perf(chat): hidden panes stop polling, rows stop re-rendering, a covered terminal stops drawing

The Workspace keeps panes of other workspaces and tabs mounted (display:none),
and every one of them kept following the live stream as if shown.

- useOnScreen (IntersectionObserver): ConversationView, the outline and the
  700 ms menu scan skip while their pane is hidden and catch up once on show.
- A new_event refetches the tail at most every 1.5 s (leading + trailing).
- MessageList: WorkGroup/MessageRow/EditedFiles compare only their own blocks
  and results, so a tail append no longer re-renders every row.
- A terminal under the chat is moved off the viewport with a transform, so
  xterm pauses drawing without a resize.
- PaneChat and TerminalView are memoized; LaneConsolePane passes a stable onExit.
- RunningStep's clock and the outline poll skip unchanged or hidden updates.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

client/src/components/run/ChatOutline.tsx

@@ -16,7 +16,14 @@
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
-import { useEffect, useState, type ComponentType, type DragEvent, type ReactNode } from "react";
+import {
+  useEffect,
+  useState,
+  type ComponentType,
+  type DragEvent,
+  type ReactNode,
+  type RefObject,
+} from "react";
 import { useTranslation } from "react-i18next";
 import { Link } from "react-router-dom";
 import { useSettingsHref } from "../../lib/settingsLink";
@@ -35,6 +42,8 @@ import {
   X,
 } from "lucide-react";
 import { api, type SessionOutline } from "../../lib/api";
+import { keepIfSame } from "../../lib/keepIfSame";
+import { isShown } from "../../hooks/useOnScreen";
 import { displayName, extOf } from "./ChatFilePreview";
 import { dragAttachments, dragSkill, type Attachment } from "../../lib/promptAttach";
 
@@ -49,25 +58,30 @@ const EMPTY: SessionOutline = {
   mcp: [],
 };
 
-/** The session's outline, re-read on a visibility-gated poll. */
-export function useSessionOutline(sessionId: string): SessionOutline {
+/** The session's outline, re-read on a visibility-gated poll — skipped too
+ *  while `onScreen` says the pane is hidden (another workspace or tab, kept
+ *  mounted). An unchanged answer keeps the old object: no re-render. */
+export function useSessionOutline(
+  sessionId: string,
+  onScreen?: RefObject<boolean>
+): SessionOutline {
   const [outline, setOutline] = useState<SessionOutline>(EMPTY);
   useEffect(() => {
     let live = true;
     const load = () =>
       api.sessions
         .outline(sessionId)
-        .then((o) => live && setOutline({ ...EMPTY, ...o }))
+        .then((o) => live && setOutline(keepIfSame<SessionOutline>({ ...EMPTY, ...o })))
         .catch(() => {});
     void load();
     const timer = window.setInterval(() => {
-      if (document.visibilityState === "visible") void load();
+      if (onScreen ? isShown(onScreen) : document.visibilityState === "visible") void load();
     }, POLL_MS);
     return () => {
       live = false;
       window.clearInterval(timer);
     };
-  }, [sessionId]);
+  }, [sessionId, onScreen]);
   return outline;
 }
 
@@ -271,7 +285,7 @@ export function ChatOutline({
                   </span>
                 ) : (
                   <span
-                    className={`h-4 w-4 flex-shrink-0 rounded-full border-2 ${task.status === "in_progress" ? "animate-pulse border-accent" : "border-border"}`}
+                    className={`h-4 w-4 flex-shrink-0 rounded-full border-2 ${task.status === "in_progress" ? "animate-pulse-dot border-accent" : "border-border"}`}
                   />
                 )}
                 <span