[0.87] Bootstrap Metro from InitializeCore until setup-env is graph-reachable

[zeyap]

Summary

Fresh 0.87 projects redbox on launch:

Failed to call into JavaScript module method RCTDeviceEventEmitter.emit().
Module has not been registered as callable.
Registered callable JavaScript modules (n = 1): AppRegistry.

Only AppRegistry is registered as callable — i.e. core initialization never runs.

Root cause (#57475)

Core init runs via Metro's serializer.getModulesRunBeforeMainModule. Metro (metro/src/lib/getAppendScripts.js) only emits the run-before __r() for a module already present in the bundle graph, and silently skips it otherwise:

const paths = [...options.runBeforeMainModule, entryPoint];
for (const path of paths) {
  if (modules.some((module) => module.path === path)) {  // only if already in the graph
    /* __r(moduleId) */
  }
}

#57475 switched the run-before target from Libraries/Core/InitializeCore → src/setup-env.js.

• InitializeCore.js is reachable (imported by Libraries/ReactPrivate/ReactNativePrivateInitializeCore.js).
• src/setup-env.js is imported by nothing → not in the graph → silently skipped → core init never runs.

The two modules are functionally identical (both call setUpDefaultReactNativeEnvironment().default()), so only reachability changed.

Evidence (bundle tail)

Run-before target	Bundle tail	Boots?
src/setup-env.js (current)	__r(0);	❌
Libraries/Core/InitializeCore (this PR)	__r(110); __r(0);	✅

Ruled out: Metro cache (cold --reset-cache identical), stale Metro, and #57484 (./src/* exports removal — restoring it did not help).

Scope — interim stopgap

This only reverts the internal Metro bootstrap target back to InitializeCore. It does not touch the public react-native/setup-env entry point or its deprecation of InitializeCore — those ship unchanged.

The proper fix (make setup-env graph-reachable, or make Metro treat getModulesRunBeforeMainModule entries as graph roots) should land on main and supersede this. cc @huntie — this is your setup-env stack; flagging for the durable fix. Note main uses equivalent wiring (its follow-up #57498 is cosmetic — resolves to the same unreachable file), so main is likely affected too.

Changelog

[General][Fixed] - Fix apps failing to boot ("RCTDeviceEventEmitter not registered as callable") caused by core init not running.

Test Plan

• yarn test-release-local -t RNTestProject -p iOS: app boots without the redbox.
• Bundle tail contains __r(<InitializeCore>); __r(0); instead of just __r(0);.

[github-actions]

Caution

Missing Changelog

Please add a Changelog to your PR description. See Changelog format

[huntie]

(Resolved by reactwg/react-native-releases#1338. #57498 is non-cosmetic — but also this happened to due a race condition/selective picking with #57484.)