fix(studio): close the review findings that survived the stack

Selector reads now go through one inverse of `idSelector`. Every writer emits
`[id="01-hook-hero"]` for an id a `#id` selector can't address, but the readers
still matched `#id` only, so the post-commit keyframe-cache refresh, the AST
load and the remove-all-keyframes clear all silently skipped exactly the ids
`idSelector` was added to support.

A keyframe merged from two tweens with different eases kept whichever ease
iterated last. Readers that don't check `easeAmbiguous` showed a curve from a
different animation than an edit would target, so the ambiguous flag now clears
`ease` instead of leaving an arbitrary one behind.

One tolerance for "the playhead is on this keyframe". The motion-path drag used
0.05% while the toolbar and the playhead apply used 1%, so a drag that landed a
fraction of a percent off an authored waypoint skipped the update-point branch
and appended a near-duplicate. `buildTemporalArcKeyframes` now owns the
invariant and replaces any keyframe inside the tolerance, rather than trusting
each caller's own pre-check.

The pending-retime bookkeeping matches on keyframe identity, not just on
"something is near that percentage" — an evenly spaced row cleared the entry off
an unrelated sibling. The neighbour clamp composes pending destinations in
before sorting, so a second drag can't cross a neighbour that already moved.

Also: `keyframeCache`/`gsapAnimations` setters return the same state for a write
that changes nothing (every no-op re-rendered every subscriber), the auto-expand
set drops clips that left the source so an undo/paste under the same id expands
again, `invalidateGsapCache` has a stable identity instead of re-creating the
whole timeline edit context each render, the studio test hook deletes its window
key rather than leaving it enumerable as undefined, and the past-last-row
extrapolation documents why it uses TRACK_H where the pre-first-row branch uses
row 0's own height.

Covers `idFromSelector` round-trips, the insert boundary band across plain,
expanded and unusable row heights, and the collapsed selection key for a
colon-bearing element id.

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

@@ -1,5 +1,8 @@
 import { describe, it, expect } from "vitest";
 import {
+  CLIP_Y,
+  INSERT_BOUNDARY_BAND,
+  getTimelineInsertBoundaryBand,
   RULER_H,
   TRACK_H,
   LANE_H,
@@ -225,6 +228,7 @@ describe("getTimelineScrubTime", () => {
         clientX: 500,
         viewportLeft: 0,
         scrollLeft: 0,
+        contentOrigin: GUTTER + TRACKS_LEFT_PAD,
         pixelsPerSecond: 0,
         duration: 10,
       }),
@@ -232,3 +236,25 @@ describe("getTimelineScrubTime", () => {
     expect(at(origin + 250, Number.NaN)).toBe(0);
   });
 });
+
+// The only production hook keeping resolveInsertRow's band aligned with the
+// rendered clip inset once rows can be taller than TRACK_H. Pinned directly so a
+// change to CLIP_Y or the invalid-height fallback can't silently drift it.
+describe("getTimelineInsertBoundaryBand", () => {
+  it("matches the fixed band for a plain track row", () => {
+    expect(getTimelineInsertBoundaryBand(TRACK_H)).toBe(INSERT_BOUNDARY_BAND);
+    expect(getTimelineInsertBoundaryBand(TRACK_H)).toBe(CLIP_Y / TRACK_H);
+  });
+
+  it("shrinks as the row grows, so the band stays CLIP_Y pixels tall", () => {
+    const expanded = TRACK_H + 2 * LANE_H;
+    expect(getTimelineInsertBoundaryBand(expanded)).toBeCloseTo(CLIP_Y / expanded, 10);
+    expect(getTimelineInsertBoundaryBand(expanded)).toBeLessThan(INSERT_BOUNDARY_BAND);
+  });
+
+  it("falls back to the plain-track band for a height that is not usable", () => {
+    for (const height of [0, -10, Number.NaN]) {
+      expect(getTimelineInsertBoundaryBand(height)).toBe(INSERT_BOUNDARY_BAND);
+    }
+  });
+});