🐛 fix(chat): reset activeTopicId when switching agent/group (#11523)

When switching agents via dropdown menu, the activeTopicId was not being
reset, causing messages to be saved to the wrong topic bucket. This fix
adds useEffect hooks to AgentIdSync and GroupIdSync components to detect
agent/group changes and synchronously reset activeTopicId.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

src/app/[variants]/(main)/agent/_layout/AgentIdSync.tsx

@@ -1,4 +1,5 @@
-import { useUnmount } from 'ahooks';
+import { usePrevious, useUnmount } from 'ahooks';
+import { useEffect } from 'react';
 import { useParams } from 'react-router-dom';
 import { createStoreUpdater } from 'zustand-utils';
 
@@ -9,10 +10,20 @@ const AgentIdSync = () => {
   const useStoreUpdater = createStoreUpdater(useAgentStore);
   const useChatStoreUpdater = createStoreUpdater(useChatStore);
   const params = useParams<{ aid?: string }>();
+  const prevAgentId = usePrevious(params.aid);
 
   useStoreUpdater('activeAgentId', params.aid);
   useChatStoreUpdater('activeAgentId', params.aid ?? '');
 
+  // Reset activeTopicId when switching to a different agent
+  // This prevents messages from being saved to the wrong topic bucket
+  useEffect(() => {
+    // Only reset topic when switching between agents (not on initial mount)
+    if (prevAgentId !== undefined && prevAgentId !== params.aid) {
+      useChatStore.getState().switchTopic(null, { skipRefreshMessage: true });
+    }
+  }, [params.aid, prevAgentId]);
+
   // Clear activeAgentId when unmounting (leaving chat page)
   useUnmount(() => {
     useAgentStore.setState({ activeAgentId: undefined });

src/app/[variants]/(main)/group/_layout/GroupIdSync.tsx

@@ -1,4 +1,5 @@
-import { useUnmount } from 'ahooks';
+import { usePrevious, useUnmount } from 'ahooks';
+import { useEffect } from 'react';
 import { useParams } from 'react-router-dom';
 import { createStoreUpdater } from 'zustand-utils';
 
@@ -10,6 +11,7 @@ const GroupIdSync = () => {
   const useAgentGroupStoreUpdater = createStoreUpdater(useAgentGroupStore);
   const useChatStoreUpdater = createStoreUpdater(useChatStore);
   const params = useParams<{ gid?: string }>();
+  const prevGroupId = usePrevious(params.gid);
   const router = useQueryRoute();
 
   // Sync groupId to agentGroupStore and chatStore
@@ -19,6 +21,15 @@ const GroupIdSync = () => {
   // Inject router to agentGroupStore for navigation
   useAgentGroupStoreUpdater('router', router);
 
+  // Reset activeTopicId when switching to a different group
+  // This prevents messages from being saved to the wrong topic bucket
+  useEffect(() => {
+    // Only reset topic when switching between groups (not on initial mount)
+    if (prevGroupId !== undefined && prevGroupId !== params.gid) {
+      useChatStore.getState().switchTopic(null, { skipRefreshMessage: true });
+    }
+  }, [params.gid, prevGroupId]);
+
   // Clear activeGroupId when unmounting (leaving group page)
   useUnmount(() => {
     useAgentGroupStore.setState({ activeGroupId: undefined, router: undefined });