fix(highways): address review — bg-key alias, drum cam guard, resolver tests

Three review findings on the per-panel camera work:

- highway_3d: _bgPanelKey() resolved splitscreen via window.feedBackSplitscreen
  only, while _freeCamFor() uses the feedBackSplitscreen||slopsmithSplitscreen
  alias it claims to "mirror". If the rename lands, per-panel background settings
  would silently stop being per-panel while the camera stayed per-panel. Resolve
  the alias the same way in _bgPanelKey.
- drum_highway_3d: applyCamera()'s "before first positionCamera()" guard tested
  `_camBaseH == null`, but _camBaseH/_camBaseD were initialized to 0, so the guard
  never fired (and could apply a base-0 pose for a frame). Initialize to null.
- keys + drum: the PR claimed the Camera Director resolver was unit-checked, but
  nothing exercised it. Extract the resolver into pure, exported helpers
  (_resolveFreeCam + _ssApi), delegate the per-instance _freeCamFor to them, and
  add tests/camera_bridge.test.js covering per-panel select, global fallback,
  null-when-absent, throw-safety, and the slopsmith-alias resolution. Drum 15→21,
  keys 50→56, all pass; behavior unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Kris Anderson <topkoa@gmail.com>

plugins/drum_highway_3d/screen.js

@@ -1361,6 +1361,29 @@
         } catch (_) { /* dispatch unavailable — persisted value applies next init */ }
     };
 
+    /* ======================================================================
+     *  Camera Director bridge resolver (pure — exported via createFactory.__test)
+     * ====================================================================== */
+
+    // Resolve the active splitscreen API, defensive on the global-name rename in
+    // flight (feedBackSplitscreen is canonical; slopsmithSplitscreen is the legacy
+    // alias). Returns null when splitscreen isn't present.
+    function _ssApi() { return window.feedBackSplitscreen || window.slopsmithSplitscreen || null; }
+
+    // Given the splitscreen API, THIS window's per-panel camera map, and the
+    // global camera, return this panel's camera under splitscreen, else the
+    // global, else null (Camera Director absent → stock framing). Throw-safe on
+    // panelIndexFor so a misbehaving splitscreen build can't break framing.
+    function _resolveFreeCam(canvas, ss, panelsMap, globalCam) {
+        if (panelsMap && ss && typeof ss.panelIndexFor === 'function') {
+            try {
+                const i = ss.panelIndexFor(canvas);
+                if (i != null && panelsMap[i]) return panelsMap[i];
+            } catch (e) { /* ignore */ }
+        }
+        return globalCam || null;
+    }
+
     /* ======================================================================
      *  Renderer factory
      * ====================================================================== */
@@ -1414,7 +1437,7 @@
         let _sparkPts = null, _sparkPos = null, _sparkCol = null, _sparkVel = null, _sparkLife = null;
         let _fxLastWall = 0;          // wall clock for FX integration (sparks, pulse decay)
         let _kickPulse = 0;           // kick-hit camera-dip + floor-wash envelope
-        let _camBaseH = 0, _camBaseD = 0;  // positionCamera's unpulsed pose
+        let _camBaseH = null, _camBaseD = null;  // positionCamera's unpulsed pose (null until it first runs; applyCamera's guard depends on this)
         let _gaussTex = null;         // shared soft-falloff texture for flash quads
         let _laneFlashQuads = [];     // pooled additive quad per hand lane (z=0)
         let _kickFlashQuad = null;    // full-width flash quad for the kick bar
@@ -2651,23 +2674,12 @@
             cam.lookAt(0, 0, -AHEAD * TS * 0.45);
         }
 
-        // 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); null when Camera Director is
-        // absent → 100% stock framing. Defensive on the splitscreen global name
-        // (rename in flight: feedBackSplitscreen vs slopsmithSplitscreen).
+        // Camera Director bridge for THIS panel — delegates to the pure, unit-
+        // tested _resolveFreeCam / _ssApi (see the resolver block above the
+        // factory). Reads the live globals: per-panel map __h3dCamCtlPanels →
+        // this panel's camera, else the global __h3dCamCtl, else null (stock).
         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);
-                        if (i != null && map[i]) return map[i];
-                    } catch (e) { /* ignore */ }
-                }
-            }
-            return window.__h3dCamCtl || null;
+            return _resolveFreeCam(canvas, _ssApi(), window.__h3dCamCtlPanels, window.__h3dCamCtl);
         }
 
         // Per-frame camera write: static base pose (positionCamera) + kick-pulse Y
@@ -3617,6 +3629,8 @@
     // vm-loaded with no DOM/WebGL; everything here must stay side-effect
     // free to call).
     window.slopsmithViz_drum_highway_3d.__test = {
+        _resolveFreeCam,
+        _ssApi,
         _variantForHit,
         _classifyTiming,
         readFxSettings,

plugins/drum_highway_3d/tests/camera_bridge.test.js

@@ -0,0 +1,68 @@
+// Camera Director bridge resolver tests: per-panel select, global fallback,
+// null-when-absent, throw-safety, and the splitscreen global-name alias. Loads
+// screen.js in a bare vm window and exercises the __test exports (no DOM/WebGL).
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const vm = require('node:vm');
+
+function load() {
+    const window = {
+        console,
+        location: { protocol: 'http:', host: 'localhost' },
+        slopsmith: {},
+    };
+    window.window = window;
+    window.globalThis = window;
+    const context = vm.createContext(window);
+    const src = fs.readFileSync(path.join(__dirname, '..', 'screen.js'), 'utf8');
+    vm.runInContext(src, context, { filename: 'screen.js' });
+    return { window, __test: window.slopsmithViz_drum_highway_3d.__test };
+}
+
+test('_resolveFreeCam: per-panel camera under splitscreen', () => {
+    const { __test } = load();
+    const c0 = {}, c1 = {};
+    const ss = { panelIndexFor: (c) => (c === c0 ? 0 : 1) };
+    const map = { 0: { id: 'p0' }, 1: { id: 'p1' } };
+    assert.equal(__test._resolveFreeCam(c0, ss, map, { id: 'g' }).id, 'p0');
+    assert.equal(__test._resolveFreeCam(c1, ss, map, { id: 'g' }).id, 'p1');
+});
+
+test('_resolveFreeCam: falls back to global when there is no panel map', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, null, g), g);
+});
+
+test('_resolveFreeCam: falls back to global when the panel has no map entry', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => 3 };            // index 3 absent from map
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_resolveFreeCam: null when Camera Director is absent (no global)', () => {
+    const { __test } = load();
+    assert.equal(__test._resolveFreeCam({}, null, null, null), null);
+    assert.equal(__test._resolveFreeCam({}, { panelIndexFor: () => 0 }, {}, undefined), null);
+});
+
+test('_resolveFreeCam: throw-safe on panelIndexFor → falls back to global', () => {
+    const { __test } = load();
+    const g = { id: 'global' };
+    const ss = { panelIndexFor: () => { throw new Error('boom'); } };
+    assert.equal(__test._resolveFreeCam({}, ss, { 0: {} }, g), g);
+});
+
+test('_ssApi: null when neither global set; slopsmith alias; feedBack canonical wins', () => {
+    const { window, __test } = load();
+    assert.equal(__test._ssApi(), null);
+    const legacy = { panelIndexFor: () => 0 };
+    window.slopsmithSplitscreen = legacy;
+    assert.equal(__test._ssApi(), legacy);            // legacy alias picked up
+    const current = { panelIndexFor: () => 1 };
+    window.feedBackSplitscreen = current;
+    assert.equal(__test._ssApi(), current);           // canonical name takes precedence
+});