Capstone: a food delivery order system, live, Weeks 1 to 6

A full 45-minute interview that uses every week so far: clarify a 5 million order a day platform and choose push over polling, estimate 230 orders and 7,000 writes a second and a real-time tier of about 600,000 connections on 5 gateways, sketch an event-driven architecture on top of the Week 6 notification platform, then deep-dive into an outbox with stable order IDs, idempotent Stripe payments, race-free driver assignment, the order saga, live tracking with coalesced locations and sequenced status, rate limits and backpressure, three notification lanes with the inbox, the restaurant's socket and driver presence, and finish with 10x scaling, edge cases, alerts, and what to build first.