refactor(webui): shrink fork implementation

webui/src/components/thread/ThreadShell.tsx

@@ -278,8 +278,6 @@ export function ThreadShell({
   const [filePreviewPath, setFilePreviewPath] = useState<string | null>(null);
   const [filePreviewClosing, setFilePreviewClosing] = useState(false);
   const [filePreviewWidth, setFilePreviewWidth] = useState(FILE_PREVIEW_DEFAULT_WIDTH);
-  const [forkError, setForkError] = useState<string | null>(null);
-  const [forkHydratingChatId, setForkHydratingChatId] = useState<string | null>(null);
   const shellRef = useRef<HTMLElement | null>(null);
   const filePreviewWidthRef = useRef(FILE_PREVIEW_DEFAULT_WIDTH);
   const filePreviewCloseTimerRef = useRef<number | null>(null);
@@ -288,7 +286,6 @@ export function ThreadShell({
   const messageCacheRef = useRef<Map<string, UIMessage[]>>(new Map());
   /** Last chatId we associated with the in-memory thread (for cache-on-switch). */
   const prevChatIdForCacheRef = useRef<string | null>(null);
-  const prevChatIdForComposerRef = useRef<string | null>(chatId);
   /** Skip one message-cache write right after chatId changes (messages may not match yet). */
   const skipLayoutCacheRef = useRef(false);
   const appliedHistoryVersionRef = useRef<Map<string, number>>(new Map());
@@ -340,12 +337,6 @@ export function ThreadShell({
     };
   }, []);
 
-  useEffect(() => {
-    if (prevChatIdForComposerRef.current === chatId) return;
-    prevChatIdForComposerRef.current = chatId;
-    setForkError(null);
-  }, [chatId]);
-
   const displayMessages = useMemo(() => projectWebuiThreadMessages(messages), [messages]);
 
   const showHeroComposer = messages.length === 0 && !loading;
@@ -455,12 +446,6 @@ export function ThreadShell({
     setMessages(projectWebuiThreadMessages(historical));
   }, [chatId, historical, setMessages]);
 
-  useEffect(() => {
-    if (!chatId || loading || forkHydratingChatId !== chatId) return;
-    setForkHydratingChatId(null);
-    setScrollToBottomSignal((value) => value + 1);
-  }, [chatId, forkHydratingChatId, loading]);
-
   useLayoutEffect(() => {
     if (chatId) {
       const prev = prevChatIdForCacheRef.current;
@@ -539,7 +524,6 @@ export function ThreadShell({
 
   const handleThreadSend = useCallback(
     (content: string, images?: SendImage[], options?: SendOptions) => {
-      setForkError(null);
       setScrollToBottomSignal((value) => value + 1);
       send(content, images, withWorkspaceScope(options));
     },
@@ -637,21 +621,13 @@ export function ThreadShell({
   const handleForkFromMessage = useCallback(
     async (beforeUserIndex: number) => {
       if (!chatId || !onForkChat) return;
-      setForkError(null);
       const forkedChatId = await onForkChat(chatId, beforeUserIndex);
-      if (!forkedChatId) {
-        setForkError(t("thread.fork.failed", {
-          defaultValue: "Could not fork this chat. Try again.",
-        }));
-        return;
-      }
+      if (!forkedChatId) return;
       messageCacheRef.current.delete(forkedChatId);
       appliedHistoryVersionRef.current.delete(forkedChatId);
       pendingCanonicalHydrateRef.current.add(forkedChatId);
-      setForkHydratingChatId(forkedChatId);
-      setForkError(null);
     },
-    [chatId, onForkChat, t],
+    [chatId, onForkChat],
   );
 
   const composer = (
@@ -665,7 +641,7 @@ export function ThreadShell({
       {session ? (
         <ThreadComposer
           onSend={handleThreadSend}
-          disabled={!chatId || forkHydratingChatId === chatId}
+          disabled={!chatId}
           isStreaming={isStreaming}
           placeholder={
             showHeroComposer
@@ -692,7 +668,6 @@ export function ThreadShell({
           workspaceError={workspaceError}
           onWorkspaceScopeChange={onWorkspaceScopeChange}
           pendingQueueKey={chatId}
-          externalError={forkError}
         />
       ) : (
         <ThreadComposer
@@ -776,7 +751,6 @@ export function ThreadShell({
           showScrollToBottomButton={!!session}
           cliApps={cliApps}
           mcpPresets={mcpPresets}
-          allMessages={displayMessages}
           forkBoundaryMessageCount={forkBoundaryMessageCount}
           onOpenFilePreview={historyKey ? handleOpenFilePreview : undefined}
           onForkFromMessage={onForkChat ? handleForkFromMessage : undefined}