fix(chat): 对话区接近底部时正文突然上跳：去掉回贴区吸附并修正末端锚定口径

crates/agent-gateway/web/src/app/GatewayApp.tsx

@@ -246,6 +246,11 @@ function useGatewayAppController() {
     viewport: transcriptViewport,
     listenerRoot: transcriptScrollAreaRoot,
     trackKeys: true,
+    // 回贴区为 0：只有真正到达底部（8px 容差内）才恢复跟随。默认的 192px
+    // 回贴区会在滚轮下行进入该区间的那一 tick 直接 pin 到底，读者看到的是
+    // 正文突然上跳一段（复现页实测单 tick 231px），即"磁吸"。到达底部后向下
+    // 滚轮、手势落底、指针在底部释放三种路径仍会重新贴底。
+    config: { reattachZonePx: 0 },
   });
   // 楼层导航：当前楼层由转写区上报，跳转经 navRef 直达虚拟列表；粘底跟随
   // 激活时程序化滚动会被立即拽回底部——跳转前先按「跳入历史」语义解除跟随。

crates/agent-gateway/web/src/app/workbench/GatewayConversationPaneHost.tsx

@@ -39,6 +39,7 @@ import {
   mergePendingUploadedFiles,
   type PendingUploadedFile,
 } from "@liveagent/ui/lib/chat/uploadedFiles";
+import { useScrollFollow } from "@liveagent/ui/lib/chat-scroll/useScrollFollow";
 import { toTrajectoryMessages } from "@liveagent/ui/lib/trajectory/transcriptMessages";
 import {
   ChatComposerBar,
@@ -616,41 +617,27 @@ export function GatewayConversationPaneHost(props: GatewayConversationPaneHostPr
     if (composerRef.current) pageComposerRef.current = composerRef.current;
   });
 
-  // ---- 转录滚动跟随:贴底自动跟进,用户上滚即释放,支持一键回底 ------------
-  const viewportRef = useRef<HTMLDivElement | null>(null);
-  const followingRef = useRef(true);
-  const [following, setFollowing] = useState(true);
-  const detachScrollRef = useRef<(() => void) | null>(null);
-  const setViewport = useCallback((element: HTMLDivElement | null) => {
-    detachScrollRef.current?.();
-    detachScrollRef.current = null;
-    viewportRef.current = element;
-    if (!element) return;
-    element.scrollTop = element.scrollHeight;
-    const handleScroll = () => {
-      const nearBottom = element.scrollHeight - element.scrollTop - element.clientHeight < 48;
-      followingRef.current = nearBottom;
-      setFollowing(nearBottom);
-    };
-    element.addEventListener("scroll", handleScroll, { passive: true });
-    detachScrollRef.current = () => element.removeEventListener("scroll", handleScroll);
-  }, []);
-  useEffect(() => () => detachScrollRef.current?.(), []);
+  // ---- 转录滚动跟随 -----------------------------------------------------
+  // 背景 Pane 与主 Pane 共用同一套滚动跟随引擎：主 Pane 的视口由 GatewayApp
+  // 持有的引擎接管（经 primary.setTranscriptViewport 接线），本地这套只在
+  // 非主态生效。回贴区为 0：只有真正到达底部才恢复跟随。此前这里手写了一套
+  // "距底不足 48px 即视为跟随、行数一变就写 scrollTop" 的逻辑，读者停在底部
+  // 附近时会被每次流式增量吸回底部，而且与桌面端各 Pane 的引擎语义不一致。
+  const usePrimary = Boolean(isPrimary && primary);
+  const [paneScrollAreaRoot, setPaneScrollAreaRoot] = useState<HTMLDivElement | null>(null);
+  const [paneViewport, setPaneViewport] = useState<HTMLDivElement | null>(null);
+  const { handle: paneFollow, following: paneFollowing } = useScrollFollow({
+    viewport: paneViewport,
+    listenerRoot: paneScrollAreaRoot,
+    enabled: !usePrimary,
+    config: { reattachZonePx: 0 },
+  });
+  // 会话切换后落在最新消息上，与桌面端 ChatTranscript 一致。
+  // biome-ignore lint/correctness/useExhaustiveDependencies: conversationId 是有意的重置信号，动作由 handle 执行。
+  useLayoutEffect(() => {
+    if (!usePrimary) paneFollow.stickToBottom();
+  }, [conversationId, paneFollow, usePrimary]);
   const rowCount = transcript.rows.length;
-  // biome-ignore lint/correctness/useExhaustiveDependencies: 行数/修订变化时按跟随态贴底,效果体不直接读取它们。
-  useEffect(() => {
-    const viewport = viewportRef.current;
-    if (!viewport || !followingRef.current) return;
-    viewport.scrollTop = viewport.scrollHeight;
-  }, [rowCount, transcript.revision]);
-  const jumpToBottom = useCallback(() => {
-    const viewport = viewportRef.current;
-    if (!viewport) return;
-    viewport.scrollTop = viewport.scrollHeight;
-    followingRef.current = true;
-    setFollowing(true);
-  }, []);
-  const isViewportFollowing = useCallback(() => followingRef.current, []);
 
   // ---- 每会话模型/用量/进度/审批 -------------------------------------------
   const selectedValue = selection
@@ -738,12 +725,15 @@ export function GatewayConversationPaneHost(props: GatewayConversationPaneHostPr
     );
   }
 
-  const usePrimary = Boolean(isPrimary && primary);
-  const transcriptFollowing = usePrimary ? (primary?.viewportFollowing ?? following) : following;
+  const transcriptFollowing = usePrimary
+    ? (primary?.viewportFollowing ?? paneFollowing)
+    : paneFollowing;
   const transcriptIsViewportFollowing =
-    usePrimary && primary?.isViewportFollowing ? primary.isViewportFollowing : isViewportFollowing;
+    usePrimary && primary?.isViewportFollowing
+      ? primary.isViewportFollowing
+      : paneFollow.isFollowing;
   const handleJumpToBottom =
-    usePrimary && primary?.onJumpToBottom ? primary.onJumpToBottom : jumpToBottom;
+    usePrimary && primary?.onJumpToBottom ? primary.onJumpToBottom : paneFollow.jumpToBottom;
   const transcriptTree = (
     <GatewayTranscript
       conversationId={conversationId}
@@ -837,11 +827,11 @@ export function GatewayConversationPaneHost(props: GatewayConversationPaneHostPr
           ) : (
             <div className="gateway-transcript-scroll-shell">
               <ScrollArea
-                ref={usePrimary ? primary?.setTranscriptScrollAreaRoot : undefined}
+                ref={usePrimary ? primary?.setTranscriptScrollAreaRoot : setPaneScrollAreaRoot}
                 viewportRef={
                   usePrimary && primary?.setTranscriptViewport
                     ? primary.setTranscriptViewport
-                    : setViewport
+                    : setPaneViewport
                 }
                 className="gateway-transcript-scroll"
               >