perf(studio): virtualize timeline marquee selection (#2707)

packages/studio/src/player/components/Timeline.tsx

@@ -398,6 +398,7 @@ export const Timeline = memo(function Timeline({
     handlePointerDown,
     handlePointerMove,
     handlePointerUp,
+    handlePointerCancel,
   } = useTimelineRangeSelection({
     scrollRef,
     ppsRef,
@@ -410,10 +411,11 @@ export const Timeline = memo(function Timeline({
     isDragging,
     setShowPopover,
     elementsRef: expandedElementsRef,
-    trackOrderRef,
+    clipIndex,
     rowGeometryRef,
     onSelectElement,
     contentOrigin,
+    sessionEpoch,
   });
   setRangeSelectionRef.current = setRangeSelection; // stable ref consumed by useTimelineClipDrag
 
@@ -484,7 +486,8 @@ export const Timeline = memo(function Timeline({
         }}
         onPointerMove={handlePointerMove}
         onPointerUp={handlePointerUp}
-        onLostPointerCapture={handlePointerUp}
+        onPointerCancel={handlePointerCancel}
+        onLostPointerCapture={handlePointerCancel}
       >
         <TimelineCanvas
           major={major}

packages/studio/src/player/components/timelineMarquee.test.ts

@@ -5,8 +5,11 @@ import {
   isTimelineRulerPress,
   getMarqueeRect,
   getTimelineClipRect,
+  getMarqueeClipCandidates,
   computeMarqueeSelection,
 } from "./timelineMarquee";
+import { createTimelineClipIndex } from "../lib/timelineClipIndex";
+import type { TimelineElement } from "../store/playerStore";
 import {
   GUTTER,
   LANE_H,
@@ -14,6 +17,7 @@ import {
   RULER_H,
   CLIP_Y,
   TRACKS_LEFT_PAD,
+  createTimelineRowGeometry,
   getTimelineRowTop,
 } from "./timelineLayout";
 
@@ -95,9 +99,13 @@ describe("getMarqueeRect", () => {
 
 describe("getTimelineClipRect", () => {
   const trackOrder = [0, 2, 5];
+  const geometry = createTimelineRowGeometry(
+    trackOrder,
+    trackOrder.map(() => TRACK_H),
+  );
 
   it("maps start/duration to x via pps and the track row to y via the shared row→y helper", () => {
-    const rect = getTimelineClipRect({ start: 2, duration: 3, track: 2 }, trackOrder, 100, GUTTER);
+    const rect = getTimelineClipRect({ start: 2, duration: 3, track: 2 }, geometry, 100, GUTTER);
     expect(rect).toEqual({
       left: GUTTER + 200,
       top: getTimelineRowTop(1) + CLIP_Y,
@@ -107,54 +115,48 @@ describe("getTimelineClipRect", () => {
   });
 
   it("places the first visible track below the ruler + top breathing pad", () => {
-    const rect = getTimelineClipRect({ start: 0, duration: 1, track: 0 }, trackOrder, 50, GUTTER);
+    const rect = getTimelineClipRect({ start: 0, duration: 1, track: 0 }, geometry, 50, GUTTER);
     expect(rect?.top).toBe(getTimelineRowTop(0) + CLIP_Y);
     expect(rect?.left).toBe(GUTTER);
   });
 
   it("uses the row index in trackOrder, not the raw track number", () => {
-    const rect = getTimelineClipRect({ start: 0, duration: 1, track: 5 }, trackOrder, 50, GUTTER);
+    const rect = getTimelineClipRect({ start: 0, duration: 1, track: 5 }, geometry, 50, GUTTER);
     expect(rect?.top).toBe(getTimelineRowTop(2) + CLIP_Y);
   });
 
   it("uses cumulative tops and the resolved height for an expanded row", () => {
     const rowHeights = [TRACK_H + 2 * LANE_H, TRACK_H, TRACK_H];
+    const expandedGeometry = createTimelineRowGeometry(trackOrder, rowHeights);
     const rect = getTimelineClipRect(
       { start: 0, duration: 1, track: 0 },
-      trackOrder,
+      expandedGeometry,
       50,
       GUTTER,
-      rowHeights,
     );
     expect(rect).toMatchObject({
       top: getTimelineRowTop(0, rowHeights) + CLIP_Y,
-      height: rowHeights[0] - CLIP_Y * 2,
+      height: TRACK_H - CLIP_Y * 2,
     });
     expect(
-      getTimelineClipRect({ start: 0, duration: 1, track: 2 }, trackOrder, 50, GUTTER, rowHeights)
-        ?.top,
+      getTimelineClipRect({ start: 0, duration: 1, track: 2 }, expandedGeometry, 50, GUTTER)?.top,
     ).toBe(getTimelineRowTop(1, rowHeights) + CLIP_Y);
   });
 
   it("enforces the 4px minimum rendered width", () => {
-    const rect = getTimelineClipRect(
-      { start: 0, duration: 0.01, track: 0 },
-      trackOrder,
-      10,
-      GUTTER,
-    );
+    const rect = getTimelineClipRect({ start: 0, duration: 0.01, track: 0 }, geometry, 10, GUTTER);
     expect(rect?.width).toBe(4);
   });
 
   it("returns null for a track that is not displayed or an invalid pps", () => {
     expect(
-      getTimelineClipRect({ start: 0, duration: 1, track: 9 }, trackOrder, 100, GUTTER),
+      getTimelineClipRect({ start: 0, duration: 1, track: 9 }, geometry, 100, GUTTER),
     ).toBeNull();
     expect(
-      getTimelineClipRect({ start: 0, duration: 1, track: 0 }, trackOrder, 0, GUTTER),
+      getTimelineClipRect({ start: 0, duration: 1, track: 0 }, geometry, 0, GUTTER),
     ).toBeNull();
     expect(
-      getTimelineClipRect({ start: 0, duration: 1, track: 0 }, trackOrder, NaN, GUTTER),
+      getTimelineClipRect({ start: 0, duration: 1, track: 0 }, geometry, NaN, GUTTER),
     ).toBeNull();
   });
 });
@@ -162,6 +164,10 @@ describe("getTimelineClipRect", () => {
 describe("computeMarqueeSelection", () => {
   // Two visible tracks: row 0 = track 0, row 1 = track 1. pps 100.
   const trackOrder = [0, 1];
+  const rowGeometry = createTimelineRowGeometry(
+    trackOrder,
+    trackOrder.map(() => TRACK_H),
+  );
   const pps = 100;
   const clips = [
     { id: "a", start: 0, duration: 1, track: 0 }, // x [32,132], row 0
@@ -175,7 +181,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: ORIGIN, top: row0Top, width: 50, height: 10 };
     const { ids, primaryId } = computeMarqueeSelection({
       clips,
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: ORIGIN,
       marquee,
@@ -188,7 +194,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: ORIGIN, top: row0Top, width: 60, height: row1Top - row0Top + 5 };
     const { ids } = computeMarqueeSelection({
       clips,
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: ORIGIN,
       marquee,
@@ -200,7 +206,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: ORIGIN + 140, top: row0Top, width: 50, height: 10 };
     const { ids } = computeMarqueeSelection({
       clips,
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: ORIGIN,
       marquee,
@@ -212,7 +218,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: GUTTER + 140, top: row0Top, width: 50, height: 10 };
     const { ids, primaryId } = computeMarqueeSelection({
       clips,
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: GUTTER,
       marquee,
@@ -226,7 +232,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: GUTTER, top: row1Top, width: 100, height: 10 };
     const { ids, primaryId } = computeMarqueeSelection({
       clips,
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: GUTTER,
       marquee,
@@ -240,10 +246,11 @@ describe("computeMarqueeSelection", () => {
     const wide = { left: ORIGIN, top: row0Top, width: 320, height: 10 };
     const narrow = { left: ORIGIN, top: row0Top, width: 80, height: 10 };
     expect(
-      computeMarqueeSelection({ clips, trackOrder, pps, contentOrigin: ORIGIN, marquee: wide }).ids,
+      computeMarqueeSelection({ clips, rowGeometry, pps, contentOrigin: ORIGIN, marquee: wide })
+        .ids,
     ).toEqual(new Set(["a", "b"]));
     expect(
-      computeMarqueeSelection({ clips, trackOrder, pps, contentOrigin: ORIGIN, marquee: narrow })
+      computeMarqueeSelection({ clips, rowGeometry, pps, contentOrigin: ORIGIN, marquee: narrow })
         .ids,
     ).toEqual(new Set(["a"]));
   });
@@ -252,7 +259,7 @@ describe("computeMarqueeSelection", () => {
     const marquee = { left: 0, top: 0, width: 10000, height: 10000 };
     const { ids } = computeMarqueeSelection({
       clips: [{ id: "x", start: 0, duration: 1, track: 7 }],
-      trackOrder,
+      rowGeometry,
       pps,
       contentOrigin: GUTTER,
       marquee,
@@ -260,3 +267,44 @@ describe("computeMarqueeSelection", () => {
     expect(ids).toEqual(new Set());
   });
 });
+
+describe("getMarqueeClipCandidates", () => {
+  it("queries only the intersecting rows and time span", () => {
+    const rowGeometry = createTimelineRowGeometry([0, 1, 2], [TRACK_H, TRACK_H, TRACK_H]);
+    const near: TimelineElement = { id: "near", tag: "div", start: 1, duration: 1, track: 1 };
+    const wrongTime: TimelineElement = {
+      id: "wrong-time",
+      tag: "div",
+      start: 20,
+      duration: 1,
+      track: 1,
+    };
+    const wrongRow: TimelineElement = {
+      id: "wrong-row",
+      tag: "div",
+      start: 1,
+      duration: 1,
+      track: 2,
+    };
+    const clipIndex = createTimelineClipIndex([
+      [0, []],
+      [1, [near, wrongTime]],
+      [2, [wrongRow]],
+    ]);
+
+    expect(
+      getMarqueeClipCandidates({
+        clipIndex,
+        rowGeometry,
+        marquee: {
+          left: ORIGIN + 100,
+          top: getTimelineRowTop(1),
+          width: 100,
+          height: TRACK_H - 1,
+        },
+        pps: 100,
+        contentOrigin: ORIGIN,
+      }),
+    ).toEqual([near]);
+  });
+});

packages/studio/src/player/components/timelineMarquee.ts

@@ -1,5 +1,7 @@
-import { RULER_H, CLIP_Y, getTimelineRowHeight, getTimelineRowTop } from "./timelineLayout";
+import { RULER_H, CLIP_Y, TRACK_H, type TimelineRowGeometry } from "./timelineLayout";
 import { rectsOverlap, type Rect } from "../../utils/marqueeGeometry";
+import { queryTimelineClipIndex, type TimelineClipIndex } from "../lib/timelineClipIndex";
+import type { TimelineElement } from "../store/playerStore";
 
 /** Pointer must travel at least this far (either axis) before a pointerdown on
  *  the empty timeline body becomes a marquee drag instead of a plain click. */
@@ -62,23 +64,22 @@ export function getMarqueeRect(
 /**
  * A clip's rendered rect in canvas/content coordinates (the same space the
  * marquee rect lives in): x from the shared content origin + start * pps, y from the clip's row
- * index within the visible track order (cumulative row top + CLIP_Y).
+ * index within the canonical row geometry (cumulative row top + CLIP_Y).
  * Returns null when the clip's track is not currently displayed.
  */
 export function getTimelineClipRect(
   clip: Pick<MarqueeClipInput, "start" | "duration" | "track">,
-  trackOrder: number[],
+  rowGeometry: TimelineRowGeometry,
   pps: number,
   contentOrigin: number,
-  rowHeights: readonly number[] = [],
 ): Rect | null {
-  const row = trackOrder.indexOf(clip.track);
+  const row = rowGeometry.getRowIndex(clip.track);
   if (row < 0 || !Number.isFinite(pps) || pps <= 0) return null;
   return {
     left: contentOrigin + clip.start * pps,
-    top: getTimelineRowTop(row, rowHeights) + CLIP_Y,
+    top: rowGeometry.getRowTop(row) + CLIP_Y,
     width: Math.max(clip.duration * pps, MIN_CLIP_W),
-    height: getTimelineRowHeight(row, rowHeights) - CLIP_Y * 2,
+    height: TRACK_H - CLIP_Y * 2,
   };
 }
 
@@ -90,29 +91,56 @@ export interface MarqueeSelectionResult {
   primaryId: string | null;
 }
 
+/** Narrow a marquee hit test to the intersecting logical rows and time span. */
+export function getMarqueeClipCandidates(input: {
+  clipIndex: TimelineClipIndex;
+  rowGeometry: TimelineRowGeometry;
+  marquee: Rect;
+  pps: number;
+  contentOrigin: number;
+}): readonly TimelineElement[] {
+  if (!(input.pps > 0) || input.marquee.width <= 0 || input.marquee.height <= 0) return [];
+  const lastRow = input.rowGeometry.rowKeys.length - 1;
+  const first = Math.max(0, Math.floor(input.rowGeometry.getRowFromY(input.marquee.top)));
+  const last = Math.min(
+    lastRow,
+    Math.floor(input.rowGeometry.getRowFromY(input.marquee.top + input.marquee.height)),
+  );
+  if (first > last) return [];
+  const paddingSeconds = MIN_CLIP_W / input.pps;
+  const start = Math.max(
+    0,
+    (input.marquee.left - input.contentOrigin) / input.pps - paddingSeconds,
+  );
+  const end =
+    (input.marquee.left + input.marquee.width - input.contentOrigin) / input.pps + paddingSeconds;
+  if (end <= start) return [];
+
+  const candidates: TimelineElement[] = [];
+  for (let row = first; row <= last; row += 1) {
+    const rowKey = input.rowGeometry.rowKeys[row];
+    if (rowKey === undefined) continue;
+    candidates.push(...queryTimelineClipIndex(input.clipIndex, rowKey, { start, end }));
+  }
+  return candidates;
+}
+
 /**
  * Live marquee selection: every clip whose rendered rect intersects the marquee.
  * `baseSelection` (shift/cmd-additive) is unioned in but never affects primaryId.
  */
 export function computeMarqueeSelection(input: {
   clips: MarqueeClipInput[];
-  trackOrder: number[];
+  rowGeometry: TimelineRowGeometry;
   pps: number;
   contentOrigin: number;
   marquee: Rect;
   baseSelection?: Iterable<string>;
-  rowHeights?: readonly number[];
 }): MarqueeSelectionResult {
   const ids = new Set<string>(input.baseSelection ?? []);
   let primaryId: string | null = null;
   for (const clip of input.clips) {
-    const rect = getTimelineClipRect(
-      clip,
-      input.trackOrder,
-      input.pps,
-      input.contentOrigin,
-      input.rowHeights,
-    );
+    const rect = getTimelineClipRect(clip, input.rowGeometry, input.pps, input.contentOrigin);
     if (rect && rectsOverlap(rect, input.marquee)) {
       ids.add(clip.id);
       primaryId = clip.id;

packages/studio/src/player/components/useTimelineRangeSelection.test.tsx

@@ -0,0 +1,204 @@
+// @vitest-environment happy-dom
+
+import React, { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { usePlayerStore, type TimelineElement } from "../store/playerStore";
+import { createTimelineRowGeometry, getTimelineRowTop } from "./timelineLayout";
+import { createTimelineClipIndex } from "../lib/timelineClipIndex";
+import { useTimelineRangeSelection } from "./useTimelineRangeSelection";
+import { configureTimelineTestViewport } from "./timelineTestViewport";
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+const elements: TimelineElement[] = [
+  { id: "first", tag: "div", start: 1, duration: 1, track: 0 },
+  { id: "offscreen", tag: "div", start: 2, duration: 1, track: 50 },
+  { id: "base", tag: "div", start: 8, duration: 1, track: 99 },
+];
+const tracks = Array.from({ length: 100 }, (_, index) => index);
+const geometry = createTimelineRowGeometry(
+  tracks,
+  tracks.map(() => 48),
+);
+const clipIndex = createTimelineClipIndex(
+  tracks.map((track) => [track, elements.filter((element) => element.track === track)]),
+);
+const FIRST_ROW_Y = getTimelineRowTop(0) + 4;
+const OFFSCREEN_ROW_Y = getTimelineRowTop(50) + 40;
+
+function pointer(
+  currentTarget: HTMLElement,
+  pointerId: number,
+  clientX: number,
+  clientY: number,
+  init: Partial<React.PointerEvent> = {},
+): React.PointerEvent {
+  return {
+    button: 0,
+    clientX,
+    clientY,
+    ctrlKey: false,
+    metaKey: false,
+    shiftKey: false,
+    pointerId,
+    currentTarget,
+    target: currentTarget,
+    ...init,
+  } as React.PointerEvent;
+}
+
+function renderHarness(sessionEpoch = 1) {
+  usePlayerStore.setState({ timelineSessionEpoch: sessionEpoch });
+  const host = document.createElement("div");
+  const scroll = document.createElement("div");
+  scroll.setPointerCapture = vi.fn();
+  configureTimelineTestViewport(scroll, geometry.canvasHeight);
+  host.append(scroll);
+  document.body.append(host);
+  const root = createRoot(host);
+  let api: ReturnType<typeof useTimelineRangeSelection> | null = null;
+  const ppsRef = { current: 100 };
+  const dragScrollRaf = { current: 0 };
+  const isDragging = { current: false };
+  const elementsRef = { current: elements };
+  const rowGeometryRef = { current: geometry };
+  const seekFromX = vi.fn();
+
+  function Probe({ epoch }: { epoch: number }) {
+    api = useTimelineRangeSelection({
+      scrollRef: { current: scroll },
+      ppsRef,
+      effectiveDuration: 60,
+      pps: 100,
+      seekFromX,
+      autoScrollDuringDrag: vi.fn(),
+      dragScrollRaf,
+      isDragging,
+      setShowPopover: vi.fn(),
+      elementsRef,
+      clipIndex,
+      rowGeometryRef,
+      contentOrigin: 0,
+      sessionEpoch: epoch,
+    });
+    return null;
+  }
+
+  act(() => root.render(<Probe epoch={sessionEpoch} />));
+  return {
+    scroll,
+    root,
+    get api() {
+      if (!api) throw new Error("selection harness did not render");
+      return api;
+    },
+    rerender(epoch: number) {
+      usePlayerStore.setState({ timelineSessionEpoch: epoch });
+      act(() => root.render(<Probe epoch={epoch} />));
+    },
+    seekFromX,
+  };
+}
+
+function dragMarquee(
+  view: ReturnType<typeof renderHarness>,
+  options: { secondPointer?: boolean; release?: boolean } = {},
+): void {
+  act(() => {
+    view.api.handlePointerDown(pointer(view.scroll, 7, 0, FIRST_ROW_Y));
+    if (options.secondPointer) {
+      view.api.handlePointerDown(pointer(view.scroll, 8, 500, FIRST_ROW_Y));
+    }
+    view.api.handlePointerMove(pointer(view.scroll, 7, 400, OFFSCREEN_ROW_Y));
+    if (options.release) {
+      view.api.handlePointerUp(pointer(view.scroll, 7, 400, OFFSCREEN_ROW_Y));
+    }
+  });
+}
+
+function expectSelectedIds(...ids: string[]): void {
+  expect(usePlayerStore.getState().selectedElementIds).toEqual(new Set(ids));
+}
+
+function unmountHarness(view: ReturnType<typeof renderHarness>): void {
+  act(() => view.root.unmount());
+}
+
+afterEach(() => {
+  usePlayerStore.getState().reset();
+  document.body.innerHTML = "";
+});
+
+describe("useTimelineRangeSelection", () => {
+  it("marquee-selects model clips across unmounted virtual rows", () => {
+    const view = renderHarness();
+    dragMarquee(view);
+
+    expect(document.querySelectorAll("[data-clip]")).toHaveLength(0);
+    expectSelectedIds("first", "offscreen");
+    unmountHarness(view);
+  });
+
+  it("ignores another pointer and restores the pre-drag selection on cancellation", () => {
+    usePlayerStore.getState().setSelectedElementId("base");
+    const view = renderHarness();
+    dragMarquee(view);
+    act(() => view.api.handlePointerUp(pointer(view.scroll, 8, 400, OFFSCREEN_ROW_Y)));
+    expectSelectedIds("first", "offscreen");
+
+    act(() => view.api.handlePointerCancel(pointer(view.scroll, 7, 400, OFFSCREEN_ROW_Y)));
+    expect(usePlayerStore.getState().selectedElementId).toBe("base");
+    expectSelectedIds("base");
+    unmountHarness(view);
+  });
+
+  it("keeps the original pointer owner when a second pointer presses", () => {
+    const view = renderHarness();
+    dragMarquee(view, { secondPointer: true, release: true });
+
+    expectSelectedIds("first", "offscreen");
+    unmountHarness(view);
+  });
+
+  it("commits a ruler click at its pointerdown position without requiring pointer movement", () => {
+    const view = renderHarness();
+
+    act(() => {
+      view.api.handlePointerDown(pointer(view.scroll, 7, 375, 5));
+      view.api.handlePointerUp(pointer(view.scroll, 7, 375, 5));
+    });
+
+    expect(view.seekFromX).toHaveBeenNthCalledWith(1, 375);
+    expect(view.seekFromX).toHaveBeenNthCalledWith(2, 375);
+    unmountHarness(view);
+  });
+
+  it("does not clear a finalized range when capture is lost after pointerup", () => {
+    const view = renderHarness();
+
+    act(() => {
+      view.api.handlePointerDown(pointer(view.scroll, 7, 100, 80, { shiftKey: true }));
+      view.api.handlePointerMove(pointer(view.scroll, 7, 300, 80, { shiftKey: true }));
+      view.api.handlePointerUp(pointer(view.scroll, 7, 300, 80, { shiftKey: true }));
+    });
+    const finalized = view.api.rangeSelection;
+    expect(finalized).toMatchObject({ start: 1, end: 3 });
+
+    act(() => view.api.handlePointerCancel(pointer(view.scroll, 7, 300, 80)));
+    expect(view.api.rangeSelection).toEqual(finalized);
+    unmountHarness(view);
+  });
+
+  it("cancels a live marquee when the project session changes", () => {
+    usePlayerStore.getState().setSelectedElementId("base");
+    const view = renderHarness(1);
+    dragMarquee(view);
+    usePlayerStore.getState().setSelectedElementId("base");
+    view.rerender(2);
+
+    expect(usePlayerStore.getState().selectedElementId).toBe("base");
+    expectSelectedIds("base");
+    unmountHarness(view);
+  });
+});

packages/studio/src/player/components/useTimelineRangeSelection.ts

@@ -10,6 +10,7 @@ import { liveTime, usePlayerStore } from "../store/playerStore";
 import { getTimelineScrubTime } from "./timelineLayout";
 import {
   computeMarqueeSelection,
+  getMarqueeClipCandidates,
   getMarqueeRect,
   isMarqueeDrag,
   isTimelineRulerPress,
@@ -17,6 +18,7 @@ import {
 } from "./timelineMarquee";
 import type { Rect } from "../../utils/marqueeGeometry";
 import type { TimelineRowGeometry } from "./timelineLayout";
+import type { TimelineClipIndex } from "../lib/timelineClipIndex";
 
 interface UseTimelineRangeSelectionInput {
   scrollRef: React.RefObject<HTMLDivElement | null>;
@@ -30,10 +32,11 @@ interface UseTimelineRangeSelectionInput {
   isDragging: React.RefObject<boolean>;
   setShowPopover: (v: boolean) => void;
   elementsRef: React.RefObject<TimelineElement[]>;
-  trackOrderRef: React.RefObject<number[]>;
+  clipIndex: TimelineClipIndex;
   rowGeometryRef: React.RefObject<TimelineRowGeometry>;
   onSelectElement?: (element: TimelineElement | null) => void;
   contentOrigin: number;
+  sessionEpoch: number;
 }
 
 interface MarqueeDragState {
@@ -73,16 +76,21 @@ function commitMarqueeSelection(
   rect: Rect,
   additive: boolean,
   marquee: MarqueeDragState,
-  elements: TimelineElement[],
-  trackOrder: number[],
-  rowHeights: readonly number[],
+  clipIndex: TimelineClipIndex,
+  rowGeometry: TimelineRowGeometry,
   pps: number,
   contentOrigin: number,
 ): void {
+  const candidates = getMarqueeClipCandidates({
+    clipIndex,
+    rowGeometry,
+    marquee: rect,
+    pps,
+    contentOrigin,
+  });
   const { ids, primaryId } = computeMarqueeSelection({
-    clips: toMarqueeClips(elements),
-    trackOrder,
-    rowHeights,
+    clips: toMarqueeClips([...candidates]),
+    rowGeometry,
     pps,
     contentOrigin,
     marquee: rect,
@@ -95,6 +103,28 @@ function commitMarqueeSelection(
   store.setSelectedElementIds(ids);
 }
 
+function canStartPointerGesture(
+  event: React.PointerEvent,
+  activePointerId: number | null,
+  sessionEpoch: number,
+): boolean {
+  return (
+    event.button === 0 &&
+    activePointerId === null &&
+    sessionEpoch === usePlayerStore.getState().timelineSessionEpoch
+  );
+}
+
+function isMarqueePress(
+  point: { x: number; y: number } | null,
+  scrollRect: DOMRect | undefined,
+  clientY: number,
+): point is { x: number; y: number } {
+  return (
+    point !== null && scrollRect !== undefined && !isTimelineRulerPress(clientY, scrollRect.top)
+  );
+}
+
 export function useTimelineRangeSelection({
   scrollRef,
   ppsRef,
@@ -107,10 +137,11 @@ export function useTimelineRangeSelection({
   isDragging,
   setShowPopover,
   elementsRef,
-  trackOrderRef,
+  clipIndex,
   rowGeometryRef,
   onSelectElement,
   contentOrigin,
+  sessionEpoch,
 }: UseTimelineRangeSelectionInput) {
   const isRangeSelecting = useRef(false);
   const rangeAnchorTime = useRef(0);
@@ -126,6 +157,17 @@ export function useTimelineRangeSelection({
 
   const seekRafRef = useRef(0);
   const pendingClientXRef = useRef(0);
+  const activePointerIdRef = useRef<number | null>(null);
+  const gestureEpochRef = useRef<number | null>(null);
+  const sessionEpochRef = useRef(sessionEpoch);
+  sessionEpochRef.current = sessionEpoch;
+
+  const isGestureSessionCurrent = useCallback(
+    () =>
+      gestureEpochRef.current === sessionEpochRef.current &&
+      gestureEpochRef.current === usePlayerStore.getState().timelineSessionEpoch,
+    [],
+  );
 
   // Marquee (rubber-band) multi-select on the empty timeline body.
   const marqueeRef = useRef<MarqueeDragState | null>(null);
@@ -159,7 +201,7 @@ export function useTimelineRangeSelection({
   const applyMarqueeAtClient = useCallback(
     (clientX: number, clientY: number, shiftKey: boolean) => {
       const marquee = marqueeRef.current;
-      if (!marquee) return;
+      if (!marquee || !isGestureSessionCurrent()) return;
       const point = toContentPoint(clientX, clientY);
       if (!point) return;
       if (!marquee.active && !isMarqueeDrag(marquee.originX, marquee.originY, point.x, point.y)) {
@@ -175,14 +217,13 @@ export function useTimelineRangeSelection({
         rect,
         additive,
         marquee,
-        elementsRef.current ?? [],
-        trackOrderRef.current ?? [],
-        rowGeometryRef.current.rowHeights,
+        clipIndex,
+        rowGeometryRef.current,
         ppsRef.current,
         contentOrigin,
       );
     },
-    [toContentPoint, elementsRef, trackOrderRef, rowGeometryRef, ppsRef, contentOrigin],
+    [toContentPoint, isGestureSessionCurrent, clipIndex, rowGeometryRef, ppsRef, contentOrigin],
   );
 
   const stopMarqueeAutoScroll = useCallback(() => {
@@ -203,14 +244,16 @@ export function useTimelineRangeSelection({
     const marquee = marqueeRef.current;
     const pointer = marqueePointerRef.current;
     const scroll = scrollRef.current;
-    if (!marquee || !pointer || !scroll) return;
+    if (!marquee || !pointer || !scroll || !isGestureSessionCurrent()) {
+      return;
+    }
     if (!applyTimelineAutoScrollStep(scroll, pointer.clientX, pointer.clientY)) return;
 
     // Re-run at the SAME client point: toContentPoint folds in the new scroll, so
     // the marquee's moving corner tracks the revealed content.
     applyMarqueeAtClient(pointer.clientX, pointer.clientY, pointer.shiftKey);
     marqueeScrollRaf.current = requestAnimationFrame(stepMarqueeAutoScroll);
-  }, [scrollRef, applyMarqueeAtClient]);
+  }, [scrollRef, applyMarqueeAtClient, isGestureSessionCurrent]);
 
   const syncMarqueeAutoScroll = useCallback(
     (clientX: number, clientY: number, shiftKey: boolean) => {
@@ -235,6 +278,8 @@ export function useTimelineRangeSelection({
   const beginRangeSelection = useCallback(
     (e: React.PointerEvent) => {
       (e.currentTarget as HTMLElement).setPointerCapture(e.pointerId);
+      activePointerIdRef.current = e.pointerId;
+      gestureEpochRef.current = sessionEpochRef.current;
       isRangeSelecting.current = true;
       setShowPopover(false);
       const rect = scrollRef.current?.getBoundingClientRect();
@@ -248,9 +293,31 @@ export function useTimelineRangeSelection({
     [scrollRef, pps, setShowPopover, contentOrigin],
   );
 
+  const beginScrub = useCallback(
+    (clientX: number) => {
+      isDragging.current = true;
+      setIsScrubbing(true);
+      pendingClientXRef.current = clientX;
+      seekFromX(clientX);
+    },
+    [isDragging, seekFromX],
+  );
+
+  const beginMarquee = useCallback((point: { x: number; y: number }, additive: boolean) => {
+    const base = snapshotSelection();
+    marqueeRef.current = {
+      originX: point.x,
+      originY: point.y,
+      baseIds: base.ids,
+      basePrimary: base.primary,
+      additive,
+      active: false,
+    };
+  }, []);
+
   const handlePointerDown = useCallback(
     (e: React.PointerEvent) => {
-      if (e.button !== 0) return;
+      if (!canStartPointerGesture(e, activePointerIdRef.current, sessionEpochRef.current)) return;
       if (e.shiftKey) {
         beginRangeSelection(e);
         return;
@@ -258,6 +325,8 @@ export function useTimelineRangeSelection({
       shiftClickClipRef.current = null;
       if ((e.target as HTMLElement).closest("[data-clip]")) return;
       (e.currentTarget as HTMLElement).setPointerCapture(e.pointerId);
+      activePointerIdRef.current = e.pointerId;
+      gestureEpochRef.current = sessionEpochRef.current;
       setRangeSelection(null);
       setShowPopover(false);
       const point = toContentPoint(e.clientX, e.clientY);
@@ -266,30 +335,15 @@ export function useTimelineRangeSelection({
       // y (which folds in scrollTop) breaks once the body is scrolled down and
       // the stuck ruler visually overlays scrolled-away track rows.
       const scrollRect = scrollRef.current?.getBoundingClientRect();
-      if (!point || !scrollRect || isTimelineRulerPress(e.clientY, scrollRect.top)) {
-        isDragging.current = true;
-        setIsScrubbing(true);
-        // Seed the pending coordinate so a press with no pointermove still
-        // replays THIS x on pointerup. `updateScrubDrag` is the only other
-        // writer, so without this a plain click settles on the ref's initial
-        // 0 and clamps the playhead back to t=0.
-        pendingClientXRef.current = e.clientX;
-        seekFromX(e.clientX);
+      if (!isMarqueePress(point, scrollRect, e.clientY)) {
+        beginScrub(e.clientX);
         return;
       }
       // Empty body press → pending marquee. A plain click (no drag past the
       // threshold) deselects on pointerup; a drag draws the marquee. Never scrubs.
-      const base = snapshotSelection();
-      marqueeRef.current = {
-        originX: point.x,
-        originY: point.y,
-        baseIds: base.ids,
-        basePrimary: base.primary,
-        additive: e.metaKey || e.ctrlKey,
-        active: false,
-      };
+      beginMarquee(point, e.metaKey || e.ctrlKey);
     },
-    [beginRangeSelection, seekFromX, scrollRef, isDragging, setShowPopover, toContentPoint],
+    [beginRangeSelection, beginScrub, beginMarquee, scrollRef, setShowPopover, toContentPoint],
   );
 
   // Scrub-drag update: live playhead feedback (liveTime) + RAF-throttled seek.
@@ -325,18 +379,27 @@ export function useTimelineRangeSelection({
     [scrollRef, pps, seekFromX, autoScrollDuringDrag, isDragging, contentOrigin],
   );
 
+  const updateRangeSelection = useCallback(
+    (e: React.PointerEvent) => {
+      const scroll = scrollRef.current;
+      const rect = scroll?.getBoundingClientRect();
+      if (!scroll || !rect) return;
+      const x = e.clientX - rect.left + scroll.scrollLeft - contentOrigin;
+      setRangeSelection((previous) =>
+        previous
+          ? { ...previous, end: Math.max(0, x / pps), anchorX: e.clientX, anchorY: e.clientY }
+          : null,
+      );
+    },
+    [contentOrigin, pps, scrollRef],
+  );
+
   const handlePointerMove = useCallback(
     (e: React.PointerEvent) => {
+      if (!isGestureSessionCurrent()) return;
+      if (activePointerIdRef.current !== null && e.pointerId !== activePointerIdRef.current) return;
       if (isRangeSelecting.current) {
-        const rect = scrollRef.current?.getBoundingClientRect();
-        if (rect) {
-          const x = e.clientX - rect.left + (scrollRef.current?.scrollLeft ?? 0) - contentOrigin;
-          setRangeSelection((prev) =>
-            prev
-              ? { ...prev, end: Math.max(0, x / pps), anchorX: e.clientX, anchorY: e.clientY }
-              : null,
-          );
-        }
+        updateRangeSelection(e);
         return;
       }
       const marquee = marqueeRef.current;
@@ -351,13 +414,12 @@ export function useTimelineRangeSelection({
       updateScrubDrag(e.clientX);
     },
     [
-      pps,
-      scrollRef,
       isDragging,
       applyMarqueeAtClient,
       syncMarqueeAutoScroll,
       updateScrubDrag,
-      contentOrigin,
+      updateRangeSelection,
+      isGestureSessionCurrent,
     ],
   );
 
@@ -403,17 +465,15 @@ export function useTimelineRangeSelection({
     [stopMarqueeAutoScroll, elementsRef, onSelectElement],
   );
 
-  const handlePointerUp = useCallback(() => {
-    if (isRangeSelecting.current) {
-      finishRangeSelection();
-      return;
-    }
-    const marquee = marqueeRef.current;
-    if (marquee) {
-      finishMarquee(marquee);
-      return;
-    }
-    if (!isDragging.current) return;
+  const canFinishPointerGesture = useCallback(
+    (e?: React.PointerEvent) => {
+      const pointerId = activePointerIdRef.current;
+      return pointerId !== null && (!e || e.pointerId === pointerId) && isGestureSessionCurrent();
+    },
+    [isGestureSessionCurrent],
+  );
+
+  const finishScrub = useCallback(() => {
     if (seekRafRef.current) {
       cancelAnimationFrame(seekRafRef.current);
       seekRafRef.current = 0;
@@ -422,7 +482,69 @@ export function useTimelineRangeSelection({
     isDragging.current = false;
     setIsScrubbing(false);
     cancelAnimationFrame(dragScrollRaf.current);
-  }, [isDragging, dragScrollRaf, seekFromX, finishRangeSelection, finishMarquee]);
+  }, [dragScrollRaf, isDragging, seekFromX]);
+
+  const handlePointerUp = useCallback(
+    (e?: React.PointerEvent) => {
+      if (!canFinishPointerGesture(e)) return;
+      activePointerIdRef.current = null;
+      gestureEpochRef.current = null;
+      if (isRangeSelecting.current) {
+        finishRangeSelection();
+        return;
+      }
+      const marquee = marqueeRef.current;
+      if (marquee) {
+        finishMarquee(marquee);
+        return;
+      }
+      if (isDragging.current) finishScrub();
+    },
+    [canFinishPointerGesture, finishRangeSelection, finishMarquee, finishScrub, isDragging],
+  );
+
+  const cancelActiveGesture = useCallback(
+    (updateUi: boolean, restoreSelection: boolean) => {
+      activePointerIdRef.current = null;
+      gestureEpochRef.current = null;
+      isRangeSelecting.current = false;
+      isDragging.current = false;
+      stopMarqueeAutoScroll();
+      if (seekRafRef.current) {
+        cancelAnimationFrame(seekRafRef.current);
+        seekRafRef.current = 0;
+      }
+      cancelAnimationFrame(dragScrollRaf.current);
+      dragScrollRaf.current = 0;
+
+      const marquee = marqueeRef.current;
+      marqueeRef.current = null;
+      if (restoreSelection && marquee?.active) {
+        const store = usePlayerStore.getState();
+        store.setSelectedElementId(marquee.basePrimary);
+        store.setSelectedElementIds(marquee.baseIds);
+      }
+      if (updateUi) {
+        setMarqueeRect(null);
+        setRangeSelection(null);
+        setIsScrubbing(false);
+      }
+    },
+    [dragScrollRaf, isDragging, stopMarqueeAutoScroll],
+  );
+
+  const handlePointerCancel = useCallback(
+    (e?: React.PointerEvent) => {
+      if (
+        activePointerIdRef.current === null ||
+        (e && activePointerIdRef.current !== null && e.pointerId !== activePointerIdRef.current)
+      ) {
+        return;
+      }
+      cancelActiveGesture(true, isGestureSessionCurrent());
+    },
+    [cancelActiveGesture, isGestureSessionCurrent],
+  );
 
   // Escape: cancel an in-flight marquee (restores the pre-drag selection);
   // otherwise clear any lingering multi-selection.
@@ -432,15 +554,11 @@ export function useTimelineRangeSelection({
       const store = usePlayerStore.getState();
       const marquee = marqueeRef.current;
       if (marquee) {
-        marqueeRef.current = null;
-        stopMarqueeAutoScroll();
-        setMarqueeRect(null);
-        if (marquee.active) {
-          // Primary FIRST (see commitMarqueeSelection): it collapses the set, so
-          // restore the pre-drag primary before repopulating the base ids.
-          store.setSelectedElementId(marquee.basePrimary);
-          store.setSelectedElementIds(marquee.baseIds);
-        }
+        cancelActiveGesture(true, true);
+        return;
+      }
+      if (isRangeSelecting.current || isDragging.current) {
+        cancelActiveGesture(true, true);
         return;
       }
       // Escape with no marquee clears the whole selection — primary AND set.
@@ -451,7 +569,21 @@ export function useTimelineRangeSelection({
     };
     window.addEventListener("keydown", onKeyDown);
     return () => window.removeEventListener("keydown", onKeyDown);
-  }, [stopMarqueeAutoScroll]);
+  }, [cancelActiveGesture, isDragging]);
+
+  const previousSessionEpochRef = useRef(sessionEpoch);
+  useEffect(() => {
+    if (previousSessionEpochRef.current === sessionEpoch) return;
+    previousSessionEpochRef.current = sessionEpoch;
+    cancelActiveGesture(true, false);
+  }, [cancelActiveGesture, sessionEpoch]);
+
+  useEffect(
+    () => () => {
+      cancelActiveGesture(false, isGestureSessionCurrent());
+    },
+    [cancelActiveGesture, isGestureSessionCurrent],
+  );
 
   return {
     rangeSelection,
@@ -462,5 +594,6 @@ export function useTimelineRangeSelection({
     handlePointerDown,
     handlePointerMove,
     handlePointerUp,
+    handlePointerCancel,
   };
 }

packages/studio/src/player/components/useTimelineRangeSelectionScrub.test.tsx

@@ -9,6 +9,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { mountReactHarness } from "../../hooks/domSelectionTestHarness";
 import { useTimelineRangeSelection } from "./useTimelineRangeSelection";
 import { getTimelineRowGeometry } from "./timelineLayout";
+import { createTimelineClipIndex } from "../lib/timelineClipIndex";
 
 (globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
 
@@ -60,7 +61,6 @@ function setup(): { handlers: () => Handlers; seekFromX: ReturnType<typeof vi.fn
   const dragScrollRaf = { current: 0 };
   const isDragging = { current: false };
   const elementsRef = { current: [] };
-  const trackOrderRef = { current: [] };
   const rowGeometryRef = { current: getTimelineRowGeometry([]) };
 
   function Probe(): null {
@@ -75,7 +75,8 @@ function setup(): { handlers: () => Handlers; seekFromX: ReturnType<typeof vi.fn
       isDragging,
       setShowPopover: vi.fn(),
       elementsRef,
-      trackOrderRef,
+      clipIndex: createTimelineClipIndex([]),
+      sessionEpoch: 0,
       rowGeometryRef,
       contentOrigin: 0,
     });