fix(pi): single-flight managed extension materialization

electron/coding-runtime/pi/extension-host.ts

@@ -139,6 +139,7 @@ export class PiManagedExtensionHost {
   private readonly registrations = new Map<string, WorkerRegistrationRecord>();
   private readonly runBindings = new Map<string, string>();
   private readonly requestFlights = new Set<Promise<void>>();
+  private readonly extensionMaterializations = new Map<string, Promise<string>>();
   private subagentBridge: PiExtensionSubagentBridge | undefined;
   private productTools: PiProductTools | undefined;
   private server: Server | null = null;
@@ -183,7 +184,15 @@ export class PiManagedExtensionHost {
     }
     const bridgeUrl = await this.start();
     await mkdir(input.extensionsDir, { recursive: true });
-    const extensionPath = await materializeMakelorePiExtension(input.extensionsDir);
+    let materialization = this.extensionMaterializations.get(input.extensionsDir);
+    if (!materialization) {
+      materialization = materializeMakelorePiExtension(input.extensionsDir).catch((error) => {
+        this.extensionMaterializations.delete(input.extensionsDir);
+        throw error;
+      });
+      this.extensionMaterializations.set(input.extensionsDir, materialization);
+    }
+    const extensionPath = await materialization;
     const role = input.role ?? 'parent';
     if (role === 'child' && !input.runId?.trim()) {
       throw new Error('Child extension registration requires a parent run id');