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

tests/js/highway_3d_render_order.test.js

@@ -41,6 +41,9 @@ const fs = require('node:fs');
 const path = require('node:path');
 
 const SCREEN_JS = path.join(__dirname, '..', '..', 'plugins', 'highway_3d', 'screen.js');
+// Since h3d-carve-1b, RENDER_ORDER_* constants and renderOrderForLayerAtZ
+// live in geometry.js; screen.js imports them.
+const GEOMETRY_JS = path.join(__dirname, '..', '..', 'plugins', 'highway_3d', 'src', 'geometry.js');
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -53,9 +56,16 @@ function src() {
     return _src;
 }
 
-/** Parses the declared render-order layer stack from screen.js. */
+let _geo;
+/** Returns the cached geometry source (render-order constants + renderOrderForLayerAtZ). */
+function geo() {
+    if (!_geo) _geo = fs.readFileSync(GEOMETRY_JS, 'utf8');
+    return _geo;
+}
+
+/** Parses the declared render-order layer stack from geometry.js. */
 function layers() {
-    const match = src().match(/const\s+RENDER_ORDER_LAYER_STACK\s*=\s*Object\.freeze\(\s*\[([\s\S]*?)\]\s*\)/);
+    const match = geo().match(/const\s+RENDER_ORDER_LAYER_STACK\s*=\s*Object\.freeze\(\s*\[([\s\S]*?)\]\s*\)/);
     assert.ok(match, 'RENDER_ORDER_LAYER_STACK must be declared');
     return Array.from(match[1].matchAll(/'([^']+)'/g), m => m[1]);
 }
@@ -70,7 +80,7 @@ function layerIndex(name) {
 
 /** Reads the render-order base used for objects at z = 0. */
 function zZeroRenderOrder() {
-    const match = src().match(/const\s+RENDER_ORDER_AT_Z_ZERO\s*=\s*(-?\d+(?:\.\d+)?)\s*;/);
+    const match = geo().match(/const\s+RENDER_ORDER_AT_Z_ZERO\s*=\s*(-?\d+(?:\.\d+)?)\s*;/);
     assert.ok(match, 'RENDER_ORDER_AT_Z_ZERO must be declared');
     return Number(match[1]);
 }
@@ -301,14 +311,15 @@ test('chordFrameRenderOrder uses renderOrderForLayerAtZ(z, CHORD_FRAME)', () =>
         /const\s+chordFrameRenderOrder\s*=\s*renderOrderForLayerAtZ\(\s*z\s*,\s*'CHORD_FRAME'\s*\)\s*;/,
         'chordFrameRenderOrder must use renderOrderForLayerAtZ(z, CHORD_FRAME)',
     );
-    assert.match(src(), /const\s+RENDER_ORDER_LAYER_INDEX\s*=\s*Object\.freeze\(\s*RENDER_ORDER_LAYER_STACK\.reduce\(/);
-    assert.match(src(), /const\s+layerIndex\s*=\s*RENDER_ORDER_LAYER_INDEX\[layerName\]\s*;/);
-    assert.match(src(), /if\s*\(\s*layerIndex\s*===\s*undefined\s*\)\s*throw\s+new\s+Error\(`Unknown 3D highway depth layer: \$\{layerName\}`\)\s*;/);
-    assert.match(src(), /const\s+depthRenderOrder\s*=\s*Math\.max\(\s*RENDER_ORDER_FAR_CLAMP\s*,\s*Math\.round\(\s*RENDER_ORDER_AT_Z_ZERO\s*\+\s*worldZ\s*\/\s*K\s*\)\s*\)\s*;/);
+    // renderOrderForLayerAtZ implementation lives in geometry.js since h3d-carve-1b.
+    assert.match(geo(), /const\s+RENDER_ORDER_LAYER_INDEX\s*=\s*Object\.freeze\(\s*RENDER_ORDER_LAYER_STACK\.reduce\(/);
+    assert.match(geo(), /const\s+layerIndex\s*=\s*RENDER_ORDER_LAYER_INDEX\[layerName\]\s*;/);
+    assert.match(geo(), /if\s*\(\s*layerIndex\s*===\s*undefined\s*\)\s*throw\s+new\s+Error\(`Unknown 3D highway depth layer: \$\{layerName\}`\)\s*;/);
+    assert.match(geo(), /const\s+depthRenderOrder\s*=\s*Math\.max\(\s*RENDER_ORDER_FAR_CLAMP\s*,\s*Math\.round\(\s*RENDER_ORDER_AT_Z_ZERO\s*\+\s*worldZ\s*\/\s*K\s*\)\s*\)\s*;/);
     // Layer is a sub-unit fraction so the integer depth bucket strictly
     // dominates (a farther object can't outrank a nearer one via a higher
     // layer); the layer only breaks ties within the same depth bucket.
-    assert.match(src(), /return\s+depthRenderOrder\s*\+\s*layerIndex\s*\/\s*RENDER_ORDER_LAYER_STACK\.length\s*;/);
+    assert.match(geo(), /return\s+depthRenderOrder\s*\+\s*layerIndex\s*\/\s*RENDER_ORDER_LAYER_STACK\.length\s*;/);
     assert.ok(layerIndex('CHORD_FRAME') < layerIndex('NOTE_OUTLINE'));
 });