Function useChatMessages

cli/src/hooks/use-chat-messages.ts:57–254

({
  messages,
  setMessages,
}: UseChatMessagesOptions)

 * @returns Message tree, pagination state, and handlers
 */
export function useChatMessages({
  messages,
  setMessages,
}: UseChatMessagesOptions): UseChatMessagesReturn {
  // Message pagination state
  const [visibleMessageCount, setVisibleMessageCount] =
    useState(MESSAGE_BATCH_SIZE)

  // Reset visible message count when messages are cleared or conversation changes
  useEffect(() => {
    if (messages.length <= MESSAGE_BATCH_SIZE) {
      setVisibleMessageCount(MESSAGE_BATCH_SIZE)
    }
  }, [messages.length])

  // Ref to track user-initiated collapse (prevents auto-scroll during collapse)
  const isUserCollapsingRef = useRef<boolean>(false)

  /**
   * Returns true if user is currently collapsing.
   * Used by scroll management to prevent auto-scroll during collapse.
   */
  const isUserCollapsing = useCallback(() => {
    return isUserCollapsingRef.current
  }, [])

  /**
   * Toggles the collapsed state of a block or agent message.
   * Handles both top-level agent messages and nested content blocks.
   */
  const handleCollapseToggle = useCallback(
    (id: string) => {
      // Set flag to prevent auto-scroll during user-initiated collapse
      isUserCollapsingRef.current = true

      // Find and toggle the block's isCollapsed property
      setMessages((prevMessages) => {
        return prevMessages.map((message) => {
          // Handle agent variant messages
          if (message.variant === 'agent' && message.id === id) {
            const wasCollapsed = message.metadata?.isCollapsed ?? false
            return {
              ...message,
              metadata: {
                ...message.metadata,
                isCollapsed: !wasCollapsed,
                userOpened: wasCollapsed, // Mark as user-opened if expanding
              },
            }
          }

          // Handle blocks within messages
          if (!message.blocks) return message

          const updateBlocksRecursively = (
            blocks: ContentBlock[],
          ): ContentBlock[] => {
            let foundTarget = false