fix chat ux and ai model

web/app/chat/page.js

@@ -84,6 +84,7 @@ function ChatPage() {
   const [convsLoading, setConvsLoading] = useState(false);
   const [closedExpanded, setClosedExpanded] = useState(false);
   const [selectedFile, setSelectedFile] = useState(null);
+  const [switchingConv, setSwitchingConv] = useState(false);
 
   const messagesEndRef = useRef(null);
   const messagesAreaRef = useRef(null);
@@ -108,11 +109,14 @@ function ChatPage() {
     lastScrolledIdRef.current = lastMsg.id;
     const area = messagesAreaRef.current;
     if (!area) return;
-    const nearBottom = area.scrollHeight - area.scrollTop - area.clientHeight < 80;
-    if (nearBottom) {
+    const isOwn = lastMsg.senderId === user?.id;
+    if (isOwn) {
       area.scrollTop = area.scrollHeight;
+    } else {
+      const nearBottom = area.scrollHeight - area.scrollTop - area.clientHeight < 80;
+      if (nearBottom) area.scrollTop = area.scrollHeight;
     }
-  }, [messages]);
+  }, [messages, user?.id]);
 
   const fetchMessages = useCallback(async (convId) => {
     if (!token || !convId) return;
@@ -416,10 +420,10 @@ function ChatPage() {
     if (stompRef.current) { stompRef.current.deactivate(); stompRef.current = null; }
     setMessages([]);
     setError(null);
-    setLoadingConv(true);
+    setSwitchingConv(true);
     await fetchConversation(convId);
     await fetchMessages(convId);
-    setLoadingConv(false);
+    setSwitchingConv(false);
     connectStomp(convId);
     router.replace(`/chat?id=${convId}`, { scroll: false });
   }
@@ -640,6 +644,11 @@ function ChatPage() {
                   </div>
                 );
               })}
+              {switchingConv && (
+                <div style={{ textAlign: "center", padding: "1rem", color: "#aaa", fontSize: "0.85rem" }}>
+                  Loading messages…
+                </div>
+              )}
               <div ref={messagesEndRef} />
             </div>