fix(studio): fix array-form keyframe writes, diamond click-deselect, and nested video sync

- fs.watch's async 'error' event had no listener, crashing the preview
  server on EMFILE (exhausted OS watch handles)
- moveKeyframeInScript/resizeKeyframedTweenInScript/removeAllKeyframesFromScript
  required object-form keyframes: {"0%": {...}}, silently no-opping on
  array-form keyframes: [{...}, {...}]
- a keyframe diamond click's auto-synthesized native click event bubbled
  to the ancestor clip's onClick, which toggles selection off when the
  clip is already selected (the state every diamond click happens in)
- the clip's trim-resize handles (z-index 4) visually and functionally
  covered any keyframe diamond within their 14px edge strip
- synthesizeFlatTweenKeyframes didn't recognize a collapsed
  duration:0 + immediateRender static hold (what remove-all-keyframes
  produces) as non-animated, so it kept showing a phantom diamond after
  Delete All Keyframes
- resolveMediaStartSeconds's fast path for elements with their own
  data-start discarded the host composition's inherited start offset,
  so a video nested inside a sub-composition played from the root
  timeline's time instead of holding until its parent scene began

Fixes #1838

packages/cli/src/server/fileWatcher.test.ts

@@ -1,6 +1,14 @@
-import { describe, expect, it } from "vitest";
+import { EventEmitter } from "node:events";
+import { describe, expect, it, vi } from "vitest";
 
-import { shouldWatchProjectFile } from "./fileWatcher.js";
+const mockWatcher = new EventEmitter() as EventEmitter & { close: () => void };
+mockWatcher.close = vi.fn();
+
+vi.mock("node:fs", () => ({
+  watch: vi.fn(() => mockWatcher),
+}));
+
+const { shouldWatchProjectFile, createProjectWatcher } = await import("./fileWatcher.js");
 
 describe("shouldWatchProjectFile", () => {
   it("watches files that can affect the project signature", () => {
@@ -17,3 +25,15 @@ describe("shouldWatchProjectFile", () => {
     expect(shouldWatchProjectFile(".hyperframes/cache.json")).toBe(false);
   });
 });
+
+describe("createProjectWatcher", () => {
+  // Regression: fs.watch can fail asynchronously (e.g. EMFILE from exhausted
+  // OS watch handles) via an 'error' event, not a thrown exception. An
+  // EventEmitter 'error' with no listener crashes the whole process — this
+  // must degrade gracefully instead, per the sibling synchronous-failure path.
+  it("does not crash the process when the underlying watcher emits 'error'", () => {
+    createProjectWatcher("/fake/project/dir");
+    expect(() => mockWatcher.emit("error", new Error("EMFILE"))).not.toThrow();
+    expect(mockWatcher.close).toHaveBeenCalled();
+  });
+});

packages/cli/src/server/fileWatcher.ts

@@ -47,6 +47,15 @@ export function createProjectWatcher(projectDir: string): ProjectWatcher {
         }
       }, DEBOUNCE_MS);
     });
+    // fs.watch can fail asynchronously too (e.g. EMFILE from exhausted OS watch
+    // handles) — that surfaces as an 'error' event, not a thrown exception. An
+    // EventEmitter 'error' with no listener crashes the whole process, so this
+    // listener is required for the same "degrade gracefully" the catch below
+    // already promises for the synchronous failure mode.
+    watcher.on("error", () => {
+      watcher?.close();
+      watcher = null;
+    });
   } catch {
     // fs.watch may fail on some platforms — degrade gracefully (no auto-refresh)
   }