fix(core,studio): silence hidden audio in preview, and call it mute

Preview scheduled every audio[data-start] regardless of data-hidden, so a
hidden audio track was silent in the export but audible in preview — render
was already correct, this was a preview-only parity bug. Web Audio scheduling
now skips (and re-syncs on toggle) any audio clip under a data-hidden
ancestor; the HTMLMedia per-tick volume path folds the same check into
effectiveVolume without touching el.muted (transport-owned). Ships unflagged
since it's a bugfix restoring parity.

Also relabels the eye as Mute/Muted on audio-only track rows (icon,
strikethrough label, undo-history copy), gated behind the new
audio-track-mute canary — the relabel is a copy/UX change, kept separate from
the behavior fix above.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/studio/src/hooks/timelineTrackVisibility.test.ts

@@ -194,6 +194,87 @@ describe("toggleTimelineTrackHidden", () => {
 
     expect(recordEdit.mock.calls[0]?.[0]?.label).toBe("Show track 2");
   });
+
+  it("labels an audio-only track Mute/Unmute instead of Hide/Show", async () => {
+    const files = new Map([
+      ["index.html", `<div id="voiceover" data-start="0" data-duration="2"></div>`],
+    ]);
+    stubProjectFiles(files);
+
+    const recordEdit = vi.fn();
+
+    await toggleTimelineTrackHidden({
+      projectId: "project-1",
+      activeCompPath: "index.html",
+      timelineElements: [element({ id: "voiceover", domId: "voiceover", track: 0, tag: "audio" })],
+      track: 0,
+      hidden: true,
+      previewIframe: null,
+      writeProjectFile: async () => {},
+      recordEdit,
+      domEditSaveTimestampRef: { current: 0 },
+      pendingTimelineEditPathRef: { current: new Set() },
+    });
+
+    expect(recordEdit.mock.calls[0]?.[0]?.label).toBe("Mute track 1");
+  });
+
+  it("labels unmuting an audio-only track back on", async () => {
+    const files = new Map([
+      ["index.html", `<div id="voiceover" data-start="0" data-duration="2" data-hidden=""></div>`],
+    ]);
+    stubProjectFiles(files);
+
+    const recordEdit = vi.fn();
+
+    await toggleTimelineTrackHidden({
+      projectId: "project-1",
+      activeCompPath: "index.html",
+      timelineElements: [
+        element({ id: "voiceover", domId: "voiceover", track: 0, tag: "audio", hidden: true }),
+      ],
+      track: 0,
+      hidden: false,
+      previewIframe: null,
+      writeProjectFile: async () => {},
+      recordEdit,
+      domEditSaveTimestampRef: { current: 0 },
+      pendingTimelineEditPathRef: { current: new Set() },
+    });
+
+    expect(recordEdit.mock.calls[0]?.[0]?.label).toBe("Unmute track 1");
+  });
+
+  it("keeps Hide/Show wording for a mixed (audio + visual) track", async () => {
+    const files = new Map([
+      [
+        "index.html",
+        `<div id="voiceover" data-start="0" data-duration="2"></div>
+<div id="caption" data-start="0" data-duration="2"></div>`,
+      ],
+    ]);
+    stubProjectFiles(files);
+
+    const recordEdit = vi.fn();
+
+    await toggleTimelineTrackHidden({
+      projectId: "project-1",
+      activeCompPath: "index.html",
+      timelineElements: [
+        element({ id: "voiceover", domId: "voiceover", track: 0, tag: "audio" }),
+        element({ id: "caption", domId: "caption", track: 0, tag: "div" }),
+      ],
+      track: 0,
+      hidden: true,
+      previewIframe: null,
+      writeProjectFile: async () => {},
+      recordEdit,
+      domEditSaveTimestampRef: { current: 0 },
+      pendingTimelineEditPathRef: { current: new Set() },
+    });
+
+    expect(recordEdit.mock.calls[0]?.[0]?.label).toBe("Hide track 1");
+  });
 });
 
 describe("toggleTimelineElementHidden", () => {

packages/studio/src/hooks/timelineTrackVisibility.ts

@@ -7,6 +7,7 @@ import {
   trackDisplaySuffix,
 } from "../player/components/timelineTrackDisplay";
 import { saveProjectFilesWithHistory } from "../utils/studioFileHistory";
+import { isAudioTimelineElement } from "../utils/timelineInspector";
 import { readTagSnippetByTarget, type PatchOperation } from "../utils/sourcePatcher";
 import {
   applyPatchByTarget,
@@ -218,12 +219,21 @@ export async function toggleTimelineTrackHidden({
   const suffix = trackDisplaySuffix(
     trackDisplayNumber(timelineTrackOrder(timelineElements), track),
   );
+  const trackElements = timelineElements.filter((element) => element.track === track);
+  const isAudioOnlyTrack = trackElements.length > 0 && trackElements.every(isAudioTimelineElement);
+  const label = isAudioOnlyTrack
+    ? hidden
+      ? `Mute track${suffix}`
+      : `Unmute track${suffix}`
+    : hidden
+      ? `Hide track${suffix}`
+      : `Show track${suffix}`;
   return setElementsHidden({
     projectId,
     activeCompPath,
-    elements: timelineElements.filter((element) => element.track === track),
+    elements: trackElements,
     hidden,
-    label: hidden ? `Hide track${suffix}` : `Show track${suffix}`,
+    label,
     previewIframe,
     writeProjectFile,
     recordEdit,