From bc73c411f0bbf2b5e79c362ec78300ff5f08c520 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miguel=20=C3=81ngel?= <miguel.sierra@heygen.com>
Date: Mon, 28 Sep 2026 03:37:32 +0000
Subject: [PATCH] feat(studio): let a host app mount the timeline toolbar, undo
 buttons, meters and clipboard (#4629)

* feat(studio): let a host app mount the timeline toolbar, undo buttons, meters and clipboard

* test(studio): lock in history button rules and trim duplicate export tests
---
 .../TimelineHistoryButtons.dom.test.tsx       | 39 ++++++++-
 .../src/components/TimelineHistoryButtons.tsx | 40 ++++++----
 .../src/components/TimelineToolbar.test.tsx   | 10 ++-
 .../studio/src/components/TimelineToolbar.tsx | 18 +++--
 .../components/nle/AudioMeterStrip.test.tsx   | 29 ++++++-
 .../src/components/nle/AudioMeterStrip.tsx    | 35 +++++---
 .../src/components/pointerTargetSize.test.tsx |  2 +-
 .../src/hooks/useClipboard.source.test.ts     | 11 +++
 packages/studio/src/hooks/useClipboard.ts     |  2 +-
 packages/studio/src/index.ts                  |  8 ++
 .../studio/src/timelineChromeExports.test.tsx | 79 +++++++++++++++++++
 11 files changed, 235 insertions(+), 38 deletions(-)
 create mode 100644 packages/studio/src/timelineChromeExports.test.tsx

diff --git a/packages/studio/src/components/TimelineHistoryButtons.dom.test.tsx b/packages/studio/src/components/TimelineHistoryButtons.dom.test.tsx
index 230093002b..34346678a1 100644
--- a/packages/studio/src/components/TimelineHistoryButtons.dom.test.tsx
+++ b/packages/studio/src/components/TimelineHistoryButtons.dom.test.tsx
@@ -16,8 +16,10 @@ const handleUndo = vi.fn();
 const handleRedo = vi.fn();
 const trackStudioEvent = vi.fn();
 
+const studioShell = { editHistory, handleUndo, handleRedo };
+let shell: typeof studioShell | null = studioShell;
 vi.mock("../contexts/StudioContext", () => ({
-  useStudioShellContext: () => ({ editHistory, handleUndo, handleRedo }),
+  useStudioShellContextOptional: () => shell,
 }));
 vi.mock("../utils/studioTelemetry", () => ({ trackStudioEvent }));
 
@@ -31,6 +33,7 @@ beforeEach(() => {
     undoLabel: undefined,
     redoLabel: undefined,
   });
+  shell = studioShell;
   vi.clearAllMocks();
 });
 
@@ -115,3 +118,37 @@ it("classifies Undo and Redo for the hotkey filters at their new location (KTD13
     expect(shouldIgnorePlaybackShortcutTarget(el), label).toBe(true);
   }
 });
+
+it("takes a host's history props over the shell's", async () => {
+  editHistory.canUndo = true;
+  editHistory.redoLabel = "shell move";
+  const onUndo = vi.fn();
+  const onRedo = vi.fn();
+  const host = mount(
+    <TimelineHistoryButtons
+      canUndo={false}
+      canRedo
+      redoLabel="host trim"
+      onUndo={onUndo}
+      onRedo={onRedo}
+    />,
+  );
+
+  expect(button(host, "Undo").disabled).toBe(true);
+  act(() => button(host, "Redo").focus());
+  await act(async () => {
+    await new Promise((resolve) => setTimeout(resolve, 0));
+  });
+  expect(document.querySelector('[role="tooltip"]')?.textContent).toContain("Redo host trim");
+  click(button(host, "Redo"));
+
+  expect(onRedo).toHaveBeenCalledTimes(1);
+  expect(handleRedo).not.toHaveBeenCalled();
+});
+
+it("keeps a button disabled when it has no handler, whatever canUndo/canRedo say", () => {
+  shell = null;
+  const host = mount(<TimelineHistoryButtons canUndo canRedo />);
+
+  for (const label of ["Undo", "Redo"]) expect(button(host, label).disabled).toBe(true);
+});
diff --git a/packages/studio/src/components/TimelineHistoryButtons.tsx b/packages/studio/src/components/TimelineHistoryButtons.tsx
index e779e8c75a..e9f75481b2 100644
--- a/packages/studio/src/components/TimelineHistoryButtons.tsx
+++ b/packages/studio/src/components/TimelineHistoryButtons.tsx
@@ -1,4 +1,4 @@
-import { useStudioShellContext } from "../contexts/StudioContext";
+import { useStudioShellContextOptional } from "../contexts/StudioContext";
 import { RotateCcw, RotateCw } from "../icons/SystemIcons";
 import { trackStudioEvent } from "../utils/studioTelemetry";
 import { historyTooltipLabel } from "../utils/studioHelpers";
@@ -7,13 +7,14 @@ import { Tooltip } from "./ui";
 
 interface HistoryButtonProps {
   action: "undo" | "redo";
-  enabled: boolean;
+  can: boolean;
   label: string | undefined;
-  onClick: () => Promise<void> | void;
+  onClick: (() => Promise<void> | void) | undefined;
 }
 
-function HistoryButton({ action, enabled, label, onClick }: HistoryButtonProps) {
+function HistoryButton({ action, can, label, onClick }: HistoryButtonProps) {
   const Icon = action === "undo" ? RotateCcw : RotateCw;
+  const enabled = Boolean(onClick) && can;
   return (
     <Tooltip label={historyTooltipLabel(action, label)}>
       <button
@@ -23,7 +24,7 @@ function HistoryButton({ action, enabled, label, onClick }: HistoryButtonProps)
         className={enabled ? flatIdle : flatDisabled}
         onClick={() => {
           trackStudioEvent("toolbar_action", { action });
-          void onClick();
+          void onClick?.();
         }}
       >
         <Icon size={16} />
@@ -32,22 +33,33 @@ function HistoryButton({ action, enabled, label, onClick }: HistoryButtonProps)
   );
 }
 
-/** Undo and Redo, on the one edit-history path the shell already owns. */
-export function TimelineHistoryButtons() {
-  const { editHistory, handleUndo, handleRedo } = useStudioShellContext();
+export interface TimelineHistoryButtonsProps {
+  canUndo?: boolean;
+  canRedo?: boolean;
+  undoLabel?: string;
+  redoLabel?: string;
+  onUndo?: () => Promise<void> | void;
+  onRedo?: () => Promise<void> | void;
+}
+
+/** Undo and Redo: a host's props win, else the shell's edit history. */
+export function TimelineHistoryButtons(props: TimelineHistoryButtonsProps) {
+  const shell = useStudioShellContextOptional();
+  const onUndo = props.onUndo ?? shell?.handleUndo;
+  const onRedo = props.onRedo ?? shell?.handleRedo;
   return (
     <>
       <HistoryButton
         action="undo"
-        enabled={editHistory.canUndo}
-        label={editHistory.undoLabel}
-        onClick={handleUndo}
+        can={props.canUndo ?? shell?.editHistory.canUndo ?? false}
+        label={props.undoLabel ?? shell?.editHistory.undoLabel}
+        onClick={onUndo}
       />
       <HistoryButton
         action="redo"
-        enabled={editHistory.canRedo}
-        label={editHistory.redoLabel}
-        onClick={handleRedo}
+        can={props.canRedo ?? shell?.editHistory.canRedo ?? false}
+        label={props.redoLabel ?? shell?.editHistory.redoLabel}
+        onClick={onRedo}
       />
     </>
   );
diff --git a/packages/studio/src/components/TimelineToolbar.test.tsx b/packages/studio/src/components/TimelineToolbar.test.tsx
index 55b6aecaae..87c1fa4403 100644
--- a/packages/studio/src/components/TimelineToolbar.test.tsx
+++ b/packages/studio/src/components/TimelineToolbar.test.tsx
@@ -12,7 +12,7 @@ import { AudioMeterStrip } from "./nle/AudioMeterStrip";
 import { TimelineToolbar } from "./TimelineToolbar";
 
 vi.mock("../contexts/StudioContext", () => ({
-  useStudioShellContext: () => ({
+  useStudioShellContextOptional: () => ({
     previewIframeRef: { current: null },
     editHistory: { canUndo: false, canRedo: false },
     handleUndo: vi.fn(),
@@ -214,3 +214,11 @@ describe("TimelineToolbar audio meters", () => {
     }
   });
 });
+
+describe("TimelineToolbar add beat", () => {
+  it("shows Add beat by default, as Studio does", () => {
+    const { host, root } = renderToolbar();
+    expect(host.querySelector('button[aria-label="Add beat at playhead"]')).not.toBeNull();
+    act(() => root.unmount());
+  });
+});
diff --git a/packages/studio/src/components/TimelineToolbar.tsx b/packages/studio/src/components/TimelineToolbar.tsx
index dc435d148f..e9342a063d 100644
--- a/packages/studio/src/components/TimelineToolbar.tsx
+++ b/packages/studio/src/components/TimelineToolbar.tsx
@@ -19,7 +19,7 @@ import { Tooltip } from "./ui";
 import { AudioMetersIcon } from "./icons/AudioMetersIcon";
 import { RippleEditIcon } from "./icons/RippleEditIcon";
 import { flatActive, flatBtn, flatDisabled, flatIdle } from "./timelineToolbarStyles";
-import { TimelineHistoryButtons } from "./TimelineHistoryButtons";
+import { TimelineHistoryButtons, type TimelineHistoryButtonsProps } from "./TimelineHistoryButtons";
 import { Scissors } from "../icons/SystemIcons";
 import type { GsapAnimation } from "@hyperframes/core/gsap-parser";
 import type { DomEditSelection } from "./editor/domEditingTypes";
@@ -33,9 +33,11 @@ interface DomEditSessionSlice extends EnableKeyframesSession {
   selectedGsapAnimations: GsapAnimation[];
 }
 
-interface TimelineToolbarProps {
+export interface TimelineToolbarProps {
   domEditSession?: DomEditSessionSlice;
   onSplitElement?: (element: TimelineElement, splitTime: number) => void;
+  history?: TimelineHistoryButtonsProps;
+  showAddBeat?: boolean;
 }
 
 interface KeyframeToggleState {
@@ -127,7 +129,12 @@ function useKeyframeToggle(session?: DomEditSessionSlice) {
 }
 
 // fallow-ignore-next-line complexity
-export function TimelineToolbar({ domEditSession, onSplitElement }: TimelineToolbarProps) {
+export function TimelineToolbar({
+  domEditSession,
+  onSplitElement,
+  history,
+  showAddBeat = true,
+}: TimelineToolbarProps) {
   const activeTool = usePlayerStore((s) => s.activeTool);
   const setActiveTool = usePlayerStore((s) => s.setActiveTool);
   const timelineSnapEnabled = usePlayerStore((s) => s.timelineSnapEnabled);
@@ -195,7 +202,7 @@ export function TimelineToolbar({ domEditSession, onSplitElement }: TimelineTool
     <div className="border-b border-neutral-800/60">
       <div className="flex items-center justify-between px-2 py-0.5">
         <div className="flex items-center gap-0.5">
-          <TimelineHistoryButtons />
+          <TimelineHistoryButtons {...history} />
           <Tooltip label="Selection tool (V)">
             <button
               type="button"
@@ -416,7 +423,8 @@ export function TimelineToolbar({ domEditSession, onSplitElement }: TimelineTool
               );
             })()}
           {(() => {
-            // Always rendered (CapCut-style): before beat analysis loads (or when
+            if (!showAddBeat) return null;
+            // Rendered whenever shown (CapCut-style): before beat analysis loads (or when
             // the project has no analyzed music) the button fades to a disabled
             // state instead of unmounting, so the toolbar layout never shifts.
             const canAdd = beatAnalysisReady && canAddBeatAt(currentTime);
diff --git a/packages/studio/src/components/nle/AudioMeterStrip.test.tsx b/packages/studio/src/components/nle/AudioMeterStrip.test.tsx
index e0faab59c0..bd5a387822 100644
--- a/packages/studio/src/components/nle/AudioMeterStrip.test.tsx
+++ b/packages/studio/src/components/nle/AudioMeterStrip.test.tsx
@@ -11,6 +11,7 @@ import { useAudioMetersVisible } from "../../utils/audioMeterVisibility";
 import { SILENT_CHANNEL } from "../../utils/audioMeterMath";
 import {
   AudioMeterStrip,
+  type AudioMeterStripProps,
   evictGoneMeterState,
   followMeterHook,
   stepAndPaintStrips,
@@ -20,8 +21,9 @@ import {
 
 const iframe = { contentWindow: null as unknown };
 const previewIframeRef = { current: iframe };
+let shell: { previewIframeRef: typeof previewIframeRef } | null = { previewIframeRef };
 vi.mock("../../contexts/StudioContext", () => ({
-  useStudioShellContext: () => ({ previewIframeRef }),
+  useStudioShellContextOptional: () => shell,
 }));
 
 const onSetAudioGroupAttributeLive = vi.fn();
@@ -88,6 +90,7 @@ const tick = () => {
 };
 
 beforeEach(() => {
+  shell = { previewIframeRef };
   frames = [];
   vi.stubGlobal("requestAnimationFrame", (cb: FrameRequestCallback) => frames.push(cb));
   vi.stubGlobal("cancelAnimationFrame", () => {});
@@ -103,11 +106,11 @@ afterEach(() => {
   vi.unstubAllGlobals();
 });
 
-function mount() {
+function mount(props: AudioMeterStripProps = {}) {
   const host = document.createElement("div");
   document.body.append(host);
   const root = createRoot(host);
-  act(() => root.render(<AudioMeterStrip />));
+  act(() => root.render(<AudioMeterStrip {...props} />));
   roots.push(root);
   return { host, root };
 }
@@ -177,6 +180,26 @@ describe("AudioMeterStrip", () => {
     expect(second.read).toHaveBeenCalled();
   });
 
+  it("reads a host's preview iframe over the shell's", () => {
+    usePlayerStore.setState({ elements: [clip({ audioGroup: "vo" })] });
+    const shellHook = makeHook();
+    setHook(shellHook);
+    const hostHook = makeHook();
+    const hostIframe = { contentWindow: { __hf: { audioMeter: hostHook } } };
+    mount({ previewIframeRef: { current: hostIframe as unknown as HTMLIFrameElement } });
+    tick();
+    expect(hostHook.start).toHaveBeenCalledTimes(1);
+    expect(shellHook.start).not.toHaveBeenCalled();
+  });
+
+  it("mounts with no shell and no preview iframe", () => {
+    shell = null;
+    usePlayerStore.setState({ elements: [clip({ audioGroup: "vo" })] });
+    const { host } = mount();
+    tick();
+    expect(host.querySelector("[data-testid=audio-meter-strip]")).not.toBeNull();
+  });
+
   it("keeps authored gain 2 above unity and writes exactly 1 at the midpoint", () => {
     usePlayerStore.setState({ elements: [clip({ audioGroup: "vo", audioGroupVolume: 2 })] });
     const { host } = mount();
diff --git a/packages/studio/src/components/nle/AudioMeterStrip.tsx b/packages/studio/src/components/nle/AudioMeterStrip.tsx
index ac929380eb..57ae349251 100644
--- a/packages/studio/src/components/nle/AudioMeterStrip.tsx
+++ b/packages/studio/src/components/nle/AudioMeterStrip.tsx
@@ -20,7 +20,7 @@ import type { StereoLevel } from "@hyperframes/core/runtime/levelTap";
 import { usePlayerStore } from "../../player";
 import { clampNumber } from "../../utils/studioHelpers";
 import { useAudioMetersVisible } from "../../utils/audioMeterVisibility";
-import { useStudioShellContext } from "../../contexts/StudioContext";
+import { useStudioShellContextOptional } from "../../contexts/StudioContext";
 import { useTimelineEditContextOptional } from "../../contexts/TimelineEditContext";
 import {
   METER_DB_MARKS,
@@ -107,7 +107,7 @@ function useVolumeHandlers(): {
 
 type PreviewWindow = (Window & { __hf?: { audioMeter?: AudioMeterHook } }) | null | undefined;
 
-function readHook(iframe: HTMLIFrameElement | null): AudioMeterHook | null {
+function readHook(iframe: HTMLIFrameElement | null | undefined): AudioMeterHook | null {
   try {
     return (iframe?.contentWindow as PreviewWindow)?.__hf?.audioMeter ?? null;
   } catch {
@@ -123,9 +123,8 @@ function paintPeak(el: HTMLElement | null, peak: number): void {
   el.style.setProperty("transform", peak >= 1 ? "translateY(1px)" : "none");
 }
 
-/** The fill is a fixed green/amber/red backdrop; painting only moves the dark
- *  mask that covers the unlit top portion, so a loud peak lights the real red
- *  band instead of tinting a flat colour brighter. */
+/** The fill is a fixed green/amber/red backdrop; painting only moves the dark mask that covers the unlit top
+ *  portion, so a loud peak lights the real red band instead of tinting a flat colour brighter. */
 function paint(bars: StripBars | undefined, channels: Pair): void {
   channels.forEach((ch, i) => {
     bars?.[i]?.mask?.style.setProperty("height", `${(1 - ch.level) * 100}%`);
@@ -179,8 +178,13 @@ export function stepAndPaintStrips(
 }
 
 /** One rAF loop re-reads the hook off the live preview window, so a reloaded iframe is followed. */
-function useMeterLoop(strips: Strip[], bars: RefObject<Map<string | null, StripBars>>) {
-  const { previewIframeRef } = useStudioShellContext();
+function useMeterLoop(
+  strips: Strip[],
+  bars: RefObject<Map<string | null, StripBars>>,
+  iframeRef: RefObject<HTMLIFrameElement | null> | undefined,
+) {
+  const shell = useStudioShellContextOptional();
+  const previewIframeRef = iframeRef ?? shell?.previewIframeRef;
   const stripsRef = useRef(strips);
   stripsRef.current = strips;
   useEffect(() => {
@@ -190,7 +194,7 @@ function useMeterLoop(strips: Strip[], bars: RefObject<Map<string | null, StripB
     const state = new Map<string | null, Pair>();
     const tick = (now: number) => {
       raf = requestAnimationFrame(tick);
-      active = followMeterHook(active, readHook(previewIframeRef.current));
+      active = followMeterHook(active, readHook(previewIframeRef?.current));
       const levels = active?.read();
       const dt = now - last;
       last = now;
@@ -395,14 +399,21 @@ function MeterStrip({
   );
 }
 
-export const AudioMeterStrip = memo(function AudioMeterStrip() {
+export interface AudioMeterStripProps {
+  /** Pass a stable ref (useRef): a new object each render restarts the meter loop. */
+  previewIframeRef?: RefObject<HTMLIFrameElement | null>;
+}
+
+export const AudioMeterStrip = memo(function AudioMeterStrip({
+  previewIframeRef,
+}: AudioMeterStripProps) {
   const visible = useAudioMetersVisible((s) => s.visible);
   const projectHasAudio = useProjectHasAudio();
   if (!visible || !projectHasAudio) return null;
-  return <MeterStripBody />;
+  return <MeterStripBody previewIframeRef={previewIframeRef} />;
 });
 
-function MeterStripBody() {
+function MeterStripBody({ previewIframeRef }: AudioMeterStripProps) {
   const strips = useStrips();
   const bars = useRef(new Map<string | null, StripBars>());
   const register = useRef((id: string | null, b: StripBars | null) => {
@@ -410,7 +421,7 @@ function MeterStripBody() {
     else bars.current.delete(id);
   }).current;
   const { onLive, onCommit } = useVolumeHandlers();
-  useMeterLoop(strips, bars);
+  useMeterLoop(strips, bars, previewIframeRef);
   return (
     <div
       data-testid="audio-meter-strip"
diff --git a/packages/studio/src/components/pointerTargetSize.test.tsx b/packages/studio/src/components/pointerTargetSize.test.tsx
index 4e34dd332f..602c2aa58a 100644
--- a/packages/studio/src/components/pointerTargetSize.test.tsx
+++ b/packages/studio/src/components/pointerTargetSize.test.tsx
@@ -7,7 +7,7 @@ import { CompositionsTab } from "./sidebar/CompositionsTab";
 import { TimelineToolbar } from "./TimelineToolbar";
 
 vi.mock("../contexts/StudioContext", () => ({
-  useStudioShellContext: () => ({
+  useStudioShellContextOptional: () => ({
     editHistory: { canUndo: false, canRedo: false },
     handleUndo: vi.fn(),
     handleRedo: vi.fn(),
diff --git a/packages/studio/src/hooks/useClipboard.source.test.ts b/packages/studio/src/hooks/useClipboard.source.test.ts
index 715d7bf24a..c6782e8d10 100644
--- a/packages/studio/src/hooks/useClipboard.source.test.ts
+++ b/packages/studio/src/hooks/useClipboard.source.test.ts
@@ -338,3 +338,14 @@ describe("a copy that fails", () => {
     expect(deleted).toEqual([]);
   });
 });
+
+describe("with no DOM edit session", () => {
+  it("refuses copy, cut and duplicate when nothing is selected", async () => {
+    clearSelection();
+    const { clipboard, deleted } = mountClipboard();
+    expect(clipboard().handleCopy()).toBe(false);
+    expect(await clipboard().handleCut()).toBe(false);
+    expect(await clipboard().handleDuplicate()).toBe(false);
+    expect(deleted).toEqual([]);
+  });
+});
diff --git a/packages/studio/src/hooks/useClipboard.ts b/packages/studio/src/hooks/useClipboard.ts
index 1075b09dfc..9f7f2bd40e 100644
--- a/packages/studio/src/hooks/useClipboard.ts
+++ b/packages/studio/src/hooks/useClipboard.ts
@@ -33,7 +33,7 @@ interface RecordEditInput {
   files: Record<string, { before: string; after: string }>;
 }
 
-interface UseClipboardOptions {
+export interface UseClipboardOptions {
   projectId: string | null;
   activeCompPath: string | null;
   domEditSelectionRef: React.MutableRefObject<DomEditSelection | null>;
diff --git a/packages/studio/src/index.ts b/packages/studio/src/index.ts
index 6e675c1f33..baed6432e4 100644
--- a/packages/studio/src/index.ts
+++ b/packages/studio/src/index.ts
@@ -184,6 +184,14 @@ export type { TimelinePaneProps } from "./components/nle/TimelinePane";
 export { TimelineEditProvider } from "./contexts/TimelineEditContext";
 export type { TimelineEditCallbacks } from "./player/components/timelineCallbacks";
 export type { BlockedTimelineEditIntent } from "./player/components/timelineEditing";
+export { TimelineToolbar } from "./components/TimelineToolbar";
+export type { TimelineToolbarProps } from "./components/TimelineToolbar";
+export { TimelineHistoryButtons } from "./components/TimelineHistoryButtons";
+export type { TimelineHistoryButtonsProps } from "./components/TimelineHistoryButtons";
+export { AudioMeterStrip } from "./components/nle/AudioMeterStrip";
+export type { AudioMeterStripProps } from "./components/nle/AudioMeterStrip";
+export { useClipboard } from "./hooks/useClipboard";
+export type { UseClipboardOptions } from "./hooks/useClipboard";
 
 export {
   playSeamTransitionLoop,
diff --git a/packages/studio/src/timelineChromeExports.test.tsx b/packages/studio/src/timelineChromeExports.test.tsx
new file mode 100644
index 0000000000..1fa3554787
--- /dev/null
+++ b/packages/studio/src/timelineChromeExports.test.tsx
@@ -0,0 +1,79 @@
+// @vitest-environment happy-dom
+// Mounts the timeline chrome by package name with no StudioShellProvider, as a host app does.
+import { act } from "react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import {
+  AudioMeterStrip,
+  TimelineHistoryButtons,
+  TimelineToolbar,
+  useClipboard,
+  usePlayerStore,
+  type UseClipboardOptions,
+} from "@hyperframes/studio";
+import { installReactActEnvironment, mountReactHarness } from "./hooks/domSelectionTestHarness";
+import { useAudioMetersVisible } from "./utils/audioMeterVisibility";
+
+installReactActEnvironment();
+
+afterEach(() => {
+  document.body.innerHTML = "";
+  usePlayerStore.setState({ elements: [], selectedElementId: null });
+  useAudioMetersVisible.setState(useAudioMetersVisible.getInitialState());
+});
+
+describe("timeline chrome package exports, outside Studio's shell", () => {
+  it("mounts the toolbar with the host's history and no Add beat", async () => {
+    const onUndo = vi.fn();
+    const root = mountReactHarness(
+      <TimelineToolbar history={{ canUndo: true, onUndo }} showAddBeat={false} />,
+    );
+    const undo = document.querySelector<HTMLButtonElement>('button[aria-label="Undo"]');
+    act(() => undo?.click());
+    expect(onUndo).toHaveBeenCalledTimes(1);
+    expect(document.querySelector('button[aria-label="Add beat at playhead"]')).toBeNull();
+    await act(async () => root.unmount());
+  });
+
+  it("mounts the history buttons disabled when given nothing", async () => {
+    const root = mountReactHarness(<TimelineHistoryButtons />);
+    const buttons = Array.from(document.querySelectorAll("button"));
+    expect(buttons.map((b) => b.disabled)).toEqual([true, true]);
+    await act(async () => root.unmount());
+  });
+
+  it("mounts the meter strip on the host's preview iframe", async () => {
+    usePlayerStore.setState({
+      elements: [{ id: "music", tag: "audio", start: 0, duration: 4, track: 0 }],
+    });
+    useAudioMetersVisible.setState({ visible: true });
+    const root = mountReactHarness(<AudioMeterStrip previewIframeRef={{ current: null }} />);
+    expect(document.querySelector('[data-testid="audio-meter-strip"]')).not.toBeNull();
+    await act(async () => root.unmount());
+  });
+
+  it("runs the clipboard with no DOM edit session", async () => {
+    const toasts: string[] = [];
+    const options: UseClipboardOptions = {
+      projectId: "p",
+      activeCompPath: "index.html",
+      domEditSelectionRef: { current: null },
+      showToast: (message) => toasts.push(message),
+      writeProjectFile: async () => {},
+      recordEdit: async () => {},
+      reloadPreview: () => {},
+      handleTimelineElementsDelete: async () => {},
+      handleDomEditElementDelete: async () => {},
+      previewIframeRef: { current: null },
+      waitForPendingDomEditSaves: async () => {},
+    };
+    const api: { current: ReturnType<typeof useClipboard> | null } = { current: null };
+    function Harness() {
+      api.current = useClipboard(options);
+      return null;
+    }
+    const root = mountReactHarness(<Harness />);
+    expect(api.current?.handleCopy()).toBe(false);
+    expect(toasts).toEqual(["Nothing selected to copy."]);
+    await act(async () => root.unmount());
+  });
+});