fix(studio): close the review findings in this PR instead of at the stack tip

The R1/R3 residuals on this PR were fixed at the top of the stack, so they
only cleared once every branch above landed. They belong here, next to the
code they correct:

- `idFromSelector` inverts `idSelector` for both regex readers, so the
  post-commit cache refresh stops skipping the CSS-unsafe ids `idSelector`
  exists to support.
- `deduplicateKeyframes` drops `ease` when it is ambiguous; the flag was the
  only honest answer and the last-writer-wins curve belonged to an arbitrary
  colliding tween.
- `isStaticPositionHold` is now the single owner of the hold skip. The
  `sourceAnimations` filter and the `allKeyframes` filter had diverged on
  whether `immediateRender` counts as a property.
- The keyframe-cache setters no-op when the write changes nothing, instead of
  handing every subscriber a fresh Map.
- `reset()` clears `focusedEaseSegment`.
- The test hook `delete`s its window key rather than setting it to undefined,
  so feature detection still works.
- The `toClipKeyframes` fixture uses `as unknown as T` with the justification
  CONTRIBUTING.md asks for.

packages/studio/src/hooks/gsapTweenSynth.ts

@@ -5,6 +5,23 @@ import type {
 } from "@hyperframes/core/gsap-parser";
 import { PROPERTY_DEFAULTS } from "./gsapShared";
 
+/**
+ * A static position hold (only x/y, no real motion) is a `set`, not a keyframe —
+ * it must not synthesize a diamond. Covers both `tl.set(...)` and the
+ * `tl.to({ duration: 0, immediateRender: true })` hold that remove-all-keyframes
+ * collapses to (otherwise shown as a stray 0% keyframe).
+ *
+ * Single owner: the collapsed keyframe cache and the expanded property lanes'
+ * `gsapAnimations` map MUST agree on it, or a hold draws a phantom expanded lane
+ * with no matching collapsed diamond.
+ */
+export function isStaticPositionHold(anim: GsapAnimation): boolean {
+  if (anim.keyframes) return false;
+  if (anim.method !== "set" && (anim.duration ?? 0) !== 0) return false;
+  const propKeys = Object.keys(anim.properties).filter((k) => k !== "immediateRender");
+  return propKeys.length > 0 && propKeys.every((k) => k === "x" || k === "y");
+}
+
 export function deduplicateKeyframes<
   T extends GsapPercentageKeyframe & { animationId?: string; easeAmbiguous?: boolean },
 >(keyframes: T[]): T[] {
@@ -25,7 +42,14 @@ export function deduplicateKeyframes<
       ) {
         existing.easeAmbiguous = true;
       }
-      if (kf.ease) existing.ease = kf.ease;
+      // Whichever tween iterated last used to win `ease`, so the merged
+      // keyframe carried an arbitrary one of the colliding curves. Readers that
+      // do not check easeAmbiguous (drag readouts, lane hints) then showed a
+      // curve belonging to a different animation than the one an edit targets.
+      // Drop it instead: ambiguous means "no single ease", and the flag is the
+      // only honest answer.
+      if (existing.easeAmbiguous) delete existing.ease;
+      else if (kf.ease) existing.ease = kf.ease;
     } else {
       byPct.set(kf.percentage, { ...kf, properties: { ...kf.properties } });
     }