feat(studio): route GSAP keyframe add through SDK (§3.5 PR2) (#1470)

Co-authored-by: Miguel Ángel <miguel07alm@protonmail.com>

packages/core/src/parsers/gsapWriter.acorn.test.ts

@@ -269,6 +269,14 @@ describe("T6c — keyframe write ops", () => {
     expect((result.match(/"50%"/g) ?? []).length).toBe(1);
   });
 
+  it("addKeyframeToScript merges a new property into an existing keyframe, preserving siblings", () => {
+    // 50% already holds { opacity: 0.7 }; adding x must NOT drop opacity.
+    const result = addKeyframeToScript(SCRIPT_D, "#box-to-200-visual", 50, { x: 100 });
+    expect(result).toContain("opacity: 0.7");
+    expect(result).toContain("x: 100");
+    expect((result.match(/"50%"/g) ?? []).length).toBe(1);
+  });
+
   it("removeKeyframeFromScript removes the target percentage", () => {
     // Remove 50% from 0%/50%/100% → leaves 0%/100% (no collapse in T6c)
     const result = removeKeyframeFromScript(SCRIPT_D, "#box-to-200-visual", 50);

packages/core/src/parsers/gsapWriterAcorn.ts

@@ -774,7 +774,17 @@ export function addKeyframeToScript(
   // Emit exactly one overwrite per changed node, plus one insert for a new key.
   const ms = new MagicString(src);
   if (existing) {
-    ms.overwrite(existing.prop.value.start, existing.prop.value.end, recordToCode(targetRecord));
+    // Merge into the existing keyframe at this percentage, preserving sibling
+    // properties — overwrite only the given keys. (A whole-value overwrite here
+    // would silently drop other properties already keyframed at this percent.)
+    if (existing.prop.value?.type === "ObjectExpression") {
+      for (const [k, v] of Object.entries(properties)) {
+        upsertProp(ms, existing.prop.value, k, v);
+      }
+      if (ease !== undefined) upsertProp(ms, existing.prop.value, "ease", ease);
+    } else {
+      ms.overwrite(existing.prop.value.start, existing.prop.value.end, recordToCode(targetRecord));
+    }
   } else {
     insertNewKeyframe(ms, kfNode, percentage, `${percentage}%`, recordToCode(targetRecord));
   }