fix(dashboard): wire scroll-to-top pagination instead of loading all messages

- Remove fetchAllMessagesInChat/fetchAllMessages helpers
- Keep limit:50 for initial load in useChat and useQuickChat
- Add IntersectionObserver sentinel at top of ChatView message list to
  trigger loadMoreMessages() when user scrolls to the top
- Keep stale-session guards (activeSessionRef checks) from original PR
- Tests: revert assertions back to { limit: 50 }

packages/dashboard/app/components/ChatView.tsx

@@ -946,6 +946,8 @@ export function ChatView({ projectId, addToast, experimentalFeatures }: ChatView
     stopStreaming,
     pendingMessage,
     clearPendingMessage,
+    loadMoreMessages,
+    hasMoreMessages,
     searchQuery,
     setSearchQuery,
     filteredSessions,
@@ -1031,6 +1033,7 @@ export function ChatView({ projectId, addToast, experimentalFeatures }: ChatView
   }, [fileMention.mentionActive]);
 
   const messagesEndRef = useRef<HTMLDivElement>(null);
+  const loadMoreSentinelRef = useRef<HTMLDivElement>(null);
   const mobileSessionMenuRef = useRef<HTMLDivElement>(null);
   const roomSwitcherRef = useRef<HTMLDivElement>(null);
   const isUserScrollingRef = useRef(false);
@@ -1233,6 +1236,22 @@ export function ChatView({ projectId, addToast, experimentalFeatures }: ChatView
     };
   }, []);
 
+  useEffect(() => {
+    const sentinel = loadMoreSentinelRef.current;
+    if (!sentinel || !hasMoreMessages) return;
+
+    const observer = new IntersectionObserver(
+      (entries) => {
+        if (entries[0].isIntersecting) {
+          void loadMoreMessages();
+        }
+      },
+      { threshold: 0.1 },
+    );
+    observer.observe(sentinel);
+    return () => observer.disconnect();
+  }, [hasMoreMessages, loadMoreMessages]);
+
   const getActiveThreadId = useCallback(() => {
     return roomThreadActive ? (rooms.activeRoom?.id ?? null) : (activeSession?.id ?? null);
   }, [roomThreadActive, rooms.activeRoom?.id, activeSession?.id]);
@@ -3123,6 +3142,11 @@ export function ChatView({ projectId, addToast, experimentalFeatures }: ChatView
 
         {/* Messages */}
         <div className="chat-messages" ref={messagesContainerRef} onScroll={updateScrollState}>
+          <div ref={loadMoreSentinelRef} className="chat-load-more-sentinel">
+            {hasMoreMessages && messagesLoading && (
+              <div className="chat-loading-older">Loading older messages…</div>
+            )}
+          </div>
           {isStreaming ? (
             <>
               {messages.map((message) => (

packages/dashboard/app/hooks/useChat.ts

@@ -239,26 +239,6 @@ function mapChatMessageToInfo(message: ChatMessage): ChatMessageInfo {
   };
 }
 
-/**
- * Fetch all messages for a session, paginating through the API's 200-message cap.
- * Used for the initial full load so sessions with >50 messages are never truncated.
- */
-async function fetchAllMessagesInChat(
-  sessionId: string,
-  projectId: string | undefined,
-): Promise<ChatMessageInfo[]> {
-  const PAGE = 200;
-  const all: ChatMessageInfo[] = [];
-  let offset = 0;
-  for (;;) {
-    const data = await fetchChatMessages(sessionId, { limit: PAGE, offset }, projectId);
-    all.push(...data.messages.map(mapChatMessageToInfo));
-    if (data.messages.length < PAGE) break;
-    offset += PAGE;
-  }
-  return all;
-}
-
 export function useChat(
   projectId?: string,
   addToast?: (msg: string, type?: "success" | "error" | "warning") => void,
@@ -471,24 +451,18 @@ export function useChat(
       }
 
       try {
+        const data = await fetchChatMessages(sessionId, { limit: 50, ...opts }, projectId);
+        const mappedMessages = data.messages.map(mapChatMessageToInfo);
         if (isPaginationRequest) {
-          // Prepend older messages (forward pagination, used when hasMoreMessages)
+          if (activeSessionRef.current?.id === sessionId) {
-          const requestSessionId = sessionId;
-          const data = await fetchChatMessages(sessionId, { limit: 50, ...opts }, projectId);
-          if (activeSessionRef.current?.id === requestSessionId) {
-            const mappedMessages = data.messages.map(mapChatMessageToInfo);
             setMessages((prev) => [...mappedMessages, ...prev]);
             setHasMoreMessages(data.messages.length >= 50);
           }
         } else {
-          // Initial full load — fetch all messages, never truncate at 50
-          const allMessages = await fetchAllMessagesInChat(sessionId, projectId);
           if (activeSessionRef.current?.id === sessionId) {
-            setMessages(allMessages);
+            setMessages(mappedMessages);
-            if (cacheKey) {
+            setHasMoreMessages(data.messages.length >= 50);
-              writeCache(cacheKey, allMessages, { maxBytes: 500_000 });
+            if (cacheKey) writeCache(cacheKey, mappedMessages, { maxBytes: 500_000 });
-            }
-            setHasMoreMessages(false); // all messages loaded — inside guard
           }
         }
       } catch {

packages/dashboard/app/hooks/useQuickChat.ts

@@ -183,22 +183,6 @@ function mapChatMessageToInfo(message: ChatMessage): ChatMessageInfo {
   };
 }
 
-/**
- * Fetch all messages for a session, paginating through the API's 200-message cap.
- * Replaces the former hardcoded `limit: 50` that silently truncated long sessions.
- */
-async function fetchAllMessages(sessionId: string, projectId?: string): Promise<ChatMessageInfo[]> {
-  const PAGE = 200; // API hard cap (Math.min(limit, 200))
-  const all: ChatMessageInfo[] = [];
-  let offset = 0;
-  for (;;) {
-    const data = await fetchChatMessages(sessionId, { limit: PAGE, offset }, projectId);
-    all.push(...data.messages.map(mapChatMessageToInfo));
-    if (data.messages.length < PAGE) break;
-    offset += PAGE;
-  }
-  return all;
-}
 /**
  * Hook for the QuickChatFAB component.
  * Provides chat session management and SSE streaming for real-time AI responses.
@@ -346,8 +330,8 @@ export function useQuickChat(
         isStreamingRef.current = false;
         streamRef.current = null;
         lastAttachedGenerationRef.current = null;
-        void fetchAllMessages(sessionId, projectId).then((msgs) => {
+        void fetchChatMessages(sessionId, { limit: 50 }, projectId).then((data) => {
-          if (activeSessionRef.current?.id === sessionId) setMessages(msgs);
+          if (activeSessionRef.current?.id === sessionId) setMessages(data.messages.map(mapChatMessageToInfo));
         }).catch(() => {});
         flushPendingMessage();
       },
@@ -363,8 +347,8 @@ export function useQuickChat(
         if (!options?.silent) {
           addToast?.(errorMessage, "error");
         }
-        void fetchAllMessages(sessionId, projectId).then((msgs) => {
+        void fetchChatMessages(sessionId, { limit: 50 }, projectId).then((data) => {
-          if (activeSessionRef.current?.id === sessionId) setMessages(msgs);
+          if (activeSessionRef.current?.id === sessionId) setMessages(data.messages.map(mapChatMessageToInfo));
         }).catch(() => {});
         flushPendingMessage();
       },
@@ -444,8 +428,8 @@ export function useQuickChat(
     setMessagesLoading(true);
     try {
       const sessionId = activeSession.id;
-      const msgs = await fetchAllMessages(sessionId, projectId);
+      const data = await fetchChatMessages(sessionId, { limit: 50 }, projectId);
-      if (activeSessionRef.current?.id === sessionId) setMessages(msgs);
+      if (activeSessionRef.current?.id === sessionId) setMessages(data.messages.map(mapChatMessageToInfo));
     } catch (err) {
       console.error("[useQuickChat] Failed to load messages:", err);
     } finally {
@@ -489,8 +473,8 @@ export function useQuickChat(
           clearInterval(interval);
           // Reload messages to pick up the completed assistant message
           const sessionId = activeSession.id;
-          const msgs = await fetchAllMessages(sessionId, projectId);
+          const data = await fetchChatMessages(sessionId, { limit: 50 }, projectId);
-          if (activeSessionRef.current?.id === sessionId) setMessages(msgs);
+          if (activeSessionRef.current?.id === sessionId) setMessages(data.messages.map(mapChatMessageToInfo));
           setStreamingText("");
           setStreamingThinking("");
           setStreamingToolCalls([]);
@@ -512,8 +496,8 @@ export function useQuickChat(
     setMessagesLoading(true);
     try {
       const sessionId = activeSession.id;
-      const msgs = await fetchAllMessages(sessionId, projectId);
+      const data = await fetchChatMessages(sessionId, { limit: 50 }, projectId);
-      if (activeSessionRef.current?.id === sessionId) setMessages(msgs);
+      if (activeSessionRef.current?.id === sessionId) setMessages(data.messages.map(mapChatMessageToInfo));
     } catch (err) {
       console.error("[useQuickChat] Failed to reload messages:", err);
     } finally {