fix: 迭代计数修复 — stateChange 也携带迭代号，双通道同步

- IPC handler 将 stateChange 事件转发到渲染进程
- useAgentStream 同时监听 streamEvent 和 stateChange 更新迭代
- 切换会话/发消息时重置 currentIteration 为 0
- 添加 console.log 诊断日志

src/hooks/useAgentStream.ts

@@ -39,7 +39,8 @@ export function useAgentStream(): void {
       const store = useAgentStore.getState();
 
       // 每次收到迭代号时同步更新
-      if (data.iteration != null) {
+      if (data.iteration != null && data.iteration !== store.currentIteration) {
+        console.log(`[useAgentStream] iteration: ${store.currentIteration} → ${data.iteration} (event: ${data.type})`);
         store.setCurrentIteration(data.iteration);
       }
 
@@ -195,12 +196,18 @@ export function useAgentStream(): void {
     };
   }, []);
 
-  // 监听状态变化事件
+  // 监听状态变化事件（含迭代号）
   useEffect(() => {
     if (!window.metona?.agent?.onStateChange) return;
 
     const unsubscribe = window.metona.agent.onStateChange((state: unknown) => {
-      // 状态变化由主进程推送，UI 已通过 streamEvent 处理
+      const data = state as { sessionId?: string; iteration?: number; state?: string; previous?: string; current?: string };
+      if (data.iteration != null) {
+        const store = useAgentStore.getState();
+        if (data.iteration !== store.currentIteration) {
+          store.setCurrentIteration(data.iteration);
+        }
+      }
     });
 
     return () => unsubscribe();