feat(react-signals-transform): add native rolldown plugin

packages/react-signals-transform/CHANGELOG.md

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+## 0.1.0 (2026-03-15)
+
+### Features
+
+- add the React Signals transform plugin

packages/react-signals-transform/README.md

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+# @rolldown/plugin-react-signals-transform [![npm](https://img.shields.io/npm/v/@rolldown/plugin-react-signals-transform.svg)](https://npmx.dev/package/@rolldown/plugin-react-signals-transform)
+
+Rolldown plugin for the React Signals transform.
+
+It applies the Signals React transform during Rolldown builds with Rolldown's native magic string pipeline, so React components and hooks can automatically subscribe to signal reads without wiring Babel up manually.
+
+## Install
+
+```bash
+pnpm add -D @rolldown/plugin-react-signals-transform
+pnpm add react @preact/signals-react
+```
+
+## Usage
+
+```ts
+import reactSignalsTransform from '@rolldown/plugin-react-signals-transform'
+
+export default {
+  plugins: [
+    reactSignalsTransform({
+      mode: 'auto',
+    }),
+  ],
+}
+```
+
+## Options
+
+This plugin forwards the same options as `@preact/signals-react-transform`:
+
+- `mode`
+- `importSource`
+- `detectTransformedJSX`
+- `experimental`
+
+Example:
+
+```ts
+reactSignalsTransform({
+  detectTransformedJSX: true,
+  experimental: {
+    debug: true,
+  },
+})
+```
+
+## Notes
+
+- Run it before other JSX transforms.
+- The generated code imports `useSignals` from `@preact/signals-react/runtime` by default.
+- When your code is already compiled to `react/jsx-runtime` or `React.createElement`, enable `detectTransformedJSX`.
+
+## License
+
+MIT
+
+## Credits
+
+The transform logic is adapted from [`packages/react-transform`](https://github.com/preactjs/signals/tree/main/packages/react-transform) in the Preact Signals repository. The test cases are ported from the same package.

packages/react-signals-transform/package.json

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+{
+  "name": "@rolldown/plugin-react-signals-transform",
+  "version": "0.1.0",
+  "description": "Rolldown plugin for the React Signals transform",
+  "keywords": [
+    "plugin",
+    "react",
+    "rolldown",
+    "rolldown-plugin",
+    "signals"
+  ],
+  "homepage": "https://github.com/rolldown/plugins/tree/main/packages/react-signals-transform#readme",
+  "bugs": {
+    "url": "https://github.com/rolldown/plugins/issues"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/rolldown/plugins.git",
+    "directory": "packages/react-signals-transform"
+  },
+  "files": [
+    "dist"
+  ],
+  "type": "module",
+  "exports": "./dist/index.mjs",
+  "scripts": {
+    "dev": "tsdown --watch",
+    "build": "tsdown",
+    "test": "vitest --project react-signals-transform",
+    "prepublishOnly": "pnpm run build"
+  },
+  "dependencies": {
+    "rolldown-string": "^0.3.0"
+  },
+  "devDependencies": {
+    "@preact/signals-core": "^1.12.1",
+    "@preact/signals-react": "^3.9.1",
+    "@types/react": "^18.3.23",
+    "@types/react-dom": "^18.3.7",
+    "jsdom": "^26.1.0",
+    "prettier": "^3.6.2",
+    "react": "^18.2.0",
+    "react-dom": "^18.2.0",
+    "rolldown": "^1.0.0-rc.9",
+    "vite": "^8.0.0"
+  },
+  "peerDependencies": {
+    "@preact/signals-react": "^3.9.1",
+    "react": "^16.14.0 || 17.x || 18.x || 19.x",
+    "rolldown": "^1.0.0-rc.9",
+    "vite": "^8.0.0"
+  },
+  "peerDependenciesMeta": {
+    "vite": {
+      "optional": true
+    }
+  },
+  "engines": {
+    "node": ">=22.12.0 || ^24.0.0"
+  },
+  "compatiblePackages": {
+    "schemaVersion": 1,
+    "rollup": {
+      "type": "incompatible",
+      "reason": "Uses Rolldown-specific APIs"
+    }
+  }
+}