refactor(h3d-carve-1b): extract render-order, note-key, camera-bootstrap, fretMid to src/geometry.js

Move 9 symbols verbatim from screen.js factory scope to geometry.js:
- RENDER_ORDER_LAYER_STACK, RENDER_ORDER_LAYER_INDEX, RENDER_ORDER_AT_Z_ZERO,
  RENDER_ORDER_FAR_CLAMP — compile-time constants, now exported from geometry.js
- renderOrderForLayerAtZ — pure fn; reads K + RENDER_ORDER_* from geometry scope
- _noteKey, lowerBoundT — hot-path helpers; no external deps
- hwyFirstRelevantFrettedTime — camera bootstrap scan; no external deps
- fretMid → geoFretMid(f, uniform) — same fretX delegator pattern as Cut 1;
  screen.js keeps: const fretMid = f => geoFretMid(f, _h3dFretUniform); (1 beyond-subst)

screen.js import line updated to import all 9 new exports; tombstones replace
each original definition.

Source-scan retargets:
- highway_3d_render_order.test.js: layers()/zZeroRenderOrder() now read
  GEOMETRY_JS; the 5 renderOrderForLayerAtZ-internals asserts in
  chordFrameRenderOrder test retargeted to geo() (call-site assert stays on src()).
- highway_3d_camera_bootstrap.test.js: extractFn now reads geoSrc (GEOMETRY_JS);
  sourceBetween wiring tests remain on SCREEN_JS.
- highway_3d_panel_controls.test.js: sandbox stubs extended with 9 new names.

Class-killer tests added to highway_3d_geometry.test.js (8 new tests, 180 total):
- RENDER_ORDER_LAYER_STACK length + first/last entries
- RENDER_ORDER_LAYER_INDEX spot-checks (CHORD_FILL=0, NOTE_CORE=10)
- renderOrderForLayerAtZ far-clamp (worldZ=-5 gives 50, not 33 without max)
- renderOrderForLayerAtZ unknown-layer throws
- _noteKey |0 truncation (1.5,3)=150003 not float-derived 150008
- lowerBoundT strict lower-bound (3 in [{t:1},{t:3},{t:5}] gives 1, not 2)
- hwyFirstRelevantFrettedTime smoke (empty → null)
- geoFretMid sentinel (f=0 gives -2K≈-0.015, not 0) + ratio invariant

Mutation analysis confirmed all 8 tests fail under their named mutation before
committing (per Toby r1 lesson).

Base run (a1f7ad5): 172/172 pass.
Post-cut run: 180/180 pass.
Command: node --test tests/js/highway_3d*.test.js plugins/highway_3d/tests/*.test.js

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014uZ169yfoFYArXz962g7KW

plugins/highway_3d/screen.js

@@ -6,7 +6,7 @@
 // main player and per-panel in splitscreen without any architectural
 // changes.
 
-import { geoFretX, dZ, slideTrailEnd, camBaseDistU, camLowFretPullbackU, computeBPM, _makeGaussTex } from './src/geometry.js'; // h3d-carve-1
+import { geoFretX, dZ, slideTrailEnd, camBaseDistU, camLowFretPullbackU, computeBPM, _makeGaussTex, RENDER_ORDER_LAYER_STACK, RENDER_ORDER_LAYER_INDEX, RENDER_ORDER_AT_Z_ZERO, RENDER_ORDER_FAR_CLAMP, renderOrderForLayerAtZ, _noteKey, lowerBoundT, hwyFirstRelevantFrettedTime, geoFretMid } from './src/geometry.js'; // h3d-carve-1b
 
 (function () {
     'use strict';
@@ -971,58 +971,8 @@ import { geoFretX, dZ, slideTrailEnd, camBaseDistU, camLowFretPullbackU, compute
     /** 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;
-    }
+    // RENDER_ORDER_LAYER_STACK, RENDER_ORDER_LAYER_INDEX, RENDER_ORDER_AT_Z_ZERO,
+    // RENDER_ORDER_FAR_CLAMP, renderOrderForLayerAtZ — moved to src/geometry.js (h3d-carve-1b).
 
     /** Match `nextNoteByString` onset to this note (float + chart rounding; avoids ghost / glow flicker). */
     const NEXT_ON_STRING_T_EPS = 0.06;
@@ -1285,80 +1235,7 @@ import { geoFretX, dZ, slideTrailEnd, camBaseDistU, camLowFretPullbackU, compute
         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;
-    }
-
-    /**
-     * Return the chart time of the first fretted event that can still affect
-     * the camera at `now`, or the next fretted onset after it.
-     *
-     * This is intentionally a one-time full-chart scan. It runs only when a
-     * new song/arrangement's arrays first arrive, allowing the camera to frame
-     * the opening phrase during a silent intro instead of waiting for that
-     * phrase to enter the live targeting window. Open strings do not define a
-     * horizontal fret target, and malformed/out-of-range strings are ignored.
-     *
-     * Events already inside the behind-window, plus older sustains that are
-     * still ringing at `now`, return `now` so bootstrap framing matches the
-     * ordinary live path. Future events return their onset time.
-     */
-    function hwyFirstRelevantFrettedTime(notes, chords, now, behind, stringCount) {
-        const nStrings = Number.isFinite(stringCount) ? Math.max(0, Math.floor(stringCount)) : 0;
-        const cameraFloor = now - Math.max(0, Number(behind) || 0);
-        let first = Infinity;
-
-        const validFretted = n => n
-            && n.f > 0
-            && Number.isInteger(n.s)
-            && n.s >= 0
-            && n.s < nStrings;
-        const consider = (eventTime, sustain) => {
-            const t = Number(eventTime);
-            if (!Number.isFinite(t)) return;
-            const sus = Number(sustain);
-            const end = t + (Number.isFinite(sus) && sus > 0 ? sus : 0);
-            if (t < cameraFloor && end < now) return;
-            const relevantTime = t <= now ? now : t;
-            if (relevantTime < first) first = relevantTime;
-        };
-
-        if (notes) {
-            for (const n of notes) {
-                if (validFretted(n)) consider(n.t, n.sus);
-            }
-        }
-        if (chords) {
-            for (const ch of chords) {
-                if (!ch || !ch.notes) continue;
-                for (const cn of ch.notes) {
-                    if (validFretted(cn)) consider(ch.t, cn.sus);
-                }
-            }
-        }
-        return Number.isFinite(first) ? first : null;
-    }
+    // _noteKey, lowerBoundT, hwyFirstRelevantFrettedTime — moved to src/geometry.js (h3d-carve-1b).
 
     // Last arrangement <anchor> at or before chart time `t` (sorted by .time).
     // Mirrors static/highway.js getAnchorAt — until t reaches the first anchor’s
@@ -1540,7 +1417,7 @@ import { geoFretX, dZ, slideTrailEnd, camBaseDistU, camLowFretPullbackU, compute
         _bgEmitChange('fretSpacing');
     };
 
-    const fretMid = f => (f <= 0 ? -2 * K : (fretX(f - 1) + fretX(f)) / 2);
+    const fretMid = f => geoFretMid(f, _h3dFretUniform); // h3d-carve-1b: delegator (1 beyond-subst)
     /** 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));