Great catch and honestly a perfect demonstration of exactly what Flostep is for.

The payment flow on the site is a simplified demo diagram. But you're absolutely right that stepping through a diagram like this is one of the best ways to catch edge cases before they become bugs, that's one of the core use cases we see.

Would love to know: is this something you'd use in PR reviews to catch issues like this early?

It’s hard to imagine someone creating these for PRs? Unless it was auto-generated, but even then it’d only be relevant for fairly large/novel PRs — and then it’s functionally the same as documentation use case.

You’d also probably need some mechanism to visually diff the flowcharts to participate in discussions/changes