Offline

Closing the frontend track and the pillar. The client faces the same scale and failure the backend does, and has to stay trustworthy through it: graceful degradation, retry with backoff, offline and flaky-network handling. Then the cross-cut that ties the pillar together, auth that scales, client-side rate limiting, and frontend observability that closes the loop back to knowing your numbers. Plus the native reality of un-hot-fixable clients.