fix(studio): address family B timeline review findings

- revert diamond selection when a rejected retime leaves the source in place
- clear project-local ease focus and expansion on player store reset
- share one static-position-hold predicate across the tween cache
- invalidate the GSAP cache even when a group timing rewrite throws
- stamp each lane keyframe's ease from its own source tween
- memoize property lanes and row offsets so memo'd diamond lanes hold
- use the editable tween duration for drag position commits
- restore the pre-t=0 pad in the all-collapsed content origin
- clamp the drag ghost and drop placeholder to the collapsed clip height
- aria-expanded on the layer disclosure, aria-pressed plus state-specific
  labels on the keyframe toggle, 24px chevron targets, focus-visible parity

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

@@ -93,7 +93,11 @@ export function KeyframeEaseList({
           ? "Custom"
           : (EASE_LABELS[segEase] ?? segEase);
         return (
-          <div key={`${i}-${kf.percentage}`} className="rounded-md bg-neutral-900/50">
+          <div
+            key={`${i}-${kf.percentage}`}
+            data-ease-segment-pct={kf.percentage}
+            className="rounded-md bg-neutral-900/50"
+          >
             <button
               type="button"
               onClick={() => onToggle(isExpanded ? null : kf.percentage)}

packages/studio/src/hooks/gsapDragPositionCommit.ts

@@ -2,9 +2,9 @@ import type { GsapAnimation } from "@hyperframes/core/gsap-parser";
 import type { DomEditSelection } from "../components/editor/domEditingTypes";
 import { usePlayerStore } from "../player/store/playerStore";
 import { resolveTweenStart, resolveTweenDuration } from "../utils/globalTimeCompiler";
+import { resolveEditableTweenDuration } from "./gsapShared";
 import { roundTo3 } from "../utils/rounding";
 import { computeDraggedGsapPosition } from "./draggedGsapPosition";
-import { resolveEditableTweenDuration } from "./gsapShared";
 import {
   type GsapDragCommitCallbacks,
   computeCurrentPercentage,
@@ -159,7 +159,7 @@ async function commitFlatViaKeyframes(
 ): Promise<void> {
   const ct = usePlayerStore.getState().currentTime;
   const ts = resolveTweenStart(anim);
-  const td = resolveTweenDuration(anim);
+  const td = resolveEditableTweenDuration(anim, selection);
   const { activeKeyframePct, setActiveKeyframePct } = usePlayerStore.getState();
   const outsideRange =
     activeKeyframePct == null && ts !== null && td > 0 && (ct < ts - 0.01 || ct > ts + td + 0.01);
@@ -324,7 +324,7 @@ export async function commitGsapPositionFromDrag(
     const dragProps: Record<string, number> = { x: newX, y: newY };
 
     const ts = resolveTweenStart(effectiveAnim);
-    const td = resolveTweenDuration(effectiveAnim);
+    const td = resolveEditableTweenDuration(effectiveAnim, selection);
     const outsideRange = ts !== null && td > 0 && (ct < ts - 0.01 || ct > ts + td + 0.01);
     const hasSelectedKeyframe = usePlayerStore.getState().activeKeyframePct != null;
     if (outsideRange && !hasSelectedKeyframe) {
@@ -352,7 +352,7 @@ export async function commitGsapPositionFromDrag(
   } else if (anim.method === "from" || anim.method === "fromTo") {
     const ct = usePlayerStore.getState().currentTime;
     const ts = resolveTweenStart(anim);
-    const td = resolveTweenDuration(anim);
+    const td = resolveEditableTweenDuration(anim, selection);
     const hasSelectedKeyframe = usePlayerStore.getState().activeKeyframePct != null;
     const outsideRange =
       !hasSelectedKeyframe && ts !== null && td > 0 && (ct < ts - 0.01 || ct > ts + td + 0.01);
@@ -372,7 +372,7 @@ export async function commitGsapPositionFromDrag(
 
       if (existingPosAnim?.keyframes) {
         const posTs = resolveTweenStart(existingPosAnim);
-        const posTd = resolveTweenDuration(existingPosAnim);
+        const posTd = resolveEditableTweenDuration(existingPosAnim, selection);
         if (posTs !== null) {
           await extendTweenAndAddKeyframe(
             selection,

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

@@ -390,4 +390,36 @@ describe("deleteSelectedKeyframes", () => {
       expect.objectContaining({ softReload: true }),
     );
   });
+
+  it("drops keyframes that belong to other elements", () => {
+    // A stale selection from a previously active element must not delete
+    // anything on the element that is active now.
+    usePlayerStore.setState({
+      selectedElementId: "card",
+      selectedKeyframes: new Set([
+        timelineKeyframeSelectionKey("card", {
+          percentage: 30,
+          tweenPercentage: 20,
+          propertyGroup: "position",
+          animationId: "card-position",
+        }),
+        timelineKeyframeSelectionKey("other", {
+          percentage: 70,
+          tweenPercentage: 80,
+          propertyGroup: "position",
+          animationId: "card-position",
+        }),
+      ]),
+    });
+    const handleGsapRemoveKeyframe =
+      vi.fn<(animId: string, pct: number, options?: Partial<CommitMutationOptions>) => void>();
+
+    deleteSelectedKeyframes({
+      selectedGsapAnimations: [{ id: "card-position", keyframes: {} }],
+      handleGsapRemoveKeyframe,
+    });
+
+    expect(handleGsapRemoveKeyframe).toHaveBeenCalledTimes(1);
+    expect(handleGsapRemoveKeyframe.mock.calls[0]?.[1]).toBe(20);
+  });
 });

packages/studio/src/hooks/useGsapTweenCache.ts

@@ -330,9 +330,14 @@ export function useGsapAnimationsForElement(
   // fallow-ignore-next-line complexity
   useEffect(() => {
     if (!elementId) return;
-    // No property-group filter: ungrouped tweens are recorded here as well.
+    // Same admission rule as the keyframe cache below (hold skip included) and
+    // no property-group filter: the two stores must agree, or a hold draws an
+    // expanded property lane with no collapsed diamond behind it and an
+    // ungrouped tween draws diamonds with no lane source.
     const sourceAnimations = animations.filter(
-      (animation) => animation.keyframes || synthesizeFlatTweenKeyframes(animation),
+      (animation) =>
+        !isStaticPositionHold(animation) &&
+        (animation.keyframes || synthesizeFlatTweenKeyframes(animation)),
     );
     if (sourceAnimations.length > 0)
       writeGsapAnimationsForElement(sourceFile, elementId, sourceAnimations);

packages/studio/src/hooks/useStudioContextValue.ts

@@ -96,6 +96,9 @@ export function useInspectorState(
       inspectorPanelActive,
       inspectorButtonActive:
         STUDIO_INSPECTOR_PANELS_ENABLED && !rightCollapsed && inspectorPanelActive,
+      // Deliberately wider than shouldShowSelectedDomBounds: the on-canvas path
+      // handles ARE the arc-drag affordance, so gating them on an open Inspector
+      // would make keyframe path editing reachable only from a side panel.
       shouldShowMotionPath: !!domEditSelection && !isPlaying && !isGestureRecording,
       // Keep the selection box drawn even when the Inspector is collapsed —
       // closing the panel shouldn't visually deselect the element.

packages/studio/src/hooks/useTimelineGroupEditing.ts

@@ -312,25 +312,32 @@ export function useTimelineGroupEditing({
         // reload (see the trackOnly doc above). Mixed batches (any start
         // change) keep the full fallback below.
         if (trackOnly) return;
-        await finishGroupTimingGsapFallback({
+        // The timing persist above already committed to disk, so the cached
-          projectId,
+        // GSAP read is stale whether or not the position rewrite succeeded —
-          iframe: previewIframeRef.current,
+        // invalidate on the error path too (matches the single-element path's
-          reloadPreview,
+        // `.finally`), or a failed rewrite leaves the editor reading old tweens.
-          label: "Move timeline clips",
+        try {
-          errorLabel: "Failed to shift GSAP positions",
+          await finishGroupTimingGsapFallback({
-          coalesceKey,
+            projectId,
-          recordEdit,
+            iframe: previewIframeRef.current,
-          activeCompPath,
+            reloadPreview,
-          changes,
+            label: "Move timeline clips",
-          resolveChangePath: (element) => targetPathFor(element, activeCompPath),
+            errorLabel: "Failed to shift GSAP positions",
-          mutateChange: (change, changePath) => {
+            coalesceKey,
-            const delta = change.start - change.element.start;
+            recordEdit,
-            const domId = change.element.domId;
+            activeCompPath,
-            if (delta === 0 || !domId) return null;
+            changes,
-            return shiftGsapPositions(projectId, changePath, domId, delta);
+            resolveChangePath: (element) => targetPathFor(element, activeCompPath),
-          },
+            mutateChange: (change, changePath) => {
-        });
+              const delta = change.start - change.element.start;
-        invalidateGsapCache?.();
+              const domId = change.element.domId;
+              if (delta === 0 || !domId) return null;
+              return shiftGsapPositions(projectId, changePath, domId, delta);
+            },
+          });
+        } finally {
+          invalidateGsapCache?.();
+        }
       }).catch((error) => {
         // Failed persist: revert the optimistic duration readout + live root
         // alongside the gesture owner's store rollback.
@@ -410,34 +417,40 @@ export function useTimelineGroupEditing({
             coalesceMs,
           );
         }
-        await finishGroupTimingGsapFallback({
+        // See the move path: the timing persist is already on disk, so the GSAP
-          projectId,
+        // cache must be invalidated even when the position rewrite throws.
-          iframe: previewIframeRef.current,
+        try {
-          reloadPreview,
+          await finishGroupTimingGsapFallback({
-          label: "Resize timeline clips",
+            projectId,
-          errorLabel: "Failed to scale GSAP positions",
+            iframe: previewIframeRef.current,
-          coalesceKey,
+            reloadPreview,
-          recordEdit,
+            label: "Resize timeline clips",
-          activeCompPath,
+            errorLabel: "Failed to scale GSAP positions",
-          changes,
+            coalesceKey,
-          resolveChangePath: (element) => targetPathFor(element, activeCompPath),
+            recordEdit,
-          mutateChange: (change, changePath) => {
+            activeCompPath,
-            const domId = change.element.domId;
+            changes,
-            const timingChanged =
+            resolveChangePath: (element) => targetPathFor(element, activeCompPath),
-              change.start !== change.element.start || change.duration !== change.element.duration;
+            mutateChange: (change, changePath) => {
-            if (!timingChanged || !domId) return null;
+              const domId = change.element.domId;
-            return scaleGsapPositions(
+              const timingChanged =
-              projectId,
+                change.start !== change.element.start ||
-              changePath,
+                change.duration !== change.element.duration;
-              domId,
+              if (!timingChanged || !domId) return null;
-              change.element.start,
+              return scaleGsapPositions(
-              change.element.duration,
+                projectId,
-              change.start,
+                changePath,
-              change.duration,
+                domId,
-            );
+                change.element.start,
-          },
+                change.element.duration,
-        });
+                change.start,
-        invalidateGsapCache?.();
+                change.duration,
+              );
+            },
+          });
+        } finally {
+          invalidateGsapCache?.();
+        }
       }).catch((error) => {
         // Failed persist: revert the optimistic duration readout + live root
         // alongside the gesture owner's store rollback.

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

@@ -31,6 +31,7 @@ export function LayerDisclosureRow({
     >
       <button
         type="button"
+        aria-expanded={isExpanded}
         aria-label={`${isExpanded ? "Collapse" : "Expand"} ${name} keyframes`}
         title={`${isExpanded ? "Collapse" : "Expand"} keyframe lanes`}
         className="flex h-5 w-4 shrink-0 items-center justify-center rounded border-0 bg-transparent p-0 text-white/55 hover:text-white focus-visible:outline focus-visible:outline-1 focus-visible:outline-[#3CE6AC]"
@@ -47,10 +48,9 @@ export function LayerDisclosureRow({
           style={{ transform: isExpanded ? "rotate(90deg)" : undefined }}
         />
       </button>
-      <span
+      {/* Decorative: the disclosure button above already names the row's keyframe
-        aria-label="Layer keyframe indicator"
+          state, and aria-label on a plain span is not exposed reliably anyway. */}
-        className="shrink-0 text-[13px] leading-none text-white/40"
+      <span aria-hidden="true" className="shrink-0 text-[13px] leading-none text-white/40">
-      >
         ◇
       </span>
       <span className="min-w-0 flex-1 truncate font-medium" title={name}>

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

@@ -108,7 +108,7 @@ function renderBasicTimeline() {
 }
 
 describe("Timeline provider boundary", () => {
-  it("keeps all-collapsed horizontal positions at the 32px gutter", () => {
+  it("keeps all-collapsed horizontal positions at the gutter plus the pre-t=0 pad", () => {
     usePlayerStore.setState({
       duration: 11,
       timelineReady: true,
@@ -121,13 +121,13 @@ describe("Timeline provider boundary", () => {
     const { root, clip, trackHeader, rulerTick, rulerOrigin, playhead } =
       renderTimelineGeometry("clip-1");
 
-    expect(trackHeader.style.width).toBe("32px");
+    expect(trackHeader.style.width).toBe(`${GUTTER + TRACKS_LEFT_PAD}px`);
     expect(clip.style.left).toBe("1000px");
     expect(clip.style.height).toBe("");
     expect(clip.style.bottom).toBe(`${CLIP_Y}px`);
-    expect(rulerOrigin.style.width).toBe("32px");
+    expect(rulerOrigin.style.width).toBe(`${GUTTER + TRACKS_LEFT_PAD}px`);
     expect(rulerTick.style.left).toBe("999.5px");
-    expect(playhead.style.left).toBe(`${1032 - PLAYHEAD_HEAD_W / 2}px`);
+    expect(playhead.style.left).toBe(`${GUTTER + TRACKS_LEFT_PAD + 1000 - PLAYHEAD_HEAD_W / 2}px`);
     expect(playhead.style.width).toBe(`${PLAYHEAD_HEAD_W}px`);
     expect(
       resolveTimelineAssetDrop(

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

@@ -21,7 +21,7 @@ import { useTimelineEditPinning } from "./useTimelineEditPinning";
 import { useTimelineStackingSync } from "./useTimelineStackingSync";
 import { useTimelineGeometry } from "./useTimelineGeometry";
 import { useAutoExpandKeyframedClips } from "./useAutoExpandKeyframedClips";
-import { GUTTER, LABEL_COL_W, generateTicks } from "./timelineLayout";
+import { GUTTER, LABEL_COL_W, TRACKS_LEFT_PAD, generateTicks } from "./timelineLayout";
 import { useTimelineScrollViewport } from "./useTimelineScrollViewport";
 import { STUDIO_PREVIEW_FPS } from "../lib/time";
 import { useResolvedTimelineEditCallbacks } from "./useResolvedTimelineEditCallbacks";
@@ -127,7 +127,10 @@ export const Timeline = memo(function Timeline({
     [gsapAnimations],
   );
   const labelMode = STUDIO_KEYFRAMES_ENABLED && hasKeyframedClips;
-  const contentOrigin = labelMode ? LABEL_COL_W + GUTTER : GUTTER;
+  // Without the label column the pre-t=0 breathing room is still TRACKS_LEFT_PAD
+  // (dropping it would jam clip 0 against the gutter on every non-keyframed
+  // composition); in label mode the 232px label column already provides it.
+  const contentOrigin = labelMode ? LABEL_COL_W + GUTTER : GUTTER + TRACKS_LEFT_PAD;
   const contentGutter = labelMode ? GUTTER : 0;
   const setSelectedElementId = usePlayerStore((s) => s.setSelectedElementId);
   const currentTime = usePlayerStore((s) => s.currentTime);

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

@@ -47,6 +47,11 @@ export const TimelineCanvas = memo(function TimelineCanvas(props: TimelineCanvas
   const draggedRowIndex =
     draggedClip?.started === true ? displayTrackOrder.indexOf(draggedClip.previewTrack) : -1;
   const draggedRowHeight = getTimelineRowHeight(draggedRowIndex, props.rowHeights);
+  // A clip bar in an EXPANDED row still renders at TRACK_H (the property lanes
+  // occupy the rest of the row — see TimelineLanes' clipHeight), so the drag
+  // ghost and drop placeholder must clamp to it or they stretch to the full
+  // expanded row height and stop matching the clip being dragged.
+  const draggedClipHeight = Math.min(draggedRowHeight, TRACK_H) - CLIP_Y * 2;
   const {
     onResizeElement,
     onMoveElement,
@@ -177,7 +182,7 @@ export const TimelineCanvas = memo(function TimelineCanvas(props: TimelineCanvas
             top: getTimelineRowTop(draggedRowIndex, props.rowHeights) + CLIP_Y,
             left: props.contentOrigin + draggedClip.previewStart * props.pps,
             width: Math.max(draggedClip.element.duration * props.pps, 4),
-            height: draggedRowHeight - CLIP_Y * 2,
+            height: draggedClipHeight,
             border: "1px solid rgba(60,230,172,0.55)",
             background: "rgba(60,230,172,0.12)",
             borderRadius: 4,
@@ -230,7 +235,7 @@ export const TimelineCanvas = memo(function TimelineCanvas(props: TimelineCanvas
             top: activeDraggedPosition.top,
             left: activeDraggedPosition.left,
             width: Math.max(activeDraggedElement.duration * props.pps, 4),
-            height: draggedRowHeight - CLIP_Y * 2,
+            height: draggedClipHeight,
             zIndex: 40,
           }}
         >

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

@@ -375,12 +375,23 @@ export const TimelineDiamondLane = memo(function TimelineDiamondLane({
                 pendingRetimeRef.current.delete(kfKey);
               }
             };
+            // A rejected drop (the destination time is already occupied) snaps
+            // the diamond back to its source position, so the pending entry AND
+            // the selection have to revert with it — parking on the ghost drop
+            // position strands the playhead + selection on a keyframe that does
+            // not exist there.
+            const revertRetime = () => {
+              clearPending();
+              onClickKeyframe?.(fromTarget);
+            };
             void onMoveKeyframe?.(fromTarget, res.toClipPct).then((committed) => {
-              if (!committed) clearPending();
+              if (!committed) revertRetime();
-            }, clearPending);
+            }, revertRetime);
             // A retime still targeted this exact diamond — park/select it at its
             // new position, same as a plain click, or a drag that actually moved
-            // something looks identical to one that silently did nothing.
+            // something looks identical to one that silently did nothing. Done
+            // optimistically so the gesture stays responsive; revertRetime puts
+            // it back if the move is rejected.
             onClickKeyframe?.({
               ...target,
               percentage: res.toClipPct,

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

@@ -1,4 +1,4 @@
-import type { MouseEvent as ReactMouseEvent, RefObject } from "react";
+import { useMemo, type MouseEvent as ReactMouseEvent, type RefObject } from "react";
 import {
   classifyPropertyGroup,
   type GsapAnimation,
@@ -59,6 +59,14 @@ function sourceGroups(animations: readonly GsapAnimation[]) {
   return groups;
 }
 
+/** Resolve the ease from THIS keyframe's own source tween. A lane can merge
+ *  several tweens, so a shared lane-level fallback would label a segment with a
+ *  different animation's ease than the one the ease editor targets (it routes
+ *  by animationId). */
+function keyframeEase(keyframe: { ease?: string }, animation: GsapAnimation): string | undefined {
+  return keyframe.ease ?? animation.keyframes?.easeEach ?? animation.ease;
+}
+
 function groupKeyframes(
   animations: readonly GsapAnimation[],
   group: PropertyGroupName,
@@ -79,6 +87,7 @@ function groupKeyframes(
         tweenPercentage: keyframe.percentage,
         propertyGroup: group,
         animationId: animation.id,
+        ease: keyframeEase(keyframe, animation),
       });
     }
   }
@@ -116,15 +125,33 @@ export function TimelinePropertyLanes({
   onMoveKeyframe,
   suppressClickRef,
 }: TimelinePropertyLanesProps) {
-  if (clipWidthPx < 20 || clipDuration <= 0) return null;
+  // Memoized: TimelineDiamondLane is React.memo'd, and rebuilding the lanes (and
-  const lanes = getTimelinePropertyLanes(animations, clipStart, clipDuration);
+  // a fresh keyframesData literal per lane) on every render would re-render every
+  // diamond in every expanded clip on each playhead tick.
+  const lanes = useMemo(
+    () =>
+      clipWidthPx < 20 || clipDuration <= 0
+        ? []
+        : getTimelinePropertyLanes(animations, clipStart, clipDuration),
+    [animations, clipStart, clipDuration, clipWidthPx],
+  );
+  const laneData = useMemo(
+    () =>
+      lanes.map((lane) => ({
+        ...lane,
+        keyframesData: { format: "percentage" as const, keyframes: lane.keyframes },
+      })),
+    [lanes],
+  );
 
-  if (lanes.length === 0) return null;
+  if (laneData.length === 0) return null;
   return (
     <>
-      {lanes.map(({ group, animations: groupAnimations, keyframes }, laneIndex) => (
+      {laneData.map(({ group, keyframesData }, laneIndex) => (
         <div
           key={group}
+          role="group"
+          aria-label={`${group} keyframes`}
           data-property-group={group}
           data-timeline-property-lane=""
           data-timeline-lane-top={getTimelineLaneTop(laneIndex)}
@@ -137,10 +164,7 @@ export function TimelinePropertyLanes({
           }}
         >
           <TimelineDiamondLane
-            keyframesData={{ format: "percentage", keyframes }}
+            keyframesData={keyframesData}
-            globalEase={
-              groupAnimations[0]?.keyframes?.easeEach ?? groupAnimations[0]?.ease ?? "none"
-            }
             clipWidthPx={clipWidthPx}
             clipHeightPx={LANE_H}
             accentColor={accentColor}

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

@@ -32,6 +32,7 @@ function animation(
   keyframes: Array<{
     percentage: number;
     properties: Record<string, number | string>;
+    ease?: string;
   }>,
 ): GsapAnimation {
   return {
@@ -126,7 +127,7 @@ describe("TimelineTrackHeader", () => {
     const onTogglePropertyGroupKeyframe = vi.fn();
     const view = renderHeader({ currentTime: 0.5, onTogglePropertyGroupKeyframe });
 
-    click(view.host, "Toggle Opacity keyframe");
+    click(view.host, "Add Opacity keyframe");
     expect(onTogglePropertyGroupKeyframe).toHaveBeenLastCalledWith(
       ELEMENT,
       expect.objectContaining({
@@ -139,7 +140,7 @@ describe("TimelineTrackHeader", () => {
     );
 
     view.rerender({ currentTime: 1, onTogglePropertyGroupKeyframe });
-    click(view.host, "Toggle Opacity keyframe");
+    click(view.host, "Remove Opacity keyframe");
     expect(onTogglePropertyGroupKeyframe).toHaveBeenLastCalledWith(
       ELEMENT,
       expect.objectContaining({
@@ -214,13 +215,13 @@ describe("TimelineTrackHeader", () => {
   it("fills the toggle diamond exactly at that group's keyframe", () => {
     const view = renderHeader({ currentTime: 0.5 });
     const positionToggle = view.host.querySelector<HTMLButtonElement>(
-      'button[aria-label="Toggle Position keyframe"]',
+      'button[aria-label="Add Position keyframe"]',
     );
     expect(positionToggle?.textContent).toBe("◇");
 
     view.rerender({ currentTime: 1 });
     expect(
-      view.host.querySelector<HTMLButtonElement>('button[aria-label="Toggle Position keyframe"]')
+      view.host.querySelector<HTMLButtonElement>('button[aria-label="Remove Position keyframe"]')
         ?.textContent,
     ).toBe("◆");
     act(() => view.root.unmount());
@@ -241,6 +242,36 @@ describe("TimelineTrackHeader", () => {
     act(() => view.root.unmount());
   });
 
+  it("samples mid-segment values along the segment's ease, not linearly", () => {
+    // GSAP hangs a segment's ease on the keyframe it arrives at, so 0% -> 50%
+    // runs power2.in. Half way through that segment power2.in(0.5) = 0.125, so
+    // the readout is 12.5/6.25 and NOT the linear 50/25.
+    const eased = animation("eased-position", "position", [
+      { percentage: 0, properties: { x: 0, y: 0 } },
+      { percentage: 50, properties: { x: 100, y: 50 }, ease: "power2.in" },
+      { percentage: 100, properties: { x: 200, y: 100 }, ease: "power2.in" },
+    ]);
+    const onTogglePropertyGroupKeyframe = vi.fn();
+    const view = renderHeader({
+      animations: [eased],
+      currentTime: 0.5,
+      onTogglePropertyGroupKeyframe,
+    });
+
+    expect(view.host.querySelector('[data-property-group="position"]')?.textContent).toContain(
+      "12.5, 6.25",
+    );
+
+    // The same sampled value is what an added keyframe gets stamped with, so a
+    // header insert lands on the existing curve instead of deforming it.
+    click(view.host, "Add Position keyframe");
+    expect(onTogglePropertyGroupKeyframe).toHaveBeenCalledOnce();
+    expect(onTogglePropertyGroupKeyframe.mock.calls[0][1]).toMatchObject({
+      properties: { x: 12.5, y: 6.25 },
+    });
+    act(() => view.root.unmount());
+  });
+
   it("disables the previous chevron at or before the group's first keyframe", () => {
     const view = renderHeader({ currentTime: 0 });
     const prevAt0 = view.host.querySelector<HTMLButtonElement>(

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

@@ -129,6 +129,14 @@ function PropertyGroupNavigation({
   onSeek?: (time: number) => void;
   children: React.ReactNode;
 }) {
+  // The 12x20px glyph is all the lane row has room for, so the WCAG 24x24
+  // target is met with a centered transparent ::before overlay instead of a
+  // bigger box; focus-visible matches every other control in this header.
+  const CHEVRON_BUTTON_CLASS =
+    "relative h-5 w-3 border-0 bg-transparent p-0 text-white/55 hover:text-white disabled:text-white/15 " +
+    "focus-visible:outline focus-visible:outline-1 focus-visible:outline-[#3CE6AC] " +
+    "before:absolute before:left-1/2 before:top-1/2 before:h-6 before:w-6 " +
+    "before:-translate-x-1/2 before:-translate-y-1/2 before:content-['']";
   const seekTo = (keyframe: { percentage: number } | null) => {
     if (keyframe) {
       onSeek?.(expandedElement.start + (keyframe.percentage / 100) * expandedElement.duration);
@@ -140,7 +148,7 @@ function PropertyGroupNavigation({
         type="button"
         aria-label={`Previous ${label} keyframe`}
         disabled={!navigation.prevKeyframe}
-        className="h-5 w-3 border-0 bg-transparent p-0 text-white/55 hover:text-white disabled:text-white/15"
+        className={CHEVRON_BUTTON_CLASS}
         onClick={(event) => {
           event.stopPropagation();
           seekTo(navigation.prevKeyframe);
@@ -153,7 +161,7 @@ function PropertyGroupNavigation({
         type="button"
         aria-label={`Next ${label} keyframe`}
         disabled={!navigation.nextKeyframe}
-        className="h-5 w-3 border-0 bg-transparent p-0 text-white/55 hover:text-white disabled:text-white/15"
+        className={CHEVRON_BUTTON_CLASS}
         onClick={(event) => {
           event.stopPropagation();
           seekTo(navigation.nextKeyframe);
@@ -242,7 +250,8 @@ function PropertyGroupHeaderRow({
       >
         <button
           type="button"
-          aria-label={`Toggle ${label} keyframe`}
+          aria-pressed={!!navigation.currentKeyframe}
+          aria-label={`${navigation.currentKeyframe ? "Remove" : "Add"} ${label} keyframe`}
           title={`${navigation.currentKeyframe ? "Remove" : "Add"} ${label} keyframe`}
           className="flex h-5 w-4 shrink-0 items-center justify-center border-0 bg-transparent p-0 text-[11px] text-[#3CE6AC] focus-visible:outline focus-visible:outline-1 focus-visible:outline-[#3CE6AC]"
           onClick={(event) => {

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

@@ -77,12 +77,24 @@ function validRowHeight(height: number | undefined): number {
   return height;
 }
 
+/**
+ * Memoized by the rowHeights array identity: a marquee/drag pointer tick calls
+ * getTimelineRowTop once per clip, and each call would otherwise rebuild the
+ * whole cumulative array (O(clips x rows) allocations per tick). rowHeights is
+ * itself memoized upstream (useTimelineTrackLayout), so the identity is stable
+ * for the life of a gesture. Callers must treat the result as read-only.
+ */
+const rowOffsetsCache = new WeakMap<readonly number[], number[]>();
+
 /** Cumulative top offsets, including the final bottom boundary. */
 export function getTimelineRowOffsets(rowHeights: readonly number[]): number[] {
+  const cached = rowOffsetsCache.get(rowHeights);
+  if (cached) return cached;
   const offsets = [0];
   for (const height of rowHeights) {
     offsets.push((offsets[offsets.length - 1] ?? 0) + validRowHeight(height));
   }
+  rowOffsetsCache.set(rowHeights, offsets);
   return offsets;
 }
 

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

@@ -4,6 +4,7 @@
  * reads to a human. Kept apart from the header's JSX so a formatting change and
  * a layout change never touch the same file.
  */
+import gsap from "gsap";
 import {
   classifyPropertyGroup,
   type GsapAnimation,
@@ -16,31 +17,59 @@ function roundValue(value: number): string {
   return String(Math.round(value * 100) / 100);
 }
 
+/** GSAP applies a keyframe's `ease` to the segment ARRIVING at it, so the curve
+ *  between two keyframes is named by the later one (with the tween-level
+ *  `easeEach`/`ease` as the fallback). Sampling linearly would report a value the
+ *  element never has at that time, and stamp that wrong value onto a keyframe
+ *  added from the track header. Unknown ease names parse to undefined -> linear. */
+function easedProgress(progress: number, animation: GsapAnimation, ease?: string): number {
+  const resolved = ease ?? animation.keyframes?.easeEach ?? animation.ease;
+  if (!resolved || resolved === "none") return progress;
+  return gsap.parseEase(resolved)?.(progress) ?? progress;
+}
+
+interface PropertyStop {
+  percentage: number;
+  value: number | string;
+  ease?: string;
+}
+
+function propertyStops(animation: GsapAnimation, property: string): PropertyStop[] {
+  return (animation.keyframes?.keyframes ?? [])
+    .filter((keyframe) => property in keyframe.properties)
+    .map((keyframe) => ({
+      percentage: keyframe.percentage,
+      value: keyframe.properties[property],
+      ease: keyframe.ease,
+    }));
+}
+
+/** A pair only interpolates when both ends are numeric and actually span time;
+ *  string values (colors, keywords) and zero-width pairs hold the earlier value.
+ *  Returns the numeric ends so the caller needs no cast to use them. */
+function interpolableEnds(
+  before: PropertyStop,
+  after: PropertyStop,
+): { from: number; to: number } | null {
+  if (typeof before.value !== "number" || typeof after.value !== "number") return null;
+  if (before.percentage === after.percentage) return null;
+  return { from: before.value, to: after.value };
+}
+
 function propertyValueAt(
   animation: GsapAnimation,
   property: string,
   tweenPercentage: number,
 ): number | string | undefined {
-  const keyframes = animation.keyframes?.keyframes ?? [];
+  const stops = propertyStops(animation, property);
-  const values = keyframes
+  const before = stops.filter((stop) => stop.percentage <= tweenPercentage).at(-1);
-    .filter((keyframe) => property in keyframe.properties)
+  const after = stops.find((stop) => stop.percentage >= tweenPercentage);
-    .map((keyframe) => ({
-      percentage: keyframe.percentage,
-      value: keyframe.properties[property],
-    }));
-  const before = values.filter((value) => value.percentage <= tweenPercentage).at(-1);
-  const after = values.find((value) => value.percentage >= tweenPercentage);
   if (!before) return after?.value;
   if (!after) return before.value;
-  if (
+  const ends = interpolableEnds(before, after);
-    typeof before.value !== "number" ||
+  if (!ends) return before.value;
-    typeof after.value !== "number" ||
-    before.percentage === after.percentage
-  ) {
-    return before.value;
-  }
   const progress = (tweenPercentage - before.percentage) / (after.percentage - before.percentage);
-  return before.value + (after.value - before.value) * progress;
+  return ends.from + (ends.to - ends.from) * easedProgress(progress, animation, after.ease);
 }
 
 /** Every property of `group` this animation touches, sampled at `tweenPercentage`. */