diff --git a/src/pages/chat/ChatPage.tsx b/src/pages/chat/ChatPage.tsx
index a74ce78..30cd59b 100644
--- a/src/pages/chat/ChatPage.tsx
+++ b/src/pages/chat/ChatPage.tsx
@@ -15,6 +15,7 @@ import { useChatSender } from './hooks/useChatSender';
 import { markdownToPlainText } from './utils/copy';
 
 const lastRoomKey = (agentId: string) => `chat:lastRoom:${agentId}`;
+const isValidRoomId = (v: string | null): v is string => !!v && !String(v).startsWith('legacy_');
 
 export default function ChatPage() {
   const { id } = useParams();
@@ -36,11 +37,14 @@ export default function ChatPage() {
 
   useEffect(() => {
     if (!id) return;
+    abortRef.current?.abort();
+    setRoomId(null);
+    setHighlightId(null);
 
     const s = searchParams.get('session');
     const m = searchParams.get('msg');
 
-    if (s) {
+    if (isValidRoomId(s)) {
       setRoomId(s);
       try {
         localStorage.setItem(lastRoomKey(id), s);
@@ -55,6 +59,12 @@ export default function ChatPage() {
       }
       return;
     }
+    if (s && !isValidRoomId(s)) {
+      const next = new URLSearchParams(searchParams);
+      next.delete('session');
+      next.delete('msg');
+      setSearchParams(next, { replace: true });
+    }
 
     const saved = (() => {
       try {
@@ -63,10 +73,17 @@ export default function ChatPage() {
         return null;
       }
     })();
-    if (saved) {
+    if (isValidRoomId(saved)) {
       setRoomId(saved);
       return;
     }
+    if (saved && !isValidRoomId(saved)) {
+      try {
+        localStorage.removeItem(lastRoomKey(id));
+      } catch {
+        // ignore
+      }
+    }
 
     (async () => {
       try {
diff --git a/src/pages/chat/hooks/useChatData.ts b/src/pages/chat/hooks/useChatData.ts
index 0f60eb5..d39131e 100644
--- a/src/pages/chat/hooks/useChatData.ts
+++ b/src/pages/chat/hooks/useChatData.ts
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import type { Agent, BranchInfo, ChatMessage, ModelOverrides } from '../../../api';
 import { AgentAPI, ChatAPI } from '../../../api';
 import { parseAgentModels } from '../utils/agentModels';
@@ -18,6 +18,7 @@ export function useChatData(args: {
   const [agentList, setAgentList] = useState<Agent[]>([]);
   const [messages, setMessages] = useState<ChatMessage[]>([]);
   const [branches, setBranches] = useState<Record<string, BranchInfo>>({});
+  const loadSeqRef = useRef(0);
 
   const loadAgent = async () => {
     if (!agentId) {
@@ -49,18 +50,14 @@ export function useChatData(args: {
 
   const loadMessages = async () => {
     if (!roomId) return;
-    const his = await ChatAPI.history(roomId);
+    const seq = ++loadSeqRef.current;
+    const rid = roomId;
+    const his = await ChatAPI.history(rid);
+    if (seq !== loadSeqRef.current) return;
+    if (rid !== roomId) return;
     setMessages(Array.isArray(his.messages) ? his.messages : []);
     setBranches(his.branches || {});
     requestAnimationFrame(() => {
-      if (highlightId) {
-        const el = document.getElementById('msg-' + highlightId);
-        if (el) {
-          el.scrollIntoView({ behavior: 'smooth', block: 'center' });
-          setTimeout(() => setHighlightId(null), 3000);
-          return;
-        }
-      }
       if (!initialScrollDoneRef.current) {
         scrollBottom(true);
         initialScrollDoneRef.current = true;
@@ -78,9 +75,12 @@ export function useChatData(args: {
     if (!agentId) {
       setAgent(null);
       setMessages([]);
+      setBranches({});
       setOverrides(() => ({}));
       return abort;
     }
+    setMessages([]);
+    setBranches({});
     loadAgent();
     setOverrides(() => ({}));
     return abort;
@@ -89,13 +89,22 @@ export function useChatData(args: {
 
   useEffect(() => {
     initialScrollDoneRef.current = false;
-  }, [agentId]);
+  }, [agentId, roomId]);
 
   useEffect(() => {
     if (!roomId) return;
     loadMessages();
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [roomId, highlightId, agentId]);
+  }, [roomId]);
+
+  useEffect(() => {
+    if (!highlightId) return;
+    const el = document.getElementById('msg-' + highlightId);
+    if (!el) return;
+    el.scrollIntoView({ behavior: 'smooth', block: 'center' });
+    const t = setTimeout(() => setHighlightId(null), 3000);
+    return () => clearTimeout(t);
+  }, [highlightId, setHighlightId]);
 
   return {
     agent,