perf: v2.5.10 — ready for 10+ concurrent users, leaner locally

Measured on a copy of a real 1.2 GB / 253K-event database, 10 simulated
browsers + 10 hooks/s for 90 s: event-loop delay p99 1239 ms → 32 ms (max
2.0 s → 94 ms), 266 failed requests → 0, 74 → 111 requests/s served, server
RSS 633 → 346 MB. Entry bundle 975 KB raw → 394 KB (106 KB brotli).

Server
- /api/analytics: the events-table scans run in the read worker
  (scoped-stats eventAggregates, read-pool job analyticsEvents); runRead takes
  maxAgeMs — analytics 10 s, /api/workflows 30 s — keyed by the args
- /api/workflows/skill-usage: +event_type and a tool_name range instead of
  LIKE, so it uses idx_events_tool (784 ms → a few ms)
- idx_events_session_type_tool (session_id, event_type, tool_name,
  created_at) replaces idx_events_session_type: covering reads for session
  stats, the hook dedupes and the import resume point (1.2 s → 20 ms); 64 MB
  cache_size and 256 MB mmap_size on both connections
- WAL: the server sets wal_autocheckpoint = 0 and checkpoints PASSIVE every
  DASHBOARD_WAL_CHECKPOINT_MS (5 s) from the read worker's own writable
  connection; a failed checkpoint restores the automatic one (hook COMMIT p95
  109 ms → 15 ms at 100 hooks/s)
- tmux: one list-sessions answers a whole GET /api/lanes and the heal beat
  (liveSessions), shared for 1 s and cleared by this process's new/kill —
  GET /api/run's sync spawns had blocked 60 s of a 90 s run; the heal beat
  skips tmux when nothing runs; attach options chained into 2 spawns
- hooks: TurnDuration/APIError deduped against one read per hook instead of a
  query per transcript entry (23 ms/hook on a 763-turn session); one lane
  scan per hook; hourly upserts skip rows that did not grow; frames are sent
  after the transaction commits (and after the pane binding); new_event
  carries its row id; a split pane's (slot 1–9) hooks no longer rebind the
  lane's session_id
- watchdog liveness probe runs ps asynchronously; transcript newline scan via
  indexOf; startup subagent backfill fingerprints the files it already checked
- pty attach: backpressure (pause past 1 MB unsent, resume under 256 KB)
- static: hashed assets served from their pre-compressed .br/.gz sibling

Client
- hidden tabs neither refetch on WS events nor poll (useLiveRefresh, panes,
  lane cards, git header, changes panel, settings); no per-tab hourly
  /updates/check (the server already checks)
- refetch storms throttled (workspace tree/session list 3 s, /api/run only on
  a run-key change, notification pane lookup only when shown); WS reconnect
  jitter; terminal retry backoff 1.5 → 30 s, stops on 1008
- heavier throttles for aggregates (15 s) and detail views; Monitor keepIfSame;
  GET in-flight dedupe in request()
- lazy Dashboard/History, xterm (with the first terminal), lane modals, Sagi
  (only while enabled); only the active locale loads; Workspace chunk
  prefetched on a /workspace deep link
- Sagi: no work while disabled, pupil via CSS variables, memo avatar
- build: .br/.gz siblings, sourcemap hidden; service worker no longer caches
  /assets/ (cache v3 drops the old one)

Tests: scripts/test-server.js drops the GIT_DIR-family variables a hook
exports, so a suite run from a linked worktree's pre-commit can no longer
commit into the real repository or set core.bare.

Docs: ARCHITECTURE, DATABASE, API, DEPLOYMENT, client README,
docs/plans/perf/README.md (audit, checklist, results).

client/src/components/Sagi/Sagi.tsx

@@ -1,7 +1,10 @@
 /**
  * @file Sagi.tsx
- * @description Floating mascot companion shell. Mounts once (next to UpdateNotifier
- *   in Layout) so it persists across routes and shares the single WebSocket.
+ * @description Floating mascot companion shell. Mounted once by `SagiMount` (next
+ *   to UpdateNotifier in Layout), which loads this chunk only while the mascot is
+ *   enabled; `Sagi` gates on the same preference itself, and the body (brain,
+ *   tick, WS reducer) runs only while it is on. Persists across routes and
+ *   shares the single WebSocket.
  *   Owns the open/closed panel state, the ⌘B / Esc shortcuts, reduced-motion
  *   detection, and route navigation. Reactive personality + status/Ask come
  *   from useSagiBrain; the avatar is draggable (AssistiveTouch-style) via
@@ -81,6 +84,7 @@ import { SpeechBubble } from "./SpeechBubble";
 import { SagiPanel } from "./SagiPanel";
 import { useSagiBrain } from "./useSagiBrain";
 import { useSagiPosition } from "./useSagiPosition";
+import { useSagiEnabled } from "./SagiMount";
 import { matchIntent } from "./intents";
 import { sagiPrefs } from "./prefs";
 import { api } from "../../lib/api";
@@ -195,9 +199,13 @@ function SagiFlyout({
   );
 }
 
+/** Renders nothing — and runs no hook below — while the mascot is disabled. */
 export function Sagi() {
+  return useSagiEnabled() ? <SagiBody /> : null;
+}
+
+function SagiBody() {
   const { t } = useTranslation("settings");
-  const [enabled, setEnabled] = useState(() => sagiPrefs.getEnabled());
   const [pet, setPet] = useState(() => sagiPrefs.getPet());
   const [size, setSize] = useState(() => sagiPrefs.getSize());
   const [open, setOpen] = useState(false);
@@ -209,11 +217,11 @@ export function Sagi() {
   const brain = useSagiBrain();
   const place = useSagiPosition(size);
 
-  // Keep enabled, the pet and its size in sync with Settings / other tabs.
+  // Keep the pet and its size in sync with Settings / other tabs (enabled is
+  // the `Sagi` gate's: it unmounts this body when the mascot is turned off).
   useEffect(
     () =>
       sagiPrefs.subscribe(() => {
-        setEnabled(sagiPrefs.getEnabled());
         setPet(sagiPrefs.getPet());
         setSize(sagiPrefs.getSize());
       }),
@@ -223,7 +231,6 @@ export function Sagi() {
   // ⌘B / Ctrl+B toggles the panel; Esc closes it. Only while the mascot is
   // shown, and never from an editable field, where Ctrl+B belongs to the field.
   useEffect(() => {
-    if (!enabled) return;
     const onKey = (e: KeyboardEvent) => {
       if ((e.metaKey || e.ctrlKey) && e.key.toLowerCase() === "b") {
         if (isEditable(e.target) || isEditable(document.activeElement)) return;
@@ -235,7 +242,7 @@ export function Sagi() {
     };
     window.addEventListener("keydown", onKey);
     return () => window.removeEventListener("keydown", onKey);
-  }, [enabled]);
+  }, []);
 
   const onNavigate = useCallback(
     (route: string) => {
@@ -279,8 +286,6 @@ export function Sagi() {
     [brain, navigate, t]
   );
 
-  if (!enabled) return null;
-
   const anchor: Anchor = {
     left: place.left,
     top: place.top,