Features
How the rules become a working product
Where State machines answers "what are the rules", this section answers "how is it actually built".
Buying and paying
Checkout pipeline — what runs before the money moves, and the invariant that keeps a charge from ever outrunning a guard. Payments, anti-fraud & saved cards — how a charge is scored, how a card is saved, where installments are decided.
Getting paid
Payout lifecycle — from a paid order to money in the seller's bank, and every guard on the way.
Photos
Image upload architecture — upload, analysis, attachment, and delivery through Cloudflare.
Running it
Observability — Sentry and structured logging, and what still works without them.