diff --git a/frontend/src/features/tasks/components/chat/ChatArea.tsx b/frontend/src/features/tasks/components/chat/ChatArea.tsx
index 91c1832c7..9e9373fed 100644
--- a/frontend/src/features/tasks/components/chat/ChatArea.tsx
+++ b/frontend/src/features/tasks/components/chat/ChatArea.tsx
@@ -116,7 +116,7 @@ function ChatAreaContent({
   const { quote, clearQuote, formatQuoteForMessage } = useQuote()
 
   // Task context
-  const { selectedTaskDetail, setSelectedTask, accessDenied } = useTaskContext()
+  const { selectedTask, selectedTaskDetail, setSelectedTask, accessDenied } = useTaskContext()
 
   // Use useTaskStateMachine hook for reactive state updates (SINGLE SOURCE OF TRUTH per AGENTS.md)
   const { state: taskState } = useTaskStateMachine(selectedTaskDetail?.id)
@@ -313,12 +313,14 @@ function ChatAreaContent({
   useEffect(() => {
     if (filteredTeams.length === 0) return
 
-    // Extract team ID from task detail
+    // Extract team ID from task detail or selectedTask as fallback
+    // selectedTask is set immediately when clicking a task from history
+    // selectedTaskDetail may take time to load and may not include team info
     const detailTeamId = selectedTaskDetail?.team
       ? typeof selectedTaskDetail.team === 'number'
         ? selectedTaskDetail.team
         : (selectedTaskDetail.team as Team).id
-      : null
+      : selectedTask?.team_id || null
 
     // Case 1: Sync from task detail (HIGHEST PRIORITY)
     // Only sync when URL taskId matches taskDetail.id to prevent race conditions
@@ -389,6 +391,7 @@ function ChatAreaContent({
     }
   }, [
     filteredTeams,
+    selectedTask,
     selectedTaskDetail,
     taskIdFromUrl,
     selectedTeam,
diff --git a/frontend/src/features/tasks/components/chat/useChatStreamHandlers.tsx b/frontend/src/features/tasks/components/chat/useChatStreamHandlers.tsx
index da224381b..2b5b7eae1 100644
--- a/frontend/src/features/tasks/components/chat/useChatStreamHandlers.tsx
+++ b/frontend/src/features/tasks/components/chat/useChatStreamHandlers.tsx
@@ -452,6 +452,16 @@ export function useChatStreamHandlers({
       const message = overrideMessage?.trim() || taskInputMessage.trim()
       if (!message && !shouldHideChatInput) return
 
+      // Check if team is selected before sending
+      if (!selectedTeam?.id) {
+        toast({
+          variant: 'destructive',
+          title: t('chat:errors.team_not_selected') || '请选择智能体',
+          description: t('chat:errors.team_not_selected_description') || '请从列表中选择一个智能体后开始对话',
+        })
+        return
+      }
+
       if (!isAttachmentReadyToSend) {
         toast({
           variant: 'destructive',
diff --git a/frontend/src/features/tasks/contexts/taskContext.tsx b/frontend/src/features/tasks/contexts/taskContext.tsx
index a7c9a24f5..9fa588512 100644
--- a/frontend/src/features/tasks/contexts/taskContext.tsx
+++ b/frontend/src/features/tasks/contexts/taskContext.tsx
@@ -711,10 +711,9 @@ export const TaskContextProvider = ({ children }: { children: ReactNode }) => {
     }
   }
 
-  // Trigger task detail refresh and manage WebSocket room when selectedTask changes
-  // NOTE: joinTask is called here, and SocketContext's joinTask already has deduplication logic
-  // (joinedTasksRef.current.has(taskId) check), so multiple calls are safe but wasteful.
-  // We only call joinTask when isConnected is true to avoid unnecessary calls.
+  // Effect 1: Handle task selection changes
+  // When selectedTask changes, leave old room and join new room
+  // This effect only reacts to selectedTask changes, not isConnected
   useEffect(() => {
     const currentTaskId = selectedTask?.id ?? null
     const previousTaskId = previousTaskIdRef.current
@@ -728,8 +727,8 @@ export const TaskContextProvider = ({ children }: { children: ReactNode }) => {
     previousTaskIdRef.current = currentTaskId
 
     if (selectedTask) {
-      // Only join task room when WebSocket is connected
-      // This prevents duplicate joins when both selectedTask and isConnected change
+      // Join task room when WebSocket is connected
+      // joinTask has built-in deduplication, so it's safe to call multiple times
       if (isConnected) {
         joinTask(selectedTask.id)
       }
@@ -738,14 +737,22 @@ export const TaskContextProvider = ({ children }: { children: ReactNode }) => {
     } else {
       setSelectedTaskDetail(null)
     }
+    // Note: isConnected is intentionally NOT in dependencies - reconnect logic is handled by Effect 2
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [selectedTask, leaveTask, joinTask, isConnected])
+  }, [selectedTask, leaveTask, joinTask])
 
-  // NOTE: Removed separate isConnected useEffect to prevent duplicate joinTask calls.
-  // The selectedTask useEffect above now handles both cases:
-  // 1. When selectedTask changes (and isConnected is true)
-  // 2. When isConnected changes (and selectedTask is set)
-  // This is because we added isConnected to the dependency array.
+  // Effect 2: Handle WebSocket reconnection
+  // When WebSocket reconnects (isConnected changes from false to true),
+  // rejoin the current task room to resume real-time updates
+  useEffect(() => {
+    // Only proceed if WebSocket is connected and there is a selected task
+    if (isConnected && selectedTask) {
+      // Rejoin the task room to ensure we receive real-time updates
+      // joinTask has built-in deduplication (joinedTasksRef), so it's safe to call again
+      joinTask(selectedTask.id)
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [isConnected])
 
   // Mark task as viewed when selectedTaskDetail is loaded
   // This ensures we have the correct status and timestamps from the backend
diff --git a/frontend/src/i18n/locales/en/chat.json b/frontend/src/i18n/locales/en/chat.json
index 5d7587df5..eb179493a 100644
--- a/frontend/src/i18n/locales/en/chat.json
+++ b/frontend/src/i18n/locales/en/chat.json
@@ -257,7 +257,9 @@
     "container_oom": "Executor out of memory: Please start a new conversation to retry, or contact administrator to increase memory allocation",
     "container_error": "Executor error: Container has stopped running. Please start a new conversation to retry",
     "generic_error": "Request failed: Unknown error, please try again or contact administrator",
-    "copy_error": "Copy error details"
+    "copy_error": "Copy error details",
+    "team_not_selected": "No Agent Selected",
+    "team_not_selected_description": "Please select an agent from the list to start a conversation"
   },
   "clarification": {
     "title": "Smart Follow-up",
diff --git a/frontend/src/i18n/locales/zh-CN/chat.json b/frontend/src/i18n/locales/zh-CN/chat.json
index cb7982753..3b99052c1 100644
--- a/frontend/src/i18n/locales/zh-CN/chat.json
+++ b/frontend/src/i18n/locales/zh-CN/chat.json
@@ -235,7 +235,9 @@
     "container_oom": "执行环境内存不足：请新建一个对话任务重试，或联系管理员增加内存配置",
     "container_error": "执行环境异常：容器已停止运行，请新建一个对话任务重试",
     "generic_error": "请求失败：未知错误，请重试或联系管理员",
-    "copy_error": "复制错误详情"
+    "copy_error": "复制错误详情",
+    "team_not_selected": "未选择智能体",
+    "team_not_selected_description": "请从列表中选择一个智能体后开始对话"
   },
   "clarification": {
     "title": "智能追问 (Smart Follow-up)",