Update agent guidance, move to AGENTS.md (#57944)

Summary:
Pull Request resolved: #57944

The V1 of our `CLAUDE.md` was mostly contributor boilerplate. Revise this towards a plan overview of the repo — giving the agent immediate context on working in the codebase (and reducing exploratory file reads).

Also moves `CLAUDE.md` to `AGENTS.md`, for interop with non-Claude harnesses — `CLAUDE.md` is now a pointer to this source.

New contents:

- Repo structure
- Common commands
- Gotchas
- Contributing guidelines

This remains intentionally high level rather than exhaustive, to keep the context window lean. We can move towards nested `AGENTS.md` files over time.

**Notes**

- `CONTRIBUTING.md` is unchanged — already a short pointer to reactnative.dev. (Possible candidate for later deletion.)

Changelog: [Internal]

Reviewed By: Abbondanzo

Differential Revision: D115564651

fbshipit-source-id: 8e237cd1ab6189632bf59b2bd865c5f06fef8bcc

Author: huntie

AGENTS.md

@@ -0,0 +1,53 @@
+# React Native
+
+A framework for building native applications using React.
+
+This file provides guidance for coding agents working in this repository.
+
+## Repo structure
+
+React Native is a monorepo: the `react-native` package, the packages published alongside it, and the apps and tooling used to develop them.
+
+| Path | Contents |
+| --- | --- |
+| `packages/react-native/Libraries` | JavaScript source (Flow) — the legacy location, with code gradually moving to `src/private` |
+| `packages/react-native/src/private` | JavaScript source (Flow) |
+| `packages/react-native/ReactCommon` | Shared C++ — Fabric renderer, TurboModules, JSI, Yoga, `jsinspector-modern` |
+| `packages/react-native/ReactAndroid` | Android runtime (Kotlin, Java, JNI) |
+| `packages/react-native/{React,ReactApple}` | Apple runtime (Objective-C++, Swift) |
+| `packages/rn-tester` | RNTester — test app showcasing each core component and API, plus a `Playground` scratch surface |
+| `packages/*` | Other published packages — Metro config, Codegen, ESLint config, dev-middleware, React Native DevTools frontend |
+| `private/*` | Unpublished — the `helloworld` sample app, the `react-native-fantom` test runner |
+| `scripts/*` | Repository tooling — build, test, release, and CI scripts |
+
+Architecture notes live in `__docs__` directories beside the code they describe, indexed by [`__docs__/README.md`](__docs__/README.md). Treat them as reference for the subsystem you are working in, not as required reading.
+
+## Common commands
+
+Run these from the repository root:
+
+| Command | Purpose |
+| --- | --- |
+| `yarn test <path>` | Jest unit tests, found in `__tests__` directories |
+| `yarn fantom <path>` | [Fantom](private/react-native-fantom/__docs__/README.md) integration tests, named `*-itest.js` |
+| `yarn lint` | ESLint |
+| `yarn format` | Prettier and clang-format |
+| `yarn flow-check` | Flow |
+| `yarn start`, `yarn android` | Metro, and RNTester on Android. See [RNTester](packages/rn-tester/README.md) for iOS |
+
+Native builds use Gradle on Android, and CocoaPods or Swift Package Manager on iOS. See [Building from source](https://reactnative.dev/contributing/how-to-build-from-source).
+
+## Gotchas
+
+- JavaScript sources are typed with Flow, and the public API is exported from `packages/react-native/index.js`. TypeScript types are generated from those sources, and `packages/react-native/ReactNativeApi.d.ts` is a committed snapshot of that API — run `yarn build-types` to regenerate both whenever the public API changes.
+- The public native API is snapshotted as well: C++ under `scripts/cxx-api` (`yarn cxx-api-build`), and Android in `packages/react-native/ReactAndroid/api/ReactAndroid.api`. CI validates both.
+- Native modules and components are declared by JavaScript specs (`Native*.js`, `*NativeComponent.js`), from which their native counterparts are generated. Do not hand-edit generated code.
+- `CHANGELOG.md` is compiled at release time. Changelog entries belong in the pull request description.
+
+## Contributing guidelines
+
+- Keep each change focused — no unrelated refactors, formatting, or dependency updates.
+- Complete the pull request template — the motivation and the user-visible effect, and a [changelog entry](https://reactnative.dev/contributing/changelogs-in-pull-requests) with its category and type tags.
+- In the test plan, give the exact commands you ran and their results, plus screenshots or a video for user-interface changes.
+
+See [CONTRIBUTING.md](CONTRIBUTING.md) for the full process, including how to report bugs.

CLAUDE.md

@@ -1,24 +1 @@
-# Contributing to React Native
-
-This file provides guidance for coding agents contributing to React Native.
-These requirements apply to every contribution, regardless of how it was
-created.
-
-## Contributor guidelines
-
-- Read [Contributing to React Native](CONTRIBUTING.md) and the [Code of Conduct](CODE_OF_CONDUCT.md) before making changes.
-- Keep changes focused on the requested issue. Do not include unrelated refactors, formatting changes, or dependency updates.
-- Explain the motivation and user-visible effect of the change in the pull request summary.
-- Add or update tests for every behavior change. For user-facing changes, update an existing RNTester example or add a focused example when applicable.
-- Run the most relevant tests and linters. In the test plan, include the exact commands and results, plus screenshots or videos for user-interface changes.
-- Add a changelog entry using the format documented in [Changelogs in Pull Requests](https://reactnative.dev/contributing/changelogs-in-pull-requests). Use the pull request template's category and type tags.
-- Do not open a pull request or issue on someone's behalf unless they have explicitly asked you to do so.
-
-## Issue guidelines
-
-- Use the [issue chooser](https://github.com/react/react-native/issues/new/choose) and select the template that matches the problem. Blank issues are not accepted.
-- Search the [existing issues](https://github.com/react/react-native/issues) before filing a new one.
-- Verify bugs against a currently supported React Native release and provide the React Native version, affected platforms, clear reproduction steps, environment information, and relevant logs.
-- Every bug report must include a public reproducer. Prefer an `RNTesterPlayground.js` change, an [Expo Snack](https://snack.expo.dev/) for a focused UI problem, or a project created from the [React Native reproducer template](https://github.com/react-native-community/reproducer-react-native). See [How to Report a Bug](https://reactnative.dev/contributing/how-to-report-a-bug) for details.
-- Report Expo, Metro, documentation, and third-party library problems to their respective repositories. Use the support resources linked by the issue chooser for questions and help.
-- Discuss feature requests and API proposals in [Discussions and Proposals](https://github.com/react-native-community/discussions-and-proposals) instead of filing a bug report.
+@AGENTS.md