diff --git a/web/src/hooks/useChat.ts b/web/src/hooks/useChat.ts
index 43b3c4d..703dbe6 100644
--- a/web/src/hooks/useChat.ts
+++ b/web/src/hooks/useChat.ts
@@ -30,6 +30,7 @@ import type {
   StreamDelta,
   StreamEnd,
   ExecutionCompleted,
+  WsError,
   WsInbound,
 } from '../types/protocol'
 
@@ -87,8 +88,8 @@ interface UseChatReturn {
 
   // 子智能体导航方法
   enterSubAgentView: (taskId: string, description: string, subagentType?: string) => Command
-  exitSubAgentView: () => void
-  navigateToSubAgentLevel: (index: number) => void
+  exitSubAgentView: () => Command | null
+  navigateToSubAgentLevel: (index: number) => Command | null
 
   // 记忆状态
   memories: MemorySummary[]
@@ -216,6 +217,9 @@ export function useChat(): UseChatReturn {
     if (message.type === 'stream_delta' || message.type === 'stream_end') {
       return (message as StreamDelta | StreamEnd).subagent_task_id
     }
+    if (message.type === 'execution_completed' || message.type === 'error') {
+      return (message as ExecutionCompleted | WsError).subagent_task_id
+    }
     return undefined
   }
 
@@ -337,6 +341,36 @@ export function useChat(): UseChatReturn {
     }
     // stream_end: no-op, assistant_response will replace
     if (message.type === 'stream_end') return
+    // execution_completed: 更新栈顶 status 为 completed
+    if (message.type === 'execution_completed') {
+      setSubAgentStack((prev) => {
+        if (prev.length === 0) return prev
+        const top = prev[prev.length - 1]
+        const newStack = [...prev]
+        newStack[newStack.length - 1] = { ...top, status: 'completed' }
+        return newStack
+      })
+      return
+    }
+    // error: 更新栈顶 status 为 error，并追加错误消息
+    if (message.type === 'error') {
+      const errMsg = message as WsError
+      const errorChatMsg: ChatMessage = {
+        id: generateMessageId(),
+        role: 'assistant',
+        content: `Error: ${errMsg.message}`,
+        timestamp: (message as any).timestamp ?? Math.floor(Date.now() / 1000),
+        type: 'message',
+      }
+      setSubAgentStack((prev) => {
+        if (prev.length === 0) return prev
+        const top = prev[prev.length - 1]
+        const newStack = [...prev]
+        newStack[newStack.length - 1] = { ...top, status: 'error', messages: [...top.messages, errorChatMsg] }
+        return newStack
+      })
+      return
+    }
     // Other messages: assistant_response replaces streamed message by ID
     const chatMsg = serverMessageToChatMessage(message)
     if (chatMsg) {
@@ -352,6 +386,10 @@ export function useChat(): UseChatReturn {
             newStack[newStack.length - 1] = { ...top, messages: updated }
             return newStack
           }
+        } else if (message.type === 'tool_call' || message.type === 'tool_result' || message.type === 'tool_pending') {
+          // 按 id 去重，避免 load_task_messages 并发调用导致重复
+          const exists = top.messages.some(m => m.id === chatMsg.id)
+          if (exists) return prev
         }
         const newStack = [...prev]
         newStack[newStack.length - 1] = { ...top, messages: [...top.messages, chatMsg] }
@@ -360,6 +398,81 @@ export function useChat(): UseChatReturn {
     }
   }
 
+  // 追加消息到栈中非栈顶的匹配层（按 taskId 匹配），在 setSubAgentStack updater 内部完成所有判断
+  const appendToSubAgentLayerMessage = (taskId: string, message: WsOutbound) => {
+    setSubAgentStack((prev) => {
+      const idx = prev.findIndex(v => v.taskId === taskId)
+      if (idx < 0) return prev
+      const layer = prev[idx]
+
+      // execution_completed: 更新该层 status 为 completed
+      if (message.type === 'execution_completed') {
+        const newStack = [...prev]
+        newStack[idx] = { ...layer, status: 'completed' }
+        return newStack
+      }
+      // error: 更新该层 status 为 error，并追加错误消息
+      if (message.type === 'error') {
+        const errMsg = message as WsError
+        const errorChatMsg: ChatMessage = {
+          id: generateMessageId(),
+          role: 'assistant',
+          content: `Error: ${errMsg.message}`,
+          timestamp: (message as any).timestamp ?? Math.floor(Date.now() / 1000),
+          type: 'message',
+        }
+        const newStack = [...prev]
+        newStack[idx] = { ...layer, status: 'error', messages: [...layer.messages, errorChatMsg] }
+        return newStack
+      }
+      // stream_delta: accumulate into existing message by ID, or create new
+      if (message.type === 'stream_delta') {
+        const msg = message as StreamDelta
+        const existingIdx = layer.messages.findIndex(m => m.id === msg.id && m.type === 'message')
+        if (existingIdx >= 0) {
+          const updated = [...layer.messages]
+          const existing = updated[existingIdx]
+          updated[existingIdx] = {
+            ...existing,
+            content: existing.content + msg.delta,
+            reasoningContent: msg.reasoning_delta
+              ? (existing.reasoningContent || '') + msg.reasoning_delta
+              : existing.reasoningContent,
+          }
+          const newStack = [...prev]
+          newStack[idx] = { ...layer, messages: updated }
+          return newStack
+        }
+        const chatMsg = serverMessageToChatMessage(message)
+        if (!chatMsg) return prev
+        const newStack = [...prev]
+        newStack[idx] = { ...layer, messages: [...layer.messages, chatMsg] }
+        return newStack
+      }
+      // stream_end: no-op
+      if (message.type === 'stream_end') return prev
+      // 其他消息：assistant_response 按 id 替换，tool_call/tool_result/tool_pending 按 id 去重
+      const chatMsg = serverMessageToChatMessage(message)
+      if (!chatMsg) return prev
+      if (message.type === 'assistant_response') {
+        const existingIdx = layer.messages.findIndex(m => m.id === chatMsg.id && m.type === 'message')
+        if (existingIdx >= 0) {
+          const updated = [...layer.messages]
+          updated[existingIdx] = chatMsg
+          const newStack = [...prev]
+          newStack[idx] = { ...layer, messages: updated }
+          return newStack
+        }
+      } else if (message.type === 'tool_call' || message.type === 'tool_result' || message.type === 'tool_pending') {
+        const exists = layer.messages.some(m => m.id === chatMsg.id)
+        if (exists) return prev
+      }
+      const newStack = [...prev]
+      newStack[idx] = { ...layer, messages: [...layer.messages, chatMsg] }
+      return newStack
+    })
+  }
+
   // Sync backend user message ID to the last local user message,
   // so that created_by_message_id (backend UUID) can match DOM data-message-id
   const applyUserMessageId = useCallback((userMessageId: string) => {
@@ -404,6 +517,8 @@ export function useChat(): UseChatReturn {
         setSubAgentStack((prev) => {
           if (prev.length === 0) return prev
           const top = prev[prev.length - 1]
+          // 校验 task_id 匹配，避免快速切换视图时 A 的状态写到 B
+          if (msg.task_id !== top.taskId) return prev
           const newStack = [...prev]
           newStack[newStack.length - 1] = {
             ...top,
@@ -501,8 +616,9 @@ export function useChat(): UseChatReturn {
         }
         return
       }
-      // 丢弃其他子智能体的消息，避免 fall through 到主消息处理
+      // 非栈顶子智能体消息：遍历栈其余层查找匹配 taskId，命中则追加到对应层；未命中也丢弃
       if (msgSubagentTaskId) {
+        appendToSubAgentLayerMessage(msgSubagentTaskId, message)
         return
       }
     }
@@ -672,6 +788,8 @@ export function useChat(): UseChatReturn {
       case 'execution_completed': {
         // 智能体执行完全结束（不再有后续工具调用或 LLM 迭代）
         const msg = message as ExecutionCompleted
+        // 子智能体的完成事件不操作主视图（由子智能体视图分支处理或丢弃）
+        if (getSubagentTaskId(message)) return
         // 按 topic_id 隔离：只处理当前话题的完成信号
         if (msg.topic_id && msg.topic_id !== selectedTopicRef.current) return
         setIsLoading(false)
@@ -792,6 +910,8 @@ export function useChat(): UseChatReturn {
       }
 
       case 'error': {
+        // 子智能体的错误事件不操作主视图（由子智能体视图分支处理或丢弃）
+        if (getSubagentTaskId(message)) return
         setMessages((prev) => [
           ...prev,
           {
@@ -989,19 +1109,27 @@ export function useChat(): UseChatReturn {
     }
   }, [])
 
-  const exitSubAgentView = useCallback(() => {
+  const exitSubAgentView = useCallback((): Command | null => {
+    let command: Command | null = null
     setSubAgentStack((prev) => {
       if (prev.length <= 1) {
         subAgentViewRef.current = null
         return []
       }
       const newStack = prev.slice(0, -1)
-      subAgentViewRef.current = newStack[newStack.length - 1]
-      return newStack
+      const newTop = newStack[newStack.length - 1]
+      subAgentViewRef.current = newTop
+      // 清空目标层 messages + status 置 loading，并准备重新拉取命令
+      const clearedStack = [...newStack]
+      clearedStack[clearedStack.length - 1] = { ...newTop, messages: [], status: 'loading' }
+      command = { type: 'load_task_messages', task_id: newTop.taskId }
+      return clearedStack
     })
+    return command
   }, [])
 
-  const navigateToSubAgentLevel = useCallback((index: number) => {
+  const navigateToSubAgentLevel = useCallback((index: number): Command | null => {
+    let command: Command | null = null
     setSubAgentStack((prev) => {
       if (index < 0) {
         // -1 means go back to main session (clear all)
@@ -1010,9 +1138,14 @@ export function useChat(): UseChatReturn {
       }
       if (index >= prev.length) return prev
       const newStack = prev.slice(0, index + 1)
-      subAgentViewRef.current = newStack.length > 0 ? newStack[newStack.length - 1] : null
-      return newStack
+      const newTop = newStack[newStack.length - 1]
+      subAgentViewRef.current = newTop
+      const clearedStack = [...newStack]
+      clearedStack[clearedStack.length - 1] = { ...newTop, messages: [], status: 'loading' }
+      command = { type: 'load_task_messages', task_id: newTop.taskId }
+      return clearedStack
     })
+    return command
   }, [])
 
   // 记忆方法
diff --git a/web/src/types/protocol.ts b/web/src/types/protocol.ts
index 6dece06..1822ea5 100644
--- a/web/src/types/protocol.ts
+++ b/web/src/types/protocol.ts
@@ -95,6 +95,7 @@ export interface WsError {
   code: string
   message: string
   timestamp?: number
+  subagent_task_id?: string
 }
 
 export interface TaskStarted {
@@ -282,6 +283,7 @@ export interface ExecutionCompleted {
   type: 'execution_completed'
   topic_id?: string
   timestamp?: number
+  subagent_task_id?: string
 }
 
 export type WsOutbound =