- UsageStore with async SQLite persistence via aiosqlite
- Background batch writer for non-blocking event persistence
- Auto-subscribes to UsageTracker for transparent capture
- Query methods: query(), get_billing_summary(), get_daily_usage()
- REST API endpoints: /usage/history, /usage/billing, /usage/daily
- Filtering by org_id, agent_id, model, time range
- 18 new tests for persistence layer
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
