feat(h3d-carve-15): extract U-section (per-frame renderer) into src/renderer.js

- createRenderer factory DI: 241 params (consts, fn-refs, 33 pool getters,
  material/settings/camera/ND getters, 35 setters)
- screen.js: tombstone + createRenderer wiring after createNoteRenderer +
  createCamera wirings (§1 ruling: createNoteRenderer called from screen.js)
- Restore createArp wiring + _resetStringDependentCaches to screen.js
  (accidentally dropped during carve; both needed in IIFE scope)
- smoothNow: correction 3 — setter form setFrameNow(v); return v (no bare
  return (_frameNow = raw))
- _applyNoteCamTargets callers: 2 sites (7940/9923); correction 2 verified
- lookaheadSmoothCamStep callers: 3 sites (9963/9974/9978); correction 2 verified
- plugin.json: bump 3.50.0 → 3.51.0

Tests (16 files updated to scan renderer.js):
- highway_3d_renderer.test.js: new, 15 tests — export contract, DI count
  (241), tombstone, caller-list corrections, smoothNow semantics, ordering
- highway_3d_arp_deferral.test.js: add renderer.js scan (deferChordGems /
  noteStreamCoversArpShape moved to renderer.js)
- highway_3d_lean_sustain.test.js: add renderer.js scan; update to
  setLeanSus/getLeanSus() getter form
- highway_3d_smooth_clock_pause.test.js: fix literal-newline syntax error;
  update to setClkAudioT/setClkPerf/setFrameNow setter form;
  update new-sample regex to match getClkAudioT()
- highway_3d_slide_target.test.js: add renderer.js to src scan
- highway_3d_sustain_rail.test.js: assert against rendererSrc (pattern
  moved from U-section)
- highway_chart_transform.test.js: add utils.js scan (_openStringPitchLabels-
  ForTuning moved to src/utils.js by h3d-carve-3)
- highway_note_state.test.js: add renderer.js scan (_ndGetNoteState /
  _ndHasProvider captures in renderer.js update())
- highway_3d_camera_bootstrap.test.js: setter form for camSnapped/curX/
  measureStarts; renderer.js added to scan
- highway_3d_camera_framing.test.js: renderer.js added; setMeasureStarts/
  setCamSnapped setter form in assertions

Suite: 1395/1396 (test 46 pre-existing failure unrelated to carve-15)

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

tests/js/highway_3d_sustain_rail.test.js

@@ -13,23 +13,26 @@ const fs = require('node:fs');
 const path = require('node:path');
 
 const SCREEN_JS = path.join(__dirname, '..', '..', 'plugins', 'highway_3d', 'screen.js');
+const RENDERER_JS = path.join(__dirname, '..', '..', 'plugins', 'highway_3d', 'src', 'renderer.js');
 
 test('sustain rails are gated on multi-note chords with a known box width within AHEAD', () => {
     // Each chord in a sequence (including repeats) draws a rail from its onset
     // to the next chord's onset, chaining together to cover the full handshape
     // duration visually. Single notes have no chord frame to anchor a rail to.
-    const src = fs.readFileSync(SCREEN_JS, 'utf8');
+    // h3d-carve-15: sustain-rail block moved to renderer.js
+    const rendererSrc = fs.readFileSync(RENDERER_JS, 'utf8');
     assert.match(
-        src,
+        rendererSrc,
         /if\s*\(\s*chShape\.size\s*>\s*1\s*&&\s*chordOpenBoxW\s*!=\s*null\s*&&\s*chDt\s*<\s*AHEAD\s*\)/,
         'sustain-rail block must stay gated on chShape.size > 1, chordOpenBoxW and chDt < AHEAD',
     );
 });
 
 test('sustain rails pick arpeggio color for arpeggio frames, teal otherwise', () => {
-    const src = fs.readFileSync(SCREEN_JS, 'utf8');
+    // h3d-carve-15: rail color expression moved to renderer.js
+    const rendererSrc = fs.readFileSync(RENDERER_JS, 'utf8');
     assert.match(
-        src,
+        rendererSrc,
         /chordHighwayLavenderArpVisual\s*\?\s*ARPEGGIO_RIM_BLUE_HEX\s*:\s*CHORD_BOX_TEAL_HEX/,
         'rail color must select ARPEGGIO_RIM_BLUE_HEX for arpeggio frames and CHORD_BOX_TEAL_HEX for chords',
     );