fix(studio): harden composition timeline reliability (#2615)

* fix(studio): preserve composition playback continuity

* feat(studio): drag compositions into the timeline

* fix(studio): collapse expanded composition move aliases

* fix(studio): make timeline cuts atomic

* fix(studio): group inspector gesture history

* test(studio): cover masked text selection

* fix(studio): harden composition timeline reliability

* fix(studio): satisfy CI source gates

* fix(studio): harden composition mutation requests

packages/studio/src/utils/timelineElementSplit.ts

@@ -22,10 +22,14 @@ export function isSplitTimeWithinBounds(
 }
 
 export function canSplitElement(el: TimelineElement): boolean {
+  const hasStableIdentity = Boolean(el.hfId || el.domId || el.selector);
+  const hasValidRate =
+    el.playbackRate == null || (Number.isFinite(el.playbackRate) && el.playbackRate > 0);
   return (
     !el.timelineLocked &&
     el.timingSource !== "implicit" &&
-    !el.compositionSrc &&
+    hasStableIdentity &&
+    hasValidRate &&
     !!el.duration &&
     Number.isFinite(el.duration)
   );