test(server): assert StdioServerTransport absent from root barrel; clarify subpath comment

Server stdio uses only type-level node:stream imports (erased), so the
NODE_ONLY regex cannot detect re-export regressions. Add an explicit
symbol-absence check and correct the misleading comment in src/stdio.ts.

Author: felixweinberger

packages/server/src/stdio.ts

@@ -1,7 +1,8 @@
 // Subpath entry for the stdio server transport.
 //
-// Exported separately from the root entry so that bundling `@modelcontextprotocol/server` for browser or
-// Cloudflare Workers targets does not pull in `node:stream`. Import from `@modelcontextprotocol/server/stdio`
-// only in process-stdio runtimes (Node.js, Bun, Deno).
+// Exported separately from the root entry to keep `StdioServerTransport` out of the default bundle
+// surface — server stdio has only type-level Node imports, but matching the client's `./stdio`
+// subpath gives consumers a consistent shape across packages. Import from
+// `@modelcontextprotocol/server/stdio` only in process-stdio runtimes (Node.js, Bun, Deno).
 
 export { StdioServerTransport } from './server/stdio.js';

packages/server/test/server/barrelClean.test.ts

@@ -32,9 +32,12 @@ describe('@modelcontextprotocol/server root entry is browser-safe', () => {
         }
     }, 60_000);
 
-    test('dist/index.mjs contains no process-stdio runtime imports', () => {
-        const entry = join(distDir, 'index.mjs');
-        expect(readFileSync(entry, 'utf8')).not.toMatch(NODE_ONLY);
+    test('dist/index.mjs does not export StdioServerTransport and has no process-stdio runtime imports', () => {
+        const entry = readFileSync(join(distDir, 'index.mjs'), 'utf8');
+        // Server stdio has only type-level node:stream imports (erased at compile time), so the
+        // meaningful regression check is that the symbol itself is absent from the root barrel.
+        expect(entry).not.toMatch(/\bexport\s*\{[^}]*\bStdioServerTransport\b/);
+        expect(entry).not.toMatch(NODE_ONLY);
     });
 
     test('chunks transitively imported by dist/index.mjs contain no process-stdio runtime imports', () => {