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

[zeyap]

Supersedes #57551 (which was cut before #57498 and became conflicting). This version is rebased on the current 0.87-stable and keeps the #57498 specifier style (no reintroduced path import).

Summary

Fresh 0.87 projects redbox on launch — e.g.:

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

(The named module varies — HMRClient.setup(), RCTDeviceEventEmitter.emit() — it's whichever callable module native calls first.) n = 1: AppRegistry is the tell: 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. Note #57498 was cosmetic (same resolved file), so it does not fix this.

Evidence (bundle tail)

Run-before target	Bundle tail	Boots?
setup-env (current)	__r(0);	❌
InitializeCore (this PR)	__r(<InitializeCore>); __r(0);	✅

Verified end-to-end via test-release-local -t RNTestProject -p iOS. Ruled out: Metro cache (cold --reset-cache identical), stale Metro, and #57484 (./src/* exports removal).

Scope — interim stopgap

Only the internal Metro bootstrap target reverts to InitializeCore. The public react-native/setup-env entry point and its deprecation of InitializeCore are unchanged.

The durable 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. main uses equivalent wiring, so it's likely affected too.

Changelog

[General][Fixed] - Fix apps failing to boot ("... 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

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