Fixing a silent race condition in a no-code checkout

The challenge

A no-code e-commerce shop was losing orders under load. Checkout would occasionally drop an order with no error and no trace — revenue vanishing with nothing to point to.

The context

The platform was assembled from no-code building blocks with no automated tests. The failure only appeared under concurrent checkouts, which made it nearly impossible to catch by hand.

What we did

• Reproduced the failure by simulating concurrent checkouts until the race surfaced.
• Traced it to an unguarded step that could run twice and drop the order.
• Fixed the sequencing and made the step idempotent so a retry can't lose data.
• Added an end-to-end regression test that gates checkout on every change.

The outcome

The race is fixed and can't come back unnoticed — a regression test now runs on every change and blocks a checkout that would drop orders.