11 min read
Every Payment Has a Liability Owner
EMV authorization is the easy part. The hard problems are timeouts, retries, SoftPOS lifecycle gaps, store-and-forward declines, and the financial question that remains when two …
3 pages
Idempotency
11 min read
The €400 Wallet Problem: Concurrency, Lost Updates, and Where to Serialize
Two POS terminals charging the same benefit wallet at the same instant expose the classic lost-update problem. Four serialization strategies — pessimistic locks, optimistic …
8 min read
Double Charges: The Hardest Problem in Payments Is Remembering You Already Did
A duplicate charge is rarely a coding bug. It is a distributed system losing certainty about whether an authorization already happened — and then guessing wrong. Why blind retries …