fix(studio): persist canvas z-order actions correctly for static elements

An adversarial review of the canvas context-menu z-order pipeline (Bring to
Front / Forward / Backward / Send to Back) found the resolver math sound but
the glue between the menu and the commit hook broken:

- The menu optimistically wrote style.zIndex AND position: relative to the
  live elements BEFORE the commit hook ran. The hook decides whether to
  persist position by checking getComputedStyle(el).position === 'static' —
  always false after the pre-apply — so the position patch was never
  persisted on the menu path and the reorder silently reverted at the
  post-commit reload for any nested/static element (root clips survive only
  because the runtime forces position:absolute). The same pre-apply made the
  failure rollback capture the already-mutated values, restoring the broken
  state on persist errors. The menu no longer pre-applies; the hook owns the
  live writes (it already applied both synchronously) and now sees true
  priors. Siblings without a persistable identity still get their z applied
  live-only so a renumber stays visually coherent.
- The commit hook's entry.key store-sync plumbing had zero production
  callers; the store zIndex went stale until full reload. All three callers
  (canvas menu via PreviewOverlays, timeline lane z-sync, LayersPanel) now
  derive and pass the timeline store key (new deriveTimelineStoreKey helper).
- patchElementBatch discarded the server's per-patch matched[]; unresolvable
  siblings persisted partially and silently. Unmatched targets now warn and
  report save-failure telemetry (z-reorder-unmatched) without rolling back
  the matched subset.
- template/noscript elements counted as painting siblings, so renumber
  fallbacks wrote z-index/position into <template> tags in the source file.
  Excluded from the sibling family.
- The default undo coalesce key merged DISTINCT z actions within 300ms into
  one undo entry; the action kind is now part of the key (LayersPanel drags
  keep coalescing within a drag; explicit lane-move gesture keys untouched).
- rectsIntersect comment claimed touching rects intersect; the strict
  inequalities say otherwise — comment fixed.

packages/studio/src/hooks/useDomEditCommits.ts

@@ -61,6 +61,34 @@ interface RecordEditInput {
   files: Record<string, { before: string; after: string }>;
 }
 
+/** Human-readable identifier for a batch patch target (for the unmatched warning). */
+function describeBatchPatchTarget(patch: DomEditPatchBatch["patches"][number]): string {
+  return patch.target.id ?? patch.target.hfId ?? patch.target.selector ?? "(unaddressed)";
+}
+
+/**
+ * Surface server-reported unmatched patches. The matched subset already
+ * persisted, so this must NOT throw (a throw would roll back applied state) —
+ * warn and emit save-failure telemetry with a distinct reason instead.
+ */
+function reportUnmatchedBatchPatches(batch: DomEditPatchBatch, matched: boolean[]): void {
+  const unmatchedIds = batch.patches
+    .filter((_, index) => matched[index] === false)
+    .map(describeBatchPatchTarget);
+  if (unmatchedIds.length === 0) return;
+  console.warn(
+    `[studio] z-index reorder: server could not match ${unmatchedIds.length} patch target(s) in ` +
+      `${batch.sourceFile} (their z-order will revert on reload):`,
+    unmatchedIds.join(", "),
+  );
+  trackStudioSaveFailure({
+    source: "dom_edit",
+    error: new Error(`Batch patch target(s) unmatched: ${unmatchedIds.join(", ")}`),
+    filePath: batch.sourceFile,
+    mutationType: "z-reorder-unmatched",
+  });
+}
+
 async function patchElementBatch(projectId: string, batch: DomEditPatchBatch) {
   const before = await readProjectFileContent(projectId, batch.sourceFile);
   const response = await fetch(
@@ -77,8 +105,10 @@ async function patchElementBatch(projectId: string, batch: DomEditPatchBatch) {
   }
   const result = (await response.json()) as {
     changed?: boolean;
+    matched?: boolean[];
     content?: string;
   };
+  if (Array.isArray(result.matched)) reportUnmatchedBatchPatches(batch, result.matched);
   return {
     sourceFile: batch.sourceFile,
     changed: result.changed === true,