fix(h3d-carve-4): export _bcLoadSettings + _bcFfIdx; add caller-coverage test (Creed HIGH)

screen.js H/P-section render path at lines 15396-15402 calls _bcLoadSettings()
and _bcFfIdx() (3×) — both moved to bc-panel.js in cut 4 but omitted from the
export list.  Browser: first render() after bcCtrl creation → ReferenceError;
seek/loop fast-forward index also dead.  Suite was green because no test
executed the butterchurn render path.

Fix:
- export _bcLoadSettings and _bcFfIdx from bc-panel.js
- add both to the tagged import in screen.js

Class-killer (test 12 — generic, not instance-specific):
  Extracts all exports from bc-panel.js, all imports in screen.js's
  bc-panel.js import clause, then asserts no exported symbol appears as a
  bare reference in the screen.js IIFE body without being imported.
  Generic: adding a new export + new caller without updating the import → RED.

Own grep (audit):
  grep (non-comment lines, all private _bc* names from bc-panel.js):
    _bcLoadSettings  1 hit  (line 15396)
    _bcFfIdx         3 hits (lines 15400-15402)
    all others: 0 hits
  Only the two symbols Creed found.

Mutation-verify:
  remove _bcLoadSettings from screen.js import →
    node --test tests/js/highway_3d_bc_panel.test.js
    tests 12   pass 11   fail 1   (test 12 RED)  ✓
  restore →
    node --test tests/js/highway_3d*.test.js plugins/highway_3d/tests/*.test.js
    tests 222   pass 222   fail 0               ✓ GREEN

Plan §8 amended: exports 2→4 with dated note.

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

tests/js/highway_3d_bc_panel.test.js

@@ -178,6 +178,50 @@ test('screen.js imports _bcCreateController and _bcIsDesktop from src/bc-panel.j
         'screen.js must import _bcIsDesktop from ./src/bc-panel.js');
 });
 
+// ── 12. screen.js has no bare caller references to private bc-panel.js symbols ─
+
+test('every bc-panel.js export referenced in screen.js IIFE is in the import statement', () => {
+    // Mutation: remove _bcLoadSettings (or any other export) from the screen.js import
+    // → symbol is exported by bc-panel.js, referenced in the IIFE, but not bound via
+    // import → ReferenceError at runtime.  This is the class Creed HIGH found on
+    // cut 4 (screen.js:15396-15402: _bcLoadSettings + _bcFfIdx called but not imported).
+    //
+    // Method (generalised):
+    //   exported  = all _bc* symbols with `export` keyword in bc-panel.js
+    //   imported  = all symbols in screen.js's `from './src/bc-panel.js'` import clause
+    //   leaked    = exported symbols that appear as bare refs in screen.js IIFE
+    //               but are NOT in imported
+    // Adding a new export and a new caller without updating the import → leaked is
+    // non-empty → test RED.
+    const bcSrc = src();
+    const scrSrc = screenSrc();
+
+    // All exported _bc* symbols from bc-panel.js.
+    const exported = new Set(
+        [...bcSrc.matchAll(/^export\s+(?:const|let|var|function)\s+(_bc\w+)/mg)].map(m => m[1])
+    );
+
+    // Symbols actually imported from bc-panel.js in screen.js.
+    const importMatch = scrSrc.match(/import\s+\{([^}]+)\}\s+from\s+['"]\.\/src\/bc-panel\.js['"]/);
+    const imported = new Set(
+        importMatch ? importMatch[1].split(',').map(s => s.trim()).filter(Boolean) : []
+    );
+
+    // IIFE body: strip import lines and line comments to avoid false positives.
+    const noImports  = scrSrc.replace(/^import\s+.*\n/gm, '');
+    const noComments = noImports.replace(/\/\/[^\n]*/g, '');
+
+    // Exported symbols referenced in the IIFE body but absent from the import list.
+    const leaked = [...exported].filter(
+        sym => new RegExp('\\b' + sym + '\\b').test(noComments) && !imported.has(sym)
+    );
+
+    assert.deepStrictEqual(leaked, [],
+        'screen.js references bc-panel.js exports that are not in its import clause: ' +
+        leaked.join(', ') +
+        ' — add them to the import { … } from \'./src/bc-panel.js\' line in screen.js');
+});
+
 // ── 11. screen.js IIFE no longer defines moved B-section symbols ──────────────
 
 test('screen.js IIFE does not redeclare _bcCreateController or _bcLoadLib', () => {