test: sending to multiple agents, including remote

ref: N25B-441

src/control_backend/core/agent_system.py

@@ -60,6 +60,9 @@ class BaseAgent(ABC):
         self._tasks: set[asyncio.Task] = set()
         self._running = False
 
+        self._internal_pub_socket: None | azmq.Socket = None
+        self._internal_sub_socket: None | azmq.Socket = None
+
         # Register immediately
         AgentDirectory.register(name, self)
 
@@ -141,7 +144,7 @@ class BaseAgent(ABC):
                 self.logger.debug(f"Sent message {message.body} to {message.to} via regular inbox.")
             else:
                 # Apparently target agent is on a different process, send via ZMQ
-                topic = f"internal/{message.to}".encode()
+                topic = f"internal/{receiver}".encode()
                 body = message.model_dump_json().encode()
                 await self._internal_pub_socket.send_multipart([topic, body])
                 self.logger.debug(f"Sent message {message.body} to {message.to} via ZMQ.")