fix: improve message counter initialization with bootstrap check

Add hasBootstrappedRef to track component initialization and prevent
counting messages during the initial render. This fixes the new message
counter behavior when messages load on component mount and ensures
accurate message tracking when autoScroll is disabled.

web/src/components/AssistantChat/HappyThread.tsx

@@ -82,6 +82,7 @@ export function HappyThread(props: {
     const prevRenderedCountRef = useRef(props.renderedMessagesCount)
     const autoScrollEnabledRef = useRef(autoScrollEnabled)
     const newMessageCountRef = useRef(newMessageCount)
+    const hasBootstrappedRef = useRef(false)
 
     // Keep refs in sync with state
     useEffect(() => {
@@ -121,10 +122,22 @@ export function HappyThread(props: {
         const currentCount = props.renderedMessagesCount
         const wasLoadingMore = wasLoadingMoreRef.current
         wasLoadingMoreRef.current = props.isLoadingMoreMessages
+
+        if (props.isLoadingMessages) {
+            prevRenderedCountRef.current = currentCount
+            return
+        }
+
+        if (!hasBootstrappedRef.current) {
+            hasBootstrappedRef.current = true
+            prevRenderedCountRef.current = currentCount
+            return
+        }
+
         prevRenderedCountRef.current = currentCount
 
         // Skip during loading states
-        if (props.isLoadingMoreMessages || props.isLoadingMessages) {
+        if (props.isLoadingMoreMessages) {
             return
         }
 
@@ -154,6 +167,7 @@ export function HappyThread(props: {
         setAutoScrollEnabled(true)
         setNewMessageCount(0)
         prevRenderedCountRef.current = 0
+        hasBootstrappedRef.current = false
     }, [props.sessionId])
 
     const handleLoadMore = useCallback(() => {