothing.
+                    side: T.DoubleSide, forceSinglePass: true,
+                });
+                sm.userData.h3dTechMeshMat = base;
+            }
+            // First conversion for this mesh: the pTechPlane pool factory gave
+            // it a placeholder MeshBasicMaterial that the caller is about to
+            // overwrite with the clone below. Dispose it now — once
+            // mesh.material is reassigned the placeholder is orphaned and
+            // teardown's scene.traverse() pass can no longer reach it, so it
+            // would leak one GPU material per pooled mesh for the renderer's
+            // lifetime.
+            if (!perMesh && mesh.material && mesh.material !== base) {
+                mesh.material.dispose?.();
+            }
+            if (!perMesh) {
+                perMesh = new Map();
+                mesh.userData.h3dTechMeshMatCloneByMap = perMesh;
+            }
+            const clone = base.clone();
+            perMesh.set(sm.map, clone);
+            _techMeshMatClones.add(clone);
+            return clone;
+        }
+
+        function _disposeOpenStringPitchSprites() {
+            // Tuning-label materials are clones of cached txtMat() entries, so
+            // they share the .map (CanvasTexture) with the canonical txtCache
+            // material. Disposing the map here would invalidate every other
+            // material that references the same cached glyph; teardown()'s
+            // txtCache loop is the single owner of those textures.
+            for (const m of _tuningLabelMats) {
+                try { m.dispose(); } catch (_) { /* idempotent */ }
+            }
+            _tuningLabelMats = [];
+            _tuningLabelSprites = [];
+            _lastOpenStringLblSig = '';
+            if (!tuningLblG) return;
+            while (tuningLblG.children.length) tuningLblG.remove(tuningLblG.children[0]);
+        }
+
+        function _openStringLabelSignature(bundle, labels) {
+            const si = bundle && bundle.songInfo;
+            const tun = si && si.tuning;
+            let tStr = '';
+            if (Array.isArray(tun)) tStr = tun.slice(0, labels.length).join(',');
+            else if (bundle && Array.isArray(bundle.tuning)) tStr = bundle.tuning.slice(0, labels.length).join(',');
+            const capo =
+                si && Number.isFinite(si.capo) ? si.capo
+                    : (bundle && Number.isFinite(bundle.capo) ? bundle.capo : '');
+            const arrIdx = si && si.arrangement_index != null ? si.arrangement_index : '';
+            let palSig = '';
+            const nLab = labels.length;
+            if (activePalette) {
+                // activePalette entries are numeric hex (PALETTES) or already hex strings;
+                // convert without instantiating T.Color per string — this signature is
+                // built every frame inside _syncOpenStringPitchLabels.
+                const lim = Math.min(activePalette.length, nLab);
+                for (let i = 0; i < lim; i++) {
+                    if (i > 0) palSig += '/';
+                    const c = activePalette[i];
+                    palSig += typeof c === 'number' ? (c >>> 0).toString(16) : String(c);
+                }
+            }
+            return `${nStr}|${capo}|${tStr}|${arrIdx}|${labels.join(',')}|${palSig}|${_textSizeMul.toFixed(3)}|${boardStringStartX.toFixed(6)}|${boardTuningLabelX.toFixed(6)}`;
+        }
+
+        function _syncOpenStringPitchLabels(bundle) {
+            if (!tuningLblG || !T || !bundle) return;
+            if (!tuningLabelsVisible) {
+                tuningLblG.visible = false;
+                if (_tuningLabelSprites.length) _disposeOpenStringPitchSprites();
+                _lastOpenStringLblSig = '';
+                return;
+            }
+            tuningLblG.visible = true;
+            // Cheap-key fast path: compare the inputs that drive the label content
+            // against last frame. The signature string + labels array build are
+            // both per-frame allocators, so skipping them when nothing changed
+            // saves a chunk of GC pressure in the hot render loop.
+            const si = bundle.songInfo;
+            const tunRef = (si && Array.isArray(si.tuning)) ? si.tuning : null;
+            const bundleTunRef = Array.isArray(bundle.tuning) ? bundle.tuning : null;
+            const capo =
+                si && Number.isFinite(si.capo) ? si.capo
+                    : (Number.isFinite(bundle.capo) ? bundle.capo : NaN);
+            const arrIdx = si && si.arrangement_index != null ? si.arrangement_index : undefined;
+            if (
+                _tuningLabelSprites.length === nStr &&
+                _lastSyncTuningRef === tunRef &&
+                _lastSyncBundleTuningRef === bundleTunRef &&
+                Object.is(_lastSyncCapo, capo) &&
+                _lastSyncArrIdx === arrIdx &&
+                _lastSyncPaletteRef === activePalette &&
+                _lastSyncNStr === nStr &&
+                _lastSyncTextSizeMul === _textSizeMul &&
+                _lastSyncStartX === boardStringStartX &&
+                _lastSyncLabelX === boardTuningLabelX
+            ) return;
+            // One of the inputs changed — fall through to the canonical signature
+            // check (catches value-equal-but-different-ref tuning arrays).
+            const labels = _openStringPitchLabelsForTuning(bundle, si, nStr);
+            const sig = _openStringLabelSignature(bundle, labels);
+            // Refresh cheap-key cache regardless of signature outcome so future
+            // frames can fast-path even when the sig matched.
+            _lastSyncTuningRef = tunRef;
+            _lastSyncBundleTuningRef = bundleTunRef;
+            _lastSyncCapo = capo;
+            _lastSyncArrIdx = arrIdx;
+            _lastSyncPaletteRef = activePalette;
+            _lastSyncNStr = nStr;
+            _lastSyncTextSizeMul = _textSizeMul;
+            _lastSyncStartX = boardStringStartX;
+            _lastSyncLabelX = boardTuningLabelX;
+            if (sig === _lastOpenStringLblSig && _tuningLabelSprites.length === nStr) return;
+            _disposeOpenStringPitchSprites();
+            _lastOpenStringLblSig = sig;
+            // Left of nut/cordas — centered on headstock mass so text does not sit on the strings.
+            const labelX = boardTuningLabelX;
+            const zLabel = -0.08 * K;
+            const scalePx = 2.42 * _textSizeMul * K;
+            for (let s = 0; s < nStr; s++) {
+                const hex = '#' + new T.Color(activePalette[s % activePalette.length]).getHexString();
+                const mat = txtMat(labels[s] || '?', hex, false, 'noteFret').clone();
+                mat.depthTest = false;
+                mat.depthWrite = false;
+                mat.transparent = true;
+                const sp = new T.Sprite(mat);
+                sp.center.set(0, 0.5);
+                sp.scale.set(scalePx, scalePx, 1);
+                sp.position.set(labelX, sY(s), zLabel);
+                sp.renderOrder = 8;
+                tuningLblG.add(sp);
+                _tuningLabelSprites.push(sp);
+                _tuningLabelMats.push(mat);
+            }
+        }
+
+        // ── Object pool ────────────────────────────────────────────────────
+        // ── Opt-in perf bench harness (feedBack#226) ──────────────────────
+        // Enable with `?h3dbench=1` on the player URL. Aggregates per-segment
+        // timings of update() into a console.log every _PB_REPORT_MS.
+        //
+        // When the bench is OFF, pbBeg/pbEnd/pbReportTick are bound to a
+        // single shared empty function literal when this renderer
+        // instance is created (createHighway() runs once per panel, not
+        // once per module load) — V8 typically inlines empty bodies and
+        // the call sites have minimized overhead in the hot path.
+        // (Previously they had `if (!_perfBench) return;` guards, which
+        // still cost a function-call frame per mark site per frame;
+        // Copilot review on #413.) Inlining is a JIT heuristic, not a
+        // language guarantee.
+        const _perfBench = (() => {
+            try { return new URLSearchParams(location.search).get('h3dbench') === '1'; }
+            catch (_) { return false; }
+        })();
+        let pbBeg, pbEnd, pbReportTick;
+        if (_perfBench) {
+            const _PB_NAMES = ['frame', 'state', 'next', 'mat', 'noteDraw', 'chordDraw', 'render'];
+            const _pbStart = new Float64Array(_PB_NAMES.length);
+            const _pbAcc = _PB_NAMES.map(() => []);
+            const _PB_REPORT_MS = 5000;
+            let _pbReportStart = 0;
+            let _pbFrameCount = 0;
+            pbBeg = function pbBeg(idx) { _pbStart[idx] = performance.now(); };
+            pbEnd = function pbEnd(idx) {
+                _pbAcc[idx].push(performance.now() - _pbStart[idx]);
+            };
+            pbReportTick = function pbReportTick() {
+                const now = performance.now();
+                if (_pbReportStart === 0) {
+                    // First call: discard the sample(s) that already
+                    // landed in _pbAcc from the very first frame's
+                    // pbEnd() calls, so fps and segment stats span the
+                    // same frame set on every reported window.
+                    _pbReportStart = now;
+                    _pbFrameCount = 0;
+                    for (let i = 0; i < _PB_NAMES.length; i++) _pbAcc[i].length = 0;
+                    return;
+                }
+                _pbFrameCount++;
+                if (now - _pbReportStart < _PB_REPORT_MS) return;
+                const dur = now - _pbReportStart;
+                const fps = (_pbFrameCount / dur * 1000).toFixed(1);
+                const parts = [];
+                for (let i = 0; i < _PB_NAMES.length; i++) {
+                    const arr = _pbAcc[i];
+                    if (!arr.length) { parts.push(`${_PB_NAMES[i]}=-`); continue; }
+                    arr.sort((a, b) => a - b);
+                    const n = arr.length;
+                    // Nearest-rank: ceil(p · n) - 1, clamped to [0, n-1].
+                    // Avoids the off-by-one where Math.floor(n * 0.95)
+                    // returns the last element (effectively the max)
+                    // for small samples (e.g. n=20 → idx 19).
+                    const p50 = arr[Math.max(0, Math.ceil(0.50 * n) - 1)];
+                    const p95 = arr[Math.max(0, Math.ceil(0.95 * n) - 1)];
+                    const mx = arr[n - 1];
+                    parts.push(`${_PB_NAMES[i]} p50=${p50.toFixed(2)} p95=${p95.toFixed(2)} max=${mx.toFixed(2)}`);
+                    arr.length = 0;
+                }
+                console.log(`[h3dbench] ${fps}fps (${_pbFrameCount} frames) over ${(dur/1000).toFixed(1)}s — ${parts.join(' | ')}`);
+                _pbReportStart = now;
+                _pbFrameCount = 0;
+            };
+        } else {
+            pbBeg = pbEnd = pbReportTick = function () {};
+        }
+
+        function pool(parent, mk) {
+            const a = [];
+            let n = 0;
+            return {
+                get() {
+                    if (n < a.length) {
+                        const o = a[n++];
+                        o.visible = true;
+                        if (o.center && o.center.isVector2) o.center.set(0.5, 0.5);
+                        return o;
+                    }
+                    const o = mk(); parent.add(o); a.push(o); n++; return o;
+                },
+                reset() { for (let i = 0; i < n; i++) a[i].visible = false; n = 0; },
+                // Pre-allocate `cap` slots at construction so the first dense
+                // playback frames don't pay the new-Mesh allocation cost
+                // mid-RAF (felt as a stall on 7/8-string charts where the
+                // visible-note count outruns the lazy-grow path). Lazy growth
+                // past `cap` still works — this is amortisation, not a cap.
+                //
+                // Coerce `cap` to a non-negative int32: a float would still
+                // work but a callsite passing `Infinity` (or `NaN`) would
+                // otherwise spin the while-loop until OOM. `cap | 0`
+                // truncates floats, clamps Infinity → 0, and turns NaN → 0;
+                // Math.max(0, …) keeps negatives out.
+                warm(cap) {
+                    // Local rename to avoid shadowing the pool's outer
+                    // `n` (the in-use index advanced by get() / reset()).
+                    const targetLen = Math.max(0, cap | 0);
+                    while (a.length < targetLen) { const o = mk(); o.visible = false; parent.add(o); a.push(o); }
+                    return this;
+                },
+            };
+        }
+
+        // Returns indices of the longest consecutive run in a sorted integer
+        // array as { start, len } — `sorted[start..start+len)` is the run.
+        // Avoids the two per-call sub-array allocations of the previous
+        // implementation (best + cur arrays grown via .push), at the cost
+        // of one small 2-key result object. Net: callers in the chord-
+        // diagram render path no longer churn arrays per visible chord.
+        function longestConsecutiveRun(sorted) {
+            let bestStart = -1, bestLen = 0;
+            let curStart = -1, curLen = 0;
+            for (let i = 0; i < sorted.length; i++) {
+                if (curLen === 0 || sorted[i] === sorted[curStart + curLen - 1] + 1) {
+                    if (curLen === 0) curStart = i;
+                    curLen++;
+                } else {
+                    if (curLen > bestLen) { bestLen = curLen; bestStart = curStart; }
+                    curStart = i; curLen = 1;
+                }
+            }
+            if (curLen > bestLen) { bestLen = curLen; bestStart = curStart; }
+            return { start: bestStart, len: bestLen };
+        }
+
+        /* ── Lyrics overlay (2D canvas on top of WebGL) ─────────────────── */
+        function drawChordDiagram(ctx, opts) {
+            const {
+                name, frets,
+                opacity = 1,
+                entranceT = 1.0,
+                canvasW = 600, canvasH = 400,
+                inverted = false,
+                sizeSlider = 0.5,
+                position = 'tl',
+                nStr = 6,
+                lyricsBottom = 0,
+                stackOffset = 0,
+            } = opts;
+
+            // Responsive sizing — CELL derived from panel height + user slider.
+            // COLS is the resolved string count from the caller (via resolveStringCount)
+            // so bass (4), extended (7/8) arrangements render correctly.
+            const COLS = nStr, ROWS = 4;
+            // Minimum column span required for PATH B (bracket extension / detection).
+            // Math.min(COLS-1, 4) scales with string count:
+            //   4-string bass → 3  (max possible span, so 2-4-4-2 shapes qualify)
+            //   6-string      → 4  (excludes D major span=2 / common 2-string coincidences)
+            //   8-string      → 4  (muted outer strings still leave span ≥ 4 for real barres)
+            const MIN_BARRE_SPAN = Math.min(COLS - 1, 4);
+            // Maps diagram column index → chord-template frets-array index.
+            // Templates are high-e-first: frets[0]=high e, frets[COLS-1]=low E.
+            // Non-inverted display (col 0 = high e): getStrIdx(0) = 0        → frets[0]      = high e.
+            // Inverted display     (col 0 = low E):  getStrIdx(0) = COLS-1   → frets[COLS-1] = low E.
+            const getStrIdx = col => inverted ? (COLS - 1 - col) : col;
+            const sizeF  = DIAG_SIZE_MIN + (DIAG_SIZE_MAX - DIAG_SIZE_MIN) * sizeSlider;
+
+            // startFret / isFirstPos must be known before CELL so that fretLabelW
+            // can be measured and factored into the width cap.  The old
+            // canvasW/(COLS+1.5) guard only approximated 2*PAD and ignored the
+            // extra left padding reserved for non-first-position "Nfr" labels.
+            const playedFrets = frets.filter(f => f > 0);
+            const minFret     = playedFrets.length > 0 ? Math.min(...playedFrets) : 1;
+            const startFret   = Math.max(1, minFret);
+            const isFirstPos  = startFret === 1;
+
+            // Phase 1 — height + hard-cap estimate, used only to size the label font.
+            // Cap against the vertical space available below lyricsBottom so that the
+            // diagram does not overflow into the lyrics banner on short split panels with
+            // wrapped lyric rows.  Only top-corner positions can overlap the lyrics banner,
+            // so lyricsBottom is only subtracted when position is 'tl' or 'tr'; for 'bl'
+            // and 'br' the full canvas height is available.
+            // Clamp to at least 1 so font/box calculations never receive 0-px input
+            // on very short panels (e.g. tiny split cells < 44 px tall).
+            const isTopCorner = position === 'tl' || position === 'tr';
+            const availH  = canvasH - (isTopCorner ? lyricsBottom : 0);
+            const cellEst = Math.max(1, Math.min(
+                Math.round(availH * sizeF / (ROWS + 3)),
+                DIAG_CELL_MAX,
+            ));
+            // Extra left padding for the "Nfr" label on non-first-position chords.
+            // Measured with ctx.measureText at cellEst so the estimate is exact.
+            let fretLabelW = 0;
+            if (!isFirstPos) {
+                // Measure inside a save/restore so this font assignment does not
+                // leak to the caller (the outer ctx.save() happens after CELL is derived).
+                ctx.save();
+                ctx.font = `italic ${Math.round(cellEst * 0.55)}px sans-serif`;
+                fretLabelW = Math.ceil(ctx.measureText(startFret + 'fr').width) + 6;
+                ctx.restore();
+            }
+
+            // Phase 2 — final CELL: cap against panel height, hard max, and panel width.
+            // Two width constraints are needed because PAD has a hard floor of 6:
+            //   A) when PAD = CELL*0.65 (large CELL):  CELL*(COLS+0.3) + fretLabelW ≤ canvasW
+            //   B) when PAD = 6 floor (small CELL):    CELL*(COLS-1)  + 12 + fretLabelW ≤ canvasW
+            // Both are included so boxW ≤ canvasW in every regime.
+            // fretLabelW was measured at cellEst ≥ CELL, so the cap is conservative.
+            const CELL   = Math.max(1, Math.min(
+                cellEst,
+                Math.floor((canvasW - fretLabelW) / (COLS + 0.3)),
+                Math.floor((canvasW - 2 * 6 - fretLabelW) / Math.max(1, COLS - 1)),
+            ));
+            const HEADER = Math.round(CELL * 1.6);
+            const MARKER = Math.round(CELL * 0.7);
+            const DOT_R  = CELL * 0.3;
+            const PAD    = Math.max(6, Math.round(CELL * 0.65));
+            const gridW  = CELL * (COLS - 1);
+            const gridH  = CELL * ROWS;
+
+            const PAD_L  = PAD + fretLabelW;
+
+            const boxW   = gridW + PAD_L + PAD;
+            const boxH   = HEADER + MARKER + gridH + PAD;
+
+            // Anchor to chosen corner. Top positions get extra vertical offset
+            // to clear the timeline plugin and song name displayed at the top.
+            // lyricsBottom is the actual bottom Y of the lyrics banner (returned by
+            // drawLyrics), so TOP_Y steps down past all lyric rows regardless of
+            // how many wrap lines the current panel width produces.
+            const E    = PAD;
+            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
+            let bx, by;
+            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
+            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
+            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
+            else                        { bx = E; by = TOP_Y + stackOffset; }
+
+            // Clamp so the box never bleeds off-canvas on narrow panels or wide string counts.
+            bx = Math.max(0, Math.min(canvasW - boxW, bx));
+            by = Math.max(0, Math.min(canvasH - boxH, by));
+
+            // Guard: the canvasH–boxH clamp above can push `by` above lyricsBottom when
+            // wrapped lyrics consume nearly the full panel height.  This applies to ALL
+            // corner positions: a bottom-corner diagram anchored near the canvas bottom can
+            // still reach up into the lyrics banner on very short or narrow panels where
+            // boxH is larger than the space below the lyrics.  In those cases skip drawing
+            // entirely rather than painting on top of the lyrics banner.
+            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
+
+            const gx = bx + PAD_L, gy = by + HEADER + MARKER;
+
+            // Ease-out quadratic entrance scale: 0.85 → 1.0.
+            const scale = 1 - 0.15 * (1 - entranceT) * (1 - entranceT);
+
+            ctx.save();
+            ctx.globalAlpha = opacity;
+
+            if (scale !== 1.0) {
+                const cx = bx + boxW / 2, cy = by + boxH / 2;
+                ctx.translate(cx, cy);
+                ctx.scale(scale, scale);
+                ctx.translate(-cx, -cy);
+            }
+
+            // Background + border.
+            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
+            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
+
+            // Split-root typography: "Dm7" → "D" large bold + "m7" smaller.
+            const rootMatch = name.match(/^([A-G][#b]?)(.*)/);
+            const root    = rootMatch ? rootMatch[1] : name;
+            const quality = rootMatch ? rootMatch[2] : '';
+            const rootSize = Math.round(CELL * 1.25);
+            const qualSize = Math.round(rootSize * 0.65);
+            ctx.textBaseline = 'middle';
+            const nameY = by + HEADER * 0.55;
+            ctx.font = `bold ${rootSize}px sans-serif`;
+            const rootW = ctx.measureText(root).width;
+            ctx.font = `${qualSize}px sans-serif`;
+            const qualW = quality ? ctx.measureText(quality).width : 0;
+            const nameBlockW = rootW + (quality ? qualW + 2 : 0);
+            const nameStartX = bx + boxW / 2 - nameBlockW / 2;
+            ctx.fillStyle = '#e8d080';
+            ctx.font = `bold ${rootSize}px sans-serif`;
+            ctx.textAlign = 'left';
+            ctx.fillText(root, nameStartX, nameY);
+            if (quality) {
+                ctx.font = `${qualSize}px sans-serif`;
+                ctx.fillStyle = 'rgba(232,208,128,0.75)';
+                ctx.fillText(quality, nameStartX + rootW + 2, nameY);
+            }
+
+            // Nut: CELL-proportional filled rect + subtle highlight line.
+            // Thickness is 40% of CELL, floored at 2 px so it stays visible on
+            // the smallest diagrams (CELL=1 on compact split panels).
+            const NUT_H = Math.round(Math.max(2, CELL * 0.4));
+            if (isFirstPos) {
+                ctx.fillStyle = '#ffffff';
+                ctx.fillRect(gx, gy - NUT_H, gridW, NUT_H);
+                ctx.fillStyle = 'rgba(255,255,255,0.4)';
+                ctx.fillRect(gx, gy - NUT_H, gridW, Math.max(1, Math.round(NUT_H * 0.25)));
+            }
+
+            // Fret label for non-first-position chords.
+            if (!isFirstPos) {
+                ctx.fillStyle = 'rgba(220,200,120,0.9)';
+                ctx.font = `italic ${Math.round(CELL * 0.55)}px sans-serif`;
+                ctx.textAlign = 'right';
+                ctx.textBaseline = 'middle';
+                ctx.fillText(startFret + 'fr', gx - 4, gy + CELL * 0.5);
+            }
+
+            // Fret lines.
+            ctx.strokeStyle = 'rgba(255,255,255,0.22)'; ctx.lineWidth = 1;
+            for (let r = (isFirstPos ? 1 : 0); r <= ROWS; r++) {
+                ctx.beginPath();
+                ctx.moveTo(gx, gy + r * CELL);
+                ctx.lineTo(gx + gridW, gy + r * CELL);
+                ctx.stroke();
+            }
+
+            // String lines with varying weight: low E heavier, high e lighter.
+            // With getStrIdx(col) = col (non-inverted): col 0 (high e) → strIdx=0 → t=0 thin;
+            // col COLS-1 (low E) → strIdx=COLS-1 → t=1 thick. Inverted mode naturally mirrors.
+            // Weights scale with CELL so strings never bleed into adjacent columns on
+            // small-CELL diagrams (e.g. CELL=1 on compact split panels).
+            for (let col = 0; col < COLS; col++) {
+                const strIdx = getStrIdx(col);
+                const t = COLS > 1 ? strIdx / (COLS - 1) : 1;  // 1=low E (thick), 0=high e (thin); guard COLS=1
+                ctx.lineWidth = Math.max(0.5, CELL * (0.05 + t * 0.10));
+                ctx.strokeStyle = 'rgba(255,255,255,0.3)';
+                ctx.beginPath();
+                ctx.moveTo(gx + col * CELL, gy);
+                ctx.lineTo(gx + col * CELL, gy + ROWS * CELL);
+                ctx.stroke();
+            }
+
+            // Barre detection — two complementary paths:
+            //
+            // PATH A (F-shape / mini-barre): at least two ADJACENT columns are at startFret.
+            //   Bracket is initially set to the consecutive run's own endpoints (not the full
+            //   startFretCols range) so isolated bass notes at the same fret can't pull the
+            //   bracket across an open gap (e.g. "2 0 2 2 0 0" stays bracketed at cols 2..3).
+            //
+            // PATH B (full-span barre / extension):
+            //   When PATH A fired: extend the bracket outward to the full outer startFret span
+            //     if the span ≥ MIN_BARRE_SPAN and every column between the outer startFret
+            //     columns is fretted (f > 0).
+            //   When PATH A did NOT fire: detect standalone full barres (e.g. x24442, x46654)
+            //     where only the two outermost strings sit at startFret.  An additional check
+            //     ensures that no intermediate column is itself at startFret — this rules out
+            //     alternating-fret voicings like "1 3 1 3 1 0" (col 2 at startFret would fire
+            //     incorrectly) while still catching B-major-style shapes where the barre
+            //     finger covers only the outer two strings.
+            //
+            // Templates are high-e-first: frets[0]=high e, frets[COLS-1]=low E.
+            // Examples (6-string, MIN_BARRE_SPAN=4):
+            //   F major [1,1,2,3,3,1]: PATH A run=[4,5] → bracket 4..5; PATH B span=5, all fretted → extends to 0..5 ✓
+            //   B major x24442:        PATH A no run; PATH B span=4, all fretted, no inner at startFret → 1..5 ✓
+            //   mini-A  x02220:        PATH A run=[2,3,4] → bracket 2..4; PATH B span=2<4 → no extension ✓
+            //   D major xx0232:        PATH A run length=1 → no PATH A; PATH B span<4 → no bracket ✓
+            //   2 0 2 2 0 0:           PATH A run=[2,3] → bracket 2..3; PATH B span=3<4 → no extension ✓
+            //   1 3 1 3 1 0:           PATH A no run; PATH B: inner col 2 at startFret → no bracket ✓
+            const startFretCols = [];
+            for (let col = 0; col < COLS; col++) {
+                if (frets[getStrIdx(col)] === startFret) startFretCols.push(col);
+            }
+            const barreRun = longestConsecutiveRun(startFretCols);
+            let hasBarreArc = barreRun.len >= 2;   // PATH A
+            let barreMinCol = hasBarreArc ? startFretCols[barreRun.start] : -1;
+            let barreMaxCol = hasBarreArc ? startFretCols[barreRun.start + barreRun.len - 1] : -1;
+
+            if (startFretCols.length >= 2) {             // PATH B
+                const minC = startFretCols[0];
+                const maxC = startFretCols[startFretCols.length - 1];
+                if (maxC - minC >= MIN_BARRE_SPAN) {
+                    let allFretted = true;
+                    for (let col = minC; col <= maxC; col++) {
+                        if (frets[getStrIdx(col)] <= 0) { allFretted = false; break; }
+                    }
+                    if (allFretted) {
+                        if (hasBarreArc) {
+                            // PATH A fired: always safe to extend to full outer span.
+                            barreMinCol = minC;
+                            barreMaxCol = maxC;
+                        } else {
+                            // PATH A did not fire: only draw a bracket when no intermediate
+                            // column sits at startFret.  Intermediate startFret columns would
+                            // indicate a scattered/alternating voicing rather than a clean
+                            // outer-edge barre (e.g. "1 3 1 3 1 0" has col 2 at startFret).
+                            let noInnerAtStartFret = true;
+                            for (let col = minC + 1; col < maxC; col++) {
+                                if (frets[getStrIdx(col)] === startFret) { noInnerAtStartFret = false; break; }
+                            }
+                            if (noInnerAtStartFret) {
+                                hasBarreArc = true;
+                                barreMinCol = minC;
+                                barreMaxCol = maxC;
+                            }
+                        }
+                    }
+                }
+            }
+            if (hasBarreArc) {
+                const barreY   = gy + CELL * 0.5;
+                const capH     = CELL * 0.22;  // vertical offset from barreY to the bracket line
+                const capHalf  = Math.max(1, Math.round(CELL * 0.3)); // half-height of the vertical end caps
+                // Straight bracket: a horizontal line with short vertical end caps.
+                // Stroke scales with CELL so it doesn't swamp tiny cells (floor at 1 px).
+                ctx.strokeStyle = 'rgba(255,255,255,0.6)'; ctx.lineWidth = Math.max(1, CELL * 0.2);
+                ctx.beginPath();
+                ctx.moveTo(gx + barreMinCol * CELL, barreY - capH);
+                ctx.lineTo(gx + barreMaxCol * CELL, barreY - capH);
+                ctx.stroke();
+                ctx.beginPath();
+                ctx.moveTo(gx + barreMinCol * CELL, barreY - capH - capHalf);
+                ctx.lineTo(gx + barreMinCol * CELL, barreY - capH + capHalf);
+                ctx.stroke();
+                ctx.beginPath();
+                ctx.moveTo(gx + barreMaxCol * CELL, barreY - capH - capHalf);
+                ctx.lineTo(gx + barreMaxCol * CELL, barreY - capH + capHalf);
+                ctx.stroke();
+            }
+
+            // Open/muted markers + finger dots.
+            // Non-inverted: col 0 = high e → getStrIdx(0)=0 → frets[0]; col COLS-1 = low E → frets[COLS-1].
+            // Inverted:     col 0 = low E → getStrIdx(0)=COLS-1 → frets[COLS-1]; col COLS-1 = high e → frets[0].
+            for (let col = 0; col < COLS; col++) {
+                const f = frets[getStrIdx(col)];
+                const sx = gx + col * CELL;
+                const markerY = gy - MARKER * 0.5;
+                if (f < 0) {
+                    const r = CELL * 0.20;
+                    ctx.strokeStyle = '#cc4444'; ctx.lineWidth = 1.5;
+                    ctx.beginPath(); ctx.moveTo(sx - r, markerY - r); ctx.lineTo(sx + r, markerY + r); ctx.stroke();
+                    ctx.beginPath(); ctx.moveTo(sx + r, markerY - r); ctx.lineTo(sx - r, markerY + r); ctx.stroke();
+                } else if (f === 0) {
+                    ctx.strokeStyle = '#88bbff'; ctx.lineWidth = 1.5;
+                    ctx.beginPath(); ctx.arc(sx, markerY, CELL * 0.22, 0, Math.PI * 2); ctx.stroke();
+                } else {
+                    const row = f - startFret;
+                    if (row >= 0 && row < ROWS) {
+                        const isBarreCol = hasBarreArc && f === startFret &&
+                                           col >= barreMinCol && col <= barreMaxCol;
+                        ctx.shadowColor = 'rgba(0,0,0,0.5)';
+                        ctx.shadowBlur = Math.min(4, CELL * 0.4);
+                        ctx.shadowOffsetX = Math.max(0.5, CELL * 0.1);
+                        ctx.shadowOffsetY = Math.max(0.5, CELL * 0.1);
+                        ctx.fillStyle = isBarreCol ? 'rgba(255,255,255,0.85)' : '#ffffff';
+                        ctx.beginPath();
+                        ctx.arc(sx, gy + row * CELL + CELL * 0.5, DOT_R, 0, Math.PI * 2);
+                        ctx.fill();
+                        ctx.shadowColor = 'transparent'; ctx.shadowBlur = 0;
+                        ctx.shadowOffsetX = 0; ctx.shadowOffsetY = 0;
+                    }
+                }
+            }
+            ctx.restore();
+            return boxH;
+        }
+
+        // Cached wrapper for drawChordDiagram. When entranceT === 1 (scale
+        // transform is identity) the diagram is rendered once to an
+        // OffscreenCanvas and reused every subsequent frame via drawImage +
+        // globalAlpha. During the 0.2 s entrance animation (entranceT < 1)
+        // the scale transform is non-trivial so we fall through to a fresh
+        // render — that window is ~12 frames at 60 fps, negligible.
+        //
+        // Returns boxH (diagram card height in px) so the draw loop can
+        // accumulate per-corner stack offsets when multiple overlays share
+        // the same corner position.
+        function _drawDiagramCached(ctx, opts) {
+            const { opacity = 1, entranceT = 1.0, canvasW, canvasH } = opts;
+            if (opacity <= 0) return 0;
+            if (entranceT < 1.0) {
+                return drawChordDiagram(ctx, opts) || 0;
+            }
+            const { name, frets, nStr, inverted, sizeSlider, position, lyricsBottom = 0, stackOffset = 0 } = opts;
+            const key = name + '|' + (frets || []).join(',') + '|' + nStr + '|' +
+                        (inverted ? 1 : 0) + '|' + sizeSlider + '|' + position + '|' +
+                        canvasW + '|' + canvasH + '|' + lyricsBottom + '|' + stackOffset;
+            let entry = _diagRenderCache.get(key);
+            if (!entry) {
+                let oc;
+                try { oc = new OffscreenCanvas(canvasW, canvasH); }
+                catch (_) { oc = document.createElement('canvas'); oc.width = canvasW; oc.height = canvasH; }
+                const boxH = drawChordDiagram(oc.getContext('2d'), { ...opts, opacity: 1, entranceT: 1 }) || 0;
+                if (_diagRenderCache.size >= _DIAG_CACHE_MAX) {
+                    _diagRenderCache.delete(_diagRenderCache.keys().next().value);
+                }
+                entry = { oc, boxH };
+                _diagRenderCache.set(key, entry);
+            }
+            ctx.save();
+            ctx.globalAlpha = opacity;
+            ctx.drawImage(entry.oc, 0, 0);
+            ctx.restore();
+            return entry.boxH;
+        }
+
+        // Two-line section card. Top line is "Now: <current>", bottom line
+        // is "Up Next: <next> in <countdown>". Explicit labels disambiguate
+        // current vs upcoming — earlier single-line variant rendered both
+        // states with the same word and was confusing during playback.
+        //
+        // Returns boxH on draw, 0 when nothing rendered. Position / size
+        // mirror the chord-diagram contract: 'tl' / 'tr' / 'bl' / 'br'
+        // anchor corners, sizeSlider in [0,1] scales card height.
+        //
+        // Hidden when:
+        //   - no sections array, or
+        //   - playback has not yet reached the first section AND there's
+        //     no upcoming-only fallback rendered (we still show "Up Next"
+        //     during the pre-roll so the user sees what's coming).
+        function drawSectionHud(ctx, opts) {
+            const {
+                sections, currentTime,
+                canvasW, canvasH,
+                position = 'tr',
+                sizeSlider = 0.5,
+                lyricsBottom = 0,
+                stackOffset = 0,
+            } = opts;
+            if (!sections || !sections.length) return 0;
+
+            // sections are time-ordered server-side; single forward scan.
+            let curIdx = -1;
+            for (let i = 0; i < sections.length; i++) {
+                if (sections[i].time <= currentTime) curIdx = i;
+                else break;
+            }
+            const cur  = curIdx >= 0 ? sections[curIdx] : null;
+            const next = (curIdx + 1 < sections.length) ? sections[curIdx + 1] : null;
+            // Pre-first-section: nothing playing yet but next is coming —
+            // still useful to render "Up Next" alone so the user gets the
+            // anticipatory cue during the song's intro silence.
+            if (!cur && !next) return 0;
+
+            const nowName = cur ? cur.name : '';
+            // Render countdown as a separate span so it can take a calmer
+            // grey-white treatment while the section name itself stays
+            // cyan. Combining them into one string would inherit the cyan
+            // fill across both, defeating the visual hierarchy promised
+            // in the FR.
+            let nextName = '';
+            let nextCountdown = '';
+            if (next) {
+                const dt = next.time - currentTime;
+                nextName = next.name;
+                nextCountdown = dt > 10
+                    ? 'in ' + Math.round(dt) + 's'
+                    : 'in ' + Math.max(0, dt).toFixed(1) + 's';
+            }
+
+            const sizeF = 0.65 + 0.85 * sizeSlider; // 0.65 .. 1.5
+            const baseH = Math.max(34, Math.min(72, Math.round(canvasH * 0.085 * sizeF)));
+            const PAD_X = Math.round(baseH * 0.45);
+            const PAD_Y = Math.round(baseH * 0.20);
+            // Per-text-element scale applied to nameSize / tagSize / lineH
+            // when the unscaled card would overflow a narrow panel
+            // (splitscreen quad layout, ultra-tall portrait). Computed
+            // below from the measured contentW vs the available width.
+            let textScale = 1.0;
+            const baseLineH    = Math.round(baseH * 0.46);
+            const baseNameSize = Math.round(baseH * 0.36);
+            const baseTagSize  = Math.round(baseH * 0.24);
+            const baseTagGap   = Math.round(baseH * 0.14);
+
+            const TAG_NOW  = 'Now:';
+            const TAG_NEXT = 'Up Next:';
+
+            // Phase-1 measurement at the unscaled font sizes — used to
+            // decide whether textScale needs to drop, and to lay out the
+            // final draw at whatever scale we land on.
+            ctx.save();
+            ctx.font = `${baseTagSize}px sans-serif`;
+            const tagNowWBase  = ctx.measureText(TAG_NOW).width;
+            const tagNextWBase = ctx.measureText(TAG_NEXT).width;
+            const countdownWBase = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
+            ctx.font = `bold ${baseNameSize}px sans-serif`;
+            const nowNameWBase  = nowName  ? ctx.measureText(nowName).width  : 0;
+            const nextNameWBase = nextName ? ctx.measureText(nextName).width : 0;
+            ctx.restore();
+
+            const lineNowWBase  = nowName  ? tagNowWBase  + baseTagGap + nowNameWBase  : 0;
+            const lineNextWBase = nextName
+                ? tagNextWBase + baseTagGap + nextNameWBase
+                  + (nextCountdown ? baseTagGap + countdownWBase : 0)
+                : 0;
+            const contentWBase  = Math.max(lineNowWBase, lineNextWBase);
+            const numLines = (nowName ? 1 : 0) + (nextName ? 1 : 0);
+            if (numLines === 0) return 0;
+
+            // Target width budget: cap at canvasW - 16 and reserve PAD_X
+            // either side. If contentWBase exceeds the budget, scale the
+            // font proportionally — clamped to 0.55 so labels stay legible
+            // even on extreme split-panel widths.
+            const maxBoxW = Math.max(40, canvasW - 16);
+            const availContentW = Math.max(1, maxBoxW - PAD_X * 2);
+            if (contentWBase > availContentW) {
+                textScale = Math.max(0.55, availContentW / contentWBase);
+            }
+
+            const lineH    = Math.max(1, Math.round(baseLineH    * textScale));
+            const nameSize = Math.max(1, Math.round(baseNameSize * textScale));
+            const tagSize  = Math.max(1, Math.round(baseTagSize  * textScale));
+            const TAG_GAP  = Math.max(1, Math.round(baseTagGap   * textScale));
+
+            // Phase-2 re-measurement at the scaled font sizes for the
+            // final layout. measureText doesn't scale linearly with font
+            // size on every glyph, so re-measuring is cheaper than
+            // multiplying the base widths by textScale and risking a
+            // half-pixel overflow.
+            ctx.save();
+            ctx.font = `${tagSize}px sans-serif`;
+            const tagNowW  = ctx.measureText(TAG_NOW).width;
+            const tagNextW = ctx.measureText(TAG_NEXT).width;
+            const countdownW = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
+            ctx.font = `bold ${nameSize}px sans-serif`;
+            const nowNameW  = nowName  ? ctx.measureText(nowName).width  : 0;
+            const nextNameW = nextName ? ctx.measureText(nextName).width : 0;
+            ctx.restore();
+
+            const lineNowW  = nowName  ? tagNowW  + TAG_GAP + nowNameW  : 0;
+            const lineNextW = nextName
+                ? tagNextW + TAG_GAP + nextNameW + (nextCountdown ? TAG_GAP + countdownW : 0)
+                : 0;
+            const contentW = Math.max(lineNowW, lineNextW);
+
+            const boxW = Math.min(maxBoxW, Math.round(contentW + PAD_X * 2));
+            const boxH = Math.round(numLines * lineH + PAD_Y * 2);
+
+            const E = Math.round(baseH * 0.25);
+            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
+            let bx, by;
+            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
+            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
+            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
+            else                        { bx = E; by = TOP_Y + stackOffset; }
+            bx = Math.max(0, Math.min(canvasW - boxW, bx));
+            by = Math.max(0, Math.min(canvasH - boxH, by));
+            // Suppress overlap with the wrapped lyrics banner regardless
+            // of corner. Bottom-corner cards on short panels can still
+            // reach up into the banner once boxH exceeds the space below
+            // the lyrics — same shape the chord diagram uses.
+            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
+
+            ctx.save();
+            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
+            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
+
+            ctx.textBaseline = 'middle';
+            ctx.textAlign = 'left';
+
+            // Layout each line with tag left-aligned, name in cyan after a
+            // small gap. Both lines share the same x origin (bx + PAD_X)
+            // so the tag column visually aligns vertically.
+            const lineX = bx + PAD_X;
+            let lineY = by + PAD_Y + lineH / 2;
+            const TAG_COLOR = 'rgba(180,190,205,0.85)';
+            const NAME_COLOR = '#00cccc';
+            const TIME_COLOR = 'rgba(220,225,235,0.9)';
+
+            if (nowName) {
+                ctx.font = `${tagSize}px sans-serif`;
+                ctx.fillStyle = TAG_COLOR;
+                ctx.fillText(TAG_NOW, lineX, lineY);
+                ctx.font = `bold ${nameSize}px sans-serif`;
+                ctx.fillStyle = NAME_COLOR;
+                ctx.fillText(nowName, lineX + tagNowW + TAG_GAP, lineY);
+                lineY += lineH;
+            }
+            if (nextName) {
+                ctx.font = `${tagSize}px sans-serif`;
+                ctx.fillStyle = TAG_COLOR;
+                ctx.fillText(TAG_NEXT, lineX, lineY);
+                const nextX = lineX + tagNextW + TAG_GAP;
+                ctx.font = `bold ${nameSize}px sans-serif`;
+                ctx.fillStyle = NAME_COLOR;
+                ctx.fillText(nextName, nextX, lineY);
+                if (nextCountdown) {
+                    ctx.font = `${tagSize}px sans-serif`;
+                    ctx.fillStyle = TIME_COLOR;
+                    ctx.fillText(nextCountdown, nextX + nextNameW + TAG_GAP, lineY);
+                }
+            }
+            ctx.restore();
+            return boxH;
+        }
+
+        // Tone-change HUD — card showing the active tone and the next upcoming
+        // tone with a countdown. Mirrors drawSectionHud's layout contract
+        // (position, size slider, lyricsBottom) but uses an amber accent colour
+        // so it reads as distinct from the cyan section card.
+        function drawToneHud(ctx, opts) {
+            const {
+                toneChanges, toneBase = '',
+                currentTime,
+                canvasW, canvasH,
+                position = 'tl',
+                sizeSlider = 0.5,
+                lyricsBottom = 0,
+                stackOffset = 0,
+            } = opts;
+
+            // Resolve active tone: toneBase before all changes, else the most
+            // recent change at or before currentTime.
+            // toneChanges items use { t, name } (not { time, name }) — both
+            // the legacy import path (server.py xml_tone_changes) and the sloppak
+            // path (lib/tones.py sloppak_tone_changes) emit "t" as the key.
+            let curName = toneBase;
+            let nextChange = null;
+            if (toneChanges && toneChanges.length) {
+                for (let i = 0; i < toneChanges.length; i++) {
+                    if (toneChanges[i].t <= currentTime) {
+                        curName = toneChanges[i].name;
+                    } else {
+                        nextChange = toneChanges[i];
+                        break;
+                    }
+                }
+            }
+            if (!curName && !nextChange) return 0;
+
+            let nextName = '';
+            let nextCountdown = '';
+            if (nextChange) {
+                const dt = nextChange.t - currentTime;
+                nextName = nextChange.name;
+                nextCountdown = dt > 10
+                    ? 'in ' + Math.round(dt) + 's'
+                    : 'in ' + Math.max(0, dt).toFixed(1) + 's';
+            }
+
+            const sizeF = 0.65 + 0.85 * sizeSlider;
+            const baseH = Math.max(34, Math.min(72, Math.round(canvasH * 0.085 * sizeF)));
+            const PAD_X = Math.round(baseH * 0.45);
+            const PAD_Y = Math.round(baseH * 0.20);
+            let textScale = 1.0;
+            const baseLineH    = Math.round(baseH * 0.46);
+            const baseNameSize = Math.round(baseH * 0.36);
+            const baseTagSize  = Math.round(baseH * 0.24);
+            const baseTagGap   = Math.round(baseH * 0.14);
+
+            const TAG_CUR  = 'Tone:';
+            const TAG_NEXT = 'Next:';
+
+            ctx.save();
+            ctx.font = `${baseTagSize}px sans-serif`;
+            const tagCurWBase  = ctx.measureText(TAG_CUR).width;
+            const tagNextWBase = ctx.measureText(TAG_NEXT).width;
+            const countdownWBase = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
+            ctx.font = `bold ${baseNameSize}px sans-serif`;
+            const curNameWBase  = curName  ? ctx.measureText(curName).width  : 0;
+            const nextNameWBase = nextName ? ctx.measureText(nextName).width : 0;
+            ctx.restore();
+
+            const lineCurWBase  = curName  ? tagCurWBase  + baseTagGap + curNameWBase  : 0;
+            const lineNextWBase = nextName
+                ? tagNextWBase + baseTagGap + nextNameWBase
+                  + (nextCountdown ? baseTagGap + countdownWBase : 0)
+                : 0;
+            const contentWBase = Math.max(lineCurWBase, lineNextWBase);
+            const numLines = (curName ? 1 : 0) + (nextName ? 1 : 0);
+            if (numLines === 0) return 0;
+
+            const maxBoxW = Math.max(40, canvasW - 16);
+            const availContentW = Math.max(1, maxBoxW - PAD_X * 2);
+            if (contentWBase > availContentW) {
+                textScale = Math.max(0.55, availContentW / contentWBase);
+            }
+
+            const lineH    = Math.max(1, Math.round(baseLineH    * textScale));
+            const nameSize = Math.max(1, Math.round(baseNameSize * textScale));
+            const tagSize  = Math.max(1, Math.round(baseTagSize  * textScale));
+            const TAG_GAP  = Math.max(1, Math.round(baseTagGap   * textScale));
+
+            ctx.save();
+            ctx.font = `${tagSize}px sans-serif`;
+            const tagCurW  = ctx.measureText(TAG_CUR).width;
+            const tagNextW = ctx.measureText(TAG_NEXT).width;
+            const countdownW = nextCountdown ? ctx.measureText(nextCountdown).width : 0;
+            ctx.font = `bold ${nameSize}px sans-serif`;
+            const curNameW  = curName  ? ctx.measureText(curName).width  : 0;
+            const nextNameW = nextName ? ctx.measureText(nextName).width : 0;
+            ctx.restore();
+
+            const lineCurW  = curName  ? tagCurW  + TAG_GAP + curNameW  : 0;
+            const lineNextW = nextName
+                ? tagNextW + TAG_GAP + nextNameW + (nextCountdown ? TAG_GAP + countdownW : 0)
+                : 0;
+            const contentW = Math.max(lineCurW, lineNextW);
+
+            const boxW = Math.min(maxBoxW, Math.round(contentW + PAD_X * 2));
+            const boxH = Math.round(numLines * lineH + PAD_Y * 2);
+
+            const E = Math.round(baseH * 0.25);
+            const TOP_Y = Math.round(Math.max(E + canvasH * 0.06, lyricsBottom + E));
+            let bx, by;
+            if      (position === 'tr') { bx = canvasW - boxW - E; by = TOP_Y + stackOffset; }
+            else if (position === 'bl') { bx = E; by = canvasH - boxH - E - stackOffset; }
+            else if (position === 'br') { bx = canvasW - boxW - E; by = canvasH - boxH - E - stackOffset; }
+            else                        { bx = E; by = TOP_Y + stackOffset; } // 'tl' default
+            bx = Math.max(0, Math.min(canvasW - boxW, bx));
+            by = Math.max(0, Math.min(canvasH - boxH, by));
+            if (lyricsBottom > 0 && by < lyricsBottom) return 0;
+
+            ctx.save();
+            ctx.fillStyle = 'rgba(8, 14, 22, 0.88)';
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.fill();
+            ctx.strokeStyle = 'rgba(255,255,255,0.15)'; ctx.lineWidth = 1;
+            ctx.beginPath(); ctx.roundRect(bx, by, boxW, boxH, 7); ctx.stroke();
+
+            ctx.textBaseline = 'middle';
+            ctx.textAlign = 'left';
+
+            const lineX = bx + PAD_X;
+            let lineY = by + PAD_Y + lineH / 2;
+            const TAG_COLOR  = 'rgba(180,190,205,0.85)';
+            const NAME_COLOR = '#ff9a3c'; // amber — distinct from section cyan
+            const TIME_COLOR = 'rgba(220,225,235,0.9)';
+
+            if (curName) {
+                ctx.font = `${tagSize}px sans-serif`;
+                ctx.fillStyle = TAG_COLOR;
+                ctx.fillText(TAG_CUR, lineX, lineY);
+                ctx.font = `bold ${nameSize}px sans-serif`;
+                ctx.fillStyle = NAME_COLOR;
+                ctx.fillText(curName, lineX + tagCurW + TAG_GAP, lineY);
+                lineY += lineH;
+            }
+            if (nextName) {
+                ctx.font = `${tagSize}px sans-serif`;
+                ctx.fillStyle = TAG_COLOR;
+                ctx.fillText(TAG_NEXT, lineX, lineY);
+                const nextX = lineX + tagNextW + TAG_GAP;
+                ctx.font = `bold ${nameSize}px sans-serif`;
+                ctx.fillStyle = NAME_COLOR;
+                ctx.fillText(nextName, nextX, lineY);
+                if (nextCountdown) {
+                    ctx.font = `${tagSize}px sans-serif`;
+                    ctx.fillStyle = TIME_COLOR;
+                    ctx.fillText(nextCountdown, nextX + nextNameW + TAG_GAP, lineY);
+                }
+            }
+            ctx.restore();
+            return boxH;
+        }
+
+        // Lyrics layout cache — measureText per syllable + row wrapping
+        // only changes when the displayed line(s), font size, or canvas
+        // width change, not per frame. Keyed below; the per-frame work is
+        // just drawing over the cached widths.
+        let _lyrRowsCache = null;
+
+        function drawLyrics(lyrics, currentTime, ctx, W, H) {
+            if (!lyrics._lines) {
+                const lines = [];
+                let line = null, word = null;
+                const flushWord = () => { if (word && word.length) line.words.push(word); word = null; };
+                const flushLine = () => { flushWord(); if (line && line.words.length) lines.push(line); line = null; };
+                for (let i = 0; i < lyrics.length; i++) {
+                    const l = lyrics[i];
+                    const raw = l.w || '';
+                    const endsLine = raw.endsWith('+');
+                    const continuesWord = raw.endsWith('-');
+                    if (line && i > 0 && l.t - (lyrics[i - 1].t + lyrics[i - 1].d) > 4.0) flushLine();
+                    if (!line) line = { words: [], start: l.t, end: l.t + l.d };
+                    if (!word) word = [];
+                    word.push(l);
+                    line.end = Math.max(line.end, l.t + l.d);
+                    if (!continuesWord) flushWord();
+                    if (endsLine) flushLine();
+                }
+                flushLine();
+                lyrics._lines = lines;
+            }
+            const allLines = lyrics._lines;
+            if (!allLines.length) return 0;
+
+            let currentIdx = -1;
+            for (let i = 0; i < allLines.length; i++) {
+                if (allLines[i].start <= currentTime) currentIdx = i;
+                else break;
+            }
+            if (currentIdx === -1) {
+                if (allLines[0].start - currentTime > 2.0) return 0;
+                currentIdx = 0;
+            }
+            const currentLine = allLines[currentIdx];
+            const nextLine = allLines[currentIdx + 1] || null;
+            const gapToNext = nextLine ? (nextLine.start - currentLine.end) : Infinity;
+            if (currentTime > currentLine.end + 0.5 && gapToNext > 3.0) return 0;
+
+            const linesToShow = [currentLine];
+            if (nextLine && gapToNext <= 3.0) linesToShow.push(nextLine);
+
+            const fontSize = Math.max(18, H * 0.028) | 0;
+            const lineY = H * 0.04;
+            const sylText = s => { const t = s.w || ''; return (t.endsWith('+') || t.endsWith('-')) ? t.slice(0, -1) : t; };
+
+            ctx.font = `bold ${fontSize}px sans-serif`;
+            let rows, spaceWidth, bgWidth;
+            const _lc = _lyrRowsCache;
+            if (_lc && _lc.lyricsRef === lyrics && _lc.idx === currentIdx
+                && _lc.shown === linesToShow.length
+                && _lc.fontSize === fontSize && _lc.W === W) {
+                rows = _lc.rows; spaceWidth = _lc.spaceWidth; bgWidth = _lc.bgWidth;
+            } else {
+                spaceWidth = ctx.measureText(' ').width;
+                const maxWidth = W * 0.8;
+
+                rows = [];
+                for (const authoredLine of linesToShow) {
+                    let row = [], rowWidth = 0;
+                    for (const wordSyls of authoredLine.words) {
+                        const parts = [];
+                        let wordWidth = 0;
+                        for (const s of wordSyls) {
+                            const text = sylText(s);
+                            const w = ctx.measureText(text).width;
+                            parts.push({ syl: s, text, width: w });
+                            wordWidth += w;
+                        }
+                        const advance = wordWidth + spaceWidth;
+                        if (row.length > 0 && rowWidth + advance > maxWidth) { rows.push(row); row = []; rowWidth = 0; }
+                        row.push({ parts, advance });
+                        rowWidth += advance;
+                    }
+                    if (row.length) rows.push(row);
+                }
+
+                bgWidth = 0;
+                for (const row of rows) {
+                    const rw = row.reduce((s, w) => s + w.advance, 0) - spaceWidth;
+                    if (rw > bgWidth) bgWidth = rw;
+                }
+                bgWidth = Math.min(bgWidth + 30, W * 0.85);
+                _lyrRowsCache = {
+                    lyricsRef: lyrics, idx: currentIdx,
+                    shown: linesToShow.length, fontSize, W,
+                    rows, spaceWidth, bgWidth,
+                };
+            }
+
+            const rowHeight = fontSize + 6;
+            const totalHeight = rows.length * rowHeight + 10;
+
+            ctx.fillStyle = 'rgba(0,0,0,0.7)';
+            ctx.beginPath();
+            const bx = W / 2 - bgWidth / 2, by = lineY - 4, br = 8;
+            ctx.moveTo(bx + br, by); ctx.lineTo(bx + bgWidth - br, by);
+            ctx.quadraticCurveTo(bx + bgWidth, by, bx + bgWidth, by + br);
+            ctx.lineTo(bx + bgWidth, by + totalHeight - br);
+            ctx.quadraticCurveTo(bx + bgWidth, by + totalHeight, bx + bgWidth - br, by + totalHeight);
+            ctx.lineTo(bx + br, by + totalHeight);
+            ctx.quadraticCurveTo(bx, by + totalHeight, bx, by + totalHeight - br);
+            ctx.lineTo(bx, by + br);
+            ctx.quadraticCurveTo(bx, by, bx + br, by);
+            ctx.closePath();
+            ctx.fill();
+
+            ctx.textAlign = 'left';
+            ctx.textBaseline = 'top';
+            for (let r = 0; r < rows.length; r++) {
+                const row = rows[r];
+                const rowWidth = row.reduce((s, w) => s + w.advance, 0) - spaceWidth;
+                let xPos = W / 2 - rowWidth / 2;
+                const yPos = lineY + r * rowHeight + 2;
+                for (const w of row) {
+                    for (const part of w.parts) {
+                        const l = part.syl;
+                        const isActive = currentTime >= l.t && currentTime < l.t + l.d;
+                        const isPast = currentTime >= l.t + l.d;
+                        ctx.fillStyle = isActive ? '#4ae0ff' : isPast ? '#8899aa' : '#556677';
+                        ctx.font = `${isActive ? 'bold' : 'normal'} ${fontSize}px sans-serif`;
+                        ctx.fillText(part.text, xPos, yPos);
+                        xPos += part.width;
+                    }
+                    xPos += spaceWidth;
+                }
+            }
+            // Return the actual bottom Y of the rendered background box so callers
+            // (e.g. drawChordDiagram) can avoid overlapping it.
+            return Math.round(by + totalHeight);
+        }
+
+        /* ── Scene initialisation ─────────────────────────────────────────── */
+        function initScene() {
+            if (!highwayCanvas || !highwayCanvas.parentNode) {
+                console.error('[3D-Hwy] initScene: canvas has no parent; aborting');
+                return false;
+            }
+
+            // Reset per-song lane state
+            fretLastActiveTime.fill(0);
+
+            wrap = document.createElement('div');
+            wrap.id = 'h3d-wrap-' + _instanceId;
+            wrap.className = 'h3d-wrap';
+            wrap.dataset.h3dInstance = String(_instanceId);
+            wrap.style.cssText = 'position:absolute;top:0;left:0;right:0;z-index:2;pointer-events:none;';
+            // Mark this instance as the primary tour target so the tour engine
+            // always spotlights a unique element (selector '.h3d-wrap[data-h3d-primary]')
+            // rather than the first of potentially many splitscreen wraps.
+            document.querySelectorAll('.h3d-wrap[data-h3d-primary]').forEach(
+                el => el.removeAttribute('data-h3d-primary'));
+            wrap.setAttribute('data-h3d-primary', '');
+            highwayCanvas.parentNode.insertBefore(wrap, highwayCanvas.nextSibling);
+
+            // Subscribe to highway:visibility (feedBack#246) so the
+            // .h3d-wrap overlay hides in sync with the feedBack canvas.
+            // The wrap is a sibling of #highway, so display:none on
+            // #highway leaves us painting full-screen otherwise.
+            // Guarded lazy bind: tolerate hosts that don't yet expose
+            // feedBack.on/off (older feedBack versions, headless
+            // tests).
+            if (window.feedBack
+                && typeof window.feedBack.on === 'function'
+                && typeof window.feedBack.off === 'function') {
+                _visibilityHandler = (e) => {
+                    if (!wrap) return;
+                    // Filter by canvas identity (splitscreen-safe).
+                    // Each createHighway() instance emits its own
+                    // visibility events on the shared feedBack bus —
+                    // without this gate, one hidden panel would also
+                    // hide every other panel's 3D overlay.
+                    if (!e || !e.detail || e.detail.canvas !== highwayCanvas) return;
+                    const v = e.detail.visible;
+                    wrap.style.display = v === false ? 'none' : '';
+                };
+                try {
+                    window.feedBack.on('highway:visibility', _visibilityHandler);
+                } catch (e) {
+                    _visibilityHandler = null;
+                }
+                // Track canvas-replaced so the visibility handler's
+                // identity gate continues to match after core swaps the
+                // <canvas> element for a context-type change.
+                _canvasReplacedHandler = (e) => {
+                    if (!e || !e.detail) return;
+                    // Only update if the swap involves OUR canvas — in
+                    // splitscreen each panel has its own canvas.
+                    if (e.detail.oldCanvas !== highwayCanvas) return;
+                    highwayCanvas = e.detail.newCanvas;
+                    // Re-sync wrap visibility from the new canvas in
+                    // case its initial displayed-state differs.
+                    if (wrap) {
+                        const v = highwayCanvas && highwayCanvas.offsetParent !== null;
+                        wrap.style.display = v ? '' : 'none';
+                    }
+                };
+                try {
+                    window.feedBack.on('highway:canvas-replaced', _canvasReplacedHandler);
+                } catch (e) {
+                    _canvasReplacedHandler = null;
+                }
+                // Sync once at bind time: the event is transition-only,
+                // so if the canvas was already hidden when we mounted
+                // (e.g. plugin loaded while splitscreen was active),
+                // we'd never receive an emit and would leave the wrap
+                // visible. Compute from the local highwayCanvas (not
+                // window.highway.isVisible) so splitscreen panels get
+                // their own per-instance answer instead of inheriting
+                // the main highway's state.
+                if (_visibilityHandler) {
+                    try {
+                        const initialVisible = highwayCanvas
+                            && highwayCanvas.offsetParent !== null;
+                        wrap.style.display = initialVisible ? '' : 'none';
+                    } catch (e) { /* ignore — initial sync is best-effort */ }
+                }
+            }
+
+            // powerPreference hints the platform to use the discrete /
+            // high-performance GPU and a higher power profile for this WebGL
+            // context. On laptops / iGPU+dGPU machines (Windows, macOS) it
+            // steers GPU selection to the dGPU; on single-dGPU desktops it
+            // requests the high-performance power profile. (It does not by
+            // itself force NVIDIA's utilisation-driven clock ramp on Linux.)
+            ren = new T.WebGLRenderer({ antialias: true, powerPreference: 'high-performance', alpha: true });
+            _probe = new T.Vector3();
+            ren.setClearColor(0x101820, _bcActive() ? 0 : 1);
+            wrap.appendChild(ren.domElement);
+
+            // WebGL context-loss recovery (see the _ctxLost declaration). Bound
+            // on Three's own canvas — the context that actually resets on a GPU
+            // reset / alt-tab. preventDefault() keeps the context restorable
+            // instead of letting the loss escalate to a render-process crash;
+            // _ctxLost then makes draw() bail so no GL work runs on the dead
+            // context; on restore we reset the viewport and resume (Three
+            // re-uploads geometry/materials/textures lazily on the next render).
+            _onCtxLost = (e) => {
+                if (e && typeof e.preventDefault === 'function') e.preventDefault();
+                _ctxLost = true;
+                console.warn('[3D-Hwy] WebGL context lost — pausing render until it is restored.');
+            };
+            _onCtxRestored = () => {
+                _ctxLost = false;
+                console.warn('[3D-Hwy] WebGL context restored — resuming render.');
+                try { const s = canvasSize(highwayCanvas); if (s.w > 0 && s.h > 0) applySize(s.w, s.h); } catch (err) {}
+            };
+            ren.domElement.addEventListener('webglcontextlost', _onCtxLost, false);
+            ren.domElement.addEventListener('webglcontextrestored', _onCtxRestored, false);
+
+            lyricsCanvas = document.createElement('canvas');
+            lyricsCanvas.style.cssText = 'position:absolute;top:0;left:0;pointer-events:none;z-index:1;';
+            lyricsCtx = lyricsCanvas.getContext('2d');
+            wrap.appendChild(lyricsCanvas);
+
+            scene = new T.Scene();
+            scene.fog = new T.Fog(0x101820, FOG_START * 0.8, FOG_END * 1.2);
+
+            cam = new T.PerspectiveCamera(BASE_VFOV, 1, 0.01, FOG_END * 3);
+
+            ambLight = new T.AmbientLight(0xffffff, 0.85);
+            scene.add(ambLight);
+            dirLight = new T.DirectionalLight(0xffffff, 0.8);
+            dirLight.position.set(40 * K, 120 * K, 80 * K);
+            scene.add(dirLight);
+            _applyCinematic();
+
+            fretG = new T.Group(); scene.add(fretG);
+            tuningLblG = new T.Group(); scene.add(tuningLblG);
+            noteG = new T.Group(); scene.add(noteG);
+            // Hit sparks (#3): a pooled additive Points cloud; a small burst fires at a
+            // gem on a verified hit (spawned in the verdict block, advanced in the render loop).
+            _sparkPos = new Float32Array(_SPARK_N * 3); _sparkCol = new Float32Array(_SPARK_N * 3);
+            _sparkVel = new Float32Array(_SPARK_N * 3); _sparkLife = new Float32Array(_SPARK_N);
+            {
+                const sg = new T.BufferGeometry();
+                sg.setAttribute('position', new T.BufferAttribute(_sparkPos, 3).setUsage(T.DynamicDrawUsage));
+                sg.setAttribute('color', new T.BufferAttribute(_sparkCol, 3).setUsage(T.DynamicDrawUsage));
+                const sm = new T.PointsMaterial({ size: 1.0 * K, vertexColors: true, transparent: true, opacity: 0.8, depthWrite: false, blending: T.AdditiveBlending, sizeAttenuation: true });
+                _sparkPts = new T.Points(sg, sm); _sparkPts.frustumCulled = false; _sparkPts.renderOrder = 8;
+                scene.add(_sparkPts);
+            }
+            beatG = new T.Group(); scene.add(beatG);
+            lblG = new T.Group(); scene.add(lblG);
+
+            // Rectangular note geometry
+            gNote = new T.BoxGeometry(NW, NH, ND);
+            // Per-string vertical gradient gems — colours sampled from the
+            // original colour PNGs (top highlight → deeper bottom). Each gradient
+            // string gets its own BoxGeometry clone carrying a per-vertex colour
+            // attribute; the gem core swaps to gNoteGrad[s] in drawNote while its
+            // material (mStr[s]) is white + vertexColors:true so the gradient
+            // shows pure. Strings 6/7 have no entry and fall back to flat gNote.
+            gNoteGrad = DEFAULT_GEM_GRADIENTS.map(([topHex, botHex]) => {
+                const g = new T.BoxGeometry(NW, NH, ND);
+                const _pos = g.attributes.position;
+                const _colors = new Float32Array(_pos.count * 3);
+                const _topCol = new T.Color(topHex);
+                const _botCol = new T.Color(botHex);
+                const _tmpCol = new T.Color();
+                const _halfH = NH / 2;
+                for (let i = 0; i < _pos.count; i++) {
+                    const t = (_pos.getY(i) + _halfH) / (2 * _halfH); // 0 bottom..1 top
+                    _tmpCol.copy(_botCol).lerp(_topCol, t);
+                    _colors[i * 3] = _tmpCol.r;
+                    _colors[i * 3 + 1] = _tmpCol.g;
+                    _colors[i * 3 + 2] = _tmpCol.b;
+                }
+                g.setAttribute('color', new T.BufferAttribute(_colors, 3));
+                _ownedSharedGeos.push(g);
+                return g;
+            });
+            // Seed gem colors from whatever palette is active at mount (custom
+            // colors recolor the gem bodies just like the strings/trails).
+            _recolorGemGradients();
+
+            /** Filled ring matching flying-note outline (1.1) minus core (1.0); hollow centre. */
+            function mkGhostFrameGeometry() {
+                const ow = NW * 1.1;
+                const oh = NH * 1.1;
+                const iw = NW;
+                const ih = NH;
+                const depth = ND * 2.8;
+                const shape = new T.Shape();
+                shape.moveTo(-ow / 2, -oh / 2);
+                shape.lineTo(-ow / 2, oh / 2);
+                shape.lineTo(ow / 2, oh / 2);
+                shape.lineTo(ow / 2, -oh / 2);
+                shape.lineTo(-ow / 2, -oh / 2);
+                const hole = new T.Path();
+                hole.moveTo(-iw / 2, -ih / 2);
+                hole.lineTo(iw / 2, -ih / 2);
+                hole.lineTo(iw / 2, ih / 2);
+                hole.lineTo(-iw / 2, ih / 2);
+                hole.lineTo(-iw / 2, -ih / 2);
+                shape.holes.push(hole);
+                const g = new T.ExtrudeGeometry(shape, { depth, bevelEnabled: false });
+                g.translate(0, 0, -depth / 2);
+                return g;
+            }
+
+            gSus = new T.BoxGeometry(1, 1, 1);
+            gBeat = new T.BufferGeometry().setFromPoints(
+                [new T.Vector3(0, 0, 0), new T.Vector3(1, 0, 0)],
+            );
+            // Tap chevron (open V pointing downward) — filled outline for extrusion into a solid mesh
+
+            const chevronShape = new T.Shape();
+
+            // Adjusting points for a "stubby" look
+            // Width: increased to +/- 0.8 for a broader look
+            // Height: capped at 0.2 to make it significantly shorter
+            chevronShape.moveTo(-0.6, 0.3);   // Top left point (further out, lower down)
+            chevronShape.lineTo(0, -0.1);     // Interior vertex (shallower V)
+            chevronShape.lineTo(0.6, 0.3);    // Top right point (further out, lower down)
+
+            chevronShape.lineTo(0.8, 0.0);    // Right outer thickness point
+            chevronShape.lineTo(0, -0.3);     // Bottom vertex / Outer point (less deep)
+            chevronShape.lineTo(-0.8, 0.0);   // Left outer thickness point
+
+            chevronShape.closePath();
+
+            // Create the 3D mesh geometry with a small depth
+            gTapChevron = new T.ExtrudeGeometry(chevronShape, {
+                depth: 0.04 * K,
+                bevelEnabled: false,
+            });
+
+            // Optional: Center the geometry if the pivot point feels off
+            gTapChevron.computeBoundingBox();
+            const centerOffset = -0.5 * (gTapChevron.boundingBox.max.y + gTapChevron.boundingBox.min.y);
+            gTapChevron.translate(0, centerOffset, 0);
+
+            // String materials. Strings 0..5 use a per-vertex gradient (color is
+            // white so the gradient baked into gNoteGrad[s] shows pure); strings
+            // 6/7 keep a flat colour (vertexColors:false ignores the attribute).
+            mStr = activePalette.map((c, i) => new T.MeshBasicMaterial({
+                color: i < 6 ? 0xffffff : c,
+                vertexColors: i < 6,
+                transparent: true, opacity: 1.0,
+            }));
+            mGlow = activePalette.map(c => new T.MeshLambertMaterial({
+                color: 0xffffff, emissive: c, emissiveIntensity: 1.5,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            _laneTargetColor = new T.Color(0x4488ff);
+            _fwHitColor = new T.Color(FRET_WIRE_HIT_HEX);
+            _fwHitEmissive = new T.Color(FRET_WIRE_HIT_EMISSIVE);
+            _fwHitGlow.fill(0);
+            _fwHitPrevTime = -Infinity;
+            mSus = activePalette.map(c => new T.MeshLambertMaterial({
+                color: c, transparent: true, opacity: 0.35,
+            }));
+            mWhiteOutline = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.6, transparent: true, opacity: 1.0, depthWrite: false });
+            const _outlineColors = [0xFF5552, 0xFFF352, 0x31CAFF, 0xFFAE31, 0x84FF42, 0xE639FF];
+            const _outlinePalette = activePalette.map((c, i) => _outlineColors[i] ?? c);
+            mStrHitOutline = _outlinePalette.map(c => new T.MeshLambertMaterial({
+                color: c, emissive: c, emissiveIntensity: 1.0,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            // Stronger coloured rim + body for accented notes (.ac); drawNote swaps these in behind ND hit/miss.
+            mAccentOutline = activePalette.map(c => new T.MeshLambertMaterial({
+                color: c, emissive: c, emissiveIntensity: ACCENT_RIM_BASE_EMISSIVE,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            // Same colour response as mGlow (vibrancy lerp) but separate emissive drive for extra accent punch.
+            mAccentCore = activePalette.map(c => new T.MeshLambertMaterial({
+                color: 0xffffff, emissive: c, emissiveIntensity: 1.5,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            const mkAccentHaloMats = (baseOp) => activePalette.map(c => new T.MeshBasicMaterial({
+                color: new T.Color(c),
+                transparent: true,
+                opacity: baseOp,
+                depthWrite: false,
+                depthTest: true,
+                blending: T.AdditiveBlending,
+                side: T.DoubleSide, forceSinglePass: true,
+                fog: true,
+            }));
+            mAccentHaloNear = mkAccentHaloMats(ACCENT_HALO_OP_NEAR);
+            mAccentHaloMid = mkAccentHaloMats(ACCENT_HALO_OP_MID);
+            mAccentHaloFar = mkAccentHaloMats(ACCENT_HALO_OP_FAR);
+            // Frozen per-string shell descriptors — see _accentShellsByString
+            // declaration. Materials live for the renderer's lifetime, so
+            // these refs stay valid until teardown() clears them.
+            _accentShellsByString = mAccentHaloFar.map((_, s) => Object.freeze([
+                Object.freeze({ mat: mAccentHaloFar[s],  ixy: ACCENT_HALO_XY_OUTER, iz: ACCENT_HALO_Z_OUTER, zK: 0.012 }),
+                Object.freeze({ mat: mAccentHaloMid[s],  ixy: ACCENT_HALO_XY_MID,   iz: ACCENT_HALO_Z_MID,   zK: 0.008 }),
+                Object.freeze({ mat: mAccentHaloNear[s], ixy: ACCENT_HALO_XY_INNER, iz: ACCENT_HALO_Z_INNER, zK: 0.005 }),
+            ]));
+            // Chord/arpeggio frame accent bloom — single gradient bar geometry.
+            // The 4 bloom shells (expand=1.00/1.10/1.25/1.45, op=0.90/0.65/0.38/0.18)
+            // are baked into vertex colours as their additive sum at each Y level,
+            // so one mesh per bar replaces 4 per-shell meshes (16→4 draw calls/chord).
+            // Normalised Y = ±(expand / EXPAND_MAX); EXPAND_MAX = 1.45.
+            // Values > 1.0 in the Float32Array buffer are intentional: WebGL passes
+            // them to the shader unchanged, and additive blending clips naturally.
+            if (!gHaloBar) {
+                // Y levels (normalised): ±(shell_expand / 1.45)
+                //   ±0.690 = shell 1 edge  ±0.759 = shell 2  ±0.862 = shell 3  ±1.0 = shell 4
+                // Brightness = additive sum of all shells covering that band:
+                //   |y| < 0.690 → all 4: 0.90+0.65+0.38+0.18 = 2.11
+                //   |y| < 0.759 → 3 shells: 0.65+0.38+0.18 = 1.21
+                //   |y| < 0.862 → 2 shells: 0.38+0.18 = 0.56
+                //   |y| ≤ 1.000 → shell 4 only: 0.18
+                // prettier-ignore
+                const YS = [-1.000, -0.862, -0.759, -0.690,  0.690, 0.759, 0.862, 1.000];
+                // prettier-ignore
+                const BS = [ 0.18,   0.56,   1.21,   2.11,   2.11,  1.21,  0.56,  0.18 ];
+                const N = YS.length;
+                const pos = new Float32Array(N * 2 * 3);
+                const col = new Float32Array(N * 2 * 3);
+                const idx = new Uint16Array((N - 1) * 6);
+                for (let i = 0; i < N; i++) {
+                    const y = YS[i], b = BS[i];
+                    const li = (i * 2 + 0) * 3, ri = (i * 2 + 1) * 3;
+                    pos[li]=-1; pos[li+1]=y; pos[li+2]=0;
+                    col[li]=b;  col[li+1]=b; col[li+2]=b;
+                    pos[ri]=+1; pos[ri+1]=y; pos[ri+2]=0;
+                    col[ri]=b;  col[ri+1]=b; col[ri+2]=b;
+                }
+                for (let i = 0; i < N - 1; i++) {
+                    const ii = i * 6, v = i * 2;
+                    idx[ii+0]=v+0; idx[ii+1]=v+1; idx[ii+2]=v+3;
+                    idx[ii+3]=v+0; idx[ii+4]=v+3; idx[ii+5]=v+2;
+                }
+                gHaloBar = new T.BufferGeometry();
+                gHaloBar.setAttribute('position', new T.BufferAttribute(pos, 3));
+                gHaloBar.setAttribute('color',    new T.BufferAttribute(col, 3));
+                gHaloBar.setIndex(new T.BufferAttribute(idx, 1));
+            }
+            pHaloBar = pool(noteG, () => new T.Mesh(
+                gHaloBar,
+                new T.MeshBasicMaterial({
+                    vertexColors: true,
+                    transparent: true, opacity: 1.0, depthWrite: false,
+                    blending: T.AdditiveBlending, side: T.DoubleSide, forceSinglePass: true, fog: false,
+                }),
+            ));
+            // Notedetect feedback outline (issue #9): hot magenta-red (0xff0066, hue
+            // ~345°) — distinct from the string red 0xff2828 at hue ~0°. Note rendering
+            // swaps its outline.material between mWhiteOutline / per-string
+            // mHitBright[s] / mMissOutline based on recent notedetect events.
+            mMissOutline = new T.MeshLambertMaterial({ color: 0xff0066, emissive: 0xff0066, emissiveIntensity: 1.2, transparent: true, opacity: 1.0, depthWrite: false });
+            // Transparent placeholder for front (+Z, group 4) and back (-Z, group 5)
+            // of the lateral face-fill material array. Also the default material for
+            // the pNoteEdge pool: pool consumers reassign .material before render, so
+            // the placeholder is never displayed — using an explicitly-invisible
+            // material makes that intent obvious.
+            // BoxGeometry group order: 0=+X, 1=-X, 2=+Y, 3=-Y, 4=+Z(front), 5=-Z(back)
+            mEdgeTransparent = new T.MeshBasicMaterial({ transparent: true, opacity: 0, depthWrite: false });
+            // mMissEdgeArrays: use mMissOutline (same Lambert+emissive material as the gem
+            // border) so the lateral face fill matches the outline colour exactly.
+            mMissEdgeArrays = [mMissOutline, mMissOutline, mMissOutline, mMissOutline, mEdgeTransparent, mEdgeTransparent];
+
+            // Hit: fixed neon spring-green on every string — 0x22ff88 is cyan-shifted
+            // enough to be readable even on the green string (0x30d040). The outline
+            // + lateral faces flash green regardless of which string was hit.
+            mHitBright = activePalette.map(() => new T.MeshLambertMaterial({
+                color: 0x22ff88, emissive: 0x22ff88, emissiveIntensity: 4.0 * glowMul,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            mHitBrightArrays = mHitBright.map(m => [m, m, m, m, mEdgeTransparent, mEdgeTransparent]);
+
+            // Rim flash: string-coloured, wire-fashion intensity. Colour and
+            // emissive both take the palette colour so the rim reads as the
+            // string lighting up, not as a white wash over it.
+            mRimFlash = activePalette.map((c) => new T.MeshLambertMaterial({
+                color: c, emissive: c, emissiveIntensity: 1,
+                transparent: true, opacity: 1.0, depthWrite: false,
+            }));
+            // Readability (#2 / charrette): the note gems + their outlines punch THROUGH
+            // the distance fog so upcoming notes stay legible as they render in at the
+            // horizon. The board, lane, sustains and background scenery keep their
+            // atmospheric fog — only the note-defining materials are exempted, so the
+            // highway still reads as deep while the notes never dissolve into the haze.
+            [mWhiteOutline, mMissOutline].forEach(m => { if (m) m.fog = false; });
+            [mStr, mGlow, mStrHitOutline, mHitBright, mRimFlash].forEach(arr => arr && arr.forEach(m => { if (m) m.fog = false; }));
+            // Outline materials render at a lower renderOrder than the body.
+            // The body is rendered on top with opacity:1 on hit/miss, which
+            // fully covers the outline center — only the fringe that extends
+            // past the body edges (0.2*K on each side) is visible.
+            mSusOutline     = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.3, transparent: true, opacity: 0.75, depthWrite: false });
+            mHitSusOutline  = new T.MeshLambertMaterial({ color: 0x22ff88, emissive: 0x22ff88, emissiveIntensity: 0.8, transparent: true, opacity: 0.45, depthWrite: false });
+            mBeatM = new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.25 });
+            mBeatQ = new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.07 });
+
+            // ── Board ghost: filled rim (ExtrudeGeometry w/ hole) in string colour ──
+            // Matches outline 1.1× vs core 1.0× like drawNote; centre stays empty.
+            // 3 slots per string (up to 3 simultaneous ghost previews, chart-
+            // format style): slot 0 is the "next on string" / chord / arp ghost
+            // (unchanged selection logic), slots 1/2 are independent
+            // "upcoming" lead-note previews. All slots share one geometry —
+            // it's identical (NW/NH/ND-based) regardless of string or slot,
+            // so one ExtrudeGeometry serves all nStr*3 meshes.
+            const _ghostFrameGeo = mkGhostFrameGeometry();
+            projMeshArr = activePalette.map((_, s) => [0, 1, 2].map(() => {
+                const mat = new T.MeshStandardMaterial({
+                    color: activePalette[s],
+                    emissive: activePalette[s],
+                    emissiveIntensity: 0.002,
+                    transparent: true,
+                    opacity: 0.65,
+                    roughness: 1,
+                    depthWrite: false,
+                    depthTest: false,
+                });
+                const m = new T.Mesh(_ghostFrameGeo, mat);
+                m.visible = false;
+                // Board projection ghost frame. depthTest:false above, so
+                // renderOrder alone decides stacking — keep it above the
+                // sus trails (12/13) but below note gems (20/21) so it
+                // stays visible on the fretboard without covering notes.
+                m.renderOrder = 14;
+                noteG.add(m);
+                return m;
+            }));
+
+            // ── Pools ──────────────────────────────────────────────────────
+            pNote = pool(noteG, () => new T.Mesh(gNote, mStr[0]));
+            // Pool default is the always-invisible mEdgeTransparent — every
+            // consumer reassigns .material before render (to a verdict edge
+            // material array), so the placeholder is never displayed.
+            pNoteEdge = pool(noteG, () => new T.Mesh(gNote, mEdgeTransparent));
+            pAccentHalo = pool(noteG, () => new T.Mesh(gNote, mAccentHaloFar[0]));
+            pSus = pool(noteG, () => new T.Mesh(gSus, mSus[0]));
+            pSusOutline = pool(noteG, () => new T.Mesh(gSus, mSusOutline));
+            const mkSlideRibbonGeo = () => {
+                const nVert = 4 * (SLIDE_RIBBON_SAMPLES + 1);
+                const g = new T.BufferGeometry();
+                g.setAttribute('position', new T.Float32BufferAttribute(new Float32Array(nVert * 3), 3));
+                // SLIDE_RIBBON_INDICES_ARR is the plain-Array form (see module-init
+                // comment) shared across pool meshes; setIndex() rewraps it into a
+                // fresh Uint16BufferAttribute per geometry, so the share is safe.
+                g.setIndex(SLIDE_RIBBON_INDICES_ARR);
+                // Static cross-section normals: each ring is an axis-aligned quad,
+                // so vertex normals point radially in the XY plane regardless of
+                // the slide's Z-direction curvature. Pre-fill once and skip the
+                // per-frame computeVertexNormals() pass that previously ran on
+                // every sustained-slide update (Copilot perf finding on PR #215).
+                const SQRT_HALF = Math.SQRT1_2;
+                const normals = new Float32Array(nVert * 3);
+                for (let k = 0; k <= SLIDE_RIBBON_SAMPLES; k++) {
+                    const o = k * 12;
+                    // v0 (-X,-Y), v1 (+X,-Y), v2 (+X,+Y), v3 (-X,+Y)
+                    normals[o]     = -SQRT_HALF; normals[o + 1]  = -SQRT_HALF; normals[o + 2]  = 0;
+                    normals[o + 3] =  SQRT_HALF; normals[o + 4]  = -SQRT_HALF; normals[o + 5]  = 0;
+                    normals[o + 6] =  SQRT_HALF; normals[o + 7]  =  SQRT_HALF; normals[o + 8]  = 0;
+                    normals[o + 9] = -SQRT_HALF; normals[o + 10] =  SQRT_HALF; normals[o + 11] = 0;
+                }
+                g.setAttribute('normal', new T.Float32BufferAttribute(normals, 3));
+                return g;
+            };
+            // Ribbon meshes mutate vertex positions every frame in
+            // slideRibbonUpdatePositions but the mesh itself stays at (0,0,0)
+            // and the geometry's bounding sphere is never recomputed. With
+            // frustum culling on, Three.js tests the (0,0,0)-centred bounds
+            // and culls the ribbon as soon as the camera pans away from world
+            // origin, so slides flicker in/out. Disable culling on these
+            // meshes — the ribbon footprint is small and they're already
+            // gated by t0/t1 reachability before render.
+            pSusRibbon = pool(noteG, () => {
+                const m = new T.Mesh(mkSlideRibbonGeo(), mSus[0]);
+                m.frustumCulled = false;
+                return m;
+            });
+            pSusRibbonOl = pool(noteG, () => {
+                const m = new T.Mesh(mkSlideRibbonGeo(), mSusOutline);
+                m.frustumCulled = false;
+                m.renderOrder = -3;
+                return m;
+            });
+            // One shared material per technique-mesh type. The pool factory
+            // hands out fresh meshes that all reference the same material,
+            // so a dense HO/PO passage doesn't churn N MeshLambertMaterial
+            // allocations and N GPU material switches.
+            // Transparent + no depth write/test so the tap chevron draws in
+            // the transparent pass where drawNote assigns renderOrder 1000.
+            mTapChevron = new T.MeshLambertMaterial({
+                color: 0xd4d4d4,
+                emissive: 0xd4d4d4,
+                emissiveIntensity: 0.9,
+                transparent: true,
+                opacity: 0.85,
+                side: T.DoubleSide, forceSinglePass: true,
+                depthWrite: false,
+                depthTest: false,
+            });
+            pTapChevron = pool(noteG, () => new T.Mesh(gTapChevron, mTapChevron));
+            pLbl  = pool(lblG,  () => new T.Sprite(txtMat('0', '#fff', false, 'technique')));
+            pBeat = pool(beatG, () => new T.Line(gBeat, mBeatQ));
+            pSec  = pool(lblG,  () => new T.Sprite(txtMat('', '#0dd', true, 'section')));
+
+            // Chord sustain length indicator — thin horizontal plane rails.
+            // Unit plane (1×1 in XZ) laid flat; scaled to (railWidth, 1, railLen).
+            // A horizontal plane seen from the camera looking down-forward is
+            // face-on and has real apparent thickness — unlike T.Line (always 1px).
+            // depthTest:false so they never occlude gems; renderOrder 11 places
+            // them above lane dividers (2) and chord fill (10), at the same level
+            // as chord frame edges (11), and BELOW sustain trails (12/13), note
+            // gems (dynamic ≥50), and arp brackets (18). The bloom halo (10) sits
+            // behind the core rail (11). Keeping susrail behind note sus trails
+            // prevents the rail border from covering individual note tails
+            // (sustain/vibrato/tremolo/bend). (Was 14/16 which rendered on top of
+            // 12/13 sus trails, causing the outer border to overlap tails.)
+            gSusRail = new T.PlaneGeometry(1, 1);
+            gSusRail.rotateX(-Math.PI / 2); // lay flat in XZ plane
+            mSusRailBase = new T.MeshBasicMaterial({
+                color: CHORD_BOX_TEAL_HEX,
+                transparent: true, opacity: 0.85,
+                depthTest: false, depthWrite: false,
+                fog: false, side: T.DoubleSide, forceSinglePass: true,
+            });
+            pSusRail = pool(noteG, () => {
+                const m = new T.Mesh(gSusRail, mSusRailBase.clone());
+                m.renderOrder = 5; // below strings (7) so strings render on top
+                return m;
+            });
+
+            // Bloom glow for chord sustain rails — wider plane with a gaussian
+            // falloff texture (bright centre → transparent edges in X direction)
+            // and additive blending, so it brightens whatever is behind it.
+            // renderOrder 4 places it behind the core rail (5).
+            _bloomGaussTex = _makeGaussTex(T);
+            gSusRailBloom = new T.PlaneGeometry(1, 1);
+            gSusRailBloom.rotateX(-Math.PI / 2);
+            mSusRailBloomBase = new T.MeshBasicMaterial({
+                color: CHORD_BOX_TEAL_HEX,
+                map: _bloomGaussTex,
+                transparent: true, opacity: 0.55,
+                blending: T.AdditiveBlending,
+                depthTest: false, depthWrite: false,
+                fog: false, side: T.DoubleSide, forceSinglePass: true,
+            });
+            pSusRailBloom = pool(noteG, () => {
+                const m = new T.Mesh(gSusRailBloom, mSusRailBloomBase.clone());
+                m.renderOrder = 4; // below strings (7) so strings render on top
+                return m;
+            });
+
+            // Rotatable plane pool for technique markers (pm, mt, hm, hp, H/P, bend).
+            // Unlike T.Sprite, a PlaneGeometry mesh accepts rotation.z = approachRot
+            // so markers stay coplanar with the gem as it tilts from vertical to flat.
+            gTechPlane = new T.PlaneGeometry(1, 1);
+            pTechPlane = pool(noteG, () => {
+                const m = new T.Mesh(gTechPlane, new T.MeshBasicMaterial({
+                    transparent: true, depthTest: false, depthWrite: false, side: T.DoubleSide, forceSinglePass: true,
+                }));
+                m.renderOrder = 1000;
+                return m;
+            });
+
+            // ── InstancedMesh temporaries ──────────────────────────────────────
+            _imM4    = new T.Matrix4();
+            _imPos   = new T.Vector3();
+            _imSca   = new T.Vector3();
+            _imQ     = new T.Quaternion();
+            _imAZ    = new T.Vector3(0, 0, 1);
+            _imColor = new T.Color();
+
+            // ── Shared ShaderMaterial templates ───────────────────────────────
+            // Vertex shader used by PM-X and FH-X on individual note gems.
+            // Three.js injects `USE_INSTANCING` + `instanceMatrix` attribute
+            // into the prefix when an InstancedMesh uses a ShaderMaterial.
+            const _imTechVert = [
+                'attribute float instanceAlpha;',
+                'varying float vAlpha;',
+                'varying vec2 vUv;',
+                'void main() {',
+                '    vUv = uv;',
+                '    vAlpha = instanceAlpha;',
+                '    vec4 pos = vec4(position, 1.0);',
+                '    #ifdef USE_INSTANCING',
+                '    pos = instanceMatrix * pos;',
+                '    #endif',
+                '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
+                '}',
+            ].join('\n');
+            const _imTechFrag = [
+                'uniform sampler2D map;',
+                'varying float vAlpha;',
+                'varying vec2 vUv;',
+                'void main() {',
+                '    vec4 t = texture2D(map, vUv);',
+                '    if (t.a * vAlpha < 0.01) discard;',
+                '    gl_FragColor = vec4(t.rgb, t.a * vAlpha);',
+                '}',
+            ].join('\n');
+
+            // ── PM / FH tech marker InstancedMeshes ───────────────────────────
+            // Each IM gets a geometry clone so instanceAlpha is a separate buffer.
+            const _mkTechIM = (spriteMat, alphaArr) => {
+                const geo = gTechPlane.clone();
+                const alphaAttr = new T.InstancedBufferAttribute(alphaArr, 1);
+                alphaAttr.setUsage(T.DynamicDrawUsage);
+                geo.setAttribute('instanceAlpha', alphaAttr);
+                const mat = new T.ShaderMaterial({
+                    uniforms: { map: { value: spriteMat.map } },
+                    vertexShader: _imTechVert,
+                    fragmentShader: _imTechFrag,
+                    transparent: true, depthTest: false, depthWrite: false, side: T.DoubleSide, forceSinglePass: true,
+                });
+                const im = new T.InstancedMesh(geo, mat, IM_TECH_CAP);
+                im.instanceMatrix.setUsage(T.DynamicDrawUsage);
+                im.frustumCulled = false;
+                im.count = 0;
+                noteG.add(im);
+                return { im, geo, mat };
+            };
+            { const r = _mkTechIM(palmMuteXSpriteMat(),    _imPMTechAlphaArr);
+              imPMTech = r.im; _imGPMTech = r.geo; _imPMTechMat = r.mat; imPMTech.renderOrder = 702; }
+            { const r = _mkTechIM(fretHandMuteXSpriteMat(), _imFHTechAlphaArr);
+              imFHTech = r.im; _imGFHTech = r.geo; _imFHTechMat = r.mat; imFHTech.renderOrder = 700; }
+
+            // Dynamic fret number labels (heat-coloured, updated each frame)
+            pFretLbl = pool(lblG, () => new T.Sprite(txtMat('0', '#888', false, 'fretRow')));
+
+            // Highlight lane plane over active fret range. With the anchor-driven
+            // segmented lanes we render up to fret-count × HWY_LANE_TIME_SLICES (96)
+            // pLane meshes per frame, so:
+            //   - geometry is a shared PlaneGeometry(1,1) (was per-mesh, never differed)
+            //   - 2 shared MeshBasicMaterials (odd / even stripe colour) replace the
+            //     per-mesh material clones; the per-frame opacity still travels via
+            //     the materials but is set once outside the inner loop, not per-mesh.
+            gLanePlane = new T.PlaneGeometry(1, 1);
+            mLaneOdd = new T.MeshBasicMaterial({
+                color: HWY_LANE_STRIPE_ODD_HEX, transparent: true, opacity: 0, depthWrite: false,
+            });
+            mLaneEven = new T.MeshBasicMaterial({
+                color: HWY_LANE_STRIPE_EVEN_HEX, transparent: true, opacity: 0, depthWrite: false,
+            });
+            // Tracked for explicit disposal in teardown — these materials may
+            // not be reachable via scene.traverse() if no lane was ever rendered.
+            _ownedSharedMats.push(mLaneOdd, mLaneEven);
+            _ownedSharedGeos.push(gLanePlane);
+            pLane = pool(noteG, () => new T.Mesh(gLanePlane, mLaneOdd));
+
+            gGhostFretPlane = new T.PlaneGeometry(1, 1);
+            _ownedSharedGeos.push(gGhostFretPlane);
+            const mGhostFretLblPh = new T.MeshBasicMaterial({
+                color: 0xffffff, transparent: true, depthTest: false, depthWrite: false,
+            });
+            _ownedSharedMats.push(mGhostFretLblPh);
+            pGhostFretLbl = pool(noteG, () => {
+                const m = new T.Mesh(gGhostFretPlane, mGhostFretLblPh);
+                // Must be above the proj frame (renderOrder=14) and opaque
+                // geometry — same contract as technique labels (renderOrder=1000):
+                // depthTest:false alone is insufficient, renderOrder=1000 needed.
+                m.renderOrder = 1000;
+                m.frustumCulled = false;
+                return m;
+            });
+
+            // Vertical fret dividers within active lane
+            const gLaneDivider = new T.BoxGeometry(0.15 * K, 0.15 * K, 1);
+            mLaneDivider = new T.MeshBasicMaterial({
+                color: 0x46DDE6, transparent: true, opacity: 1.00, fog: false, depthWrite: false,
+            });
+            mLaneDividerArp = new T.MeshBasicMaterial({
+                color: ARPEGGIO_RIM_BLUE_HEX,
+                transparent: true, opacity: 0.08, fog: false, depthWrite: false,
+            });
+            mLaneDividerExt = new T.MeshBasicMaterial({
+                color: 0x364D5F, transparent: true, opacity: 0.4, fog: false, depthWrite: false,
+            });
+            _ownedSharedMats.push(mLaneDivider, mLaneDividerArp, mLaneDividerExt);
+            pLaneDivider = pool(noteG, () => new T.Mesh(gLaneDivider, mLaneDivider));
+
+            // Chord frame palette (frame alpha 128, fill gradient alpha 32; MeshBasic).
+            const chR = CHORD_BOX_TEAL_HEX >> 16 & 255;
+            const chG = CHORD_BOX_TEAL_HEX >> 8 & 255;
+            const chB = CHORD_BOX_TEAL_HEX & 255;
+            const dkR = CHORD_BOX_TEAL_DARK_HEX >> 16 & 255;
+            const dkG = CHORD_BOX_TEAL_DARK_HEX >> 8 & 255;
+            const dkB = CHORD_BOX_TEAL_DARK_HEX & 255;
+            const aFill = Math.round(CHORD_BOX_FILL_GRAD_ALPHA * 255);
+            chordFrameGradTex = new T.DataTexture(
+                new Uint8Array([ chR, chG, chB, aFill, dkR, dkG, dkB, aFill, chR, chG, chB, aFill ]),
+                3, 1, T.RGBAFormat);
+            chordFrameGradTex.magFilter = T.LinearFilter;
+            chordFrameGradTex.minFilter = T.LinearFilter;
+            chordFrameGradTex.wrapS = T.ClampToEdgeWrapping;
+            chordFrameGradTex.wrapT = T.ClampToEdgeWrapping;
+            // DataTexture defaults to linear color space; flag this gradient
+            // as sRGB so the chord-box hex values match other sRGB color textures.
+            chordFrameGradTex.colorSpace = T.SRGBColorSpace;
+            chordFrameGradTex.needsUpdate = true;
+
+            const arR = ARPEGGIO_BOX_BLUE_HEX >> 16 & 255;
+            const arG = ARPEGGIO_BOX_BLUE_HEX >> 8 & 255;
+            const arB = ARPEGGIO_BOX_BLUE_HEX & 255;
+            const arDR = ARPEGGIO_BOX_BLUE_DARK_HEX >> 16 & 255;
+            const arDG = ARPEGGIO_BOX_BLUE_DARK_HEX >> 8 & 255;
+            const arDB = ARPEGGIO_BOX_BLUE_DARK_HEX & 255;
+            chordFrameGradTexArp = new T.DataTexture(
+                new Uint8Array([ arR, arG, arB, aFill, arDR, arDG, arDB, aFill, arR, arG, arB, aFill ]),
+                3, 1, T.RGBAFormat);
+            chordFrameGradTexArp.magFilter = T.LinearFilter;
+            chordFrameGradTexArp.minFilter = T.LinearFilter;
+            chordFrameGradTexArp.wrapS = T.ClampToEdgeWrapping;
+            chordFrameGradTexArp.wrapT = T.ClampToEdgeWrapping;
+            chordFrameGradTexArp.colorSpace = T.SRGBColorSpace;
+            chordFrameGradTexArp.needsUpdate = true;
+
+            pChordFrameFill = pool(noteG, () => new T.Mesh(
+                new T.PlaneGeometry(1, 1),
+                new T.MeshBasicMaterial({
+                    map: chordFrameGradTex,
+                    transparent: true,
+                    opacity: 1,
+                    depthWrite: false,
+                    depthTest: false,
+                    fog: false,
+                    side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+            pChordBox = pool(noteG, () => new T.Mesh(
+                new T.BoxGeometry(1, 1, 1),
+                new T.MeshBasicMaterial({
+                    color: CHORD_BOX_TEAL_HEX,
+                    transparent: true,
+                    opacity: CHORD_BOX_EDGE_ALPHA,
+                    depthWrite: false,
+                    depthTest: false,
+                    fog: false,
+                    side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+
+            // PM strum X fill — 4 corner regions + centre; the 4 arms (L,R,T,B) are left empty.
+            // 16 vertices, 14 triangles.
+            //  0=A(-1,1)  1=TLC(-0.48,1)  2=T(-0.012,0.257)  3=TRC(0.5,1)
+            //  4=BR(1,1)  5=REB(1,0.5)   6=R(0.476,-0.011)  7=RET(1,-0.5)
+            //  8=C(1,-1)  9=BRC(0.48,-1) 10=B(-0.003,-0.276) 11=BLC(-0.48,-1)
+            // 12=D(-1,-1) 13=LET(-1,-0.5) 14=L(-0.494,-0.011) 15=LEB(-1,0.5)
+            {
+                // prettier-ignore
+                const pos = new Float32Array([
+                    -1,      1,      0,  //  0  A
+                    -0.480,  1,      0,  //  1  TLC
+                    -0.012,  0.257,  0,  //  2  T
+                     0.500,  1,      0,  //  3  TRC
+                     1,      1,      0,  //  4  BR
+                     1,      0.5,    0,  //  5  REB
+                     0.476, -0.011,  0,  //  6  R
+                     1,     -0.5,    0,  //  7  RET
+                     1,     -1,      0,  //  8  C
+                     0.480, -1,      0,  //  9  BRC
+                    -0.003, -0.276,  0,  // 10  B
+                    -0.480, -1,      0,  // 11  BLC
+                    -1,     -1,      0,  // 12  D
+                    -1,     -0.5,    0,  // 13  LET
+                    -0.494, -0.011,  0,  // 14  L
+                    -1,      0.5,    0,  // 15  LEB
+                ]);
+                // prettier-ignore
+                const idx = new Uint16Array([
+                    // top-left corner: A,TLC,T,L,LEB
+                     0,  1,  2,
+                     0,  2, 14,
+                     0, 14, 15,
+                    // top-right corner: TRC,BR,REB,R,T
+                     3,  4,  5,
+                     3,  5,  6,
+                     3,  6,  2,
+                    // centre: T,R,B,L
+                     2,  6, 10,
+                     2, 10, 14,
+                    // bottom-right corner: RET,C,BRC,B,R
+                     7,  8,  9,
+                     7,  9, 10,
+                     7, 10,  6,
+                    // bottom-left corner: LET,L,B,BLC,D
+                    13, 14, 10,
+                    13, 10, 11,
+                    13, 11, 12,
+                ]);
+                gPMXFill = new T.BufferGeometry();
+                gPMXFill.setAttribute('position', new T.BufferAttribute(pos, 3));
+                gPMXFill.setIndex(new T.BufferAttribute(idx, 1));
+            }
+            // PM fill — InstancedMesh (black, varying alpha per chord).
+            {
+                const _imFillVert = [
+                    'attribute float instanceAlpha;',
+                    'varying float vAlpha;',
+                    'void main() {',
+                    '    vAlpha = instanceAlpha;',
+                    '    vec4 pos = vec4(position, 1.0);',
+                    '    #ifdef USE_INSTANCING',
+                    '    pos = instanceMatrix * pos;',
+                    '    #endif',
+                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
+                    '}',
+                ].join('\n');
+                const _imFillFrag = [
+                    'varying float vAlpha;',
+                    'void main() {',
+                    '    if (vAlpha <= 0.0) discard;',
+                    '    gl_FragColor = vec4(0.0, 0.0, 0.0, vAlpha);',
+                    '}',
+                ].join('\n');
+                const alphaAttr = new T.InstancedBufferAttribute(_imPMXFillAlphaArr, 1);
+                alphaAttr.setUsage(T.DynamicDrawUsage);
+                gPMXFill.setAttribute('instanceAlpha', alphaAttr);
+                _imPMXFillMat = new T.ShaderMaterial({
+                    vertexShader: _imFillVert, fragmentShader: _imFillFrag,
+                    transparent: true, depthTest: false, depthWrite: false,
+                    fog: false, side: T.DoubleSide, forceSinglePass: true,
+                });
+                imPMXFill = new T.InstancedMesh(gPMXFill, _imPMXFillMat, IM_STRUM_CAP);
+                imPMXFill.instanceMatrix.setUsage(T.DynamicDrawUsage);
+                imPMXFill.frustumCulled = false;
+                imPMXFill.renderOrder = 10.5;
+                imPMXFill.count = 0;
+                noteG.add(imPMXFill);
+            }
+
+            // FH (frethand mute) strum X fill — 5 regions: 4 corner quadrants + centre diamond.
+            // 12 vertices, 10 triangles. L/R wings stop at fx=±0.50 (no solid lateral blocks).
+            //  0=LET(-0.50,+1)  1=TLC(-0.15,+1)  2=T(0,+0.42)   3=TRC(+0.15,+1)
+            //  4=RET(+0.50,+1)  5=REB(+0.50,-1)  6=R(+0.28,0)   7=B(0,-0.42)
+            //  8=BRC(+0.15,-1)  9=BLC(-0.15,-1) 10=LEB(-0.50,-1) 11=L(-0.28,0)
+            {
+                // prettier-ignore
+                const pos = new Float32Array([
+                    -0.50,  1,      0,  //  0  LET
+                    -0.15,  1,      0,  //  1  TLC
+                     0,     0.42,   0,  //  2  T
+                     0.15,  1,      0,  //  3  TRC
+                     0.50,  1,      0,  //  4  RET
+                     0.50, -1,      0,  //  5  REB
+                     0.28,  0,      0,  //  6  R
+                     0,    -0.42,   0,  //  7  B
+                     0.15, -1,      0,  //  8  BRC
+                    -0.15, -1,      0,  //  9  BLC
+                    -0.50, -1,      0,  // 10  LEB
+                    -0.28,  0,      0,  // 11  L
+                ]);
+                // prettier-ignore
+                const idx = new Uint16Array([
+                    // top-left corner: LET,TLC,T,L
+                     0,  1,  2,
+                     0,  2, 11,
+                    // top-right corner: TRC,RET,R,T
+                     3,  4,  6,
+                     3,  6,  2,
+                    // bottom-right corner: REB,R,B,BRC
+                     5,  6,  7,
+                     5,  7,  8,
+                    // bottom-left corner: LEB,L,B,BLC
+                    10, 11,  7,
+                    10,  7,  9,
+                    // centre diamond: L,T,R,B
+                    11,  2,  6,
+                    11,  6,  7,
+                ]);
+                gFHXFill = new T.BufferGeometry();
+                gFHXFill.setAttribute('position', new T.BufferAttribute(pos, 3));
+                gFHXFill.setIndex(new T.BufferAttribute(idx, 1));
+            }
+            // FH fill — InstancedMesh (black, varying alpha per chord).
+            {
+                const _imFillVert = [
+                    'attribute float instanceAlpha;',
+                    'varying float vAlpha;',
+                    'void main() {',
+                    '    vAlpha = instanceAlpha;',
+                    '    vec4 pos = vec4(position, 1.0);',
+                    '    #ifdef USE_INSTANCING',
+                    '    pos = instanceMatrix * pos;',
+                    '    #endif',
+                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
+                    '}',
+                ].join('\n');
+                const _imFillFrag = [
+                    'varying float vAlpha;',
+                    'void main() {',
+                    '    if (vAlpha <= 0.0) discard;',
+                    '    gl_FragColor = vec4(0.0, 0.0, 0.0, vAlpha);',
+                    '}',
+                ].join('\n');
+                const alphaAttr = new T.InstancedBufferAttribute(_imFHXFillAlphaArr, 1);
+                alphaAttr.setUsage(T.DynamicDrawUsage);
+                gFHXFill.setAttribute('instanceAlpha', alphaAttr);
+                _imFHXFillMat = new T.ShaderMaterial({
+                    vertexShader: _imFillVert, fragmentShader: _imFillFrag,
+                    transparent: true, depthTest: false, depthWrite: false,
+                    fog: false, side: T.DoubleSide, forceSinglePass: true,
+                });
+                imFHXFill = new T.InstancedMesh(gFHXFill, _imFHXFillMat, IM_STRUM_CAP);
+                imFHXFill.instanceMatrix.setUsage(T.DynamicDrawUsage);
+                imFHXFill.frustumCulled = false;
+                imFHXFill.renderOrder = 10.5;
+                imFHXFill.count = 0;
+                noteG.add(imFHXFill);
+            }
+
+            // PM X lines — 8 segments baked as thin quads in ±1 normalised space.
+            // Scale the pool mesh by (innerW*0.5, -innerH*0.5, ...) per chord;
+            // the Y-negated scale matches the XLINES convention (fya>0 = below centre).
+            if (!gPMXLines) {
+                const HT = 0.016; // normalised half-thickness ≈ lw/hH for a typical chord
+                // prettier-ignore
+                const XLINES = [
+                    [-1.000, -0.500, -0.494, -0.011],
+                    [-1.000,  0.500, -0.494, -0.011],
+                    [ 1.000, -0.500,  0.476, -0.011],
+                    [ 1.000,  0.500,  0.476, -0.011],
+                    [-0.480,  1.000, -0.012,  0.257],
+                    [ 0.500,  1.000, -0.012,  0.257],
+                    [ 0.480, -1.000,  0.000, -0.276],
+                    [-0.480, -1.000, -0.006, -0.276],
+                ];
+                const pos = new Float32Array(XLINES.length * 4 * 3);
+                const idx = new Uint16Array(XLINES.length * 6);
+                for (let i = 0; i < XLINES.length; i++) {
+                    const [xa, ya, xb, yb] = XLINES[i];
+                    const dx = xb - xa, dy = yb - ya;
+                    const il = 1 / Math.sqrt(dx * dx + dy * dy);
+                    const nx = -dy * il, ny = dx * il;
+                    const vi = i * 12, ii = i * 6, vb = i * 4;
+                    pos[vi+0]=xa+nx*HT; pos[vi+1]=ya+ny*HT; pos[vi+2]=0;
+                    pos[vi+3]=xb+nx*HT; pos[vi+4]=yb+ny*HT; pos[vi+5]=0;
+                    pos[vi+6]=xb-nx*HT; pos[vi+7]=yb-ny*HT; pos[vi+8]=0;
+                    pos[vi+9]=xa-nx*HT; pos[vi+10]=ya-ny*HT; pos[vi+11]=0;
+                    idx[ii+0]=vb;   idx[ii+1]=vb+1; idx[ii+2]=vb+2;
+                    idx[ii+3]=vb;   idx[ii+4]=vb+2; idx[ii+5]=vb+3;
+                }
+                gPMXLines = new T.BufferGeometry();
+                gPMXLines.setAttribute('position', new T.BufferAttribute(pos, 3));
+                gPMXLines.setIndex(new T.BufferAttribute(idx, 1));
+            }
+            // PM lines — InstancedMesh (varying color + alpha per chord).
+            // instanceColor (THREE built-in) carries baseRimHex per instance;
+            // instanceAlpha carries the per-chord opacity.
+            {
+                const _imLinesVert = [
+                    'attribute float instanceAlpha;',
+                    'varying float vAlpha;',
+                    'varying vec3 vColor;',
+                    'void main() {',
+                    '    vAlpha = instanceAlpha;',
+                    '    #ifdef USE_INSTANCING_COLOR',
+                    '    vColor = instanceColor;',
+                    '    #else',
+                    '    vColor = vec3(1.0);',
+                    '    #endif',
+                    '    vec4 pos = vec4(position, 1.0);',
+                    '    #ifdef USE_INSTANCING',
+                    '    pos = instanceMatrix * pos;',
+                    '    #endif',
+                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
+                    '}',
+                ].join('\n');
+                const _imLinesFrag = [
+                    'varying float vAlpha;',
+                    'varying vec3 vColor;',
+                    'void main() {',
+                    '    if (vAlpha <= 0.0) discard;',
+                    '    gl_FragColor = vec4(vColor, vAlpha);',
+                    '}',
+                ].join('\n');
+                const alphaAttr = new T.InstancedBufferAttribute(_imPMXLinesAlphaArr, 1);
+                alphaAttr.setUsage(T.DynamicDrawUsage);
+                gPMXLines.setAttribute('instanceAlpha', alphaAttr);
+                _imPMXLinesMat = new T.ShaderMaterial({
+                    vertexShader: _imLinesVert, fragmentShader: _imLinesFrag,
+                    transparent: true, depthTest: false, depthWrite: false,
+                    fog: false, side: T.DoubleSide, forceSinglePass: true,
+                });
+                imPMXLines = new T.InstancedMesh(gPMXLines, _imPMXLinesMat, IM_STRUM_CAP);
+                imPMXLines.instanceMatrix.setUsage(T.DynamicDrawUsage);
+                imPMXLines.frustumCulled = false;
+                imPMXLines.renderOrder = 11;
+                // Eagerly initialise instanceColor so USE_INSTANCING_COLOR is
+                // defined when the shader is compiled on the first draw.
+                _imColor.set(1, 1, 1);
+                imPMXLines.setColorAt(0, _imColor);
+                imPMXLines.instanceColor.setUsage(T.DynamicDrawUsage);
+                imPMXLines.count = 0;
+                noteG.add(imPMXLines);
+            }
+
+            // FH X lines — same scheme, 8 segments from the FH_XLINES pattern
+            if (!gFHXLines) {
+                const HT = 0.022; // slightly wider — FH wings are shorter, need more visual weight
+                // prettier-ignore
+                const FH_XLINES = [
+                    [-0.50,  1.00, -0.28,  0.00],
+                    [-0.50, -1.00, -0.28,  0.00],
+                    [ 0.50,  1.00,  0.28,  0.00],
+                    [ 0.50, -1.00,  0.28,  0.00],
+                    [-0.15, -1.00,  0.00, -0.42],
+                    [ 0.15, -1.00,  0.00, -0.42],
+                    [ 0.15,  1.00,  0.00,  0.42],
+                    [-0.15,  1.00,  0.00,  0.42],
+                ];
+                const pos = new Float32Array(FH_XLINES.length * 4 * 3);
+                const idx = new Uint16Array(FH_XLINES.length * 6);
+                for (let i = 0; i < FH_XLINES.length; i++) {
+                    const [xa, ya, xb, yb] = FH_XLINES[i];
+                    const dx = xb - xa, dy = yb - ya;
+                    const il = 1 / Math.sqrt(dx * dx + dy * dy);
+                    const nx = -dy * il, ny = dx * il;
+                    const vi = i * 12, ii = i * 6, vb = i * 4;
+                    pos[vi+0]=xa+nx*HT; pos[vi+1]=ya+ny*HT; pos[vi+2]=0;
+                    pos[vi+3]=xb+nx*HT; pos[vi+4]=yb+ny*HT; pos[vi+5]=0;
+                    pos[vi+6]=xb-nx*HT; pos[vi+7]=yb-ny*HT; pos[vi+8]=0;
+                    pos[vi+9]=xa-nx*HT; pos[vi+10]=ya-ny*HT; pos[vi+11]=0;
+                    idx[ii+0]=vb;   idx[ii+1]=vb+1; idx[ii+2]=vb+2;
+                    idx[ii+3]=vb;   idx[ii+4]=vb+2; idx[ii+5]=vb+3;
+                }
+                gFHXLines = new T.BufferGeometry();
+                gFHXLines.setAttribute('position', new T.BufferAttribute(pos, 3));
+                gFHXLines.setIndex(new T.BufferAttribute(idx, 1));
+            }
+            // FH lines — InstancedMesh (varying color + alpha per chord).
+            {
+                const _imLinesVert = [
+                    'attribute float instanceAlpha;',
+                    'varying float vAlpha;',
+                    'varying vec3 vColor;',
+                    'void main() {',
+                    '    vAlpha = instanceAlpha;',
+                    '    #ifdef USE_INSTANCING_COLOR',
+                    '    vColor = instanceColor;',
+                    '    #else',
+                    '    vColor = vec3(1.0);',
+                    '    #endif',
+                    '    vec4 pos = vec4(position, 1.0);',
+                    '    #ifdef USE_INSTANCING',
+                    '    pos = instanceMatrix * pos;',
+                    '    #endif',
+                    '    gl_Position = projectionMatrix * modelViewMatrix * pos;',
+                    '}',
+                ].join('\n');
+                const _imLinesFrag = [
+                    'varying float vAlpha;',
+                    'varying vec3 vColor;',
+                    'void main() {',
+                    '    if (vAlpha <= 0.0) discard;',
+                    '    gl_FragColor = vec4(vColor, vAlpha);',
+                    '}',
+                ].join('\n');
+                const alphaAttr = new T.InstancedBufferAttribute(_imFHXLinesAlphaArr, 1);
+                alphaAttr.setUsage(T.DynamicDrawUsage);
+                gFHXLines.setAttribute('instanceAlpha', alphaAttr);
+                _imFHXLinesMat = new T.ShaderMaterial({
+                    vertexShader: _imLinesVert, fragmentShader: _imLinesFrag,
+                    transparent: true, depthTest: false, depthWrite: false,
+                    fog: false, side: T.DoubleSide, forceSinglePass: true,
+                });
+                imFHXLines = new T.InstancedMesh(gFHXLines, _imFHXLinesMat, IM_STRUM_CAP);
+                imFHXLines.instanceMatrix.setUsage(T.DynamicDrawUsage);
+                imFHXLines.frustumCulled = false;
+                imFHXLines.renderOrder = 11;
+                _imColor.set(1, 1, 1);
+                imFHXLines.setColorAt(0, _imColor);
+                imFHXLines.instanceColor.setUsage(T.DynamicDrawUsage);
+                imFHXLines.count = 0;
+                noteG.add(imFHXLines);
+            }
+
+            // Pool-based strum-indicator replacements.  The IM approach above uses
+            // a fixed renderOrder per mesh type, which lets far-chord X marks overdraw
+            // gems/frames of nearer chords. Pools give per-chord Z-proportional renderOrder.
+            // Geometries are shared with the (now empty) IMs — MeshBasicMaterial
+            // ignores the instanceAlpha / instanceColor attributes on the geometry.
+            pPMXFill = pool(noteG, () => new T.Mesh(
+                gPMXFill,
+                new T.MeshBasicMaterial({
+                    color: 0x000000, transparent: true, opacity: 1,
+                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+            pFHXFill = pool(noteG, () => new T.Mesh(
+                gFHXFill,
+                new T.MeshBasicMaterial({
+                    color: 0x000000, transparent: true, opacity: 1,
+                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+            pMuteXLines = pool(noteG, () => new T.Mesh(
+                gPMXLines,
+                new T.MeshBasicMaterial({
+                    color: 0xffffff, transparent: true, opacity: 1,
+                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+            pFHXLines = pool(noteG, () => new T.Mesh(
+                gFHXLines,
+                new T.MeshBasicMaterial({
+                    color: 0xffffff, transparent: true, opacity: 1,
+                    depthWrite: false, depthTest: false, fog: false, side: T.DoubleSide, forceSinglePass: true,
+                }),
+            ));
+
+            pChordLbl   = pool(lblG,  () => new T.Sprite(txtMat('', '#e8d080', true, 'chord').clone()));
+            // Single shared barre material — all pool meshes reference it,
+            // so _applyGlow() can mutate emissiveIntensity once and every
+            // recycled / future-allocated barre mesh picks up the change.
+            mBarre = new T.MeshLambertMaterial({ color: 0xffffff, emissive: 0xffffff, emissiveIntensity: 0.9 * glowMul, transparent: true, depthWrite: false });
+            pBarreLine  = pool(noteG, () => new T.Mesh(new T.BoxGeometry(1, 1, 1), mBarre));
+            // Shared 1×1×1 box geometry — brackets can require many pooled
+            // meshes per frame, so per-mesh BoxGeometry allocation would
+            // duplicate buffers and create unnecessary GPU disposal work.
+            // Disposed once in teardown (alongside the other shared geos).
+            if (!gArpBracket) gArpBracket = new T.BoxGeometry(1, 1, 1);
+            pArpBracket = pool(noteG, () => new T.Mesh(
+                gArpBracket,
+                new T.MeshBasicMaterial({
+                    color: 0xffffff,
+                    transparent: true,
+                    opacity: 1.0,
+                    depthWrite: false,
+                    depthTest: false,
+                    fog: false,
+                }),
+            ));
+
+            // Per-note fret number below note with connector line
+            pNoteFretLabel = pool(lblG, () => {
+                const _nfl = new T.Sprite(txtMat('0', FRET_LABEL_GOLD_HEX, false, 'noteFret').clone());
+                _nfl.material.fog = false;
+                _nfl.material.depthTest = false;
+                return _nfl;
+            });
+            // Teaching marks fg/sd labels (§6.2.2). One pool, two get()s per note
+            // (finger + degree); the texture is swapped per draw via material.map.
+            pTeachMarkLbl = pool(lblG, () => {
+                const _tml = new T.Sprite(txtMat('0', '#7fd1ff', false, 'teachMark').clone());
+                _tml.material.fog = false;
+                _tml.material.depthTest = false;
+                return _tml;
+            });
+            pConnectorLine = pool(noteG, () => new T.Line(
+                new T.BufferGeometry().setFromPoints([new T.Vector3(0, 0, 0), new T.Vector3(0, 1, 0)]),
+                new T.LineBasicMaterial({ color: 0xaaaaaa, transparent: true, opacity: 0.5, depthTest: false }),
+            ));
+            pDropLine = pool(noteG, () => new T.Line(
+                new T.BufferGeometry().setFromPoints([new T.Vector3(0, 0, 0), new T.Vector3(0, 1, 0)]),
+                new T.LineBasicMaterial({ color: 0xffffff, transparent: true, opacity: 0.35 }),
+            ));
+
+            // Fret-column reference markers (visual cue for X-position to fret-number).
+            // Each sprite gets its own clone so the per-frame material.map swap
+            // (dark vs light grey) doesn't poison neighbours sharing the same
+            // cached texture map.
+            // fog:false prevents the scene fog from gradually dimming the sprite
+            // as it enters the far end of the highway — opacity is managed
+            // manually with a short fade-in so the number appears at its
+            // final size the moment it becomes visible rather than seeming to
+            // emerge from a tiny dim spec at the horizon.
+            pFretColMarker = pool(lblG, () => {
+                const _sp = new T.Sprite(txtMat('0', '#666666', false, 'noteFret').clone());
+                // fog=false: prevents scene fog from dimming the sprite as it enters the
+                // far end of the highway.  Opacity is managed by the manual fade-in ramp
+                // so the number appears smoothly instead of emerging as a dim spec.
+                _sp.material.fog = false;
+                return _sp;
+            });
+
+            // ── Pre-warm pools (feedBack#226) ─────────────────────────────
+            // Dense 7/8-string charts can outrun the lazy-grow path in the
+            // first 1-2s of playback, stalling those frames with `new T.Mesh`
+            // allocations *and* growing noteG forever (the pool only hides on
+            // reset). Pay the cost up front instead.
+            //
+            // Trade-off: pre-warming attaches the same meshes to noteG even
+            // on 4/6-string charts that may never use them all. The cost is
+            // paid at boardInit (during the load spinner — wall-clock time
+            // users were already waiting on), so the steady-state win on
+            // playback FPS is worth the init-time scene-graph footprint.
+            // Caps sized for a typical visible-window worst case (NOT the
+            // theoretical max across MAX_RENDER_STRINGS); lazy growth past
+            // the warm cap still works for genuinely dense outliers.
+            const _WARM_NOTE = 48;
+            const _WARM_CHORD = 12;
+            const _WARM_LANE = 32;
+            const _WARM_BEAT = 24;
+            pNote.warm(_WARM_NOTE);
+            pNoteEdge.warm(_WARM_NOTE);
+            pAccentHalo.warm(_WARM_NOTE);
+            pSus.warm(_WARM_NOTE);
+            pSusOutline.warm(_WARM_NOTE);
+            pSusRibbon.warm(_WARM_NOTE / 2);
+            pSusRibbonOl.warm(_WARM_NOTE / 2);
+            pTapChevron.warm(_WARM_CHORD);
+            pLbl.warm(_WARM_NOTE);
+            pSusRail.warm(_WARM_CHORD);
+            pSusRailBloom.warm(_WARM_CHORD);
+            pTechPlane.warm(_WARM_CHORD);
+            pNoteFretLabel.warm(_WARM_NOTE);
+            pTeachMarkLbl.warm(_WARM_NOTE);
+            pChordFrameFill.warm(_WARM_CHORD);
+            pChordBox.warm(_WARM_CHORD);
+            pChordLbl.warm(_WARM_CHORD);
+            pBarreLine.warm(_WARM_CHORD);
+            pArpBracket.warm(_WARM_CHORD);
+            pHaloBar.warm(_WARM_CHORD);
+            pFretLbl.warm(_WARM_LANE);
+            pLane.warm(_WARM_LANE * 2);  // anchor-driven lanes × time slices
+            pLaneDivider.warm(_WARM_LANE);
+            pGhostFretLbl.warm(_WARM_LANE);
+            pFretColMarker.warm(_WARM_LANE);
+            pConnectorLine.warm(_WARM_NOTE / 2);
+            pDropLine.warm(_WARM_NOTE / 2);
+            pBeat.warm(_WARM_BEAT);
+            pSec.warm(8);
+
+            _bgLoadSettings();
+            buildBoard();
+            // Apply the scene color theme now that settings + board exist. Sets
+            // the clear color + fog tint (board plane was themed in buildBoard).
+            // For the default theme this is identical to the hardcoded values
+            // initScene seeded above, so nothing changes for existing users.
+            _applyBgTheme();
+
+            // Background animations (#13). Read settings keyed by this
+            // panel and mount the active style's meshes. Subscribe to
+            // in-app settings changes (settings.html via window.h3dBgSet*)
+            // so they propagate without a reload. Manual localStorage
+            // edits don't fire the pub-sub and require a reload.
+            // Push the freshly-loaded vibrancy/glow values into the
+            // materials. _bgLoadSettings only triggers a palette re-apply
+            // when the palette ID actually changed, so a fresh-init user
+            // on the default palette would otherwise keep the hardcoded
+            // construction-time material values until they touched a
+            // slider.
+            _applyVibrancy();
+            _applyGlow();
+            // inlayLabelsVisible was applied before buildBoard() via _bgLoadSettings.
+            bgGroup = new T.Group();
+            // Note: renderOrder on a Group is a no-op (Three.js Groups
+            // are transforms, not rendered objects, so renderOrder only
+            // affects the actual meshes inside). _bgMountStyle stamps
+            // renderOrder = -1 on every child after build, which IS what
+            // forces background to render before gameplay geometry.
+            // Combined with the deeper-than-note-range placements below,
+            // background never paints over notes.
+            scene.add(bgGroup);
+            _bgMountStyle();
+            _bgListener = (changedKey) => {
+                if (changedKey === 'fretSpacing') {
+                    // _h3dFretUniform + the fretX-derived scalars were already
+                    // updated globally in h3dSetFretSpacing. Rebuild this
+                    // panel's static board geometry (fret wires, lanes, inlays)
+                    // so it re-lays-out for the new spacing; per-frame note
+                    // geometry reads fretX live and needs no rebuild.
+                    if (fretG) buildBoard();
+                    return;
+                }
+                if (changedKey === 'inlayLabelsVisible') {
+                    _bgLoadSettings();
+                    // Flip visibility on the already-built sprites; no
+                    // need to rebuild the board (cheaper, preserves the
+                    // shared materials and avoids palette re-apply churn).
+                    for (const lbl of _inlayLabels) lbl.visible = inlayLabelsVisible;
+                    return;
+                }
+                if (changedKey === 'nutHeadstockVisible') {
+                    _bgLoadSettings();
+                    if (nutHeadstockGroup) nutHeadstockGroup.visible = nutHeadstockVisible;
+                    return;
+                }
+                if (changedKey === 'tuningLabelsVisible') {
+                    _bgLoadSettings();
+                    _lastOpenStringLblSig = '';
+                    if (_tuningLabelSprites.length) _disposeOpenStringPitchSprites();
+                    return;
+                }
+                if (changedKey === 'nutColor' || changedKey === 'headstockColor') {
+                    _bgLoadSettings();
+                    if (fretG) buildBoard();
+                    for (const lbl of _inlayLabels) lbl.visible = inlayLabelsVisible;
+                    return;
+                }
+                if (changedKey === 'reactive' || changedKey === 'showFretOnNote' ||
+                    changedKey === 'fretNumberGhostScope' ||
+                    changedKey === 'cameraSmoothing' || changedKey === 'zoomSmoothing' ||
+                    changedKey === 'tiltSmoothing' || changedKey === 'cameraLockLow' ||
+                    changedKey === 'cameraLockZoom' || changedKey === 'cameraMode' ||
+                    changedKey === 'textSize' ||
+                    changedKey === 'chordDiagramSize' || changedKey === 'chordDiagramPosition' ||
+                    changedKey === 'fretColumnMarkerCadence' ||
+                    changedKey === 'sectionLabelsOnHighway' ||
+                    changedKey === 'sectionHudVisible' ||
+                    changedKey === 'sectionHudPosition' ||
+                    changedKey === 'sectionHudSize' ||
+                    changedKey === 'toneHudVisible' ||
+                    changedKey === 'toneHudPosition' ||
+                    changedKey === 'toneHudSize' ||
+                    changedKey === 'projectionVisible' ||
+                    changedKey === 'slideArrowApproachVisible' ||
+                    changedKey === 'slideArrowNeckVisible' ||
+                    changedKey === 'slideArrowChainPreviewVisible') {
+                    // Flag flips don't need a mesh rebuild — just refresh
+                    // the per-instance state for the next frame to consult.
+                    // Same shape for showFretOnNote (#12), cameraSmoothing
+                    // (#34), the zoom/tilt smoothing follow-ups, and
+                    // cameraLockLow — all read per-frame in update() /
+                    // camUpdate().
+                    _bgLoadSettings();
+                    return;
+                }
+                if (changedKey === 'vibrancy') {
+                    _bgLoadSettings();
+                    _applyVibrancy();
+                    return;
+                }
+                if (changedKey === 'glow') {
+                    _bgLoadSettings();
+                    _applyGlow();
+                    return;
+                }
+                if (changedKey === 'palette') {
+                    // Palette change has three effects:
+                    //  1. _bgLoadSettings -> _applyPaletteToMaterials
+                    //     retints the per-instance shared materials
+                    //     (notes, glows, sustain trails, projection).
+                    //  2. buildBoard rebuilds the fretboard meshes
+                    //     (LineBasicMaterial lane lines + per-string
+                    //     BoxGeometry materials). These are created at
+                    //     build time with palette-baked colors and
+                    //     aren't reachable from _applyPaletteToMaterials.
+                    //  3. lights bg style bakes palette colors into
+                    //     sprite quads at build time, so it needs a
+                    //     full mesh rebuild — fire _bgRebuild when
+                    //     that style is active.
+                    _bgLoadSettings();
+                    if (fretG) buildBoard();
+                    if (bgStyleId === 'lights') _bgRebuild();
+                    return;
+                }
+                if (changedKey === 'bgTheme' || changedKey === 'hwTheme') {
+                    // A scene-color axis changed (background = bgTheme:
+                    // clear+fog; highway = hwTheme: board plane + lane). Recolor
+                    // in place — no mesh rebuild needed (the board plane material
+                    // is mutated via _boardPlaneMat, the lane via mLaneOdd/Even).
+                    // _applyBgTheme reapplies both axes from their own keys, so
+                    // changing one dropdown retints only its half.
+                    _bgLoadSettings();
+                    _applyBgTheme();
+                    return;
+                }
+                if (changedKey === 'customImageDataUrl') {
+                    // Asset bytes changed. Rebuild only when the image
+                    // style is active — otherwise the new bytes will
+                    // pick up next time the user picks `image`.
+                    _bgLoadSettings();
+                    if (bgStyleId === 'image') _bgRebuild();
+                    return;
+                }
+                if (changedKey === 'customImageName') {
+                    // Display-only metadata; no mesh rebuild.
+                    _bgLoadSettings();
+                    return;
+                }
+                if (changedKey === 'customVideoName') {
+                    // Filename change → new <video> source. Rebuild
+                    // only when the video style is currently active;
+                    // otherwise the new bytes pick up next time the
+                    // user picks `video`.
+                    _bgLoadSettings();
+                    if (bgStyleId === 'video') _bgRebuild();
+                    return;
+                }
+                if (changedKey === 'intensity') {
+                    _bgLoadSettings();
+                    // Image style reads s.intensity per frame inside
+                    // update() to scale the drift speed, so a live
+                    // mutation is enough — no need to tear down and
+                    // re-decode the texture for every slider change.
+                    // The procedural styles bake intensity into mesh
+                    // count, opacity, and size at build time, so they
+                    // still need a full rebuild.
+                    if (bgStyleId === 'image' && bgState) {
+                        bgState.intensity = bgIntensity;
+                        return;
+                    }
+                    _bgRebuild();
+                    return;
+                }
+                if (changedKey === 'venueScene') {
+                    _bgRebuild();
+                    return;
+                }
+                if (changedKey === 'venueInstrumentPov') {
+                    if (_bgEffectiveStyleId() === 'venue' && bgState) {
+                        _venueSwapPlateIfNeeded(bgState);
+                    }
+                    return;
+                }
+                if (!changedKey || changedKey === 'style') {
+                    _bgRebuild();
+                }
+            };
+            _bgSubscribe(_bgListener);
+
+            // Notedetect feedback (#9). Listen for hit/miss events on
+            // window. Notedetect dispatches both globally and on its
+            // instanceRoot; the global fire is fine for our case since
+            // each 3dhighway panel just stores any event into its own
+            // queue and renders only the matching note. Listeners are
+            // per-panel so destroy() can cleanly remove them; cost is
+            // a per-event branch + push, negligible vs per-frame work.
+            // Validate every payload field we'll later compare against
+            // chart-data fields (s, f, t). drawNote compares with
+            // Math.abs(m.noteTime - n.t) and trusts the values are
+            // finite, so reject any payload missing one of those
+            // fields here rather than letting bogus data into the
+            // arrays. Prune expired marks on every push so the arrays
+            // settle back to empty when notedetect stops emitting —
+            // drawNote's fast-path short-circuit
+            // (`if (_ndHitMarks.length || _ndMissMarks.length)`) only
+            // works if expired entries don't linger.
+            const _ndNormalizeMark = (d) => {
+                if (!d) return null;
+                const note = d.note || d.chartNote;
+                if (!note) return null;
+                if (!Number.isFinite(note.s) || !Number.isFinite(note.f) || !Number.isFinite(d.noteTime)) return null;
+                const labels = [];
+                if (d.timingState && d.timingState !== 'OK' && Number.isFinite(d.timingError)) {
+                    labels.push({
+                        text: `${d.timingState === 'EARLY' ? '↑' : '↓'} ${d.timingError > 0 ? '+' : ''}${d.timingError}ms`,
+                        color: '#ffb347',
+                    });
+                }
+                if (d.pitchState && d.pitchState !== 'OK' && Number.isFinite(d.pitchError)) {
+                    labels.push({
+                        text: `${d.pitchState === 'SHARP' ? '♯' : '♭'} ${d.pitchError > 0 ? '+' : ''}${d.pitchError}¢`,
+                        color: '#66c7ff',
+                    });
+                }
+                return { s: note.s, f: note.f, noteTime: d.noteTime, labels, timingState: d.timingState || null };
+            };
+            const _ndPushMark = (arr, d) => {
+                const mark = _ndNormalizeMark(d);
+                if (!mark) return arr;
+                const now = performance.now();
+                // Prune expired entries unconditionally. The dedupe path
+                // below can extend expiresAt of any entry (including arr[0]),
+                // so an arr[0] gate is not reliable — it would prevent
+                // pruning entries that expired behind a refreshed front
+                // entry, allowing the array to grow unbounded. These arrays
+                // are tiny (a handful of marks at most), so an unconditional
+                // filter() is negligible and always correct.
+                if (arr.length !== 0) {
+                    const live = arr.filter(m => m.expiresAt > now);
+                    arr.length = 0;
+                    if (live.length) arr.push(...live);
+                }
+                const existing = arr.find(m =>
+                    m.s === mark.s && m.f === mark.f && Math.abs(m.noteTime - mark.noteTime) < _ND_TIME_EPS
+                );
+                if (existing) {
+                    existing.labels = mark.labels.length ? mark.labels : existing.labels;
+                    existing.expiresAt = Math.max(existing.expiresAt, now + _ND_TTL_MS);
+                    return arr;
+                }
+                arr.push({ ...mark, expiresAt: now + _ND_TTL_MS });
+                return arr;
+            };
+            _ndOnHit = (e) => { _ndHitMarks = _ndPushMark(_ndHitMarks, e.detail); };
+            _ndOnMiss = (e) => { _ndMissMarks = _ndPushMark(_ndMissMarks, e.detail); };
+            window.addEventListener('notedetect:hit', _ndOnHit);
+            window.addEventListener('notedetect:miss', _ndOnMiss);
+            if (window.feedBack &&
+                    typeof window.feedBack.on  === 'function' &&
+                    typeof window.feedBack.off === 'function') {
+                _ndOnBusHit  = (e) => { _ndHitMarks  = _ndPushMark(_ndHitMarks,  e.detail); };
+                _ndOnBusMiss = (e) => { _ndMissMarks = _ndPushMark(_ndMissMarks, e.detail); };
+                window.feedBack.on('note:hit', _ndOnBusHit);
+                window.feedBack.on('note:miss', _ndOnBusMiss);
+            }
+
+            // Score FX (notedetect ≥1.13). notedetect dispatches each fx
+            // detail object twice in the same task: first explicitly on
+            // window (unscoped), then as a bubbling CustomEvent from its
+            // per-panel instanceRoot (scoped). Element-targeted copies are
+            // authoritative — accept only the ones whose root lives in this
+            // panel's container. The window copy is DEFERRED a task: by the
+            // time it runs, the element copy (same detail reference) has
+            // either arrived — making the window copy a duplicate to drop —
+            // or it never will (detector root not attached to the DOM), in
+            // which case the window copy is the compat fallback. This keeps
+            // splitscreen panels from rendering each other's FX even for
+            // the first event of a session.
+            _fxResolvePalette();
+            _fxOnFx = (e) => {
+                const d = e && e.detail;
+                if (!d) return;
+                const t = e.target;
+                if (t && t.parentElement) {
+                    _fxElemSeen.add(d);
+                    if (!highwayCanvas || !t.parentElement.contains(highwayCanvas)) return;
+                    _fxHandle(d);
+                    return;
+                }
+                const gen = _fxGen;
+                setTimeout(() => {
+                    if (gen !== _fxGen) return;   // torn down (or re-inited) meanwhile
+                    if (_fxElemSeen.has(d)) return;
+                    _fxHandle(d);
+                }, 0);
+            };
+            window.addEventListener('notedetect:fx', _fxOnFx);
+            if (window.feedBack && typeof window.feedBack.on === 'function'
+                    && typeof window.feedBack.off === 'function') {
+                _fxOnSkin = () => _fxResolvePalette();
+                window.feedBack.on('notedetect:skin', _fxOnSkin);
+            }
+
+            return true;
+        }
+
+        function _bgLoadSettings() {
+            const panelKey = _bgPanelKey(highwayCanvas);
+            bgStyleId = _bgReadSetting(panelKey, 'style');
+            bgIntensity = _bgReadSetting(panelKey, 'intensity');
+            bgReactive = _bgReadSetting(panelKey, 'reactive');
+            // Per-render opt-out (captured from the mount bundle in init): force
+            // the reactive background off for THIS instance, overriding the shared
+            // setting without writing it back. Re-applied here so it sticks across
+            // setting reloads.
+            if (_bgReactiveOptOut) bgReactive = false;
+            if (bgStyleId === 'butterchurn') bgReactive = false; // Butterchurn owns the <audio> tap
+            const newPaletteId = _bgReadSetting(panelKey, 'palette');
+            let newPalette;
+            if (newPaletteId === 'custom') {
+                // Resolve user colors into the stable _customPalette array,
+                // mutated in place so the reference identity is preserved.
+                let stored = null;
+                const raw = _bgReadSetting(panelKey, 'customColors');
+                if (typeof raw === 'string') { try { stored = JSON.parse(raw); } catch (_) { /* corrupt */ } }
+                for (let i = 0; i < _customPalette.length; i++) {
+                    const v = Array.isArray(stored) ? _h3dHexToInt(stored[i]) : null;
+                    _customPalette[i] = (v != null) ? v : PALETTES.default[i];
+                }
+                newPalette = _customPalette;
+            } else {
+                newPalette = PALETTES[newPaletteId] || PALETTES.default;
+            }
+            // Signature guards the in-place custom case: when the user edits a
+            // color the reference stays === activePalette, so compare contents
+            // too to force a retint. _bgPaletteSig caches the applied colors.
+            const newSig = newPalette.join(',');
+            if (newPalette !== activePalette || newSig !== _bgPaletteSig) {
+                activePalette = newPalette;
+                _bgPaletteSig = newSig;
+                _applyPaletteToMaterials();
+            }
+            bgThemeId = _bgReadSetting(panelKey, 'bgTheme');
+            // Highway axis. ONE-TIME BACKWARD-COMPAT BACKFILL: the first time we
+            // load with no stored hwTheme (pre-split installs, or anyone who only
+            // ever touched the old single "Scene colors" control), seed hwTheme
+            // FROM the background pick AND PERSIST it, so an existing 'cathode'
+            // selection looks byte-identical right after the upgrade. Persisting
+            // immediately (rather than re-inheriting on every read) is what keeps
+            // the two axes truly INDEPENDENT thereafter: once hwTheme is stored,
+            // changing the Background dropdown no longer drags the Highway
+            // surface along, and the settings UI's Highway value can never
+            // disagree with what's rendered. Written without _bgEmitChange so the
+            // backfill can't re-enter the change listener.
+            if (_bgHasStored(panelKey, 'hwTheme')) {
+                hwThemeId = _bgReadSetting(panelKey, 'hwTheme');
+            } else {
+                hwThemeId = bgThemeId;
+                _bgMemFallback.hwTheme = String(bgThemeId);
+                try { localStorage.setItem('h3d_bg_hwTheme', String(bgThemeId)); } catch (_) { /* storage blocked — mem fallback still seeds the read */ }
+            }
+            showFretOnNote = _bgReadSetting(panelKey, 'showFretOnNote');
+            fretNumberGhostScope = _bgReadSetting(panelKey, 'fretNumberGhostScope');
+            cameraSmoothing = _bgReadSetting(panelKey, 'cameraSmoothing');
+            // Mirror-at-first-read: zoom + tilt sliders inherit cameraSmoothing
+            // when the user has never explicitly written them. Once the user
+            // moves either slider, the corresponding _bgHasStored() flips
+            // true and the read becomes independent.
+            zoomSmoothing = _bgHasStored(panelKey, 'zoomSmoothing')
+                ? _bgReadSetting(panelKey, 'zoomSmoothing')
+                : cameraSmoothing;
+            tiltSmoothing = _bgHasStored(panelKey, 'tiltSmoothing')
+                ? _bgReadSetting(panelKey, 'tiltSmoothing')
+                : cameraSmoothing;
+            cameraLockLow = _bgReadSetting(panelKey, 'cameraLockLow');
+            cameraLockZoom = _bgReadSetting(panelKey, 'cameraLockZoom');
+            cameraMode = _bgReadSetting(panelKey, 'cameraMode');
+            textSize             = _bgReadSetting(panelKey, 'textSize');
+            vibrancy             = _bgReadSetting(panelKey, 'vibrancy');
+            glowMul              = _bgReadSetting(panelKey, 'glow');
+            _hitFx               = _bgReadSetting(panelKey, 'hitFx');
+            _sparks              = _bgReadSetting(panelKey, 'sparks');
+            _cinematic           = _bgReadSetting(panelKey, 'cinematic');
+            _verdictMarks        = _bgReadSetting(panelKey, 'verdictMarks');
+            _timingFx            = _bgReadSetting(panelKey, 'timingFx');
+            _streakFx            = _bgReadSetting(panelKey, 'streakFx');
+            _bloom               = _bgReadSetting(panelKey, 'bloom');
+            _applyCinematic();
+            fpsVisible           = _bgReadSetting(panelKey, 'fpsVisible');
+            fretDividersVisible  = _bgReadSetting(panelKey, 'fretDividersVisible');
+            chordDiagramVisible  = _bgReadSetting(panelKey, 'chordDiagramVisible');
+            chordDiagramSize     = _bgReadSetting(panelKey, 'chordDiagramSize');
+            chordDiagramPosition = _bgReadSetting(panelKey, 'chordDiagramPosition');
+            fretColumnMarkerCadence = _bgReadSetting(panelKey, 'fretColumnMarkerCadence');
+            inlayLabelsVisible = _bgReadSetting(panelKey, 'inlayLabelsVisible');
+            sectionLabelsOnHighway = _bgReadSetting(panelKey, 'sectionLabelsOnHighway');
+            sectionHudVisible      = _bgReadSetting(panelKey, 'sectionHudVisible');
+            sectionHudPosition     = _bgReadSetting(panelKey, 'sectionHudPosition');
+            sectionHudSize         = _bgReadSetting(panelKey, 'sectionHudSize');
+            toneHudVisible         = _bgReadSetting(panelKey, 'toneHudVisible');
+            toneHudPosition        = _bgReadSetting(panelKey, 'toneHudPosition');
+            toneHudSize            = _bgReadSetting(panelKey, 'toneHudSize');
+            nutHeadstockVisible    = _bgReadSetting(panelKey, 'nutHeadstockVisible');
+            tuningLabelsVisible    = _bgReadSetting(panelKey, 'tuningLabelsVisible');
+            nutColor               = _bgReadSetting(panelKey, 'nutColor');
+            headstockColor         = _bgReadSetting(panelKey, 'headstockColor');
+            projectionVisible      = _bgReadSetting(panelKey, 'projectionVisible');
+            slideArrowApproachVisible = _bgReadSetting(panelKey, 'slideArrowApproachVisible');
+            slideArrowNeckVisible     = _bgReadSetting(panelKey, 'slideArrowNeckVisible');
+            slideArrowChainPreviewVisible = _bgReadSetting(panelKey, 'slideArrowChainPreviewVisible');
+            _vibrancyIdleOp = 0.4  + 0.6  * vibrancy;
+            _vibrancyProjOp = 0.15 + 0.35 * vibrancy;
+            // Custom image asset is a single GLOBAL slot — bytes are
+            // shared across panels (per-panel choice is which style
+            // each panel renders, not which asset). Reading via
+            // _bgReadSetting would let a stray h3d_bg_panel<idx>_*
+            // override silently re-introduce the per-panel asset
+            // duplication this design deliberately avoids (and
+            // h3dBgClearCustomImage wouldn't reach those overrides).
+            // Read globals directly instead.
+            //
+            // Precedence: in-memory fallback BEFORE localStorage. The
+            // setter always populates _bgMemFallback (even when the
+            // localStorage write fails on quota), so the fallback
+            // holds the most-recent staged value. Reading localStorage
+            // first would mean a failed write leaves the renderer
+            // pointed at the previous asset while settings.html shows
+            // a "session-only" warning claiming the new bytes are in
+            // effect — UI and renderer would silently disagree.
+            const memDataUrl = _bgMemFallback.customImageDataUrl;
+            const memName    = _bgMemFallback.customImageName;
+            try {
+                const gDataUrl = (memDataUrl !== undefined) ? memDataUrl : localStorage.getItem('h3d_bg_customImageDataUrl');
+                const gName    = (memName    !== undefined) ? memName    : localStorage.getItem('h3d_bg_customImageName');
+                bgCustomImageDataUrl = (gDataUrl != null) ? gDataUrl : BG_DEFAULTS.customImageDataUrl;
+                bgCustomImageName    = (gName    != null) ? gName    : BG_DEFAULTS.customImageName;
+            } catch (_) {
+                bgCustomImageDataUrl = (memDataUrl !== undefined) ? memDataUrl : BG_DEFAULTS.customImageDataUrl;
+                bgCustomImageName    = (memName    !== undefined) ? memName    : BG_DEFAULTS.customImageName;
+            }
+            // Custom video filename: also a single global slot, same
+            // mem-first precedence as the image keys (a quota-failed
+            // setItem leaves _bgMemFallback ahead of localStorage).
+            const memVideoName = _bgMemFallback.customVideoName;
+            try {
+                const gVideoName = (memVideoName !== undefined) ? memVideoName : localStorage.getItem('h3d_bg_customVideoName');
+                bgCustomVideoName = (gVideoName != null) ? gVideoName : BG_DEFAULTS.customVideoName;
+            } catch (_) {
+                bgCustomVideoName = (memVideoName !== undefined) ? memVideoName : BG_DEFAULTS.customVideoName;
+            }
+        }
+        // Live-swap palette by mutating existing materials in place.
+        // Three.js colors propagate to all sharing meshes on the next
+        // render — no rebuild, no GC. The mGlow material was authored
+        // with .color = white and the per-string color in .emissive
+        // only; we preserve that here so the glow look stays consistent
+        // before/after a palette swap rather than tinting the diffuse
+        // white. Lane lines and drop lines that read
+        // activePalette[s] per frame pick up automatically. Per-string
+        // fretboard materials built inside buildBoard() are independent
+        // and aren't reachable from here — buildBoard re-runs from the
+        // palette listener to regenerate them with the new colors.
+        //
+        // projMeshArr holds filled rim meshes (ExtrudeGeometry frame); centre
+        // is open. Palette + vibrancy mutate each mesh's material like mStr.
+        function _applyPaletteToMaterials() {
+            for (let s = 0; s < activePalette.length; s++) {
+                const c = activePalette[s];
+                if (mStr[s]) {
+                    // Gradient strings (0..5) keep a white base so the per-vertex
+                    // colours in gNoteGrad[s] show pure; only flat strings (6/7)
+                    // take the palette colour. mStr is MeshBasicMaterial (no
+                    // emissive) — guard the legacy emissive retint.
+                    if (s >= 6) mStr[s].color.setHex(c);
+                    if (mStr[s].emissive) mStr[s].emissive.setHex(c);
+                }
+                if (mGlow[s]) mGlow[s].emissive.setHex(c);
+                if (mRimFlash[s]) {
+                    mRimFlash[s].color.setHex(c);
+                    mRimFlash[s].emissive.setHex(c);
+                }
+                if (mSus[s]) mSus[s].color.setHex(c);
+                if (mStrHitOutline[s]) {
+                    mStrHitOutline[s].color.setHex(c);
+                    mStrHitOutline[s].emissive.setHex(c);
+                }
+                if (mAccentOutline[s]) {
+                    mAccentOutline[s].color.setHex(c);
+                    mAccentOutline[s].emissive.setHex(c);
+                }
+                if (mAccentCore[s]) mAccentCore[s].emissive.setHex(c);
+                // Verdict materials use fixed colours (0x22ff88 hit, 0xff0066 miss)
+                // that are independent of the string palette — no retint needed.
+                for (const haloArr of [mAccentHaloNear, mAccentHaloMid, mAccentHaloFar]) {
+                    if (haloArr[s]) haloArr[s].color.setHex(c);
+                }
+                if (projMeshArr && projMeshArr[s]) {
+                    for (const pm of projMeshArr[s]) {
+                        if (pm.material) {
+                            pm.material.color.setHex(c);
+                            pm.material.emissive.setHex(c);
+                        }
+                    }
+                }
+            }
+            // Per-string gem bodies (strings 0..5) are a baked per-vertex
+            // gradient (gNoteGrad), not a flat material — recolor them too so a
+            // custom palette reaches the note/sustain/vibrato gem bodies.
+            _recolorGemGradients();
+            // Re-apply vibrancy: mGlow's color is a lerp between white and
+            // the palette colour, so a palette swap must rebuild that
+            // lerp from the new endpoints. Skipped pre-init when mGlow
+            // isn't allocated yet — _applyVibrancy() guards on that.
+            _applyVibrancy();
+        }
+
+        // Recompute the per-vertex gem-gradient colors from the active palette.
+        // Built-in palettes (and unchanged slots of a custom palette) keep the
+        // hand-tuned DEFAULT_GEM_GRADIENTS stops so the stock look is preserved;
+        // a custom slot derives a top-highlight / bottom-shade from its base
+        // color. Mutates the existing 'color' attribute in place (no geometry
+        // churn, pooled note meshes pick it up next frame).
+        function _recolorGemGradients() {
+            if (!T || !gNoteGrad || !gNoteGrad.length) return;
+            const isCustom = (activePalette === _customPalette);
+            const topCol = new T.Color(), botCol = new T.Color(), tmp = new T.Color();
+            const halfH = NH / 2;
+            for (let s = 0; s < gNoteGrad.length; s++) {
+                const g = gNoteGrad[s];
+                if (!g || !g.attributes || !g.attributes.color) continue;
+                const base = activePalette[s];
+                let topHex, botHex;
+                if (isCustom && base !== PALETTES.default[s]) {
+                    // Match the SUBTLE stock gem shading (bottom ≈ 0.78 of a
+                    // near-base top), so a custom gem reads as a flat-ish gem
+                    // in the chosen color rather than a strong gradient.
+                    topHex = _lightenInt(base, 0.05);
+                    botHex = _darkenInt(base, 0.78);
+                } else {
+                    const stops = DEFAULT_GEM_GRADIENTS[s];
+                    if (!stops) continue; // strings 6/7 have no gradient geometry
+                    topHex = stops[0];
+                    botHex = stops[1];
+                }
+                topCol.setHex(topHex);
+                botCol.setHex(botHex);
+                const pos = g.attributes.position;
+                const colAttr = g.attributes.color;
+                for (let i = 0; i < pos.count; i++) {
+                    const t = (pos.getY(i) + halfH) / (2 * halfH); // 0 bottom..1 top
+                    tmp.copy(botCol).lerp(topCol, t);
+                    colAttr.setXYZ(i, tmp.r, tmp.g, tmp.b);
+                }
+                colAttr.needsUpdate = true;
+            }
+        }
+
+        // Vibrancy + glow live-update helpers. Both walk the same
+        // material set _applyPaletteToMaterials walks (plus the static
+        // outline / technique materials) and mutate uniform-backed
+        // properties — colour, opacity, emissiveIntensity. No
+        // material.needsUpdate flag is needed for these; Three.js
+        // re-reads them on the next render call. mGlow.emissiveIntensity
+        // and BASE_GLOW/MAX_GLOW/IDLE_OP are NOT written here — those
+        // are stomped per-frame inside updateStringHighlights() and the
+        // anticipation loop in update(), so they read glowMul /
+        // _vibrancyIdleOp / vibrancy directly each frame instead.
+        function _applyVibrancy() {
+            const t = vibrancy;
+            const idleOp     = 0.4  + 0.6  * t;  // mStr / IDLE_OP source
+            // projIdleOp drives the projMeshArr ghost-frame opacity and is
+            // read by drawNote() as `_vibrancyProjOp`, which layers a
+            // per-frame factor on top.
+            const projIdleOp = 0.15 + 0.35 * t;
+            const susOp      = 0.35 + 0.45 * t;  // mSus
+            const lineGlowOp = 0.15 + 0.35 * t;  // thin Line glow layer behind each string
+            for (let s = 0; s < activePalette.length; s++) {
+                if (mStr[s])  mStr[s].opacity  = idleOp;
+                if (mSus[s])  mSus[s].opacity  = susOp;
+                if (mGlow[s]) {
+                    // Hit-note body lerps from white (current pastel
+                    // look — colour comes through the emissive only)
+                    // toward the palette colour as vibrancy → 1, so at
+                    // vibrancy=1 the white-wash on hit notes goes away.
+                    if (!_paletteColorTmp && T) _paletteColorTmp = new T.Color();
+                    if (_paletteColorTmp) {
+                        mGlow[s].color.setHex(0xffffff).lerp(_paletteColorTmp.setHex(activePalette[s]), t);
+                    }
+                }
+                if (mAccentCore[s]) {
+                    if (!_paletteColorTmp && T) _paletteColorTmp = new T.Color();
+                    if (_paletteColorTmp) {
+                        mAccentCore[s].color.setHex(0xffffff).lerp(_paletteColorTmp.setHex(activePalette[s]), t);
+                    }
+                }
+                if (projMeshArr && projMeshArr[s]) {
+                    for (const pm of projMeshArr[s]) {
+                        if (pm.material) pm.material.opacity = projIdleOp;
+                    }
+                }
+            }
+            // stringLines[s].material.opacity is overwritten by
+            // updateStringHighlights() every frame, so the closed-form
+            // value would be stomped. updateStringHighlights() reads
+            // _vibrancyIdleOp directly instead — keep that in sync.
+            for (let s = 0; s < stringLineGlows.length; s++) {
+                const line = stringLineGlows[s];
+                if (line && line.material) line.material.opacity = lineGlowOp;
+            }
+            _vibrancyIdleOp = idleOp;
+            _vibrancyProjOp = projIdleOp;
+        }
+        function _applyGlow() {
+            const g = glowMul;
+            for (let s = 0; s < activePalette.length; s++) {
+                if (mStr[s])  mStr[s].emissiveIntensity  = 0.002 * g;
+                // mGlow[s].emissiveIntensity is per-frame in update();
+                // see Phase 4 comment block.
+                if (projMeshArr && projMeshArr[s]) {
+                    for (const pm of projMeshArr[s]) {
+                        if (pm.material) pm.material.emissiveIntensity = 0.002 * g;
+                    }
+                }
+                if (mStrHitOutline[s]) mStrHitOutline[s].emissiveIntensity = 1.0 * g;
+                if (mAccentOutline[s]) mAccentOutline[s].emissiveIntensity = ACCENT_RIM_BASE_EMISSIVE * g;
+                // mAccentCore[].emissiveIntensity is per-frame in update()
+                // alongside mGlow (accent fill boost).
+            }
+            if (mWhiteOutline) mWhiteOutline.emissiveIntensity = 0.6 * g;
+            if (mMissOutline)  mMissOutline.emissiveIntensity  = 1.2 * g;
+            for (let s = 0; s < mHitBright.length; s++) {
+                if (mHitBright[s]) mHitBright[s].emissiveIntensity = 4.0 * g;
+            }
+            if (mSusOutline)      mSusOutline.emissiveIntensity      = 0.3 * g;
+            if (mHitSusOutline)   mHitSusOutline.emissiveIntensity   = 0.7 * g;
+            if (mTapChevron)   mTapChevron.emissiveIntensity   = 0.9 * g;
+            if (mBarre)        mBarre.emissiveIntensity        = 0.9 * g;
+            for (let si = 0; si < activePalette.length; si++) {
+                if (mAccentHaloNear[si]) mAccentHaloNear[si].opacity = ACCENT_HALO_OP_NEAR * g;
+                if (mAccentHaloMid[si]) mAccentHaloMid[si].opacity = ACCENT_HALO_OP_MID * g;
+                if (mAccentHaloFar[si]) mAccentHaloFar[si].opacity = ACCENT_HALO_OP_FAR * g;
+            }
+        }
+        function _bgEffectiveStyleId() {
+            return _venueSceneOverride ? 'venue' : bgStyleId;
+        }
+        // The 'butterchurn' bg-style renders a WebGL MilkDrop canvas BEHIND a
+        // transparent highway via the self-contained _bc* controller (top of file),
+        // NOT a Three.js fog-scenery style (its scenery falls back to 'off'). Mount
+        // is idempotent and driven by the bg-style dropdown through _bgMountStyle.
+        function _bcActive() { return bgStyleId === 'butterchurn'; }
+        function _bcSyncMode() {
+            if (_bcActive()) {
+                // Recreate when there's no controller, or the last one died during
+                // async init (lib/WebGL failure) — a dead controller self-cleaned,
+                // so retry here instead of leaving the style permanently broken.
+                if ((!bcCtrl || (bcCtrl.dead && bcCtrl.dead())) && wrap) {
+                    if (bcCtrl) bcCtrl = null;
+                    // audioProvider reuses this instance's shared analyser (the
+                    // fog scenery's #audio / stems tap) so the browser path never
+                    // opens a second createMediaElementSource on #audio.
+                    try { bcCtrl = _bcCreateController(wrap, () => canvasSize(highwayCanvas), () => { try { return _bgGetAnalyser(); } catch (e) { return null; } }); }
+                    catch (e) { console.warn('[3D-Hwy] Butterchurn init failed', e); }
+                }
+                if (ren) ren.setClearColor(0x101820, 0); // transparent so the visualizer shows through
+            } else if (bcCtrl) {
+                try { bcCtrl.destroy(); } catch (e) {}
+                bcCtrl = null;
+                _applyBgTheme(); // restore the opaque themed clear
+            }
+        }
+        function _bgMountStyle() {
+            const effectiveId = _bgEffectiveStyleId();
+            const style = BG_STYLES[effectiveId] || BG_STYLES.off;
+            // Build into a fresh stage group so a partial throw can't
+            // orphan meshes inside bgGroup. On success the stage joins
+            // bgGroup atomically; on failure the stage and everything
+            // in it are disposed and bgState stays null.
+            const stage = new T.Group();
+            let result = null;
+            try {
+                result = style.build(stage, {
+                    intensity: bgIntensity,
+                    palette: activePalette,
+                    customImageDataUrl: bgCustomImageDataUrl,
+                    customVideoName: bgCustomVideoName,
+                    cam: cam,
+                }) || null;
+            } catch (e) {
+                console.error('[3D-Hwy] bg style build failed', effectiveId, e);
+                _bgDisposeGroupTree(stage);
+                bgState = null;
+                bgStage = null;
+                bgMountedStyleId = null;
+                return;
+            }
+            // renderOrder on a Group doesn't propagate to its children
+            // (Three.js sorts by per-object renderOrder, and a Group is a
+            // transform, not a rendered object). Stamp every mesh in the
+            // stage so transparent bg objects always sort behind notes
+            // regardless of their z relative to gameplay geometry.
+            stage.traverse((c) => { c.renderOrder = -1; });
+            bgGroup.add(stage);
+            bgStage = stage;
+            bgState = result;
+            bgMountedStyleId = effectiveId;
+            _bcSyncMode();
+        }
+        function _bgUnmountStyle() {
+            const mountedId = bgMountedStyleId || _bgEffectiveStyleId();
+            const style = BG_STYLES[mountedId] || BG_STYLES.off;
+            try { style.teardown(bgState); } catch (e) { console.error('[3D-Hwy] bg teardown', e); }
+            bgState = null;
+            // Belt + suspenders: even if a style's teardown forgets to
+            // dispose something, the stage tree dispose mops up.
+            if (bgStage) {
+                bgStage.parent?.remove(bgStage);
+                _bgDisposeGroupTree(bgStage);
+                bgStage = null;
+            }
+            bgMountedStyleId = null;
+        }
+        // Recursively dispose geometries / materials attached to an
+        // Object3D tree, then detach. Used as a safety net during
+        // _bgMountStyle failures and on _bgUnmountStyle.
+        //
+        // Deliberately does NOT dispose material.map textures — texture
+        // lifetime belongs to whoever allocated the texture. The
+        // silhouettes style allocates a per-layer CanvasTexture wrapping
+        // the shared _silCanvas bitmap, and disposes those textures in
+        // its own teardown. Disposing them here would double-dispose,
+        // and any future plugin texture sharing across panels (e.g. an
+        // upcoming custom-background feature) would break the same way.
+        // Style teardown owns texture release.
+        function _bgDisposeGroupTree(obj) {
+            if (!obj) return;
+            obj.traverse((child) => {
+                child.geometry?.dispose?.();
+                const mat = child.material;
+                if (mat) {
+                    const mats = Array.isArray(mat) ? mat : [mat];
+                    for (const m of mats) m?.dispose?.();
+                }
+            });
+            obj.parent?.remove(obj);
+        }
+        function _bgRebuild() {
+            if (!bgGroup) return;
+            // Order matters: teardown must run against the (style id,
+            // state) pair that built the meshes, so unmount BEFORE
+            // reloading settings. Reload, then mount with the new id.
+            _bgUnmountStyle();
+            _bgLoadSettings();
+            _bgMountStyle();
+            _bgApplyVenueSceneFog(_venueSceneOverride);
+            // Reset dt accounting so the first frame after a switch
+            // doesn't see a huge "since last update" window — that
+            // would clamp to 0.1 and visibly snap motion / rotation.
+            _bgLastT = 0;
+        }
+        // Venue-only fog/clear/ambient tuning — darker near field, less
+        // washed-out gray haze over the playable highway. Restored when
+        // venue deactivates.
+        function _bgApplyVenueSceneFog(active) {
+            if (!scene || !scene.fog) return;
+            if (active) {
+                scene.fog.color.setHex(0x080c12);
+                scene.fog.near = FOG_START * 0.98;
+                scene.fog.far = FOG_END * 0.98;
+                // Keep the clear transparent while Butterchurn is active so the
+                // venue scene doesn't occlude the visualizer behind the highway.
+                if (ren) ren.setClearColor(0x080c12, _bcActive() ? 0 : 1);
+                if (ambLight) ambLight.intensity = 0.68;
+            } else {
+                // Restore the user's scene-color theme (clear + fog) rather than
+                // the old hardcoded gray, so deactivating venue doesn't wipe a
+                // chosen background theme. _applyBgTheme reads the current theme.
+                scene.fog.near = FOG_START * 0.8;
+                scene.fog.far = FOG_END * 1.2;
+                if (ambLight) ambLight.intensity = 0.85;
+                _applyBgTheme();
+            }
+        }
+
+        // Apply BOTH scene-color axes, each from its own setting key:
+        //   • BACKGROUND (bgThemeId): the WebGL clear color + the distance-fog
+        //     tint. Skipped while the venue scene is active (venue owns those —
+        //     see _bgApplyVenueSceneFog).
+        //   • HIGHWAY (hwThemeId): the fretboard/highway-surface plane + the lit
+        //     highway lane strip (the bright quad under the gems) + its dimmer
+        //     alternating row. Always themed; venue doesn't touch them.
+        // The two axes are independent, so picking a different id in each mixes
+        // freely. Safe to call any time; called from initScene, buildBoard, and
+        // the scene-theme listener (so a live switch of EITHER dropdown retints
+        // only its half immediately).
+        //
+        // The lane fields are OPTIONAL on a highway theme: one that omits `lane`
+        // / `laneDim` falls back to the stock lit/dim lane hexes, so every
+        // existing/neutral highway theme stays byte-identical (default blue lane
+        // unchanged). Only colored highway themes opt into a coordinated lane.
+        function _applyBgTheme() {
+            // --- Background axis: clear + fog ---
+            const bg = _bgBackgroundColors(bgThemeId);
+            if (!_venueSceneOverride) {
+                if (scene && scene.fog) scene.fog.color.setHex(bg.fog);
+                if (ren) ren.setClearColor(bg.clear, _bcActive() ? 0 : 1);
+            }
+            // --- Highway axis: board plane + lane ---
+            const hw = _bgHighwayColors(hwThemeId);
+            if (_boardPlaneMat) _boardPlaneMat.color.setHex(hw.board);
+            // Lit lane strip + its dimmer alternating row. Fall back to the
+            // hardcoded stock lane colors when the highway theme omits them.
+            const laneLit = (typeof hw.lane === 'number') ? hw.lane : HWY_LANE_STRIPE_ODD_HEX;
+            const laneDim = (typeof hw.laneDim === 'number') ? hw.laneDim : HWY_LANE_STRIPE_EVEN_HEX;
+            if (mLaneOdd) mLaneOdd.color.setHex(laneLit);
+            if (mLaneEven) mLaneEven.color.setHex(laneDim);
+            // Keep the (otherwise vestigial) lane target color in sync with the
+            // lit lane so any future lane-blend consumer reads the themed value.
+            if (_laneTargetColor) _laneTargetColor.setHex(laneLit);
+            else _laneTargetColor = new T.Color(laneLit);
+        }
+
+        /* ── Fretboard (static geometry) ────────────────────────────────── */
+        function _h3dHexOrDefault(hexStr, defHex) {
+            const d = defHex || BG_DEFAULTS.nutColor;
+            const s = (typeof hexStr === 'string' && /^#[0-9a-fA-F]{6}$/.test(hexStr.trim()))
+                ? hexStr.trim().toLowerCase()
+                : d;
+            return parseInt(s.slice(1), 16);
+        }
+        // Cinematic lighting (#2): darken ambient so emissive gems have a dark
+        // surround to pop against; strengthen the key light for modelling.
+        // Toggle via the 'cinematic' setting so it's directly comparable.
+        function _applyCinematic() {
+            if (!ambLight || !dirLight) return;
+            ambLight.intensity = _cinematic ? 0.45 : 0.85;
+            dirLight.intensity = _cinematic ? 1.15 : 0.8;
+        }
+        // #5 early/late: tint the hit feedback by timing — on-time green, early cyan,
+        // late amber. Falls back to green when timing is unknown (pure-provider path).
+        function _timingHex(ts) {
+            if (!_timingFx || !ts || ts === 'OK') return 0x22ff88;
+            if (ts === 'EARLY') return 0x35d6ff;
+            if (ts === 'LATE')  return 0xffb84d;
+            return 0x22ff88;
+        }
+        function _sparkBurst(x, y, z, hex, count) {
+            if (!_sparkPts || count <= 0) return;
+            const r = ((hex >> 16) & 255) / 255, g = ((hex >> 8) & 255) / 255, b = (hex & 255) / 255;
+            let made = 0;
+            for (let i = 0; i < _SPARK_N && made < count; i++) {
+                if (_sparkLife[i] > 0) continue;
+                const j = i * 3, ang = Math.random() * Math.PI * 2, sp = (5 + Math.random() * 12) * K;
+                _sparkPos[j] = x; _sparkPos[j + 1] = y; _sparkPos[j + 2] = z;
+                _sparkVel[j] = Math.cos(ang) * sp; _sparkVel[j + 1] = (12 + Math.random() * 24) * K; _sparkVel[j + 2] = Math.sin(ang) * sp * 0.55;
+                _sparkCol[j] = r; _sparkCol[j + 1] = g; _sparkCol[j + 2] = b;
+                _sparkLife[i] = 0.30 + Math.random() * 0.16; made++;
+            }
+        }
+        function _sparkUpdate(dt) {
+            if (!_sparkPts) return;
+            const grav = 55 * K; let any = false;
+            for (let i = 0; i < _SPARK_N; i++) {
+                if (_sparkLife[i] <= 0) continue;
+                const j = i * 3;
+                _sparkLife[i] -= dt;
+                if (_sparkLife[i] <= 0) { _sparkCol[j] = _sparkCol[j + 1] = _sparkCol[j + 2] = 0; continue; }
+                any = true;
+                _sparkVel[j + 1] -= grav * dt;
+                _sparkPos[j] += _sparkVel[j] * dt; _sparkPos[j + 1] += _sparkVel[j + 1] * dt; _sparkPos[j + 2] += _sparkVel[j + 2] * dt;
+                const fade = 1 - Math.min(1, dt * 3.2);
+                _sparkCol[j] *= fade; _sparkCol[j + 1] *= fade; _sparkCol[j + 2] *= fade;
+            }
+            _sparkPts.geometry.attributes.position.needsUpdate = true;
+            _sparkPts.geometry.attributes.color.needsUpdate = true;
+            _sparkPts.visible = any;
+        }
+        // #4 Bloom: lazy-load the vendored postprocessing addons and build an
+        // EffectComposer (RenderPass -> UnrealBloomPass -> OutputPass/ACES). Returns
+        // the composer once ready, or null (caller falls back to a direct render).
+        function _bloomEnsure() {
+            if (_composer) return _composer;
+            if (_bloomLoad || !ren || !scene || !cam) return null;
+            const A = '/static/vendor/three/addons/';
+            _bloomLoad = Promise.all([
+                import(A + 'postprocessing/EffectComposer.js'),
+                import(A + 'postprocessing/RenderPass.js'),
+                import(A + 'postprocessing/UnrealBloomPass.js'),
+                import(A + 'postprocessing/OutputPass.js'),
+            ]).then(([EC, RP, UB, OP]) => {
+                try {
+                    const sz = canvasSize(highwayCanvas) || { w: 1280, h: 720 };
+                    const w = Math.max(2, sz.w | 0), h = Math.max(2, sz.h | 0);
+                    // Multisampled (WebGL2 MSAA) HalfFloat target so anti-aliasing
+                    // survives the bloom path — EffectComposer's default target has no
+                    // `samples`, which is why bloom-on looked jagged (worst on non-Retina
+                    // DPR1 displays that have no supersampling cushion).
+                    const _bloomRT = new T.WebGLRenderTarget(w, h, { type: T.HalfFloatType, samples: 4 });
+                    const comp = new EC.EffectComposer(ren, _bloomRT);
+                    comp.addPass(new RP.RenderPass(scene, cam));
+                    _bloomPass = new UB.UnrealBloomPass(new T.Vector2(w, h), 0.65, 0.5, 0.82); // strength, radius, threshold (high → only emissive blooms)
+                    comp.addPass(_bloomPass);
+                    comp.addPass(new OP.OutputPass());
+                    comp.setSize(w, h);
+                    _bloomW = w; _bloomH = h; _composer = comp;
+                } catch (e) { console.warn('[3D-Hwy] bloom init failed', e); _composer = null; }
+            }).catch((e) => console.warn('[3D-Hwy] bloom modules failed', e));
+            return null;
+        }
+        function buildBoard() {
+            // Dispose before clearing (traverse: nut/headstock may live in a Group).
+            while (fretG.children.length) {
+                const child = fretG.children[0];
+                child.traverse((o) => {
+                    if (o instanceof T.Sprite) return;
+                    // fretTubeGeo is shared across all fret meshes — disposing it
+                    // per-mesh here would fire one redundant dispose event per
+                    // fret. Skip it; it's disposed exactly once below.
+                    if (o.geometry !== fretTubeGeo) o.geometry?.dispose?.();
+                    const mat = o.material;
+                    if (mat) {
+                        const mats = Array.isArray(mat) ? mat : [mat];
+                        for (const m of mats) m?.dispose?.();
+                    }
+                });
+                fretG.remove(child);
+            }
+            stringLines = [];
+            stringLineGlows = [];
+            // Fret wire materials were already disposed by the child.traverse()
+            // above (each is attached 1:1 to a fret mesh) — just clear the
+            // tracking array. The shared fretTubeGeo was skipped by that
+            // traverse, so dispose it exactly once here.
+            fretWireMats = [];
+            fretTubeGeo?.dispose?.();
+            fretTubeGeo = null;
+
+            const board = boardSpanX();
+            const bw = board.width + 4 * K;
+
+            // Fretboard plane — spans exactly from hit line (Z=0) to the note
+            // spawn horizon (-AHEAD * TS), so the far edge aligns with AHEAD.
+            const blAhead = TS * AHEAD;
+            const pg = new T.PlaneGeometry(bw, blAhead);
+            // Board (highway-surface) color comes from the active HIGHWAY scene
+            // theme (default theme = the original 0x08080e). Kept on
+            // _boardPlaneMat so _applyBgTheme can recolor it live without
+            // rebuilding the board.
+            const pm = new T.MeshLambertMaterial({ color: _bgHighwayColors(hwThemeId).board, transparent: true, opacity: 0.6 });
+            _boardPlaneMat = pm;
+            const p = new T.Mesh(pg, pm);
+            p.rotation.x = -Math.PI / 2;
+            p.position.set(board.center, S_BASE - NH / 2 - 2 * K, -blAhead / 2);
+            fretG.add(p);
+
+            // Thin Line strings (glow layer). Retained in stringLineGlows[]
+            // so vibrancy slider changes can mutate opacity in place
+            // without rebuilding the board geometry.
+            // Nut lateral layout (matches headstock block below): playing strings start at the
+            // fretboard-facing edge so they never project through nut/headstock.
+            const mir = _leftyCached ? -1 : 1;
+            const nutLenX = 1.55 * K;
+            const nutXC = -0.78 * K * mir;
+            const xHeadLeft = -6.85 * K * mir;
+            const nutRearX = nutXC - nutLenX * 0.5;
+            const nutFrontX = nutXC + nutLenX * 0.5;
+            const nutJoinX = nutFrontX + 0.03 * K;
+            const bridgeTipX = xFret(NFRETS) + 2 * K * mir;
+            boardStringStartX = Math.min(nutJoinX, bridgeTipX);
+            boardTuningLabelX = (nutRearX + xHeadLeft) * 0.5 - 0.15 * K * mir;
+            const stringEndX = Math.max(nutJoinX, bridgeTipX);
+            const strSpan = Math.max(stringEndX - boardStringStartX, 1.5 * K);
+
+            const lineGlowOp = 0.15 + 0.35 * vibrancy;
+            for (let s = 0; s < nStr; s++) {
+                const pts = [new T.Vector3(boardStringStartX, sY(s), 0), new T.Vector3(stringEndX, sY(s), 0)];
+                const g = new T.BufferGeometry().setFromPoints(pts);
+                const line = new T.Line(g, new T.LineBasicMaterial({ color: activePalette[s], transparent: true, opacity: lineGlowOp }));
+                line.renderOrder = 7; // above sus rails (4/5), below chord fill (10)
+                fretG.add(line);
+                stringLineGlows.push(line);
+            }
+
+            // BoxGeometry strings — emissive glow driven by updateStringHighlights()
+            for (let s = 0; s < nStr; s++) {
+                const g = new T.BoxGeometry(strSpan, STR_THICK, STR_THICK);
+                // Each string gets its own material instance so emissiveIntensity is per-string
+                // (and per-frame opacity is set by updateStringHighlights via _vibrancyIdleOp)
+                const mat = new T.MeshStandardMaterial({
+                    color: activePalette[s], emissive: activePalette[s],
+                    emissiveIntensity: 0.002,
+                    transparent: true, opacity: _vibrancyIdleOp, roughness: 1,
+                });
+                const mesh = new T.Mesh(g, mat);
+                mesh.renderOrder = renderOrderForLayerAtZ(0, 'BOARD_STRING');
+                mesh.position.set(boardStringStartX + strSpan * 0.5, sY(s), 0);
+                fretG.add(mesh);
+                stringLines.push(mesh);
+            }
+
+            // Guitar nut + headstock — grouped so visibility + colors are user-tunable.
+            {
+                nutHeadstockGroup = new T.Group();
+                const yTopN = Math.max(sY(0), sY(nStr - 1));
+                const yBottomN = Math.min(sY(0), sY(nStr - 1));
+                const yMidN = (yTopN + yBottomN) / 2;
+                const spanY = Math.abs(yTopN - yBottomN) + S_GAP * 1.05;
+
+                const nutD = 0.95 * K;
+                const nutZc = -0.62 * K;
+                const nutH = spanY * 1.06;
+                const nutHalfH = nutH * 0.5;
+
+                const zBack = -1.38 * K;
+                const zJoint = -0.58 * K;
+
+                const nutInt = _h3dHexOrDefault(nutColor, BG_DEFAULTS.nutColor);
+                const hsInt = _h3dHexOrDefault(headstockColor, BG_DEFAULTS.headstockColor);
+                const nutBase = new T.Color(nutInt);
+                const nutHi = nutBase.clone().lerp(new T.Color(0xffffff), 0.14);
+                const nutGro = nutBase.clone().multiplyScalar(0.72);
+                const hsBase = new T.Color(hsInt);
+                const hsDarkC = hsBase.clone().multiplyScalar(0.76);
+
+                const mapleMat = new T.MeshStandardMaterial({
+                    color: hsBase, roughness: 0.55, metalness: 0.02,
+                });
+                const mapleDark = new T.MeshStandardMaterial({
+                    color: hsDarkC, roughness: 0.62, metalness: 0.02,
+                });
+
+                const coreLen = Math.max(Math.abs(nutRearX - xHeadLeft), 2 * K);
+                const coreCX = (nutRearX + xHeadLeft) * 0.5;
+                const headCoreD = 1.05 * K;
+                const headCore = new T.Mesh(
+                    new T.BoxGeometry(coreLen, spanY * 1.12, headCoreD),
+                    mapleDark,
+                );
+                headCore.position.set(coreCX, yMidN, zBack - headCoreD * 0.35);
+                nutHeadstockGroup.add(headCore);
+
+                const xs = 14;
+                const ys = 12;
+                const yLo = yMidN - spanY * 0.58;
+                const yHi = yMidN + spanY * 0.58;
+                const posR = new Float32Array((xs + 1) * (ys + 1) * 3);
+                const idxR = [];
+                let ri = 0;
+                for (let j = 0; j <= ys; j++) {
+                    const v = j / ys;
+                    const wy = yLo + v * (yHi - yLo);
+                    const yArc = 1 - Math.abs((wy - yMidN) / (spanY * 0.55 + 1e-6));
+                    const yArcCl = Math.max(0, Math.min(1, yArc));
+                    for (let i = 0; i <= xs; i++) {
+                        const u = i / xs;
+                        const wx = xHeadLeft + u * (nutRearX - xHeadLeft);
+                        const smooth = Math.sin(u * Math.PI * 0.5);
+                        let wz = zBack + (zJoint - zBack) * smooth;
+                        wz += 0.14 * K * yArcCl * yArcCl;
+                        posR[ri++] = wx;
+                        posR[ri++] = wy;
+                        posR[ri++] = wz;
+                    }
+                }
+                const row = xs + 1;
+                for (let j = 0; j < ys; j++) {
+                    for (let i = 0; i < xs; i++) {
+                        const a = j * row + i;
+                        const b = a + row;
+                        idxR.push(a, b, a + 1, b, b + 1, a + 1);
+                    }
+                }
+                const rampGeo = new T.BufferGeometry();
+                rampGeo.setAttribute('position', new T.BufferAttribute(posR, 3));
+                rampGeo.setIndex(idxR);
+                rampGeo.computeVertexNormals();
+                nutHeadstockGroup.add(new T.Mesh(rampGeo, mapleMat));
+
+                const boneMat = new T.MeshStandardMaterial({
+                    color: nutBase, roughness: 0.38, metalness: 0.02,
+                });
+                const boneTop = new T.MeshStandardMaterial({
+                    color: nutHi, roughness: 0.32, metalness: 0.02,
+                });
+                const grooveMat = new T.MeshStandardMaterial({
+                    color: nutGro, roughness: 0.85, metalness: 0,
+                });
+
+                const nutBody = new T.Mesh(
+                    new T.BoxGeometry(nutLenX, nutH, nutD),
+                    boneMat,
+                );
+                nutBody.position.set(nutXC, yMidN, nutZc);
+                nutHeadstockGroup.add(nutBody);
+
+                const crownR = nutLenX * 0.52;
+                const crownSeg = new T.CylinderGeometry(
+                    crownR, crownR, nutLenX * 0.92, 20, 1, true,
+                    Math.PI * 0.08, Math.PI * 0.42,
+                );
+                const crown = new T.Mesh(crownSeg, boneTop);
+                crown.rotation.z = Math.PI * 0.5;
+                crown.position.set(
+                    nutXC,
+                    yMidN + nutHalfH - 0.02 * K,
+                    nutZc + nutD * 0.22,
+                );
+                nutHeadstockGroup.add(crown);
+
+                const slotDrop = 0.11 * K;
+                const slotHalfW = STR_THICK * 1.15;
+                const slotZ = nutZc + nutD * 0.12;
+                for (let st = 0; st < nStr; st++) {
+                    const gr = new T.Mesh(
+                        new T.BoxGeometry(slotHalfW * 2, slotDrop, nutD * 0.42),
+                        grooveMat,
+                    );
+                    gr.position.set(nutXC, sY(st), slotZ);
+                    nutHeadstockGroup.add(gr);
+                }
+                nutHeadstockGroup.visible = nutHeadstockVisible;
+                fretG.add(nutHeadstockGroup);
+            }
+
+            // Fret wires — bowed metal TubeGeometry (backported from
+            // highway_babylon). Board-string and fret-wire layers live in
+            // RENDER_ORDER_LAYER_STACK so the fretboard draws above note
+            // symbols and below fret labels.
+            // Tube (not T.Line): WebGL ignores linewidth > 1px on almost all
+            // platforms, so Line objects always render as hairlines. The tube
+            // bows in Z (middle strings pushed away from camera) so the row of
+            // frets reads as wrapping a cylindrical neck — see FRET_BOW_DZ.
+            // MeshStandardMaterial (vs the old flat MeshBasic): the scene's
+            // ambient+directional light glints across the rounded surface for a
+            // polished-steel look; the per-frame gold albedo (in-anchor) then
+            // reads as brass. depthTest:false: string BoxGeometry (MeshStandard,
+            // depthWrite:true) writes depth at Z=+STR_THICK/2; wires near Z=0
+            // would fail the depth test at string pixels despite higher layer.
+            // Colors are updated each frame by the fretWireMats loop in update(),
+            // which drives every wire to one of two tiers: FRET_WIRE_IDLE_* by
+            // default, FRET_WIRE_ACTIVE_* inside the anchor lane. The material is
+            // created at the idle tier so frame 0 (before update() first runs)
+            // already matches.
+            const yTop = Math.max(sY(0), sY(nStr - 1));
+            const yBottom = Math.min(sY(0), sY(nStr - 1));
+            const wireH = (yTop + S_GAP * 0.3) - (yBottom - S_GAP * 0.3);
+            const wireMidY = (yTop + yBottom) / 2;
+            // Single shared geometry centered at x=0, local Y -half..+half,
+            // bowed in Z by FRET_BOW_DZ * [0,0.6,1,0.6,0]. Reused by every fret
+            // (only mesh position differs). Symmetric in Y → invert/lefty-safe.
+            const yHalf = wireH * 0.5;
+            const zMults = [0, 0.6, 1, 0.6, 0];
+            const tubePath = zMults.map((zm, i) => new T.Vector3(
+                0,
+                -yHalf + (wireH * i) / (zMults.length - 1),
+                FRET_BOW_DZ * zm,
+            ));
+            const tubeCurve = new T.CatmullRomCurve3(tubePath);
+            fretTubeGeo = new T.TubeGeometry(
+                tubeCurve, FRET_TUBE_SEG, FRET_TUBE_RADIUS, FRET_TUBE_RADIAL, false,
+            );
+            for (let f = 0; f <= NFRETS; f++) {
+                const x = xFret(f);
+                const mat = new T.MeshStandardMaterial({
+                    color: FRET_WIRE_IDLE_HEX, metalness: FRET_METALNESS, roughness: FRET_ROUGHNESS,
+                    emissive: FRET_EMISSIVE,
+                    // depthWrite:false (matches other transparent overlays here):
+                    // a transparent fret must not write depth or it can occlude
+                    // later-drawn transparent elements despite depthTest:false.
+                    transparent: true, opacity: FRET_WIRE_IDLE_OP, depthTest: false, depthWrite: false,
+                });
+                const fw = new T.Mesh(fretTubeGeo, mat);
+                fw.position.set(x, wireMidY, 0);
+                fw.renderOrder = renderOrderForLayerAtZ(0, 'BOARD_FRET_WIRE');
+                fretG.add(fw);
+                fretWireMats[f] = mat;
+            }
+
+            // Fret dots — flat circles (CircleGeometry) lying in the XY plane and
+            // facing +Z so they always appear as perfect circles from the camera.
+            // depthWrite:false so they don't steal the depth buffer from the
+            // transparent string meshes. Slight negative Z recessed under the
+            // string plane. Radius 10% below the former 1.5*K dots.
+            const dotRZ = (1.5 * K * 0.9);
+            const dg = new T.CircleGeometry(dotRZ, 64);
+            const dm = new T.MeshBasicMaterial({
+                color: 0x556677,
+                transparent: true,
+                opacity: 1,
+                depthWrite: false,
+            });
+            const dotZBack = -STR_THICK * 0.85;
+            const my = (sY(0) + sY(nStr - 1)) / 2;
+            const addDot = (x, y) => {
+                const d = new T.Mesh(dg, dm);
+                d.position.set(x, y, dotZBack);
+                // Above the dynamic lane (1) and its dividers (2) so the
+                // translucent blue lane no longer paints over and hides the
+                // inlay; still well below strings / wires / notes,
+                // so those keep drawing on top of the inlay.
+                d.renderOrder = 3;
+                fretG.add(d);
+            };
+            for (const f of DOTS) {
+                const cx = xFretMid(f);
+                if (DDOTS.has(f)) {
+                    addDot(cx, my - S_GAP * 0.7);
+                    addDot(cx, my + S_GAP * 0.7);
+                } else {
+                    addDot(cx, my);
+                }
+            }
+
+            // Fret inlay number labels — sprites sitting just behind the hit line
+            // (Z = -K) so camera-distance sorting in the transparent pass puts
+            // them before notes at Z = 0, letting notes paint on top.
+            // Materials are cloned from the txtMat cache with depthWrite:false so
+            // the sprites don't write stale depth values that would clip incoming
+            // notes (which arrive from large negative Z). Clones are tracked in
+            // _inlayMats for explicit disposal on rebuild and destroy().
+            // Scale uses (0.5 + textSize) directly — _textSizeMul is stale here
+            // (only refreshed at the top of update()); update() rescales live.
+            for (const m of _inlayMats) m.dispose();
+            _inlayMats = [];
+            _inlayLabels = [];
+            for (const f of INLAY_LABEL_FRETS) {
+                const mat = txtMat(f, '#7abfcc', false, 'fretRow').clone();
+                mat.depthWrite = false;
+                mat.opacity = 0.55;
+                const lbl = new T.Sprite(mat);
+                const scale = 5.5 * (0.5 + textSize) * fretLabelScaleForFret(f);
+                lbl.scale.set(scale * K, scale * K, 1);
+                lbl.position.set(xFretMid(f), yTop - S_GAP * 0.4, -K);
+                lbl.visible = inlayLabelsVisible;
+                fretG.add(lbl);
+                _inlayLabels.push(lbl);
+                _inlayMats.push(mat);
+            }
+        }
+
+        /* ── String glow (called each frame) ────────────────────────────── */
+        function updateStringHighlights(noteState) {
+            // Glow slider scales both the idle floor and anticipation peak,
+            // so glowMul=0 fully silences the per-string emissive pulse.
+            // Vibrancy controls the idle opacity floor — anticipation
+            // still rides on top regardless of vibrancy so play-feedback
+            // through the opacity channel survives even at glowMul=0.
+            //
+            // Folded with the post-noteState mGlow / mAccentCore writes
+            // (was a separate `for (s = 0; s < nStr)` loop in update()),
+            // so the per-string scratch arrays stay hot in L1 across all
+            // material writes for a given string.
+            const BASE_GLOW = 0.02 * glowMul;
+            const MAX_GLOW  = 3.5  * glowMul;
+            const IDLE_OP   = _vibrancyIdleOp;
+            const g = glowMul;
+            const venueGemMul = _venueSceneOverride ? VENUE_GEM_EMISSIVE_MUL : 1;
+
+            for (let s = 0; s < nStr; s++) {
+                const mesh = stringLines[s];
+                if (mesh) {
+                    const intensity = Math.max(
+                        noteState.stringSustain[s] ? 1 : 0,
+                        noteState.stringAnticipation[s] || 0,
+                    );
+                    mesh.material.emissiveIntensity = BASE_GLOW + intensity * MAX_GLOW;
+                    mesh.material.opacity = IDLE_OP + intensity * (1 - IDLE_OP);
+                    mesh.scale.set(1, 1 + intensity * 0.3, 1 + intensity * 0.3);
+                }
+                // Hit-note emissive — same write pattern as the standalone
+                // loop that previously lived at update()'s post-call site.
+                // The glow slider scales it here since this assignment
+                // stomps anything _applyGlow() set statically.
+                const bg = noteState.strGlow[s] * g;
+                if (mGlow[s]) mGlow[s].emissiveIntensity = bg * venueGemMul;
+                if (mAccentCore[s]) {
+                    mAccentCore[s].emissiveIntensity =
+                        (bg + noteState.accentFillBoost[s] * g) * venueGemMul;
+                }
+            }
+        }
+
+        /* ── Lookahead fret bounds + smooth camera ───────────────────────── */
+        // End time of the lookahead window = start of the measure that is
+        // CAM_LOOKAHEAD_MEASURES measures ahead of the current one. Uses the
+        // _measureStarts cache (times of beats with measure !== -1). With no
+        // beats it falls back to CAM_LOOKAHEAD_SEC seconds. Past the last known
+        // measure it extrapolates using the average measure duration.
+        function lookaheadEndTime(now) {
+            const ms = _measureStarts;
+            if (!ms || ms.length === 0) return now + CAM_LOOKAHEAD_SEC;
+            // Binary search: lo = first index with ms[lo] > now.
+            let lo = 0, hi = ms.length;
+            while (lo < hi) { const mid = (lo + hi) >> 1; if (ms[mid] <= now) lo = mid + 1; else hi = mid; }
+            const curIdx = lo - 1;                       // current measure (-1 if before the first)
+            const targetIdx = curIdx + CAM_LOOKAHEAD_MEASURES;
+            if (targetIdx >= 0 && targetIdx < ms.length) return ms[targetIdx];
+            // Past the last measure: extrapolate using the average measure duration.
+            if (ms.length >= 2) {
+                const avg = (ms[ms.length - 1] - ms[0]) / (ms.length - 1);
+                if (avg > 0) return ms[ms.length - 1] + (targetIdx - (ms.length - 1)) * avg;
+            }
+            return now + CAM_LOOKAHEAD_SEC;
+        }
+
+        function lookaheadComputeFretBounds(now, anchors, notes, chords) {
+            const tEnd = lookaheadEndTime(now);
+            let minF = 99;
+            let maxF = 0;
+            let any = false;
+            if (anchors && anchors.length) {
+                for (let tt = now; tt <= tEnd + 1e-9; tt += 0.125) {
+                    const a = getChartAnchorAt(anchors, tt);
+                    if (!a) continue;
+                    let fStart = Math.round(Number(a.fret));
+                    if (!Number.isFinite(fStart) || fStart < 1) fStart = 1;
+                    let w = Number(a.width);
+                    if (!Number.isFinite(w)) w = 4;
+                    w = Math.max(1, Math.round(w));
+                    const fHi = Math.min(NFRETS, fStart + w - 1);
+                    minF = Math.min(minF, fStart);
+                    maxF = Math.max(maxF, fHi);
+                    any = true;
+                }
+            }
+            const consider = f => {
+                if (!(f > 0)) return;
+                minF = Math.min(minF, f);
+                maxF = Math.max(maxF, f);
+                any = true;
+            };
+            if (notes) {
+                let i = lowerBoundT(notes, now);
+                for (; i < notes.length; i++) {
+                    const n = notes[i];
+                    if (n.t > tEnd) break;
+                    if (!validString(n.s)) continue;
+                    consider(n.f);
+                }
+            }
+            if (chords) {
+                let i = lowerBoundT(chords, now);
+                for (; i < chords.length; i++) {
+                    const ch = chords[i];
+                    if (ch.t > tEnd) break;
+                    if (!ch.notes) continue;
+                    for (const cn of ch.notes) {
+                        if (!validString(cn.s)) continue;
+                        consider(cn.f);
+                    }
+                }
+            }
+            if (!any || minF > maxF) return null;
+            return { minF, maxF };
+        }
+
+        function lookaheadTargetWorldX(minF, maxF) {
+            const wb = CAM_FRET_EDGE_BLEND;
+            const middle = (xFretMid(minF) + xFretMid(maxF)) * 0.5;
+            const weighted = 0.6 * xFret(0) + 0.4 * xFret(NFRETS);
+            return middle * (1 - wb) + weighted * wb;
+        }
+
+        function lookaheadSmoothCamStep(dtSec, tgtXWorld, tgtSpanInt) {
+            const d = Math.min(0.2, Math.max(1e-4, dtSec));
+            const fs = 1 - Math.pow(1 - CAM_FOCUS_BLEND_RATE, d);
+            _lookaheadCamX = tgtXWorld * fs + _lookaheadCamX * (1 - fs);
+            _lookaheadFretSpan = tgtSpanInt * fs + _lookaheadFretSpan * (1 - fs);
+        }
+
+        /* ── Camera target helper ────────────────────────────────────────── */
+        // Compute and apply tgtX + tgtDist from note-window-accumulated data.
+        // Used by BOTH the snap pre-pass (before drawNote() calls, skipDistHyst=true)
+        // and the main per-frame camera-target block (skipDistHyst=false) so the
+        // two paths can never drift out of sync.
+        //
+        // wX/wSum        recency-weighted fret-position centroid accumulator
+        // distMin/Max    min/max fret seen in the camera targeting window
+        // distGot        true iff at least one fretted note was in the window
+        // camHystF       X-axis hysteresis factor (from cameraSmoothing)
+        // camDistHystF   dist hysteresis factor (from zoomSmoothing)
+        // skipDistHyst   true on the snap/first-data frame — no previous tgtDist
+        //                state exists, so bypass the dead-zone gate
+        //
+        // Side-effects: updates tgtX, tgtDist, prevLowFretBonus.
+        // Returns: computed lockActive flag (caller is responsible for setting
+        //          prevLockActive from the returned value).
+        function _applyNoteCamTargets(wX, wSum, distMin, distMax, distGot,
+                                      camHystF, camDistHystF, skipDistHyst) {
+            const lockActive = cameraLockLow && (!distGot || distMax <= 12);
+            if (lockActive) {
+                // Locked view: frets 0-12 fit in frame, with the peak
+                // low-fret bonus baked in so nut chords stay framed.
+                // Both halves derive from the same helpers as the
+                // dynamic branch so future tuning of the base zoom
+                // curve or low-fret pullback can't desync them.
+                const lockedBaseU  = camBaseDistU(12);
+                const lockedBonusU = camLowFretPullbackU(1);
+                // cameraLockZoom slider 0..1 blends between MIN (closest)
+                // and MAX (furthest). Default 0.5 maps to ~1.0× so existing
+                // users see the same locked view as before this slider.
+                const lockZoomMul  = CAM_LOCK_ZOOM_MIN +
+                    (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
+                tgtX             = xFretMid(CAM_LOCK_CENTER_FRET);
+                tgtDist          = (lockedBaseU + lockedBonusU) * K * lockZoomMul;
+                prevLowFretBonus = lockedBonusU;
+            } else if (distGot) {
+                // Base zoom scales by fret count (distMax - distMin).
+                const baseDistU     = camBaseDistU(distMax - distMin);
+                // Low-fret pullback: world-X distance between frets is
+                // logarithmic, so a 2-fret span at the nut takes much
+                // more horizontal screen than the same span at fret 12.
+                // The base term scales by *fret count*, not world-X
+                // span, so low-fret clusters were under-allotted camera
+                // distance and clipped at the left edge (e.g. F power
+                // chord at fret 1 partially off-screen). Add a tapered
+                // bonus that kicks in below fret 5 and peaks at fret 1
+                // (≈16 extra fret-span units, i.e. 16*K world-units of
+                // distance), without affecting mid/high neck framing.
+                const lowFretBonusU = camLowFretPullbackU(distMin);
+                if (skipDistHyst) {
+                    // First data frame — no previous tgtDist state; apply
+                    // directly without the hysteresis dead-zone check.
+                    tgtDist = (baseDistU + lowFretBonusU) * K;
+                } else {
+                    // tgtDist scales at (3 * K) per fret-span unit, so the
+                    // hysteresis threshold (a fret-span dead zone) converts
+                    // to tgtDist-space by multiplying by 3 * K — NOT by
+                    // FRET_WIDTH_MID, which is X-axis world-units-per-fret
+                    // and a different unit (would over-tighten the gate by
+                    // ~4x at SCALE = 2.25).
+                    //
+                    // Hysteresis is applied to the BASE portion only. The
+                    // lowFretBonus changes by 4 fret-span units per integer
+                    // fret near the nut, which sits below the default-
+                    // cameraSmoothing (cs=0.5) dead zone of ~8.25 fret-span
+                    // units (= 2.75 * 3) and would otherwise be suppressed
+                    // for fret 2 → 1 / 3 → 1 transitions — exactly the
+                    // corrections this bonus exists to provide. So gate the
+                    // base, then always reflect bonus changes on top by
+                    // tracking the last-committed bonus contribution
+                    // (prevLowFretBonus) and adjusting tgtDist for its
+                    // delta whether or not the base hysteresis fires.
+                    //
+                    // First frame after a lock release bypasses the gate
+                    // entirely so a >12 fret note that disengaged the lock
+                    // is guaranteed to widen the view. Without this, a
+                    // small span jump (12→13 frets) at default settings
+                    // can sit inside the dead zone and the camera fails
+                    // to follow the high note that just opened the lock.
+                    const candidateBase = baseDistU * K;
+                    const baseTgt       = tgtDist - prevLowFretBonus * K;
+                    const justUnlocked  = prevLockActive;
+                    if (justUnlocked || Math.abs(candidateBase - baseTgt) > camDistHystF * 3 * K) {
+                        tgtDist = (baseDistU + lowFretBonusU) * K;
+                    } else if (lowFretBonusU !== prevLowFretBonus) {
+                        tgtDist = baseTgt + lowFretBonusU * K;
+                    }
+                }
+                prevLowFretBonus = lowFretBonusU;
+            }
+            // X-axis: recency-weighted centroid with a hysteresis dead zone
+            // so small cluster shifts don't trigger visible pan motion.
+            if (!lockActive && wSum > 0) {
+                const candidateX = wX / wSum;
+                if (Math.abs(candidateX - tgtX) > camHystF * FRET_WIDTH_MID) tgtX = candidateX;
+            }
+            return lockActive;
+        }
+
+        /** Tolerate RS/sloppak boolean-ish ``true`` / ``1`` forms. */
+        function truthyChartFlag(v) {
+            if (v === true || v === 1) return true;
+            if (v === '1') return true;
+            return typeof v === 'string' && v.toLowerCase() === 'true';
+        }
+
+        /** RS / sloppak `hd` (highDensity); tolerate occasional string forms. */
+        function chordWireHighDensity(ch) {
+            return truthyChartFlag(ch && ch.hd);
+        }
+
+        /**
+         * Per spec, `displayName` is the UI label for a chord template
+         * (defaulting to `name` when the chart didn't set it). Always go
+         * through this helper so name vs. displayName drift can't surface
+         * the wrong label or break displayName-based dedupe heuristics.
+         */
+        function chordTemplateLabel(tmpl) {
+            if (!tmpl) return '';
+            const d = tmpl.displayName;
+            if (typeof d === 'string' && d.length > 0) return d;
+            const n = tmpl.name;
+            return typeof n === 'string' ? n : '';
+        }
+
+        /**
+         * Arpeggio styling is driven by authored metadata, not by post-hoc
+         * note-stream inference. Prefer explicit hand-shape flags and fall back
+         * to template markers when present.
+         */
+        function chordTemplateMarkedArpeggio(cid, chordTemplates) {
+            if (cid == null || !chordTemplates) return false;
+            const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
+            if (!tmpl) return false;
+            if (truthyChartFlag(tmpl.arp) || truthyChartFlag(tmpl.arpeggio)) return true;
+            const displayName = typeof tmpl.displayName === 'string' ? tmpl.displayName.toLowerCase() : '';
+            if (displayName.includes('-arp')) return true;
+            const name = typeof tmpl.name === 'string' ? tmpl.name.toLowerCase() : '';
+            return name.endsWith('(arp)') || name.includes(' arpeggio');
+        }
+
+        function handShapeMarkedArpeggio(hs, chordTemplates) {
+            if (!hs) return false;
+            if (truthyChartFlag(hs.arp) || truthyChartFlag(hs.arpeggio)) return true;
+            return chordTemplateMarkedArpeggio(hsChordIdNorm(hs), chordTemplates);
+        }
+
+        /**
+         * Matching hand-shape metadata for a chord onset. ``explicit`` follows
+         * authored arpeggio markers only; note inference is handled separately
+         * by the callers that still need it for non-visual behavior.
+         *
+         * Cached per chord: result depends only on (ch, hss, chordTemplates),
+         * all chart-static for the lifetime of an arrangement. The cache is
+         * swapped on (hss, templates) ref change so an arrangement switch
+         * cannot resurrect stale entries. Empty-input case bypasses the cache
+         * — it returns a fresh sentinel anyway and isn't hot enough to share.
+         */
+        const _HINT_NONE = Object.freeze({ explicit: false, covered: false, hs: null });
+        let _hintCache = new WeakMap();
+        let _hintCacheHsRef = null;
+        let _hintCacheTplRef = null;
+        function chordHandShapeArpeggioHint(ch, hss, chordTemplates) {
+            if (!hss || hss.length === 0) return _HINT_NONE;
+            if (_hintCacheHsRef !== hss || _hintCacheTplRef !== chordTemplates) {
+                _hintCache = new WeakMap();
+                _hintCacheHsRef = hss;
+                _hintCacheTplRef = chordTemplates;
+            }
+            const cached = _hintCache.get(ch);
+            if (cached !== undefined) return cached;
+            const t = ch.t;
+            const cid = ch.id;
+            let result = _HINT_NONE;
+            for (let i = 0; i < hss.length; i++) {
+                const hs = hss[i];
+                const tLo = hsStart(hs);
+                const tHi = hsEnd(hs);
+                if (Number.isNaN(tLo) || Number.isNaN(tHi)) continue;
+                if (t + 1e-4 < tLo || t > tHi + 1e-4) continue;
+                const hsCid = hsChordIdNorm(hs);
+                if (hsCid !== cid && Number(hsCid) !== Number(cid)) continue;
+                const explicit = handShapeMarkedArpeggio(hs, chordTemplates);
+                result = { explicit, covered: true, hs };
+                break;
+            }
+            _hintCache.set(ch, result);
+            return result;
+        }
+
+        /** Build ``ch.notes`` from ``chordTemplates[cid].frets`` (-1 omitted). */
+        function chordNotesFromTemplate(cid, templates) {
+            if (templates == null || cid == null) return [];
+            const tmpl = templates[cid] ?? templates[Number(cid)];
+            if (!tmpl || !Array.isArray(tmpl.frets)) return [];
+            const out = [];
+            for (let si = 0; si < tmpl.frets.length; si++) {
+                const f = tmpl.frets[si];
+                if (f >= 0 && validString(si)) out.push({ s: si, f, sus: 0 });
+            }
+            return out;
+        }
+
+        /**
+         * Chart-format fingerpicking passages often have ``<handShape>`` + per-string
+         * ``<note>`` rows but **no** ``<chord>`` events. The 3D chord frame / arp
+         * styling only runs over ``bundle.chords``, so synthesize minimal chord
+         * rows at each hand-shape onset when the chart omits them.
+         */
+        function mergeHandShapeSynthChords(realChords, handShapes, chordTemplates) {
+            if (!handShapes || handShapes.length === 0) return realChords;
+            const reals = realChords && realChords.length ? realChords : [];
+            const synth = [];
+            const seenSynth = new Set();
+            const tol = 0.028;
+            /**
+             * Suppress a synth chord box when a real chord with the **same trimmed
+             * display name** played within this window — Custom songs commonly authors
+             * several ``<chordTemplate>`` rows that share a display name (with
+             * trailing-whitespace IDs) for fingering variants. The follow-up
+             * hand-shape with no chord row is a fingering hint, not a new strum
+             * (e.g. Jackson 5 "I Want You Back" ~0:27 — Fm7 cid=18 strum followed
+             * by Fm7 cid=19 hand-shape, which earlier produced a stacked second
+             * "Fm7" label and an extra chord frame).
+             */
+            const SAME_NAME_RUN_S = 0.5;
+            const trimmedTemplateName = (cid) => {
+                if (cid == null || !chordTemplates) return '';
+                const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
+                // custom songs commonly authors several <chordTemplate> rows that share
+                // a displayName for fingering variants; the suppression
+                // heuristic in the surrounding code dedupes on the *label*,
+                // not the underlying name, so go through chordTemplateLabel.
+                return chordTemplateLabel(tmpl).trim();
+            };
+            outer: for (let i = 0; i < handShapes.length; i++) {
+                const hs = handShapes[i];
+                const cid = hs.chord_id != null ? hs.chord_id : hs.chordId;
+                const st = hs.start_time != null ? hs.start_time : hs.startTime;
+                if (cid == null || st == null || Number.isNaN(Number(st))) continue;
+                const key = `${cid}|${Number(st).toFixed(3)}`;
+                if (seenSynth.has(key)) continue;
+                seenSynth.add(key);
+                const myName = trimmedTemplateName(cid);
+                for (let j = 0; j < reals.length; j++) {
+                    const ch = reals[j];
+                    const rid = ch.id;
+                    const sameId = rid === cid || Number(rid) === Number(cid);
+                    if (sameId && Math.abs(ch.t - st) <= tol) continue outer;
+                    // A real strum at the same onset already represents this
+                    // chord — never synthesize a phantom on top of it. The
+                    // id/name checks alone miss hand-shapes whose template
+                    // differs from (or shares no name with) the coincident real
+                    // chord — e.g. an edited chart that left a stale hand-shape
+                    // template pointing at the pre-edit shape, which then drew a
+                    // spurious second power chord beside the real one.
+                    if (Math.abs(ch.t - st) <= tol) continue outer;
+                    if (!sameId && myName !== '') {
+                        const otherName = trimmedTemplateName(rid);
+                        if (otherName === myName
+                            && st > ch.t
+                            && st - ch.t <= SAME_NAME_RUN_S) {
+                            continue outer;
+                        }
+                    }
+                }
+                const notes = chordNotesFromTemplate(cid, chordTemplates);
+                if (notes.length === 0) continue;
+                const et = hs.end_time != null ? hs.end_time : hs.endTime;
+                synth.push({
+                    t: st,
+                    id: cid,
+                    // `hd` is the chart-format `highDensity` wire field (gallops /
+                    // repeated strums), not an arpeggio carrier — arpeggio
+                    // intent is read directly from the hand-shape via
+                    // chordHandShapeArpeggioHint() downstream. Keep `hd` false
+                    // so chordWireHighDensity() / label-suppression behave the
+                    // same as for any other non-gallop chord row.
+                    hd: false,
+                    notes,
+                    /** Hand-shape fill-in (no authored chord row) — skip note-stream arp frame. */
+                    h3dSynth: true,
+                    /** Hand-shape end time — used to draw the shape-sustain border for non-arp cases. */
+                    h3dSynthEnd: et != null ? Number(et) : null,
+                });
+            }
+            if (synth.length === 0) return reals;
+            const merged = reals.concat(synth);
+            merged.sort((a, b) => {
+                const dt = a.t - b.t;
+                if (Math.abs(dt) > 1e-6) return dt;
+                const ia = Number(a.id);
+                const ib = Number(b.id);
+                return (ia - ib) || 0;
+            });
+            return merged;
+        }
+
+        /**
+         * Merge chart-format ``chordTemplates[id].frets`` with live ``chordNote`` rows.
+         * Cached via WeakMap on the chord object — chord data never changes after
+         * chart load, so the Map is computed once and reused every frame.
+         * The init-time callers (fillArpeggioGhostInferFlags) pass ephemeral `fakeCh`
+         * objects that are never seen again, so they bypass the cache naturally.
+         */
+        let _chordShapeCache = new WeakMap();
+        // Reset the validString()/nStr-dependent chord caches. Called when nStr
+        // changes so a string count discovered after the first frame (e.g. a
+        // 7-string chart whose stringCount arrives in song_info) doesn't leave
+        // string-6+ notes filtered out of cached chord shapes/signatures.
+        function _resetStringDependentCaches() {
+            _filterValidNotesCache = new WeakMap();
+            _chordSigCache = new WeakMap();
+            _chordShapeCache = new WeakMap();
+            // mergeHandShapeSynthChords() is nStr-dependent too: its synth
+            // notes come from chordNotesFromTemplate() -> validString(). The
+            // merge result is memoised by input identity (not nStr), so force a
+            // recompute or string-6+ template notes stay dropped from synth
+            // chords after the count grows.
+            _mergeCacheResult = null;
+        }
+        function mergeChordShape(ch, chordNotes, templates) {
+            if (_chordShapeCache.has(ch)) return _chordShapeCache.get(ch);
+            const shape = new Map();
+            const tid = ch && ch.id != null ? ch.id : null;
+            const tmpl = (tid != null && templates)
+                ? (templates[tid] ?? templates[Number(tid)])
+                : null;
+            if (tmpl && Array.isArray(tmpl.frets)) {
+                for (let si = 0; si < tmpl.frets.length; si++) {
+                    if (!validString(si)) continue;
+                    const f = tmpl.frets[si];
+                    if (f >= 0) shape.set(si, f);
+                }
+            }
+            for (let i = 0; i < chordNotes.length; i++) {
+                const cn = chordNotes[i];
+                if (!validString(cn.s)) continue;
+                if (cn.f < 0) shape.delete(cn.s);
+                else shape.set(cn.s, cn.f);
+            }
+            _chordShapeCache.set(ch, shape);
+            return shape;
+        }
+
+        function hitTimesQualifyArpeggioSpread(hitTimes) {
+            if (hitTimes.length < 2) return false;
+            hitTimes.sort((a, b) => a - b);
+            const spread = hitTimes[hitTimes.length - 1] - hitTimes[0];
+            if (spread >= 0.03) return true;
+            return hitTimes.length >= 4 && spread >= 0.016;
+        }
+
+        /** RS XML / IPC payloads use snake_case or camelCase field names. */
+        function hsStart(hs) {
+            if (!hs) return NaN;
+            const v = hs.start_time != null ? hs.start_time : hs.startTime;
+            if (v == null) return NaN;
+            const n = Number(v);
+            return Number.isNaN(n) ? NaN : n;
+        }
+        function hsEnd(hs) {
+            if (!hs) return NaN;
+            const v = hs.end_time != null ? hs.end_time : hs.endTime;
+            if (v == null) return NaN;
+            const n = Number(v);
+            return Number.isNaN(n) ? NaN : n;
+        }
+        function hsChordIdNorm(hs) {
+            if (!hs) return null;
+            const v = hs.chord_id != null ? hs.chord_id : hs.chordId;
+            return v == null ? null : v;
+        }
+
+        /** ``<handShape>`` chart duration in seconds (snake_case or camelCase XML). */
+        function handShapeChartSpanSec(hs) {
+            const a = hsStart(hs), b = hsEnd(hs);
+            if (Number.isNaN(a) || Number.isNaN(b)) return 0;
+            return Math.max(0, b - a);
+        }
+
+        /**
+         * When ``hd`` is missing/false, detect arpeggio from the **note** stream
+         * using the **full voicing** (template ∪ chord notes). RS often stores the
+         * plucks only in ``notes[]``, not as duplicate chord rows.
+         *
+         * @param {{ tLo: number, tHi: number } | null} [timeWin]
+         *        When set (e.g. from ``<handShape>`` span), scan staggered picks
+         *        across the whole held-shape window — RS often omits ``arp`` and ``hd``.
+         */
+        // Cached per chord: result depends on (ch, shape, notesArr) and an
+        // optional timeWin which itself is a function of the chord's matching
+        // <handShape>. Both inputs are chart-static, so the cache invalidates
+        // on (notesArr, hss) ref change — `hss` is threaded in purely as the
+        // invalidation key for the chord-loop caller, which passes a stable
+        // `ch` (reused across frames) and a timeWin that is null until
+        // bundle.handShapes arrives over the WS; without the hss check the
+        // null-timeWin result would stick once handShapes loaded late. shape
+        // comes from mergeChordShape(ch) which is also chart-static, so it
+        // doesn't enter the invalidation key directly. The cache deliberately
+        // stores boolean results; a sentinel distinguishes "not computed"
+        // from "false".
+        let _arpInferCache = new WeakMap();
+        let _arpInferCacheNotesRef = null;
+        let _arpInferCacheHssRef = null;
+        function inferArpeggioFromNotePattern(ch, shape, notesArr, timeWin, hss = null) {
+            if (!notesArr || notesArr.length === 0 || shape.size < 2) return false;
+            if (_arpInferCacheNotesRef !== notesArr || _arpInferCacheHssRef !== hss) {
+                _arpInferCache = new WeakMap();
+                _arpInferCacheNotesRef = notesArr;
+                _arpInferCacheHssRef = hss;
+            }
+            const cached = _arpInferCache.get(ch);
+            if (cached !== undefined) return cached;
+            const result = _inferArpeggioFromNotePatternUncached(ch, shape, notesArr, timeWin);
+            _arpInferCache.set(ch, result);
+            return result;
+        }
+        function _inferArpeggioFromNotePatternUncached(ch, shape, notesArr, timeWin) {
+            const tHi = timeWin ? timeWin.tHi : ch.t + 2.35;
+            const tLo = timeWin ? timeWin.tLo : ch.t - 0.28;
+            let i2 = lowerBoundT(notesArr, tLo - 0.02);
+            const hitTimes = [];
+            const hitStrings = new Set();
+            for (; i2 < notesArr.length; i2++) {
+                const n = notesArr[i2];
+                if (n.t > tHi) break;
+                if (n.t < tLo) continue;
+                if (!validString(n.s)) continue;
+                const ef = shape.get(n.s);
+                if (ef === undefined || ef !== n.f) continue;
+                hitTimes.push(n.t);
+                hitStrings.add(n.s);
+            }
+            if (!hitTimesQualifyArpeggioSpread(hitTimes)) return false;
+            // A genuine arpeggio SWEEPS across the held shape, so its standalone
+            // notes land on MULTIPLE strings of the shape. When every matching
+            // hit is on a single string, this is a repeated single-string run
+            // (e.g. a palm-muted gallop hammering the chord's root) that happens
+            // to share one string/fret with the chord — NOT an arpeggio. Inferring
+            // one here deferred the chord's gems and made the power chord render as
+            // just that one repeated note (bar 25 of starlight). Require ≥2 strings.
+            if (hitStrings.size < 2) return false;
+            // Strumming/gallop rejection — far more hits than the shape has
+            // strings means the chord's notes are being re-struck repeatedly
+            // (a riff/gallop reusing both power-chord notes), not swept once as
+            // an arpeggio. This guard used to live inside `if (timeWin)`, so it
+            // was skipped for charts with no hand-shapes (timeWin null) — which
+            // let dense two-string gallops over a power chord infer a bogus
+            // arpeggio and defer the chord's gems (bar 88 of starlight: a
+            // (s5:4,s6:2) chord whose root+fifth recur ~16x over 2 s). Apply it
+            // with the actual window span whether or not a hand-shape is present.
+            const winSpan = timeWin ? (timeWin.tHi - timeWin.tLo) : (tHi - tLo);
+            if (winSpan > ARP_INFER_MULTI_STRUM_WIN_MIN_S
+                && hitTimes.length > shape.size + ARP_INFER_MULTI_STRUM_HIT_SLACK) {
+                return false;
+            }
+            if (timeWin) {
+                if (winSpan < 0.70 && hitTimes.length < 4) {
+                    const spread = hitTimes[hitTimes.length - 1] - hitTimes[0];
+                    if (spread < ARP_INFER_STRUM_VS_ARP_SPREAD_MIN_S) return false;
+                }
+                // Reject when too few staggered hits for a genuine sweep across
+                // the held shape — see ARP_INFER_MIN_HITS_VS_SHAPE_CAP.
+                const minHits = Math.min(shape.size, ARP_INFER_MIN_HITS_VS_SHAPE_CAP);
+                if (hitTimes.length < minHits) return false;
+            }
+            return true;
+        }
+
+        /**
+         * True when standalone note rows already cover every string/fret in the
+         * arpeggio shape, so drawing the chord gems too would duplicate the same
+         * authored passage.
+         */
+        // Cached per chord: result depends on (ch, shape, notesArr) — chart-
+        // static; the cache invalidates on notesArr ref change. The same
+        // ``ch`` may be queried multiple times per frame from the chord
+        // render loop (deferChordGems / _deferFallback / suppressSynthChord),
+        // so survival across frames is also useful.
+        let _arpCoverCache = new WeakMap();
+        let _arpCoverCacheNotesRef = null;
+        function chordShapeCoveredByStandaloneNotes(ch, shape, notesArr, timeWin) {
+            if (!notesArr || notesArr.length === 0 || !shape || shape.size === 0) return false;
+            if (_arpCoverCacheNotesRef !== notesArr) {
+                _arpCoverCache = new WeakMap();
+                _arpCoverCacheNotesRef = notesArr;
+            }
+            const cached = _arpCoverCache.get(ch);
+            if (cached !== undefined) return cached;
+            const tLo = (timeWin ? timeWin.tLo : ch.t - ARP_FRAME_ONSET_PAD_S) - NEXT_ON_STRING_T_EPS;
+            const tHi = (timeWin ? timeWin.tHi : ch.t + ARP_FRAME_ONSET_CLUSTER_S) + NEXT_ON_STRING_T_EPS;
+            let i2 = lowerBoundT(notesArr, tLo);
+            const matchedStrings = new Set();
+            let result = false;
+            for (; i2 < notesArr.length; i2++) {
+                const n = notesArr[i2];
+                if (n.t > tHi) break;
+                if (!validString(n.s) || matchedStrings.has(n.s)) continue;
+                const ef = shape.get(n.s);
+                if (ef === undefined || ef !== n.f) continue;
+                matchedStrings.add(n.s);
+                if (matchedStrings.size >= shape.size) { result = true; break; }
+            }
+            _arpCoverCache.set(ch, result);
+            return result;
+        }
+
+        /**
+         * Notes in an inferred arpeggio passage are charted in ``notes[]`` with
+         * staggered times; treat them like chord-cluster notes for chart-format-style
+         * board-ghost fret digits (``fromChord`` + template column).
+         */
+        function arpeggioChordIdForNote(n, handShapes, chordTemplates, notesArr) {
+            if (!handShapes || handShapes.length === 0 || !notesArr || notesArr.length === 0) return null;
+            if (!validString(n.s)) return null;
+            for (let i = 0; i < handShapes.length; i++) {
+                const hs = handShapes[i];
+                const hsLo = hsStart(hs);
+                const hsHi = hsEnd(hs);
+                if (Number.isNaN(hsLo) || Number.isNaN(hsHi)) continue;
+                if (n.t + 1e-4 < hsLo || n.t > hsHi + 1e-4) continue;
+                const cid = hsChordIdNorm(hs);
+                if (cid == null) continue;
+                const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
+                if (!tmpl || !Array.isArray(tmpl.frets)) continue;
+                const tf = tmpl.frets[n.s];
+                if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
+                const synthNotes = chordNotesFromTemplate(cid, chordTemplates);
+                if (synthNotes.length === 0) continue;
+                const fakeCh = { t: hsLo, id: cid, notes: synthNotes };
+                const shape = mergeChordShape(fakeCh, synthNotes, chordTemplates);
+                const tw = { tLo: hsLo - 0.06, tHi: hsHi + 0.06 };
+                if (handShapeChartSpanSec(hs) < ARP_INFER_MIN_HAND_SHAPE_SPAN_S) continue;
+                if (inferArpeggioFromNotePattern(fakeCh, shape, notesArr, tw, handShapes)) return cid;
+            }
+            return null;
+        }
+
+        /**
+         * Per-frame warmup: ``inferArpeggioFromNotePattern`` depends only on
+         * ``handShape × chart``, not on the candidate note — the old path
+         * recomputed it for every visible note (O(notecount × hs × notescan)).
+         * Fill ``outFlags[i]`` with the boolean once per ``handShapes[i]``.
+         */
+        function fillArpeggioGhostInferFlags(handShapes, chordTemplates, notesArr, outFlags, outSynthOnsetSet = null) {
+            for (let i = 0; i < handShapes.length; i++) {
+                let infer = false;
+                const hs = handShapes[i];
+                if (handShapeChartSpanSec(hs) < ARP_INFER_MIN_HAND_SHAPE_SPAN_S) {
+                    outFlags[i] = false;
+                    continue;
+                }
+                const cid = hsChordIdNorm(hs);
+                if (cid != null && notesArr.length > 0) {
+                    const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
+                    if (tmpl && Array.isArray(tmpl.frets)) {
+                        const synthNotes = chordNotesFromTemplate(cid, chordTemplates);
+                        if (synthNotes.length > 0) {
+                            const hsLo = hsStart(hs);
+                            const hsHi = hsEnd(hs);
+                            const fakeCh = { t: hsLo, id: cid, notes: synthNotes };
+                            const shape = mergeChordShape(fakeCh, synthNotes, chordTemplates);
+                            const tw = { tLo: hsLo - 0.06, tHi: hsHi + 0.06 };
+                            infer = inferArpeggioFromNotePattern(fakeCh, shape, notesArr, tw, handShapes);
+                            // Chord-hold gate: inferArpeggioFromNotePattern can fire true
+                            // when open-string notes coincidentally match the template's
+                            // open positions but only a SINGLE fretted (f>0) string is
+                            // actually played at the handshape onset. Treat that as a
+                            // chord hold (not an arpeggio) — clear the arp flag, no
+                            // brackets. The original implementation also intended to
+                            // record a synthetic sustain extending to hsEnd for the
+                            // onset note, but that read-side was never wired up; the
+                            // visual decay-before-handshape-end is benign.
+                            if (infer) {
+                                let _frettedCount = 0;
+                                let _onsetNote = null;
+                                const _fSeen = new Set();
+                                let _ci = lowerBoundT(notesArr, tw.tLo - 0.02);
+                                for (; _ci < notesArr.length; _ci++) {
+                                    const _cn = notesArr[_ci];
+                                    if (_cn.t > tw.tHi + 0.02) break;
+                                    if (_cn.t < tw.tLo) continue;
+                                    if (!validString(_cn.s)) continue;
+                                    if (shape.get(_cn.s) !== _cn.f) continue;
+                                    if (_cn.f > 0 && !_fSeen.has(_cn.s)) {
+                                        _frettedCount++;
+                                        _fSeen.add(_cn.s);
+                                        if (_onsetNote === null) _onsetNote = _cn;
+                                    }
+                                }
+                                if (_frettedCount <= 1 && _onsetNote !== null) {
+                                    outFlags[i] = false;
+                                    continue; // chord hold handled — skip onset-match and outFlags assignment
+                                }
+                            }
+                            // Non-arp template inferred as arpeggio: suppress brackets.
+                            // Only explicit arp-marked templates (arp:true / displayName "-arp")
+                            // should show [ ] / < > bracket markers.
+                            if (infer && outSynthOnsetSet != null
+                                && !handShapeMarkedArpeggio(hs, chordTemplates)) {
+                                outSynthOnsetSet.add(hsLo);
+                            }
+                            // Also treat as arp ghost when the hs generated a suppressed
+                            // synth chord: any standalone note in the onset window matches
+                            // any shape string. Handles patterns where inferArpeggioFromNotePattern
+                            // returns false (e.g. repeated arpeggio across a long hs span
+                            // triggers the multi-strum rejection), but the player still
+                            // needs the "hold this shape" ghost fret numbers on the board.
+                            if (!infer) {
+                                const _oLo = hsLo - ARP_FRAME_ONSET_PAD_S;
+                                const _oHi = hsLo + ARP_FRAME_ONSET_CLUSTER_S;
+                                let _oi = lowerBoundT(notesArr, _oLo - 0.02);
+                                for (; _oi < notesArr.length; _oi++) {
+                                    const _on = notesArr[_oi];
+                                    if (_on.t > _oHi) break;
+                                    if (_on.t < _oLo) continue;
+                                    if (shape.get(_on.s) === _on.f) {
+                                        infer = true;
+                                        // Only suppress brackets when the handshape is NOT an
+                                        // explicit arpeggio (arp:true template / displayName "-arp").
+                                        // Genuine arp handshapes reached via onset-match still need
+                                        // the [ ] bracket markers — only non-arp synth chords are
+                                        // "false positives" that should hide the brackets.
+                                        if (outSynthOnsetSet != null
+                                            && !handShapeMarkedArpeggio(hs, chordTemplates)) {
+                                            outSynthOnsetSet.add(hsLo);
+                                        }
+                                        break;
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+                outFlags[i] = infer;
+            }
+        }
+
+        // Chart-static WeakMap cache: note object → chord-id (or null sentinel).
+        // The result depends only on the note's (t, s, f) and the chart's handShapes
+        // + chordTemplates, which never change after load. Keyed by note object so
+        // switching songs/arrangements drops the entries with the old array.
+        const _ARP_CID_NULL = Object.freeze({});
+        const _arpCidCache = new WeakMap();
+        function arpeggioChordIdForNoteWithInferCache(n, handShapes, chordTemplates, notesArr, hsInferFlags) {
+            const cached = _arpCidCache.get(n);
+            if (cached !== undefined) return cached === _ARP_CID_NULL ? null : cached;
+            let result = null;
+            if (!handShapes || handShapes.length === 0 || !notesArr || notesArr.length === 0 || !hsInferFlags) {
+                result = arpeggioChordIdForNote(n, handShapes, chordTemplates, notesArr);
+            } else if (validString(n.s)) {
+                for (let i = 0; i < handShapes.length; i++) {
+                    if (!hsInferFlags[i]) continue;
+                    const hs = handShapes[i];
+                    const hsLo = hsStart(hs);
+                    const hsHi = hsEnd(hs);
+                    if (Number.isNaN(hsLo) || Number.isNaN(hsHi)) continue;
+                    if (n.t + 1e-4 < hsLo || n.t > hsHi + 1e-4) continue;
+                    const cid = hsChordIdNorm(hs);
+                    if (cid == null) continue;
+                    const tmpl = chordTemplates?.[cid] ?? chordTemplates?.[Number(cid)];
+                    if (!tmpl || !Array.isArray(tmpl.frets)) continue;
+                    const tf = tmpl.frets[n.s];
+                    if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
+                    result = cid;
+                    break;
+                }
+            }
+            _arpCidCache.set(n, result === null ? _ARP_CID_NULL : result);
+            return result;
+        }
+
+        /** Returns {start, end} chart-time bounds of the arpeggio handshape that contains
+         *  this note, or null when not found.  Uses hsInferFlags to skip ruled-out
+         *  handshapes; falls back to a full scan when hsInferFlags is null. */
+        // WeakMap cache — arpHsBoundsForNote result is chart-static (note, handShapes,
+        // and hsInferFlags never change after chart load). Each renderer instance has
+        // its own WeakMap, so splitscreen panels don't interfere.
+        // Sentinel: _ARP_BOUNDS_NULL = {} distinguishes "no matching hs" from "uncached".
+        const _ARP_BOUNDS_NULL = Object.freeze({});
+        const _arpBoundsCache = new WeakMap();
+        function arpHsBoundsForNote(n, handShapes, hsInferFlags) {
+            if (!handShapes || handShapes.length === 0) return null;
+            const cached = _arpBoundsCache.get(n);
+            if (cached !== undefined) return cached === _ARP_BOUNDS_NULL ? null : cached;
+            let result = null;
+            for (let i = 0; i < handShapes.length; i++) {
+                if (hsInferFlags && !hsInferFlags[i]) continue;
+                const hs = handShapes[i];
+                const lo = hsStart(hs);
+                const hi = hsEnd(hs);
+                if (Number.isNaN(lo) || Number.isNaN(hi)) continue;
+                if (n.t + 1e-4 < lo || n.t > hi + 1e-4) continue;
+                result = { start: lo, end: hi };
+                break;
+            }
+            _arpBoundsCache.set(n, result === null ? _ARP_BOUNDS_NULL : result);
+            return result;
+        }
+
+        function handShapeIsArpeggioForLaneRail(hs, chordTemplates) {
+            return handShapeMarkedArpeggio(hs, chordTemplates);
+        }
+
+        /**
+         * Chart-time window for purple rails: hand-shape span clipped to matching
+         * ``chords[].t`` and template notes in the passage — same times that drive
+         * the 3D arpeggio frame (``ch.t`` + note stream), avoiding rails that start
+         * before the box or end before the last arpeggiated note.
+         */
+        function effectiveArpRailChartBoundsForHandShape(hs, chords, chordTemplates, notesArr) {
+            let shapeLo = hsStart(hs);
+            const _hsEndOrig = hsEnd(hs);
+            let shapeHi = _hsEndOrig;
+            const cid = hsChordIdNorm(hs);
+            if (Number.isNaN(shapeLo) || Number.isNaN(shapeHi)) {
+                return { shapeLo: 1e9, shapeHi: -1e9 };
+            }
+            if (notesArr && notesArr.length > 0 && chordTemplates && cid != null) {
+                const tmpl = chordTemplates[cid] ?? chordTemplates[Number(cid)];
+                if (tmpl && Array.isArray(tmpl.frets)) {
+                    let tFirst = null;
+                    let tLast = null;
+                    for (let i = 0; i < notesArr.length; i++) {
+                        const n = notesArr[i];
+                        if (n.t + 1e-4 < shapeLo - 0.18 || n.t > shapeHi + 0.45) continue;
+                        if (!validString(n.s)) continue;
+                        const tf = tmpl.frets[n.s];
+                        if (typeof tf !== 'number' || tf < 0 || n.f !== tf) continue;
+                        if (tFirst === null || n.t < tFirst) tFirst = n.t;
+                        if (tLast === null || n.t > tLast) tLast = n.t;
+                    }
+                    if (tFirst != null) shapeLo = Math.max(shapeLo, tFirst);
+                    if (tLast != null) shapeHi = Math.max(shapeHi, tLast);
+                }
+            }
+            if (chords && chords.length && cid != null) {
+                let tMinC = null;
+                let tMaxC = null;
+                for (let j = 0; j < chords.length; j++) {
+                    const ch = chords[j];
+                    if (ch.id !== cid && Number(ch.id) !== Number(cid)) continue;
+                    if (ch.t + 1e-4 < shapeLo || ch.t > shapeHi + 0.28) continue;
+                    if (tMinC === null || ch.t < tMinC) tMinC = ch.t;
+                    if (tMaxC === null || ch.t > tMaxC) tMaxC = ch.t;
+                }
+                if (tMinC != null) shapeLo = Math.max(shapeLo, tMinC);
+                if (tMaxC != null) shapeHi = Math.max(shapeHi, tMaxC);
+            }
+            shapeLo -= ARP_HWY_RAIL_START_LEAD_S;
+            // Only extend past the handshape end when notes/chords genuinely reach
+            // beyond it — otherwise the tail would make the rail visually larger
+            // than the actual handshape duration (e.g. 0.38 s / 1.3 s ≈ 29% extra).
+            if (shapeHi > _hsEndOrig) shapeHi += ARP_HWY_RAIL_END_TAIL_S;
+            return { shapeLo, shapeHi };
+        }
+
+        /** Cache the authored arpeggio marker per hand shape. */
+        function fillLaneRailHandShapeFlags(handShapes, chordTemplates, outFlags) {
+            const nHs = handShapes.length;
+            for (let i = 0; i < nHs; i++) {
+                outFlags[i] = handShapeIsArpeggioForLaneRail(handShapes[i], chordTemplates);
+            }
+        }
+
+        function fillArpeggioRailShapeBoundsCaches(
+            handShapes, chords, chordTemplates, notesArr, laneRailFlags, loOut, hiOut,
+        ) {
+            const nHs = handShapes.length;
+            for (let i = 0; i < nHs; i++) {
+                if (!laneRailFlags[i]) continue;
+                const b = effectiveArpRailChartBoundsForHandShape(
+                    handShapes[i], chords, chordTemplates, notesArr,
+                );
+                loOut[i] = b.shapeLo;
+                hiOut[i] = b.shapeHi;
+            }
+        }
+
+        /** ``[tChartLo,tChartHi]`` chart times that a lane slice covers (see module ``BEHIND`` / approach ``dt``). */
+        function arpeggioLaneOuterRailChartIntervalOverlaps(
+            tChartLo,
+            tChartHi,
+            handShapes,
+            boundLo,
+            boundHi,
+            laneRailFlags,
+        ) {
+            if (!handShapes || handShapes.length === 0) return false;
+            if (!laneRailFlags) return false;
+            if (tChartHi < tChartLo) {
+                const s = tChartLo;
+                tChartLo = tChartHi;
+                tChartHi = s;
+            }
+            for (let i = 0; i < handShapes.length; i++) {
+                if (!laneRailFlags[i]) continue;
+                const shapeLo = boundLo[i];
+                const shapeHi = boundHi[i];
+                if (tChartHi < shapeLo - 1e-4 || tChartLo > shapeHi + 1e-4) continue;
+                return true;
+            }
+            return false;
+        }
+
+        function arpeggioLaneOuterRailLaneSlice(
+            dt0, dt1, nowClock,
+            handShapes, boundLo, boundHi, laneRailFlags,
+        ) {
+            const tLo = nowClock + Math.min(dt0, dt1) - BEHIND;
+            const tHi = nowClock + Math.max(dt0, dt1) - BEHIND;
+            return arpeggioLaneOuterRailChartIntervalOverlaps(
+                tLo, tHi, handShapes, boundLo, boundHi, laneRailFlags,
+            );
+        }
+
+        /**
+         * True when **chart time** ``chartT`` falls inside an arpeggio hand-shape.
+         * Uses a short end tail only — no ``CHORD_HWY_LINGER_S`` — so purple lane
+         * rails match visible highway slices and do not leak after shapes end.
+         */
+        function arpeggioLaneOuterRailAtChartTime(
+            chartT, handShapes, boundLo, boundHi, laneRailFlags,
+        ) {
+            return arpeggioLaneOuterRailChartIntervalOverlaps(
+                chartT, chartT, handShapes, boundLo, boundHi, laneRailFlags,
+            );
+        }
+
+        /**
+         * Same ``chordAccent ? ft *= 1.22`` as the 3D arpeggio chord rim so lane
+         * rails match an accented frame when the active hand shape links to a
+         * chord row that carries ``.ac`` notes.
+         */
+        function arpeggioLaneDividerFrameAccentMul(nowT, handShapes, chords, boundLo, boundHi, laneRailFlags) {
+            if (!handShapes || handShapes.length === 0 || !chords || chords.length === 0) return 1;
+            if (!laneRailFlags) return 1;
+            for (let i = 0; i < handShapes.length; i++) {
+                if (!laneRailFlags[i]) continue;
+                const shapeLo = boundLo[i];
+                const shapeHi = boundHi[i];
+                if (nowT + 1e-4 < shapeLo || nowT > shapeHi + 1e-4) continue;
+
+                const cid = hsChordIdNorm(handShapes[i]);
+                if (cid == null) return 1;
+                for (let j = 0; j < chords.length; j++) {
+                    const ch = chords[j];
+                    if (ch.id !== cid && Number(ch.id) !== Number(cid)) continue;
+                    if (Math.abs(ch.t - hsStart(handShapes[i])) > 0.12) continue;
+                    const chordNotes = ch.notes ? filterValidNotes(ch.notes) : [];
+                    if (chordNotes.some(cn => cn.ac)) return 1.22;
+                    return 1;
+                }
+                return 1;
+            }
+            return 1;
+        }
+
+        /** World-scale XY for purple lane rails = arpeggio ``ftSide`` / ``gLaneDivider`` edge (0.15×K). */
+        function arpeggioLaneDividerXYScaleMatchFrameRim(accentMul = 1) {
+            const yA = sY(0), yB = sY(nStr - 1);
+            const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
+            const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
+            const fullChordBoxH = yMaxF - yMinF;
+            let ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
+            if (accentMul !== 1 && accentMul > 0) ft *= accentMul;
+            const ftSide = ft * 1.55;
+            return ftSide / (0.15 * K);
+        }
+
+        /* ── Fret-label measure-skip rule ───────────────────────────────── */
+        // For each (note_time, fret) pair across standalone notes and chord
+        // notes, determine which ones are allowed to display their fret
+        // indicator number. Rule: per fret (regardless of string), show the
+        // number only on the first note in a given measure; suppress it for
+        // the immediately following measure; then allow it again (current
+        // measure + 2).
+        // Key scheme: Math.round(t * 25) * 100 + fret  (40 ms time buckets).
+        // Using a coarse time-bucket (not exact time) ensures that a synthetic
+        // chord template whose .t differs from the corresponding standalone
+        // arpeggio note by a few ms still resolves to the same key.
+        // Only standalone notes (notesArr) populate the set; regular chord notes
+        // never show labels, and synthetic chord notes share frets/onsets with
+        // their arpeggio counterparts, so the same keys are found at lookup time.
+        // Returns a Set of numeric keys (Math.round(t*25)*100 + fret).
+        function _buildFretLabelSet(notesArr, _chordsArr, beatsArr) {
+            const events = [];
+            if (notesArr) {
+                for (let _i = 0; _i < notesArr.length; _i++) {
+                    const _n = notesArr[_i];
+                    if (_n.f > 0) events.push({ t: _n.t, f: _n.f });
+                }
+            }
+            // Chord events intentionally excluded: regular chord notes don't show
+            // fret labels; synthetic chord notes share frets with arpeggio note-stream
+            // notes already captured above, so no separate chord processing needed.
+            events.sort((a, b) => a.t - b.t);
+            const beats = beatsArr || [];
+            let beatIdx = 0;
+            let currentMeasure = 0;
+            const nextShowMeasure = new Map(); // fret → next measure where label is allowed
+            const allowed = new Set();
+            for (let _ei = 0; _ei < events.length; _ei++) {
+                const { t, f } = events[_ei];
+                // Advance beats pointer: find the current measure for time t.
+                while (beatIdx < beats.length && beats[beatIdx].time <= t + 1e-4) {
+                    if (beats[beatIdx].measure >= 0) currentMeasure = beats[beatIdx].measure;
+                    beatIdx++;
+                }
+                const nextM = nextShowMeasure.get(f) ?? 0;
+                if (currentMeasure >= nextM) {
+                    // Time-bucket key: 40 ms groups absorb timing jitter while
+                    // still distinguishing notes at different positions in the measure.
+                    allowed.add(Math.round(t * 25) * 100 + f);
+                    // Suppress this fret for the next measure; re-allow at +2.
+                    nextShowMeasure.set(f, currentMeasure + 2);
+                }
+            }
+            return allowed;
+        }
+
+        // Smoothed playback clock for this frame. Called once per frame at the
+        // top of update(); camUpdate() reads the stored _frameNow afterward so
+        // notes and camera share one clock. See the _clk* state block above.
+        function smoothNow(bundle) {
+            const raw = bundle.currentTime;
+            const p = performance.now();
+            // Host pause signal (feedBack core's bundle.isPlaying): when the
+            // chart clock isn't advancing (paused / stalled / mid-seek), don't
+            // extrapolate forward against a frozen audio sample — that creeps
+            // the highway ahead by up to the interp cap and then snaps back
+            // when dt finally crosses 0.1. Re-anchor to raw so the next
+            // playing frame resumes from a clean segment. `=== false` so
+            // downlevel hosts (isPlaying undefined) fall through to the
+            // staleness-based cap below, preserving prior behavior there.
+            if (bundle.isPlaying === false) {
+                _clkAudioT = raw;
+                _clkPerf = p;
+                _clkRate = 1;
+                return (_frameNow = raw);
+            }
+            if (raw !== _clkAudioT) {
+                // New audio sample — re-anchor and refine the rate estimate.
+                if (!Number.isNaN(_clkPerf)) {
+                    const dP = (p - _clkPerf) / 1000;
+                    if (dP > 0.001 && dP < 0.5) {
+                        const r = (raw - _clkAudioT) / dP;
+                        _clkRate = (r > 0.05 && r < 5) ? r : 1; // seek/loop → reset
+                    } else if (dP >= 0.5) {
+                        _clkRate = 1; // long gap (paused / tab inactive)
+                    }
+                }
+                _clkAudioT = raw;
+                _clkPerf = p;
+                return (_frameNow = raw);
+            }
+            // Same audio sample as last call — interpolate forward, capped so a
+            // stalled main thread or paused audio can't run the clock away.
+            const dt = (p - _clkPerf) / 1000;
+            if (dt <= 0 || dt > 0.1) return (_frameNow = raw);
+            return (_frameNow = _clkAudioT + _clkRate * dt);
+        }
+
+        /* ── Per-frame rendering ─────────────────────────────────────────── */
+        // ── GPU pre-warm (perf: first-appearance hitches) ─────────────────
+        // Three.js compiles a material's shader program and uploads a
+        // texture the first frame the owning object renders — profiled as
+        // mid-song frame spikes (getParameters / texSubImage2D). Pay those
+        // costs during init (load spinner) instead:
+        //   _prewarmStatic()      — ren.compile() over the fully-built scene
+        //                           + deterministic label textures (fret
+        //                           numbers in every per-frame style/colour
+        //                           combo).
+        //   _prewarmChart(bundle) — chart-dependent labels (chord template
+        //                           names, section names); needs the ready
+        //                           bundle, so it runs once from the first
+        //                           draw() after each init.
+        // txtMat() rasterises into the unbounded cache these draws hit
+        // anyway; ren.initTexture() forces the GPU upload now.
+        // Swap a pooled label sprite's cached texture WITHOUT recompiling.
+        // Setting material.needsUpdate bumps material.version, which forces
+        // Three.js through getParameters/getProgramCacheKey on the next
+        // render. Swapping one non-null texture for another does NOT change
+        // the compiled program (the USE_MAP define is unchanged); only a
+        // null <-> non-null transition does, and pooled label sprites are
+        // constructed with a non-null map, so in practice this never
+        // recompiles. (Note: the DOMINANT getParameters churn turned out to
+        // be Three's transparent-DoubleSide two-pass path — see the
+        // forceSinglePass comment in _spriteMat2MeshMat — this helper
+        // removes the label-swap contribution on top of that.)
+        function _setLabelMap(sprite, srcMat) {
+            const m = sprite.material;
+            if (m.map === srcMat.map) return;
+            const nullnessChanged = (m.map == null) !== (srcMat.map == null);
+            m.map = srcMat.map;
+            if (nullnessChanged) m.needsUpdate = true;
+        }
+
+        let _chartPrewarmed = false;
+        function _prewarmTex(mat) {
+            if (mat && mat.map && ren) ren.initTexture(mat.map);
+        }
+        function _prewarmStatic() {
+            // MAINTENANCE NOTE: this list must cover every deterministic
+            // (chart-independent) material/texture the per-frame paths can
+            // request lazily. Adding a new label style or sprite factory to
+            // drawNote()/update() without warming it here silently
+            // reintroduces a first-appearance texSubImage2D/compile spike
+            // mid-song. Chart-dependent labels (chord names, section names)
+            // live in _prewarmChart.
+            try {
+                if (ren && scene && cam) ren.compile(scene, cam);
+            } catch (e) { console.warn('[3D-Hwy] prewarm compile:', e); }
+            try {
+                // Fret-number labels in the per-frame style/colour combos.
+                for (let f = 0; f <= NFRETS; f++) {
+                    _prewarmTex(txtMat(f, FRET_LABEL_GOLD_HEX, false, 'noteFret'));
+                    _prewarmTex(txtMat(f, FRET_LABEL_GOLD_HEX, false, 'fretRow'));
+                    _prewarmTex(txtMat(f, FRET_LABEL_IDLE_HEX, false, 'fretRow'));
+                    _prewarmTex(txtMat(f, '#ffffff', false, 'ghostFret'));
+                }
+                // Teaching marks (drawNote _drawTeachMark): finger hints
+                // T/1-4 (teachFg) and scale degrees 0-11 (teachSd).
+                _prewarmTex(txtMat('T', '#7fd1ff', false, 'teachFg'));
+                for (let i = 1; i <= 4; i++) _prewarmTex(txtMat(String(i), '#7fd1ff', false, 'teachFg'));
+                for (let i = 0; i <= 11; i++) _prewarmTex(txtMat(String(i), '#ffcc66', false, 'teachSd'));
+                // Technique sprite factories (own caches, keyed by packed
+                // number): PM/FH mute X, hammer/pull triangles, bend
+                // chevron stacks, slide direction arrows — per string
+                // colour of the active palette.
+                _prewarmTex(palmMuteXSpriteMat());
+                _prewarmTex(fretHandMuteXSpriteMat());
+                const _nWarm = Math.min(
+                    Math.max(nStr, 6),
+                    (activePalette && activePalette.length) || 0);
+                for (let s = 0; s < _nWarm; s++) {
+                    const hex = activePalette[s] || 0xffffff;
+                    _prewarmTex(triMat(true, hex));
+                    _prewarmTex(triMat(false, hex));
+                    for (let st = 1; st <= 4; st++) _prewarmTex(bendChevronMat(st, hex));
+                    const arrowHex = darkenHex(hex, 0.55);
+                    _prewarmTex(slideArrowMat(true, arrowHex));
+                    _prewarmTex(slideArrowMat(false, arrowHex));
+                }
+            } catch (e) { console.warn('[3D-Hwy] prewarm labels:', e); }
+        }
+        function _prewarmChart(bundle) {
+            try {
+                const tpls = bundle && bundle.chordTemplates;
+                if (Array.isArray(tpls)) {
+                    for (const tpl of tpls) {
+                        if (tpl && tpl.name) _prewarmTex(txtMat(tpl.name, '#e8d080', true, 'chord'));
+                    }
+                }
+                const secs = bundle && bundle.sections;
+                if (Array.isArray(secs)) {
+                    for (const s of secs) {
+                        if (s && s.name) _prewarmTex(txtMat(s.name, '#00cccc', true, 'section'));
+                    }
+                }
+            } catch (e) { console.warn('[3D-Hwy] prewarm chart labels:', e); }
+        }
+
+        function update(bundle) {
+            pbBeg(0);
+            // [verdict glow] Apply the level-driven verdict brightness captured
+            // last frame (1-frame lag is imperceptible), then reset for this
+            // frame's capture in the gem path below. vg = 1 when no provider
+            // alpha was seen (legacy event path / note_detect off), leaving the
+            // authored 4.0/0.7 × glowMul brightness from _applyGlow() untouched.
+            // Only the verdict-only materials (mHitBright + its face-fill arrays,
+            // and the hit sustain outline) are scaled — never mStrHitOutline,
+            // which is the default rim for every fretted note.
+            {
+                const vg = _ndVerdictSawAlpha ? _ndVerdictMaxAlpha : 1;
+                const venueGemMul = _venueSceneOverride ? VENUE_GEM_EMISSIVE_MUL : 1;
+                for (let s = 0; s < mHitBright.length; s++) {
+                    if (mHitBright[s]) mHitBright[s].emissiveIntensity = 4.0 * glowMul * vg * venueGemMul;
+                }
+                if (mHitSusOutline) mHitSusOutline.emissiveIntensity = 0.7 * glowMul * vg * venueGemMul;
+                _ndVerdictMaxAlpha = 0;
+                _ndVerdictSawAlpha = false;
+            }
+            // Lean sustain rendering is the default (see declaration above):
+            // the trail/ribbon outline always draws; only the additive rail
+            // bloom halo is dropped. The full look (with bloom) is an opt-out.
+            // localStorage.getItem is a synchronous storage read — polled at
+            // ~1 Hz instead of every frame; the console flag still takes
+            // effect live (within a second).
+            if ((_leanSusPollCounter++ % 60) === 0) {
+                try {
+                    _leanSus = localStorage.getItem('h3d_full_sus') !== '1';
+                } catch (_) { _leanSus = true; }
+            }
+            // Materialize the text-size multiplier from the user's slider.
+            // textSize ∈ [0,1]; _textSizeMul ∈ [0.5, 1.5] with 0.5 ↦ 1.0×
+            // so default behaviour matches what the renderer did pre-slider.
+            _textSizeMul = 0.5 + textSize;
+            // Rescale inlay labels to track the live text-size slider.
+            // buildBoard() sets an initial scale using (0.5 + textSize) but
+            // _textSizeMul is only authoritative from here onward.
+            // Guard: only update when the multiplier actually changed.
+            if (_textSizeMul !== _textSizeMulApplied) {
+                _textSizeMulApplied = _textSizeMul;
+                for (let i = 0; i < _inlayLabels.length; i++) {
+                    const f = INLAY_LABEL_FRETS[i];
+                    const s = 5.5 * _textSizeMul * K * fretLabelScaleForFret(f);
+                    _inlayLabels[i].scale.set(s, s, 1);
+                }
+            }
+            _syncOpenStringPitchLabels(bundle);
+
+            pNote.reset(); pNoteEdge.reset(); pSus.reset(); pSusOutline.reset(); pSusRibbon.reset(); pSusRibbonOl.reset(); pTapChevron.reset(); pAccentHalo.reset(); pLbl.reset();
+            pBeat.reset(); pSec.reset();
+            if (projMeshArr) for (const arr of projMeshArr) for (const m of arr) m.visible = false;
+            pFretLbl.reset(); pLane.reset(); pLaneDivider.reset();
+            if (pGhostFretLbl) pGhostFretLbl.reset();
+            _scrGhostUpcomingCount.fill(0, 0, nStr);
+            pChordBox.reset(); pChordFrameFill.reset(); pChordLbl.reset(); pBarreLine.reset(); pArpBracket.reset(); pHaloBar.reset();
+            _imPMTechCount = _imFHTechCount = 0;
+            _imPMXFillCount = _imPMXLinesCount = _imFHXFillCount = _imFHXLinesCount = 0;
+            if (pPMXFill) pPMXFill.reset();
+            if (pFHXFill) pFHXFill.reset();
+            if (pMuteXLines) pMuteXLines.reset();
+            if (pFHXLines) pFHXLines.reset();
+            pNoteFretLabel.reset(); pConnectorLine.reset(); pDropLine.reset();
+            pTeachMarkLbl.reset();
+            pFretColMarker.reset(); pSusRail.reset(); pSusRailBloom.reset(); pTechPlane.reset();
+            // Clear per-frame queues in-place (avoid reallocating the array object).
+            _ndLabels.length = 0;
+            let hwyLaneArpOuterDividers = false;
+
+            // Prune expired notedetect marks once per frame instead of
+            // once per drawNote call (issue #9 perf nit). drawNote then
+            // only does the bounded (s, f, t) match — no per-note
+            // performance.now() / filter() needed. No arr[0] gate: the
+            // dedupe path can refresh any entry's expiresAt, so gating on
+            // arr[0] would silently skip expired entries behind it.
+            _ndFrameNowMs = performance.now();
+            // In-place prune — avoids allocating a new array every frame.
+            // Marks are tiny (0–5 entries typically), so a backwards splice
+            // loop is cheap and keeps the existing array object alive.
+            if (_ndHitMarks.length) {
+                for (let _pi = _ndHitMarks.length - 1; _pi >= 0; _pi--) {
+                    if (_ndHitMarks[_pi].expiresAt <= _ndFrameNowMs) _ndHitMarks.splice(_pi, 1);
+                }
+            }
+            if (_ndMissMarks.length) {
+                for (let _pi = _ndMissMarks.length - 1; _pi >= 0; _pi--) {
+                    if (_ndMissMarks[_pi].expiresAt <= _ndFrameNowMs) _ndMissMarks.splice(_pi, 1);
+                }
+            }
+            // feedBack#254 — capture core's per-note judgment provider for
+            // this frame's drawNote() calls (held-sustain glow + lit gems).
+            // bundle.getNoteState is ALWAYS present (the core stub returns
+            // null when no provider is registered), so its existence isn't
+            // a "detect mode active" signal on its own.
+            // bundle.getNoteStateProvider exposes the registered provider
+            // (or null) directly — drive cull-window / chord-rim-floor
+            // extensions off that so they don't activate in non-detect
+            // mode. Downlevel hosts without getNoteStateProvider fall
+            // back to the existence check, matching pre-PR behavior on
+            // those builds.
+            _ndGetNoteState = (bundle && typeof bundle.getNoteState === 'function') ? bundle.getNoteState : null;
+            _ndHasProvider = (bundle && typeof bundle.getNoteStateProvider === 'function')
+                ? bundle.getNoteStateProvider() != null
+                : !!_ndGetNoteState;
+
+            const now = smoothNow(bundle);
+            const t0 = now - BEHIND;
+            const t1 = now + AHEAD;
+            // With a verdict provider attached, keep notes and chord frames
+            // in the outer loop past BEHIND so async verdicts (~0.4 s late)
+            // still land while drawable; per-note / per-frame culling is
+            // tightened back below.
+            const ndVerdictT0 = _ndHasProvider
+                ? now - Math.max(BEHIND, NOTEDETECT_GEM_VERDICT_WINDOW)
+                : t0;
+            // Prune _chordVerdicts latches whose chord has fully scrolled
+            // past the loop's verdict-window cull. Forward playback never
+            // re-encounters a chord, so without this prune the map would
+            // grow unbounded for the rest of the song (each chord onset
+            // contributes one entry, ~hundreds for a typical song).
+            // verdictKey is now an integer encoded by _encodeChordVerdictKey
+            // — time component sits in the upper bits, so a direct
+            // ``k < pruneBeforeKey`` test prunes correctly without
+            // parseFloat / String.slice on every entry.
+            //
+            // Backward seek (now < lastNow): every latched entry's
+            // chord time is now ahead of `now`, the forward-only check
+            // below would skip them all and the map would grow on every
+            // loop. Clear wholesale — the chord-loop's `chDt > 0` eviction
+            // re-creates entries as chords re-enter the pre-hit window.
+            //
+            // Forward playback: iterate every entry. An earlier `break`
+            // optimization assumed Map insertion order tracked chord
+            // time, but entries are inserted when a verdict OBSERVATION
+            // lands — so a later chord whose verdict arrived first could
+            // sit before an earlier chord whose verdict was still
+            // pending, and breaking on the first in-window entry would
+            // leave the now-older later-inserted entries un-pruned. Full
+            // scan is O(n) but n is bounded (chord count in the song,
+            // ~hundreds) so the per-frame cost is microseconds.
+            if (_ndHasProvider && _chordVerdictsLastNow !== null && now < _chordVerdictsLastNow - 0.25) {
+                // Backward seek — wipe all verdict latches so notes re-judge
+                // from scratch regardless of whether chords were present.
+                _chordVerdicts.clear();
+                _susVerdictLatch.clear();
+                // Score-pop dedup too: a practice loop / rewind re-judges
+                // the same popKeys, and the wall-time TTL alone would
+                // suppress their fresh "+N" pops for up to 4 s.
+                _fxSeen.clear();
+            }
+            if (_ndHasProvider && _chordVerdicts.size > 0) {
+                if (_chordVerdictsLastNow !== null && now < _chordVerdictsLastNow - 0.25) {
+                    // already cleared above
+                } else {
+                    const pruneBefore = ndVerdictT0 - 0.5; // safety margin
+                    const pruneBeforeKey = Math.round(pruneBefore * _CV_KEY_TIME_MUL) * _CV_KEY_TIME_SLOT;
+                    for (const k of _chordVerdicts.keys()) {
+                        if (k < pruneBeforeKey) _chordVerdicts.delete(k);
+                    }
+                }
+            }
+            _chordVerdictsLastNow = now;
+
+            const notes = bundle.notes;
+            // Skip the merge when inputs are identity-equal to the last
+            // frame's; mergeHandShapeSynthChords is chart-static.
+            let chords;
+            if (_mergeCacheResult !== null
+                && _mergeCacheChordsRef === bundle.chords
+                && _mergeCacheHsRef === bundle.handShapes
+                && _mergeCacheTplRef === bundle.chordTemplates) {
+                chords = _mergeCacheResult;
+            } else {
+                chords = mergeHandShapeSynthChords(
+                    bundle.chords,
+                    bundle.handShapes,
+                    bundle.chordTemplates,
+                );
+                _mergeCacheResult = chords;
+                _mergeCacheChordsRef = bundle.chords;
+                _mergeCacheHsRef = bundle.handShapes;
+                _mergeCacheTplRef = bundle.chordTemplates;
+            }
+
+            let arpGhostHsInfer = null;
+            const hsForArpGhost = bundle.handShapes;
+            if (hsForArpGhost && hsForArpGhost.length && notes && notes.length) {
+                const nHs = hsForArpGhost.length;
+                while (_arpGhostHsInferScratch.length < nHs) _arpGhostHsInferScratch.push(false);
+                // fillArpeggioGhostInferFlags is chart-static — skip if
+                // the input refs match the previous frame's.
+                if (_arpGhostInferRefHs !== hsForArpGhost
+                    || _arpGhostInferRefNotes !== notes
+                    || _arpGhostInferRefTpl !== bundle.chordTemplates) {
+                    _arpSynthOnsetHsSet.clear();
+                    fillArpeggioGhostInferFlags(hsForArpGhost, bundle.chordTemplates, notes, _arpGhostHsInferScratch, _arpSynthOnsetHsSet);
+                    _arpGhostInferRefHs = hsForArpGhost;
+                    _arpGhostInferRefNotes = notes;
+                    _arpGhostInferRefTpl = bundle.chordTemplates;
+                }
+                arpGhostHsInfer = _arpGhostHsInferScratch;
+            }
+
+            // ── Arpeggio-persist pre-pass ─────────────────────────────────
+            // Notes in active arpeggio handshapes must keep rendering their
+            // fretboard ghost + brackets until arpBounds.end, even after
+            // their onset+sustain exits the normal back-window (t0 = now-0.5s).
+            // Build a Set of "t_s" keys so the notes loop can skip the normal
+            // window check for these notes.
+            // Reuse hoisted Set — clear instead of reallocating every frame.
+            _scrArpPersistKeys.clear();
+            const _arpPersistKeys = _scrArpPersistKeys;
+            if (arpGhostHsInfer && bundle.handShapes && notes) {
+                for (let _hi = 0; _hi < bundle.handShapes.length; _hi++) {
+                    if (!arpGhostHsInfer[_hi]) continue;
+                    const _hs = bundle.handShapes[_hi];
+                    const _lo = hsStart(_hs), _hi2 = hsEnd(_hs);
+                    if (Number.isNaN(_lo) || Number.isNaN(_hi2)) continue;
+                    if (now > _hi2 + 0.05) continue; // arpeggio already ended
+                    // Only persist notes that have already exited the normal back-window
+                    // (onset+sustain < t0). Notes still in the window enter the loop via
+                    // the normal check; future notes are gated by the t1 check below.
+                    const _nLo = lowerBoundT(notes, _lo - 0.01);
+                    for (let _ni = _nLo; _ni < notes.length; _ni++) {
+                        const _n = notes[_ni];
+                        if (_n.t > _hi2 + 0.05) break;
+                        if (_n.t + (_n.sus || 0) < t0) {
+                            _arpPersistKeys.add(_noteKey(_n.t, _n.s));
+                        }
+                    }
+                }
+            }
+
+            // ── Slide-target gem-suppression pre-pass (chart-static) ──────
+            // Detects notes in bundle.notes that are the slide/link destination
+            // of a preceding note. The gem (outline+core) is suppressed via
+            // skipBody=true, but the sustain/slide trail still renders because
+            // the trail block is now outside the !skipBody gate in drawNote().
+            //
+            // NOTE: an authored `linkNext` flag is NOT present in bundle.notes —
+            // note_to_wire() in lib/song.py emits only t, s, f, sus, sl, slu,
+            // bn, ho, po, hm, hp, pm, mt, vb, tr, ac, tp. So this is an
+            // intentional timing/fret heuristic, not a link-flag lookup.
+            //
+            // Two source patterns (source has sus > 0):
+            //   Case 1 — source has sl/slu: destination.f === source's slide target
+            //   Case 2 — same fret (hold), destination has sl/slu (hold→slide)
+            //
+            // Sources can be single notes OR chord notes (bundle.chords).
+            if (notes !== _slideTargetNotesRef || bundle.chords !== _slideTargetChordsRef) {
+                _slideTargetSet = null;
+                if (notes && notes.length) {
+                    const stSet = new Set();
+                    const checkSrc = (srcT, srcS, srcF, srcSus, srcSl) => {
+                        if (!(srcSus > 0)) return;
+                        const endT = srcT + srcSus;
+                        // Reuse the renderer's shared next-on-string tolerance
+                        // rather than a separate hardcoded literal.
+                        const EPS = NEXT_ON_STRING_T_EPS;
+                        let lo = 0, hi = notes.length;
+                        while (lo < hi) { const m = (lo + hi) >> 1; if (notes[m].t < endT - EPS) lo = m + 1; else hi = m; }
+                        for (let j = lo; j < notes.length; j++) {
+                            const q = notes[j];
+                            if (q.t > endT + EPS) break;
+                            if (q.s !== srcS || q.t <= srcT || Math.abs(q.t - endT) >= EPS) continue;
+                            const qSl = (Number.isFinite(q.sl) && q.sl >= 0) ? q.sl
+                                      : (Number.isFinite(q.slu) && q.slu >= 0) ? q.slu : -1;
+                            if (srcSl >= 0 && q.f === srcSl) { stSet.add(_noteKey(q.t, q.s)); break; } // case 1
+                            if (q.f === srcF && qSl >= 0)    { stSet.add(_noteKey(q.t, q.s)); break; } // case 2
+                        }
+                    };
+                    for (let i = 0; i < notes.length; i++) {
+                        const p = notes[i];
+                        checkSrc(p.t, p.s, p.f, p.sus,
+                            (Number.isFinite(p.sl) && p.sl >= 0) ? p.sl : (Number.isFinite(p.slu) && p.slu >= 0) ? p.slu : -1);
+                    }
+                    const rc = bundle.chords;
+                    if (rc && rc.length) {
+                        for (let ci = 0; ci < rc.length; ci++) {
+                            const ch = rc[ci]; if (!ch.notes) continue;
+                            for (let ni = 0; ni < ch.notes.length; ni++) {
+                                const cn = ch.notes[ni];
+                                checkSrc(ch.t, cn.s, cn.f, cn.sus,
+                                    (Number.isFinite(cn.sl) && cn.sl >= 0) ? cn.sl : (Number.isFinite(cn.slu) && cn.slu >= 0) ? cn.slu : -1);
+                            }
+                        }
+                    }
+                    if (stSet.size > 0) _slideTargetSet = stSet;
+                }
+                _slideTargetNotesRef = notes;
+                _slideTargetChordsRef = bundle.chords;
+            }
+
+            /** Arpeggio lane purple rails — authored-marker cache + bounds cache. */
+            let laneRailArpHsFlags = null;
+            let laneRailBoundLo = null;
+            let laneRailBoundHi = null;
+            const hsLaneRail = bundle.handShapes;
+            const notesArrForRails = notes || [];
+            if (hsLaneRail && hsLaneRail.length) {
+                const nHsL = hsLaneRail.length;
+                while (_arpLaneRailHsScratch.length < nHsL) _arpLaneRailHsScratch.push(false);
+                while (_arpRailBoundLoScratch.length < nHsL) {
+                    _arpRailBoundLoScratch.push(0);
+                    _arpRailBoundHiScratch.push(0);
+                }
+                // Authored-marker flags depend only on (handShapes, templates).
+                if (_laneRailFlagsRefHs !== hsLaneRail
+                    || _laneRailFlagsRefTpl !== bundle.chordTemplates) {
+                    fillLaneRailHandShapeFlags(hsLaneRail, bundle.chordTemplates, _arpLaneRailHsScratch);
+                    _laneRailFlagsRefHs = hsLaneRail;
+                    _laneRailFlagsRefTpl = bundle.chordTemplates;
+                }
+                // Bounds cache depends on (handShapes, chords, templates, notes).
+                if (_laneRailBoundsRefHs !== hsLaneRail
+                    || _laneRailBoundsRefChords !== chords
+                    || _laneRailBoundsRefTpl !== bundle.chordTemplates
+                    || _laneRailBoundsRefNotes !== notesArrForRails) {
+                    fillArpeggioRailShapeBoundsCaches(
+                        hsLaneRail,
+                        chords ?? [],
+                        bundle.chordTemplates,
+                        notesArrForRails,
+                        _arpLaneRailHsScratch,
+                        _arpRailBoundLoScratch,
+                        _arpRailBoundHiScratch,
+                    );
+                    _laneRailBoundsRefHs = hsLaneRail;
+                    _laneRailBoundsRefChords = chords;
+                    _laneRailBoundsRefTpl = bundle.chordTemplates;
+                    _laneRailBoundsRefNotes = notesArrForRails;
+                }
+                laneRailArpHsFlags = _arpLaneRailHsScratch;
+                laneRailBoundLo = _arpRailBoundLoScratch;
+                laneRailBoundHi = _arpRailBoundHiScratch;
+            }
+            const beats = bundle.beats;
+            // Rebuild the fret-label visibility set whenever the chart changes.
+            if (notes !== _fretLabelNotesRef) {
+                _fretLabelAllowed = _buildFretLabelSet(notes, chords, beats);
+                _fretLabelNotesRef = notes;
+            }
+            // Rebuild the measure-start time cache whenever beats change. Only
+            // beats that begin a measure carry measure >= 0; intra-measure beats
+            // (measure === -1) are skipped. Drives the lookahead window.
+            if (beats !== _measureStartsRef) {
+                _measureStartsRef = beats;
+                const _ms = [];
+                if (beats) {
+                    for (let _bi = 0; _bi < beats.length; _bi++) {
+                        const _b = beats[_bi];
+                        if (_b && Number.isFinite(_b.measure) && _b.measure >= 0) _ms.push(_b.time);
+                    }
+                }
+                _measureStarts = _ms;
+            }
+            const sections = bundle.sections;
+            const anchors = bundle.anchors;
+
+            // ── Fret wire anchor highlight ─────────────────────────────────
+            // Default all wires to gray; wires inside the active anchor range
+            // turn gold to match the dynamic highway lane boundary exactly.
+            // Uses laneBoundsFromAnchor() — the same helper the lane uses —
+            // so the gold fret wires on the board align with the lane edges:
+            //   dMin = fret - 1,  dMax = fret + width - 1
+            // e.g. { fret:3, width:4 } → dMin=2, dMax=6 → wires 2,3,4,5,6 gold.
+            if (fretWireMats.length) {
+                const _fwBounds = anchors && anchors.length
+                    ? anchorLaneBoundsAt(anchors, now) : null;
+                const _fwMin = _fwBounds ? _fwBounds.dMin : -1;
+                const _fwMax = _fwBounds ? _fwBounds.dMax : -1;
+                for (let _f = 0; _f <= NFRETS; _f++) {
+                    const _m = fretWireMats[_f];
+                    if (!_m) continue;
+                    if (_fwMin >= 0 && _f >= _fwMin && _f <= _fwMax) {
+                        _m.color.setHex(FRET_WIRE_ACTIVE_HEX);
+                        _m.opacity = FRET_WIRE_ACTIVE_OP;
+                    } else {
+                        _m.color.setHex(FRET_WIRE_IDLE_HEX);
+                        _m.opacity = FRET_WIRE_IDLE_OP;
+                    }
+                    // Baseline emissive every frame: the hit-flash pass below
+                    // lerps these toward FRET_WIRE_HIT_* in place, so they must
+                    // be re-seeded or a flash would never fade back out.
+                    _m.emissive.setHex(FRET_EMISSIVE);
+                    _m.emissiveIntensity = 1;
+                }
+            }
+
+            const lookaheadBoundsNow = (cameraMode === 'lookahead')
+                ? lookaheadComputeFretBounds(now, anchors, notes, chords)
+                : null;
+
+            // Open-string note width: same outer span as chord frame (anchor + padX,
+            // or default 4-fret window when chart has no anchor at t).
+            const padChordOpenX = NW * 0.4;
+            const openNoteLaneBoxW = chartTime => {
+                const chAncB = anchorLaneBoundsAt(anchors, chartTime);
+                if (chAncB) {
+                    const xl = fretX(chAncB.dMin);
+                    const xr = fretX(chAncB.dMax);
+                    if (xr > xl) return (xr - xl) + padChordOpenX * 2;
+                }
+                const spanF = 4;
+                const fMinCh = 1;
+                const fMaxCh = fMinCh + spanF - 1;
+                const xl = fretX(fMinCh - 1);
+                const xr = fretX(Math.max(fMaxCh, fMinCh + 2));
+                if (xr > xl) return (xr - xl) + padChordOpenX * 2;
+                return 40 * K;
+            };
+
+            // ── Frame state ───────────────────────────────────────────────
+            // Reuse hoisted scratch arrays — reset only the live [0..nStr) /
+            // [0..NFRETS] range instead of allocating new arrays every frame.
+            _scrStringSustain.fill(false, 0, nStr);
+            _scrStringAnticipation.fill(0, 0, nStr);
+            _scrFretHeat.fill(0);           // always NFRETS+1, cheap flat fill
+            _fwHitIn.fill(0);               // this frame's confirmed-hit frets
+            _rimFlashIn.fill(0);            // this frame's per-string rim-flash alphas
+            _fwChordAcc.clear();
+            _scrStrGlow.fill(0.5, 0, nStr);
+            _scrAccentFillBoost.fill(0, 0, nStr);
+            const noteState = {
+                stringSustain:    _scrStringSustain,
+                stringAnticipation: _scrStringAnticipation,
+                fretHeat:         _scrFretHeat,
+                strGlow:          _scrStrGlow,
+                /** Per-string extra drive for `.ac` gem fill only (`mAccentCore`). */
+                accentFillBoost:  _scrAccentFillBoost,
+            };
+
+            pbBeg(1);
+            // Compute sustain / anticipation / fret heat / per-string glow.
+            // Use lowerBoundT to skip notes far in the past (>30s sustain is
+            // unrealistic); break once notes are >2s ahead (nothing beyond
+            // contributes to fretHeat/anticipation/strGlow).
+            if (notes) {
+                const _fsLo = lowerBoundT(notes, now - 30);
+                for (let _ni = _fsLo; _ni < notes.length; _ni++) {
+                    const n = notes[_ni];
+                    if (!validString(n.s)) continue;
+                    const dt = n.t - now;
+                    if (dt > 2.0) break;
+                    const susEnd = n.t + (n.sus || 0);
+                    if (dt > 0 && dt < 0.6)
+                        noteState.stringAnticipation[n.s] = Math.max(noteState.stringAnticipation[n.s], 1 - dt / 0.6);
+                    if (n.f > 0) {
+                        if (now >= n.t && now <= susEnd) noteState.fretHeat[n.f] = 1;
+                        else if (n.t > now) noteState.fretHeat[n.f] = Math.max(noteState.fretHeat[n.f], Math.max(0, 1 - dt / 2));
+                    }
+                    if (now >= n.t && now <= susEnd) noteState.stringSustain[n.s] = true;
+                    const sustained = dt < 0 && (n.sus || 0) > 0 && now <= susEnd;
+                    const hitDist = Math.abs(dt);
+                    if (hitDist < 0.15 || sustained) {
+                        const hitFade = sustained ? 0.7 : (1 - hitDist / 0.15);
+                        noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], 1.0 + hitFade * 1.5);
+                    }
+                }
+            }
+            if (chords) {
+                // Skip chords further than 30s in the past (covers any sustained chord).
+                const _cfsLo = lowerBoundT(chords, now - 30);
+                for (let _cni = _cfsLo; _cni < chords.length; _cni++) {
+                    const ch = chords[_cni];
+                    if (!ch.notes) continue;
+                    const dt = ch.t - now;
+                    if (dt > 2.0) break;
+                    const chordNotes = filterValidNotes(ch.notes);
+                    if (chordNotes.length === 0) continue;
+                    let maxSus = 0;
+                    for (const n of chordNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
+                    const susEnd = ch.t + maxSus;
+                    for (const cn of chordNotes) {
+                        if (dt > 0 && dt < 0.6)
+                            noteState.stringAnticipation[cn.s] = Math.max(noteState.stringAnticipation[cn.s], 1 - dt / 0.6);
+                        if (cn.f > 0) {
+                            if (now >= ch.t && now <= susEnd) { noteState.fretHeat[cn.f] = 1; continue; }
+                            if (ch.t > now) noteState.fretHeat[cn.f] = Math.max(noteState.fretHeat[cn.f], Math.max(0, 1 - dt / 2));
+                        }
+                    }
+                    if (now >= ch.t && now <= susEnd)
+                        for (const cn of chordNotes) noteState.stringSustain[cn.s] = true;
+                    const sustained = dt < 0 && maxSus > 0 && now <= susEnd;
+                    const hitDist = Math.abs(dt);
+                    if (hitDist < 0.15 || sustained) {
+                        const hitFade = sustained ? 0.7 : (1 - hitDist / 0.15);
+                        for (const cn of chordNotes) {
+                            noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], 1.0 + hitFade * 1.5);
+                        }
+                    }
+                }
+            }
+
+            pbEnd(1);
+            pbBeg(2);
+            // ── Next-note-by-string lookahead (for anticipation projection) ──
+            // Ghost projection window is 0.6s; fretLastActiveTime needs +2s.
+            // Use lowerBoundT to skip past notes and break at +2s.
+            _scrNextNoteByString.fill(null, 0, nStr);
+            const nextNoteByString = _scrNextNoteByString;
+            if (notes) {
+                const _nnLo = lowerBoundT(notes, now);
+                for (let _ni = _nnLo; _ni < notes.length; _ni++) {
+                    const n = notes[_ni];
+                    if (n.t > now + 2) break;
+                    if (!validString(n.s)) continue;
+                    if (!nextNoteByString[n.s] || n.t < nextNoteByString[n.s].t) nextNoteByString[n.s] = n;
+                    if (n.f > 0) fretLastActiveTime[n.f] = now;
+                }
+            }
+            if (chords) {
+                // Time-sorted: lowerBoundT skips past historical chords in O(log N)
+                // instead of walking the entire prefix every frame.
+                const _ncLo = lowerBoundT(chords, now);
+                for (let _ci = _ncLo; _ci < chords.length; _ci++) {
+                    const ch = chords[_ci];
+                    if (ch.t > now + 2) break;
+                    if (!ch.notes || ch.t <= now) continue;
+                    for (const cn of ch.notes) {
+                        if (!validString(cn.s)) continue;
+                        if (!nextNoteByString[cn.s] || ch.t < nextNoteByString[cn.s].t) {
+                            // Reuse per-string scratch object — avoids `{ ...cn, t }` spread allocation.
+                            const _sd = _scrNextNoteByStringData[cn.s];
+                            Object.assign(_sd, cn);
+                            _sd.t = ch.t;
+                            nextNoteByString[cn.s] = _sd;
+                        }
+                        if (cn.f > 0) fretLastActiveTime[cn.f] = now;
+                    }
+                }
+            }
+
+            _drawNextByString = nextNoteByString;
+            _drawChordTemplates = bundle.chordTemplates ?? null;
+            _drawAnchors = anchors ?? null;
+            _drawTeachingMarks = !!bundle.teachingMarksVisible;
+            // Default on: only an explicit false (older bundles omit the flag) hides fg.
+            _showFingerHints = bundle.fingerHintsVisible !== false;
+
+            // ── Recent-past event per string (for _nextAnyT deadline) ─────
+            // Once a note/chord passes `now` it leaves _drawNextByString,
+            // resetting _nextAnyT and letting old gems linger too long.
+            // Scan back at least CHORD_HWY_LINGER_S so the deadline logic
+            // can see every event that lands inside any active linger
+            // window (chord frame linger and gem linger both cap at
+            // CHORD_HWY_LINGER_S — a tighter scan would miss events in
+            // (now - CHORD_HWY_LINGER_S, now - 0.6) and let the frame
+            // linger past the next event).
+            {
+                // Hoisted scratch — avoids `new Array(nStr).fill(...)` every frame.
+                const _recArr = _scrRecentByString;
+                for (let i = 0; i < nStr; i++) _recArr[i] = -Infinity;
+                if (notes) {
+                    let _ri = lowerBoundT(notes, now);
+                    for (let i = _ri - 1; i >= 0; i--) {
+                        const n = notes[i];
+                        if (n.t < now - CHORD_HWY_LINGER_S) break;
+                        if (validString(n.s) && n.t > _recArr[n.s]) _recArr[n.s] = n.t;
+                    }
+                }
+                if (chords) {
+                    // Time-sorted: start at the last chord ≤ now instead of
+                    // chords.length-1 (which walks past every future chord
+                    // when `now` is early in the song).
+                    //
+                    // lowerBoundT returns the first index with t >= now. If
+                    // chords share the same timestamp, walk forward through
+                    // the t===now run to the LAST one (so all duplicates at
+                    // `now` are included — the original `if (ch.t > now)
+                    // continue` scan-from-end included them all). When no
+                    // chord is exactly at `now`, start one slot back.
+                    const _ncHi = lowerBoundT(chords, now);
+                    let _ci = _ncHi;
+                    if (_ci < chords.length && chords[_ci].t === now) {
+                        while (_ci + 1 < chords.length && chords[_ci + 1].t === now) _ci++;
+                    } else {
+                        _ci -= 1;
+                    }
+                    for (; _ci >= 0; _ci--) {
+                        const ch = chords[_ci];
+                        if (ch.t < now - CHORD_HWY_LINGER_S) break;
+                        if (!ch.notes) continue;
+                        for (const cn of ch.notes) {
+                            if (validString(cn.s) && ch.t > _recArr[cn.s]) _recArr[cn.s] = ch.t;
+                        }
+                    }
+                }
+                _drawRecentByString = _recArr;
+            }
+
+            // ── Sorted union of next/recent event times ──────────────────
+            // Populate the scalar scratch used by _firstEventTimeGreaterThan
+            // — at most 2 * nStr finite values, then sorted ascending.
+            // Float64Array.subarray returns a view, so .sort() runs in place
+            // over the live prefix without copying or allocating.
+            // Pulls directly from _drawNextByString / _drawRecentByString
+            // (closure-scoped, populated just above) so we're independent of
+            // the recent-event prepass's inner-block ``_recArr`` alias.
+            _scrEventTimesLen = 0;
+            for (let s = 0; s < nStr; s++) {
+                const nf = _drawNextByString[s];
+                if (nf) {
+                    const tn = nf.t;
+                    if (Number.isFinite(tn)) _scrEventTimes[_scrEventTimesLen++] = tn;
+                }
+                const rt = _drawRecentByString[s];
+                if (Number.isFinite(rt)) _scrEventTimes[_scrEventTimesLen++] = rt;
+            }
+            if (_scrEventTimesLen > 1) {
+                _scrEventTimes.subarray(0, _scrEventTimesLen).sort();
+            }
+
+            // ── Ghost preview gap prepass ──────────────────────────────────
+            // For each note/chord in the upcoming 0.65s window, record the
+            // onset time of its immediate predecessor on the same string.
+            // drawNote() uses this to shrink the ghost preview window from
+            // the fixed 0.6s down to min(0.6, gap) so in dense passages the
+            // fret label doesn't float 0.6s ahead with no gem in sight.
+            //
+            // Two-pointer merge over time-sorted notes + chords so the
+            // predecessor is correct even when notes and chords interleave.
+            // Map with numeric key avoids per-frame string allocation;
+            // key = Math.round(t*1e4)*10 + s (unique for notes > 0.1 ms apart).
+            // Buffer is hoisted (_scrGhostPrevBuf) and cleared at the top of
+            // the prepass; per-string predecessor tracker likewise (_scrGhostLastT).
+            _scrGhostPrevBuf.clear();
+            const _ghostPrevBuf = _scrGhostPrevBuf;
+            {
+                for (let _i = 0; _i < nStr; _i++) _scrGhostLastT[_i] = -Infinity;
+                const _gLastT = _scrGhostLastT;
+                let _gni = notes ? lowerBoundT(notes, now - 1) : 0;
+                let _gci = 0;
+                if (chords) while (_gci < chords.length && chords[_gci].t < now - 1) _gci++;
+                while (true) {
+                    const nt = (notes && _gni < notes.length) ? notes[_gni].t : Infinity;
+                    const ct = (chords && _gci < chords.length) ? chords[_gci].t : Infinity;
+                    const minT = nt <= ct ? nt : ct;
+                    if (minT > now + 0.65 || minT === Infinity) break;
+                    if (nt <= ct) {
+                        const n = notes[_gni++];
+                        if (validString(n.s)) {
+                            _ghostPrevBuf.set(Math.round(n.t * 1e4) * 10 + n.s, _gLastT[n.s]);
+                            _gLastT[n.s] = n.t;
+                        }
+                    } else {
+                        const ch = chords[_gci++];
+                        if (ch.notes) for (const cn of ch.notes) {
+                            if (validString(cn.s)) {
+                                _ghostPrevBuf.set(Math.round(ch.t * 1e4) * 10 + cn.s, _gLastT[cn.s]);
+                                _gLastT[cn.s] = ch.t;
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Ramp strGlow while the board ghost is visible so the flying note
+            // core + rim read as one solid string-coloured shape with proj.
+            // Window is (0, PROJ_WIN_MERGE=0.6s) — use lowerBoundT + break.
+            const PROJ_WIN_MERGE = 0.6;
+            if (notes) {
+                const _sgLo = lowerBoundT(notes, now);
+                for (let _ni = _sgLo; _ni < notes.length; _ni++) {
+                    const n = notes[_ni];
+                    if (!validString(n.s) || n.f <= 0) continue;
+                    const dt = n.t - now;
+                    if (dt >= PROJ_WIN_MERGE) break;
+                    const nn = nextNoteByString[n.s];
+                    if (!nn || Math.abs(nn.t - n.t) > NEXT_ON_STRING_T_EPS) continue;
+                    const blend = 1 - dt / PROJ_WIN_MERGE;
+                    noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], 1.0 + blend * 1.2);
+                }
+            }
+            if (chords) {
+                const _projLo = lowerBoundT(chords, now);
+                for (let _pci = _projLo; _pci < chords.length; _pci++) {
+                    const ch = chords[_pci];
+                    if (!ch.notes || ch.t <= now) continue;
+                    const dt = ch.t - now;
+                    if (dt >= PROJ_WIN_MERGE) break;
+                    const chordNotes = filterValidNotes(ch.notes);
+                    for (const cn of chordNotes) {
+                        if (cn.f <= 0) continue;
+                        const nn = nextNoteByString[cn.s];
+                        if (!nn || Math.abs(nn.t - ch.t) > NEXT_ON_STRING_T_EPS) continue;
+                        const blend = 1 - dt / PROJ_WIN_MERGE;
+                        noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], 1.0 + blend * 1.2);
+                    }
+                }
+            }
+
+            // Accent: brighter note body (`mGlow` in drawNote) instead of the old '>' sprite.
+            // Notes are sorted — break once past the AHEAD window.
+            if (notes) {
+                const _acLo = lowerBoundT(notes, now - AHEAD);
+                for (let _ni = _acLo; _ni < notes.length; _ni++) {
+                    const n = notes[_ni];
+                    if (!validString(n.s) || !n.ac) continue;
+                    const dt = n.t - now;
+                    if (dt > AHEAD) break;
+                    const susEnd = n.t + (n.sus || 0);
+                    const hasSus = (n.sus || 0) > 0;
+                    if (dt < -ACCENT_NOTE_LINGER_EPS && (!hasSus || now > susEnd)) continue;
+                    noteState.strGlow[n.s] = Math.max(noteState.strGlow[n.s], ACCENT_NOTE_STR_GLOW);
+                    noteState.accentFillBoost[n.s] = Math.max(
+                        noteState.accentFillBoost[n.s],
+                        ACCENT_NOTE_FILL_BOOST,
+                    );
+                }
+            }
+            if (chords) {
+                const _acChordLo = lowerBoundT(chords, now - 30);
+                for (let _aci = _acChordLo; _aci < chords.length; _aci++) {
+                    const ch = chords[_aci];
+                    if (!ch.notes) continue;
+                    const dt = ch.t - now;
+                    if (dt > AHEAD) break;
+                    const chordNotes = filterValidNotes(ch.notes);
+                    if (!chordNotes.length) continue;
+                    let maxSus = 0;
+                    for (const x of chordNotes) if ((x.sus || 0) > maxSus) maxSus = x.sus;
+                    const susEnd = ch.t + maxSus;
+                    const hasChordSus = maxSus > 0;
+                    if (dt < -ACCENT_NOTE_LINGER_EPS && (!hasChordSus || now > susEnd)) continue;
+                    for (const cn of chordNotes) {
+                        if (!validString(cn.s) || !cn.ac) continue;
+                        noteState.strGlow[cn.s] = Math.max(noteState.strGlow[cn.s], ACCENT_NOTE_STR_GLOW);
+                        noteState.accentFillBoost[cn.s] = Math.max(
+                            noteState.accentFillBoost[cn.s],
+                            ACCENT_NOTE_FILL_BOOST,
+                        );
+                    }
+                }
+            }
+
+            pbEnd(2);
+            pbBeg(3);
+            // mGlow / mAccentCore emissive writes are folded into
+            // updateStringHighlights() — same per-string scratch reads,
+            // one pass.
+            updateStringHighlights(noteState);
+            pbEnd(3);
+
+            // Active frets (notes in cooldown window) + highway intensity
+            _scrActiveFrets.clear();
+            const activeFrets = _scrActiveFrets;
+            let highwayIntensity = 0;
+            for (let f = 1; f <= NFRETS; f++) {
+                if (now - fretLastActiveTime[f] < FRET_COOLDOWN) activeFrets.add(f);
+            }
+
+            // Camera targeting — steady mode (#34): recency-weighted centroid +
+            // hysteresis over [camT0, camT1]. In lookahead mode, see
+            // lookaheadBoundsNow + lookaheadSmoothCamStep().
+            let cs = 0;
+            let camAhead = CAM_TGT_AHEAD_C;
+            let camTau = CAM_TGT_TAU_C;
+            let camHystF = CAM_TGT_HYST_C;
+            let camT0 = now - CAM_TGT_BEHIND;
+            let camT1 = now + camAhead;
+            let camWX = 0, camWSum = 0;
+            let camDistMin = 99, camDistMax = 0, camDistGot = false;
+            const camDistHystF = CAM_DIST_HYST_T + (CAM_DIST_HYST_C - CAM_DIST_HYST_T) * zoomSmoothing;
+            if (!(cameraMode === 'lookahead')) {
+                cs = cameraSmoothing;
+                camAhead = CAM_TGT_AHEAD_T + (CAM_TGT_AHEAD_C - CAM_TGT_AHEAD_T) * cs;
+                camTau = CAM_TGT_TAU_T + (CAM_TGT_TAU_C - CAM_TGT_TAU_T) * cs;
+                camHystF = CAM_TGT_HYST_T + (CAM_TGT_HYST_C - CAM_TGT_HYST_T) * cs;
+                camT0 = now - CAM_TGT_BEHIND;
+                camT1 = now + camAhead;
+            }
+
+            // Classic path (#34): tgtDist hysteresis tracks fret span over the
+            // narrowed [camT0, camT1]; lookahead mode uses lookaheadBoundsNow + span smoothing.
+            //
+            // Sustain extension: the outer loop keeps notes/chords
+            // whose sustain still rings into the visible window —
+            // n.t + (n.sus || 0) >= t0 for notes, ch.t + maxSus >= t0
+            // for chords — via the continue-filters below at the top
+            // of the single-note and chord branches. camT0 is narrower
+            // than t0, so an onset can age past camT0 while still
+            // being on screen and audible. Mirror that past-side
+            // allowance here so a held low-fret chord keeps
+            // contributing to both camDist (zoom) and camWX (X
+            // target); otherwise the camera dollies/pans away
+            // mid-sustain, re-clipping the very chord the low-fret
+            // pullback was added to keep on screen. The future side
+            // (camT1) is left alone so the #34 invariant (distant
+            // high-fret onsets don't pre-pull the camera) still holds.
+
+            // ── Song-change detection ─────────────────────────────────────────
+            // reconnect() (used for arrangement switches and splitscreen song
+            // changes) does not call renderer.destroy/init, so _camSnapped and
+            // _camPreScanned would persist into the new song and the snap pre-pass
+            // would never fire again.  Detect the change by comparing the current
+            // song+arrangement identity against the last-seen key, and reset the
+            // camera snap state (and the camera position itself) whenever it flips.
+            {
+                const si = bundle.songInfo;
+                // bundle.songInfo has no filename field (the WS song_info message
+                // never includes it).  Use window.feedBack.currentSong.filename
+                // — set by highway.js from the WS URL — combined with the
+                // arrangement index as a reliable per-song-arrangement key.
+                const currentSong = window.feedBack && window.feedBack.currentSong;
+                const key = currentSong ? currentSong.filename + '\0' + (si ? (si.arrangement_index ?? '') : '') : null;
+                if (key !== null && key !== _songKey) {
+                    _songKey = key;
+                    _camSnapped = false;
+                    _camPreScanned = false;
+                    tgtX = curX = xFretMid(CAM_LOCK_CENTER_FRET);
+                    tgtDist = curDist = CAM_DIST_BASE;
+                    prevLowFretBonus = 0;
+                    prevLockActive = false;
+                    _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
+                    _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
+                    _lookaheadCamPrevNow = null;
+                    _lookaheadLowBonusU = 0;
+                    _lookaheadHiNeckLatch = false;
+                    // Drop the previous song's measure-start cache. Otherwise
+                    // lookaheadEndTime() would size the lookahead window off the
+                    // old measure grid (with the new song's now reset to ~0 this
+                    // yields a wrong/huge tEnd) until the new beats arrive and
+                    // rebuild it — the resulting huge fret span over-zooms the
+                    // first-data snap and stays latched. Clearing it falls back
+                    // to the seconds window for this frame; the rebuild repopulates
+                    // it next frame once bundle.beats is the new array.
+                    _measureStarts = []; _measureStartsRef = null;
+                    // Drop the clock anchor so the new song's currentTime
+                    // re-anchors cleanly instead of measuring a bogus rate
+                    // across the seek-to-0 discontinuity.
+                    _clkAudioT = NaN; _clkPerf = NaN; _clkRate = 1;
+                }
+            }
+
+            // ── Camera pre-pass (first-data snap) ────────────────────────────
+            // Before any drawNote() call, iterate notes/chords to accumulate
+            // the camera targeting data for THIS frame.  If this is the first
+            // frame where fretted notes appear in the targeting window, snap
+            // curX/curDist directly to the computed targets so open-string note
+            // placement (which reads curX) and the camera are consistent on the
+            // snap frame.  After the snap _camSnapped is true and this block
+            // becomes a permanent no-op.  Open-string notes (f === 0) do not
+            // contribute to preWX/preWSum and therefore do not trigger the snap.
+            if (!_camSnapped) {
+                // One-time full-chart scan (runs exactly once when both bundle.notes
+                // and bundle.chords are available).  If no fretted note exists
+                // anywhere in either array the snap can never fire, so we disable
+                // the per-frame pre-pass immediately to avoid permanent overhead.
+                // Both arrays are checked because some arrangements have fretted
+                // notes only inside chords (chord-only charts, keys arrangements).
+                if (!_camPreScanned && notes && chords) {
+                    _camPreScanned = true;
+                    const hasFrettedNote  = notes.some(n => n.f > 0 && validString(n.s));
+                    const hasFrettedChord = chords.some(
+                        ch => ch.notes && ch.notes.some(cn => cn.f > 0 && validString(cn.s)));
+                    if (!hasFrettedNote && !hasFrettedChord) _camSnapped = true;
+                }
+                if (!_camSnapped) {
+                    if (cameraMode === 'lookahead') {
+                        const bd = lookaheadBoundsNow;
+                        if (bd) {
+                            _lookaheadCamX = lookaheadTargetWorldX(bd.minF, bd.maxF);
+                            _lookaheadFretSpan = Math.max(1, bd.maxF - bd.minF + 1);
+                            const lockSnapEl = cameraLockLow && bd.maxF <= 12;
+                            if (lockSnapEl) {
+                                const lockedBaseU = camBaseDistU(12);
+                                const lockedBonusU = camLowFretPullbackU(1);
+                                const lockZoomMul = CAM_LOCK_ZOOM_MIN +
+                                    (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
+                                tgtX = xFretMid(CAM_LOCK_CENTER_FRET);
+                                tgtDist = (lockedBaseU + lockedBonusU) * K * lockZoomMul;
+                                prevLowFretBonus = lockedBonusU;
+                                _lookaheadLowBonusU = lockedBonusU;
+                            } else {
+                                const baseDU = camBaseDistU(_lookaheadFretSpan);
+                                const lowBU = camLowFretPullbackU(bd.minF);
+                                tgtDist = (baseDU + lowBU) * K;
+                                prevLowFretBonus = lowBU;
+                                _lookaheadLowBonusU = lowBU;
+                                tgtX = _lookaheadCamX;
+                            }
+                            curX = tgtX;
+                            curDist = tgtDist;
+                            _camSnapped = true;
+                            _lookaheadCamPrevNow = now;
+                        }
+                    } else {
+                    let preWX = 0, preWSum = 0, preDistMin = 99, preDistMax = 0, preDistGot = false;
+                    if (notes) {
+                        for (const n of notes) {
+                            // bundle.notes is time-sorted: skip fully-expired sustains,
+                            // break once the onset is beyond the camera window.
+                            if (n.t + (n.sus || 0) < camT0) continue;
+                            if (n.t > camT1) break;
+                            if (!validString(n.s)) continue;
+                            const nInWin  = n.f > 0 && n.t >= camT0;
+                            const nSusNow = n.f > 0 && n.t < camT0 && n.t + (n.sus || 0) >= now;
+                            if (nInWin || nSusNow) {
+                                const w = Math.exp(-Math.abs(n.t - now) / camTau);
+                                preWX += xFretMid(n.f) * w; preWSum += w;
+                                if (n.f < preDistMin) preDistMin = n.f;
+                                if (n.f > preDistMax) preDistMax = n.f;
+                                preDistGot = true;
+                            }
+                        }
+                    }
+                    if (chords) {
+                        for (const ch of chords) {
+                            if (!ch.notes) continue;
+                            // bundle.chords is time-sorted: break once onset is beyond window.
+                            if (ch.t > camT1) break;
+                            const chNotes = filterValidNotes(ch.notes);
+                            if (!chNotes.length) continue;
+                            let maxSus = 0;
+                            for (const n of chNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
+                            if (ch.t + maxSus < camT0) continue; // fully expired
+                            const chOnsetInWin = ch.t >= camT0;
+                            const chSusNow     = ch.t < camT0 && ch.t + maxSus >= now;
+                            if (!chOnsetInWin && !chSusNow) continue;
+                            const chW = Math.exp(-Math.abs(ch.t - now) / camTau);
+                            for (const cn of chNotes) {
+                                const cnOk = chOnsetInWin || (chSusNow && ch.t + (cn.sus || 0) >= now);
+                                if (cn.f > 0 && cnOk) {
+                                    preWX += xFretMid(cn.f) * chW; preWSum += chW;
+                                    if (cn.f < preDistMin) preDistMin = cn.f;
+                                    if (cn.f > preDistMax) preDistMax = cn.f;
+                                    preDistGot = true;
+                                }
+                            }
+                        }
+                    }
+                    if (preWSum > 0) {
+                        _applyNoteCamTargets(preWX, preWSum, preDistMin, preDistMax, preDistGot,
+                                             camHystF, camDistHystF, /* skipDistHyst= */ true);
+                        curX    = tgtX;
+                        curDist = tgtDist;
+                        _camSnapped = true;
+                    }
+                    } // end steady-mode pre-pass branch
+                } // end !_camSnapped (post-prescan guard)
+            }
+
+            pbBeg(4);
+            // ── Single notes ──────────────────────────────────────────────
+            // Reset the per-frame fret-label dedup set so stacked labels from
+            // multiple strings at the same onset/fret (arpeggio, synth chord) don't repeat.
+            _frameLabeledKeys.clear();
+            // Tracks which (chordId → Set<stringIndex>) pairs already had
+            // brackets drawn by the note-stream loop, so the chord loop can
+            // skip duplicate bracket draws for the same string.
+            // Hoisted Map — clear (rather than reallocate) so the per-frame
+            // chord-bracket dedupe doesn't churn GC in dense arpeggio passages.
+            // (The inner Sets stored as values lose their Map reference on
+            // .clear() and get GC'd along with the keys; only the outer Map
+            // is reused.)
+            _scrNoteStreamBracketStrings.clear();
+            const _noteStreamBracketStrings = _scrNoteStreamBracketStrings;
+            _scrLastFretForString.fill(undefined, 0, nStr);
+            const lastFretForString = _scrLastFretForString;
+            if (notes) {
+                // Start 30s before now — conservative enough to include any arpeggio
+                // persist window while skipping the bulk of old notes in long songs.
+                // The arpPersistKeys check below guards the rare notes that are even
+                // older and still visible (only possible for unrealistically long HS).
+                const _noteRenderLo = lowerBoundT(notes, now - 30);
+                for (let _ni = _noteRenderLo; _ni < notes.length; _ni++) {
+                    const n = notes[_ni];
+                    if (n.f > 0 && n.t > now && n.t < now + 2) activeFrets.add(n.f);
+                    if (n.t > now) {
+                        const dt = n.t - now;
+                        if (dt < AHEAD) highwayIntensity = Math.max(highwayIntensity, 1 - dt / AHEAD);
+                    }
+                    // Far-future notes are always skipped — arpGhostActive
+                    // timing handles when the ghost appears for upcoming arp notes.
+                    // Notes are time-sorted so everything beyond t1 can be skipped entirely.
+                    if (n.t > t1) break;
+                    // Past-window arp notes are exempted from the back-window skip
+                    // so their fretboard ghost + brackets persist until arpBounds.end.
+                    // ndVerdictT0 extends the window when a note-detect provider is
+                    // attached so async verdicts still land while drawable.
+                    const _inArpPersist = _arpPersistKeys.has(_noteKey(n.t, n.s));
+                    if (!_inArpPersist && n.t + (n.sus || 0) < ndVerdictT0) continue;
+                    if (!validString(n.s)) continue;
+                    // Suppress the gem for linkNext slide-target notes (skipBody=true).
+                    // The sustain/slide trail still renders because it now lives outside
+                    // the !skipBody gate in drawNote().
+                    const _isSlideTgt = !!(_slideTargetSet && _slideTargetSet.has(_noteKey(n.t, n.s)));
+                    // Always show the fret label — suppressing it for repeated frets on the same
+                    // string caused the label to be invisible throughout the note's flight and
+                    // only appear moments before being played (when the previous note's linger
+                    // window expired).  Each note now owns its label for its full flight.
+                    const skipLabel = false;
+                    let singleOpenX;
+                    if (n.f === 0) {
+                        const ab = anchorLaneBoundsAt(anchors, n.t);
+                        if (ab) singleOpenX = (xFret(ab.dMin) + xFret(ab.dMax)) / 2;
+                    }
+                    const singleOpenLaneW = n.f === 0 ? openNoteLaneBoxW(n.t) : undefined;
+                    const arGhostCid = arpeggioChordIdForNoteWithInferCache(
+                        n,
+                        bundle.handShapes,
+                        bundle.chordTemplates,
+                        notes,
+                        arpGhostHsInfer,
+                    );
+                    const _arpBoundsForNote = arGhostCid != null
+                        ? arpHsBoundsForNote(n, bundle.handShapes, arpGhostHsInfer)
+                        : null;
+                    drawNote(
+                        n,
+                        now,
+                        singleOpenX,
+                        skipLabel,
+                        _isSlideTgt,
+                        GHOST_HOLD_AFTER_ONSET,
+                        singleOpenLaneW,
+                        arGhostCid != null,
+                        arGhostCid,
+                        arGhostCid != null,
+                        _arpBoundsForNote,
+                        _ghostPrevBuf.get(Math.round(n.t * 1e4) * 10 + n.s) ?? -Infinity,
+                        _arpBoundsForNote !== null, // showDropLine: white line for arp note-stream notes
+                    );
+                    if (arGhostCid != null) {
+                        const _arpBounds = _arpBoundsForNote;
+                        if (_arpBounds) {
+                            // Synth-onset-match handshapes show ghost fret numbers but not [ ] brackets.
+                            if (!_arpSynthOnsetHsSet.has(_arpBounds.start)) {
+                                // Open-string bracket X: always use the anchor at the
+                                // handshape START time (not n.t, not now) so the bracket
+                                // position stays fixed throughout the arpeggio even when
+                                // the chart anchor changes mid-pattern.
+                                const _arpBrktAncB = n.f === 0
+                                    ? anchorLaneBoundsAt(anchors, _arpBounds.start)
+                                    : null;
+                                const _bx = n.f === 0
+                                    ? (_arpBrktAncB
+                                        ? (xFret(_arpBrktAncB.dMin) + xFret(_arpBrktAncB.dMax)) / 2
+                                        : (singleOpenX !== undefined ? singleOpenX : curX))
+                                    : xFretMid(n.f);
+                                const _openHalfW = (() => {
+                                    if (n.f !== 0) return null;
+                                    if (_arpBrktAncB) {
+                                        const _xl = xFret(_arpBrktAncB.dMin), _xr = xFret(_arpBrktAncB.dMax);
+                                        if (_xr > _xl) return Math.max(0.22, (_xr - _xl + NW * 0.4 * 2) * 0.96 / (40 * K)) * 20 * K;
+                                    }
+                                    return singleOpenLaneW != null ? Math.max(0.22, singleOpenLaneW * 0.96 / (40 * K)) * 20 * K : null;
+                                })();
+                                drawArpBrackets(_bx, sY(n.s), _arpBounds.start - now, _arpBounds.end, now, n.s, n.f === 0, _openHalfW);
+                                // Record that this (chordId:occurrenceStart, string) pair has brackets
+                                // so the chord loop doesn't draw a second set on the same string.
+                                // Key includes the arp occurrence start time so two separate arp
+                                // sequences sharing the same chord template ID don't suppress each other.
+                                const _nsbKey = arGhostCid + ':' + _arpBoundsForNote.start;
+                                let _nsbSet = _noteStreamBracketStrings.get(_nsbKey);
+                                if (!_nsbSet) { _nsbSet = new Set(); _noteStreamBracketStrings.set(_nsbKey, _nsbSet); }
+                                _nsbSet.add(n.s);
+                            }
+                        }
+                    }
+                    lastFretForString[n.s] = n.f;
+                    // Onset in window OR started before the window but
+                    // still sustaining right now. Gate sustain carry-over
+                    // against the current frame time so camera framing
+                    // releases as soon as the sustain is no longer
+                    // rendered on screen.
+                    if (!(cameraMode === 'lookahead')) {
+                    const nInWin = n.t >= camT0 && n.t <= camT1;
+                    const nSusActive = n.t < camT0 && n.t + (n.sus || 0) >= now;
+                    if (n.f > 0 && (nInWin || nSusActive)) {
+                        // Symmetric decay around now: previously this
+                        // clamped n.t - now at 0, giving every past-
+                        // onset note weight 1. That was a tolerable
+                        // approximation when the past window was 0.2 s
+                        // (camT0), but the sustain extension widens
+                        // the past side to seconds for held notes — a
+                        // 2-second-old ringing sustain would otherwise
+                        // pin camWX as strongly as a fresh note and
+                        // stale-out the framing for the current
+                        // phrase. Math.abs lets old sustains decay on
+                        // the same time-constant as future notes,
+                        // matching each mode's intent: twitchy
+                        // (camTau=0.35 s) drops a 0.2 s-old note's
+                        // weight to ~0.56 (consistent with "react to
+                        // recent only"), calm (camTau=0.9 s) to ~0.80
+                        // (consistent with "average a wider window").
+                        // Weight is still 1 at onset.
+                        const w = Math.exp(-Math.abs(n.t - now) / camTau);
+                        camWX   += xFretMid(n.f) * w;
+                        camWSum += w;
+                        if (n.f < camDistMin) camDistMin = n.f;
+                        if (n.f > camDistMax) camDistMax = n.f;
+                        camDistGot = true;
+                    }
+                    }
+                }
+            }
+
+            pbEnd(4);
+            pbBeg(5);
+            // ── Chords ────────────────────────────────────────────────────
+            if (chords) {
+                // Single-pass shape-run tracking: the previous pre-loop scanned
+                // every chord (and re-allocated chordShapeSignature() per chord)
+                // each frame, even though the render loop already iterates the
+                // full array. We compute runSig inline once per chord and reuse
+                // it for both first-in-run detection and isRepeat below.
+                // SHAPE_RUN_GAP_S also resets the run when the time gap from
+                // the previous chord exceeds the same 0.5 s window used for
+                // isRepeat — a chord shape that re-appears after a real
+                // musical gap should re-show its label, not be treated as a
+                // continuing run from many bars ago.
+                const SHAPE_RUN_GAP_S = 0.5;
+                let runSigPrev = null;
+                let prevAnyChordTime = -Infinity;
+                let prevChordSig = null;
+                let prevChordTime = -1;
+
+                // Skip past chords that are too old to render. The per-chord filter
+                // (ch.t + _chFilterSus >= ndVerdictT0) passes the earliest chord when
+                // ch.t >= ndVerdictT0 - AHEAD (worst case: _chFilterSus = AHEAD for a
+                // chord with no explicit sustain). Binary search avoids iterating
+                // hundreds of past chords every frame in dense PM/FH sections.
+                const _chordsLoIdx = lowerBoundT(chords, ndVerdictT0 - AHEAD);
+                // Prime shape-run tracking from the chord immediately before the window
+                // so isRepeat and firstInShapeRun are correct on the first visible chord.
+                if (_chordsLoIdx > 0) {
+                    const _pc = chords[_chordsLoIdx - 1];
+                    if (_pc && _pc.notes) {
+                        const _ps = chordShapeSignature(_pc);
+                        if (_ps !== null) {
+                            runSigPrev = _ps;
+                            prevAnyChordTime = _pc.t;
+                            prevChordSig = _ps;
+                            prevChordTime = _pc.t;
+                        }
+                    }
+                }
+
+                for (let ci = _chordsLoIdx; ci < chords.length; ci++) {
+                    const ch = chords[ci];
+                    // Chords are time-sorted — everything beyond t1 is outside the
+                    // visible window and contributes nothing (activeFrets needs t<now+2,
+                    // highwayIntensity needs dt<AHEAD, both < t1).
+                    if (ch.t > t1) break;
+                    const runSig = chordShapeSignature(ch);
+                    let firstInShapeRun;
+                    if (runSig === null) {
+                        firstInShapeRun = true;
+                    } else {
+                        const gap = ch.t - prevAnyChordTime;
+                        firstInShapeRun = (runSig !== runSigPrev) || gap > SHAPE_RUN_GAP_S;
+                        runSigPrev = runSig;
+                        // Only valid chords update the run-gap clock — an entry
+                        // whose runSig is null (no notes / unusable chordId)
+                        // shouldn't make the next real chord look like a tiny
+                        // gap and silently fall into a "still in the run" state.
+                        prevAnyChordTime = ch.t;
+                    }
+                    if (!ch.notes) continue;
+                    // Filter chord notes to in-range strings once. All
+                    // chord-level aggregations (maxSus, repeat-chord
+                    // signature, open-string centroid, frame-box bounds,
+                    // active-fret highlights, camera-window dist) read
+                    // from chordNotes so a clamped 9th-string note can't,
+                    // for instance, extend the chord's linger beyond its
+                    // visible sustain.
+                    const chordNotes = filterValidNotes(ch.notes);
+                    if (chordNotes.length === 0) continue;
+                    const chShape = mergeChordShape(ch, chordNotes, bundle.chordTemplates);
+
+                    if (ch.t > now) {
+                        const dt = ch.t - now;
+                        if (dt < AHEAD) highwayIntensity = Math.max(highwayIntensity, 1 - dt / AHEAD);
+                    }
+                    if (ch.t > now && ch.t < now + 2)
+                        for (const cn of chordNotes) { if (cn.f > 0) activeFrets.add(cn.f); }
+
+                    let maxSus = 0;
+                    for (const n of chordNotes) if ((n.sus || 0) > maxSus) maxSus = n.sus;
+                    // When maxSus=0 (no explicit sustain on chord notes, including
+                    // all h3dSynth chords) use AHEAD as the filter window so the
+                    // chord stays in the loop long enough for a handshape-derived
+                    // sustain rail to finish drawing. The rail itself gates on
+                    // _dtSusEnd>0, so chords with no actual sustain produce no
+                    // visual artifact despite staying in the loop longer.
+                    // ndVerdictT0 extends the window when a note-detect provider is
+                    // attached so async verdicts still land while drawable.
+                    const _chFilterSus = maxSus > 0 ? maxSus : AHEAD;
+                    if (ch.t + _chFilterSus < ndVerdictT0) continue;
+                    if (ch.t > t1) break;
+
+                    // Repeat-chord detection (consecutive same shape, short gap).
+                    // Reuses runSig computed at loop entry — same signature as the
+                    // dedicated chordShapeSignature() call we used to make twice.
+                    // Synthetic chords (h3dSynth — injected at handshape onsets by
+                    // mergeHandShapeSynthChords) are never real strums, so they must
+                    // not update prevChordSig/prevChordTime. Without this guard a
+                    // real chord whose handshape generates a synth onset at the
+                    // handshape start_time (e.g. a slide-in where the real strum
+                    // falls mid-handshape, > 28 ms after the onset) would see the
+                    // synth as its "previous chord" and be falsely flagged isRepeat.
+                    const isRepeat = runSig !== null && prevChordSig === runSig && Math.abs(ch.t - prevChordTime) < 0.5;
+                    if (!ch.h3dSynth) {
+                        prevChordSig = runSig;
+                        prevChordTime = ch.t;
+                    }
+
+                    // Anchor selection for chord frame + open-string X + sustain rails:
+                    // • Upcoming (chDtEarly > 0): onset time — frame previews the correct
+                    //   neck region before the chord hits the line.
+                    // • Past, actively sustaining (now < ch.t + maxSus): onset time — frame
+                    //   stays at the frets where the chord was struck. Using `now` here
+                    //   causes the frame to jump to whichever anchor is active at `now`,
+                    //   which may be a different/wider region and makes the sustain box
+                    //   appear in the wrong fret zone ("invading" adjacent anchors).
+                    // • Past, linger-only (sustain expired or chord had no sustain): `now`
+                    //   — brief fade-out frame tracks the current lane position so it
+                    //   doesn't visibly drift while the lane has already transitioned.
+                    const chDtEarly = ch.t - now;
+                    const _chAnchorT = chDtEarly > 0 ? ch.t
+                        : (maxSus > 0 && now < ch.t + maxSus) ? ch.t
+                        : now;
+                    const chAncB = anchorLaneBoundsAt(anchors, _chAnchorT);
+                    // Open-string X: chart <anchor> lane centre when present (not curX /
+                    // fretted centroid), matching highway span.
+                    let chordCX = curX;
+                    if (chAncB) chordCX = (xFret(chAncB.dMin) + xFret(chAncB.dMax)) / 2;
+                    else {
+                        let cxL = Infinity, cxR = -Infinity, fretted = 0;
+                        for (const cn of chordNotes) {
+                            if (cn.f > 0) {
+                                const fx = xFretMid(cn.f);
+                                if (fx < cxL) cxL = fx;
+                                if (fx > cxR) cxR = fx;
+                                fretted++;
+                            }
+                        }
+                        if (fretted > 0) chordCX = (cxL + cxR) / 2;
+                    }
+
+                    // Horizontals for chord frame + open-string mesh width. With anchors,
+                    // span matches HWY lane columns (wire dMin..dMax); no extra pad.
+                    let chordFrameXL = null, chordFrameXR = null, chordOpenBoxW = null;
+                    let chordFrameAnchorMatched = false;
+                    if (chShape.size > 1) {
+                        let fMinCh = 99, fMaxCh = 0, anyFretted = false;
+                        for (const [, f] of chShape) {
+                            if (f > 0) {
+                                anyFretted = true;
+                                fMinCh = Math.min(fMinCh, f);
+                                fMaxCh = Math.max(fMaxCh, f);
+                            }
+                        }
+                        // Prefer the anchor span so chord frames and arpeggio
+                        // frames align with the highway lane window — BUT only
+                        // when the chord's fretted notes actually fall within
+                        // the anchor range. If the anchor at this chord's time
+                        // doesn't cover the chord's frets (e.g. a chord at frets
+                        // 2–4 with an anchor locked to frets 5–8), the framebox
+                        // would clip the very gems it's supposed to contain, so
+                        // fall back to chord-fret-based bounds instead.
+                        const anchorCoversChordFrets = chAncB && anyFretted
+                            ? (fMinCh >= chAncB.dMin && fMaxCh <= chAncB.dMax)
+                            : true; // all-open chord: anchor centre is fine
+                        if (chAncB && anchorCoversChordFrets) {
+                            chordFrameXL = xFret(chAncB.dMin);
+                            chordFrameXR = xFret(chAncB.dMax);
+                            chordFrameAnchorMatched = true;
+                        } else if (anyFretted) {
+                            chordFrameXL = xFret(fMinCh - 1);
+                            chordFrameXR = xFret(Math.max(fMaxCh, fMinCh + 2));
+                        } else {
+                            const wNut = openNoteLaneBoxW(ch.t);
+                            chordFrameXL = chordCX - wNut * 0.5;
+                            chordFrameXR = chordCX + wNut * 0.5;
+                        }
+                        if (chordFrameXL != null && chordFrameXR != null) {
+                            const span = Math.abs(chordFrameXR - chordFrameXL);
+                            if (span > 1e-8) {
+                                // Anchor-driven lane stripes span [dMin..dMax] wire-to-wire with
+                                // no horizontal pad — match that ONLY when the frame is actually
+                                // following the anchor (all-open chord, fallback path). The
+                                // fretted-span path always pads so the frame breathes around
+                                // the outermost fretted notes; without the pad it sat exactly
+                                // on the fret lines and looked clipped.
+                                if (chordFrameAnchorMatched) chordOpenBoxW = span;
+                                else {
+                                    const padX = NW * 0.4;
+                                    chordOpenBoxW = span + padX * 2;
+                                }
+                            }
+                        }
+                    }
+
+                    const laneWForOpenStrings = (chordOpenBoxW != null && chordOpenBoxW > 1e-8)
+                        ? chordOpenBoxW
+                        : openNoteLaneBoxW(ch.t);
+
+                    const hsHintFrame = chordHandShapeArpeggioHint(ch, bundle.handShapes, bundle.chordTemplates);
+                    const hsTimeWinFrame = hsHintFrame.hs
+                        ? { tLo: hsStart(hsHintFrame.hs) - 0.06, tHi: hsEnd(hsHintFrame.hs) + 0.06 }
+                        : null;
+                    // chordShapeCoveredByStandaloneNotes is now cached per
+                    // chord (see _arpCoverCache), so a direct call from the
+                    // deferChordGems short-circuit chain is both lazy
+                    // (skipped for branches that don't need it) AND O(1)
+                    // when re-hit later in the same frame. The previous
+                    // per-chord IIFE memo is therefore redundant — drop it
+                    // to avoid the per-chord closure allocation in dense
+                    // PM/FH passages.
+                    const inferredArpPattern = (!hsHintFrame.hs
+                        || handShapeChartSpanSec(hsHintFrame.hs) >= ARP_INFER_MIN_HAND_SHAPE_SPAN_S)
+                        && inferArpeggioFromNotePattern(
+                            ch, chShape, notes, hsTimeWinFrame, bundle.handShapes);
+                    // Only suppress the chord gems when standalone notes really
+                    // cover the arpeggio shape; otherwise explicit/synth hand
+                    // shapes can produce an empty lavender frame with no notes
+                    // inside (e.g. template-marked `-arp` chord rows).
+                    // Lazy wrapper so the note-stream scan is skipped when
+                    // neither branch needs it (short-circuit evaluation).
+                    const noteStreamCoversArpShape = () => chordShapeCoveredByStandaloneNotes(ch, chShape, notes);
+                    const deferChordGems = (ch.h3dSynth && noteStreamCoversArpShape())
+                        || inferredArpPattern
+                        || (hsHintFrame.explicit && hsHintFrame.covered && noteStreamCoversArpShape());
+                    /**
+                     * Lavender chord frame + purple highway rails: authored
+                     * arpeggio metadata only. RS ``highDensity`` marks gallops /
+                     * repeated strums on the same voicing (e.g. Frantic ~2:46) —
+                     * not arpeggio; keep ``hd`` for sustain-ribbon width via
+                     * ``chordSusTrailMatchArpFrame``.
+                     *
+                     * Only the chord that INITIATES the handshape span gets
+                     * the lavender treatment — subsequent strums of the same
+                     * voicing within the same handshape window are repeats and
+                     * render as ordinary chord frames. Proximity to
+                     * hsStart() (≤ 100 ms) identifies the initiating chord
+                     * regardless of how wide the span is.
+                     */
+                    const _hsStartT = hsHintFrame.hs ? hsStart(hsHintFrame.hs) : NaN;
+                    const chordHighwayLavenderArpVisual = hsHintFrame.explicit
+                        && !isNaN(_hsStartT) && Math.abs(ch.t - _hsStartT) <= 0.1;
+                    const chordSusTrailMatchArpFrame = chordWireHighDensity(ch)
+                        || chordHighwayLavenderArpVisual;
+
+                    // Onset in window OR chord started before the window
+                    // but is still sustaining right now. Gate sustain
+                    // carry-over against the current frame time so camera
+                    // framing releases as soon as the chord is no longer
+                    // rendered on screen.
+                    const chOnsetInWin = ch.t >= camT0 && ch.t <= camT1;
+                    const chSusActive  = ch.t < camT0 && ch.t + maxSus >= now;
+                    const chWindowed   = chOnsetInWin || chSusActive;
+                    // Symmetric decay — see matching comment in the
+                    // single-note branch. The chord-wide chW uses
+                    // ch.t (not per-note onset) since chord notes
+                    // share a strum time.
+                    const chW          = chWindowed ? Math.exp(-Math.abs(ch.t - now) / camTau) : 0;
+                    // Next-chord tail: same voicing (``highDensity`` gallop) keeps full linger + optional
+                    // fade suppression inside [hold−fade, hold]; a voicing change clips the tail to the
+                    // chart gap so D5→D#5 (~185 ms) does not stack two cyan frames (Frantic ~2:47).
+                    let cjNext = null;
+                    for (let j = ci + 1; j < chords.length; j++) {
+                        const cj = chords[j];
+                        if (!cj?.notes) continue;
+                        if (filterValidNotes(cj.notes).length === 0) continue;
+                        cjNext = cj;
+                        break;
+                    }
+                    // Nearest following event (chord OR single note) — used by
+                    // chordTailMul so the framebox vanishes the moment any next
+                    // event is played, not just when the next chord arrives.
+                    // Pull from the same sorted scalar scratch used by drawNote
+                    // — the per-string Math.min walk became O(log N) over the
+                    // shared 2*nStr buffer.
+                    const _chFirstEventAfter = _firstEventTimeGreaterThan(ch.t + 1e-6);
+                    const _chNextEventT = cjNext != null
+                        ? Math.min(cjNext.t, _chFirstEventAfter)
+                        : _chFirstEventAfter;
+                    let chordTailHoldS = CHORD_HWY_LINGER_S;
+                    let chordNextSoon = false;
+                    if (cjNext && cjNext.t > ch.t + 1e-6) {
+                        // Clip the hold tail to the gap for both same-voicing (repeat)
+                        // and different-voicing chords. The chordTailMul instant-cut
+                        // check handles the precise zero at onset; the clipped holdS
+                        // prevents the outer gate and hwyPostHitTailFadeMul from
+                        // lingering past that point.
+                        chordTailHoldS = Math.min(CHORD_HWY_LINGER_S, Math.max(cjNext.t - ch.t, 1e-3));
+                    }
+                    // feedBack#254 — engine verdicts land ~0.4 s after the
+                    // chord crosses; on a fast different-voicing sequence
+                    // the clip above can shrink the rim's draw life below
+                    // that, so the green/red latch is set but the rim isn't
+                    // drawn anymore. When a verdict provider is attached,
+                    // floor the hold at NOTEDETECT_GEM_VERDICT_WINDOW so
+                    // the tinted rim is actually visible.
+                    //
+                    // This deliberately overrides the "voicing-change clip
+                    // prevents two stacked cyan frames" behavior documented
+                    // above (the D5→D#5 / Frantic ~2:47 case): the post-hit
+                    // z clamp (Math.min(0, dZ(chDt)) below) pins extended
+                    // frames at z=0, so the two frames do overlap in plane
+                    // — they're distinguished by their now-tinted rim
+                    // colors (green/red verdict vs teal default) rather
+                    // than perspective depth. In detect mode that's the
+                    // right trade: verdict visibility beats the cleaner
+                    // approach silhouette. Without detect mode the
+                    // original clip still applies.
+                    if (_ndHasProvider && chordTailHoldS < NOTEDETECT_GEM_VERDICT_WINDOW) {
+                        chordTailHoldS = NOTEDETECT_GEM_VERDICT_WINDOW;
+                    }
+                    const chordTailFadeS = Math.min(CHORD_HWY_FADE_S, chordTailHoldS);
+
+                    // ── Approaching-arpeggio first-note identification ──────────────────
+                    // When an authored arpeggio chord frame is still approaching (not yet
+                    // at the hit line), only the first note to be played is shown as a gem.
+                    // All others are suppressed until chDtEarly <= 0 so the frame doesn't
+                    // flood the player's view with simultaneous gems before they arrive.
+                    // The first note is the earliest match in the note stream within the
+                    // handshape window. If no note-stream note matches the chord shape
+                    // within the handshape (i.e. there is no sequential arpeggio pattern),
+                    // _arpApproachFirstNote stays null and ALL chord gems are shown — this
+                    // handles chords that are played simultaneously even when tagged as arp.
+                    let _arpApproachFirstNote = null;
+                    if (chordHighwayLavenderArpVisual && !deferChordGems
+                        && chDtEarly > 0 && hsHintFrame.hs) {
+                        const _aHsLo = hsStart(hsHintFrame.hs);
+                        const _aHsHi = hsEnd(hsHintFrame.hs);
+                        let _aFirstT = Infinity;
+                        const _aNLo = lowerBoundT(notes, _aHsLo - 0.08);
+                        for (let _ani = _aNLo; _ani < notes.length; _ani++) {
+                            const _an = notes[_ani];
+                            if (_an.t > _aHsHi + 0.08) break;
+                            if (!validString(_an.s)) continue;
+                            for (const _acn of chordNotes) {
+                                if (_acn.s === _an.s && _acn.f === _an.f && _an.t < _aFirstT) {
+                                    _aFirstT = _an.t;
+                                    _arpApproachFirstNote = _acn;
+                                    break;
+                                }
+                            }
+                        }
+                        // No fallback to chordNotes[0]: if the note stream has no sequential
+                        // notes matching this shape, the chord is played simultaneously and
+                        // all gems must be shown.
+                    }
+
+                    // ── Deferred-arpeggio gem fallback ─────────────────────────────────
+                    // When gems are deferred to the note stream (deferChordGems=true) but
+                    // no individual note matching the chord shape falls within the chord's
+                    // onset cluster window, the frame box has no gems at its Z position.
+                    // Show all chord gems as a preview so the frame box isn't empty.
+                    // Uses the same onset window as chordShapeCoveredByStandaloneNotes so
+                    // the fallback deactivates precisely when the stream truly covers the
+                    // onset. Inlined (not an IIFE) to skip the per-chord closure allocation.
+                    let _deferFallback = false;
+                    if (deferChordGems && chDtEarly > 0) {
+                        _deferFallback = true;
+                        const _fLo = ch.t - ARP_FRAME_ONSET_PAD_S;
+                        const _fHi = ch.t + ARP_FRAME_ONSET_CLUSTER_S;
+                        let _fi = lowerBoundT(notes, _fLo - 0.02);
+                        for (; _fi < notes.length; _fi++) {
+                            const _fn = notes[_fi];
+                            if (_fn.t > _fHi) break;
+                            if (_fn.t < _fLo) continue;
+                            const _fef = chShape.get(_fn.s);
+                            if (_fef !== undefined && _fef === _fn.f) { _deferFallback = false; break; }
+                        }
+                    }
+
+                    // Suppress gems AND frame for hand-shape-synthesized chords whose
+                    // notes are already rendered individually via the note stream. Showing
+                    // chord gems or a framebox for a synth chord that duplicates the note
+                    // stream looks like phantom notes/chords. Check: any standalone note
+                    // matching any shape string in the onset window → player is already
+                    // guided by the note stream. Weaker than chordShapeCoveredByStandaloneNotes
+                    // (all strings covered) to handle patterns where one shape string only
+                    // appears well after the onset cluster (e.g. Walk intro, string 5 at
+                    // +0.7 s outside the 0.26 s window). Inlined for the same reason as
+                    // _deferFallback above.
+                    let suppressSynthChord = false;
+                    if (ch.h3dSynth && notes && chShape.size > 0) {
+                        const _sLo = ch.t - ARP_FRAME_ONSET_PAD_S;
+                        const _sHi = ch.t + ARP_FRAME_ONSET_CLUSTER_S;
+                        let _si = lowerBoundT(notes, _sLo - 0.02);
+                        for (; _si < notes.length; _si++) {
+                            const _sn = notes[_si];
+                            if (_sn.t > _sHi) break;
+                            if (_sn.t < _sLo) continue;
+                            if (chShape.get(_sn.s) === _sn.f) { suppressSynthChord = true; break; }
+                        }
+                    }
+
+                    // suppressSynthChord: skip gems + frame but still call drawNote with
+                    // skipBody=true so the board projection (fret ghost on fretboard) renders
+                    // for all shape strings — shows the hand position like a chord would.
+                    // chordLinksSlide: true when any chord note has a direct sl/slu marker,
+                    // OR when the chord's sustain connects (via case-2 linkNext) to a note
+                    // in bundle.notes that has a slide.  Repeated chords matching either
+                    // condition are treated as normal chords so the player sees the gem.
+                    let chordLinksSlide = chordNotes.some(cn =>
+                        (Number.isFinite(cn.sl) && cn.sl >= 0) ||
+                        (Number.isFinite(cn.slu) && cn.slu >= 0));
+                    if (!chordLinksSlide && isRepeat && maxSus > 0 && notes) {
+                        const _EPS = NEXT_ON_STRING_T_EPS;
+                        outer: for (const cn of chordNotes) {
+                            if (!(cn.sus > 0)) continue;
+                            const _endT = ch.t + cn.sus;
+                            let _ji = lowerBoundT(notes, _endT - _EPS);
+                            for (; _ji < notes.length; _ji++) {
+                                const _q = notes[_ji];
+                                if (_q.t > _endT + _EPS) break;
+                                if (_q.s !== cn.s || Math.abs(_q.t - _endT) >= _EPS) continue;
+                                if ((Number.isFinite(_q.sl) && _q.sl >= 0) ||
+                                    (Number.isFinite(_q.slu) && _q.slu >= 0)) {
+                                    chordLinksSlide = true; break outer;
+                                }
+                            }
+                        }
+                    }
+                    if (!deferChordGems || _deferFallback || suppressSynthChord) {
+                        for (const cn of chordNotes) {
+                            // Suppress non-first gems while an authored arpeggio frame
+                            // approaches — but not for the deferred fallback path, where
+                            // all chord gems serve as the only visual preview.
+                            // _arpApproachFirstNote is null when no sequential note-stream
+                            // pattern was found, so simultaneous chords are unaffected.
+                            // suppressSynthChord: show all shape strings for the projection.
+                            if (!_deferFallback && !suppressSynthChord && _arpApproachFirstNote !== null && cn !== _arpApproachFirstNote) continue;
+                            // Only suppress labels on repeated chord shapes (not on first-in-run);
+                            // removed the lastFretForString check — same fix as single notes above.
+                            const skipLabel = !firstInShapeRun;
+                            // Reuse _scrChordNote scratch instead of `{ ...cn }` spread
+                            // (avoids per-chord-note object allocation every frame).
+                            Object.assign(_scrChordNote, cn);
+                            _scrChordNote.t   = ch.t;
+                            _scrChordNote.sus = cn.sus || 0;
+                            // `fhm` is omit-when-false in the wire format (unlike `mt`/`pm`
+                            // which are always emitted). Before 5913129, chord-level
+                            // fretHandMute was folded into `mt` (always-emitted), so
+                            // Object.assign would overwrite any stale value. After that
+                            // commit fhm is its own field — absent on non-muted notes —
+                            // so Object.assign leaves a stale `true` from a previous
+                            // muted chord note untouched. Reset it explicitly here.
+                            _scrChordNote.fhm = cn.fhm || false;
+                            // Same stale-scratch hazard for the bend shape:
+                            // `bnv`/`bt` are omit-when-default on the wire, so a
+                            // chord note without them would otherwise inherit the
+                            // previous note's curve (and bendSemisAtTime would
+                            // apply the wrong contour). Reset explicitly.
+                            _scrChordNote.bnv = Array.isArray(cn.bnv) ? cn.bnv : undefined;
+                            _scrChordNote.bt  = cn.bt || 0;
+                            // Same stale-scratch hazard for the teaching marks
+                            // (§6.2.2): fg/sd are omit-when-default on the wire,
+                            // so a chord note without them must reset to -1 or it
+                            // inherits the previous note's finger/degree label.
+                            _scrChordNote.fg  = Number.isInteger(cn.fg) ? cn.fg : -1;
+                            _scrChordNote.sd  = Number.isInteger(cn.sd) ? cn.sd : -1;
+                            drawNote(
+                                _scrChordNote,
+                                now,
+                                cn.f === 0 ? chordCX : undefined,
+                                skipLabel,
+                                (isRepeat && !chordLinksSlide) || suppressSynthChord,
+                                chordTailHoldS,
+                                cn.f === 0 ? laneWForOpenStrings : undefined,
+                                true,
+                                ch.id,
+                                chordSusTrailMatchArpFrame,
+                                null,
+                                _ghostPrevBuf.get(Math.round(ch.t * 1e4) * 10 + cn.s) ?? -Infinity,
+                                chordHighwayLavenderArpVisual || suppressSynthChord || chordWireHighDensity(ch),
+                            );
+                            lastFretForString[cn.s] = cn.f;
+                            // gate by THIS note's own sustain against the
+                            // current render time — drawNote has already
+                            // dropped short-sustain notes whose ringing has
+                            // ended, so they should not keep pulling the
+                            // camera frame wider than the notes actually
+                            // still on screen (chord-wide maxSus would
+                            // over-pullback for mixed-sustain chords).
+                            if (!(cameraMode === 'lookahead')) {
+                            const cnSustainOk = chOnsetInWin || (chSusActive && ch.t + (cn.sus || 0) >= now);
+                            if (cn.f > 0 && cnSustainOk) {
+                                camWX += xFretMid(cn.f) * chW;
+                                camWSum += chW;
+                                if (cn.f < camDistMin) camDistMin = cn.f;
+                                if (cn.f > camDistMax) camDistMax = cn.f;
+                                camDistGot = true;
+                            }
+                            }
+                        }
+                    }
+
+                    // ── Arpeggio note brackets [ ] ────────────────────────
+                    // Drawn only for explicitly authored arpeggio frames
+                    // (chordHighwayLavenderArpVisual = explicit handshape arp mark).
+                    // Covers both paths: gems shown directly from the chord
+                    // (!deferChordGems) and the deferred-fallback preview path
+                    // (_deferFallback). The inferred-arpeggio path (inferredArpPattern
+                    // only, no explicit mark) intentionally does NOT draw brackets —
+                    // the inference heuristic can false-positive on fast strummed
+                    // chords, and brackets on non-arp chords confuse players.
+                    // Note-stream arpeggios draw their own brackets in the notes[]
+                    // loop above (for notes already in AHEAD). The chord loop covers
+                    // any strings whose notes haven't entered AHEAD yet — _nsBrackets
+                    // prevents duplicates for strings already handled by notes[].
+                    if (chordHighwayLavenderArpVisual) {
+                        const _arpBracketDt = ch.t - now;
+                        if (_arpBracketDt < AHEAD) {
+                            const _arpEnd = (hsHintFrame.hs && !isNaN(hsEnd(hsHintFrame.hs)))
+                                ? hsEnd(hsHintFrame.hs)
+                                : ch.t + maxSus + CHORD_HWY_LINGER_S;
+                            // The notes[] loop already drew brackets for any note-stream
+                            // note that entered AHEAD, recording (chordId:occurrenceStart → strings)
+                            // in _noteStreamBracketStrings. Use the same composite key (template id +
+                            // handshape start time) so two arp occurrences sharing a chord template
+                            // ID are treated as distinct occurrences — not one suppressing the other.
+                            const _nsBracketsKey = ch.id + ':' + _hsStartT;
+                            const _nsBrackets = _noteStreamBracketStrings.get(_nsBracketsKey);
+                            // Open-string bracket X: anchor at handshape start so
+                            // position stays fixed even when chordCX drifts with now.
+                            const _arpChBrktAncB = !isNaN(_hsStartT)
+                                ? anchorLaneBoundsAt(anchors, _hsStartT)
+                                : null;
+                            const _arpChBrktOpenX = _arpChBrktAncB
+                                ? (xFret(_arpChBrktAncB.dMin) + xFret(_arpChBrktAncB.dMax)) / 2
+                                : (chordCX ?? curX);
+                            const _arpChBrktOpenW = (() => {
+                                if (_arpChBrktAncB) {
+                                    const _xl = xFret(_arpChBrktAncB.dMin), _xr = xFret(_arpChBrktAncB.dMax);
+                                    if (_xr > _xl) return _xr - _xl + NW * 0.4 * 2;
+                                }
+                                return laneWForOpenStrings;
+                            })();
+                            for (const cn of chordNotes) {
+                                if (!validString(cn.s)) continue;
+                                if (_nsBrackets && _nsBrackets.has(cn.s)) continue;
+                                const _bx = cn.f === 0
+                                    ? _arpChBrktOpenX
+                                    : xFretMid(cn.f);
+                                const _openHalfW = (cn.f === 0 && _arpChBrktOpenW != null)
+                                    ? Math.max(0.22, _arpChBrktOpenW * 0.96 / (40 * K)) * 20 * K
+                                    : null;
+                                drawArpBrackets(_bx, sY(cn.s), _arpBracketDt, _arpEnd, now, cn.s, cn.f === 0, _openHalfW);
+                            }
+                        }
+                    }
+
+                    // Chord frame-box: rim bars + interior fill gradient.
+                    const chDt = chDtEarly; // already computed above for anchor selection
+                    const chordTailMul = (() => {
+                        // When a next event (chord OR single note) has already crossed
+                        // the hit line, hide this frame immediately — no fadeout overlap
+                        // when another event is already playing.
+                        if (chDt < 0 && _chNextEventT < Infinity && now >= _chNextEventT) {
+                            return 0;
+                        }
+                        return hwyPostHitTailFadeMul(chDt, chordTailHoldS, chordNextSoon, chordTailFadeS);
+                    })();
+                    if (chShape.size > 1 && chDt > -chordTailHoldS && chDt < AHEAD && chordOpenBoxW != null
+                        && (!suppressSynthChord || chordTemplateMarkedArpeggio(ch.id, bundle.chordTemplates))
+                    ) {
+                        const z = Math.min(0, dZ(chDt));
+                        const width = chordOpenBoxW;
+                        const xLeft = chordFrameXL;
+                        const xRight = chordFrameXR;
+                        const cx = (xLeft + xRight) * 0.5;
+                        const yA = sY(0), yB = sY(nStr - 1);
+                        const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
+                        const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
+                        const fullChordBoxH = yMaxF - yMinF;
+                        let height = fullChordBoxH;
+                        if (isRepeat) height *= 0.5;
+                        // Repeat frames use half height but anchor at yMinF (board
+                        // level) rather than centering in the string range. With the
+                        // camera tilted downward, a centered half-height frame puts
+                        // its bottom bar mid-strings — far above the board — causing
+                        // perspective-induced apparent X-misalignment with the lane
+                        // tiles (which sit at board level). Anchoring at yMinF keeps
+                        // the bottom bar near the board so both frame and lane tile
+                        // edges share the same projected screen X.
+                        const yBot = yMinF;
+                        const yTop = yMinF + height;
+                        const cY = (yBot + yTop) * 0.5;
+                        const fade = Math.max(0, 1 - chDt / AHEAD);
+                        const chordAccent = chordNotes.some(cn => cn.ac);
+
+                        // Rim thickness from full vertical span — repeat halves inner height only,
+                        // not bar thickness vs first chord — see CHORD_FRAME_RIM_* tuning.
+                        let ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
+                        if (chordAccent) ft *= 1.22;
+                        // Lavender frame: authored arpeggio marker only.
+                        // RS ``highDensity`` is kept out — it tags gallops & repeated
+                        // strums (Frantic ~2:46), not arpeggio.
+                        const isArpeggioFrame = chordHighwayLavenderArpVisual;
+                        const ftSide = isArpeggioFrame ? ft * 1.55 : ft;
+                        let rimHex = isArpeggioFrame ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
+                        // Capture the neutral frame color before any verdict overwrite.
+                        // Used for the mute X lines so hit/miss feedback only shows on
+                        // the outer borders of the framebox, not inside the X pattern.
+                        const baseRimHex = rimHex;
+                        // feedBack#254 — once the chord crosses the hit
+                        // line, tint the teal frame by the note-state
+                        // provider verdict: green on a clean grab, red on a
+                        // miss. The verdict is async (the engine verifier
+                        // reports ~0.4 s after the line), so the frame stays
+                        // teal while the verdict is still pending — it must
+                        // not flash red before the verdict lands. The green/
+                        // red verdict is latched in _chordVerdicts so it
+                        // can't flicker as constituent glows decay.
+                        // Only engages when a scorer is attached. Arpeggio
+                        // frames keep their blue identity.
+                        // Per-occurrence key — ch.id is the template id
+                        // (reused across same-shape chord occurrences) so
+                        // composing it with ch.t gives one entry per
+                        // physical onset in the chart.
+                        const verdictKey = _encodeChordVerdictKey(ch);
+                        // Evict any stale latch the next time the chord
+                        // re-enters the pre-hit window (rewinds, section
+                        // loops, full restarts). Bounds Map growth too.
+                        if (chDt > 0 && _chordVerdicts.has(verdictKey)) {
+                            _chordVerdicts.delete(verdictKey);
+                        }
+                        // The verdict scan no longer skips authored-handshape
+                        // frames — power chords sometimes carry an explicit
+                        // handshape (RS authoring quirk), which previously
+                        // dropped them into the `isArpeggioFrame` path and
+                        // left them lavender-blue regardless of hit/miss.
+                        // A true arpeggio (handshape over a real sweeping
+                        // note run) is unaffected: its constituents are
+                        // standalone notes judged at their own times, so the
+                        // scan's query at `ch.t` finds nothing for them and
+                        // the frame keeps its lavender default.
+                        if (chDt <= 0 && _ndHasProvider && !isArpeggioFrame) {
+                            const latched = _chordVerdicts.get(verdictKey);
+                            if (latched === 'green') {
+                                rimHex = CHORD_BOX_HIT_BRIGHT_HEX;
+                            } else if (latched === 'red') {
+                                rimHex = CHORD_BOX_MISS_DARK_HEX;
+                            } else if (latched === 'unmatched') {
+                                // The first scan past the verdict window
+                                // came up empty (no constituent ever had a
+                                // state — most often a true arpeggio frame
+                                // whose actual notes are judged at their
+                                // own times, not at ch.t). Skip the
+                                // per-frame provider scan and keep the
+                                // frame's default identity (lavender for
+                                // arpeggios, teal for chords). See the
+                                // unmatched-latch below.
+                            } else {
+                                // Latch both green AND red:
+                                //   - any constituent 'miss' → red latched.
+                                //     One decisive miss verdict means the
+                                //     chord can't be all-hit; without
+                                //     latching, the rim would fall back to
+                                //     teal once noteStateFor's miss-wash
+                                //     window (~0.6 s TTL) expires and the
+                                //     state returns null again.
+                                //   - all hit/active → green latched.
+                                //   - else (no miss yet, some constituents
+                                //     still null) → keep teal default. A
+                                //     partial state must not flash red on
+                                //     a chord whose verdicts arrive
+                                //     incrementally.
+                                let allHit = chordNotes.length > 0;
+                                let anyMiss = false;
+                                let anyState = false;  // true if any constituent had a non-null state this scan
+                                for (const cn of chordNotes) {
+                                    let cs = null;
+                                    try { cs = _ndGetNoteState(cn, ch.t); } catch (e) { cs = null; }
+                                    const st = (cs && typeof cs === 'object') ? cs.state : cs;
+                                    if (st === 'hit' || st === 'active') {
+                                        anyState = true;
+                                    } else if (st === 'miss') {
+                                        // First miss decides the chord — no
+                                        // point querying the rest of the
+                                        // constituents this frame; the rim
+                                        // is about to be red-latched below.
+                                        // Short-circuits provider calls in
+                                        // chord-dense passages.
+                                        allHit = false;
+                                        anyMiss = true;
+                                        anyState = true;
+                                        break;
+                                    } else {
+                                        // null — undecided yet
+                                        allHit = false;
+                                    }
+                                }
+                                if (anyMiss) {
+                                    _chordVerdicts.set(verdictKey, 'red');
+                                    rimHex = CHORD_BOX_MISS_DARK_HEX;
+                                } else if (allHit) {
+                                    _chordVerdicts.set(verdictKey, 'green');
+                                    rimHex = CHORD_BOX_HIT_BRIGHT_HEX;
+                                } else if (chDt < -_ND_UNMATCHED_LATCH_AFTER && !anyState) {
+                                    // The engine verdict typically lands
+                                    // ~0.4 s after the chord crosses the
+                                    // line, so after the
+                                    // _ND_UNMATCHED_LATCH_AFTER threshold
+                                    // we've already waited well past the
+                                    // verdict-arrival window. If no
+                                    // constituent ever returned a non-
+                                    // null state by then, there's no
+                                    // verdict coming for this chord
+                                    // (true arpeggio frames: their actual
+                                    // notes are judged at their own
+                                    // times, never at ch.t — the scan
+                                    // at ch.t finds nothing forever).
+                                    //
+                                    // Latch 'unmatched' so subsequent
+                                    // frames skip the provider scan
+                                    // entirely. The threshold must be
+                                    // INSIDE the chord frame's visible
+                                    // draw window — `chordTailHoldS` is
+                                    // floored to NOTEDETECT_GEM_VERDICT_
+                                    // WINDOW (0.75 s) in detect mode, so
+                                    // chord frames stop drawing at
+                                    // `chDt < -0.75`; a latch threshold
+                                    // at `-NOTEDETECT_GEM_VERDICT_WINDOW`
+                                    // (i.e. exactly -0.75) is unreachable
+                                    // because the draw gate kicks the
+                                    // frame out of the loop first. Place
+                                    // the threshold ~0.55 s past line so
+                                    // it fires for ~0.2 s of the remaining
+                                    // visible window — enough frames to
+                                    // catch and skip future re-scans.
+                                    //
+                                    // The !anyState guard keeps the
+                                    // partial-resolve case (one cn 'hit',
+                                    // another still null) scanning until
+                                    // anyMiss / allHit commits it.
+                                    _chordVerdicts.set(verdictKey, 'unmatched');
+                                }
+                                // else: no verdict yet → leave teal default
+                            }
+                        }
+
+                        if (chDt > 0) { // framebox only on highway, not on the fretboard
+                        const repDim = isRepeat ? 0.78 : 1;
+                        const edgeOp = fade * chordTailMul;
+                        const thickZ = Math.max(CHORD_FRAME_RIM_Z_MIN * K, ft * CHORD_FRAME_RIM_Z_SCAL);
+                        // Per-depth layer stack: chord frames, gems, technique markers,
+                        // and fret labels all derive from RENDER_ORDER_LAYER_STACK so new layers
+                        // have one vocabulary instead of ad hoc arithmetic at call sites.
+                        // Sub-increments of 0.0001 for intra-chord ordering; safe for any
+                        // chord gap >= 0.001 s.
+                        const chordFrameRenderOrder = renderOrderForLayerAtZ(z, 'CHORD_FRAME');
+                        const drawFrameBox = (px, py, sx, sy, ord, hex = rimHex, op = edgeOp) => {
+                            const b = pChordBox.get();
+                            b.renderOrder = ord;
+                            b.material.color.setHex(hex);
+                            b.position.set(px, py, z);
+                            b.scale.set(sx, sy, thickZ);
+                            b.rotation.set(0, 0, 0);
+                            b.material.opacity = op;
+                        };
+                        const sideHex = isArpeggioFrame ? rimHex : 0x163137;
+
+                        const innerW = Math.max(width - 2 * ftSide, width * 0.45);
+                        const innerH = Math.max(height - 2 * ft, height * 0.3);
+                        const fill = pChordFrameFill.get();
+                        fill.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_FILL');
+                        fill.rotation.set(0, 0, 0);
+                        fill.position.set(cx, cY, z - 0.004 * K);
+                        fill.scale.set(innerW, innerH, 1);
+                        fill.material.opacity = fade * repDim * chordTailMul;
+                        // Swapping `map` between two non-null gradient textures
+                        // doesn't change shader-defining state, so no needsUpdate
+                        // — that flag would otherwise force a recompile per frame.
+                        fill.material.map = isArpeggioFrame ? chordFrameGradTexArp : chordFrameGradTex;
+                        fill.material.color.setRGB(1, 1, 1);
+
+                        const withTopFrame = !isRepeat;
+                        // Non-repeat tapers the upper side bars + draws a thin top bar;
+                        // hoisted out so ySideHi can match the actual top-bar thickness
+                        // (using ft would leave a visible gap between the thin top bar
+                        // and the side bars meeting it).
+                        const ftThin = ftSide * 0.22;
+
+                        const ySideLo = yBot + ft;
+                        const ySideHi = withTopFrame ? yTop - ftThin : yTop - ft * 0.15;
+                        const sideH = Math.max(ySideHi - ySideLo, ft * 1.25);
+                        const sideCy = ySideLo + sideH * 0.5;
+
+                        // Bottom bar: thin teal (like top bar) + dark corners on top.
+                        {
+                            const botCW = Math.min(sideH * (isRepeat ? 0.5 : 0.25), width * 0.4);
+                            drawFrameBox(cx, yBot + ftThin * 0.5, width, ftThin, chordFrameRenderOrder);
+                            drawFrameBox(cx + width * 0.5 - botCW * 0.5, yBot + ft * 0.5, botCW, ft, chordFrameRenderOrder + 0.0001, sideHex);
+                            drawFrameBox(cx - width * 0.5 + botCW * 0.5, yBot + ft * 0.5, botCW, ft, chordFrameRenderOrder + 0.0002, sideHex);
+                        }
+
+                        if (isRepeat) {
+                            // Lower 30%: thick dark segment
+                            const repLoH = sideH * 0.3;
+                            const repLoCy = ySideLo + repLoH * 0.5;
+                            drawFrameBox(cx - width * 0.5 + ftSide * 0.5, repLoCy, ftSide, repLoH, chordFrameRenderOrder + 0.0001, sideHex);
+                            drawFrameBox(cx + width * 0.5 - ftSide * 0.5, repLoCy, ftSide, repLoH, chordFrameRenderOrder + 0.0001, sideHex);
+                            // Upper 70%: thin teal segment (same style as non-repeat upper)
+                            const repHiH = sideH - repLoH;
+                            const repHiCy = ySideLo + repLoH + repHiH * 0.5;
+                            drawFrameBox(cx - width * 0.5 + ftThin * 0.5, repHiCy, ftThin, repHiH, chordFrameRenderOrder + 0.0001);
+                            drawFrameBox(cx + width * 0.5 - ftThin * 0.5, repHiCy, ftThin, repHiH, chordFrameRenderOrder + 0.0001);
+                        } else {
+                            // Non-repeat: thick sides up to repeat-frame height, then taper to thin above.
+                            const threshY = yBot + fullChordBoxH * 0.5; // top of what a repeat frame would be
+
+                            // Lower thick segment (ySideLo → threshY)
+                            const loSideH = Math.max(Math.min(threshY, ySideHi) - ySideLo, 0);
+                            if (loSideH > 0) {
+                                const loCy = ySideLo + loSideH * 0.5;
+                                drawFrameBox(cx - width * 0.5 + ftSide * 0.5, loCy, ftSide, loSideH, chordFrameRenderOrder + 0.0001, sideHex);
+                                drawFrameBox(cx + width * 0.5 - ftSide * 0.5, loCy, ftSide, loSideH, chordFrameRenderOrder + 0.0001, sideHex);
+                            }
+
+                            // Upper thin segment (threshY → ySideHi)
+                            const hiSideH = Math.max(ySideHi - threshY, 0);
+                            if (hiSideH > 0) {
+                                const hiCy = threshY + hiSideH * 0.5;
+                                drawFrameBox(cx - width * 0.5 + ftThin * 0.5, hiCy, ftThin, hiSideH, chordFrameRenderOrder + 0.0001);
+                                drawFrameBox(cx + width * 0.5 - ftThin * 0.5, hiCy, ftThin, hiSideH, chordFrameRenderOrder + 0.0001);
+                            }
+
+                            // Top bar: thin
+                            drawFrameBox(cx, yTop - ftThin * 0.5, width, ftThin, chordFrameRenderOrder);
+                        }
+
+                        // Accent bloom on frame edges: 4 additive shells with
+                        // Gaussian-style falloff. Each border expands only in its
+                        // perpendicular axis so bloom never leaves the frame boundary:
+                        //   horizontal bars (top/bottom) → expand Y only
+                        //   vertical bars (left/right)   → expand X only
+                        if (chordAccent && pHaloBar) {
+                            // Bloom only on the teal (thin) parts of the frame — the dark
+                            // "#163137" L-corners are deliberately left without bloom so they
+                            // remain visibly dark (same appearance as non-accent chords).
+                            const haloHex = isArpeggioFrame ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
+                            const EXPAND_MAX = 1.45;
+                            const dynamicOp = fade * chordTailMul;
+                            const drawHaloBar = (px, py, scaleX, scaleY, rotZ) => {
+                                const b = pHaloBar.get();
+                                b.material.color.setHex(haloHex);
+                                b.material.opacity = dynamicOp;
+                                b.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_EDGE_GLOW');
+                                b.position.set(px, py, z - 0.001 * K);
+                                b.scale.set(scaleX, scaleY * EXPAND_MAX * 0.5, thickZ * 2.0);
+                                b.rotation.set(0, 0, rotZ);
+                            };
+                            // Bottom: center-only bloom (skip dark corner areas)
+                            const _bCW = Math.min(sideH * (isRepeat ? 0.5 : 0.25), width * 0.4);
+                            const centerBotW = width - 2 * _bCW;
+                            if (centerBotW > 0)
+                                drawHaloBar(cx, yBot + ft * 0.5, centerBotW * 0.5, ft, 0);
+                            // Top bar
+                            if (withTopFrame)
+                                drawHaloBar(cx, yTop - ftThin * 0.5, width * 0.5, ftThin, 0);
+                            // Lateral: bloom only on the upper thin-teal segment (skip dark lower segment)
+                            if (isRepeat) {
+                                const repLoH = sideH * 0.3;
+                                const repHiH = sideH - repLoH;
+                                if (repHiH > 0) {
+                                    const repHiCy = ySideLo + repLoH + repHiH * 0.5;
+                                    drawHaloBar(cx - width * 0.5 + ftSide * 0.5, repHiCy, repHiH * 0.5, ftSide, Math.PI * 0.5);
+                                    drawHaloBar(cx + width * 0.5 - ftSide * 0.5, repHiCy, repHiH * 0.5, ftSide, Math.PI * 0.5);
+                                }
+                            } else {
+                                const threshY = yBot + fullChordBoxH * 0.5;
+                                const hiSideH = Math.max(ySideHi - threshY, 0);
+                                if (hiSideH > 0) {
+                                    const hiCy = threshY + hiSideH * 0.5;
+                                    drawHaloBar(cx - width * 0.5 + ftSide * 0.5, hiCy, hiSideH * 0.5, ftSide, Math.PI * 0.5);
+                                    drawHaloBar(cx + width * 0.5 - ftSide * 0.5, hiCy, hiSideH * 0.5, ftSide, Math.PI * 0.5);
+                                }
+                            }
+                        }
+                        const chordName = chordTemplateLabel(bundle.chordTemplates?.[ch.id]);
+                        if (chordName && firstInShapeRun && !chordWireHighDensity(ch)) {
+                            const lblW = 28 * K, lblH = 9 * K;
+                            const lbl = pChordLbl.get();
+                            const mat = txtMat(chordName, '#e8d080', true, 'chord');
+                            _setLabelMap(lbl, mat);
+                            lbl.material.opacity = Math.min(1, 0.3 + fade * 0.7) * chordTailMul;
+                            // Gold chord name: slight +X shift from flush-left so it sits farther right.
+                            const lblWS = lblW * _textSizeMul;
+                            const lblHS = lblH * _textSizeMul;
+                            const frameLeft = cx - width / 2;
+                            const nameShiftX = NW * 0.94;
+                            const nameVertTuck = NH * 0.02;
+                            lbl.position.set(
+                                frameLeft - lblWS / 2 + nameShiftX,
+                                yMaxF + lblHS / 2 - nameVertTuck,
+                                z);
+                            lbl.scale.set(lblWS, lblHS, 1);
+                        }
+
+                        // Harmony annotations (§6.3.1 / §6.6) — the chord's
+                        // function (fn.rn Roman numeral) and template voicing,
+                        // stacked above the chord name. Gated by the
+                        // teaching-marks opt-in (mirrors the 2D overlay). Display
+                        // only — never grading.
+                        if (_drawTeachingMarks && firstInShapeRun && !chordWireHighDensity(ch)) {
+                            const _tmpl = bundle.chordTemplates?.[ch.id];
+                            const _h = chordHarmonyLabels(ch.fn, _tmpl?.voicing, _tmpl?.caged, _tmpl?.guideTones);
+                            if (_h.rn || _h.voicing || _h.caged || _h.guideTones) {
+                                const hlW = 24 * K * _textSizeMul;
+                                const hlH = 9 * K * _textSizeMul;
+                                const frameLeft = cx - width / 2;
+                                const baseX = frameLeft - hlW / 2 + NW * 0.94;
+                                const opacity = Math.min(1, 0.3 + fade * 0.7) * chordTailMul;
+                                // Start one chord-name-height above the name and
+                                // stack upward so labels never overlap the gems.
+                                let hy = yMaxF + hlH * 1.6;
+                                const _drawHarmony = (text, colorHex) => {
+                                    if (!text) return;
+                                    const s = pChordLbl.get();
+                                    const m = txtMat(text, colorHex, true, 'chord');
+                                    _setLabelMap(s, m);
+                                    s.material.opacity = opacity;
+                                    s.position.set(baseX, hy, z);
+                                    s.scale.set(hlW, hlH, 1);
+                                    hy += hlH;
+                                };
+                                _drawHarmony(_h.rn, '#ffcc66');         // sd teaching color
+                                _drawHarmony(_h.voicing, '#7fd1ff');    // fg teaching color
+                                _drawHarmony(_h.caged, '#a0ffa0');      // CAGED shape teaching color
+                                _drawHarmony(_h.guideTones, '#d0a0ff'); // guide-tone teaching color
+                            }
+                        }
+
+                        // Shape-based barre detection for the 3D indicator.
+                        // Drives off chord notes alone — independent of label
+                        // availability, so charts whose chordTemplates lack a
+                        // .name still show the barre line.
+                        // Matches drawChordDiagram PATH A + PATH B so the highway
+                        // line and overlay bracket always agree on the same shapes:
+                        //   PATH A: 2+ adjacent strings at the minimum fret.
+                        //   PATH B: outer-edge full-span barre (e.g. B major x24442)
+                        //           where the two outer strings are at the minimum fret,
+                        //           every intermediate string is fretted (f>0), and no
+                        //           intermediate string also sits at the minimum fret.
+                        // Scattered voicings like "1 3 1 3 1 0" (strings 0,2,4 at
+                        // fret 1 but no two adjacent, and string 2 sits at min fret)
+                        // correctly produce no indicator.
+                        {
+                            let bFret = Infinity;
+                            for (const [, f] of chShape) {
+                                if (f > 0) bFret = Math.min(bFret, f);
+                            }
+                            // Collect strings at minimum fret into scratch array (no allocation)
+                            _scrAtMinFretLen = 0;
+                            if (bFret < Infinity) {
+                                for (const [s, f] of chShape) {
+                                    if (f === bFret) _scrAtMinFretArr[_scrAtMinFretLen++] = s;
+                                }
+                                // insertion sort — array is ≤8 elements
+                                for (let _ii = 1; _ii < _scrAtMinFretLen; _ii++) {
+                                    const _v = _scrAtMinFretArr[_ii];
+                                    let _jj = _ii - 1;
+                                    while (_jj >= 0 && _scrAtMinFretArr[_jj] > _v) {
+                                        _scrAtMinFretArr[_jj + 1] = _scrAtMinFretArr[_jj]; _jj--;
+                                    }
+                                    _scrAtMinFretArr[_jj + 1] = _v;
+                                }
+                            }
+                            // Inline longestConsecutiveRun (no array allocation)
+                            let _barreRunStart = -1, _barreRunLen = 0;
+                            {
+                                let _curStart = -1, _curLen = 0;
+                                for (let _ri = 0; _ri < _scrAtMinFretLen; _ri++) {
+                                    const _rv = _scrAtMinFretArr[_ri];
+                                    if (_curLen === 0 || _rv === _scrAtMinFretArr[_ri - 1] + 1) {
+                                        if (_curLen === 0) _curStart = _rv;
+                                        _curLen++;
+                                    } else {
+                                        if (_curLen > _barreRunLen) { _barreRunLen = _curLen; _barreRunStart = _curStart; }
+                                        _curStart = _rv; _curLen = 1;
+                                    }
+                                }
+                                if (_curLen > _barreRunLen) { _barreRunLen = _curLen; _barreRunStart = _curStart; }
+                            }
+                            let is3dBarre    = _barreRunLen >= 2;   // PATH A
+                            let barreMinStr3d = is3dBarre ? _barreRunStart : -1;
+                            let barreMaxStr3d = is3dBarre ? _barreRunStart + _barreRunLen - 1 : -1;
+
+                            // PATH B: outer-edge full-span barre
+                            const MIN_BARRE_SPAN_3D = Math.min(nStr - 1, 4);
+                            if (_scrAtMinFretLen >= 2) {
+                                const minS = _scrAtMinFretArr[0];
+                                const maxS = _scrAtMinFretArr[_scrAtMinFretLen - 1];
+                                if (maxS - minS >= MIN_BARRE_SPAN_3D) {
+                                    // chShape is already a Map<s, f> — query it directly
+                                    // instead of building a transient Set<s> every frame.
+                                    let allFretted = true;
+                                    for (let si = minS; si <= maxS; si++) {
+                                        if (!chShape.has(si) || chShape.get(si) <= 0) { allFretted = false; break; }
+                                    }
+                                    if (allFretted) {
+                                        if (is3dBarre) {
+                                            // PATH A fired: extend to full outer span.
+                                            barreMinStr3d = minS; barreMaxStr3d = maxS;
+                                        } else {
+                                            // PATH A did not fire: only draw if no inner
+                                            // string also sits at the minimum fret.
+                                            let innerAtMinFret = false;
+                                            for (let _ai = 1; _ai < _scrAtMinFretLen - 1; _ai++) {
+                                                const _as = _scrAtMinFretArr[_ai];
+                                                if (_as > minS && _as < maxS) { innerAtMinFret = true; break; }
+                                            }
+                                            if (!innerAtMinFret) {
+                                                is3dBarre = true;
+                                                barreMinStr3d = minS; barreMaxStr3d = maxS;
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+
+                            if (is3dBarre && chDt <= 0) {
+                                const bx = xFretMid(bFret);
+                                const yTop = Math.max(sY(barreMinStr3d), sY(barreMaxStr3d));
+                                const yBot = Math.min(sY(barreMinStr3d), sY(barreMaxStr3d));
+                                const lineH = yTop - yBot;
+                                const bl = pBarreLine.get();
+                                bl.position.set(bx, (yTop + yBot) / 2, 0.05 * K);
+                                bl.scale.set(0.5 * K, lineH, 0.5 * K);
+                                bl.material.opacity = 0.8 * chordTailMul;
+                            }
+                        }
+
+                        // ── Chord fret numbers at the base of the highway ───────────────
+                        // Show fret number per unique fretted position for non-repeated
+                        // chords so the player can read the shape at a glance.
+                        if (!isRepeat) {
+                            const _chFretLblAlpha = Math.min(1.0, (AHEAD - chDt) / 0.35) * chordTailMul;
+                            const _seenChordFrets = new Set();
+                            for (const [, f] of chShape) {
+                                if (f <= 0 || _seenChordFrets.has(f)) continue;
+                                _seenChordFrets.add(f);
+                                const lbl = pNoteFretLabel.get();
+                                const mat = txtMat(f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
+                                _setLabelMap(lbl, mat);
+                                lbl.position.set(xFretMid(f), yMinF, z);
+                                lbl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_FRET_LABEL');
+                                const _flS = 7.0 * K * (1 + 0.4 * chDt / AHEAD) * _textSizeMul * fretLabelScaleForFret(f);
+                                lbl.scale.set(_flS, _flS, 1);
+                                lbl.material.opacity = _chFretLblAlpha;
+                            }
+                        }
+
+                        // ── Palm-mute strum indicator — pool (fill + lines) ──────────────
+                        // Per-chord Z-proportional renderOrder: muted fill/lines and
+                        // frame edges all use the named layer offsets above.
+                        if (isRepeat && chordNotes.some(cn => cn.pm)) {
+                            if (pPMXFill) {
+                                const xf = pPMXFill.get();
+                                xf.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_FILL');
+                                xf.material.opacity = edgeOp * CHORD_BOX_EDGE_ALPHA;
+                                xf.position.set(cx, cY, z - 0.0045 * K);
+                                xf.scale.set(innerW * 0.5, -innerH * 0.5, 1);
+                                xf.rotation.set(0, 0, 0);
+                            }
+                            if (pMuteXLines) {
+                                const xl = pMuteXLines.get();
+                                xl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_LINE');
+                                xl.material.opacity = edgeOp * 0.85;
+                                xl.material.color.setHex(baseRimHex);
+                                xl.position.set(cx, cY, z - 0.005 * K);
+                                xl.scale.set(innerW * 0.5, -innerH * 0.5, thickZ * 0.5);
+                                xl.rotation.set(0, 0, 0);
+                            }
+                        }
+
+                        // ── Frethand-mute strum indicator — pool (fill + lines) ───────────
+                        if (isRepeat && chordNotes.some(cn => cn.mt || cn.fhm)) {
+                            if (pFHXFill) {
+                                const xf = pFHXFill.get();
+                                xf.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_FILL');
+                                xf.material.opacity = edgeOp * CHORD_BOX_EDGE_ALPHA;
+                                xf.position.set(cx, cY, z - 0.0045 * K);
+                                xf.scale.set(innerW * 0.5, -innerH * 0.5, 1);
+                                xf.rotation.set(0, 0, 0);
+                            }
+                            if (pFHXLines) {
+                                const xl = pFHXLines.get();
+                                xl.renderOrder = renderOrderForLayerAtZ(z, 'CHORD_STRUM_LINE');
+                                xl.material.opacity = edgeOp * 0.85;
+                                xl.material.color.setHex(baseRimHex);
+                                xl.position.set(cx, cY, z - 0.005 * K);
+                                xl.scale.set(innerW * 0.5, -innerH * 0.5, thickZ * 0.5);
+                                xl.rotation.set(0, 0, 0);
+                            }
+                        }
+
+                        } // end if (chDt > 0) — framebox + PM/FH mute only on highway
+
+                    }
+
+                    // ── Chord sustain length indicator — 3D plane rails ─────────────
+                    // Left + right rail as plane meshes (PlaneGeometry +
+                    // MeshBasicMaterial) in the WebGL scene so they respect
+                    // renderOrder (16) and never occlude note gems (20/21).
+                    // isRepeat chords also draw their rail: each repeat shows a
+                    // segment from its own onset to the next chord's onset (or the
+                    // handshape end, whichever is shorter), chaining together to
+                    // cover the full handshape duration visually.
+                    if (chShape.size > 1 && chordOpenBoxW != null && chDt < AHEAD) {
+                        // Cap handshape-derived sustain at the gap to the next chord.
+                        // Each chord (including repeats) only extends to the next
+                        // chord's onset, so the rail never lingers past the anchor
+                        // region of the current chord.
+                        const _nextChordGap = (ci + 1 < chords.length)
+                            ? chords[ci + 1].t - ch.t
+                            : Infinity;
+                        // Use the time remaining in the handshape from this chord's
+                        // onset (hsEnd - ch.t), NOT the full handshape span. When
+                        // multiple chords share the same handshape window (e.g. A5
+                        // at 63.527 and again at 64.137 both fall inside the same
+                        // handshape start=63.527 end=64.239), each chord after the
+                        // first starts mid-handshape. Using the full span (0.712s)
+                        // for the mid-handshape chord gives a rail that extends
+                        // 0.611s — far past the handshape end — causing the
+                        // "elongated border" that visually swallows subsequent
+                        // single notes. Clamping to (hsEnd - ch.t) gives 0.102s,
+                        // which correctly terminates at the handshape boundary.
+                        const _hsSus = (maxSus === 0 && !deferChordGems && hsHintFrame && hsHintFrame.hs)
+                            ? Math.min(Math.max(0, hsEnd(hsHintFrame.hs) - ch.t), _nextChordGap)
+                            : 0;
+                        // "Chord hold": suppressed non-arp synth chord where deferChordGems
+                        // zeroed _hsSus. Use h3dSynthEnd (= handshape end_time) instead.
+                        const _synthSus = (suppressSynthChord && ch.h3dSynth
+                            && !chordTemplateMarkedArpeggio(ch.id, bundle.chordTemplates)
+                            && ch.h3dSynthEnd != null)
+                            ? Math.max(0, ch.h3dSynthEnd - ch.t)
+                            : 0;
+                        const _rawSus = maxSus > 0 ? maxSus : Math.max(_hsSus, _synthSus);
+                        // Apply the 0.4 s visual-minimum only to chords with an
+                        // explicit note sustain (maxSus > 0). Handshape-derived
+                        // sustain (_hsSus, already capped at _nextChordGap) must
+                        // not be inflated — that would undo the gallop cap and
+                        // cause the rail to reappear at the old anchor position.
+                        const _effSus = maxSus > 0
+                            ? Math.max(_rawSus, 0.4)
+                            : _rawSus;
+                        const _dtSusEnd  = chDt + _effSus;
+                        if (_dtSusEnd > 0) {
+                            // Clip the rail at the next anchor boundary so it doesn't
+                            // extend into a different fret zone. The lane (pLane) slices
+                            // correctly per-anchor; a single-segment rail at fixed X would
+                            // visually "invade" the neighbouring region when anchors change
+                            // within the sustain window.
+                            let _dtSusEndRail = _dtSusEnd;
+                            if (anchors && anchors.length) {
+                                const _susAbsT = chDt > 0 ? ch.t : now;
+                                if (getChartAnchorAt(anchors, _susAbsT) !==
+                                    getChartAnchorAt(anchors, now + _dtSusEnd)) {
+                                    // Binary search: first anchor starting strictly after _susAbsT.
+                                    let _lo = 0, _hi = anchors.length;
+                                    while (_lo < _hi) {
+                                        const _mid = (_lo + _hi) >>> 1;
+                                        if (anchors[_mid].time <= _susAbsT) _lo = _mid + 1;
+                                        else _hi = _mid;
+                                    }
+                                    if (_lo < anchors.length)
+                                        _dtSusEndRail = anchors[_lo].time - now;
+                                }
+                            }
+                            const _zNear = chDt > 0 ? dZ(chDt) : 0;
+                            const _zFar  = dZ(Math.min(_dtSusEndRail, AHEAD));
+                            const _railLen = _zNear - _zFar;
+                            if (_railLen > 0.001) {
+                                const _yA   = sY(0), _yB = sY(nStr - 1);
+                                const _yBot = Math.min(_yA, _yB) - S_GAP * 0.8;
+                                const _fadeAhead = chDt > 0 ? Math.max(0, 1 - chDt / AHEAD) : 1;
+                                const _fadeSus   = Math.min(1, _dtSusEnd / 0.25);
+                                const _op  = _fadeAhead * _fadeSus * 0.9;
+                                const _hex = chordHighwayLavenderArpVisual ? ARPEGGIO_RIM_BLUE_HEX : CHORD_BOX_TEAL_HEX;
+                                const _railW = 1.875 * K; // visual width of each rail strip
+                                const _zMid  = _zNear - _railLen * 0.5; // centre in Z
+                                for (const [_rx, _inDir] of [[chordFrameXL, -1], [chordFrameXR, 1]]) {
+                                    const _rxIn = _rx + _inDir * _railW * 0.5;
+                                    // Core rail
+                                    const rl = pSusRail.get();
+                                    rl.material.color.setHex(_hex);
+                                    rl.material.opacity = _op;
+                                    rl.position.set(_rxIn, _yBot, _zMid);
+                                    rl.scale.set(_railW, 1, _railLen);
+                                    // Bloom glow — wider gaussian plane, additive blending
+                                    if (!_leanSus) {
+                                        const bl = pSusRailBloom.get();
+                                        bl.material.color.setHex(_hex);
+                                        bl.material.opacity = _op * 0.8;
+                                        bl.position.set(_rxIn, _yBot + 0.001, _zMid);
+                                        bl.scale.set(3 * K, 1, _railLen);
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Fret span of the dynamic highway lane (wire dMin .. dMax). Reused
+            // so fret-column measure markers stay inside the same horizontal
+            // band as the blue track — previously markers used every inlay
+            // fret and stuck out past the lane whenever the camera narrowed.
+            let hwyLaneFretClipMin = null, hwyLaneFretClipMax = null;
+
+            const handShapesRails = bundle.handShapes;
+            hwyLaneArpOuterDividers = !!(handShapesRails && handShapesRails.length && laneRailArpHsFlags
+                && arpeggioLaneOuterRailAtChartTime(
+                    now, handShapesRails, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
+                ));
+            const arpLaneRimAccentMul = hwyLaneArpOuterDividers && laneRailArpHsFlags && handShapesRails
+                ? arpeggioLaneDividerFrameAccentMul(
+                    now, handShapesRails, chords, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
+                )
+                : 1;
+            const arpLaneS = hwyLaneArpOuterDividers
+                ? arpeggioLaneDividerXYScaleMatchFrameRim(arpLaneRimAccentMul)
+                : 1;
+
+            // ── Fret-wire hit flash (apply) ───────────────────────────────
+            // Runs here, after the note + chord draw loops, so it sees this
+            // frame's verdicts (_fwHitIn) rather than the previous frame's —
+            // the base tier loop that seeds color/opacity/emissive sits far
+            // above, before any note has been drawn.
+            //
+            // _fwHitGlow decays exponentially in CHART time, so the tail is
+            // frame-rate independent and honours playback speed. Seeking
+            // backward resets it — otherwise a flash from a hit we jumped away
+            // from would linger on the wire.
+            if (fretWireMats.length && _fwHitColor) {
+                // Resolve accumulated chord hits: a chord's flash frames the
+                // LANE, not its own shape. The lit lane strip spans the anchor's
+                // width (min ~4 frets), which can run a fret past the chord's
+                // outermost fret — and a bracket one wire INSIDE the lit lane
+                // reads as misaligned. So a chord lights the anchor lane's edge
+                // wires: the exact wires the lane strip spans, and the same pair
+                // open strings already use. The shape's own outer pair (wire
+                // behind the lowest fret, wire at the highest) survives only as
+                // the fallback for charts with no anchors.
+                for (const _fwE of _fwChordAcc.values()) {
+                    const _fwA = Math.max(_fwE.a, _fwE.openA);
+                    if (_fwA <= 0) continue;
+                    let _w0 = -1, _w1 = -1;
+                    const _fwB = anchorLaneBoundsAt(_drawAnchors, _fwE.t);
+                    if (_fwB) {
+                        _w0 = _fwB.dMin;
+                        _w1 = _fwB.dMax;
+                    } else if (_fwE.maxF >= _fwE.minF) {
+                        _w0 = Math.max(0, _fwE.minF - 1);
+                        _w1 = Math.min(NFRETS, _fwE.maxF);
+                    }
+                    if (_w0 < 0) continue; // all-open chord on an anchor-less chart
+                    if (_fwA > _fwHitIn[_w0]) _fwHitIn[_w0] = _fwA;
+                    if (_fwA > _fwHitIn[_w1]) _fwHitIn[_w1] = _fwA;
+                }
+
+                const _fwDt = now - _fwHitPrevTime;
+                if (!(_fwDt >= 0) || _fwDt > 1) _fwHitGlow.fill(0); // first frame, seek, or long stall
+                const _fwDecay = (_fwDt > 0 && _fwDt <= 1)
+                    ? Math.exp(-_fwDt / FRET_WIRE_HIT_DECAY)
+                    : 0;
+                _fwHitPrevTime = now;
+                // Decay EVERY wire's glow state, but flash only the OUTERMOST
+                // pair of lit wires. Fast passages overlap their decay tails, so
+                // without this a run of consecutive notes lights a picket fence
+                // of wires at once; collapsing to the outer pair keeps the whole
+                // lit span reading as ONE bracket — the same rule chords already
+                // follow, applied across everything currently glowing. Interior
+                // wires keep decaying invisibly (the base tier loop re-seeds
+                // their materials each frame), so the bracket tightens naturally
+                // as outer tails expire.
+                let _fwLo = -1, _fwHi = -1;
+                for (let _f = 0; _f <= NFRETS; _f++) {
+                    const _g = Math.max(_fwHitIn[_f], _fwHitGlow[_f] * _fwDecay);
+                    _fwHitGlow[_f] = _g;
+                    if (_g < 0.004) continue;   // below perceptible
+                    if (_fwLo < 0) _fwLo = _f;
+                    _fwHi = _f;
+                }
+                for (let _i = 0; _i < 2; _i++) {
+                    const _f = _i === 0 ? _fwLo : _fwHi;
+                    if (_f < 0) break;                       // nothing lit
+                    if (_i === 1 && _f === _fwLo) break;     // single wire lit
+                    const _g = _fwHitGlow[_f];
+                    const _m = fretWireMats[_f];
+                    if (!_m) continue;
+                    _m.color.lerp(_fwHitColor, _g);
+                    _m.emissive.lerp(_fwHitEmissive, _g);
+                    _m.emissiveIntensity = 1 + (FRET_WIRE_HIT_INTENSITY - 1) * _g;
+                    _m.opacity += (FRET_WIRE_HIT_OP - _m.opacity) * _g;
+                }
+
+                // Gem-rim flash: same intensity ramp as the wires, in the
+                // string's own colour. No decay tail of our own — the material
+                // is only ever ASSIGNED while the provider confirms the note,
+                // and the provider's alpha already fades; when it goes silent
+                // the outline reverts and idle intensity is irrelevant.
+                for (let _s = 0; _s < mRimFlash.length; _s++) {
+                    const _m = mRimFlash[_s];
+                    if (_m) _m.emissiveIntensity = 1 + (FRET_WIRE_HIT_INTENSITY - 1) * _rimFlashIn[_s];
+                }
+            }
+
+            // ── Dynamic highway lane ──────────────────────────────────────
+            // Chart <anchor> tags drive the lane whenever they exist — do not
+            // require nearby notes (activeFrets) or camera-driven activity.
+            const hasChartAnchors = anchors && anchors.length;
+            if (hasChartAnchors || activeFrets.size > 0) {
+                // Lane tint: one translucent quad per playable fret column, exact
+                // wire→wire span (no horizontal pad) — see HWY_LANE_STRIPE_*.
+                const boardY = S_BASE - NH / 2 - 2 * K;
+
+                if (hasChartAnchors) {
+                    const nearB = laneBoundsFromAnchor(getChartAnchorAt(anchors, now));
+                    if (nearB) {
+                        hwyLaneFretClipMin = nearB.dMin;
+                        hwyLaneFretClipMax = nearB.dMax;
+                    }
+
+                    // Span the full (AHEAD + BEHIND) window so the lane's far edge
+                    // lands at dZ(AHEAD) = -AHEAD*TS, aligned with the note horizon.
+                    // Using just AHEAD here made the far edge stop at -TS*(AHEAD-BEHIND),
+                    // leaving the last BEHIND seconds of notes without a lane underneath.
+                    const sliceDt = (AHEAD + BEHIND) / HWY_LANE_TIME_SLICES;
+                    // Single-pass build-and-merge into the parallel-array
+                    // scratch buffers. Consecutive slices that resolve to the
+                    // same anchor bounds collapse into one segment by extending
+                    // its z1; otherwise a new entry appends. No per-frame array
+                    // or {b,z0,z1} object allocations.
+                    _laneSegLen = 0;
+                    for (let k = 0; k < HWY_LANE_TIME_SLICES; k++) {
+                        const dt0 = k * sliceDt;
+                        const dt1 = (k + 1) * sliceDt;
+                        const tC = now + (dt0 + dt1) * 0.5 - BEHIND;
+                        const b = laneBoundsFromAnchor(getChartAnchorAt(anchors, tC));
+                        if (!b) continue;
+                        // The lane STOPS AT THE HIT LINE (z = 0) — issue #991. The
+                        // slice window starts BEHIND seconds in the past, so the
+                        // first slices map to positive z, i.e. past the hit line
+                        // toward the player. Nothing is ever drawn there: notes and
+                        // chord frames clamp to Math.min(0, dZ(dt)), so that strip
+                        // is lane with nothing on it. Clamp the NEAR edge only —
+                        // the far edge stays at dZ(AHEAD+BEHIND)+TS*BEHIND = -AHEAD*TS,
+                        // aligned with the note horizon, exactly as before.
+                        const z0 = Math.min(0, dZ(dt0) + TS * BEHIND);
+                        const z1 = Math.min(0, dZ(dt1) + TS * BEHIND);
+                        // Slice lies entirely past the hit line -> zero length, nothing
+                        // to draw. Skip before the arp probe so it costs nothing.
+                        if (z0 === z1) continue;
+                        const arpSlice = (laneRailArpHsFlags && handShapesRails && handShapesRails.length)
+                            ? arpeggioLaneOuterRailLaneSlice(
+                                dt0, dt1, now,
+                                handShapesRails, laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
+                            )
+                            : false;
+                        if (_laneSegLen > 0
+                            && _laneSegDMin[_laneSegLen - 1] === b.dMin
+                            && _laneSegDMax[_laneSegLen - 1] === b.dMax
+                            && arpSlice === _laneSegArp[_laneSegLen - 1]) {
+                            _laneSegZ1[_laneSegLen - 1] = z1;
+                            _laneSegTHi[_laneSegLen - 1] = tC;
+                        } else if (_laneSegLen > 0
+                            && _laneSegDMin[_laneSegLen - 1] === b.dMin
+                            && _laneSegDMax[_laneSegLen - 1] === b.dMax
+                            && arpSlice !== _laneSegArp[_laneSegLen - 1]) {
+                            _laneSegDMin[_laneSegLen] = b.dMin;
+                            _laneSegDMax[_laneSegLen] = b.dMax;
+                            _laneSegZ0[_laneSegLen] = z0;
+                            _laneSegZ1[_laneSegLen] = z1;
+                            _laneSegTLo[_laneSegLen] = tC;
+                            _laneSegTHi[_laneSegLen] = tC;
+                            _laneSegArp[_laneSegLen] = arpSlice;
+                            _laneSegLen++;
+                        } else {
+                            _laneSegDMin[_laneSegLen] = b.dMin;
+                            _laneSegDMax[_laneSegLen] = b.dMax;
+                            _laneSegZ0[_laneSegLen] = z0;
+                            _laneSegZ1[_laneSegLen] = z1;
+                            _laneSegTLo[_laneSegLen] = tC;
+                            _laneSegTHi[_laneSegLen] = tC;
+                            _laneSegArp[_laneSegLen] = arpSlice;
+                            _laneSegLen++;
+                        }
+                    }
+                    {
+                        const laneOp = (HWY_LANE_STRIPE_OP_BASE + highwayIntensity * HWY_LANE_STRIPE_OP_INT)
+                            * (_venueSceneOverride ? VENUE_LANE_OP_BOOST : 1);
+                        // 2 shared materials (odd/even); opacity travels via the
+                        // material so set it once per frame, not per mesh.
+                        mLaneOdd.opacity = laneOp;
+                        mLaneEven.opacity = laneOp;
+                        for (let s = 0; s < _laneSegLen; s++) {
+                            const segZ0 = _laneSegZ0[s];
+                            const segZ1 = _laneSegZ1[s];
+                            const stripLen = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
+                            const zc = (segZ0 + segZ1) * 0.5;
+                            const fLow = _laneSegDMin[s] + 1;
+                            const fHi = _laneSegDMax[s];
+                            for (let f = fLow; f <= fHi; f++) {
+                                const xl = xFret(f - 1), xr = xFret(f);
+                                const laneW = Math.abs(xr - xl);
+                                const lane = pLane.get();
+                                lane.position.set((xl + xr) * 0.5, boardY + 0.02 * K, zc);
+                                lane.rotation.x = -Math.PI / 2;
+                                lane.scale.set(laneW, stripLen, 1);
+                                const odd = ((f - fLow) & 1) === 0;
+                                lane.material = odd ? mLaneOdd : mLaneEven;
+                                lane.renderOrder = 1;
+                            }
+                        }
+                    }
+
+                    {
+                        const yPos = boardY + 0.03 * K;
+                        const divOpArp = Math.min(0.92, 0.16 + highwayIntensity * 0.42);
+                        if (mLaneDividerArp) {
+                            mLaneDividerArp.opacity = divOpArp;
+                        }
+
+                        for (let s = 0; s < _laneSegLen; s++) {
+                            const segZ0 = _laneSegZ0[s];
+                            const segZ1 = _laneSegZ1[s];
+                            const dz = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
+                            const zMid = (segZ0 + segZ1) * 0.5;
+                            const dMinSeg = _laneSegDMin[s];
+                            const dMaxSeg = _laneSegDMax[s];
+                            const fDiv0 = Math.floor(dMinSeg);
+                            const fDiv1 = Math.ceil(dMaxSeg);
+                            for (let f = fDiv0; f <= fDiv1; f++) {
+                                if (_laneSegArp[s] && (f === fDiv0 || f === fDiv1)) continue;
+                                const div = pLaneDivider.get();
+                                div.position.set(xFret(f), yPos, zMid);
+                                div.material = mLaneDivider;
+                                div.scale.set(1, 1, dz);
+                                div.renderOrder = 2;
+                            }
+                        }
+                        for (let s = 0; s < _laneSegLen; s++) {
+                            if (!_laneSegArp[s]) continue;
+                            const dMinSeg = _laneSegDMin[s];
+                            const dMaxSeg = _laneSegDMax[s];
+                            const fL = Math.floor(dMinSeg);
+                            const fR = Math.ceil(dMaxSeg);
+                            const segZ0 = _laneSegZ0[s];
+                            const segZ1 = _laneSegZ1[s];
+                            const arpRailLen = Math.max(Math.abs(segZ1 - segZ0), 1e-6);
+                            const zArpMid = (segZ0 + segZ1) * 0.5;
+                            const tMidSeg = (_laneSegTLo[s] + _laneSegTHi[s]) * 0.5;
+                            const arpMulSeg = (laneRailArpHsFlags && handShapesRails && handShapesRails.length)
+                                ? arpeggioLaneDividerFrameAccentMul(
+                                    tMidSeg, handShapesRails, chords,
+                                    laneRailBoundLo, laneRailBoundHi, laneRailArpHsFlags,
+                                )
+                                : 1;
+                            const arpSSeg = arpeggioLaneDividerXYScaleMatchFrameRim(arpMulSeg);
+                            for (const xf of [fL, fR]) {
+                                const div = pLaneDivider.get();
+                                div.position.set(xFret(xf), yPos, zArpMid);
+                                div.material = mLaneDividerArp;
+                                div.scale.set(arpSSeg, arpSSeg, arpRailLen);
+                                div.renderOrder = 2;
+                            }
+                        }
+                    }
+                } else {
+                    let dMin, dMax;
+                    let divMin, divMax;
+                    let minF = 99, maxF = 0;
+                    activeFrets.forEach(f => { if (f > 0) { minF = Math.min(minF, f); maxF = Math.max(maxF, f); } });
+                    dMin = minF - 1;
+                    dMax = maxF;
+                    const HWY_LANE_SPAN = 4;
+                    let span = dMax - dMin;
+                    if (span > HWY_LANE_SPAN) {
+                        dMin = Math.round((dMin + dMax - HWY_LANE_SPAN) / 2);
+                        dMax = dMin + HWY_LANE_SPAN;
+                        if (dMax > NFRETS) {
+                            dMax = NFRETS;
+                            dMin = dMax - HWY_LANE_SPAN;
+                        }
+                        if (dMin < 0) {
+                            dMin = 0;
+                            dMax = HWY_LANE_SPAN;
+                        }
+                    } else if (span < HWY_LANE_SPAN) {
+                        const need = HWY_LANE_SPAN - span;
+                        dMax = Math.min(NFRETS, dMax + need);
+                        if (dMax - dMin < HWY_LANE_SPAN) {
+                            dMin = Math.max(0, dMin - (HWY_LANE_SPAN - (dMax - dMin)));
+                        }
+                    }
+                    if (dMax < dMin) dMax = dMin;
+                    hwyLaneFretClipMin = dMin;
+                    hwyLaneFretClipMax = dMax;
+                    divMin = dMin;
+                    divMax = dMax;
+
+                    // Far edge at -AHEAD*TS (the note horizon), near edge at the
+                    // hit line (z = 0) — the lane does not run past it toward the
+                    // player, where nothing is ever drawn (#991). Spanning
+                    // AHEAD+BEHIND and shifting by +TS*BEHIND put the near edge at
+                    // +TS*BEHIND; spanning AHEAD alone keeps the same far edge.
+                    const laneLen = TS * AHEAD;
+                    const zLane = -laneLen / 2;
+                    const laneOp = (HWY_LANE_STRIPE_OP_BASE + highwayIntensity * HWY_LANE_STRIPE_OP_INT)
+                        * (_venueSceneOverride ? VENUE_LANE_OP_BOOST : 1);
+                    mLaneOdd.opacity = laneOp;
+                    mLaneEven.opacity = laneOp;
+                    const fLow = dMin + 1;
+                    const fHi = dMax;
+                    for (let f = fLow; f <= fHi; f++) {
+                        const xl = xFret(f - 1), xr = xFret(f);
+                        const laneWStrip = Math.abs(xr - xl);
+                        const lane = pLane.get();
+                        lane.position.set((xl + xr) / 2, boardY + 0.02 * K, zLane);
+                        lane.rotation.x = -Math.PI / 2;
+                        lane.scale.set(laneWStrip, laneLen, 1);
+                        const odd = ((f - fLow) & 1) === 0;
+                        lane.material = odd ? mLaneOdd : mLaneEven;
+                        lane.renderOrder = 1;
+                    }
+
+                    if (highwayIntensity > 0.05) {
+                        // Matches the lane above: ends at the hit line (#991).
+                        const divLen = TS * AHEAD;
+                        const yPos = boardY + 0.03 * K;
+                        const divOp2 = 0.02 + highwayIntensity * 0.1;
+                        const divOpArp2 = Math.min(0.92, 0.16 + highwayIntensity * 0.42);
+                        if (mLaneDivider && mLaneDividerArp) {
+                            mLaneDivider.opacity = divOp2;
+                            mLaneDividerArp.opacity = divOpArp2;
+                        }
+                        const fDivA = Math.floor(divMin);
+                        const fDivB = Math.ceil(divMax);
+                        for (let f = fDivA; f <= fDivB; f++) {
+                            if (hwyLaneArpOuterDividers && (f === fDivA || f === fDivB)) continue;
+                            const div = pLaneDivider.get();
+                            div.position.set(xFret(f), yPos, -divLen * 0.5);
+                            div.material = mLaneDivider;
+                            div.scale.set(1, 1, divLen);
+                            div.renderOrder = 2;
+                        }
+                        if (hwyLaneArpOuterDividers) {
+                            for (const xf of [fDivA, fDivB]) {
+                                const div = pLaneDivider.get();
+                                div.position.set(xFret(xf), yPos, zLane);
+                                div.material = mLaneDividerArp;
+                                div.scale.set(arpLaneS, arpLaneS, laneLen);
+                                div.renderOrder = 2;
+                            }
+                        }
+                    }
+                }
+
+                // ── Fret boundary extension lines ─────────────────────────
+                if (mLaneDividerExt && fretDividersVisible) {
+                    // Same hit-line stop as the lane (#991) — otherwise these lines
+                    // would be the only floor geometry still running past it.
+                    const extLaneLen = TS * AHEAD;
+                    const extZMid = -extLaneLen / 2;
+                    const extYPos = boardY + 0.03 * K;
+                    mLaneDividerExt.opacity = Math.max(0.3, 0.3 + highwayIntensity * 0.15);
+                    for (let f = 0; f <= NFRETS; f++) {
+                        const div = pLaneDivider.get();
+                        div.position.set(xFret(f), extYPos, extZMid);
+                        div.material = mLaneDividerExt;
+                        div.scale.set(1, 1, extLaneLen);
+                        div.renderOrder = 2;
+                    }
+                }
+            }
+
+            // ── Dynamic fret number row (heat-coloured) ───────────────────
+            // Two-part fix for issue #35:
+            //  1. renderOrder = 1000 forces these sprites to the end of
+            //     the transparent queue so they always paint on top of
+            //     notes, sustain trails, lane plane, etc. depthTest is
+            //     already disabled by txtMat(), but `depthTest: false`
+            //     only exempts the sprite from depth comparison — it
+            //     doesn't pin draw order. Without an explicit
+            //     renderOrder, a note rendered after the label in the
+            //     transparent pass would still overdraw it. Match the
+            //     pattern already used for lane and dividers.
+            //  2. Y-offset bumped from S_GAP * 0.6 to S_GAP * 1.4 so the
+            //     label band sits clearly below the lowest string in
+            //     screen space, even at the largest active scale
+            //     (intensity-driven, up to ~5.7 * K vertical extent).
+            //     This buys a real visual gap between notes-on-the-
+            //     lowest-string and the row, on top of the renderOrder
+            //     guarantee — labels never share screen with what's
+            //     happening on the playing strings just above them.
+            {
+                const yBottom = Math.min(sY(0), sY(nStr - 1));
+                // anchorSpan: [f0, f1] = [anchor.fret, anchor.fret + width - 1]
+                // e.g. { fret:3, width:4 } → f0=3, f1=6 → frets 3,4,5,6 gold.
+                const anchorSpan = anchorPlayedFretSpanAt(anchors, now);
+                for (let f = 1; f <= NFRETS; f++) {
+                    const isInAnchor = anchorSpan
+                        && f >= anchorSpan.f0 && f <= anchorSpan.f1;
+                    const isMainFret = DOTS.includes(f);
+                    // Rule 1: show gray label only on main frets (dot positions).
+                    // Rule 2: show gold label on any fret inside the anchor range.
+                    // Non-main frets outside the anchor range are hidden entirely.
+                    if (!isInAnchor && !isMainFret) continue;
+                    const lb = pFretLbl.get();
+                    lb.material = txtMat(f,
+                        isInAnchor ? FRET_LABEL_GOLD_HEX : FRET_LABEL_IDLE_HEX,
+                        false, 'fretRow');
+                    lb.position.set(xFretMid(f), yBottom - S_GAP * 1.4, 0.5 * K);
+                    lb.material.opacity = isInAnchor ? 1.0 : 0.55;
+                    const scale = 5.95 * _textSizeMul * fretLabelScaleForFret(f);
+                    lb.scale.set(scale * K, scale * K, 1);
+                    lb.renderOrder = 1000;
+                }
+            }
+
+            // ── Beat lines ────────────────────────────────────────────────
+            if (beats) {
+                const board = boardSpanX();
+                const bw2 = board.width + 4 * K;
+                let lastM = -1;
+                for (const b of beats) {
+                    const meas = b.measure !== lastM; lastM = b.measure;
+                    if (b.time < t0 || b.time > t1) continue;
+                    const bl2 = pBeat.get();
+                    bl2.material = meas ? mBeatM : mBeatQ;
+                    bl2.scale.set(bw2, 1, 1);
+                    bl2.position.set(board.min - 2 * K, S_BASE - NH / 2 - 1.5 * K, dZ(b.time - now));
+                }
+            }
+
+            // ── Section labels ────────────────────────────────────────────
+            // Gated on sectionLabelsOnHighway (advanced setting, default off).
+            // The HUD card (drawSectionHud, called from the lyricsCtx block in
+            // draw()) is the primary surface for section info; the on-highway
+            // sprites are kept as an opt-in for users who want the in-scene cue.
+            if (sections && sectionLabelsOnHighway) {
+                const labelY = Math.max(sY(0), sY(nStr - 1)) + 8 * K;
+                for (const s of sections) {
+                    if (s.time < t0 || s.time > t1) continue;
+                    const sp = pSec.get();
+                    sp.material = txtMat(s.name, '#00cccc', true, 'section');
+                    sp.scale.set(20 * K * _textSizeMul, 5 * K * _textSizeMul, 1);
+                    sp.position.set(xFret(12), labelY, dZ(s.time - now));
+                }
+            }
+
+            // ── Fret-column reference markers ─────────────────────────────
+            // Every Nth measure, spawn a row of fret-number sprites on the
+            // board floor that scroll toward the hit line and vanish at Z=0.
+            // With a chart <anchor>, which frets appear follows the inlay
+            // cadence (DOTS) centred on the snapped anchor fret (~2 positions
+            // back and ~3 forward in that list, e.g. anchor 7 → 3,5,7,9,12,15).
+            // Without anchors, all DOTS positions are candidates; octave + lane
+            // clipping apply. With <anchor>, the cadence row ignores both so
+            // frets before/after the lane still show as reference. Light grey
+            // when that fret is in the active set, dark grey otherwise.
+            //
+            // Per-wave gate cache: hasLow/hasHigh/fretList snapshotted at first
+            // sight of a wave so the render decision stays stable through
+            // the wave's full flight. Without this, activeFrets shifting
+            // mid-song would drop markers mid-flight (user-reported bug:
+            // "numbers disappear before they get all the way towards me").
+            if (beats && fretColumnMarkerCadence > 0) {
+                // Prune stale wave cache entries (wave already past now).
+                if (_fretMarkerWaveCache.size > 0) {
+                    for (const k of _fretMarkerWaveCache.keys()) {
+                        if (k < now) _fretMarkerWaveCache.delete(k);
+                    }
+                }
+                const minStringY = Math.min(sY(0), sY(nStr - 1));
+                const labelY = minStringY - S_GAP * 0.8;
+                for (const b of beats) {
+                    // Non-downbeats are encoded as measure=-1; only actual
+                    // measure starts (measure >= 0) can spawn marker waves.
+                    if (b.measure < 0) continue;
+                    if (b.time < 0 || b.time > t1) continue;
+                    if (b.time <= now) continue;
+                    if ((b.measure | 0) % fretColumnMarkerCadence !== 0) continue;
+
+                    // Snapshot the active-range gate at first sight of this
+                    // wave. We scan notes/chords in a 2s window starting at
+                    // b.time rather than activeFrets, because activeFrets only
+                    // covers now+2s and waves first become visible up to
+                    // AHEAD (3s) ahead — using activeFrets would cache
+                    // {hasLow:false, hasHigh:false} for far waves and suppress
+                    // the entire row for its full flight.
+                    let cached = _fretMarkerWaveCache.get(b.time);
+                    if (!cached) {
+                        let hasLow = false, hasHigh = false;
+                        const wT0 = b.time, wT1 = b.time + 2;
+                        // notes and chords are time-sorted; binary-search to the
+                        // first entry >= wT0, then break once past wT1 to avoid
+                        // O(song_length) work per newly-seen wave.
+                        if (notes) {
+                            const startI = lowerBoundT(notes, wT0);
+                            for (let i = startI; i < notes.length; i++) {
+                                const n = notes[i];
+                                if (n.t > wT1) break;
+                                if (!validString(n.s) || n.f <= 0) continue;
+                                if (n.f <= 12) hasLow = true; else hasHigh = true;
+                                if (hasLow && hasHigh) break;
+                            }
+                        }
+                        if ((!hasLow || !hasHigh) && chords) {
+                            const startI = lowerBoundT(chords, wT0);
+                            outer: for (let i = startI; i < chords.length; i++) {
+                                const ch = chords[i];
+                                if (ch.t > wT1) break outer;
+                                if (!ch.notes) continue;
+                                for (const cn of ch.notes) {
+                                    if (!validString(cn.s) || cn.f <= 0) continue;
+                                    if (cn.f <= 12) hasLow = true; else hasHigh = true;
+                                    if (hasLow && hasHigh) break outer;
+                                }
+                            }
+                        }
+                        const anc = anchors && anchors.length ? getChartAnchorAt(anchors, b.time) : null;
+                        const anchorFret = anc != null ? Number(anc.fret) : NaN;
+                        const anchorKeyed = Number.isFinite(anchorFret) && anchorFret >= 0;
+                        const fretList = anchorKeyed
+                            ? fretColumnMarkersForAnchor(anchorFret, DOTS)
+                            : DOTS.slice();
+                        cached = { hasLow, hasHigh, fretList, anchorKeyed };
+                        _fretMarkerWaveCache.set(b.time, cached);
+                    }
+                    if (!cached.hasLow && !cached.hasHigh && !cached.anchorKeyed) continue;
+
+                    const dt = b.time - now;
+                    // Fade in over 0.35 s from the maximum lookahead distance so
+                    // the label appears at its correct final size the moment it
+                    // becomes visible, rather than gradually emerging as a tiny
+                    // dim spec through scene fog (fog is disabled on the sprite
+                    // material; this manual ramp replaces it).
+                    const _colFadeIn = Math.min(1.0, (AHEAD - dt) / 0.35);
+                    if (_colFadeIn <= 0) continue;
+
+                    const z = dZ(dt);
+                    // Sprite scale matches the per-note connector fret label
+                    // (drawNote → pNoteFretLabel) so cadence markers read the
+                    // same size at a given Z — no extra world-scale boost.
+                    const clipMin = hwyLaneFretClipMin;
+                    const clipMax = hwyLaneFretClipMax;
+                    const fretList = cached.fretList || DOTS;
+                    const anchorKeyedRow = !!cached.anchorKeyed;
+                    for (const f of fretList) {
+                        let show;
+                        if (anchorKeyedRow) {
+                            show = true;
+                        } else {
+                            if (f === 12) show = cached.hasLow || cached.hasHigh;
+                            else if (f < 12) show = cached.hasLow;
+                            else show = cached.hasHigh;
+                        }
+                        if (!show) continue;
+                        if (!anchorKeyedRow && clipMin != null && (f <= clipMin || f > clipMax)) continue;
+                        // Fixed colour — avoids mid-flight colour flips caused by
+                        // activeFrets only covering now+2s while waves appear at
+                        // AHEAD (3s), which made each marker start dark then
+                        // suddenly jump to light when its note entered the 2s window.
+                        const color = '#888888';
+                        const sp = pFretColMarker.get();
+                        const m = txtMat(f, color, false, 'noteFret');
+                        _setLabelMap(sp, m);
+                        sp.material.opacity = 0.85 * _colFadeIn;
+                        sp.position.set(xFretMid(f), labelY, z);
+                        // Z-proportional: sits between chord frame and note gem
+                        // at the same depth, so chord frames never overdraw the
+                        // marker and the marker never overdraws gems.
+                        sp.renderOrder = renderOrderForLayerAtZ(z, 'FRET_COLUMN');
+                        // Scale grows linearly from 2× at max lookahead to 1× at hit line,
+                        // combined with natural perspective attenuation the label starts
+                        // visibly larger and converges to the row-label size at z=0.
+                        const sz = 7.0 * K * (1 + 0.4 * dt / AHEAD) * _textSizeMul * fretLabelScaleForFret(f);
+                        sp.scale.set(sz, sz, 1);
+                    }
+
+                }
+            }
+
+            // ── Camera target ─────────────────────────────────────────────
+            let lockActive;
+            if (!(cameraMode === 'lookahead')) {
+                lockActive = _applyNoteCamTargets(
+                    camWX, camWSum, camDistMin, camDistMax, camDistGot,
+                    camHystF, camDistHystF, /* skipDistHyst= */ false);
+                prevLockActive = lockActive;
+            } else {
+                const lookaheadMaxF = lookaheadBoundsNow ? lookaheadBoundsNow.maxF : 0;
+                const lookaheadHasBounds = lookaheadBoundsNow != null;
+
+                let dtSec = 1 / 120;
+                if (_lookaheadCamPrevNow !== null) {
+                    const rawDt = _frameNow - _lookaheadCamPrevNow;
+                    if (rawDt > -1 && rawDt < 2) dtSec = Math.min(0.2, Math.max(1 / 960, rawDt));
+                }
+                _lookaheadCamPrevNow = _frameNow;
+                const dBlend = Math.min(0.2, Math.max(1e-4, dtSec));
+                const lowBlendFs = 1 - Math.pow(1 - CAM_FOCUS_BLEND_RATE, dBlend);
+
+                if (!lookaheadHasBounds || lookaheadMaxF <= LOOKAHEAD_LOCK_ENGAGE_MAXF)
+                    _lookaheadHiNeckLatch = false;
+                else if (lookaheadMaxF >= LOOKAHEAD_LOCK_RELEASE_MAXF)
+                    _lookaheadHiNeckLatch = true;
+
+                const lookaheadLockLowEligible = cameraLockLow
+                    && (!lookaheadHasBounds
+                        || (!_lookaheadHiNeckLatch && lookaheadMaxF <= 12));
+
+                let rawLowBU;
+                if (lookaheadLockLowEligible) {
+                    rawLowBU = camLowFretPullbackU(1);
+                } else if (lookaheadBoundsNow) {
+                    rawLowBU = camLowFretPullbackU(lookaheadBoundsNow.minF);
+                } else {
+                    rawLowBU = camLowFretPullbackU(CAM_LOCK_CENTER_FRET);
+                }
+                _lookaheadLowBonusU = rawLowBU * lowBlendFs + _lookaheadLowBonusU * (1 - lowBlendFs);
+
+                if (lookaheadLockLowEligible) {
+                    const lockedBaseU = camBaseDistU(12);
+                    const lockZoomMul = CAM_LOCK_ZOOM_MIN +
+                        (CAM_LOCK_ZOOM_MAX - CAM_LOCK_ZOOM_MIN) * cameraLockZoom;
+                    lookaheadSmoothCamStep(dtSec, xFretMid(CAM_LOCK_CENTER_FRET), 12);
+                    tgtX = _lookaheadCamX;
+                    tgtDist = (lockedBaseU + _lookaheadLowBonusU) * K * lockZoomMul;
+                    prevLowFretBonus = _lookaheadLowBonusU;
+                    lockActive = true;
+                } else {
+                    if (lookaheadBoundsNow) {
+                        const tgtWX = lookaheadTargetWorldX(
+                            lookaheadBoundsNow.minF, lookaheadBoundsNow.maxF);
+                        const tgtSpanInt = Math.max(
+                            1, lookaheadBoundsNow.maxF - lookaheadBoundsNow.minF + 1);
+                        lookaheadSmoothCamStep(dtSec, tgtWX, tgtSpanInt);
+                        tgtDist = (camBaseDistU(_lookaheadFretSpan) + _lookaheadLowBonusU) * K;
+                        prevLowFretBonus = _lookaheadLowBonusU;
+                    } else {
+                        lookaheadSmoothCamStep(dtSec, _lookaheadCamX, _lookaheadFretSpan);
+                        tgtDist = (camBaseDistU(_lookaheadFretSpan) + _lookaheadLowBonusU) * K;
+                        prevLowFretBonus = _lookaheadLowBonusU;
+                    }
+                    tgtX = _lookaheadCamX;
+                    lockActive = false;
+                }
+                prevLockActive = lockActive;
+            }
+
+            // ── Chord diagram: track chord, drive entrance + crossfade animations ─
+            {
+                let newChord = null;
+                if (chords) {
+                    // Only chords in (now - DIAG_LINGER_S, now] — use binary search
+                    // to skip past old chords, break once we pass `now`.
+                    const _dlo = lowerBoundT(chords, now - DIAG_LINGER_S);
+                    for (let _di = _dlo; _di < chords.length; _di++) {
+                        const ch = chords[_di];
+                        const chDt = ch.t - now;
+                        if (chDt > 0) break;
+                        if (!ch.notes) continue;
+                        const tmpl = bundle.chordTemplates?.[ch.id];
+                        const lbl = chordTemplateLabel(tmpl);
+                        // Last valid chord (highest t ≤ now) naturally wins since array is sorted.
+                        if (lbl && tmpl?.frets) {
+                            newChord = { name: lbl, frets: tmpl.frets, t: ch.t, t0: ch.t, chDt, nStr };
+                        }
+                    }
+                }
+
+                // Include frets in the key so two templates sharing a display name but
+                // differing in fingering each trigger a fresh crossfade/entrance.
+                const newKey = newChord ? newChord.name + '|' + newChord.frets.join(',') : null;
+                if (newKey !== _diagLastKey) {
+                    if (_diagChord && newKey !== null) {
+                        // Recompute outgoing alpha from stored event time rather than the
+                        // stale per-frame chDt; after dropped frames or seeks this prevents
+                        // the overlay jumping to a stale brightness before the crossfade.
+                        const freshChDt = _diagChord.t !== undefined ? _diagChord.t - now : _diagChord.chDt;
+                        const prevOpacity = Math.max(0, Math.min(1, 1 + freshChDt / DIAG_LINGER_S));
+                        // Only crossfade when the outgoing chord is actually visible at now.
+                        // freshChDt > 0 means the old chord is in the future (backward seek
+                        // crossed the chord boundary).  In that case _diagChord is stale, so
+                        // recompute the outgoing diagram from the chart — find the most recent
+                        // named chord that ends just before newChord.t and use it as _diagPrev
+                        // so that seeking into a historical chord transition fades correctly
+                        // rather than snapping straight to the new chord.
+                        if (freshChDt <= 0 && prevOpacity > 0) {
+                            // Use the string count the outgoing chord was captured with, not the
+                            // current nStr — an arrangement switch during a 150 ms crossfade
+                            // must not remap the outgoing diagram onto the new layout.
+                            _diagPrev = { name: _diagChord.name, frets: _diagChord.frets, nStr: _diagChord.nStr ?? nStr, t: _diagChord.t0 ?? _diagChord.t ?? now };
+                            _diagPrevStartOpacity = prevOpacity;
+                            _diagPrevOpacity = prevOpacity;
+                            _diagPrevStartT = now;
+                            // entranceT for the outgoing diagram is computed live from _diagPrev.t
+                            // each frame (see draw path), so it rewinds correctly on backward seeks
+                            // within the crossfade window — no separate snapped state needed here.
+                        } else if (freshChDt > 0) {
+                            // Backward seek: _diagChord is now in the future.
+                            // Look up the chart chord immediately before newChord.t to provide
+                            // the correct historical outgoing diagram for the crossfade.
+                            let histPrev = null;
+                            if (chords && newChord) {
+                                // Find the most recent named chord before newChord.t.
+                                // Chords are sorted ascending, so all matches are before
+                                // lowerBoundT(chords, newChord.t); iterate in order and
+                                // take the last valid one.
+                                const _hpHi = lowerBoundT(chords, newChord.t);
+                                for (let _hpi = 0; _hpi < _hpHi; _hpi++) {
+                                    const ch = chords[_hpi];
+                                    if (!ch.notes) continue;
+                                    const tmpl = bundle.chordTemplates?.[ch.id];
+                                    const lbl = chordTemplateLabel(tmpl);
+                                    if (lbl && tmpl?.frets) {
+                                        histPrev = { name: lbl, frets: tmpl.frets, t: ch.t, t0: ch.t, nStr };
+                                    }
+                                }
+                            }
+                            // Only start a crossfade if we are still within DIAG_CROSSFADE_S of
+                            // newChord.t; seeking further into the chord skips the crossfade.
+                            // Also skip if histPrev was no longer visible when newChord started
+                            // (gap longer than DIAG_LINGER_S), so only genuinely adjacent chord
+                            // transitions produce a crossfade — not seeks to just after any new
+                            // chord that happens to have an older chord somewhere earlier in the song.
+                            const elapsed = newChord ? now - newChord.t : Infinity;
+                            const histPrevVisible = histPrev && (newChord.t - histPrev.t) < DIAG_LINGER_S;
+                            if (histPrevVisible && elapsed >= 0 && elapsed < DIAG_CROSSFADE_S) {
+                                // Start at the linger opacity the outgoing chord would have had at
+                                // newChord.t during forward playback, not always 1.  This prevents
+                                // a chord that was mostly faded from appearing brighter on a seek.
+                                const histStartOpacity = Math.max(0, Math.min(1,
+                                    1 - (newChord.t - histPrev.t) / DIAG_LINGER_S));
+                                _diagPrev = histPrev;
+                                _diagPrevStartOpacity = histStartOpacity;
+                                _diagPrevOpacity = Math.max(0, histStartOpacity * (1 - elapsed / DIAG_CROSSFADE_S));
+                                _diagPrevStartT = newChord.t;
+                            } else {
+                                _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
+                                _diagPrevStartT = null;
+                            }
+                        } else {
+                            // prevOpacity <= 0: old chord already fully faded, no crossfade needed.
+                            _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
+                            _diagPrevStartT = null;
+                        }
+                    } else {
+                        _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
+                        _diagPrevStartT = null;
+                    }
+                    _diagLastKey = newKey;
+                    // Only update _diagChord when the chord key actually changes so that a
+                    // lingering chord's original nStr is preserved on subsequent frames.
+                    // (newChord is rebuilt every frame with the live nStr; unconditionally
+                    // assigning here would stomp the captured nStr if the arrangement switches
+                    // while the same chord is still in its linger window.)
+                    _diagChord = newChord;
+                } else if (newKey !== null && newChord && _diagChord) {
+                    // Same chord re-seen. Update linger expiry (t) when the event time changes.
+                    // Forward restrum (newChord.t > _diagChord.t): extend the linger window
+                    // but preserve t0 so the entrance animation is NOT replayed — avoids the
+                    // overlay jumping back to its 0.85× scale on every strum of the same chord.
+                    // Backward seek to earlier occurrence (newChord.t < _diagChord.t): update
+                    // both t and t0 to restart the entrance animation from the earlier position.
+                    if (newChord.t !== _diagChord.t) {
+                        _diagChord = newChord.t < _diagChord.t
+                            ? { ..._diagChord, t: newChord.t, t0: newChord.t }  // backward seek
+                            : { ..._diagChord, t: newChord.t };                 // forward restrum
+                    }
+                }
+
+                // Guard for backward seeks within the same chord (same key, no branch above).
+                // If _diagPrevStartT is in the future relative to now, the crossfade was set up
+                // during a later playback position that has since been seeked past. Clear it so
+                // the stale outgoing diagram does not stay fully visible at the seek target.
+                if (_diagPrev && _diagPrevStartT !== null && _diagPrevStartT > now) {
+                    _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0;
+                    _diagPrevStartT = null;
+                }
+
+                // Entrance: derived from t0 (the original appearance time, not updated on
+                // forward restrums) so repeated hits of the same chord do not replay the
+                // 0.85→1.0 scale animation. On backward seeks t0 is updated alongside t,
+                // so the animation still rewinds correctly to the earlier position.
+                const _entranceAnchor = _diagChord && (_diagChord.t0 ?? _diagChord.t);
+                _diagEntranceT = (_diagChord && _entranceAnchor !== undefined)
+                    ? Math.min(1.0, Math.max(0, (now - _entranceAnchor) / DIAG_ENTRANCE_S))
+                    : 1.0;
+
+                // Crossfade: derived from absolute start time so backward seeks within the
+                // crossfade window correctly rewind the fade. _diagPrev is kept alive (at
+                // opacity 0) until the next key change rather than destroyed here, so that a
+                // backward seek that re-enters the crossfade window can recompute a positive
+                // opacity. Seeks before _diagPrevStartT are handled by the guard above.
+                if (_diagPrev && _diagPrevStartT !== null) {
+                    const fadedT = Math.max(0, now - _diagPrevStartT);
+                    _diagPrevOpacity = Math.max(0, _diagPrevStartOpacity * (1 - fadedT / DIAG_CROSSFADE_S));
+                }
+            }
+            // ── Finalise InstancedMesh batches ────────────────────────────────
+            // Flush all 6 IMs: set visible instance count and mark buffers dirty.
+            // Must run after all drawNote() / chord-loop writes are done.
+            if (imPMTech) {
+                imPMTech.count = _imPMTechCount;
+                if (_imPMTechCount > 0) {
+                    imPMTech.instanceMatrix.needsUpdate = true;
+                    imPMTech.geometry.getAttribute('instanceAlpha').needsUpdate = true;
+                }
+            }
+            if (imFHTech) {
+                imFHTech.count = _imFHTechCount;
+                if (_imFHTechCount > 0) {
+                    imFHTech.instanceMatrix.needsUpdate = true;
+                    imFHTech.geometry.getAttribute('instanceAlpha').needsUpdate = true;
+                }
+            }
+            // These IMs are kept alive but always empty (count=0) — rendering
+            // is now handled by the pPMXFill / pMuteXLines / pFHXFill / pFHXLines
+            // pools which support per-chord Z-proportional renderOrder.
+            if (imPMXFill)  imPMXFill.count  = 0;
+            if (imPMXLines) imPMXLines.count = 0;
+            if (imFHXFill)  imFHXFill.count  = 0;
+            if (imFHXLines) imFHXLines.count = 0;
+
+            pbEnd(5);
+            pbEnd(0);
+            pbReportTick();
+        }
+
+        /**
+         * Indexed sustain ribbon (~SLIDE_RIBBON_SAMPLES longitudinal slices)
+         * for slides, bends, vibrato and tremolo — smooth contour vs stacked
+         * BoxGeometry segments.
+         */
+        function slideRibbonUpdatePositions(geom, strandBaseX, tw, th, y, sliceDur, susStart, now, n, slideSt) {
+            const pa = geom.attributes.position.array;
+            const S = SLIDE_RIBBON_SAMPLES;
+            // slideOffsetWorldX is defined at module scope so it returns a
+            // right-handed delta (built from non-lefty fretMid). strandBaseX is
+            // already lefty-mirrored via xFretMid at the call site, so the
+            // delta needs the same sign flip to keep the slide tracking the
+            // mirrored fretboard direction.
+            const dirMul = _leftyCached ? -1 : 1;
+            let v = 0;
+            for (let k = 0; k <= S; k++) {
+                const Tk = susStart + (k / S) * sliceDur;
+                const zk = dZ(Tk - now);
+                const xc = strandBaseX
+                    + dirMul * slideOffsetWorldX(n, Tk, slideSt)
+                    + tremoloOffsetWorldX(n, Tk, tw);
+                const yc = y + techniqueYOffsetWorld(n, Tk);
+                pa[v++] = xc - tw * 0.5; pa[v++] = yc - th * 0.5; pa[v++] = zk;
+                pa[v++] = xc + tw * 0.5; pa[v++] = yc - th * 0.5; pa[v++] = zk;
+                pa[v++] = xc + tw * 0.5; pa[v++] = yc + th * 0.5; pa[v++] = zk;
+                pa[v++] = xc - tw * 0.5; pa[v++] = yc + th * 0.5; pa[v++] = zk;
+            }
+            geom.attributes.position.needsUpdate = true;
+            // Normals are pre-baked at geometry creation (see mkSlideRibbonGeo);
+            // axis-aligned cross-section means they don't need per-frame recompute.
+        }
+
+        function noteHasVibrato(n) {
+            return !!(n && (n.vb || n.vibrato));
+        }
+
+        function bendVisualDirY(stringIdx) {
+            if (!Number.isFinite(stringIdx) || nStr <= 1) return 1;
+            const visualIdx = _invertedCached ? stringIdx : (nStr - 1 - stringIdx);
+            return visualIdx >= (nStr - 1) * 0.5 ? -1 : 1;
+        }
+
+        // Teaching marks (§6.2.2) — display only, never grading. Pure label
+        // helpers, mirroring static/highway.js so the two highways agree;
+        // node-tested via tests/js/highway_teaching_marks.test.js.
+        function teachingFingerLabel(fg) {
+            // fret-hand finger: '' when unset/out of range; 0 -> 'T' (thumb),
+            // 1..4 -> '1'..'4'.
+            if (!Number.isInteger(fg) || fg < 0 || fg > 4) return '';
+            return fg === 0 ? 'T' : String(fg);
+        }
+        function teachingDegreeLabel(sd) {
+            // scale degree: chromatic 0..11 above the active key tonic; '' when
+            // unset/out of range.
+            if (!Number.isInteger(sd) || sd < 0 || sd > 11) return '';
+            return String(sd);
+        }
+        /** Harmony annotations (§6.3.1 / §6.6): display labels for a chord's
+         * function (instance `fn.rn` Roman numeral) and template `voicing`,
+         * `caged` shape, and `guideTones`. '' for each when absent/malformed;
+         * `caged`/`guideTones` come back pre-formatted ("CAGED: E" / "gt 4,10").
+         * Pure; shared with the 2D highway and node-tested. Display only — never
+         * grading. */
+        function chordHarmonyLabels(fn, voicing, caged, guideTones) {
+            const rn = (fn && typeof fn.rn === 'string') ? fn.rn.trim() : '';
+            const vc = (typeof voicing === 'string') ? voicing.trim() : '';
+            const cg = (typeof caged === 'string' && /^[CAGED]$/.test(caged.trim()))
+                ? 'CAGED: ' + caged.trim() : '';
+            const gt = Array.isArray(guideTones)
+                ? guideTones.filter(n => Number.isInteger(n) && n >= 0 && n <= 11) : [];
+            return { rn, voicing: vc, caged: cg, guideTones: gt.length ? 'gt ' + gt.join(',') : '' };
+        }
+
+        function bnvSampleAt(bnv, t) {
+            // Linear interpolation of a bend curve [{t, v}] (§6.2.1; t is
+            // seconds from the note onset) at elapsed time t. Clamps to the
+            // endpoints; returns 0 for an empty/invalid curve.
+            if (!Array.isArray(bnv) || bnv.length === 0) return 0;
+            if (t <= bnv[0].t) return bnv[0].v;
+            const last = bnv[bnv.length - 1];
+            if (t >= last.t) return last.v;
+            for (let i = 1; i < bnv.length; i++) {
+                const a = bnv[i - 1], b = bnv[i];
+                if (t <= b.t) {
+                    const span = b.t - a.t;
+                    return span > 0 ? a.v + (b.v - a.v) * ((t - a.t) / span) : b.v;
+                }
+            }
+            return last.v;
+        }
+
+        function bendSemisAtTime(n, chartTime) {
+            if (!(n?.sus > 0)) return 0;
+            // When the note carries an authoritative bend curve (§6.2.1),
+            // sample its real shape at the elapsed time so the gem's Y gesture
+            // and sustain ribbon follow the actual bend (pre-bend, round-trip,
+            // release, …). Negative samples clamp to 0 (upward-only Y offset).
+            if (Array.isArray(n.bnv) && n.bnv.length) {
+                return Math.max(0, bnvSampleAt(n.bnv, chartTime - n.t));
+            }
+            const bn = Number(n?.bn) || 0;
+            if (!(bn > 0)) return 0;
+            const p = Math.max(0, Math.min(1, (chartTime - n.t) / Math.max(n.sus, 1e-6)));
+            // Fallback: synthesize rise → hold → release from the scalar peak.
+            // Ramp up over the first ~35 %, hold, then release over the last
+            // ~30 % — the bend gesture rather than a monotone climb. Drives both
+            // the sustain ribbon's Y contour and the gem's techniqueYNow offset.
+            const RISE = BEND_ENV_RISE_FRAC, REL = BEND_ENV_RELEASE_FRAC;
+            let env;
+            if (p < RISE) env = p / RISE;
+            else if (p < 1 - REL) env = 1;
+            else env = (1 - p) / REL;
+            return bn * Math.max(0, Math.min(1, env));
+        }
+
+        function vibratoSemisAtTime(n, chartTime) {
+            if (!noteHasVibrato(n) || !(n?.sus > 0)) return 0;
+            const elapsed = Math.max(0, chartTime - n.t);
+            return Math.sin(elapsed * Math.PI / VIBRATO_HALF_WAVE_S);
+        }
+
+        function techniqueYOffsetWorld(n, chartTime) {
+            if (!(n?.sus > 0)) return 0;
+            const bendSemi = bendSemisAtTime(n, chartTime);
+            const vibratoSemi = vibratoSemisAtTime(n, chartTime);
+            if (bendSemi === 0 && vibratoSemi === 0) return 0;
+            return bendVisualDirY(n.s) * BEND_HALFSTEP_WORLD_Y * (bendSemi + vibratoSemi);
+        }
+
+        function tremoloOffsetWorldX(n, chartTime, trailW) {
+            if (!(n?.tr) || !(n?.sus > 0)) return 0;
+            const elapsed = Math.max(0, chartTime - n.t);
+            const phase = (elapsed % TREMOLO_BUMP_S) / TREMOLO_BUMP_S;
+            const tri = (Math.abs(phase - 0.5) - 0.25) * 3;
+            return trailW * 0.5 * tri;
+        }
+
+        /* ── Note renderer ───────────────────────────────────────────────── */
+        // Chart-format <chordTemplates> frets: -1 = unused, 0 = open, n>0 = fret.
+        // Ghost digit for chord notes uses the template row when present so it
+        // matches the XML diagram, not a divergent chordNote.f if any.
+        function _templateFretForChordGhost(chordId, stringIdx, noteFret) {
+            if (chordId == null) return noteFret;
+            // Coerce: some upstream paths (e.g. hs.chord_id from sloppaks)
+            // hand us string ids like "12". Cf. `templates[cid] ?? templates[Number(cid)]`
+            // earlier in this file.
+            const cid = typeof chordId === 'number' ? chordId : Number(chordId);
+            if (!Number.isFinite(cid)) return noteFret;
+            const fr = _drawChordTemplates?.[cid]?.frets;
+            if (!Array.isArray(fr) || stringIdx < 0 || stringIdx >= fr.length) return noteFret;
+            const tf = fr[stringIdx];
+            if (typeof tf !== 'number' || tf < 0) return noteFret;
+            return tf;
+        }
+        // Chart-format-style ghost digit: finger position (1=index … 4=pinky) from
+        // the chord template.  Returns null when no finger data is available
+        // (GP imports emit all -1; open strings have finger 0 which we skip too
+        // since "0" is already shown via the open-string note path).
+        function _templateFingerForChordGhost(chordId, stringIdx) {
+            if (chordId == null) return null;
+            const cid = typeof chordId === 'number' ? chordId : Number(chordId);
+            if (!Number.isFinite(cid)) return null;
+            const fi = _drawChordTemplates?.[cid]?.fingers;
+            if (!Array.isArray(fi) || stringIdx < 0 || stringIdx >= fi.length) return null;
+            const tf = fi[stringIdx];
+            // -1 = unused / no data (GP imports); 0 = open string (skip — gem path handles it)
+            if (typeof tf !== 'number' || tf <= 0) return null;
+            return tf; // 1–4
+        }
+        /**
+         * Renders one board-ghost fret digit onto a pooled label mesh, flat
+         * in the board XY plane at (x, y, 0) — a Mesh (not a Sprite
+         * billboard) so perspective + projRim match the 3D ghost frame.
+         * Shared by drawNote()'s Primary ghost slot (chord/arp-aware caller
+         * resolves fretDisplay/alpha/fretForScale itself) and its Upcoming
+         * slots (always plain lead notes, where those collapse to
+         * n.f/projFactor/n.f).
+         */
+        function drawGhostFretLabel(x, y, projRim, fretDisplay, alpha, growScale, fretForScale) {
+            const lb = pGhostFretLbl.get();
+            const sprMat = txtMat(fretDisplay, '#ffffff', false, 'ghostFret');
+            const baseGhostMat = _meshMatForGhostFretDigit(sprMat);
+            let instMat = lb.userData.h3dGhostFretLblInstMat;
+            if (!instMat || instMat.map !== baseGhostMat.map) {
+                if (instMat) {
+                    try { instMat.dispose(); } catch (_) { /* idempotent */ }
+                }
+                instMat = baseGhostMat.clone();
+                instMat.transparent = true;
+                instMat.needsUpdate = true;
+                lb.userData.h3dGhostFretLblInstMat = instMat;
+            }
+            instMat.opacity = alpha;
+            instMat.depthTest = false;
+            lb.material = instMat;
+            lb.renderOrder = 1000;
+            const ghostOuterL = Math.max(NW * 1.1, NH * 1.1);
+            const ghostLblS = 0.7 * ghostOuterL * _textSizeMul * fretLabelScaleForFret(fretForScale);
+            const ghostLblScaled = ghostLblS * growScale;
+            lb.scale.set(ghostLblScaled, ghostLblScaled, 1);
+            // Z=0 matches the projection frame plane exactly — avoids parallax
+            // horizontal drift that appears when the camera is offset from the
+            // fret centre (camera sits at curX+20*K and looks toward curX, so
+            // any positive-Z offset on this label projects leftward vs the frame).
+            lb.position.set(x, y, 0);
+            lb.rotation.set(0, 0, projRim);
+        }
+
+        // skipLabel: don't draw per-note connector label (repeated fret)
+        // skipBody:  don't draw the 3D note mesh (repeat chord — still shows projection)
+        // showDropLine: draw a white vertical drop line from note to below board (arpeggio / synth chord notes)
+        function drawNote(n, now, openX, skipLabel, skipBody, linger = 0.10, openChordBoxWidth, fromChord = false, chordId, susTrailMatchArpFrame = false, arpBounds = null, prevOnsetT = -Infinity, showDropLine = false) {
+            const s = n.s;
+            // Belt + suspenders: callers already gate via validString(),
+            // but drawNote is also entered through { ...cn } chord-note
+            // spreads, so re-check here before indexing material arrays.
+            if (!validString(s)) return;
+            const nxFrame = _drawNextByString && _drawNextByString[s];
+            const dt = n.t - now;
+            const ghostHold = fromChord ? linger : GHOST_HOLD_AFTER_ONSET;
+            const nextTAligned = nxFrame != null && Math.abs(nxFrame.t - n.t) < NEXT_ON_STRING_T_EPS;
+            const ghostPastHold = dt <= 0 && dt > -ghostHold
+                && (nxFrame == null || nxFrame.t > n.t - 1e-6);
+            const isNextOnString = nextTAligned || ghostPastHold;
+            const y = sY(s);
+            const susEnd = n.t + (n.sus || 0);
+            const hasSus = n.sus > 0;
+            // Nearest event time across ALL strings strictly after this note —
+            // sourced from the sorted union of next/recent event times built
+            // once per frame in update() (see _scrEventTimes). _drawRecentByString
+            // is folded in so that once an event passes `now` (and leaves
+            // _drawNextByString) the deadline still holds: without this the
+            // next future event would reset _nextAnyT and old gems would
+            // linger after the new chord/note is already playing.
+            const _nextAnyT = _firstEventTimeGreaterThan(n.t + 1e-6);
+            // Deadline: absolute time after which the gem is culled.
+            //   Sustain long (sus >= linger): die immediately at susEnd — no tail.
+            //   Sustain short (sus < linger):  tail = linger - sus after susEnd,
+            //     capped by gap to next note (any string) so the gem disappears
+            //     when the next note arrives if it comes before the tail runs out.
+            //   No sustain: linger from onset, same gap-cap rule.
+            let _lingerDeadline;
+            if (hasSus) {
+                const extraLinger = Math.max(0, linger - (n.sus || 0));
+                // _nextAnyT cap only applies to the post-sustain linger tail.
+                // For long sustains (extraLinger = 0) the deadline is exactly
+                // susEnd — notes on other strings must not cut the held sustain
+                // short, which would hide the gem and trail mid-play.
+                _lingerDeadline = extraLinger > 0
+                    ? Math.min(susEnd + extraLinger, _nextAnyT)
+                    : susEnd;
+            } else {
+                const _gap = _nextAnyT - n.t;
+                _lingerDeadline = n.t + (_gap < linger ? _gap : linger);
+            }
+            const _overLinger = now > _lingerDeadline;
+            // For arp-persisted notes past their time: bypass the early exit so
+            // the board projection (fretboard ghost + fret labels) keeps rendering
+            // until arpBounds.end. The gem/sustain blocks are gated by arpGhostOnlyMode.
+            const arpGhostShouldRun = arpBounds != null
+                && (arpBounds.start - now) < 0.6   // same as PROJ_WIN
+                && now <= arpBounds.end + 0.05;
+            const arpGhostOnlyMode = arpGhostShouldRun
+                && _overLinger && (!hasSus || now > susEnd);
+            // Smart cull: keep the gem alive only if a note-state verdict is
+            // available to display. Probe result cached in _ndProbed/_ndProbedState
+            // so the later getNoteState query reuses it (avoids two provider calls).
+            // arpGhostShouldRun takes precedence — arp ghosts stay alive
+            // regardless of verdict state so their board projections persist.
+            let _ndProbed = false;
+            let _ndProbedState = null;
+            if (_overLinger && (!hasSus || now > susEnd) && !arpGhostShouldRun) {
+                // Prune the sustain-verdict latch before any cull-path return.
+                // The matching delete inside the sustain-render block (line ~9262)
+                // only runs when the note isn't culled — without this prune, a
+                // sustained note that crosses susEnd on the same frame as
+                // _overLinger goes true would leak its latch entry until a
+                // teardown/seek clears the Map. !hasSus notes never wrote to
+                // the latch, so Map.delete is a harmless no-op there.
+                if (hasSus) _susVerdictLatch.delete(Math.round(n.t * 1e4) * 10 + n.s);
+                if (!_ndHasProvider || dt < -NOTEDETECT_GEM_VERDICT_WINDOW) return;
+                let _ndProbe = null;
+                try { _ndProbe = _ndGetNoteState(n, n.t); } catch (e) { _ndProbe = null; }
+                _ndProbed = true;
+                _ndProbedState = _ndProbe;
+                const _probeSt = (_ndProbe && typeof _ndProbe === 'object') ? _ndProbe.state : _ndProbe;
+                if (_probeSt !== 'hit' && _probeSt !== 'active' && _probeSt !== 'miss') return;
+            }
+
+            const sustained = dt < 0 && hasSus && now <= susEnd;
+            const hitDist = Math.abs(dt);
+            const hit = hitDist < 0.15 || sustained || (_ndHasProvider && dt < 0);
+            const hitFade = sustained ? 0.7 : (hitDist < 0.15 ? 1 - hitDist / 0.15 : 0);
+            // skipBody (slide-target gem suppression) only applies to this
+            // note's own pre-hit approach — it exists so the destination's
+            // approaching gem doesn't duplicate the source note's gem, which
+            // is already sliding toward this fret. Once this note is hit,
+            // its gem must render normally so a chained slide (this note
+            // sliding on to a further fret) keeps following.
+            const effSkipBody = skipBody && dt > 0;
+            const hasTechniqueVibrato = noteHasVibrato(n);
+            const techniqueYNow = sustained ? techniqueYOffsetWorld(n, now) : 0;
+            const noteZ = sustained ? 0 : Math.min(0, dZ(dt));
+            // Per-note Z-based renderOrder: far notes get a low value (render
+            // first, get overdrawn by close geometry), close notes get a high
+            // value (render last, appear on top). RENDER_ORDER_LAYER_STACK decides
+            // the local stack for outline, core, technique symbols, and fret labels.
+            const xBase = n.f === 0 ? (openX !== undefined ? openX : curX) : xFretMid(n.f);
+            // Slide-in-progress: glide the gem (and everything anchored to it —
+            // outline, core, halo, technique markers) from its starting fret
+            // toward the slide's end fret over the sustain, the same way
+            // techniqueYOffsetWorld already offsets the gem in Y for bends.
+            const slideSt = slideTrailEnd(n);
+            // Once hit, keep gliding (and then holding at the end fret) for
+            // as long as the gem stays on screen — not just while `sustained`
+            // (now <= susEnd). Otherwise, during the brief extra moment a
+            // short note lingers after its sustain ends (see _lingerDeadline/
+            // extraLinger above), `sustained` flips false and the gem would
+            // snap back to its starting fret. slideOffsetWorldX's `p` clamps
+            // to 1 once now > susEnd, so this naturally holds at the slide's
+            // end position during that tail.
+            const slideXNow = (dt < 0 && hasSus && slideSt)
+                ? (_leftyCached ? -1 : 1) * slideOffsetWorldX(n, now, slideSt)
+                : 0;
+            const x = xBase + slideXNow;
+            const isHarm = n.hm || n.hp;
+
+            // Open chord notes: wide default mesh is capped to chord frame width.
+            const OPEN_NOTE_WORLD_W = 40 * K;
+            let openWScale = 1;
+            if (n.f === 0 && openChordBoxWidth != null && openChordBoxWidth > 1e-8) {
+                openWScale = Math.max(0.22, (openChordBoxWidth * 0.96) / OPEN_NOTE_WORLD_W);
+            }
+
+            // Hoisted so both !skipBody blocks (gem and technique labels) and
+            // the unconditional sustain trail all share one declaration.
+            // For skipBody=true (slide targets), defaults are safe no-ops.
+            const openSlabThickMul = n.f === 0 ? 1.5 : 1;
+            const approachRot = n.f > 0 ? Math.max(0, Math.min(1, dt / AHEAD)) * Math.PI / 2 : 0;
+            // Ghost preview window: capped to the gap from the previous note
+            // on this string so dense passages don't show the preview 0.6 s
+            // ahead with no visible gem. Minimum 0.05 s so the ghost isn't
+            // completely suppressed even in very tight passages.
+            const _rawGap = n.t - prevOnsetT;
+            const effectiveProjWin = _rawGap > 0 ? Math.min(0.6, Math.max(0.05, _rawGap)) : 0.6;
+            const projFactorG = Math.max(0, Math.min(1, 1 - Math.max(dt, 0) / effectiveProjWin));
+            const inGhostWin = n.f > 0 && isNextOnString && dt > -ghostHold && dt < effectiveProjWin && projFactorG > 0.001;
+            // feedBack#254 — query the provider once per note, before both !skipBody
+            // blocks, so _showHit can be a const and _ndGood is available for the
+            // sustain trail (which renders even when skipBody=true for slide targets).
+            let _ndGood = false;    // true when provider confirms hit/active
+            let _hitPunch = 1;      // #3 per-gem scale-punch on a fresh hit
+            let _ndState = null;    // 'hit'|'active'|'miss'|null; null → fall back to proximity heuristic
+            let _ndCs = null;       // raw provider response — truthy when provider returned a verdict
+            let _ndCsIsObj = false; // typeof _ndCs === 'object'
+            let _ndFaceMat = null;  // [mat×4, transparent×2] array for lateral face fill, or null
+            if (_ndGetNoteState) {
+                // Reuse the smart-cull probe result if we already called
+                // _ndGetNoteState for this gem above; otherwise probe now.
+                let _raw = null;
+                if (_ndProbed) {
+                    _raw = _ndProbedState;
+                } else {
+                    try { _raw = _ndGetNoteState(n, n.t); } catch (e) { _raw = null; }
+                }
+                if (_raw) {
+                    _ndCsIsObj = typeof _raw === 'object';
+                    const _st = _ndCsIsObj ? _raw.state : _raw;
+                    if (_st === 'miss') {
+                        _ndState = 'miss';
+                        _ndCs = _raw;
+                    } else if (_st === 'hit' || _st === 'active') {
+                        _ndState = _st;
+                        _ndGood = true;
+                        _ndCs = _raw;
+                    }
+                }
+            }
+
+            // [verdict glow] feed the provider alpha into the per-frame max so
+            // update()'s top scales the verdict-glow brightness by live level
+            // (note_detect returns alpha = live input level for held sustains,
+            // and a time-fade for fresh strikes). Only object responses carry an
+            // alpha; the latch/legacy string responses leave brightness at full.
+            if (_ndGood && _ndCsIsObj && _ndCs && typeof _ndCs.alpha === 'number') {
+                _ndVerdictSawAlpha = true;
+                if (_ndCs.alpha > _ndVerdictMaxAlpha) _ndVerdictMaxAlpha = _ndCs.alpha;
+            }
+
+            // ── Sustain verdict latch ────────────────────────────────────
+            // note_detect's hitGlowDuration (~0.5 s) and the legacy mark
+            // TTL (500 ms) both expire before a long chart sustain ends.
+            // For any sustained note, latch the verdict from EITHER source
+            // (provider _ndState OR legacy _ndHitMarks / _ndMissMarks) and
+            // re-inject it so hit/miss color persists for the full hold.
+            // Works with both the modern provider path and the legacy event
+            // path — vibrato and other long-sustain notes benefit equally.
+            if (hasSus) {
+                const _sk = Math.round(n.t * 1e4) * 10 + n.s;
+                // Resolve current verdict: provider takes priority, then
+                // fall back to scanning the legacy mark arrays so a hit or
+                // miss event that arrived this frame can seed the latch.
+                let _lv_cur = _ndState;
+                let _lv_good = _ndGood;
+                if (!_lv_cur) {
+                    for (let _mi = 0; _mi < _ndHitMarks.length; _mi++) {
+                        const _mm = _ndHitMarks[_mi];
+                        if (_mm.s === n.s && _mm.f === n.f && Math.abs(_mm.noteTime - n.t) < _ND_TIME_EPS) {
+                            _lv_cur = 'hit'; _lv_good = true; break;
+                        }
+                    }
+                    if (!_lv_cur) {
+                        for (let _mi = 0; _mi < _ndMissMarks.length; _mi++) {
+                            const _mm = _ndMissMarks[_mi];
+                            if (_mm.s === n.s && _mm.f === n.f && Math.abs(_mm.noteTime - n.t) < _ND_TIME_EPS) {
+                                _lv_cur = 'miss'; _lv_good = false; break;
+                            }
+                        }
+                    }
+                }
+                if (_lv_cur) {
+                    // Fresh verdict (provider or legacy mark) — save to latch.
+                    // Distinguish a *live* provider hit (note_detect tags its
+                    // ring-tracking 'active' responses with live:true) from a
+                    // legacy/brief one: a live hit must NOT be re-injected once
+                    // the provider goes silent (that kept muted sustains lit),
+                    // whereas the legacy event path still needs the latch to
+                    // bridge its ~0.5 s mark TTL across a long hold.
+                    const _live = _ndCsIsObj && _ndCs && _ndCs.live === true;
+                    _susVerdictLatch.set(_sk, _lv_good ? (_live ? 'hit-live' : 'hit') : 'miss');
+                    // If the verdict came from a legacy mark (provider was
+                    // silent — _ndState was null before the scan), propagate
+                    // it to _ndState/_ndGood/_ndCs now so the sustain trail
+                    // picks up the same colour this frame instead of waiting
+                    // until the mark expires and the latch re-injects it.
+                    if (!_ndState) {
+                        if (_lv_good) {
+                            _ndState = 'active'; _ndGood = true;
+                            _ndCs = 'active'; _ndCsIsObj = false;
+                        } else {
+                            _ndState = 'miss';
+                            _ndCs = 'miss'; _ndCsIsObj = false;
+                        }
+                    }
+                } else if (dt < 0 && now < susEnd) {
+                    // No current verdict — reuse latch if available.
+                    // dt < 0 guards against coloring notes that haven't
+                    // crossed the hit line yet (approaching notes must never
+                    // inherit a latch from a previous play-through).
+                    const _lv = _susVerdictLatch.get(_sk);
+                    if (_lv === 'hit') {
+                        // Legacy/brief provider or event-path hit: bridge the
+                        // gap across the hold (the mark/glow TTL expires before a
+                        // long chart sustain ends).
+                        _ndState = 'active'; _ndGood = true;
+                        _ndCs = 'active'; _ndCsIsObj = false;
+                    } else if (_lv === 'hit-live') {
+                        // Live provider is authoritative for the active glow: it
+                        // returns 'active' only while the string is actually
+                        // ringing, and null once muted / decayed. Don't re-inject
+                        // a stale 'active' (that kept a muted sustain lit) — leave
+                        // the gem un-lit when the provider is silent; a re-strike
+                        // relights it via the provider on the next frame.
+                    } else if (_lv === 'miss') {
+                        _ndState = 'miss';
+                        _ndCs = 'miss'; _ndCsIsObj = false;
+                    }
+                }
+                if (now >= susEnd) _susVerdictLatch.delete(_sk);
+            }
+
+            const _showHit = (_ndState === 'miss') ? false
+                : (_ndState ? _ndGood
+                : (hit || (n.f > 0 && inGhostWin)));
+
+            // ── Fret-wire hit flash ───────────────────────────────────────
+            // A confirmed note lights the wires that bracket it:
+            //   single, fretted (f > 0) → the wire behind it (f-1) and the wire
+            //           it's pressed against (f).
+            //   open (f = 0)  → the OUTER wires of the anchor lane. An open
+            //           string has no fret of its own, and its gem is drawn as a
+            //           wide slab spanning the lane (see xBase /
+            //           openNoteLaneBoxW), so the lane's edge wires are exactly
+            //           what the slab sits between — the same relationship a
+            //           fretted note has to its own two wires.
+            //   chord   → only the OUTERMOST wires of the whole shape, not every
+            //           wire it spans. drawNote() is the chord loop's per-note
+            //           call, so it can't see the span from here: chord hits
+            //           accumulate into _fwChordAcc and the flash pass resolves
+            //           min/max fret → outer wires once the loop has finished.
+            // Gated on _ndGood, not _showHit: only a scorer's verdict counts,
+            // never the proximity heuristic that merely means "near the line".
+            if (_ndGood) {
+                const _fwA = (_ndCsIsObj && _ndCs && typeof _ndCs.alpha === 'number')
+                    ? Math.max(0, Math.min(1, _ndCs.alpha))
+                    : 1;
+                if (fromChord) {
+                    // ch.id can be absent (pitfall #8) — fall back to the chord's
+                    // time, which is what n.t already carries for a chord note.
+                    const _fwK = (chordId !== undefined && chordId !== null) ? chordId : `t${n.t}`;
+                    let _fwE = _fwChordAcc.get(_fwK);
+                    if (!_fwE) {
+                        _fwE = { minF: Infinity, maxF: -Infinity, a: 0, openA: 0, t: n.t };
+                        _fwChordAcc.set(_fwK, _fwE);
+                    }
+                    if (n.f > 0 && n.f <= NFRETS) {
+                        if (_fwA > _fwE.a) _fwE.a = _fwA;
+                        if (n.f < _fwE.minF) _fwE.minF = n.f;
+                        if (n.f > _fwE.maxF) _fwE.maxF = n.f;
+                    } else if (n.f === 0 && _fwA > _fwE.openA) {
+                        _fwE.openA = _fwA;   // open strings in the chord → lane edges
+                    }
+                } else if (n.f > 0 && n.f <= NFRETS) {
+                    if (_fwA > _fwHitIn[n.f - 1]) _fwHitIn[n.f - 1] = _fwA;
+                    if (_fwA > _fwHitIn[n.f]) _fwHitIn[n.f] = _fwA;
+                } else if (n.f === 0) {
+                    // Sampled at the note's own time, matching how the open
+                    // slab's width is derived (openNoteLaneBoxW(n.t)) — so the
+                    // flashed wires are the ones the slab is actually drawn
+                    // between, even if the lane has since moved.
+                    const _fwB = anchorLaneBoundsAt(_drawAnchors, n.t);
+                    if (_fwB) {
+                        if (_fwA > _fwHitIn[_fwB.dMin]) _fwHitIn[_fwB.dMin] = _fwA;
+                        if (_fwA > _fwHitIn[_fwB.dMax]) _fwHitIn[_fwB.dMax] = _fwA;
+                    }
+                }
+            }
+
+            if (!effSkipBody && !arpGhostOnlyMode && !_overLinger) {
+
+                // ── Outline (slightly larger, bright emissive) ────────────
+                // Notedetect feedback (#9): if a recent hit/miss event
+                // matches this note's (s, f, t), swap the outline tint.
+                // Linear scan over a small bounded array — typical
+                // queues are 0-5 entries, expired marks pruned by the
+                // listener. Hit takes precedence over miss so the user
+                // sees the more positive feedback if both happen
+                // (shouldn't, but cheap guard).
+                let _ndOutline = (n.f > 0 && mStrHitOutline[s]) ? mStrHitOutline[s] : mWhiteOutline;
+                // update() prunes expired marks once per frame and
+                // caches performance.now() in _ndFrameNowMs so the hot
+                // path here just does the bounded match — no extra
+                // now() / filter() per note. After update()'s prune,
+                // every entry in the arrays has expiresAt > _ndFrameNowMs,
+                // so we don't re-validate inside the loop.
+                let _ndMatchedMark = null;
+                let _ndHadHitMark = false;
+                if (_ndHitMarks.length) {
+                    for (let i = 0; i < _ndHitMarks.length; i++) {
+                        const m = _ndHitMarks[i];
+                        if (m.s === n.s && m.f === n.f && Math.abs(m.noteTime - n.t) < _ND_TIME_EPS) {
+                            _ndOutline = mHitBright[s] ?? mGlow[s]; _ndFaceMat = mHitBrightArrays[s] ?? null; _ndMatchedMark = m; _ndHadHitMark = true; break;
+                        }
+                    }
+                }
+                if (!_ndHadHitMark && _ndMissMarks.length) {
+                    for (let i = 0; i < _ndMissMarks.length; i++) {
+                        const m = _ndMissMarks[i];
+                        if (m.s === n.s && m.f === n.f && Math.abs(m.noteTime - n.t) < _ND_TIME_EPS) {
+                            _ndOutline = mMissOutline; _ndFaceMat = mMissEdgeArrays; _ndMatchedMark = m; break;
+                        }
+                    }
+                }
+                if (_ndMatchedMark && _ndMatchedMark.labels && _ndMatchedMark.labels.length) {
+                    _ndLabels.push({
+                        x,
+                        y: y + NH * 1.7,
+                        z: noteZ + 0.02,
+                        labels: _ndMatchedMark.labels,
+                    });
+                }
+                // (approachRot / PROJ_WIN_G / projFactorG / inGhostWin hoisted above)
+
+                const rimXY = n.ac ? ACCENT_RIM_XY_SCALE_MUL : 1;
+                const rimZ = n.ac ? ACCENT_RIM_Z_SCALE_MUL : 1;
+
+                // feedBack#254 — apply outline + lateral face-fill overrides from provider verdict.
+                // hit/active → green outline (mHitBright[s]) + green lateral faces;
+                // miss → magenta-red outline (mMissOutline) + dark lateral faces; front/back stay transparent.
+                if (_ndCs) {
+                    const _vAlpha = (_ndCsIsObj && typeof _ndCs.alpha === 'number') ? _ndCs.alpha : 1;
+                    if (_ndState === 'miss') {
+                        _ndOutline = mMissOutline;
+                        _ndFaceMat = mMissEdgeArrays;
+                        _streakHits = 0;            // #7 break the streak (heat eases down)
+                        if (_verdictMarks) _ndLabels.push({ x, y: y + NH * 1.7, z: noteZ + 0.02, labels: [{ text: '✗', color: '#ff5a7a' }] });  // #6
+                    } else if (_ndGood) {
+                        // Rim flashes in the string's own colour, wire-fashion
+                        // (intensity applied per string in the flash pass).
+                        _ndOutline = mRimFlash[s] ?? mHitBright[s] ?? mGlow[s];
+                        _ndFaceMat = mHitBrightArrays[s] ?? null;
+                        if (_vAlpha > _rimFlashIn[s]) _rimFlashIn[s] = _vAlpha;
+                        _hitPunch = 1 + 0.22 * _hitFx * _vAlpha;   // #3 scale-punch (biggest at strike, eases)
+                        if (_verdictMarks) { const _tc = _timingHex(_ndMatchedMark && _ndMatchedMark.timingState); _ndLabels.push({ x, y: y + NH * 1.7, z: noteZ + 0.02, labels: [{ text: '✓', color: '#' + _tc.toString(16).padStart(6, '0') }] }); }  // #6 + #5
+                        if (_sparks && _hitFx > 0 && _vAlpha > 0.5) {
+                            const _spk = s + '|' + n.f + '|' + n.t.toFixed(2);
+                            if (!(_sparkSeen.get(_spk) > now)) {
+                                _sparkSeen.set(_spk, now + 1.0);
+                                if (_sparkSeen.size > 600) _sparkSeen.clear();
+                                _streakHits++;
+                                const _heatMul = _streakFx ? (1 + 0.85 * _streakHeat) : 1;   // #7 escalate
+                                _sparkBurst(x, y, noteZ, _timingHex(_ndMatchedMark && _ndMatchedMark.timingState), Math.round((4 + 7 * _hitFx) * _heatMul));
+                            }
+                        }
+                    }
+                }
+
+                // Score pop: the first frame a gem's verdict carries points
+                // (notedetect ≥1.13 object verdicts), float a "+N" above it.
+                // popKey dedupes — chord members all hand back the chord-
+                // level key, so a chord pops once, not once per gem; the
+                // _fxSeen TTL also stops a sustain's long-lived verdict from
+                // re-popping every frame.
+                if (_ndGood && _ndCsIsObj
+                        && _ndCs.points !== undefined && _ndCs.popKey != null) {
+                    _fxSpawnPop(_ndCs.popKey, _ndCs.points, _ndCs.mult,
+                        x, y + NH * 2.2, noteZ + 0.02);
+                }
+
+                // Accent: soft neon outer glow (reference: diffused halo fading out).
+                // Three additive shells drawn behind outline/core; colour = string hue.
+                // Suppressed on a provider miss verdict — a bright accent halo
+                // around a missed gem muddies the dark-core-plus-red-rim fail
+                // signal, matching the same miss-over-accent priority the
+                // gem core material applies below.
+                if (n.ac && _ndState !== 'miss' && mAccentHaloNear[s]) {
+                    const rZ = approachRot;
+                    const accentShells = _accentShellsByString[s];
+                    for (let hi = 0; hi < accentShells.length; hi++) {
+                        const sh = accentShells[hi];
+                        const glow = pAccentHalo.get();
+                        glow.material = sh.mat;
+                        glow.rotation.z = rZ;
+                        glow.position.set(x, y + techniqueYNow, noteZ - sh.zK * K);
+                        if (n.f === 0) {
+                            // Inside a chord/arpeggio frame: bloom only vertically so the
+                            // halo doesn't burst past the chord box edges horizontally.
+                            // Outside a frame: modest horizontal cap (1.4×) so it doesn't
+                            // overflow into adjacent lane visuals.
+                            const openIxy = fromChord ? 1.0 : Math.min(sh.ixy, 1.4);
+                            const slabPuff = Math.max(1.4, sh.ixy);
+                            glow.scale.set(
+                                (40 * K / NW) * rimXY * openIxy * openWScale,
+                                0.1 * openSlabThickMul * slabPuff,
+                                0.6 * rimZ * sh.iz,
+                            );
+                        } else {
+                            glow.scale.set(rimXY * sh.ixy, rimXY * sh.ixy, 2.5 * rimZ * sh.iz);
+                        }
+                    }
+                }
+                const outline = pNote.get();
+                // Verdict beats accent on the outline so hit/miss feedback isn't
+                // hidden by mAccentOutline. Mirrors the same miss-over-accent
+                // priority the accent halo guard above already applies.
+                const _ndVerdict = (_ndCs && (_ndState === 'miss' || _ndGood))
+                    || !!_ndMatchedMark;
+                outline.material = (n.ac && !_ndVerdict) ? mAccentOutline[s] : _ndOutline;
+                // outline + core share the pNote pool, so set geometry explicitly
+                // each frame (a recycled mesh may carry a gradient geometry from a
+                // prior core use). Outline always uses the plain box.
+                outline.geometry = gNote;
+                outline.renderOrder = renderOrderForLayerAtZ(noteZ, 'NOTE_OUTLINE');
+                outline.position.set(x, y + techniqueYNow, noteZ);
+                outline.rotation.z = approachRot;
+                const ndRim = 1.1;
+                if (n.f === 0) {
+                    outline.scale.set(
+                        (35 * K / NW) * ndRim * rimXY * openWScale,
+                        0.1 * ndRim * openSlabThickMul,
+                        0.6 * ndRim * rimZ,
+                    );
+                } else {
+                    outline.scale.set(ndRim * rimXY, ndRim * rimXY, 2.8 * rimZ);
+                }
+
+                // ── Lateral face fill (top / bottom / left / right only) ─────
+                // Material array: groups 0-3 (±X ±Y) get the verdict colour;
+                // groups 4-5 (+Z front / -Z back) are transparent so the large
+                // front face shows only the core body's string colour beneath.
+                if (_ndFaceMat) {
+                    const edges = pNoteEdge.get();
+                    edges.material = _ndFaceMat;
+                    edges.renderOrder = renderOrderForLayerAtZ(noteZ, 'TECHNIQUE_MARKER');
+                    edges.position.set(x, y + techniqueYNow, noteZ + 0.001);
+                    edges.rotation.z = approachRot;
+                    if (n.f === 0) {
+                        edges.scale.set(
+                            (40 * K / NW) * rimXY * openWScale * 1.02,
+                            0.1 * openSlabThickMul * 1.02,
+                            0.6 * rimZ * 1.02,
+                        );
+                    } else {
+                        edges.scale.set(rimXY * 1.02, rimXY * 1.02, 2.5 * rimZ * 1.02);
+                    }
+                }
+
+                // ── Core (filled note body) ───────────────────────────────
+                const core = pNote.get();
+                // Body always keeps the string colour. Verdict feedback is
+                // carried by the outline shell and lateral face fill.
+                core.material = n.ac ? mAccentCore[s] : mStr[s];
+                // Gradient gem body for strings 0..5; flat box otherwise.
+                core.geometry = (!n.ac && gNoteGrad[s]) ? gNoteGrad[s] : gNote;
+                core.renderOrder = renderOrderForLayerAtZ(noteZ, 'NOTE_CORE');
+                core.position.set(x, y + techniqueYNow, noteZ + 0.001);
+                core.rotation.z = approachRot;
+                if (n.f === 0) {
+                    core.scale.set(
+                        (40 * K / NW) * rimXY * openWScale,
+                        0.1 * openSlabThickMul,
+                        0.6 * rimZ,
+                    );
+                } else {
+                    core.scale.set(rimXY, rimXY, 2.5 * rimZ);
+                }
+                if (_hitPunch !== 1) core.scale.multiplyScalar(_hitPunch);   // #3 hit scale-punch
+                // Fret digits on fretted (n.f > 0) flying notes deliberately
+                // omitted: the showFretOnNote setting and its UI helper text
+                // promise digits on the fretboard ghost only, never on the
+                // gems coming down the highway. The ghost path is at
+                // pGhostFretLbl below.
+            } // end gem block — technique labels reopen !skipBody below
+
+            // ── Sustain trail ─────────────────────────────────────────────
+            // Rendered for ALL notes with sustain, including skipBody=true
+            // slide-target notes (e.g. linkNext hold→slide: gem suppressed,
+            // slide trail stays visible as the continuation of the sustain).
+            // _ndGetNoteState is queried for every note (skipBody slide
+            // targets included), so the trail picks bright mGlow[s] when the
+            // provider confirms hit/active and dim mSus[s] otherwise — a
+            // slide-target trail is not forced dim.
+            // Chord-member open strings (fromChord && f === 0) skip the
+            // sustain trail entirely — fretted constituents already carry
+            // the chord's sustains; an extra ribbon under the wide open
+            // body looked like clutter. The note BODY still draws above.
+            if (hasSus && !_overLinger && !(fromChord && n.f === 0)) {
+                    const susStart = Math.max(n.t, now);
+                    const remSus = susEnd - susStart;
+                    if (remSus > 0.01) {
+                        const sliceDur = Math.min(remSus, AHEAD);
+                        let tw = NW * 0.85 * (n.f === 0 ? openWScale : 1);
+                        let th = NH * 0.12 * (n.f === 0 ? openWScale : 1) * openSlabThickMul;
+                        if (susTrailMatchArpFrame) {
+                            const yA = sY(0), yB = sY(nStr - 1);
+                            const yMinF = Math.min(yA, yB) - S_GAP * 0.8;
+                            const yMaxF = Math.max(yA, yB) + S_GAP * 0.8;
+                            const fullChordBoxH = yMaxF - yMinF;
+                            const ft = Math.max(CHORD_FRAME_RIM_MIN * K, fullChordBoxH * CHORD_FRAME_RIM_FRAC_H);
+                            const ftSide = ft * 1.55;
+                            if (n.f > 0) {
+                                th = ftSide;
+                            } else {
+                                th = Math.max(th, ftSide * openSlabThickMul);
+                            }
+                            tw = Math.max(tw, ftSide * 1.05);
+                        }
+                        // Standalone open strings get two parallel trails
+                        // offset along X — visually echoes the wide flat
+                        // open-note body. Fretted notes keep the
+                        // single-trail path. Offsets are scaled by
+                        // `openWScale` (the same body-width scale
+                        // computed at line 7367) so the trails stay
+                        // underneath the body's edges no matter how wide
+                        // the anchor lane is. Chord-member open strings
+                        // can't reach here (guarded at the `hasSus`
+                        // check above).
+                        //
+                        // openTrailOff is always > 0 because openWScale
+                        // is clamped >= 0.22 at line 7368 (or defaults
+                        // to 1 when there's no openChordBoxWidth), so
+                        // openTrailOff >= NW * 3 * 0.22 = 3.3 * K.
+                        // No degenerate-small-offset fallback needed.
+                        const offsets = (n.f === 0)
+                            ? [-(NW * 3 * openWScale), NW * 3 * openWScale]
+                            : SINGLE_SUS_OFFSETS;
+                        const ribbonSusTrail = !!(
+                            (slideSt && n.f > 0 && (n.sus || 0) > 1e-4)
+                            || (Number(n.bn) > 0)
+                            || (Array.isArray(n.bnv) && n.bnv.length > 0)
+                            || n.tr
+                            || hasTechniqueVibrato
+                        );
+                        // Outline material for the sustain trail border — uses the
+                        // same materials as the gem border so hit/miss colours are
+                        // perceptually identical across gem outline, lateral faces,
+                        // and sustain trail rim.
+                        const _susOlMat = _ndState === 'miss' ? mMissOutline
+                            : _ndGood ? (mHitBright[s] ?? mHitSusOutline)
+                            : mSusOutline;
+                        const emitSusStrip = (xCenter, segLen, zCenter) => {
+                            // Same depth-bucket scheme as chord frames, using the
+                            // ordered sustain-trail layer so same-depth frames win
+                            // while closer trail segments still beat farther frames.
+                            const trailRenderOrder = renderOrderForLayerAtZ(Math.min(0, zCenter), 'SUSTAIN_TRAIL');
+                            for (let i = 0; i < offsets.length; i++) {
+                                const xOff = xCenter + offsets[i];
+                                const trOut = pSusOutline.get();
+                                trOut.material = _susOlMat;
+                                trOut.renderOrder = trailRenderOrder;
+                                trOut.position.set(xOff, y, zCenter);
+                                trOut.scale.set(tw + 0.4 * K, th + 0.4 * K, segLen);
+                                const tr = pSus.get();
+                                tr.material = _ndState ? mGlow[s] : mSus[s];
+                                tr.renderOrder = trailRenderOrder + 0.0005;
+                                tr.position.set(xOff, y, zCenter);
+                                tr.scale.set(tw, th, segLen);
+                            }
+                        };
+                        if (!ribbonSusTrail) {
+                            const len = sliceDur * TS;
+                            const zPos = dZ(susStart - now) - len / 2;
+                            emitSusStrip(x, len, zPos);
+                        } else {
+                            // Same depth-based renderOrder as box trail — ribbon center
+                            // at susStart + sliceDur/2, using TS so it matches dZ().
+                            const _ribDt = Math.max(0, susStart + sliceDur / 2 - now);
+                            const ribbonRenderOrder = renderOrderForLayerAtZ(-_ribDt * TS, 'SUSTAIN_TRAIL');
+                            for (let si = 0; si < offsets.length; si++) {
+                                const strandX = xBase + offsets[si];
+                                const olMesh = pSusRibbonOl.get();
+                                olMesh.renderOrder = ribbonRenderOrder;
+                                olMesh.scale.set(1, 1, 1);
+                                olMesh.rotation.set(0, 0, 0);
+                                olMesh.position.set(0, 0, 0);
+                                olMesh.material = _susOlMat;
+                                slideRibbonUpdatePositions(
+                                    olMesh.geometry, strandX,
+                                    tw + 0.4 * K, th + 0.4 * K,
+                                    y, sliceDur, susStart, now, n, slideSt,
+                                );
+                                const body = pSusRibbon.get();
+                                body.renderOrder = ribbonRenderOrder + 0.0005;
+                                body.scale.set(1, 1, 1);
+                                body.rotation.set(0, 0, 0);
+                                body.position.set(0, 0, 0);
+                                body.material = _ndState ? mGlow[s] : mSus[s];
+                                slideRibbonUpdatePositions(
+                                    body.geometry, strandX, tw, th, y,
+                                    sliceDur, susStart, now, n, slideSt,
+                                );
+                            }
+                        }
+                    }
+            }
+
+            // Shared by both slide-arrow blocks so the neck-preview arrow
+            // below can match the on-note arrow's size once the note
+            // arrives (the technique-labels block further down also reads
+            // this for its own label scaling).
+            const LBL_MULT = 1.6;
+            // Fade-in window for the neck-preview slide arrow below.
+            const GHOST_UPCOMING_WIN = 0.6;
+
+            // ── Slide direction arrow (neck preview) ─────────────────────
+            // A standalone preview of the same arrow, sitting flat on
+            // the neck (Z=0) at the note's resting fret. Full size from
+            // the moment it appears (matches the on-note arrow's size at
+            // dt=0) — just a linear fade-in over the same GHOST_UPCOMING_WIN
+            // window the board-projection ghost note uses, so the two
+            // previews feel like part of the same effect. No grow effect:
+            // tried and found too hard to see. Stops at dt <= 0, handing
+            // off to the on-note arrow.
+            //
+            // Placed outside the !effSkipBody block (unlike the on-note
+            // arrow above) so a note whose own gem is suppressed because
+            // it's the destination of a previous slide (skipBody) can
+            // still preview ITS OWN outgoing slide ahead of time — i.e.
+            // multi-leg/chained slides — when slideArrowChainPreviewVisible
+            // is on. For a normal note (skipBody === false) this behaves
+            // exactly as before.
+            if (slideArrowNeckVisible && dt > 0 && slideSt && validString(s) && !arpGhostOnlyMode && !_overLinger
+                && (!skipBody || slideArrowChainPreviewVisible)) {
+                const slideDirN = Math.sign(fretMid(slideSt.endFret) - fretMid(n.f)) * (_leftyCached ? -1 : 1);
+                if (slideDirN !== 0) {
+                    const neckAlpha = Math.max(0, Math.min(1, 1 - dt / GHOST_UPCOMING_WIN));
+                    if (neckAlpha > 0.001) {
+                        const arrowHexN = darkenHex(activePalette[s], 0.55);
+                        const arrowSmN = slideArrowMat(slideDirN > 0, arrowHexN);
+                        const arrowN = pTechPlane.get();
+                        arrowN.material = _spriteMat2MeshMat(arrowN, arrowSmN);
+                        const arrowScaleN = NH * 1.1 * LBL_MULT * _textSizeMul;
+                        arrowN.scale.set(arrowScaleN, arrowScaleN, 1);
+                        arrowN.position.set(x + slideDirN * NW * 1.15, y, 0);
+                        arrowN.rotation.z = 0;
+                        arrowN.renderOrder = renderOrderForLayerAtZ(0, 'TECHNIQUE_MARKER');
+                        arrowN.material.opacity = neckAlpha;
+                    }
+                }
+            }
+
+            if (!effSkipBody && !arpGhostOnlyMode && !_overLinger) {
+                // ── Technique labels ──────────────────────────────────────
+                // Label scale = base × LBL_MULT × distFactor (LBL_MULT
+                // declared above, shared with the neck-preview slide arrow).
+                // distFactor compensates for perspective shrink so a
+                // label far from the camera (note approaching at dt≈AHEAD)
+                // doesn't collapse to a single dim pixel. LBL_MULT bumps
+                // every base scale uniformly. Issues #21-25 track proper
+                // visual upgrades (3D arrows, ribbons, glows); this is
+                // the cheap legibility win in the meantime.
+                //
+                // Offsets scale with sLbl too. The labels grow in world
+                // units to compensate for perspective; if the offsets
+                // didn't grow, stacked labels would overlap each other
+                // and the first label would overlap the note at the
+                // AHEAD edge. In screen space the offset stays roughly
+                // constant — labels appear anchored to the note even
+                // though the world-space distance grows.
+                const distFactor = 1 + Math.max(0, Math.min(1, dt / AHEAD)) * 1.5;
+                // Fold the user's text-size multiplier into sLbl so technique
+                // labels (bend, H/P/T arrows, tremolo) plus on-body markers
+                // such as palm mute and the pinch-harmonic icon.
+                // all scale alongside the rest (`ac` accent → brighter body via mGlow).
+                const sLbl = LBL_MULT * distFactor * _textSizeMul;
+                // txtMat(..., 'technique') disables depthTest; without a high
+                // renderOrder the transparent note core (mStr) can still paint
+                // afterward and hide H/P/T, PM X, bends, etc. Same contract as
+                // fret-row labels (issue #35, CLAUDE pitfall #7 corollary).
+                const techniqueMarkerRenderOrder = renderOrderForLayerAtZ(noteZ, 'TECHNIQUE_MARKER');
+                let yo = y + techniqueYNow + NH * 0.8 * sLbl;
+                const specialMarkerScale = n.f === 0
+                    ? NH * 1.5 * sLbl * openWScale
+                    : NH * 1.5 * sLbl;
+                // ── Slide direction arrow (on the note/gem) ─────────────────
+                // A small ›/‹ chevron beside the note pointing toward the
+                // slide's destination fret. Visible for the note's whole
+                // time on screen — approaching (rides the incoming note at
+                // noteZ+K) and sustained (rides the gem as it glides via
+                // slideXNow, Edit A) — at a constant full opacity, no
+                // fade or grow.
+                if (slideArrowApproachVisible && slideSt && validString(s)) {
+                    const slideDir = Math.sign(fretMid(slideSt.endFret) - fretMid(n.f)) * (_leftyCached ? -1 : 1);
+                    if (slideDir !== 0) {
+                        const arrowHex = darkenHex(activePalette[s], 0.55);
+                        const arrowSm = slideArrowMat(slideDir > 0, arrowHex);
+                        const arrow = pTechPlane.get();
+                        arrow.material = _spriteMat2MeshMat(arrow, arrowSm);
+                        const arrowScale = NH * 1.1 * sLbl;
+                        arrow.scale.set(arrowScale, arrowScale, 1);
+                        arrow.position.set(x + slideDir * NW * 1.15, y + techniqueYNow, noteZ + K);
+                        // No rotation, ever — notes themselves rotate in
+                        // (approachRot) as they approach, but that would
+                        // tilt the ›/‹ chevron and make its left/right
+                        // direction ambiguous. Always flat.
+                        arrow.rotation.z = 0;
+                        arrow.renderOrder = techniqueMarkerRenderOrder;
+                        arrow.material.opacity = 1;
+                    }
+                }
+                // Derive the peak from bn OR the bnv curve: a note may carry an
+                // authoritative curve with bn left at 0 (bn SHOULD be the peak
+                // whenever bnv exists — this is the robustness fallback).
+                const _bnvPeak = (Array.isArray(n.bnv) && n.bnv.length)
+                    ? n.bnv.reduce((m, p) => Math.max(m, Number(p.v) || 0), 0) : 0;
+                const _bendPeak = Math.max(Number(n.bn) || 0, _bnvPeak);
+                if (_bendPeak > 0) {
+                    // Bend chevron stack — PlaneGeometry mesh so it tilts with
+                    // the gem (approachRot). Fixed world size so it perspective-
+                    // shrinks naturally without distFactor compensation.
+                    const steps = Math.max(1, Math.min(4, Math.round(_bendPeak)));
+                    const bendSm = bendChevronMat(steps, activePalette[s] || 0xffffff);
+                    const l = pTechPlane.get();
+                    l.material = _spriteMat2MeshMat(l, bendSm);
+                    const cs = NH * 2.4;
+                    l.scale.set(cs, cs, 1);
+                    l.position.set(x, y + techniqueYNow + NH * 1.1, noteZ + K);
+                    l.rotation.z = approachRot;
+                    l.renderOrder = techniqueMarkerRenderOrder;
+                    // Reserve stack space above the chevron.
+                    yo = Math.max(yo, y + techniqueYNow + NH * 2.5);
+                }
+                if (n.ho || n.po || n.tp) {
+                    if (n.ho || n.po) {
+                        // Hammer-on / pull-off: ▲/▼ triangle — PlaneGeometry mesh
+                        // so it tilts with the gem instead of billboarding.
+                        const triSm = triMat(!!n.po, activePalette[s] || 0xffffff);
+                        const tri = pTechPlane.get();
+                        tri.material = _spriteMat2MeshMat(tri, triSm);
+                        tri.scale.set(NH * 1.8, NH * 1.60, 1);
+                        tri.position.set(x, y + techniqueYNow, noteZ + K);
+                        tri.rotation.z = approachRot;
+                        tri.renderOrder = techniqueMarkerRenderOrder;
+                        // Reserve stack space above the triangle for stacked labels.
+                        yo = Math.max(yo, y + techniqueYNow + NH * 1.0);
+                    } else {
+                        const chevron = pTapChevron.get();
+                        const chevronScale = NH * 0.8 * sLbl;
+                        chevron.position.set(x, y + techniqueYNow, noteZ + 1.1 * K);
+                        chevron.rotation.z = approachRot;
+                        chevron.scale.set(chevronScale, chevronScale, 1);
+                        chevron.renderOrder = techniqueMarkerRenderOrder;
+                    }
+                }
+                // Tremolo label ('~~~') removed — trail shape already conveys it visually.
+                if (n.pm || n.mt || n.fhm) {
+                    // Muted notes: pool-based plane with per-note Z-proportional
+                    // renderOrder (techniqueMarkerRenderOrder). The previous InstancedMesh
+                    // approach used a fixed renderOrder (702/700), which made PM/FH markers from
+                    // far notes overdraw chord frames and gems of nearer chords.
+                    // PM = black X / white border; FH/MT = inverse.
+                    const _fhm = !!(n.mt || n.fhm);
+                    const _pmSprite = _fhm ? fretHandMuteXSpriteMat() : palmMuteXSpriteMat();
+                    const _pmMark = pTechPlane.get();
+                    _pmMark.material = _spriteMat2MeshMat(_pmMark, _pmSprite);
+                    _pmMark.material.opacity = _showHit ? 1.0 : 0.8;
+                    // Arms cover 62.5% of canvas → scale 1/0.625 = 1.60.
+                    const _sx = n.f === 0 ? NW * 1.60 * openWScale : NW * 1.60;
+                    _pmMark.scale.set(_sx, NH * 1.60, 1);
+                    _pmMark.position.set(x, y + techniqueYNow, noteZ + K);
+                    _pmMark.rotation.z = approachRot;
+                    _pmMark.renderOrder = techniqueMarkerRenderOrder;
+                }
+                // hm / hp — PlaneGeometry overlay sized like the palm-mute X,
+                // so the symbol only appears on the front face and matches
+                // the palm-mute marker proportions.
+                if (n.hm || n.hp) {
+                    const harmSprite = n.hm ? naturalHarmonicMat() : pinchHarmonicMat(activePalette[s]);
+                    const harmMark = pTechPlane.get();
+                    harmMark.material = _spriteMat2MeshMat(harmMark, harmSprite);
+                    harmMark.material.opacity = _showHit ? 1.0 : 0.85;
+                    const harmScaleX = n.f === 0 ? NW * 1.90 * openWScale : NW * 1.90;
+                    harmMark.scale.set(harmScaleX, NH * 2.0, 1);
+                    harmMark.position.set(x, y + techniqueYNow, noteZ + K);
+                    harmMark.rotation.z = approachRot;
+                    harmMark.renderOrder = techniqueMarkerRenderOrder;
+                }
+
+                // ── Per-note fret connector label ─────────────────────────
+                if (n.f > 0 && !skipLabel) {
+                    const minStringY = Math.min(sY(0), sY(nStr - 1));
+                    const labelY = minStringY - S_GAP * 0.8;
+                    // Fade in over 0.35s at the far end; stay at full opacity until
+                    // the note hits (dt = 0).  No pre-hit fade-out — removing it
+                    // eliminates the "label disappears before the note arrives" artifact.
+                    const alpha = dt >= 0 ? Math.min(1.0, (AHEAD - dt) / 0.35) : 0;
+                    // Arpeggio notes use the arpeggio fret-label layer at the same
+                    // depth so they stay above non-arp connector lines of the same chord.
+                    const _isArpNote = arpBounds !== null;
+
+                    // String-coloured connector line — standalone notes only.
+                    // Arpeggio and chord notes already have a drop line to the board.
+                    if (!fromChord) {
+                        const line = pConnectorLine.get();
+                        line.position.set(x, labelY, noteZ);
+                        // Half-length (50% shorter), anchored at the fret-label end.
+                        line.scale.set(1, (y - labelY) * 0.5, 1);
+                        // Tint the line with the incoming note's string colour.
+                        // mStr is white for gradient strings, so use the canonical
+                        // flat palette colour instead of the material's .color.
+                        if (activePalette[s] != null) line.material.color.setHex(activePalette[s]);
+                        line.renderOrder = renderOrderForLayerAtZ(noteZ,
+                            _isArpNote
+                                ? 'ARP_CONNECTOR_LINE'
+                                : 'CONNECTOR_LINE'
+                        );
+                        line.material.opacity = alpha * 0.8;
+                    }
+
+                    // Regular chord notes (fromChord=true, arpBounds=null) never show
+                    // fret labels — only standalone notes and arpeggio note-stream notes
+                    // (fromChord=true with arpBounds!=null) show labels.
+                    // Key uses 40 ms buckets (same formula as _buildFretLabelSet) so
+                    // the lookup matches exactly, even if the note's time drifts ±20 ms.
+                    // Frame-dedup prevents multiple strings at the same onset/fret from
+                    // stacking duplicate labels.
+                    const _flFrameKey = Math.round(n.t * 25) * 100 + n.f;
+                    const _showNum = (!fromChord || arpBounds !== null)
+                        && _fretLabelAllowed.has(_flFrameKey)
+                        && !_frameLabeledKeys.has(_flFrameKey);
+                    if (_showNum) {
+                        _frameLabeledKeys.add(_flFrameKey);
+                        const fretLabel  = pNoteFretLabel.get();
+                        const cachedMat  = txtMat(n.f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
+                        _setLabelMap(fretLabel, cachedMat);
+                        fretLabel.position.set(x, labelY, noteZ);
+                        fretLabel.renderOrder = renderOrderForLayerAtZ(noteZ,
+                            _isArpNote
+                                ? 'ARP_NOTE_FRET_LABEL'
+                                : 'NOTE_FRET_LABEL'
+                        );
+                        // Same scale ramp as fret column markers: 2× base at max lookahead,
+                        // converging to 1× at hit line.  Final size matches row labels.
+                        const flS = 7.0 * K * (1 + 0.4 * Math.max(0, dt) / AHEAD) * _textSizeMul * fretLabelScaleForFret(n.f);
+                        fretLabel.scale.set(flS, flS, 1);
+                        fretLabel.material.opacity = alpha;
+                    }
+
+                    // Teaching marks (§6.2.2) — display only, never grading. The
+                    // fret-hand finger (fg) renders by default to the right of the
+                    // fret label (hideable via the finger-hints toggle); the scale
+                    // degree (sd) is opt-in (mirrors the 2D `teachingMarksVisible`
+                    // toggle) and renders to the left.
+                    if (alpha > 0 && n.f > 0) {
+                        const _tmS = 5.0 * K * _textSizeMul * fretLabelScaleForFret(n.f);
+                        const _drawTeachMark = (text, colorHex, dx, cacheKey) => {
+                            if (!text) return;
+                            const spr = pTeachMarkLbl.get();
+                            const m = txtMat(text, colorHex, false, cacheKey);
+                            _setLabelMap(spr, m);
+                            spr.position.set(x + dx, labelY, noteZ);
+                            spr.renderOrder = renderOrderForLayerAtZ(noteZ,
+                                _isArpNote ? 'ARP_NOTE_FRET_LABEL' : 'NOTE_FRET_LABEL');
+                            spr.scale.set(_tmS, _tmS, 1);
+                            spr.material.opacity = alpha;
+                        };
+                        if (_showFingerHints) {
+                            _drawTeachMark(teachingFingerLabel(n.fg), '#7fd1ff', NW * 0.95, 'teachFg');
+                        }
+                        if (_drawTeachingMarks) {
+                            _drawTeachMark(teachingDegreeLabel(n.sd), '#ffcc66', -NW * 0.95, 'teachSd');
+                        }
+                    }
+                }
+            }
+
+            // ── Fret number for synthetic chord notes rendered with skipBody=true ──
+            // suppressSynthChord paths skip the !skipBody block entirely, so their
+            // fret label never fires from inside it. Handle them here, outside the
+            // gate. Applies the same measure-based + frame-dedup rules so that if
+            // the corresponding standalone arpeggio note already showed a label this
+            // frame, we don't duplicate it.
+            if (skipBody && fromChord && !skipLabel && n.f > 0 && dt >= 0) {
+                const _fl2FrameKey = Math.round(n.t * 25) * 100 + n.f;
+                if (_fretLabelAllowed.has(_fl2FrameKey)
+                    && !_frameLabeledKeys.has(_fl2FrameKey)) {
+                    _frameLabeledKeys.add(_fl2FrameKey);
+                    const _minStrY2 = Math.min(sY(0), sY(nStr - 1));
+                    const _labelY2  = _minStrY2 - S_GAP * 0.8;
+                    const _alpha2   = Math.min(1.0, (AHEAD - dt) / 0.35);
+                    const _isArp2   = arpBounds !== null;
+                    const fl2 = pNoteFretLabel.get();
+                    const cm2 = txtMat(n.f, FRET_LABEL_GOLD_HEX, false, 'noteFret');
+                    _setLabelMap(fl2, cm2);
+                    fl2.position.set(x, _labelY2, noteZ);
+                    fl2.renderOrder = renderOrderForLayerAtZ(noteZ,
+                        _isArp2
+                            ? 'ARP_NOTE_FRET_LABEL'
+                            : 'NOTE_FRET_LABEL'
+                    );
+                    const _flS2 = 7.0 * K * (1 + 0.4 * dt / AHEAD) * _textSizeMul * fretLabelScaleForFret(n.f);
+                    fl2.scale.set(_flS2, _flS2, 1);
+                    fl2.material.opacity = _alpha2;
+                }
+            }
+
+            // ── Drop line for chord / arpeggio notes ──────────────────────────
+            // Styled to match the standalone single-note connector: tinted with
+            // the incoming note's string colour and 50% length (anchored at the
+            // fret-label end), instead of a full-height white line to the board.
+            const _wantDropLine = pDropLine && n.f > 0 && dt >= 0 && fromChord && showDropLine && !skipBody;
+            if (_wantDropLine) {
+                const _minStrY = Math.min(sY(0), sY(nStr - 1));
+                const _dropY = _minStrY - S_GAP * 0.8;
+                const _alpha = Math.min(1.0, (AHEAD - dt) / 0.35);
+                const dl = pDropLine.get();
+                dl.position.set(x, _dropY, noteZ);
+                // Half-length, anchored at the label end (matches single notes).
+                dl.scale.set(1, (y - _dropY) * 0.5, 1);
+                // String-colour tint (palette is canonical; mStr is white for
+                // gradient strings).
+                if (activePalette[s] != null) dl.material.color.setHex(activePalette[s]);
+                dl.renderOrder = renderOrderForLayerAtZ(noteZ, 'CONNECTOR_LINE');
+                dl.material.depthTest = false;
+                dl.material.opacity = _alpha * 0.8;
+            }
+
+            // ── Board ghost: filled rim at Z=0 (up to 3 slots/string) ────
+            // Lead notes (!fromChord, so !arpGhostActive too — see arpBounds
+            // below) use a fixed GHOST_UPCOMING_WIN pre-impact ramp instead
+            // of the gap-capped effectiveProjWin, so fast same-string runs
+            // don't pop in at full size right before impact. Chords/arps
+            // keep effectiveProjWin exactly as before — effectiveProjWin /
+            // projFactorG / inGhostWin (computed above, for the separate gem
+            // pre-glow) are untouched. Arp ghosts always use the full 0.6 s
+            // window — their timing is authored, not gap-driven.
+            const _PROJ_WIN_ARP = 0.6;
+            const ghostWin = fromChord ? effectiveProjWin : GHOST_UPCOMING_WIN;
+            const projFactor = Math.max(0, Math.min(1, 1 - Math.max(dt, 0) / ghostWin));
+            // isBlocked suppresses the pre-impact ghost in a note's last 150ms
+            // so it doesn't peek out from under the incoming note body. Scoped
+            // to chord notes only (#843): for plain lead notes this previously
+            // suppressed the board-ghost frame for every sustained note's last
+            // 150ms, making it vanish right before impact and reappear during
+            // the post-hit linger ("ghosts disappearing" in dense runs). Also
+            // excludes slide notes (`!slideSt`, #862/#257): a sliding gem
+            // glides off the start fret via slideXNow, so the body no longer
+            // covers the ghost and the slide's own ghost preview should show.
+            // Gate on dt > 0 so the post-hit linger (dt ≤ 0) keeps the ghost.
+            const isBlocked = fromChord && dt > 0 && dt < 0.15 && n.sus > 0 && !slideSt;
+
+            // For arpeggio notes: ALL notes show their ghost simultaneously
+            // the moment the FIRST note enters _PROJ_WIN_ARP — exactly when
+            // isNextOnString would reveal the first note's ghost on its own.
+            // Using arpBounds.start as the shared reference makes every note
+            // in the arpeggio fade in together, keyed off that single anchor.
+            const arpDtToStart = arpBounds != null ? arpBounds.start - now : Infinity;
+            const arpProjFactor = Math.max(0, Math.min(1, 1 - Math.max(arpDtToStart, 0) / _PROJ_WIN_ARP));
+            const arpGhostActive = arpBounds != null
+                && arpDtToStart < _PROJ_WIN_ARP
+                && now <= arpBounds.end + 0.05;
+            // Ghost stays at final "on the board" orientation — not the
+            // incoming approachRot sweep — so it nests with the note at
+            // impact. projRim/projScale/bodyDim are pure functions of
+            // effSkipBody/_vibrancyProjOp; hoisted here so both the Primary
+            // ghost (below) and the Upcoming-slot ghosts (sibling block
+            // further down) can use them.
+            const projRim = 0; // harmonic gems now land horizontal (no diamond offset)
+            // _vibrancyProjOp (0.15..0.5) is the vibrancy-scaled idle floor;
+            // scale the whole opacity by (_vibrancyProjOp / 0.15) so the slider
+            // affects the projection the same way it affects note bodies.
+            const projScale = _vibrancyProjOp / 0.15;
+            // effSkipBody (= skipBody && dt > 0, #862): a slide-destination note
+            // whose own gem is suppressed pre-hit isn't dimmed once it's hit.
+            const bodyDim = effSkipBody ? 0.38 : 1;
+            if (n.f > 0 && projectionVisible && (
+                (!_overLinger && isNextOnString && dt > -ghostHold && dt < ghostWin && projFactor > 0.001 && !isBlocked)
+                || arpGhostActive
+            )) {
+                const proj = projMeshArr[s][0];
+                // Arp ghost: uniform opacity keyed off arpBounds.start so all
+                // notes fade in/out together regardless of individual dt values.
+                let arpGhostAlpha = 1;
+                if (arpGhostActive) {
+                    const remainingP = arpBounds.end - now;
+                    const fadeOutP = remainingP < 0.25 ? Math.max(0, remainingP / 0.25) : 1;
+                    arpGhostAlpha = Math.min(arpProjFactor, fadeOutP);
+                }
+                // Chart-format-style ghost: a single 0→1 progress value drives both the
+                // fade-in (opacity/emissive, below) and the grow-from-small scale
+                // on the frame mesh and fret-digit label. Reuses the existing
+                // per-path progress signals — arp ghosts use arpGhostAlpha
+                // (already 0→1, incl. fade-out tail), non-arp ghosts use
+                // projFactor (0→1 across ghostWin).
+                const ghostProgress = arpGhostActive ? arpGhostAlpha : projFactor;
+                const projGrowScale = PROJ_GROW_MIN + (1 - PROJ_GROW_MIN) * ghostProgress;
+                const rimSolid = arpGhostActive
+                    ? 0.75 * arpGhostAlpha
+                    : projFactor * 0.94;
+                proj.material.opacity = Math.min(0.96,
+                    projScale * rimSolid * (0.5 + 0.5 * glowMul) * bodyDim);
+                proj.material.emissiveIntensity = arpGhostActive
+                    ? 0.35 * arpGhostAlpha * glowMul * bodyDim
+                    : projFactor * 0.55 * glowMul * bodyDim;
+                proj.position.set(x, y, 0);
+                proj.scale.set(projGrowScale, projGrowScale, projGrowScale);
+                proj.rotation.z = projRim;
+                proj.visible = true;
+
+                const ghostFretOk = showFretOnNote && (
+                    arpGhostActive ||
+                    fretNumberGhostScope === 'all' ||
+                    (fretNumberGhostScope === 'chords' && fromChord)
+                );
+                if (ghostFretOk && pGhostFretLbl) {
+                    // chord-hand style → show finger number (1–4) from the chord
+                    // template; fall back to fret number when no finger data exists
+                    // (GP imports, open strings, non-chord notes).
+                    const ghostFretDisplay = fromChord && fretNumberGhostScope === 'chords'
+                        ? (_templateFingerForChordGhost(chordId, n.s) ?? _templateFretForChordGhost(chordId, n.s, n.f))
+                        : fromChord
+                            ? _templateFretForChordGhost(chordId, n.s, n.f)
+                            : n.f;
+                    let ghostFretLblAlpha = 1;
+                    if (arpGhostActive) {
+                        // Reuse arpGhostAlpha — already encodes fade-in (keyed
+                        // off arpBounds.start via arpProjFactor) + fade-out.
+                        ghostFretLblAlpha = arpGhostAlpha;
+                    } else if (ghostPastHold) {
+                        const nextSoon = nxFrame != null && nxFrame.t > n.t + 1e-6
+                            && (nxFrame.t - now) <= GHOST_FRET_LBL_FADE_S;
+                        const ghostFadeS = Math.min(GHOST_FRET_LBL_FADE_S, ghostHold);
+                        ghostFretLblAlpha = hwyPostHitTailFadeMul(dt, ghostHold, nextSoon, ghostFadeS);
+                    } else {
+                        // Pre-impact approach: fade the digit in alongside the
+                        // frame (projFactor), instead of popping in at full alpha.
+                        ghostFretLblAlpha = projFactor;
+                    }
+                    const _ghostFretForScale = fromChord && fretNumberGhostScope === 'chords'
+                        ? n.f
+                        : ghostFretDisplay;
+                    drawGhostFretLabel(x, y, projRim, ghostFretDisplay, ghostFretLblAlpha, projGrowScale, _ghostFretForScale);
+                }
+            }
+
+            // ── Upcoming board ghosts (slots 1/2): up to 2 additional,
+            // independent pre-impact previews per string for plain lead
+            // notes, chart-format-style. Primary (slot 0, above) already shows the
+            // very next note on this string; this sibling block shows the
+            // 1-2 notes after that, each on its own mesh with its own
+            // fixed-GHOST_UPCOMING_WIN ramp — fixes fast same-string runs
+            // where every note after the first had almost no ramp time
+            // (capped at the gap to the *previous* note on that string).
+            // !nextTAligned excludes exactly the note Primary is already
+            // showing, so a note is never drawn in two slots at once.
+            if (n.f > 0 && projectionVisible && !fromChord && !nextTAligned
+                && dt > 0 && dt < GHOST_UPCOMING_WIN) {
+                const slotIdx = 1 + _scrGhostUpcomingCount[s];
+                if (slotIdx <= 2) {
+                    _scrGhostUpcomingCount[s]++;
+                    // Same formula as Primary's projFactor for !fromChord
+                    // notes (ghostWin === GHOST_UPCOMING_WIN there too) —
+                    // keeps the size/brightness curve continuous as a note's
+                    // rank improves frame-to-frame (slot 2 → 1 → 0).
+                    const upcomingProgress = projFactor;
+                    const proj = projMeshArr[s][slotIdx];
+                    const rimSolid = upcomingProgress * 0.94;
+                    proj.material.opacity = Math.min(0.96,
+                        projScale * rimSolid * (0.5 + 0.5 * glowMul) * bodyDim);
+                    proj.material.emissiveIntensity = upcomingProgress * 0.55 * glowMul * bodyDim;
+                    const growScale = PROJ_GROW_MIN + (1 - PROJ_GROW_MIN) * upcomingProgress;
+                    proj.position.set(x, y, 0);
+                    proj.scale.set(growScale, growScale, growScale);
+                    proj.rotation.z = projRim;
+                    proj.visible = true;
+
+                    if (showFretOnNote && fretNumberGhostScope === 'all' && pGhostFretLbl) {
+                        drawGhostFretLabel(x, y, projRim, n.f, upcomingProgress, growScale, n.f);
+                    }
+                }
+            }
+        }
+
+        /**
+         * Draw  [ GEM ]  bracket pair for an arpeggio note.
+         *
+         * While the note is approaching (bracketDt > 0) the brackets travel at the
+         * same Z as the gem.  Once the note hits the line (bracketDt <= 0) the
+         * brackets sit at Z = 0 (the fretboard plane) and persist until arpEnd.
+         * They fade in with approach and fade out in the last 0.25 s of the arpeggio.
+         *
+         * Fretted notes: `[ ]` — 3 BoxGeometry bars per side (vertical + 2 caps).
+         * Open strings:  `< >` — 2 diagonal arms per side, tips at note edges.
+         *
+         * openHalfW (optional) — half-width of the open note body; when supplied,
+         * the < > tips are placed at the actual edges of the note rather than a
+         * fixed offset.
+         */
+        function drawArpBrackets(x, y, bracketDt, arpEnd, now, s, isOpen = false, openHalfW = null) {
+            if (bracketDt >= AHEAD) return;
+            if (bracketDt < 0 && now > arpEnd + 0.05) return;
+            if (!pArpBracket) return;
+
+            let alpha;
+            if (bracketDt > 0) {
+                // Match the chord frame box visibility: full opacity throughout the
+                // entire AHEAD window so brackets appear the moment the frame enters
+                // view, not after a slow linear fade from alpha≈0 at 3 s out.
+                alpha = 1;
+            } else {
+                const remaining = arpEnd - now;
+                alpha = remaining > 0.25 ? 1 : Math.max(0, remaining / 0.25);
+            }
+            if (alpha < 0.01) return;
+
+            const bracketZ = bracketDt > 0 ? Math.min(0, dZ(bracketDt)) : 0;
+            const col = activePalette[s % activePalette.length];
+            const barThick = NW * 0.09;
+            const bracketH = NH * 1.05;
+            const capLen   = NW * 0.42;
+            const xOff     = (isOpen && openHalfW != null) ? openHalfW : NW * 0.95;
+            const zOff     = 0.006 * K;
+            const ord      = 18;
+
+            if (isOpen) {
+                // < > chevron — 2 diagonal arms per side.
+                // Arm goes from tip outward; angle from positive-X axis via atan2.
+                const armLen = Math.sqrt(capLen * capLen + (bracketH * 0.5) * (bracketH * 0.5));
+                const ang    = Math.atan2(bracketH * 0.5, capLen); // upper-right arm angle
+
+                const diagBar = (px, py, rz) => {
+                    const b = pArpBracket.get();
+                    b.material.color.setHex(col);
+                    b.material.opacity = alpha;
+                    b.renderOrder = ord;
+                    b.position.set(px, py, bracketZ + zOff);
+                    b.rotation.set(0, 0, rz);
+                    b.scale.set(armLen, barThick, barThick);
+                };
+
+                // < tip at (x - xOff), arms open to the right
+                diagBar(x - xOff + capLen * 0.5, y + bracketH * 0.25,  ang);
+                diagBar(x - xOff + capLen * 0.5, y - bracketH * 0.25, -ang);
+
+                // > tip at (x + xOff), arms open to the left
+                diagBar(x + xOff - capLen * 0.5, y + bracketH * 0.25,  Math.PI - ang);
+                diagBar(x + xOff - capLen * 0.5, y - bracketH * 0.25, -Math.PI + ang);
+            } else {
+                const bar = (px, py, sw, sh) => {
+                    const b = pArpBracket.get();
+                    b.material.color.setHex(col);
+                    b.material.opacity = alpha;
+                    b.renderOrder = ord;
+                    b.position.set(px, py, bracketZ + zOff);
+                    b.rotation.set(0, 0, 0);
+                    b.scale.set(sw, sh, barThick);
+                };
+
+                // Left bracket  [  – vertical bar then caps opening to the right
+                bar(x - xOff,                     y,                  barThick, bracketH);
+                bar(x - xOff + capLen * 0.5, y + bracketH * 0.5, capLen,   barThick);
+                bar(x - xOff + capLen * 0.5, y - bracketH * 0.5, capLen,   barThick);
+
+                // Right bracket  ]  – vertical bar then caps opening to the left
+                bar(x + xOff,                     y,                  barThick, bracketH);
+                bar(x + xOff - capLen * 0.5, y + bracketH * 0.5, capLen,   barThick);
+                bar(x + xOff - capLen * 0.5, y - bracketH * 0.5, capLen,   barThick);
+            }
+        }
+
+        function drawNotedetectLabels(ctx, W, H) {
+            if (!_ndLabels.length || !cam || !_probe) return;
+            ctx.save();
+            ctx.font = 'bold 12px sans-serif';
+            ctx.textAlign = 'center';
+            ctx.textBaseline = 'middle';
+            for (const item of _ndLabels) {
+                _probe.set(item.x, item.y, item.z);
+                _probe.project(cam);
+                if (_probe.z < -1 || _probe.z > 1) continue;
+                const sx = (_probe.x * 0.5 + 0.5) * W;
+                const sy = (-_probe.y * 0.5 + 0.5) * H;
+                for (let i = 0; i < item.labels.length; i++) {
+                    const label = item.labels[i];
+                    const y = sy + (i - (item.labels.length - 1) / 2) * 15;
+                    ctx.lineWidth = 4;
+                    ctx.strokeStyle = 'rgba(0,0,0,0.8)';
+                    ctx.strokeText(label.text, sx, y);
+                    ctx.fillStyle = label.color;
+                    ctx.fillText(label.text, sx, y);
+                }
+            }
+            ctx.restore();
+        }
+
+        // Score FX overlay pass — "+N" pops rising off their gems, milestone
+        // particle bursts / multiplier ring-pulses / streak-break flickers
+        // anchored on the strike line. Same overlay layer + projection
+        // pattern as drawNotedetectLabels; costs one early-out when nothing
+        // is active.
+        function drawScoreFx(ctx, W, H) {
+            if (!cam || !_probe) return;
+            const nowMs = _ndFrameNowMs || performance.now();
+            // TTL-prune the pop dedup keys (bounded: only notes hit in the
+            // last few seconds).
+            if (_fxSeen.size) {
+                for (const [k, exp] of _fxSeen) {
+                    if (exp <= nowMs) _fxSeen.delete(k);
+                }
+            }
+            let anyPop = false;
+            for (let i = 0; i < _fxPops.length; i++) {
+                if (_fxPops[i].active) { anyPop = true; break; }
+            }
+            let anyBurst = false;
+            for (let i = 0; i < _fxBursts.length; i++) {
+                if (_fxBursts[i].active) { anyBurst = true; break; }
+            }
+            const ringAge = nowMs - _fxRingMs;
+            const breakAge = nowMs - _fxBreakMs;
+            if (!anyPop && !anyBurst && ringAge >= 600 && breakAge >= 350) return;
+
+            const pal = _fxPalette;
+            ctx.save();
+
+            // Streak-break flicker: brief red wash over the whole panel.
+            if (breakAge < 350) {
+                const a = 0.10 * (1 - breakAge / 350);
+                ctx.fillStyle = pal.miss;
+                ctx.globalAlpha = a;
+                ctx.fillRect(0, 0, W, H);
+                ctx.globalAlpha = 1;
+            }
+
+            // Strike-line center in screen px — anchor for bursts + pulses.
+            let cx = W / 2, cy = H * 0.72, centerOk = false;
+            {
+                const fretMidY = (sY(0) + sY(nStr - 1)) / 2;
+                _probe.set(curX, fretMidY, 0);
+                _probe.project(cam);
+                if (_probe.z >= -1 && _probe.z <= 1) {
+                    cx = (_probe.x * 0.5 + 0.5) * W;
+                    cy = (-_probe.y * 0.5 + 0.5) * H;
+                    centerOk = true;
+                }
+            }
+
+            // Multiplier ring-pulse: one expanding ring on tier-up; the ×4
+            // tier pulses in the secondary accent like the HUD badge.
+            if (centerOk && ringAge < 600) {
+                const t = ringAge / 600;
+                const ease = 1 - Math.pow(1 - t, 2);
+                ctx.beginPath();
+                ctx.arc(cx, cy, 20 + ease * Math.min(W, H) * 0.28, 0, Math.PI * 2);
+                ctx.strokeStyle = _fxRingMult >= 4 ? pal.accent2 : pal.accent;
+                ctx.globalAlpha = 0.6 * (1 - t);
+                ctx.lineWidth = 3;
+                ctx.stroke();
+                ctx.globalAlpha = 1;
+            }
+
+            // Milestone bursts.
+            if (anyBurst && centerOk) {
+                for (let i = 0; i < _fxBursts.length; i++) {
+                    const b = _fxBursts[i];
+                    if (!b.active) continue;
+                    const age = nowMs - b.bornMs;
+                    if (age >= _FX_BURST_LIFE_MS) { b.active = false; continue; }
+                    const t = age / _FX_BURST_LIFE_MS;
+                    ctx.globalAlpha = 1 - t;
+                    for (let j = 0; j < _FX_BURST_N; j++) {
+                        b.px[j] += b.vx[j];
+                        b.py[j] += b.vy[j];
+                        b.vy[j] += 0.08;
+                        ctx.fillStyle = (j & 1) ? pal.accent : pal.accent2;
+                        ctx.fillRect(cx + b.px[j] - 2, cy + b.py[j] - 2, 4, 4);
+                    }
+                    ctx.globalAlpha = 1;
+                }
+            }
+
+            // "+N" pops: rise off the gem and fade over the back half.
+            if (anyPop) {
+                ctx.textAlign = 'center';
+                ctx.textBaseline = 'middle';
+                for (let i = 0; i < _fxPops.length; i++) {
+                    const p = _fxPops[i];
+                    if (!p.active) continue;
+                    const age = nowMs - p.bornMs;
+                    if (age >= _FX_POP_LIFE_MS) { p.active = false; continue; }
+                    _probe.set(p.x, p.y, p.z);
+                    _probe.project(cam);
+                    if (_probe.z < -1 || _probe.z > 1) continue;
+                    const t = age / _FX_POP_LIFE_MS;
+                    const sx = (_probe.x * 0.5 + 0.5) * W;
+                    const sy2 = (-_probe.y * 0.5 + 0.5) * H - t * 30;
+                    ctx.globalAlpha = t < 0.4 ? 1 : 1 - (t - 0.4) / 0.6;
+                    ctx.font = `bold ${13 + (p.mult - 1) * 2}px '${pal.font}', sans-serif`;
+                    ctx.lineWidth = 4;
+                    ctx.strokeStyle = 'rgba(0,0,0,0.8)';
+                    ctx.strokeText(p.text, sx, sy2);
+                    ctx.fillStyle = pal.accent;
+                    ctx.fillText(p.text, sx, sy2);
+                }
+                ctx.globalAlpha = 1;
+            }
+
+            ctx.restore();
+        }
+
+        // Horizontal-FOV-hold ("Hor+"). Returns the vertical fov (deg) the
+        // camera should use for the given pane aspect. With the bridge off (or
+        // absent), or at/under the start aspect, it returns the base vertical
+        // fov unchanged — an exact no-op, so normal panes render identically to
+        // before. Past the start aspect it lowers the vertical fov to keep the
+        // horizontal cone ~constant, so the neck fills an ultra-wide pane
+        // instead of collapsing into a central sliver. Pure + finite-guarded.
+        function effectiveVfov(aspect, tune) {
+            const base = (tune && Number.isFinite(tune.baseVfov)) ? tune.baseVfov : BASE_VFOV;
+            if (!tune || !tune.enabled || !Number.isFinite(aspect) || aspect <= 0) return base;
+            const start = (Number.isFinite(tune.startAspect) && tune.startAspect > 0)
+                ? tune.startAspect : HORPLUS_START_ASPECT;
+            if (aspect <= start) return base;
+            const floor = Number.isFinite(tune.minVfovDeg) ? tune.minVfovDeg : HORPLUS_MIN_VFOV;
+            const DEG = Math.PI / 180;
+            // Held horizontal fov: explicit hfovDeg if given, else the horizontal
+            // cone the base vertical fov produces at the start aspect.
+            const hfov = (Number.isFinite(tune.hfovDeg) && tune.hfovDeg > 0)
+                ? tune.hfovDeg * DEG
+                : 2 * Math.atan(Math.tan(base * DEG / 2) * start);
+            // Vertical fov that reproduces that horizontal cone at this aspect.
+            let vfov = 2 * Math.atan(Math.tan(hfov / 2) / aspect) / DEG;
+            const blend = Number.isFinite(tune.blend) ? Math.max(0, Math.min(1, tune.blend)) : 1;
+            vfov = base + (vfov - base) * blend;            // 0 = base, 1 = full Hor+
+            if (!Number.isFinite(vfov)) return base;
+            return Math.max(floor, Math.min(base, vfov));
+        }
+
+        /* ── Camera smooth lerp ──────────────────────────────────────────── */
+        function camUpdate(bundle) {
+            const bpm = computeBPM(bundle.beats, bundle.currentTime);
+            const lerp = CAM_LERP_BASE * Math.max(bpm, 60) / 120;
+
+            // ── Horizontal-FOV-hold + optional wide-pane pose nudges ──
+            // Driven by window.__h3dAspectTune (default off → exact no-op).
+            // _resolveTuneFor(paneKey) returns the shared base with THIS pane's
+            // overrides (if any) laid on top, so a single split pane can be framed
+            // independently. The base is seeded from defaults + localStorage on
+            // first read, so a persisted tuning session applies on load without
+            // opening the panel. Every field is finite-coerced. When disabled (or
+            // splitOnly and not in a split) the tune is treated as null, so
+            // effectiveVfov returns the base vertical fov and cam.fov is restored
+            // to it. The fov write is guarded on an actual change so a steady pane
+            // costs nothing.
+            const _paneKey = _aspectPaneKey(
+                bundle && bundle.songInfo && bundle.songInfo.arrangement, _paneUid);
+            // Only feed the Target-picker registry while the tuner is open (same
+            // gate as the readout). Closed → nothing is registered, so the registry
+            // can't grow for users who never open the panel; the key is still
+            // resolved below so any saved overrides keep applying.
+            if (window.__h3dAspectPanelOpen) _aspectRegisterPane(_paneKey);
+            const _aspTune = _resolveTuneFor(_paneKey);
+            const _aspActive = !!(_aspTune && _aspTune.enabled
+                && !(_aspTune.splitOnly && !_ssActive()));
+            const _tune = _aspActive ? _aspTune : null;
+            const _vfov = effectiveVfov(_paneAspect, _tune);
+            if (Number.isFinite(_vfov) && Math.abs(_vfov - cam.fov) > 1e-4) {
+                cam.fov = _vfov;
+                cam.updateProjectionMatrix();
+            }
+            // Publish a per-pane live readout for the tuner panel (only while it's
+            // open, so the steady path stays allocation-free). Keyed by pane so
+            // the panel can show the reading for whichever target is selected.
+            if (window.__h3dAspectPanelOpen) {
+                const _ro = window.__h3dAspectReadout || (window.__h3dAspectReadout = {});
+                const _slot = _ro[_paneKey] || (_ro[_paneKey] = {});
+                _slot.aspect = _paneAspect; _slot.vfov = _vfov;
+                _ro.__last = _paneKey;
+            }
+            // Optional pose nudges (height / dolly / pitch) to chase a low-flat
+            // wide-pane look if fov alone isn't enough. Gated to wide panes and
+            // suppressed while the Camera Director owns the view (it wins).
+            const _startAspect = (_tune && Number.isFinite(_tune.startAspect) && _tune.startAspect > 0)
+                ? _tune.startAspect : HORPLUS_START_ASPECT;
+            // Resolve the Camera Director bridge once (per-panel under splitscreen,
+            // else global). Used both for the wide-pane gate and the transforms below.
+            const _freeCam = _freeCamFor(highwayCanvas);
+            const _dirActive = !!(_freeCam && _freeCam.enabled);
+            const _wide = !!(_tune && _paneAspect > _startAspect) && !_dirActive;
+            const _poseHMul = (_wide && Number.isFinite(_tune.heightMul)) ? _tune.heightMul : 1;
+            const _poseDMul = (_wide && Number.isFinite(_tune.distMul)) ? _tune.distMul : 1;
+            const _poseLookYAdd = (_wide && Number.isFinite(_tune.pitchAdd)) ? _tune.pitchAdd * K : 0;
+            const _poseLookZMul = (_wide && Number.isFinite(_tune.lookDepthMul) && _tune.lookDepthMul > 0)
+                ? _tune.lookDepthMul : 1;
+
+            curX += (tgtX - curX) * lerp;
+            // The fret-row fit guard (end of camUpdate) may dolly the camera back
+            // via _fretRowFitBoost; the span-driven tgtDist still owns zooming IN.
+            curDist += (tgtDist * _fretRowFitBoost - curDist) * lerp;
+            const dist = curDist * aspectScale;
+            const h = CAM_H_BASE * (dist / CAM_DIST_BASE);
+
+            // Zoom-interpolated framing multipliers: tight (NEAR) -> lower/closer;
+            // wide (FAR, fret 1<->20) -> higher/pulled back.
+            const _zt = Math.max(0, Math.min(1,
+                (dist - CAM_FRAME_DIST_NEAR) / (CAM_FRAME_DIST_FAR - CAM_FRAME_DIST_NEAR)));
+            const _hMul = CAM_FRAME_H_NEAR + (CAM_FRAME_H_FAR - CAM_FRAME_H_NEAR) * _zt;
+            const _dMul = CAM_FRAME_D_NEAR + (CAM_FRAME_D_FAR - CAM_FRAME_D_NEAR) * _zt;
+            const shoulderOffset = (_leftyCached ? -1 : 1) * 10 * K;
+            let _camX = curX + shoulderOffset, _camY = h * _hMul, _camZ = dist * _dMul;
+            // Optional wide-pane pose nudges (default identity → no-op).
+            if (_poseHMul !== 1) _camY *= _poseHMul;
+            if (_poseDMul !== 1) _camZ *= _poseDMul;
+            // ── Free-camera user tweaks (orbit / height / zoom / pan) ──
+            // Driven by the Camera Director plugin via the camera bridge:
+            // window.__h3dCamCtlPanels[panelIndexFor(canvas)] when split (this
+            // panel's own camera), falling back to the global window.__h3dCamCtl.
+            // Layered ON TOP of the auto-framing so note tracking still works.
+            // The bridge is read once into _freeCam and reused for both the
+            // position and the look-at transforms; every field is coerced to a
+            // finite number before use so a malformed object can never feed NaN
+            // into cam.position / cam.lookAt.
+            // _freeCam resolved above via _freeCamFor(highwayCanvas): the
+            // per-panel __h3dCamCtlPanels entry, else global __h3dCamCtl, else null.
+            const _lookAtZ = -FOCUS_D * 0.35 * _poseLookZMul;
+            if (_freeCam && _freeCam.enabled) {
+                const _distMul = Number.isFinite(_freeCam.distMul) ? _freeCam.distMul : 1;
+                const _heightMul = Number.isFinite(_freeCam.heightMul) ? _freeCam.heightMul : 1;
+                const _yaw = Number.isFinite(_freeCam.yaw) ? _freeCam.yaw : 0;
+                const _tx = curX, _ty = curLookY, _tz = _lookAtZ; // look target
+                let _vx = _camX - _tx, _vy = _camY - _ty, _vz = _camZ - _tz;
+                _vx *= _distMul; _vy *= _distMul; _vz *= _distMul; // zoom (dolly)
+                _vy *= _heightMul;                                 // height
+                const _cy = Math.cos(_yaw), _sy = Math.sin(_yaw);  // orbit around Y
+                const _rx = _vx * _cy - _vz * _sy, _rz = _vx * _sy + _vz * _cy;
+                _camX = _tx + _rx; _camY = _ty + _vy; _camZ = _tz + _rz;
+            }
+            cam.position.set(_camX, _camY, _camZ);
+
+            // Self-correcting look-at Y: project the fretboard's near-edge centre
+            // to NDC space. If it drifts toward the frame edge, nudge tgtLookY
+            // toward the fretboard centre so the camera tilts to re-frame it.
+            // This lets the camera adapt to any panel aspect ratio automatically.
+            const fretMidY = (sY(0) + sY(nStr - 1)) / 2;
+            _probe.set(curX, fretMidY, 0);                  // play-line fretboard centre
+            cam.lookAt(curX, curLookY + _poseLookYAdd, _lookAtZ);    // tentative look — needed for project()
+            cam.updateMatrixWorld();
+            _probe.project(cam);                             // _probe.y → NDC in [-1, 1]
+
+            // Keep fretboard centre in the lower third of the screen (NDC ≈ -0.35).
+            // The deadband width and correction strength are both blended
+            // between Twitchy and Calm bounds by the user's tiltSmoothing
+            // setting — twitchy = re-frame aggressively (narrow band, strong
+            // nudge); calm = let small drift ride (wide band, weak nudge).
+            const DESIRED_NDC_Y = -0.35;
+            const tiltBand   = CAM_TILT_BAND_T + (CAM_TILT_BAND_C - CAM_TILT_BAND_T) * tiltSmoothing;
+            const tiltStr    = CAM_TILT_STR_T  + (CAM_TILT_STR_C  - CAM_TILT_STR_T)  * tiltSmoothing;
+            if (_probe.y < DESIRED_NDC_Y - tiltBand || _probe.y > DESIRED_NDC_Y + tiltBand) {
+                // _probe.y too low → fretboard near bottom → tgtLookY decreases → camera tilts down → fretboard rises
+                // _probe.y too high → fretboard near top  → tgtLookY increases → camera tilts up   → fretboard drops
+                const correction = (DESIRED_NDC_Y - _probe.y) * fretMidY * tiltStr;
+                tgtLookY = Math.max(-fretMidY, Math.min(fretMidY, tgtLookY - correction));
+            }
+            curLookY += (tgtLookY - curLookY) * lerp;
+
+            // Final look-at with the corrected Y (overrides the tentative one above).
+            // User tilt (pitch) + pan offsets layer on top when the free-cam is
+            // enabled; each is coerced to a finite number to avoid a NaN look-at.
+            if (_freeCam && _freeCam.enabled) {
+                const _panX = Number.isFinite(_freeCam.panX) ? _freeCam.panX : 0;
+                const _panY = Number.isFinite(_freeCam.panY) ? _freeCam.panY : 0;
+                const _pitch = Number.isFinite(_freeCam.pitch) ? _freeCam.pitch : 0;
+                cam.lookAt(curX + _panX * K, curLookY + (_pitch + _panY) * K, _lookAtZ);
+            } else {
+                cam.lookAt(curX, curLookY + _poseLookYAdd, _lookAtZ);
+            }
+
+            // ── Fret-row fit guard ────────────────────────────────────────────
+            // Project the fret-number-row band (just below the lowest string, at
+            // the play line) with the final camera. If it sits below the safe
+            // bottom line, dolly back (raise _fretRowFitBoost → applied to the
+            // curDist lerp target next frame) until it clears; relax lazily once
+            // there's comfortable headroom. Asymmetric + deadbanded so it
+            // converges without hunting, and capped so the zoom can't pop. It
+            // cooperates with the tilt loop above rather than fighting it: pulling
+            // back shrinks the scene, the tilt loop keeps the board centre anchored
+            // at DESIRED_NDC_Y, so only the row's bottom headroom changes. Skipped
+            // while the free-cam (Camera Director) owns the view.
+            if (_freeCam && _freeCam.enabled) {
+                if (_fretRowFitBoost !== 1) _fretRowFitBoost = 1;
+            } else {
+                cam.updateMatrixWorld();
+                const _rowY = Math.min(sY(0), sY(nStr - 1)) - S_GAP * 1.4;
+                _probe.set(curX, _rowY, 0.5 * K);
+                _probe.project(cam);                              // _probe.y → NDC; < -1 = off the bottom
+                const _rowNdcY = _probe.y;
+                if (_rowNdcY < FRET_ROW_FIT_NDC_MIN) {
+                    // Row below the safe line → pull back promptly, proportional to
+                    // the deficit so it converges in a few frames without overshoot.
+                    const _need = FRET_ROW_FIT_NDC_MIN - _rowNdcY;
+                    _fretRowFitBoost = Math.min(FRET_ROW_FIT_BOOST_MAX,
+                        _fretRowFitBoost + Math.min(0.05, _need * 0.4));
+                } else if (_rowNdcY > FRET_ROW_FIT_NDC_MIN + FRET_ROW_FIT_DEADBAND
+                           && _fretRowFitBoost > 1) {
+                    // Comfortable headroom → relax the dolly back toward normal, lazily.
+                    _fretRowFitBoost = Math.max(1, _fretRowFitBoost - 0.01);
+                }
+            }
+        }
+
+        /* ── Resize helper ───────────────────────────────────────────────── */
+        function applySize(w, h) {
+            if (!ren || !cam || !wrap) return;
+            if (!Number.isFinite(w) || !Number.isFinite(h) || w <= 0 || h <= 0) return;
+            const baseDPR = _ssActive() ? Math.min(devicePixelRatio, 1.25) : Math.min(devicePixelRatio, 2);
+            ren.setPixelRatio(_renderScale * baseDPR);
+            ren.setSize(w, h);
+            // Pin the overlay to #highway's exact box so it fully covers the
+            // canvas. The wrap is anchored to top:0/left:0/right:0 of its
+            // offset parent, which only lines up with #highway when the
+            // canvas sits at the parent's origin. The v3 player can place
+            // chrome above the canvas, shifting the wrap up so its lower edge
+            // falls short of #highway — leaving a strip of the canvas exposed
+            // (the reported gap, where the previous renderer's frame showed
+            // through). The wrap is a sibling of highwayCanvas, so they share
+            // an offset parent; tracking the canvas's box keeps the overlay
+            // flush in single-player and splitscreen alike.
+            //
+            // Derive the box from the SAME getBoundingClientRect measurements
+            // that drive ren.setSize(w, h) — NOT integer offsetTop/Width — so
+            // the overlay matches the renderer exactly. Under browser zoom or
+            // fractional flex layouts the canvas lands on sub-pixel bounds;
+            // offsetWidth/Top round to whole pixels and would leave the wrap up
+            // to 1px short of (or shifted from) the canvas, reopening the
+            // exposed edge strip. Position is taken relative to the containing
+            // block's padding edge (clientTop/Left strip the parent's border),
+            // which is what `top`/`left` resolve against for the absolutely
+            // positioned wrap. Guarded on a laid-out canvas (offsetWidth/Height
+            // > 0); otherwise fall back to the static top:0/left:0/right:0.
+            if (highwayCanvas && highwayCanvas.offsetWidth > 0 && highwayCanvas.offsetHeight > 0) {
+                const _pinParent = wrap.offsetParent || highwayCanvas.parentNode;
+                const _cr = highwayCanvas.getBoundingClientRect();
+                const _pr = _pinParent ? _pinParent.getBoundingClientRect() : { top: 0, left: 0 };
+                const _pbTop = _pinParent ? _pinParent.clientTop : 0;
+                const _pbLeft = _pinParent ? _pinParent.clientLeft : 0;
+                wrap.style.top = (_cr.top - _pr.top - _pbTop) + 'px';
+                wrap.style.left = (_cr.left - _pr.left - _pbLeft) + 'px';
+                wrap.style.right = 'auto';
+                wrap.style.width = _cr.width + 'px';
+                wrap.style.height = _cr.height + 'px';
+                _wrapPinned = true;
+            } else {
+                // Canvas not laid out (e.g. init ran before #highway had a real
+                // box, or a panel hide/show where canvasSize() falls back to the
+                // parent panel). Reset to the static anchor — if we had pinned
+                // before, the old top/left/right:auto/width would otherwise stay
+                // and the wrap would reappear at a stale horizontal position on
+                // the next show. Leave _wrapPinned false so the rAF loop re-pins
+                // once the canvas materializes again.
+                wrap.style.top = '0';
+                wrap.style.left = '0';
+                wrap.style.right = '0';
+                wrap.style.width = 'auto';
+                wrap.style.height = h + 'px';
+                _wrapPinned = false;
+            }
+            if (lyricsCanvas) { lyricsCanvas.width = w; lyricsCanvas.height = h; }
+            _diagRenderCache.clear();
+            cam.aspect = w / h;
+            cam.updateProjectionMatrix();
+            aspectScale = Math.max(1, REF_ASPECT / Math.max(cam.aspect, 0.5));
+            // Cache the pane aspect for the horizontal-FOV-hold in camUpdate.
+            // cam.fov itself is owned by camUpdate (not set here) so live
+            // __h3dAspectTune edits apply every frame without a resize.
+            _paneAspect = cam.aspect;
+            _appliedW = w; _appliedH = h;
+        }
+
+        /* ── Teardown ────────────────────────────────────────────────────── */
+        function teardown() {
+            // Background animations (#13). Drop the listener first so any
+            // mid-teardown settings change doesn't try to rebuild a torn-
+            // down scene; then dispose the active style's resources.
+            if (_bgListener) { _bgUnsubscribe(_bgListener); _bgListener = null; }
+            // WebGL context-loss listeners (bound in initScene on ren.domElement).
+            // Remove before ren is disposed below so a torn-down instance can't
+            // keep firing them; reset the flag so a reused instance starts clean.
+            if (ren && ren.domElement) {
+                if (_onCtxLost) { try { ren.domElement.removeEventListener('webglcontextlost', _onCtxLost, false); } catch (e) {} }
+                if (_onCtxRestored) { try { ren.domElement.removeEventListener('webglcontextrestored', _onCtxRestored, false); } catch (e) {} }
+            }
+            _onCtxLost = _onCtxRestored = null;
+            _ctxLost = false;
+            // Notedetect listeners (issue #9). Remove on destroy so a
+            // panel that stops doesn't keep accumulating marks. Marks
+            // arrays are cleared too — they hold stale chart positions
+            // that next init() may reuse (drawNote keys on (s, f, t)).
+            if (_ndOnHit) { window.removeEventListener('notedetect:hit', _ndOnHit); _ndOnHit = null; }
+            if (_ndOnMiss) { window.removeEventListener('notedetect:miss', _ndOnMiss); _ndOnMiss = null; }
+            if (_fxOnFx) { window.removeEventListener('notedetect:fx', _fxOnFx); _fxOnFx = null; }
+            if (window.feedBack && typeof window.feedBack.off === 'function') {
+                if (_fxOnSkin) { try { window.feedBack.off('notedetect:skin', _fxOnSkin); } catch (e) {} _fxOnSkin = null; }
+                if (_ndOnBusHit)  window.feedBack.off('note:hit', _ndOnBusHit);
+                if (_ndOnBusMiss) window.feedBack.off('note:miss', _ndOnBusMiss);
+                if (_visibilityHandler) {
+                    try { window.feedBack.off('highway:visibility', _visibilityHandler); } catch (e) {}
+                }
+                if (_canvasReplacedHandler) {
+                    try { window.feedBack.off('highway:canvas-replaced', _canvasReplacedHandler); } catch (e) {}
+                }
+            }
+            _ndOnBusHit = _ndOnBusMiss = null;
+            _visibilityHandler = null;
+            _canvasReplacedHandler = null;
+            _ndHitMarks = [];
+            _ndMissMarks = [];
+            _ndLabels = [];
+            for (const p of _fxPops) p.active = false;
+            for (const b of _fxBursts) b.active = false;
+            _fxSeen.clear();
+            _fxGen++;   // invalidate any pending deferred window-copy fallbacks
+            _fxLastFxDetail = null;
+            _fxElemSeen = new WeakSet();
+            _fxRingMs = _fxBreakMs = -1e9;
+            _chordVerdicts = new Map();
+            if (bcCtrl) { try { bcCtrl.destroy(); } catch (e) {} bcCtrl = null; }
+            _bgUnmountStyle();
+            bgGroup = null; _bgLastT = 0;
+            _diagChord = null; _diagPrev = null; _diagPrevOpacity = 0; _diagPrevStartOpacity = 0; _diagPrevStartT = null;
+            _diagEntranceT = 1.0; _diagLastKey = null; _diagRenderCache.clear();
+
+            if (wrap) { wrap.remove(); wrap = null; }
+            _disposeOpenStringPitchSprites();
+            if (scene) {
+                // Don't dispose material.map textures here. Texture
+                // lifetime belongs to whoever allocated it; the bg
+                // styles' per-layer CanvasTextures (e.g. silhouettes'
+                // wrappers around the shared _silCanvas) are released
+                // in their own teardowns. txtCache textures are
+                // explicitly disposed below; mStr/mGlow/etc. don't have
+                // a .map. Disposing here would either double-free or
+                // yank a still-in-use texture out from under another
+                // mount.
+                scene.traverse((obj) => {
+                    // fretTubeGeo is shared across all fret meshes — dispose it
+                    // exactly once below, not once per mesh here.
+                    if (obj.geometry !== fretTubeGeo) obj.geometry?.dispose?.();
+                    if (obj.material) {
+                        const mats = Array.isArray(obj.material) ? obj.material : [obj.material];
+                        for (const m of mats) m?.dispose?.();
+                    }
+                });
+                // Shared chord-frame fill gradient — not owned by txtCache;
+                // MeshBasicMaterial.dispose() does not release maps.
+                chordFrameGradTex?.dispose?.();
+                chordFrameGradTexArp?.dispose?.();
+            }
+            gNote?.dispose?.(); gSus?.dispose?.(); gBeat?.dispose?.(); gSusRail?.dispose?.(); gTapChevron?.dispose?.();
+            mSusRailBase?.dispose?.(); mSusRailBase = null; gSusRail = null; pSusRail = null;
+            gSusRailBloom?.dispose?.(); mSusRailBloomBase?.dispose?.(); _bloomGaussTex?.dispose?.();
+            gSusRailBloom = null; mSusRailBloomBase = null; _bloomGaussTex = null; pSusRailBloom = null;
+            gTechPlane?.dispose?.(); gTechPlane = null; pTechPlane = null;
+            // InstancedMesh disposal — .dispose() releases instanceMatrix / instanceColor
+            // GPU buffers. Geometry and material are disposed separately below.
+            imPMTech?.dispose?.(); imPMTech = null;
+            imFHTech?.dispose?.(); imFHTech = null;
+            imPMXFill?.dispose?.(); imPMXFill = null;
+            imPMXLines?.dispose?.(); imPMXLines = null;
+            imFHXFill?.dispose?.(); imFHXFill = null;
+            imFHXLines?.dispose?.(); imFHXLines = null;
+            // Geometry clones for PM/FH tech IMs (own instanceAlpha attribute).
+            _imGPMTech?.dispose?.(); _imGPMTech = null;
+            _imGFHTech?.dispose?.(); _imGFHTech = null;
+            // ShaderMaterials for all 6 IMs.
+            _imPMTechMat?.dispose?.();  _imPMTechMat = null;
+            _imFHTechMat?.dispose?.();  _imFHTechMat = null;
+            _imPMXFillMat?.dispose?.(); _imPMXFillMat = null;
+            _imPMXLinesMat?.dispose?.(); _imPMXLinesMat = null;
+            _imFHXFillMat?.dispose?.(); _imFHXFillMat = null;
+            _imFHXLinesMat?.dispose?.(); _imFHXLinesMat = null;
+            _imM4 = _imPos = _imSca = _imQ = _imAZ = _imColor = null;
+            gHaloBar?.dispose?.(); gHaloBar = null;
+            gArpBracket?.dispose?.(); gArpBracket = null;
+            for (const m of mStr) m?.dispose?.();
+            for (const m of mGlow) m?.dispose?.();
+            for (const m of mSus) m?.dispose?.();
+            for (const m of mStrHitOutline) m?.dispose?.();
+            for (const m of mAccentOutline) m?.dispose?.();
+            for (const m of mAccentCore) m?.dispose?.();
+            for (const m of mAccentHaloNear) m?.dispose?.();
+            for (const m of mAccentHaloMid) m?.dispose?.();
+            for (const m of mAccentHaloFar) m?.dispose?.();
+            mBeatM?.dispose?.(); mBeatQ?.dispose?.();
+            // Notedetect outline materials (#9). May not be reachable
+            // via scene.traverse if no event ever fired (never attached
+            // to a mesh), so dispose explicitly.
+            mMissOutline?.dispose?.();
+            mHitSusOutline?.dispose?.();
+            mEdgeTransparent?.dispose?.(); mEdgeTransparent = null;
+            for (const m of mHitBright) m?.dispose?.(); mHitBright = []; mHitBrightArrays = [];
+            for (const m of mRimFlash) m?.dispose?.(); mRimFlash = [];
+            for (const k in txtCache) {
+                const tm = txtCache[k];
+                tm.userData.h3dGhostFretMeshMat?.dispose?.();
+                tm.userData.h3dGhostFretMeshMat = null;
+                tm.userData.h3dTechMeshMat?.dispose?.();
+                tm.userData.h3dTechMeshMat = null;
+                tm.map?.dispose();
+                tm.dispose();
+            }
+            // Technique-marker sprite materials (triMat / bendChevronMat) —
+            // own numeric-keyed cache, not reachable via txtCache.
+            for (const tm of _techMatCache.values()) {
+                tm.map?.dispose();
+                tm.dispose();
+            }
+            _techMatCache.clear();
+            // Dispose per-sprite cloned materials (e.g. pmMark._pmMat).
+            // These aren't reachable via scene.traverse once the sprite
+            // gets reassigned a different material, so the array tracks
+            // them at allocation time.
+            for (const m of _ownedClonedMats) m?.dispose?.();
+            _ownedClonedMats.length = 0;
+            // Per-mesh technique-marker clones (from _spriteMat2MeshMat).
+            // The Set tracks the live clone for each pool mesh; dispose all
+            // on teardown so no GPU material leaks between init() cycles.
+            for (const m of _techMeshMatClones) m?.dispose?.();
+            _techMeshMatClones.clear();
+            // Shared pool-factory materials/geometries (mLaneOdd/Even, etc.) —
+            // see _ownedSharedMats comment near the declaration. Dispose is
+            // idempotent so the scene.traverse() pass above won't double-free.
+            for (const m of _ownedSharedMats) m?.dispose?.();
+            _ownedSharedMats.length = 0;
+            for (const g of _ownedSharedGeos) g?.dispose?.();
+            _ownedSharedGeos.length = 0;
+            txtCache = {};
+            if (_sparkPts) { try { _sparkPts.geometry.dispose(); _sparkPts.material.dispose(); } catch (e) {} _sparkPts = null; }
+            if (_composer) { try { _composer.dispose(); if (_bloomPass && _bloomPass.dispose) _bloomPass.dispose(); } catch (e) {} _composer = null; _bloomPass = null; }
+            if (ren) { ren.dispose(); ren = null; }
+            scene = cam = noteG = beatG = lblG = fretG = tuningLblG = null;
+            ambLight = dirLight = null;
+            mStr = []; mGlow = []; mSus = []; mStrHitOutline = []; mAccentOutline = []; mAccentCore = []; mAccentHaloNear = []; mAccentHaloMid = []; mAccentHaloFar = []; _accentShellsByString = []; mWhiteOutline = mSusOutline = null; mMissOutline = null; mHitSusOutline = null; stringLines = []; stringLineGlows = []; _boardPlaneMat = null; fretWireMats = []; fretTubeGeo?.dispose?.(); fretTubeGeo = null;
+            for (const m of _inlayMats) m?.dispose?.(); _inlayMats = []; _inlayLabels = [];
+            // mTapChevron: dispose explicitly — if no tap marker ever
+            // spawned a pooled mesh, the scene.traverse() pass above never
+            // reaches this material.
+            mTapChevron?.dispose?.();
+            mTapChevron = null;
+            // mBarre is a shared material that all pBarreLine pool meshes
+            // reference. If no barre chord ever appears, the pool factory
+            // is never called, so no mesh carries mBarre into the scene
+            // and scene.traverse() will miss it. Dispose explicitly here
+            // to avoid leaking the GPU resource across panel lifecycles.
+            // Three.js dispose() is idempotent, so calling it before or
+            // after scene.traverse() is safe in both the instantiated and
+            // uninstantiated cases.
+            mBarre?.dispose?.(); mBarre = null;
+            _paletteColorTmp = null;
+            lyricsCanvas = lyricsCtx = null;
+            projMeshArr = null;
+            _probe = null;
+            _drawNextByString = null; _drawRecentByString = null;
+            _susVerdictLatch.clear();
+            _drawChordTemplates = null;
+            _drawAnchors = null;
+            _laneTargetColor = null;
+            _fwHitColor = _fwHitEmissive = null;
+            _fwHitGlow.fill(0);
+            _fwChordAcc.clear();
+            _fwHitPrevTime = -Infinity;
+            _renderScale = 1;
+            mBeatM = mBeatQ = null;
+            pNote = pNoteEdge = pSus = pSusOutline = pSusRibbon = pSusRibbonOl = pLbl = pBeat = pSec = null;
+            pFretLbl = pLane = pLaneDivider = pGhostFretLbl = pChordBox = pChordFrameFill = pChordLbl = pBarreLine = pArpBracket = pNoteFretLabel = pConnectorLine = pDropLine = pTapChevron = pAccentHalo = pHaloBar = pPMXFill = pFHXFill = pMuteXLines = pFHXLines = pTeachMarkLbl = null;
+            if (gPMXFill) { gPMXFill.dispose(); gPMXFill = null; }
+            if (gFHXFill) { gFHXFill.dispose(); gFHXFill = null; }
+            if (gPMXLines) { gPMXLines.dispose(); gPMXLines = null; }
+            if (gFHXLines) { gFHXLines.dispose(); gFHXLines = null; }
+            mLaneOdd = mLaneEven = mLaneDivider = mLaneDividerArp = gLanePlane = gGhostFretPlane = null;
+            chordFrameGradTex = chordFrameGradTexArp = null;
+            pFretColMarker = null;
+            _fretMarkerWaveCache.clear();
+            gNote = gSus = gBeat = gTapChevron = null;
+            tgtX = curX = xFretMid(CAM_LOCK_CENTER_FRET); tgtDist = curDist = CAM_DIST_BASE; tgtLookY = curLookY = 0; _fretRowFitBoost = 1; nStr = NSTR; _oobStringWarned = false;
+            _lookaheadCamX = xFretMid(CAM_LOCK_CENTER_FRET);
+            _lookaheadFretSpan = DEFAULT_LOOKAHEAD_FRET_SPAN;
+            _lookaheadCamPrevNow = null;
+            _lookaheadLowBonusU = 0;
+            _lookaheadHiNeckLatch = false;
+            _measureStarts = []; _measureStartsRef = null;
+            _clkAudioT = NaN; _clkPerf = NaN; _clkRate = 1; _frameNow = 0;
+            prevLowFretBonus = 0;
+            prevLockActive = false;
+            _camSnapped = false;
+            _camPreScanned = false;
+            _songKey = null;
+            _slideTargetSet = null;
+            _slideTargetNotesRef = null;
+            _slideTargetChordsRef = null;
+        }
+
+        function canvasSize(canvas) {
+            if (canvas) {
+                // If the canvas has zero bounds (hidden via any mechanism — inline style,
+                // CSS class, or hidden ancestor) fall back to the parent container
+                // (the splitscreen panelDiv) which is always visible and correctly sized.
+                const rect = canvas.getBoundingClientRect();
+                const target = (rect.width === 0 || rect.height === 0) && canvas.parentNode ? canvas.parentNode : canvas;
+                const sz = target === canvas ? rect : target.getBoundingClientRect();
+                if (sz.width > 0 && sz.height > 0) return { w: sz.width, h: sz.height };
+            }
+            // Reserve the full bottom area: #player-footer wraps the Section
+            // Practice bar + #player-controls. Fall back to #player-controls.
+            const ch = (document.getElementById('player-footer')
+                || document.getElementById('player-controls'))?.offsetHeight || 50;
+            return { w: innerWidth, h: innerHeight - ch };
+        }
+
+        /* ── setRenderer contract ────────────────────────────────────────── */
+        return {
+            // Tells highway.js this renderer needs a webgl2-capable canvas.
+            // Browsers lock a <canvas> to the first context type acquired,
+            // so when this renderer is installed mid-session highway.js
+            // replaces the underlying <canvas> element so getContext('webgl2')
+            // can succeed (see static/highway.js _replaceCanvas).
+            contextType: 'webgl2',
+            init(canvas, bundle) {
+                _unsubscribeFocus();
+                if (wrap || ren) {
+                    teardown();
+                }
+                _destroyed = _isReady = false;
+                _isFocused = true;
+                if (!_paneUid) _paneUid = ++_aspectPaneCounter;   // fallback pane id (no-arrangement panes)
+                _registerTunerShortcut();   // session-global tuner shortcut (self-guarded)
+                const myToken = ++_initToken;
+                highwayCanvas = canvas;
+                _invertedCached = !!(bundle && bundle.inverted);
+                _leftyCached = !!(bundle && bundle.lefty);
+                _renderScale = (bundle && bundle.renderScale) || 1;
+                // Per-render background opt-out. A plugin borrowing the highway as
+                // a visualization can set bundle.bgReactive === false to suppress
+                // the audio-reactive background for THIS instance only — without
+                // writing the shared h3d_bg_* settings (which would also change the
+                // host's own highway). Motivation: the reactive bg taps the core
+                // <audio> element, and when another consumer already holds it the
+                // setup throws + the cleanup AudioContext.close() is an audible
+                // click — which a borrower that never taps <audio> (e.g. a
+                // contained-playback practice plugin) inherits for no benefit.
+                // Default behavior is unchanged when the field is absent.
+                _bgReactiveOptOut = !!(bundle && bundle.bgReactive === false);
+
+                if (_ssActive()) {
+                    window.feedBackSplitscreen.onFocusChange(_onFocusChange);
+                    _focusSubscribed = true;
+                }
+
+                // Async-ready contract (feedBack#36 readyPromise). Resolves
+                // when Three.js loaded + scene initialised (_isReady = true).
+                // Rejects on any async failure so highway.js can revert.
+                let _resolveReady, _rejectReady;
+                this.readyPromise = new Promise((res, rej) => {
+                    _resolveReady = res;
+                    _rejectReady = rej;
+                });
+                // Shared rejection for superseded init cycles (destroy() or a
+                // newer init() started before this one completed). highway.js
+                // ignores the rejection when the renderer is no longer active.
+                const _rejectSuperseded = () => _rejectReady(new Error('superseded'));
+
+                loadThree().then(() => {
+                    if (_destroyed || _initToken !== myToken) {
+                        _rejectSuperseded();
+                        return;
+                    }
+                    try {
+                        nStr = resolveStringCount(bundle);
+                        _invertedForBoard = _invertedCached;
+                        _leftyForBoard = _leftyCached;
+                        if (!initScene()) { _unsubscribeFocus(); _rejectReady(new Error('initScene failed')); return; }
+                        // Pre-compile shaders + upload deterministic label
+                        // textures while the load spinner is still up; the
+                        // chart-dependent half runs on first draw() (bundle
+                        // arrays are only guaranteed populated post-ready).
+                        _prewarmStatic();
+                        _chartPrewarmed = false;
+                        const sz = canvasSize(highwayCanvas);
+                        // Mark ready before RAF so any resize(w,h) calls that arrive
+                        // in the meantime (e.g. from sizeCanvases()) are applied directly.
+                        _isReady = true;
+                        _resolveReady();
+                        _updateFocusState();
+                        if (sz.w > 0 && sz.h > 0) {
+                            applySize(sz.w, sz.h);
+                        } else {
+                            // Panel container not yet laid out (sizeCanvases() runs after
+                            // initPanel() in the setup sequence). Retry each frame until
+                            // the panelDiv has real dimensions.
+                            (function retrySize() {
+                                if (_destroyed || !_isReady) return;
+                                const s = canvasSize(highwayCanvas);
+                                if (s.w > 0 && s.h > 0) applySize(s.w, s.h);
+                                else requestAnimationFrame(retrySize);
+                            })();
+                        }
+                    } catch (e) {
+                        console.error('[3D-Hwy] init .then() threw:', e);
+                        _isReady = false;
+                        _unsubscribeFocus(); teardown();
+                        _rejectReady(e);
+                    }
+                }).catch(e => {
+                    if (_initToken !== myToken || _destroyed) {
+                        _rejectSuperseded();
+                        return;
+                    }
+                    console.error('[3D-Hwy] Three.js unavailable:', e);
+                    _unsubscribeFocus();
+                    _rejectReady(e);
+                });
+            },
+
+            // The host throttles paused frames to ~10 fps, on the assumption
+            // that a paused chart is a static picture and re-rendering it is
+            // pure waste (highway-constants._PAUSED_FRAME_INTERVAL_MS).
+            //
+            // That stopped being true when the venue landed. The venue backdrop
+            // is a PLAYING VIDEO and the crowd reacts on its own clock, and they
+            // are drawn into this same canvas as the highway — so throttling the
+            // highway throttled the whole room. Pausing the song dropped the
+            // venue, the crowd and the stage to 10 fps.
+            //
+            // Two independent sources of motion, and BOTH must keep their frames:
+            //
+            //  • a crowd video rolling on its own clock (career venue pack), and
+            //  • the venue scene's own fake-depth motion — the backdrop breathes,
+            //    the haze drifts, warmth pulses, the shimmer moves. That is
+            //    Math.sin(t) in the draw loop (see _venueApplyFakeDepthMotion),
+            //    so it only moves while we are actually given frames, and it runs
+            //    with NO pack at all.
+            //
+            // The throttle fires whenever the CHART CLOCK is stalled — which is
+            // not just a pause. A count-in and the credits/author overlay stall it
+            // exactly the same way, so the venue was stuttering there too.
+            //
+            // With no venue at all (plain 3D highway) the paused scene really is a
+            // still picture: motion mode reads 'off', we claim nothing, and the
+            // throttle still saves the GPU as #654 intended.
+            needsContinuousFrames() {
+                if (!_isReady || _ctxLost) return false;
+                for (const v of _venueCrowdVideos) {
+                    if (v && !v.paused && !v.ended && v.readyState >= 2) return true;
+                }
+                // 'off' also covers prefers-reduced-motion and "no venue scene".
+                try { return _venueEffectiveMotionMode() !== 'off'; } catch (_) { return false; }
+            },
+
+            draw(bundle) {
+                if (!_isReady) return;
+                if (_ctxLost) return;   // GPU context lost (alt-tab / reset) — skip until restored
+                if (!_chartPrewarmed) {
+                    _chartPrewarmed = true;
+                    _prewarmChart(bundle);
+                }
+                _invertedCached = !!bundle.inverted;
+                _leftyCached = !!bundle.lefty;
+                const newNStr = resolveStringCount(bundle);
+                const newScale = bundle.renderScale || 1;
+                const leftyChanged = _leftyCached !== _leftyForBoard;
+                if (_invertedCached !== _invertedForBoard || leftyChanged || newNStr !== nStr) {
+                    if (newNStr !== nStr) {
+                        _oobStringWarned = false;
+                        // Drop chord caches computed under the old string count
+                        // so extended-range notes (string 6+) aren't left
+                        // filtered out of cached shapes.
+                        _resetStringDependentCaches();
+                    }
+                    if (leftyChanged) {
+                        curX = -curX;
+                        tgtX = -tgtX;
+                        _lookaheadCamX = -_lookaheadCamX;
+                    }
+                    nStr = newNStr;
+                    buildBoard();
+                    _invertedForBoard = _invertedCached;
+                    _leftyForBoard = _leftyCached;
+                }
+                if (newScale !== _renderScale) {
+                    _renderScale = newScale;
+                    const s = canvasSize(highwayCanvas);
+                    if (s.w > 0 && s.h > 0) applySize(s.w, s.h);
+                }
+                // Keep the render matched to the highway canvas's real box.
+                // Two independent drifts to catch each frame:
+                //  1. Backing store (canvas.width/height) changed out from under
+                //     us — e.g. the splitscreen hw.resize override resizes the
+                //     element but never calls renderer.resize(). Also re-sizes
+                //     the lyrics overlay canvas via applySize().
+                //  2. The CSS box (canvasSize()) drifted while the backing store
+                //     held. #highway is flex:1, so its rendered height changes as
+                //     the player layout settles right after a song opens — with
+                //     no backing-store change and no window 'resize' event, so the
+                //     check above never fires. Without this the camera stays framed
+                //     for the pre-settle (too-tall) size and crops the near strings
+                //     / fret numbers until the user un/re-maximizes the window.
+                if (highwayCanvas) {
+                    // Backing-store drift (branch 1) is detected with cheap
+                    // property reads every frame. The CSS-box checks (branches
+                    // 2/3) need canvasSize() → getBoundingClientRect(), a
+                    // forced layout read — profiled at ~1.2% of throttled
+                    // main-thread time when run per frame. Throttle the box
+                    // read to every 10th frame (plus whenever the backing
+                    // store changed or the wrap isn't pinned yet): the layout
+                    // settle it exists to catch plays out over hundreds of ms
+                    // right after a song opens, so a ~166 ms detection cadence
+                    // loses nothing visible.
+                    const _bsChanged = highwayCanvas.width !== _lastHwW
+                        || highwayCanvas.height !== _lastHwH;
+                    _boxCheckCountdown = (_boxCheckCountdown + 1) % 10;
+                    if (_bsChanged || !_wrapPinned || _boxCheckCountdown === 0) {
+                        const box = canvasSize(highwayCanvas);
+                        if (_bsChanged) {
+                            _lastHwW = highwayCanvas.width;
+                            _lastHwH = highwayCanvas.height;
+                            if (box.w > 0 && box.h > 0) applySize(box.w, box.h);
+                        } else if (box.w > 0 && box.h > 0 &&
+                                (Math.abs(box.w - _appliedW) > 1 || Math.abs(box.h - _appliedH) > 1)) {
+                            applySize(box.w, box.h);
+                        } else if (!_wrapPinned && box.w > 0 && box.h > 0 &&
+                                highwayCanvas.offsetWidth > 0 && highwayCanvas.offsetHeight > 0) {
+                            //  3. The overlay pin couldn't be applied at init because
+                            //     #highway had no layout yet (offsetWidth/Height === 0),
+                            //     so applySize() only set the wrap height. The canvas has
+                            //     now laid out but to the same logical size, so neither
+                            //     drift branch above fires — re-run applySize to pin the
+                            //     wrap to the canvas box now that its offsets are real.
+                            //     Otherwise the overlay stays at top:0;left:0;right:0 and
+                            //     a strip of #highway is exposed on first load / split.
+                            applySize(box.w, box.h);
+                        }
+                    }
+                }
+                update(bundle);
+                camUpdate(bundle);
+
+                // Background animations (#13). Compute frame dt once,
+                // read audio bands when reactivity is on, delegate to
+                // the active style's update().
+                if (bgGroup && _bgEffectiveStyleId() !== 'off') {
+                    const nowMs = performance.now();
+                    const dt = _bgLastT === 0 ? 1 / 60 : Math.min(0.1, (nowMs - _bgLastT) / 1000);
+                    _bgLastT = nowMs;
+                    const bands = bgReactive ? _bgReadBands() : BG_ZERO_BANDS;
+                    const style = BG_STYLES[_bgEffectiveStyleId()];
+                    if (style && bgState) {
+                        try { style.update(bgState, bands, dt, nowMs / 1000); }
+                        catch (e) { console.error('[3D-Hwy] bg update threw', _bgEffectiveStyleId(), e); }
+                    }
+                }
+
+                // Browser: the shared analyser can change between songs (a sloppak
+                // stems swap replaces it, often on a new context) — or may not have
+                // existed when the controller mounted. Keep the visualizer bound to
+                // the LIVE analyser by comparing against what the controller
+                // actually bound (boundAnalyser()), not a separately-tracked guess:
+                // cheap reconnect when it's the same context, full controller
+                // rebuild when the context changed (cross-context connectAudio is
+                // impossible). Only act once the viz is ready (ready()), so we
+                // don't thrash a controller that's still loading async. Done before
+                // the render block so a rebuild this frame just skips one bc frame
+                // (bcCtrl goes null) without affecting the highway's own render.
+                if (bcCtrl && !_bcIsDesktop() && bcCtrl.ready && bcCtrl.ready()) {
+                    let a = null;
+                    try { a = _bgGetAnalyser(); } catch (e) { a = null; }
+                    const an = a && a.analyser;
+                    const bound = bcCtrl.boundAnalyser ? bcCtrl.boundAnalyser() : null;
+                    if (an && an !== bound) {
+                        if (!(bcCtrl.reconnectAudio && bcCtrl.reconnectAudio(a))) {
+                            // Context changed (or reconnect failed) — rebuild via the
+                            // proven destroy/create paths so the new context binds.
+                            try { bcCtrl.destroy(); } catch (e) {}
+                            bcCtrl = null;
+                            _bcSyncMode();
+                        }
+                    }
+                }
+                if (bcCtrl) {
+                    const cfg = _bcLoadSettings();
+                    const _ct = bundle.currentTime || 0;
+                    if (cfg.chartAccents) {
+                        if (_ct < _chartPrevT - 0.08 || _ct - _chartPrevT > 1.0) {
+                            _bcBeatIdx = _bcFfIdx(bundle.beats, _ct, 'time');
+                            _bcNoteIdx = _bcFfIdx(bundle.notes, _ct, 't');
+                            _bcChordIdx = _bcFfIdx(bundle.chords, _ct, 't');
+                        }
+                        const _beats = bundle.beats || [];
+                        while (_bcBeatIdx < _beats.length && _beats[_bcBeatIdx].time <= _ct) {
+                            const strong = _beats[_bcBeatIdx].measure !== undefined && _beats[_bcBeatIdx].measure !== -1;
+                            _chartEnv = Math.max(_chartEnv, strong ? 1.0 : 0.6);
+                            _bcBeatIdx++;
+                        }
+                        const _notes = bundle.notes || [];
+                        let _tintS = -1;
+                        while (_bcNoteIdx < _notes.length && _notes[_bcNoteIdx].t <= _ct) {
+                            _chartEnv = Math.max(_chartEnv, 0.6);
+                            _tintS = _notes[_bcNoteIdx].s;
+                            _bcNoteIdx++;
+                        }
+                        const _chords = bundle.chords || [];
+                        while (_bcChordIdx < _chords.length && _chords[_bcChordIdx].t <= _ct) {
+                            _chartEnv = Math.max(_chartEnv, 0.95);
+                            _bcChordIdx++;
+                        }
+                        if (_tintS >= 0 && activePalette && activePalette.length) {
+                            _bcTintTarget = activePalette[((_tintS % activePalette.length) + activePalette.length) % activePalette.length];
+                        }
+                        _chartPrevT = _ct;
+                        _chartEnv *= 0.86;
+                        bcCtrl.chart(_chartEnv * (cfg.chartStrength != null ? cfg.chartStrength : 1));
+                    } else {
+                        bcCtrl.chart(0);
+                    }
+                    if (cfg.colorTint && _bcTintTarget != null) {
+                        const tr = (_bcTintTarget >> 16) & 255, tg = (_bcTintTarget >> 8) & 255, tb = _bcTintTarget & 255;
+                        _tintR += (tr - _tintR) * 0.06; _tintG += (tg - _tintG) * 0.06; _tintB += (tb - _tintB) * 0.06;
+                        bcCtrl.tint((Math.round(_tintR) << 16) | (Math.round(_tintG) << 8) | Math.round(_tintB), cfg.tintStrength != null ? cfg.tintStrength : 0.65);
+                    } else {
+                        bcCtrl.tint(null, 0);
+                    }
+                    bcCtrl.render();
+                }
+                {
+                    const _jNow = performance.now();
+                    const _jdt = _juiceLastT === 0 ? 1 / 60 : Math.min(0.05, (_jNow - _juiceLastT) / 1000);
+                    _juiceLastT = _jNow;
+                    _sparkUpdate(_jdt);
+                    _streakHeat += (Math.min(1, _streakHits / 16) - _streakHeat) * 0.08;   // #7 ease heat
+                }
+                {
+                    const comp = (_bloom && !_ssActive()) ? _bloomEnsure() : null;
+                    if (comp) {
+                        const bsz = canvasSize(highwayCanvas);
+                        if (bsz && bsz.w > 0 && bsz.h > 0 && (bsz.w !== _bloomW || bsz.h !== _bloomH)) {
+                            comp.setSize(bsz.w | 0, bsz.h | 0); _bloomW = bsz.w | 0; _bloomH = bsz.h | 0;
+                        }
+                        if (ren.toneMapping !== T.ACESFilmicToneMapping) ren.toneMapping = T.ACESFilmicToneMapping;
+                        pbBeg(6); comp.render(); pbEnd(6);
+                    } else {
+                        if (ren.toneMapping !== T.NoToneMapping) ren.toneMapping = T.NoToneMapping;
+                        pbBeg(6); ren.render(scene, cam); pbEnd(6);
+                    }
+                }
+                if (lyricsCtx && lyricsCanvas) {
+                    lyricsCtx.clearRect(0, 0, lyricsCanvas.width, lyricsCanvas.height);
+                    // Capture the actual lyrics-banner bottom so overlay cards
+                    // step down past every wrapped row, not just a 2-row estimate.
+                    let lyricsBottom = 0;
+                    if (bundle.lyricsVisible && bundle.lyrics?.length) {
+                        lyricsBottom = drawLyrics(bundle.lyrics, bundle.currentTime, lyricsCtx, lyricsCanvas.width, lyricsCanvas.height) || 0;
+                    }
+                    drawNotedetectLabels(lyricsCtx, lyricsCanvas.width, lyricsCanvas.height);
+                    drawScoreFx(lyricsCtx, lyricsCanvas.width, lyricsCanvas.height);
+
+                    // Corner-stacking: overlays drawn first claim the topmost slot;
+                    // later overlays are pushed down by the accumulated height + gap.
+                    // Draw order (top → bottom per corner):
+                    //   1. FPS counter  — always first
+                    //   2. Section HUD
+                    //   3. Tone HUD
+                    //   4. Chord diagram — always last
+                    const STACK_GAP = 8;
+                    const cornerStack = { tl: 0, tr: 0, bl: 0, br: 0 };
+                    const stackPush = (pos, h) => {
+                        if (pos in cornerStack && h > 0) cornerStack[pos] += h + STACK_GAP;
+                    };
+
+                    // 1. FPS counter (always top-right, always topmost).
+                    // EMA update runs unconditionally so the smoothed value is accurate
+                    // even when fpsVisible is off.
+                    const _fpsNowMs = performance.now();
+                    if (_fpsLastT > 0) {
+                        const dt = _fpsNowMs - _fpsLastT;
+                        if (dt > 0) {
+                            const inst = 1000 / dt;
+                            _fpsEma = _fpsEma === 0 ? inst : _fpsEma + (inst - _fpsEma) * (1 / 30);
+                        }
+                    }
+                    _fpsLastT = _fpsNowMs;
+                    if (fpsVisible) {
+                        if (_fpsNowMs - _fpsLastSampleT > 250) {
+                            _fpsDisplay = _fpsEma;
+                            _fpsLastSampleT = _fpsNowMs;
+                        }
+                        const W = lyricsCanvas.width;
+                        const H = lyricsCanvas.height;
+                        const txt = _fpsDisplay.toFixed(1) + ' fps';
+                        lyricsCtx.save();
+                        lyricsCtx.font = 'bold 14px ui-monospace, Menlo, Consolas, monospace';
+                        lyricsCtx.textAlign = 'right';
+                        lyricsCtx.textBaseline = 'top';
+                        const _fpsPadX = 8, _fpsPadY = 4;
+                        const _fpsMetrics = lyricsCtx.measureText(txt);
+                        const _fpsBoxW = Math.ceil(_fpsMetrics.width) + _fpsPadX * 2;
+                        const _fpsBoxH = 14 + _fpsPadY * 2;
+                        const _fpsE = 8;
+                        // Keep it top-right but below the v3 Up Next pill / live HUD
+                        // (whichever is showing) so the readout is never occluded.
+                        const _fpsBaseY = Math.round(Math.max(
+                            _fpsE + H * 0.06,
+                            lyricsBottom + _fpsE,
+                            _v3TopRightChromeBottom() + _fpsE,
+                        ));
+                        const _fpsX = W - 8 - _fpsBoxW;
+                        const _fpsY = _fpsBaseY + cornerStack['tr'];
+                        lyricsCtx.fillStyle = 'rgba(0,0,0,0.55)';
+                        lyricsCtx.fillRect(_fpsX, _fpsY, _fpsBoxW, _fpsBoxH);
+                        lyricsCtx.fillStyle = _fpsDisplay >= 55 ? '#7fff9a'
+                            : _fpsDisplay >= 30 ? '#ffe84d' : '#ff6b6b';
+                        lyricsCtx.fillText(txt, _fpsX + _fpsBoxW - _fpsPadX, _fpsY + _fpsPadY);
+                        lyricsCtx.restore();
+                        stackPush('tr', _fpsBoxH);
+                    }
+
+                    // 2. Section HUD.
+                    if (sectionHudVisible && bundle.sections && bundle.sections.length) {
+                        const secH = drawSectionHud(lyricsCtx, {
+                            sections: bundle.sections,
+                            currentTime: bundle.currentTime,
+                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
+                            position: sectionHudPosition,
+                            sizeSlider: sectionHudSize,
+                            lyricsBottom,
+                            stackOffset: cornerStack[sectionHudPosition] || 0,
+                        });
+                        stackPush(sectionHudPosition, secH);
+                    }
+
+                    // 3. Tone HUD.
+                    if (toneHudVisible && (bundle.toneChanges?.length || bundle.toneBase)) {
+                        const toneH = drawToneHud(lyricsCtx, {
+                            toneChanges: bundle.toneChanges,
+                            toneBase: bundle.toneBase,
+                            currentTime: bundle.currentTime,
+                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
+                            position: toneHudPosition,
+                            sizeSlider: toneHudSize,
+                            lyricsBottom,
+                            stackOffset: cornerStack[toneHudPosition] || 0,
+                        });
+                        stackPush(toneHudPosition, toneH);
+                    }
+
+                    // 4. Chord diagram — always last (bottommost in the stack).
+                    // Draw outgoing first so the incoming diagram renders on top,
+                    // making the entrance scale-in animation visible during crossfades.
+                    // The outgoing (prev) diagram uses the same corner slot — it is
+                    // fading out while the incoming one fades in, so they share the
+                    // same stack position and don't double-count the height.
+                    if (chordDiagramVisible && _diagPrev && _diagPrevOpacity > 0) {
+                        _drawDiagramCached(lyricsCtx, {
+                            name: _diagPrev.name, frets: _diagPrev.frets,
+                            opacity: _diagPrevOpacity,
+                            entranceT: (_diagPrev.t !== undefined)
+                                ? Math.min(1.0, Math.max(0, (bundle.currentTime - _diagPrev.t) / DIAG_ENTRANCE_S))
+                                : 1.0,
+                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
+                            inverted: _invertedCached,
+                            sizeSlider: chordDiagramSize, position: chordDiagramPosition,
+                            nStr: _diagPrev.nStr ?? nStr,
+                            lyricsBottom,
+                            stackOffset: cornerStack[chordDiagramPosition] || 0,
+                        });
+                        // Don't push here — outgoing and incoming share the same slot.
+                    }
+                    if (chordDiagramVisible && _diagChord) {
+                        const diagH = _drawDiagramCached(lyricsCtx, {
+                            name: _diagChord.name, frets: _diagChord.frets,
+                            opacity: Math.max(0, 1 + (_diagChord.t - bundle.currentTime) / DIAG_LINGER_S),
+                            entranceT: _diagEntranceT,
+                            canvasW: lyricsCanvas.width, canvasH: lyricsCanvas.height,
+                            inverted: _invertedCached,
+                            sizeSlider: chordDiagramSize, position: chordDiagramPosition,
+                            nStr: _diagChord.nStr ?? nStr,
+                            lyricsBottom,
+                            stackOffset: cornerStack[chordDiagramPosition] || 0,
+                        });
+                        stackPush(chordDiagramPosition, diagH);
+                    }
+                }
+                // Draw-hook compatibility: fire hooks registered via
+                // window.highway.addDrawHook() on our 2D overlay canvas
+                // so overlay plugins (fretboard, chord-label HUDs, etc.)
+                // continue to render when the 3D renderer is active.
+                // The hooks expect a 2D context — lyricsCtx is exactly
+                // that, positioned above the WebGL surface.
+                if (lyricsCtx && lyricsCanvas &&
+                        window.highway &&
+                        typeof window.highway.fireDrawHooks === 'function') {
+                    window.highway.fireDrawHooks(
+                        lyricsCtx, lyricsCanvas.width, lyricsCanvas.height
+                    );
+                }
+            },
+
+            resize(w, h) {
+                if (!_isReady) return;
+                const s = canvasSize(highwayCanvas);
+                applySize(s.w > 0 ? s.w : w, s.h > 0 ? s.h : h);
+            },
+
+            destroy() {
+                _destroyed = true; _isReady = false; _diagChord = null; _diagPrev = null; _diagLastKey = null; _diagRenderCache.clear();
+                _lastHwW = 0; _lastHwH = 0;
+                _appliedW = 0; _appliedH = 0;
+                _paneAspect = 0;
+                if (cam && cam.fov !== BASE_VFOV) { cam.fov = BASE_VFOV; cam.updateProjectionMatrix(); }
+                _wrapPinned = false;
+                _unsubscribeFocus(); teardown();
+                highwayCanvas = null;
+            },
+        };
+    }
+
+    window.feedBackViz_highway_3d = createFactory;
+    // Per-panel control descriptors (splitscreen). The palette selector was
+    // removed — per-string colors are set via the core "Highway String Colors"
+    // UI, which drives both highways by named string.
+    window.feedBackViz_highway_3d.panelControls = [
+        {
+            key: 'cameraSmoothing',
+            label: 'Camera smoothing (X-pan)',
+            type: 'range',
+            min: 0,
+            max: 1,
+            step: 0.05,
+            default: BG_DEFAULTS.cameraSmoothing,
+        },
+        {
+            key: 'cameraLockLow',
+            label: 'Lock camera at frets 1-12',
+            type: 'toggle',
+            default: BG_DEFAULTS.cameraLockLow,
+        },
+        {
+            key: 'cameraLockZoom',
+            label: 'Locked zoom (In ↔ Out)',
+            type: 'range',
+            min: 0,
+            max: 1,
+            step: 0.05,
+            default: BG_DEFAULTS.cameraLockZoom,
+        },
+    ];
+    // Static metadata exposed on the factory:
+    //   panelControls      - optional, host-readable descriptors for a
+    //                        curated per-panel control surface. Renderer
+    //                        values still flow through _bgLoadSettings().
+    //   contextType        - required canvas context type. highway.js
+    //                        replaces the <canvas> element when the
+    //                        requested type differs from the current one,
+    //                        so this renderer can be installed mid-session
+    //                        even if the canvas was previously bound to 2D.
+    //   matchesArrangement - Auto-mode predicate. When the picker is on
+    //                        "Auto", core installs the first registered
+    //                        viz whose predicate returns truthy on the
+    //                        current song_info. Lead/Rhythm/Bass/Guitar
+    //                        arrangements route here; Keys arrangements
+    //                        are matched by the piano plugin instead.
+    //                        _canRun3D() in app.js still gates Auto from
+    //                        picking us on machines without WebGL2.
+    window.feedBackViz_highway_3d.contextType = 'webgl2';
+    window.feedBackViz_highway_3d.__test = {
+        getAnalyserForBridgeTest: _bgGetAnalyser,
+        readBandsForBridgeTest: _bgReadBands,
+        resetAnalyserBridgeForTest() { _bgBridgeKeys.clear(); _bgAudio = null; _bgAudioCore = null; _bgAudioFailedAt = 0; },
+    };
+    // Canonical guitar arrangement names (server.py: _ALLOWED_ARRANGEMENT_NAMES)
+    // are Lead / Rhythm / Bass / Combo. `guitar` is included as a safety
+    // net for sources that use a generic name (older imports, third-party
+    // sloppaks). Word boundaries (\b) keep us from accidentally matching
+    // arrangements that merely contain these as substrings (e.g. a
+    // "BasslineKeys" arrangement would otherwise match `bass`).
+    window.feedBackViz_highway_3d.matchesArrangement = function (songInfo) {
+        const arr = (songInfo && songInfo.arrangement) || '';
+        return /\b(?:lead|rhythm|bass|combo|guitar)\b/i.test(arr);
+    };
+
+    // No imperative register() call needed: feedBack#272 introduced the
+    // consolidated tour menu, which discovers this plugin's tour automatically
+    // via /api/plugins (has_tour:true from plugin.json's tour field) and
+    // gates relevance on whether highway_3d is the active viz. A register()
+    // call with only injectTriggerInto was a no-op anyway since the new menu
+    // owns trigger placement; for buildSteps / onStart / onComplete / a
+    // custom screens override, register() is still the right hook.
+
+})();