Metro babel transformer doesn't recognize .cjs config files (babel.config.cjs, .babelrc.cjs)

Description

The @react-native/metro-babel-transformer doesn't recognize .cjs babel config files, which causes silent failures when projects use "type": "module" in their package.json.

Problem

In @react-native/metro-babel-transformer/src/index.js (lines 74-88), the transformer only searches for:

• .babelrc
• .babelrc.js
• babel.config.js

When a project has "type": "module" in package.json:

• .js files are treated as ES modules by Node.js
• Babel config files that use module.exports = function(api) {...} (CommonJS) must use the .cjs extension
• Metro silently falls back to the default preset, ignoring custom plugins

This causes hard-to-debug issues. In my case, the react-native-worklets/plugin wasn't being applied, resulting in runtime errors like "Failed to create a worklet" with no indication that the babel config wasn't being loaded.

Expected behavior

Metro should also search for:

• .babelrc.cjs
• babel.config.cjs

This aligns with Babel's own configuration file resolution which supports .cjs extensions.

Workaround

Use extendsBabelConfigPath in Metro config:

// metro.config.cjs

const customConfig = {
  transformer: {
    extendsBabelConfigPath: path.resolve(__dirname, 'babel.config.cjs'),
  },
};

Environment

React Native: 0.81.5
Node.js: 24.x
pnpm monorepo with "type": "module" in package.json

Start with packages/react-native-babel-transformer/src/index.js, especially lines 74-88, and trace the existing Babel config lookup. Check behavior for projects whose package.json sets type to module, then verify that .babelrc.cjs and babel.config.cjs are discovered and custom plugins are applied instead of silently falling back to the default preset.