Scrap

Plain-words records of problems and the answers that finally landed. For finding later, and for pasting back into a session that has lost the thread. Newest first.

2026-10-23 · The till's two separate problems

The original problem. At the register, Salvo shows a gift card barcode and the cashier scans it. A barcode is a photo: the scanner sends nothing back. So Salvo cannot see whether a scan worked, and a buyer can scan, get the goods, tap "it didn't scan", and be refunded while the seller eats the card. At a store whose balance we can read, the read settles it. At a store we cannot read (Target needs a login and a fresh sign-in at the click; some long-tail stores have no page at all), nothing settles it.

Two problems that got conflated.

1. Routing input: what is the total? Today the shopper types it. A tap of a card we issue, approved for one cent, makes the terminal tell us the total. Then the gift cards cover the rest exactly, no typing, no leftover remainder. One tap. It proves nothing about the scans.
2. Proof: did the gift cards pay? A tap of our card last, for the few cents the gift cards were deliberately not asked to cover, carries the amount "total minus what the gift cards paid". That proves the scans at every store. One tap. The total is still typed.

Both at once is two taps, one at each end. Per lane the choice is: typing vs proof vs two taps.

Jordan's summary (verbatim, 2026-10-23): "for balance reads which you said is most, we can deplete the card, if no balance reads, we need scraper setup, no deplete and empty with credit line with a little bit left, and/or some reputation."

Read as:

• Store with a balance read: gift cards cover 100% of the total (deplete the card). The read after a claim is the proof. No remainder, no last tap.
• Store with a public balance page but no reader yet: build the scraper adapter; then it is the case above. Scraping is how balance reads are done.
• Store with no balance page at all: do not deplete. Leave a little for the last tap, paid from the shopper's credit line on the card we issue. That tap is the proof. Reputation on top, as a floor, never the mechanism.

What this means for the lanes. Quick lane with tap-first only (no typing, one big card, no remainder) is the smoothest flow and leaves the fraud problem exactly where it was. Use it only where a balance read exists.

Related: the roadmap's headline open problem, How fast the till is, Reading balances.