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).

server/__tests__/lanes-api.test.js

@@ -541,6 +541,30 @@ describe("hook → lane binding", () => {
     assert.equal((await request("GET", "/api/lanes")).body.lanes.length, before);
   });
 
+  it("keeps the lane's session when a split pane (slot 1–9) of the workspace sends hooks", async () => {
+    const created = await request("POST", "/api/lanes", { cwd: "/tmp/lane-split-pane" });
+    const id = created.body.lane.id;
+    const hook = (session_id, run_id) =>
+      request("POST", "/api/hooks/event", {
+        hook_type: "PostToolUse",
+        run_id,
+        data: {
+          session_id,
+          cwd: "/tmp/lane-split-pane",
+          tool_name: "Read",
+          tool_use_id: session_id,
+        },
+      });
+    await hook("sess-main", `agenthub-lane-${id}`);
+    assert.equal((await request("GET", `/api/lanes/${id}`)).body.lane.session_id, "sess-main");
+    // A split pane's session never takes the lane over…
+    await hook("sess-split", `agenthub-lane-${id}-2`);
+    assert.equal((await request("GET", `/api/lanes/${id}`)).body.lane.session_id, "sess-main");
+    // …while a session outside the dashboard still does, as before.
+    await hook("sess-outside", undefined);
+    assert.equal((await request("GET", `/api/lanes/${id}`)).body.lane.session_id, "sess-outside");
+  });
+
   it("clears needs_action only from the session that raised it, not from cross-session rebinds", async () => {
     const created = await request("POST", "/api/lanes", {
       cwd: "/tmp/lane-cross-session",