feat(coding-runtime): add managed Pi extension host

tests/unit/pi-runtime-auth-recovery.test.ts

@@ -53,6 +53,8 @@ class AuthFailureWorker implements PiConversationWorker {
     };
   }
 
+  async send(_command: PiRpcCommand): Promise<void> {}
+
   subscribe(_listener: (event: PiRpcEvent) => void): () => void { return () => undefined; }
   subscribeInvalidation(_listener: (error: PiProcessError) => void): () => void { return () => undefined; }
   async stop() { return { mode: 'stdin-close' as const, code: 0, signal: null }; }