That's a great approach - definitely adding your framing to the toolbelt, thanks for that!

kind of organically landed on a similar thing, where initial task is kept pretty simple (but not covered by common libs)

Some folk solve and code this quickly, so we add a requirement. (Generally up to a few stages - think like Advent Of Code)

Any leftover time can be spent discussion wishlist items for productionising, optimising, tests, etc..

But: plenty of people only complete the first stage, but this can absolutely be a pass too (based on comms style, approach, etc..)