fix(runtime): don't overwrite native Event/EventTarget on web

The runtime's initialize hook unconditionally replaces globalThis.Event
and globalThis.EventTarget with event-target-shim's classes. That's
necessary on RN's JSC runtime (no DOM), but on web (RN Web running in a
real browser) it stomps on the browser's native ctors.

Safari's native EventTarget.dispatchEvent() does an internal brand
check on its argument and throws

  TypeError: Argument 1 ('event') to EventTarget.dispatchEvent must be
  an instance of Event

when a polyfill instance is dispatched on a native EventTarget — even
though the polyfill mostly behaves like Event. That's enough to break
any DOM-event-driven flow in the page; the visible casualty was
FairPlay playback through @castlabs/react-native-prestoplay, where
AppleEmeManager re-dispatches a synthetic `encrypted` event onto the
<video> in response to `webkitneedkey` and Safari rejects it.

Gate both assignments on whether a native ctor is already present so
the polyfill only takes effect on platforms that genuinely lack one.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nachooya

packages/runtime/src/initialize.ts

@@ -3,10 +3,19 @@ import { getClient } from './client/index.js';
 import { disableHMRWhenReady } from './disableHMRWhenReady.js';
 import { setupJestMock } from './jest-mock.js';
 
-// Polyfill for EventTarget
+// Polyfill for EventTarget on runtimes that don't ship one (RN's JSC).
+// Do NOT overwrite when a native ctor already exists (RN Web / browsers):
+// Safari's EventTarget.dispatchEvent() does an internal brand check and
+// rejects polyfill instances with a TypeError, which breaks any
+// DOM-event-driven flow in the page — most visibly DRM (FairPlay) via
+// libraries that re-dispatch synthetic `encrypted` events.
 const Shim = require('event-target-shim');
-globalThis.Event = Shim.Event;
-globalThis.EventTarget = Shim.EventTarget;
+if (typeof globalThis.Event !== 'function') {
+  globalThis.Event = Shim.Event;
+}
+if (typeof globalThis.EventTarget !== 'function') {
+  globalThis.EventTarget = Shim.EventTarget;
+}
 
 // Setup jest mock to warn users about using Jest APIs
 setupJestMock();