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).

docs/API.md

@@ -1152,7 +1152,7 @@ head of `toolFlow.transitions` (one window pass over the events for both).
 The bundle scans every event, so it is computed in a worker thread on its own
 read-only connection (`server/lib/read-pool.js`) and never stalls another
 request, hook or websocket meanwhile. Identical requests in flight share one
-run. `AGENTHUB_READ_WORKER=0` computes it inline instead.
+run, and a result is reused for 30 s per distinct query. `AGENTHUB_READ_WORKER=0` computes it inline instead.
 
 **Status codes:**
 - **200** — the bundle, or the requested sections of it
@@ -1721,7 +1721,7 @@ sequenceDiagram
 GET /api/events
 ```
 
-Returns `{ events, limit, offset, total }`, newest first, filtered by `event_type`, `tool_name`, `agent_id`, `session_id` (each comma-separated), `q`, `from`/`to` (on `created_at`) and `sources`. Each row carries its labels, so a list page need not fetch every session and agent to name them: `session_name`, `session_cwd`, `session_lane_id`, `agent_name` and `agent_subagent_type` (each `null` when the session/agent row is missing). These columns are REST-only — the WebSocket `new_event` message is unchanged.
+Returns `{ events, limit, offset, total }`, newest first, filtered by `event_type`, `tool_name`, `agent_id`, `session_id` (each comma-separated), `q`, `from`/`to` (on `created_at`) and `sources`. Each row carries its labels, so a list page need not fetch every session and agent to name them: `session_name`, `session_cwd`, `session_lane_id`, `agent_name` and `agent_subagent_type` (each `null` when the session/agent row is missing). These columns are REST-only — the WebSocket `new_event` message does not carry them (it carries the row `id`).
 
 ---
 
@@ -2048,6 +2048,8 @@ GET /api/analytics?tz_offset=<minutes>&sources=<csv>&tool=<id>&from=<YYYY-MM-DD>
 
 The Analytics bundle (`tokens`, `total_cost`, `tool_usage`, `daily_events`, `daily_sessions`, `agent_types`, `event_types`, `avg_events_per_session`, `total_subagents`, `overview`, `agents_by_status`, `sessions_by_status`). With `from`/`to` (same rules as above) the shape is unchanged and the numbers narrow: sessions and agents count by `started_at`, events by `created_at`, and `tokens` / `total_cost` come from the cost rows of the days in the range (`token_usage` has no date, so tokens follow the spend-day split). `daily_events` and `daily_sessions` keep their 365-day window.
 
+The four numbers that scan `events` (`tool_usage`, `daily_events`, `event_types`, `avg_events_per_session`) are computed in the read worker (`server/lib/read-pool.js`) and reused for 10 s per distinct query (scope, range, `tz_offset`), so they may trail a new event by up to that long. A worker job past `AGENTHUB_READ_TIMEOUT_MS` answers **503** `EREADTIMEOUT`.
+
 #### Spend Budgets
 
 A budget is an alert rule of type `budget`, created and edited through `/api/alerts/rules`: