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/TerminalView.tsx

@@ -42,6 +42,7 @@
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 import {
+  memo,
   useEffect,
   useId,
   useMemo,
@@ -153,9 +154,22 @@ interface TerminalViewProps {
   /** Take the keyboard when it appears (default). Off for a split pane that
    *  is not the focused one, or keys would land in whichever mounted last. */
   autoFocus?: boolean;
+  /** Another layer (the pane's chat) covers it. xterm stops drawing only when
+   *  its IntersectionObserver says off screen, and a covered terminal is not —
+   *  so it is moved out of the viewport with a transform, which keeps its
+   *  layout size (no PTY resize; the chat still reads and answers its menus). */
+  covered?: boolean;
 }
 
-export function TerminalView({ runId, wsBaseUrl, onExit, autoFocus = true }: TerminalViewProps) {
+/** Memoized: the Workspace re-renders its pane tree on every lane_update, and
+ *  a terminal only cares about its own props (its owner keeps `onExit` stable). */
+export const TerminalView = memo(function TerminalView({
+  runId,
+  wsBaseUrl,
+  onExit,
+  autoFocus = true,
+  covered = false,
+}: TerminalViewProps) {
   const containerRef = useRef<HTMLDivElement>(null);
   // Read through a ref: an inline `onExit` from the parent changes identity on
   // every render, and as an effect dep it would tear the terminal down and
@@ -709,7 +723,12 @@ export function TerminalView({ runId, wsBaseUrl, onExit, autoFocus = true }: Ter
       onPasteCapture={onPaste}
       onFocus={() => notePaneFocus(runId)}
     >
-      <div ref={containerRef} className="h-full w-full" data-testid="terminal-view" />
+      <div
+        ref={containerRef}
+        className="h-full w-full"
+        style={covered ? { transform: "translateX(-300vw)" } : undefined}
+        data-testid="terminal-view"
+      />
       <p id={hintId} className="sr-only">
         {t("terminal.keyboardHint")}
       </p>
@@ -810,4 +829,4 @@ export function TerminalView({ runId, wsBaseUrl, onExit, autoFocus = true }: Ter
       )}
     </div>
   );
-}
+});