- openDb pragmas: journal_mode=WAL, synchronous=NORMAL, temp_store=MEMORY, cache_size=-8000; 3000-record stress write throughput 9514ms -> 1241ms (7.7x), single upsert ~0.3ms; read paths unchanged (<=22ms) - authUser: devices.last_seen_at now written only when stale > 60s, removing one write per authenticated request (write amplification)