fix(tone): strip any-language code fences so 'html' never leaks into art (#688)

simongonzalezdc · Sinter Test · claude · web-flow · commit 0d3eb35c2bf6 · 2026-06-10T06:44:22.000-07:00
**F13 from the investor-audit register.** The tone fence stripper's language allowlist omitted `html`, so a ```html fence after the DOCTYPE lost only its backticks — leaking a literal `html` token that rendered as visible text beside the start button in the live proof artifact. The existing leading-`html` band-aid (`normalizeToneArtifact`) is anchored without `/m` and misses mid-document residue. Fix: fence-opening lines strip generically (`/^\`\`\`[ \t]*[\w-]*[ \t]*\r?\n?/gm`). Closing-fence handling unchanged. Verification: ToneGenerator suite 15/15; the new regression reproduces the exact observed artifact shape and **fails against the old regex** (stash-verified red-green); eslint clean. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Sinter Test <liminal@example.test> Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
diff --git a/src/generators/tone/ToneGenerator.ts b/src/generators/tone/ToneGenerator.ts
@@ -90,8 +90,11 @@ export class ToneGenerator extends TierBasedGenerator {
     
     let clean = code;
     
-    // Strip markdown code fences (only at start/end, preserve code inside)
-    clean = clean.replace(/^```(?:javascript|js|typescript|ts)?\n?/gm, '');
+    // Strip markdown code fences (only at start/end, preserve code inside).
+    // The language tag must stay GENERIC: an allowlist that omitted `html`
+    // ate only the backticks of a ```html fence and leaked a bare "html"
+    // token into rendered artifacts (investor-audit F13).
+    clean = clean.replace(/^```[ \t]*[\w-]*[ \t]*\r?\n?/gm, '');
     clean = clean.replace(/\n?```$/gm, '');
     clean = clean.replace(/^```$/gm, '');
     
diff --git a/test/unit/generators/ToneGenerator.test.ts b/test/unit/generators/ToneGenerator.test.ts
@@ -88,6 +88,27 @@ describe('ToneGenerator', () => {
     expect(result).toContain('Tone.Synth');
   });
 
+  it('sanitizeCode strips html-tagged fences without leaking the language word (F13)', async () => {
+    // Regression: a ```html fence after the DOCTYPE used to lose only its
+    // backticks (language allowlist omitted html), leaving a bare "html"
+    // line that rendered as visible text beside the artifact's start button
+    // (live-creative-domains tone proof, 2026-06-10). The leading-"html"
+    // band-aid in normalizeToneArtifact is anchored without /m and misses
+    // this mid-document residue.
+    mockComplete.mockResolvedValueOnce({
+      text: '<!DOCTYPE html>\n```html\n<html><head><meta charset="UTF-8"><title>Tone.js Patch</title></head><body><button id="start">Start</button><script>document.getElementById("start").onclick=async()=>{await Tone.start();Tone.Transport.bpm.value=84;new Tone.Loop((time)=>new Tone.Synth().toDestination().triggerAttackRelease("C4","8n",time),"4n").start(0);Tone.Transport.start();};</script></body></html>\n```',
+      success: true,
+    });
+
+    const gen = new ToneGenerator();
+    const result = await gen.generate('fenced ambient synth');
+
+    expect(result).not.toMatch(/^html$/m);
+    expect(result).not.toContain('```');
+    expect(result).toContain('Tone.Transport.bpm.value=84');
+    expect(result).toContain('<html>');
+  });
+
   it('sanitizeCode strips think tags', async () => {
     mockComplete.mockResolvedValue({ text: '', success: true });
     mockToolLoop.mockResolvedValueOnce({
