test: add regression test for MCP createRequire subpath resolution

Structural verification that createRequire import and _require.resolve
usage exist in mcp-server.ts (#3603).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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');
+  });
+});