Set isStreaming=false on agent_end event, before emitting to listeners

Was only setting in finally block, after event was emitted.

packages/agent/src/agent.ts

@@ -306,6 +306,7 @@ export class Agent {
 						break;
 
 					case "agent_end":
+						this._state.isStreaming = false;
 						this._state.streamMessage = null;
 						break;
 				}