fix(express): add CJS exports to resolve ERR_PACKAGE_PATH_NOT_EXPORTED

[langverse2023]

Summary

Fixes #1858

The @modelcontextprotocol/express package only defines ESM (.mjs) entries in its exports field, which causes ERR_PACKAGE_PATH_NOT_EXPORTED for consumers using CommonJS (require()). This is a common scenario for TypeScript projects initialized with default tsconfig.json settings (e.g. module: "commonjs").

Changes

• tsdown.config.ts: Add 'cjs' to the format array so tsdown generates both .mjs and .cjs output files
• package.json: Add require conditions to the exports field for both the main entry and type definitions

Before

"exports": {
    ".": {
        "types": "./dist/index.d.mts",
        "import": "./dist/index.mjs"
    }
}

After

"exports": {
    ".": {
        "types": {
            "import": "./dist/index.d.mts",
            "require": "./dist/index.d.cts"
        },
        "import": "./dist/index.mjs",
        "require": "./dist/index.cjs"
    }
}

Test plan

• pnpm --filter @modelcontextprotocol/express build succeeds, generating both ESM and CJS output
• pnpm --filter @modelcontextprotocol/express test passes (17/17 tests)
• Verify a CJS consumer project can require('@modelcontextprotocol/express') without errors

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