Merge pull request #3685 from Tibsfox/fix/mcp-server-subpath-imports

fix(mcp): use createRequire to resolve SDK wildcard subpath imports

src/mcp-server.ts

@@ -19,6 +19,10 @@ export interface McpToolDef {
 // MCP SDK subpath imports use wildcard exports (./*) that NodeNext resolves
 // at runtime but TypeScript cannot statically type-check. We construct the
 // specifiers dynamically so tsc treats them as `any`.
+// Use createRequire to resolve wildcard subpaths — CJS resolver auto-appends
+// .js, which the ESM wildcard export map does not (#3603).
+import { createRequire } from 'node:module'
+const _require = createRequire(import.meta.url)
 const MCP_PKG = '@modelcontextprotocol/sdk'
 
 /**
@@ -42,8 +46,8 @@ export async function startMcpServer(options: {
   const { tools, version = '0.0.0' } = options
 
   const serverMod = await import(`${MCP_PKG}/server`)
-  const stdioMod = await import(`${MCP_PKG}/server/stdio`)
-  const typesMod = await import(`${MCP_PKG}/types`)
+  const stdioMod = await import(_require.resolve(`${MCP_PKG}/server/stdio`))
+  const typesMod = await import(_require.resolve(`${MCP_PKG}/types`))
 
   const Server = serverMod.Server
   const StdioServerTransport = stdioMod.StdioServerTransport

src/tests/mcp-createRequire.test.ts

@@ -0,0 +1,48 @@
+/**
+ * Regression test for #3603 — MCP server subpath imports via createRequire
+ *
+ * The ESM wildcard export map in @modelcontextprotocol/sdk does not resolve
+ * subpath imports correctly. The fix uses createRequire from node:module to
+ * resolve wildcard subpaths via the CJS resolver which auto-appends .js.
+ *
+ * Structural verification test — reads source to confirm createRequire import
+ * and _require.resolve usage exist.
+ */
+
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const source = readFileSync(join(__dirname, '..', 'mcp-server.ts'), 'utf-8');
+
+describe('MCP server createRequire subpath resolution (#3603)', () => {
+  test('createRequire is imported from node:module', () => {
+    assert.match(source, /import\s*\{\s*createRequire\s*\}\s*from\s*['"]node:module['"]/,
+      'createRequire should be imported from node:module');
+  });
+
+  test('_require is created from import.meta.url', () => {
+    assert.match(source, /createRequire\(import\.meta\.url\)/,
+      '_require should be created using createRequire(import.meta.url)');
+  });
+
+  test('_require.resolve is used for subpath imports', () => {
+    assert.match(source, /_require\.resolve\(/,
+      '_require.resolve should be used for subpath resolution');
+  });
+
+  test('server/stdio subpath uses _require.resolve', () => {
+    assert.match(source, /_require\.resolve\(`\$\{MCP_PKG\}\/server\/stdio`\)/,
+      'server/stdio import should use _require.resolve');
+  });
+
+  test('types subpath uses _require.resolve', () => {
+    assert.match(source, /_require\.resolve\(`\$\{MCP_PKG\}\/types`\)/,
+      'types import should use _require.resolve');
+  });
+});