输入框状态剥离，避免受长信息列表渲染影响；覆写滚动条状态动作，不再强制拉到最底

src/components/chat/AgentWorkspace.tsx

@@ -23,6 +23,8 @@ type AgentWorkspaceProps = {
   branchGroups: BranchGroup[];
   branchTransition: BranchTransition | null;
   isStreaming: boolean;
+  scrollContainerRef: React.RefObject<HTMLDivElement | null>;
+  onScroll: React.UIEventHandler<HTMLDivElement>;
   bottomRef: React.RefObject<HTMLDivElement | null>;
   speakingMessageId: string | null;
   speechState: SpeechState;
@@ -155,6 +157,8 @@ export const AgentWorkspace = ({
   branchGroups,
   branchTransition,
   isStreaming,
+  scrollContainerRef,
+  onScroll,
   bottomRef,
   speakingMessageId,
   speechState,
@@ -216,6 +220,8 @@ export const AgentWorkspace = ({
 
   return (
     <Box
+      ref={scrollContainerRef}
+      onScroll={onScroll}
       sx={{
         flex: 1,
         overflowY: "auto",