fix: wrap ESM overlay entries in CJS transform to avoid slow V8 ESM IPC resolver

Author: NathanFlurry

packages/nodejs/src/kernel-runtime.ts

@@ -900,6 +900,17 @@ class NodeRuntimeDriver implements RuntimeDriver {
           if (hostPath) {
             try {
               const content = readFileSync(hostPath, 'utf-8');
+              // Check if this is an ESM module. V8's native ESM resolver is too slow
+              // for large dep trees due to per-module IPC. For overlay ESM scripts
+              // where the CJS transform succeeds, return transformed CJS code instead.
+              if (this._isOverlayEsmEntry(hostPath)) {
+                const transformed = transformSourceForRequireSync(content, scriptPath);
+                if (transformed !== content) {
+                  // Transform succeeded: use CJS version (fast in-process require)
+                  return { code: transformed, filePath: scriptPath };
+                }
+                // Transform failed: fall through to raw ESM (slow but correct)
+              }
               return { code: content, filePath: scriptPath };
             } catch {
               // Fall through to the error below
@@ -913,4 +924,25 @@ class NodeRuntimeDriver implements RuntimeDriver {
     // No script or -e flag — read from stdin (not supported yet)
     throw new Error('node: missing script argument (stdin mode not supported)');
   }
+
+  /**
+   * Check if a host filesystem path points to an ESM module by reading
+   * the nearest package.json for "type": "module". Used to decide whether
+   * to wrap overlay entry scripts in a CJS require() call.
+   */
+  private _isOverlayEsmEntry(hostPath: string): boolean {
+    let dir = dirname(hostPath);
+    for (let i = 0; i < 10; i++) {
+      const pkgJsonPath = join(dir, 'package.json');
+      try {
+        const pkg = JSON.parse(readFileSync(pkgJsonPath, 'utf-8'));
+        return pkg.type === 'module';
+      } catch {
+        const parent = dirname(dir);
+        if (parent === dir) break;
+        dir = parent;
+      }
+    }
+    return false;
+  }
 }