refactor(highway): carve the constants into static/js/highway-constants.js (R3c) (#914)

29 constants, 190 lines. highway.js 4,267 -> 4,158. The first real slice, and the one that
every later one imports.

━━━ WHY ONLY THE CONSTANTS MAY LIVE AT MODULE SCOPE ━━━

createHighway() is a FACTORY, not a singleton. The constitution publishes
window.createHighway precisely so a plugin can build a SECOND highway for its own panel, and
highway.js already says so at the top of the closure:

    // R3c: per-instance mutable state in one object, so extracted renderer/ws
    // modules can close over it as a factory arg without cross-panel sharing.

So hwState — all 79 mutable properties — must NEVER become a module-level singleton: two
highways would silently share it, and one panel would drive the other's clock, scale and
colour tables. Extracted functions will take it as an ARGUMENT.

That is the OPPOSITE of the app.js carve, where a single state container (player-state.js,
library-state.js) was exactly right, because there is exactly one app. Same epic, same
language, opposite answer — because one is a singleton and the other is a factory.

These 29 are pure literals: numbers, strings and colour tables, never reassigned, never
mutated. Sharing them across instances is not merely safe, it is what you want — one copy of
the shimmer LUT bounds and the string palettes rather than one per panel. Anything with a
runtime dependency (document, window, performance, localStorage) stays in the factory;
checked, and none of these has one.

ESLint now knows static/highway.js is a module. It could not have known before this commit:
the flip (#913) changed the SCRIPT TAG, but the file had no import/export yet, so it still
parsed as a script and lint stayed green. The first `import` is what makes the config wrong.

TESTS. Four source-shape harnesses asserted `const _AUTO_SCALE_MIN = …` etc. lived in
highway.js. They now read highway.js AND every static/js/highway-*.js — deliberately, rather
than being re-pinned at whichever file currently holds a constant. Re-pinning just breaks
again on the next carve, and a source-shape assertion that silently stops finding its target
is indistinguishable from one that passes. Bite-tested: renaming two constants away fails
them.

VERIFIED. A/B against origin/main: 15 probes IDENTICAL, zero page errors. AND THE PERF GATE
PASSES AT 1.97ms against its 12ms budget — which is the point of having built it (#910)
first: these constants moved from closure scope to module scope, and V8 does not treat those
identically. It does here. Now I know rather than hope.

node 1045, pytest 2416, ESLint 0, Codex 0.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/js/highway_adaptive_scale.test.js

@@ -27,16 +27,33 @@ function extractBlock(src, signature) {
     return src.slice(start, i);
 }
 
+
+// R3c: highway.js is being carved into modules, so its source is no longer ONE file. Read the
+// whole set. Re-pinning these assertions at whichever file currently holds a constant just
+// means they break again on the next carve — and worse, a source-shape assertion that silently
+// stops finding its target is indistinguishable from one that passes.
+function highwaySources() {
+    const root = path.join(__dirname, '..', '..');
+    const jsDir = path.join(root, 'static', 'js');
+    const parts = [fs.readFileSync(path.join(root, 'static', 'highway.js'), 'utf8')];
+    for (const f of fs.readdirSync(jsDir).sort()) {
+        if (f.startsWith('highway-') && f.endsWith('.js')) {
+            parts.push(fs.readFileSync(path.join(jsDir, f), 'utf8'));
+        }
+    }
+    return parts.join('\n');
+}
+
 test('highway declares adaptive-scale state with a floor', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     assert.match(src, /hwState\._autoScale\s*=\s*1/, 'missing _autoScale multiplier');
-    assert.match(src, /const\s+_AUTO_SCALE_MIN\s*=\s*0?\.25/, 'missing _AUTO_SCALE_MIN floor (0.25)');
-    assert.match(src, /const\s+_DRAW_BUDGET_HI_MS\s*=\s*\d+/, 'missing high draw budget');
-    assert.match(src, /const\s+_DRAW_BUDGET_LO_MS\s*=\s*\d+/, 'missing low draw budget');
+    assert.match(src, /(?:export\s+)?const\s+_AUTO_SCALE_MIN\s*=\s*0?\.25/, 'missing _AUTO_SCALE_MIN floor (0.25)');
+    assert.match(src, /(?:export\s+)?const\s+_DRAW_BUDGET_HI_MS\s*=\s*\d+/, 'missing high draw budget');
+    assert.match(src, /(?:export\s+)?const\s+_DRAW_BUDGET_LO_MS\s*=\s*\d+/, 'missing low draw budget');
 });
 
 test('_effectiveRenderScale clamps user ceiling * auto factor to [MIN, 1]', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     const fn = extractBlock(src, 'function _effectiveRenderScale()');
     // Derives from the (sanitized) user ceiling and auto factor.
     assert.match(fn, /_renderScale/, 'effective scale must derive from the user _renderScale');
@@ -47,7 +64,7 @@ test('_effectiveRenderScale clamps user ceiling * auto factor to [MIN, 1]', () =
 });
 
 test('min render scale floor is user-configurable + exposed on the api (#654)', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     // Hard floor constant kept; configurable floor read from localStorage.
     assert.match(src, /hwState\._autoScaleMin\s*=/, 'missing configurable _autoScaleMin');
     assert.match(src, /localStorage\.getItem\('highwayMinRenderScale'\)/,
@@ -65,7 +82,7 @@ test('min render scale floor is user-configurable + exposed on the api (#654)',
 });
 
 test('_adaptRenderScale uses the draw budget + cooldown and re-applies via resize', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     const fn = extractBlock(src, 'function _adaptRenderScale(');
     assert.match(fn, /_DRAW_BUDGET_HI_MS/, 'must scale down past the high budget');
     assert.match(fn, /_DRAW_BUDGET_LO_MS/, 'must scale up below the low budget');
@@ -74,27 +91,27 @@ test('_adaptRenderScale uses the draw budget + cooldown and re-applies via resiz
 });
 
 test('draw() only adapts during active playback and feeds the HUD', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     const fn = extractBlock(src, 'function draw()');
     assert.match(fn, /if\s*\(\s*!_paused\s*\)\s*_adaptRenderScale/, 'must skip adaptation while paused');
     assert.match(fn, /_updatePerfHud\(\)/, 'must update the perf HUD each drawn frame');
 });
 
 test('bundle + canvas sizing use the effective scale, not the raw user value', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     assert.match(src, /renderScale\s*[:=]\s*_effectiveRenderScale\(\)/, 'bundle.renderScale must be the effective scale');
     assert.match(src, /canvas\.width\s*=\s*Math\.round\(w\s*\*\s*_effectiveRenderScale\(\)\)/, 'canvas backing store must use effective scale');
 });
 
 test('api exposes effective scale + perf stats', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     assert.match(src, /getEffectiveRenderScale\(\)\s*\{\s*return\s+_effectiveRenderScale\(\)/, 'api.getEffectiveRenderScale missing');
     assert.match(src, /getPerfStats\(\)\s*\{/, 'api.getPerfStats missing');
 });
 
 // Robustness fixes from the #655 Copilot review.
 test('render scale is sanitized on load and effective scale guards non-finite', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     assert.match(src, /parseFloat\(localStorage\.getItem\('renderScale'\)[\s\S]{0,160}?Number\.isFinite/,
         'render scale load must validate via Number.isFinite + clamp');
     const eff = extractBlock(src, 'function _effectiveRenderScale()');
@@ -102,7 +119,7 @@ test('render scale is sanitized on load and effective scale guards non-finite',
 });
 
 test('stop() tears down the perf HUD and resets per-session accumulators', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     assert.match(src, /stop\(\)\s*\{[\s\S]{0,400}?_perfHud\.remove\(\)/,
         'stop() must remove the perf HUD so it cannot strand in the DOM');
     assert.match(src, /stop\(\)\s*\{[\s\S]{0,1200}?_autoScale\s*=\s*1/,
@@ -112,7 +129,7 @@ test('stop() tears down the perf HUD and resets per-session accumulators', () =>
 });
 
 test('perf HUD throttles its localStorage flag read off the hot path', () => {
-    const src = fs.readFileSync(highwayJs, 'utf8');
+    const src = highwaySources();
     const fn = extractBlock(src, 'function _updatePerfHud()');
     assert.match(fn, /_hudFlagAt/, 'HUD must cache the flag and re-read on an interval, not every frame');
 });