chore: create cjs plugin package

docs/2026-01-05-extract-cjs-plugin.md

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+# Extract CJS Plugin to Dedicated Package
+
+## Overview
+
+Extract `cjsModuleRunnerPlugin` from `packages/plugin-rsc` into a new standalone package `@hiogawa/vite-plugin-cjs` in a dedicated repository.
+
+## Files to Extract
+
+| Source File             | Contents                                                     |
+| ----------------------- | ------------------------------------------------------------ |
+| `src/plugins/cjs.ts`    | Main plugin `cjsModuleRunnerPlugin()`, `extractPackageKey()` |
+| `src/transforms/cjs.ts` | Transform logic `transformCjsToEsm()`                        |
+| `src/plugins/shared.ts` | Only `parseIdQuery()` function (~11 lines)                   |
+
+## New Package Structure
+
+```
+@hiogawa/vite-plugin-cjs/
+├── src/
+│   ├── index.ts          # Re-export plugin from plugin.ts
+│   ├── plugin.ts         # Main plugin (from plugins/cjs.ts)
+│   ├── transform.ts      # Transform logic (from transforms/cjs.ts)
+│   └── utils.ts          # parseIdQuery helper
+├── package.json
+├── tsconfig.json
+└── tsdown.config.ts
+```
+
+## Dependencies
+
+**package.json:**
+
+```json
+{
+  "name": "@hiogawa/vite-plugin-cjs",
+  "type": "module",
+  "exports": {
+    ".": "./dist/index.js"
+  },
+  "files": ["dist"],
+  "peerDependencies": {
+    "vite": "*"
+  },
+  "dependencies": {
+    "@hiogawa/utils": "^1.7.0",
+    "es-module-lexer": "^2.0.0",
+    "estree-walker": "^3.0.3",
+    "magic-string": "^0.30.21",
+    "periscopic": "^4.0.2",
+    "vitefu": "^1.1.1"
+  }
+}
+```
+
+## Changes to plugin-rsc
+
+1. Add dependency: `"@hiogawa/vite-plugin-cjs": "^0.1.0"`
+
+2. Update `src/plugins/cjs.ts` to re-export:
+
+   ```ts
+   export { cjsModuleRunnerPlugin } from '@hiogawa/vite-plugin-cjs'
+   ```
+
+3. Remove `src/transforms/cjs.ts` (no longer needed)
+
+4. Remove `parseIdQuery` from `src/plugins/shared.ts` if unused elsewhere
+
+## Implementation Steps
+
+### Phase 1: Create new repo
+
+1. Create new repo `vite-plugin-cjs`
+2. Initialize with package.json, tsconfig.json, tsdown config
+3. Copy and adapt source files:
+   - `plugin.ts` - update imports
+   - `transform.ts` - no changes needed
+   - `utils.ts` - just `parseIdQuery`
+4. Create `index.ts` entry point
+5. Build and test locally
+
+### Phase 2: Update plugin-rsc
+
+1. Add `@hiogawa/vite-plugin-cjs` as dependency
+2. Replace `src/plugins/cjs.ts` with re-export
+3. Delete `src/transforms/cjs.ts`
+4. Check if `parseIdQuery` is used elsewhere in shared.ts
+5. Run tests to verify nothing broke
+
+## Notes
+
+- The transform expects `__vite_ssr_exportAll__` to exist at runtime (provided by Vite's module runner)
+- Plugin applies only when `env.config.dev.moduleRunnerTransform` is enabled