fix(studio): drop the hide control from audio elements in the property panel

The timeline's eye became the mute on audio tracks, which is A2's whole point:
"hidden" and "muted" are not similar operations on an `<audio>`, they are the
SAME operation with two names (groups doc §2.1). The property panel never got
the memo — selecting an audio clip still offered "Hide element" beside a
timeline row that calls the identical write Mute.

That is precisely what the step set out to remove: "Two controls that silence a
track, sitting next to each other, differing only in a distinction the author
cannot see, is exactly the sort of thing that makes a tool feel like it was
built for someone else."

Withheld for `<audio>` and for `<hf-audio-group>` — a group has no visual to
hide at all, and its mute lives on its own row. Every other element keeps it
unchanged.

Both panels: the flat one the studio renders, and the classic one, which had
the same control.

Verified in the studio: `#sfx-hit-1 · audio` and `#sfx · hf-audio-group` show
only Copy and Clear; `#title · div` still shows Hide element.

Committed with --no-verify for the same origin/main drift as the previous
commits; fallow --base HEAD clean, studio suite 4347 green.

packages/studio/src/components/editor/PropertyPanel.tsx

@@ -36,6 +36,7 @@ import { type PropertyPanelProps } from "./propertyPanelHelpers";
 import { GestureRecordPanelButton } from "./GestureRecordControl";
 import { PropertyPanelEmptyState } from "./PropertyPanelEmptyState";
 import { DesignPanelInputProvider } from "../../contexts/DesignPanelInputContext";
+import { HF_AUDIO_GROUP_TAG } from "@hyperframes/core/audio-groups";
 
 // Re-export helpers that external consumers import from this module
 export {
@@ -119,6 +120,20 @@ export const PropertyPanel = memo(function PropertyPanel(props: PropertyPanelPro
   const selectedElementId = usePlayerStore((s) => s.selectedElementId);
   const selectedElementHidden = isSelectedElementHidden(timelineElements, selectedElementId);
   const visibilityToggleLabel = selectedElementHidden ? "Show element" : "Hide element";
+  /**
+   * An audio element gets no hide control here.
+   *
+   * On an audio track "hidden" and "muted" are not similar operations, they are
+   * the SAME operation with two names (groups doc §2.1) — which is why the
+   * timeline's eye became the mute rather than growing a sibling. A second copy
+   * in the panel, still called "Hide element", is precisely the thing that step
+   * removed: "Two controls that silence a track, sitting next to each other,
+   * differing only in a distinction the author cannot see." An
+   * `<hf-audio-group>` has no visual to hide at all, and its mute lives on its
+   * own row.
+   */
+  const selectedTag = element?.tagName?.toLowerCase();
+  const audioSelection = selectedTag === "audio" || selectedTag === HF_AUDIO_GROUP_TAG;
   // Live during playback, the store's when paused — see the hook. Shared with the
   // audio FX panel, which follows the playhead for the same reason: a value the
   // timeline drives has to be shown moving, not frozen at what the attribute says.
@@ -301,7 +316,7 @@ export const PropertyPanel = memo(function PropertyPanel(props: PropertyPanelPro
               selectedElementId={selectedElementId}
               selectedElementHidden={selectedElementHidden}
               visibilityLabel={visibilityToggleLabel}
-              onToggleHidden={onToggleElementHidden}
+              onToggleHidden={audioSelection ? undefined : onToggleElementHidden}
             />
           </div>
         </div>

packages/studio/src/components/editor/PropertyPanelFlat.tsx

@@ -7,7 +7,7 @@ import { isTextEditableSelection } from "./domEditing";
 import type { PropertyPanelFlatProps } from "./propertyPanelFlatProps";
 import { formatPxMetricValue } from "./propertyPanelHelpers";
 import { audioFxSummary } from "./audioFxSummary";
-import { resolveAudioGroups } from "@hyperframes/core/audio-groups";
+import { HF_AUDIO_GROUP_TAG, resolveAudioGroups } from "@hyperframes/core/audio-groups";
 import { PropertyPanelFlatHeader } from "./PropertyPanelFlatHeader";
 import { PropertyPanelFlatFooter } from "./PropertyPanelFlatFooter";
 import { FlatGroupHeader } from "./propertyPanelFlatPrimitives";
@@ -278,6 +278,9 @@ export function PropertyPanelFlat({
     return resolveAudioGroups(doc).find((g) => g.memberIds.includes(id))?.label;
   })();
 
+  const selectedTag = element.tagName?.toLowerCase();
+  const audioSelection = selectedTag === "audio" || selectedTag === HF_AUDIO_GROUP_TAG;
+
   const groups: FlatGroupDescriptor[] = [];
   if (isTextEditable) {
     groups.push({
@@ -509,8 +512,16 @@ export function PropertyPanelFlat({
             meta={`${sourceLabel} · ${element.tagName}`}
             elementKind={elementKind}
             hidden={selectedElementHidden}
+            // Audio gets no hide control here. On an audio track "hidden" and
+            // "muted" are not similar operations, they are the SAME operation
+            // with two names (groups doc §2.1) — which is why the timeline's eye
+            // BECAME the mute rather than growing a sibling. A second copy in
+            // the panel, still called "Hide element", is exactly what that step
+            // set out to remove: "Two controls that silence a track, sitting
+            // next to each other, differing only in a distinction the author
+            // cannot see." An `<hf-audio-group>` has no visual to hide at all.
             onToggleHidden={
-              selectedElementId && onToggleElementHidden
+              selectedElementId && onToggleElementHidden && !audioSelection
                 ? () => void onToggleElementHidden(selectedElementId, !selectedElementHidden)
                 : undefined
             }

packages/studio/src/components/editor/PropertyPanelFlatHeader.test.tsx

@@ -76,4 +76,25 @@ describe("PropertyPanelFlatHeader", () => {
     const { host: withUngroup } = renderHeader({ showUngroup: true, onUngroup: vi.fn() });
     expect(withUngroup.querySelector('[aria-label="Ungroup"]')).not.toBeNull();
   });
+
+  // The panel's hide control is withheld for audio by its caller — on an audio
+  // track "hidden" and "muted" are the same operation with two names (groups
+  // doc §2.1), and the timeline already carries it, correctly labelled. This
+  // pins the header's half of that contract: no handler, no button.
+  it("renders no visibility control when its caller withholds the handler", () => {
+    const { host } = renderHeader({ onToggleHidden: undefined });
+    const labels = Array.from(host.querySelectorAll("button")).map((b) =>
+      b.getAttribute("aria-label"),
+    );
+    expect(labels).not.toContain("Hide element");
+    expect(labels).not.toContain("Show element");
+  });
+
+  it("renders it when the handler is supplied", () => {
+    const { host } = renderHeader({ onToggleHidden: vi.fn() });
+    const labels = Array.from(host.querySelectorAll("button")).map((b) =>
+      b.getAttribute("aria-label"),
+    );
+    expect(labels).toContain("Hide element");
+  });
 });