feat(studio): carry hfId on TimelineElement, wire through buildPatchTarget (R7, T5b) (#1299)

* feat(studio): carry hfId on TimelineElement, wire through buildPatchTarget (R7, T5b)

* refactor(studio): extract readHfId helper, fix empty-string normalization, add comments (R7 review)

- Extract readHfId(el) to domEditingLayers.ts — centralizes `?.trim() || undefined`
  normalisation; guards against empty-string data-hf-id reaching findTagByTarget
- Wire readHfId into domEditingLayers.ts and useDomEditCommits.ts (the one site
  that still used `?? undefined` instead of `|| undefined`)
- Re-export readHfId through domEditing.ts public API
- Add readHfId unit tests: present, absent, empty-string, whitespace-only
- Add comment on PatchTarget: runtime validation lives in findTagByTarget, type is docs-only
- Suppress pre-existing unused re-exports in timelineDOM.ts (backward-compat re-exports
  brought into fallow scope by the T5b hfId changes)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(core): clear data-hf-id on split clone to prevent dual-match (R7 review)

cloneNode(true) copies all attributes including data-hf-id. Without clearing it,
both halves of a split share the same hf-id; the server's findByHfId picks the first
match and silently patches the wrong clip. Remove the attribute from the clone so
write-back re-mints a fresh id on the next preview load.

Adds a test: splitElementInHtml — hfId clone isolation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(studio): add hfId to DomEditLayerItem + getDomLayerPatchTarget return type (R7 review)

- Add hfId to DomEditLayerItem interface (domEditingTypes.ts) so layer item
  construction in collectDomEditLayerItems compiles
- Widen getDomLayerPatchTarget return type to include hfId + populate it from
  data-hf-id attribute (domEditingElement.ts)
- Widen findDomEditSelectionTarget to check hfId-first when no id/selector
- Widen Pick types in domEditOverlayGeometry.ts and useGsapScriptCommits.ts
- Add hfId to buildMissingCompositionElements element construction
- Add hfId-targeted test coverage in domEditing.test.ts,
  domEditOverlayGeometry.test.ts, timelineIframeHelpers.test.ts
- Update hfIds.test.ts KNOWN LIMITATION labels — write-back landed in R7 T1-2

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core/src/parsers/hfIds.test.ts

@@ -100,9 +100,9 @@ describe("ensureHfIds", () => {
 });
 
 // Lock the edit-lifecycle behavior. These pin BOTH the guarantee that holds
-// once ids are persisted to source (pinning) AND the two limitations that hold
-// while they are not (design §3 write-back is not yet wired — see
-// notes/r1-stable-hf-ids-design.md "Implementation status & verified lifecycle gap").
+// once ids are persisted to source (pinning) AND the behavior for truly unpinned
+// HTML (no data-hf-id in the input — unreachable in production after write-back
+// landed in R7 Task 1-2, but still the correct contract for that path).
 describe("ensureHfIds — edit lifecycle (R1 stability)", () => {
   it("pinned id survives a content edit (the §3 write-back guarantee)", () => {
     // Element already carries data-hf-id in source (as it would after write-back).
@@ -110,25 +110,24 @@ describe("ensureHfIds — edit lifecycle (R1 stability)", () => {
     expect(idOf(ensureHfIds(edited), "p.body")).toBe("hf-abcd");
   });
 
-  it("KNOWN LIMITATION: an unpinned id changes when the element's text is edited", () => {
-    // No data-hf-id in source → every parse re-mints from content. Editing the
-    // text changes the hash, so the id drifts. This is the "pure-hash" mode the
-    // design rejected; flip this assertion to .toBe once write-back lands.
+  it("unpinned id drifts when element text is edited (pure-hash, unreachable after write-back)", () => {
+    // No data-hf-id in source → every parse re-mints from content. This path is
+    // unreachable in production after R7 write-back: the first serve pins the id.
     const before = idOf(ensureHfIds(doc(`<p class="body">Hello</p>`)), "p.body");
     const after = idOf(ensureHfIds(doc(`<p class="body">Hello world</p>`)), "p.body");
     expect(before).not.toBe(after);
   });
 
-  it("KNOWN LIMITATION: an unpinned id changes when an attribute is edited", () => {
+  it("unpinned id drifts when attribute is edited (pure-hash, unreachable after write-back)", () => {
     const before = idOf(ensureHfIds(doc(`<p class="body">x</p>`)), "p");
     const after = idOf(ensureHfIds(doc(`<p class="lead">x</p>`)), "p");
     expect(before).not.toBe(after);
   });
 
-  it("KNOWN LIMITATION: identical-content siblings have no content-stable id for the 2nd occurrence", () => {
+  it("identical-content siblings: second occurrence gets a position-derived dedup id", () => {
     // Insertion stability holds for DISTINCT content (covered elsewhere), but a
-    // second identical sibling collides and gets a position-derived dedup id —
-    // there is no content-stable handle for it. The first keeps the base id.
+    // second identical sibling collides and gets a position-derived dedup id.
+    // First element keeps the base (content-derived) id; documented in project_hfid_dedup_tiebreak.
     const single = idOf(ensureHfIds(doc(`<p class="x">same</p>`)), "p.x");
     const pair = ids(ensureHfIds(doc(`<p class="x">same</p><p class="x">same</p>`)));
     expect(pair[0]).toBe(single); // first identical element: stable, content-derived

packages/core/src/studio-api/helpers/sourceMutation.test.ts

@@ -3,6 +3,7 @@ import {
   removeElementFromHtml,
   patchElementInHtml,
   probeElementInSource,
+  splitElementInHtml,
 } from "./sourceMutation.js";
 
 describe("removeElementFromHtml", () => {
@@ -455,3 +456,14 @@ describe("T7 — data-hf-id targeting (spec for R1)", () => {
     expect(html).toContain('data-hf-id="hf-a1b2"');
   });
 });
+
+describe("splitElementInHtml — hfId clone isolation", () => {
+  it("does not copy data-hf-id to the cloned second half", () => {
+    const source = `<html><body><div data-composition-id="root"><div id="clip1" class="clip" data-start="0" data-duration="10" data-hf-id="hf-abc123"></div></div></body></html>`;
+    const { html, matched } = splitElementInHtml(source, { id: "clip1" }, 5, "clip2");
+
+    expect(matched).toBe(true);
+    const occurrences = (html.match(/data-hf-id="hf-abc123"/g) ?? []).length;
+    expect(occurrences).toBe(1);
+  });
+});

packages/core/src/studio-api/helpers/sourceMutation.ts

@@ -275,6 +275,7 @@ export function splitElementInHtml(
 
   const clone = el.cloneNode(true) as HTMLElement;
   clone.setAttribute("id", newId);
+  clone.removeAttribute("data-hf-id");
   clone.setAttribute("data-start", String(Math.round(splitTime * 1000) / 1000));
   clone.setAttribute("data-duration", String(Math.round(secondDuration * 1000) / 1000));