Blog
Notes from the build
Write-ups from my projects.
Killing it on purpose
How Invariant's crash tests stop the app at an exact line of a money transaction without any fault-injection code, and what they found.A LIMIT that overwrote a payment
Prisma's limit option on updateMany looks like a batch size. Under concurrency it let the expiry worker mark a just-paid payment as expired, and two database constraints are the only reason it didn't stick.Two workers, one order
FluxBuy oversold stock because two background workers could both decide what happened to the same order. The fix was a status that means "someone is on this".Two profit figures
A QA pass on a construction firm's finance dashboard found one project with two different profit numbers. The cause was a formula that existed twice.Interest without a cron job
CoinQuest teaches kids investing with pretend markets that grow every day. None of it runs on a schedule: each balance is worked out from two numbers whenever someone looks.Catching a stolen token
How RedAuth notices that a refresh token has been copied, and why it signs the user out of every device when it does.Fabric on a 3D jacket
Corlee's product pages wrap the fabric a buyer is looking at around a 3D shirt, jacket or pair of trousers. The whole effect is a photograph used as a repeating texture, and most of the work was in the numbers.