fix(studio): don't offer layout grouping for a selection of audio clips

Selecting two audio clips offered "Group selection", which is the layout
grouper: it wraps the members in a positioned <div> at their bounding
box, rebases each child's left/top against that origin, and adopts the
topmost member's z-index.

None of that means anything for audio. An <audio> clip has no box —
offsetWidth/Height are 0 — so the wrapper came out `width: 0px; height:
0px` with inline left/top written onto elements that are never laid out,
and the composition gained a <div> standing for nothing audible.
Confirmed against `wrapElementsInHtml` directly: it matched and wrapped,
producing exactly that.

Refused in `handleGroupSelection`, which is where the G shortcut also
lands — a hidden button cannot gate a keystroke. The panel withholds the
button as well, so the refusal is not the first the author hears of it.

The message names the alternative rather than only declining: audio's
answer to "these clips belong together" is an <hf-audio-group> bus, which
the timeline's own FX pointer already creates. A mixed selection is
refused too — the wrapper would take the audio in with the rest.

`isAudioDomElement` sits beside `isAudioTimelineElement` and delegates to
it, so the selection layer and the timeline cannot drift into disagreeing
about what counts as audio.

Six tests across both entry points, each mutation-checked.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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

@@ -71,4 +71,58 @@ describe("PropertyPanelEmptyState — flat multi-select", () => {
     expect(onClearSelection).toHaveBeenCalledTimes(1);
     act(() => root.unmount());
   });
+
+  // A layout group is a positioned wrapper around a bounding box; an <audio>
+  // clip has none (offsetWidth/Height are 0), so grouping audio produced a 0x0
+  // div with inline left/top on elements that are never laid out. Withheld
+  // rather than offered-then-refused.
+  const audioElements = (tags: string[]) =>
+    tags.map((tag, i) => ({
+      id: `el-${i}`,
+      selector: `#el-${i}`,
+      label: `El ${i}`,
+      tagName: tag,
+      element: document.createElement(tag),
+    })) as unknown as DomEditSelection[];
+
+  it("withholds Group selection when the selection includes audio", () => {
+    const { host, root } = renderInto(
+      <PropertyPanelEmptyState
+        flat
+        multiSelectCount={2}
+        multiSelectedElements={audioElements(["audio", "audio"])}
+        onGroupSelection={vi.fn()}
+      />,
+    );
+    expect(host.querySelector('[data-flat-multiselect-group="true"]')).toBeNull();
+    // Hide all still applies — hiding an audio clip is what mutes it.
+    expect(host.querySelector('[data-flat-multiselect-hide-all="true"]')).not.toBeNull();
+    act(() => root.unmount());
+  });
+
+  it("withholds it for a mixed selection too, since the wrapper would still take audio in", () => {
+    const { host, root } = renderInto(
+      <PropertyPanelEmptyState
+        flat
+        multiSelectCount={2}
+        multiSelectedElements={audioElements(["div", "audio"])}
+        onGroupSelection={vi.fn()}
+      />,
+    );
+    expect(host.querySelector('[data-flat-multiselect-group="true"]')).toBeNull();
+    act(() => root.unmount());
+  });
+
+  it("still offers it for a selection of layout elements", () => {
+    const { host, root } = renderInto(
+      <PropertyPanelEmptyState
+        flat
+        multiSelectCount={2}
+        multiSelectedElements={audioElements(["div", "span"])}
+        onGroupSelection={vi.fn()}
+      />,
+    );
+    expect(host.querySelector('[data-flat-multiselect-group="true"]')).not.toBeNull();
+    act(() => root.unmount());
+  });
 });

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

@@ -1,5 +1,6 @@
 import { Eye, Layers } from "../../icons/SystemIcons";
 import type { DomEditSelection } from "./domEditingTypes";
+import { isAudioDomElement } from "../../utils/timelineInspector";
 
 function FlatEmptyState() {
   return (
@@ -67,6 +68,7 @@ function FlatMultiSelectState({
   onHideAllSelected?: () => void;
   onClearSelection?: () => void;
 }) {
+  const hasAudio = multiSelectedElements.some((el) => isAudioDomElement(el.element));
   return (
     <div className="flex flex-col gap-3 px-4 py-3">
       <div className="flex items-center gap-3 rounded-xl border border-panel-border bg-panel-surface p-3">
@@ -124,20 +126,30 @@ function FlatMultiSelectState({
         })}
       </div>
       <div className="flex gap-2">
-        <button
-          type="button"
-          data-flat-multiselect-group="true"
-          onClick={onGroupSelection}
-          className="flex h-[34px] flex-1 items-center justify-center gap-2 rounded-lg bg-panel-hover text-[11px] font-semibold text-panel-text-0"
-        >
-          <Layers size={13} />
-          Group selection
-        </button>
+        {/* A layout group is a positioned wrapper around a bounding box, and an
+            <audio> clip has none — grouping audio produced a 0x0 div with inline
+            left/top on elements that are never laid out. `handleGroupSelection`
+            refuses the same case (it also owns the G shortcut, which no hidden
+            button can gate); withholding the button is so the refusal is not
+            the first the author hears of it. */}
+        {!hasAudio && (
+          <button
+            type="button"
+            data-flat-multiselect-group="true"
+            onClick={onGroupSelection}
+            className="flex h-[34px] flex-1 items-center justify-center gap-2 rounded-lg bg-panel-hover text-[11px] font-semibold text-panel-text-0"
+          >
+            <Layers size={13} />
+            Group selection
+          </button>
+        )}
         <button
           type="button"
           data-flat-multiselect-hide-all="true"
           onClick={onHideAllSelected}
-          className="flex h-[34px] items-center gap-1.5 rounded-lg border border-panel-border-input bg-panel-input px-3 text-[11px] font-medium text-panel-text-2"
+          className={`flex h-[34px] items-center gap-1.5 rounded-lg border border-panel-border-input bg-panel-input px-3 text-[11px] font-medium text-panel-text-2 ${
+            hasAudio ? "flex-1 justify-center" : ""
+          }`}
         >
           <Eye size={13} />
           Hide all

packages/studio/src/hooks/useDomEditSession.test.tsx

@@ -58,6 +58,8 @@ const capturedOnReorderShadow: { fn: ((targets: string[]) => void) | undefined }
   fn: undefined,
 };
 const domEditSelectionRef: { current: DomEditSelection | null } = { current: null };
+const domEditGroupSelectionsRef: { current: DomEditSelection[] } = { current: [] };
+const groupSelectionSpy = vi.fn();
 const gsapCommitMutation = Object.assign(vi.fn(), { batch: vi.fn() });
 
 function createSessionParams(
@@ -131,7 +133,7 @@ vi.mock("./useDomSelection", () => ({
     domEditHoverSelection: null,
     activeGroupElement: null,
     domEditSelectionRef,
-    domEditGroupSelectionsRef: { current: [] },
+    domEditGroupSelectionsRef,
     setActiveGroupElement: vi.fn(),
     applyDomSelection: vi.fn(),
     clearDomSelection: vi.fn(),
@@ -190,7 +192,7 @@ vi.mock("./useGsapScriptCommits", () => ({
 }));
 vi.mock("./useGroupCommits", () => ({
   useGroupCommits: () => ({
-    groupSelection: vi.fn(),
+    groupSelection: (...args: unknown[]) => groupSelectionSpy(...args),
     ungroupSelection: vi.fn(),
   }),
 }));
@@ -407,3 +409,56 @@ describe("bulk segment ease commits", () => {
     }
   });
 });
+
+// ── Grouping refuses audio ───────────────────────────────────────────────────
+//
+// A layout group is a positioned wrapper: it takes the members' bounding box,
+// rebases each child's left/top against it and adopts the topmost z-index. An
+// <audio> clip has no box — offsetWidth/Height are 0 — so this produced a 0x0
+// div with inline left/top on elements that are never laid out. Enforced here
+// rather than only by hiding the button, because the G shortcut routes through
+// the same handler and no hidden button can gate a keystroke.
+
+describe("handleGroupSelection with audio in the selection", () => {
+  const sel = (tag: string): DomEditSelection =>
+    ({
+      id: tag,
+      element: document.createElement(tag),
+      sourceFile: "index.html",
+    }) as unknown as DomEditSelection;
+
+  async function group(members: DomEditSelection[]) {
+    const { useDomEditSession } = await import("./useDomEditSession");
+    groupSelectionSpy.mockClear();
+    domEditGroupSelectionsRef.current = members;
+    const showToast = vi.fn();
+    const captured: { fn?: () => void } = {};
+    function Probe() {
+      captured.fn = useDomEditSession(createSessionParams({ showToast })).handleGroupSelection;
+      return null;
+    }
+    const root = createRoot(document.createElement("div"));
+    act(() => root.render(<Probe />));
+    act(() => captured.fn?.());
+    act(() => root.unmount());
+    domEditGroupSelectionsRef.current = [];
+    return { showToast };
+  }
+
+  it("refuses a selection of audio clips, and says where grouping audio lives", async () => {
+    const { showToast } = await group([sel("audio"), sel("audio")]);
+    expect(groupSelectionSpy).not.toHaveBeenCalled();
+    expect(String(showToast.mock.calls[0]?.[0])).toContain("bus");
+  });
+
+  it("refuses a mixed selection, since the wrapper would take the audio in too", async () => {
+    const { showToast } = await group([sel("div"), sel("audio")]);
+    expect(groupSelectionSpy).not.toHaveBeenCalled();
+    expect(String(showToast.mock.calls[0]?.[0])).toContain("layout");
+  });
+
+  it("still groups a selection of layout elements", async () => {
+    await group([sel("div"), sel("span")]);
+    expect(groupSelectionSpy).toHaveBeenCalledTimes(1);
+  });
+});

packages/studio/src/hooks/useDomEditSession.ts

@@ -1,5 +1,6 @@
 import { useCallback } from "react";
 import { trackStudioEvent } from "../utils/studioTelemetry";
+import { isAudioDomElement } from "../utils/timelineInspector";
 import type { SelectElementOptions, TimelineElement } from "../player";
 import type { ImportedFontAsset } from "../components/editor/fontAssets";
 import type { EditHistoryKind } from "../utils/editHistory";
@@ -374,6 +375,23 @@ export function useDomEditSession({
       showToast("Select at least 2 elements to group", "info");
       return;
     }
+    // A layout group is a positioned wrapper: it takes the members' bounding
+    // box, rebases each child's left/top against it, and adopts the topmost
+    // z-index. An <audio> clip has no box — offsetWidth/Height are 0 — so
+    // grouping audio produced a 0x0 div with inline left/top written onto
+    // elements that have never been laid out, and the timeline gained a
+    // wrapper standing for nothing audible. The audio answer to "these clips
+    // belong together" is an <hf-audio-group> bus, which the timeline's own FX
+    // pointer creates, so the refusal names it rather than just declining.
+    if (members.some((m) => isAudioDomElement(m.element))) {
+      showToast(
+        members.every((m) => isAudioDomElement(m.element))
+          ? "Audio clips group into a bus — use FX on the track header"
+          : "Can't group audio clips with layout elements",
+        "info",
+      );
+      return;
+    }
     trackStudioEvent("group", { action: "create", count: members.length });
     void groupSelection(members);
   }, [domEditGroupSelectionsRef, domEditSelectionRef, groupSelection, showToast]);

packages/studio/src/utils/timelineInspector.ts

@@ -4,6 +4,23 @@ const AUDIO_TIMELINE_TAGS = new Set(["audio", "music", "sfx", "sound", "narratio
 const AUDIO_SOURCE_EXT_RE = /\.(aac|flac|m4a|mp3|ogg|opus|wav)(?:[?#].*)?$/i;
 const MUSIC_ID_RE = /\b(music|bgm|soundtrack|background[-_]?music)\b/i;
 
+/**
+ * Is this DOM node an audio clip, judged the way `isAudioTimelineElement`
+ * judges a timeline element?
+ *
+ * The selection layer holds real elements rather than timeline records, and
+ * layout grouping is decided there — so it needs the same question asked of a
+ * node. Same tag set and same source-extension fallback, so the two cannot
+ * drift into disagreeing about what counts as audio.
+ */
+export function isAudioDomElement(node: Element | null | undefined): boolean {
+  if (!node) return false;
+  return isAudioTimelineElement({
+    tag: node.tagName,
+    src: node.getAttribute("src") ?? undefined,
+  });
+}
+
 export function isAudioTimelineElement(
   element: Pick<TimelineElement, "tag" | "src"> | null | undefined,
 ): boolean {