refactor(core): swap studio-api read path from recast to acorn parser (T6e) (#1392)

* refactor(core): swap studio-api read path from recast to acorn parser (T6e)

* fix(core,sdk): code-review findings — 5 correctness bugs + 2 cleanup

- gsapParserAcorn: top-level variable targets now resolved via program-scope
  null-key fallback in lookupBindingFromAncestors (const el = querySelector...)
- gsapParserAcorn: fromTo guard requires args.length >= 3, preventing undefined
  args[2]/args[3] access when fewer args supplied
- gsapWriterAcorn: remove fuzzing fallback in removeAnimationFromScript that
  silently deleted the wrong animation (from→to ID conversion)
- gsapWriterAcorn: valueToCode guards NaN → "0" to avoid broken tween props;
  safeKey regex aligned to ASCII-only (matching gsapSerialize)
- mutate: handleSetGsapTween now includes stagger in extras (was in addGsapTween
  but missing from setGsapTween)
- apply-patches: script case now mirrors stylesheet — op=remove calls
  setGsapScript("") instead of silently ignoring the patch

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

* docs(core): add trust-model header to T6d parity suite

Documents the recast-baseline trust relationship and clarifies that
motionPath parity tests live in the Phase 3b commit (PR #1379) since
the acorn motionPath parser is also added there.

Addresses #1370 R1-N1 (Rames).

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

---------

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

packages/sdk/src/engine/apply-patches.ts

@@ -207,7 +207,9 @@ function applyOne(parsed: ParsedDocument, patch: JsonPatchOp, p: ParsedPath): vo
     }
 
     case "script": {
-      if (patch.op !== "remove") {
+      if (patch.op === "remove") {
+        setGsapScript(parsed.document, "");
+      } else {
         setGsapScript(parsed.document, String(patch.value ?? ""));
       }
       break;

packages/sdk/src/engine/mutate.ts

@@ -546,6 +546,7 @@ function handleSetGsapTween(
   const extras: Record<string, unknown> = {};
   if (properties.repeat !== undefined) extras.repeat = properties.repeat;
   if (properties.yoyo !== undefined) extras.yoyo = properties.yoyo;
+  if (properties.stagger !== undefined) extras.stagger = properties.stagger;
   if (Object.keys(extras).length > 0) updates.extras = extras;
 
   const newScript = updateAnimationInScript(script, animationId, updates);