fix(iOS): keep prebuilt Headers/ in place on a Debug/Release swap - #57814

…7814)

Summary:
Fixes #57803. An iOS Release build can fail in `PrecompileModule React` with seven `include of non-modular header inside framework module` errors — but only when the build follows a Debug/Release configuration switch.

`replace-rncore-version.js` deleted and recreated `Pods/React-Core-prebuilt/Headers/` on a swap. That directory holds `module.modulemap`, which `rncore.rb` activates on every target through `-fmodule-map-file`. Nothing orders an unrelated target's dependency scan against this script phase, so a scan can run while the module map is missing. The React module is then precompiled without it, and `<yoga/...>`, `<react/...>` and `<RCTDeprecation/...>` resolve non-modularly.

Those headers never needed replacing. The prebuild compose job emits one set of ReactNativeHeaders for both configurations, so they are identical in the Debug and Release tarballs — only the compiled framework differs. This replaces `React.xcframework` and nothing else.

## Changelog:

[IOS] [FIXED] - Keep the prebuilt `Headers/` in place on a Debug/Release configuration switch so the React explicit module still resolves its module map

Pull Request resolved: #57814

Test Plan:
The premise, on the published 0.87.0-rc.3 artifacts (`ios-arm64_x86_64-simulator`):

| compared between the Debug and Release tarballs | result |
| --- | --- |
| `ReactNativeHeaders…/Headers/module.modulemap` | identical |
| `React.framework/Modules/module.modulemap` | identical |
| `ReactNativeHeaders…/Headers` tree (`diff -rq`) | 0 differences |
| `React.framework/Headers` tree (`diff -rq`) | 0 differences |

The reproducer from #57803, on Xcode 26.3 with CocoaPods 1.15.2:

| build | result |
| --- | --- |
| 0.87.0-rc.3 | **FAIL** — exit 65, 7 errors |
| 0.87.0-rc.3 + this PR | **PASS** — `** BUILD SUCCEEDED **`, 0 errors |

The swap still does its job in the passing build — it logs `Replacing React-Core-prebuilt/React.xcframework`, and the installed binary is the Release one:

```
installed:   55225ccbc283c57c614ff4caf263cb63bad3828240e62cee8893e7001774bd6c
rc3 release: 55225ccbc283c57c614ff4caf263cb63bad3828240e62cee8893e7001774bd6c
rc3 debug:   516215801a6f8a86640aae13c2f2de1bbdb95189edf124e208f528b1497c7e4c
```

A Release→Debug swap was verified the same way. Across a swap, `Headers/module.modulemap` keeps its inode while `React.xcframework` gets a new one.

## Unit tests

Adds a unit test for the script, 4 cases: correct framework installed, `Headers/module.modulemap` untouched, an Expo-generated `React-use-frameworks.modulemap` left in place, and a fail-closed case on a tarball with no `React.xcframework`. The script needed a `require.main === module` guard and one export to be importable.

```
js1 test xplat/js/react-native-github/packages/react-native/scripts/__tests__/replace-rncore-version-test.js
→ 4 passed, 4 total
```

The module-map case is a real regression test, not just a pin. Restoring the pre-fix delete-and-recreate makes it fail on the inode assertion while the other three keep passing:

```
✕ leaves Headers/module.modulemap untouched
  Expected: 735095485
  Received: 735095515
```

That only works because the fixture tarball also ships `ReactNativeHeaders.xcframework`. Without it the pre-fix code throws its fail-closed error before reaching the assertion, so the test would go red for the wrong reason and would not actually be guarding #57803.

The Expo case covers behaviour this diff removes the explicit protection for. The old save-and-restore of `React-use-frameworks.modulemap` (ada3922) is unnecessary now that only `React.xcframework` is replaced, but nothing else pins it.

## Argument parsing

`yargs` parsing moved inside the `require.main === module` guard, so importing the module no longer parses `process.argv`. Verified in both directions.

The command line still performs the swap end to end:

```
$ node replace-rncore-version.js -c Release -r <version> -p <podsRoot>
Replacing React-Core-prebuilt/React.xcframework
Updating React-Core-prebuilt/.last_build_configuration with Release
Done replacing React Native prebuilt

installed binary: binary-Release
module.modulemap inode before=735141703 after=735141703
last_build marker: Release
```

Importing with hostile argv (`-c` collides with jest's `--config`) has no side effects:

```
$ node -e "process.argv = ['node','jest','-c','jest.config.js','--version']; require('./replace-rncore-version.js')"
imported OK, exports: replaceRNCoreConfiguration
```

`arc lint` is clean on both files.

Reviewed By: zeyap

Differential Revision: D114735639

Pulled By: fabriziocucci

fbshipit-source-id: 35ead7dae9ce7ad7160005a15ecb3975817ae728