perf: cheaper ingest — no re-parse of live hooked transcripts, delta hook writes, lighter pollers

- Session sync leaves a transcript alone while hooks feed its session live
  (active, newest event a hook's, touched within DASHBOARD_SYNC_LIVE_HOOK_MS,
  default 5 min) and catches it up once quiet; a hook-created session (which
  importSession skips anyway) is only snapshotted, never parsed.
- Hook writer keeps a per-transcript mark (applied after commit): an
  unchanged TranscriptCache result skips token/compaction/API-error/turn
  writes, a grown one walks only the entries after the last one handled.
- Codex usage: one stamp query per pass instead of one row per journal;
  between full passes (first + every 5 min) only the newest day folders and
  journals written in the last hour are statted; fork parents resolved from
  the table or a full walk.
- Cursor/Antigravity polls back off to 60 s after idle passes
  (server/lib/backoff-poll.js); lane sync runs only while another dashboard
  shares the data dir (checked every 30 s).

server/README.md

@@ -1600,10 +1600,11 @@ DASHBOARD_DB_PATH=./data/dashboard.db  # SQLite database path
 DASHBOARD_AI_TOOLS_DIR=            # Extra AI Tools catalog JSON files; an id here replaces the built-in one
 AGENTHUB_SHELL_PATH=1              # 0 = never run the login shell to read its PATH (startup + Refresh)
 AGENTHUB_AI_TOOLS_SYNC=1           # 0 = never copy the newest release's AI Tools catalog (server/lib/ai-tools-sync.js, daily)
-DASHBOARD_LANE_SYNC_MS=2000        # re-broadcast lanes another dashboard on the same DB changed (PRAGMA data_version); 0 = off
+DASHBOARD_LANE_SYNC_MS=2000        # re-broadcast lanes another dashboard on the same DB changed (PRAGMA data_version), only while one runs (checked every 30 s); 0 = off
 
 # Background services
 DASHBOARD_SESSION_SYNC_MS=30000    # Continuous project-sync poll interval (ms); 0 disables the poll (watcher stays)
+DASHBOARD_SYNC_LIVE_HOOK_MS=300000 # project sync leaves a transcript alone while hooks fed its session within this window; 0 = never defer
 DASHBOARD_LIVENESS_PROBE=1         # 0 disables the dead-session liveness reap (use when hooks arrive from another machine)
 DASHBOARD_LIVENESS_IDLE_SECONDS=60 # Idle gate before the liveness reap may complete a process-less session
 DASHBOARD_REPORTS_MS=60000         # Scheduled-reports beat (ms); 0 disables the scheduler