[LoSboccacc]

but, when one starts talking about idempotence and retries the first thing that comes to mind is these are just user mediated two phases commits, where an error dialog and user interaction drive the phases instead of a distributed transaction system, by which point one can just cut the middleman and build the thing out of tested and robust components

[mooted1]

What middleman do you want to cut out? My proposal doesn't add any dependencies. It's also not possible to prevent duplicate charges if a user POSTs a form twice without idempotency keys, so idempotency is necessary.

I'm really not sure what you're actually proposing?

[LoSboccacc]

the user doing the retries