perf: rest animations, cheaper chat typing and server polls, async per-tool hooks

UI
- No animation runs forever: Sagi moods, the custom pet sprite, status dots
  (pulse-dot, pulse-slow, ping) and the chat shimmer play a few cycles and
  rest. An infinite animation kept the browser drawing 60 frames a second.
- useSagiBrain: frames that only move lastActivityAt by <1 s keep the old
  state; the 1 s tick re-renders only when the mood changes.
- ConversationView and MessageList are memoized and PaneChat passes stable
  callbacks: typing in the chat box no longer re-renders the conversation.
- The chat's 700 ms menu poll reads plain text first and scans the terminal
  cell by cell (reusing one cell) only when a row could be a menu cursor row.

Server
- GET /sessions/:id/transcript?after=N skips lines <= N before JSON.parse.
- GET /sessions/:id/outline is cached until the session's events change.
- broadcastLane uses the cached tmux.liveSessions(); tmux.hasSession answers
  "yes" from the fresh shared list instead of a synchronous spawn (50-150 ms
  per psmux call on Windows, blocking terminal echo).
- pane-mode polls every 150 ms; writeHourly writes only changed hour buckets.
- /api/metrics: agenthub_event_loop_delay_seconds{quantile}.

Hooks
- PreToolUse/PostToolUse run with "async": true (settings installer,
  plugin.json, S3 managed settings): Claude Code no longer waits a Node start
  before and after every tool call.

Committed with --no-verify at the owner's request: the pre-commit full server
suite fails on 9 tests that fail identically on 0c2f498 (lane-sync merge: no
git identity on this host; read-pool; resolveHost; codex-usage 1 ms flake).

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

client/src/components/Sagi/useSagiBrain.ts

@@ -77,6 +77,17 @@ import {
 import { pickQuip } from "./quips";
 import { sagiPrefs } from "./prefs";
 
+/** `next` differs from `prev` only by a lastActivityAt less than a second
+ *  newer — nothing the mascot shows, at the moods' 1 s resolution. */
+function onlyActivityMoved(prev: SagiState, next: SagiState): boolean {
+  if (next === prev) return true;
+  if (next.lastActivityAt - prev.lastActivityAt >= 1000) return false;
+  for (const k of Object.keys(next) as (keyof SagiState)[]) {
+    if (k !== "lastActivityAt" && next[k] !== prev[k]) return false;
+  }
+  return true;
+}
+
 const BUBBLE_MS = 4500;
 // Minimum gap between non-error bubbles, so a burst of activity doesn't spam.
 const BUBBLE_THROTTLE_MS = 3000;
@@ -153,7 +164,10 @@ export function useSagiBrain(): SagiBrain {
       setState((prev) => {
         const { state: next, pulse } = reduceSagi(prev, msg, t);
         if (pulse) showBubble(pickQuip(pulse), pulse === "error");
-        return next;
+        // Most frames only move lastActivityAt, which the moods read at a 1 s
+        // resolution: keep the old state then, so a hook burst (several
+        // frames a second) does not re-render the mascot on every frame.
+        return onlyActivityMoved(prev, next) ? prev : next;
       });
     });
     const unsubConn = eventBus.onConnection((connected) => {
@@ -169,15 +183,25 @@ export function useSagiBrain(): SagiBrain {
   // happy/worried) re-evaluate without needing a new event.
   useEffect(() => {
     // Hidden tab: no re-render; the first visible tick catches the mood up.
+    // Only a tick that changes the mood re-renders: an idle mascot is not
+    // drawn again every second for nothing.
     const id = setInterval(() => {
-      if (document.visibilityState === "visible") setTick(Date.now());
+      if (document.visibilityState !== "visible") return;
+      const now = Date.now();
+      if (deriveMood(stateRef.current, now) !== moodRef.current) setTick(now);
     }, 1000);
     return () => clearInterval(id);
   }, []);
 
   useEffect(() => () => clearTimeout(bubbleTimer.current), []);
 
-  const mood = useMemo(() => deriveMood(state, tick), [state, tick]);
+  // Judged at render time: `tick` only moves when the mood would change, so
+  // it may be old when a frame re-renders.
+  const mood = useMemo(() => deriveMood(state, Math.max(tick, Date.now())), [state, tick]);
+  const stateRef = useRef(state);
+  stateRef.current = state;
+  const moodRef = useRef(mood);
+  moodRef.current = mood;
   const status = useMemo(() => statusOf(state), [state]);
 
   const dismissBubble = useCallback(() => {