Engineering, backend APIs, full-stack apps, and applied AI.
Most POS demos assume a working connection. Real shops do not have one. The architecture that keeps a till selling through an outage — and why offline-first is an ordering decision, not a feature.
The schema decision that makes offline sync work: store append-only stock movements and derive the level, so two tills syncing in either order reach the same answer.
Writing a sale to IndexedDB, printing a receipt with no server, and an outbox that survives a browser crash mid-sale — plus why the stock number should say '~12'.
Accepting a batch that contains sales you already have, per-sale transactions so one bad record cannot poison a batch, and what to do when two tills sold the same last item.
A KHQR payment cannot be verified offline. Generating the QR locally, the pending-verification state machine, offline payment limits, and handling USD and riel in one drawer.
