fix(studio): keyframe commit routing for 3D and cross-group edits (#1762)

- pickBestAnimation is group-aware: a rotation/3D edit no longer merges into a
  position tween — a fresh same-group tween with a 0% baseline is created instead
- editing at a playhead past the tween extends it and keyframes there (matches drag)
- update-keyframe MERGES into the existing keyframe instead of overwriting, so
  editing one property no longer drops z/transformPerspective (the lens then
  animated from 0 and the element popped)
- dragging a keyframed element with a constant position tween keyframes rather
  than writing a static set

packages/parsers/src/gsapParser.ts

@@ -2348,6 +2348,23 @@ export function updateKeyframeInScript(
     // `properties` would wipe the primitive — leave the keyframe untouched.
     return script;
   }
+  // MERGE edited props into the existing keyframe, preserving props not in this edit
+  // (z, transformPerspective, rotation, …). A whole-value rebuild drops them, so editing
+  // one prop at the 0% keyframe strips z/transformPerspective and the element pops.
+  // Mirrors acorn updateKeyframeInScript; parity-locked by gsapWriterParity.corpus.
+  const existing = match.prop.value;
+  if (existing?.type === "ObjectExpression") {
+    const props = (existing.properties ?? []) as AstNode[];
+    const upsert = (key: string, valueCode: string) => {
+      const idx = props.findIndex((p: AstNode) => isObjectProperty(p) && propKeyName(p) === key);
+      const node = parseExpr(`({ ${safeKey(key)}: ${valueCode} })`).properties[0];
+      if (idx >= 0) props[idx] = node;
+      else props.push(node);
+    };
+    for (const [k, v] of Object.entries(properties)) upsert(k, valueToCode(v));
+    if (ease !== undefined) upsert("ease", JSON.stringify(ease));
+    return recast.print(loc.parsed.ast).code;
+  }
   match.prop.value = buildKeyframeValueNode(properties, ease);
   return recast.print(loc.parsed.ast).code;
 }

packages/parsers/src/gsapWriterAcorn.ts

@@ -780,10 +780,22 @@ export function updateKeyframeInScript(
   const match = findKfPropByPct(kfPropNode.value, percentage);
   if (!match) return script;
 
-  const record: Record<string, number | string> = { ...properties };
-  if (ease) record.ease = ease;
   const ms = new MagicString(script);
-  ms.overwrite(match.prop.value.start, match.prop.value.end, recordToCode(record));
+  // MERGE the edited props into the existing keyframe, preserving properties already
+  // keyframed at this percentage (z, transformPerspective, rotation, …). A whole-value
+  // overwrite DROPS every prop not in this edit — e.g. editing rotationY at the 0%
+  // keyframe would strip z / transformPerspective, so the lens then animates from 0 and
+  // the element pops. Mirrors addKeyframeToScript's merge-into-existing branch.
+  if (match.prop.value?.type === "ObjectExpression") {
+    for (const [k, v] of Object.entries(properties)) {
+      upsertProp(ms, match.prop.value, k, v);
+    }
+    if (ease !== undefined) upsertProp(ms, match.prop.value, "ease", ease);
+  } else {
+    const record: Record<string, number | string> = { ...properties };
+    if (ease) record.ease = ease;
+    ms.overwrite(match.prop.value.start, match.prop.value.end, recordToCode(record));
+  }
   return ms.toString();
 }