Yeah, solving this edge case properly can add a lot of complexity (your solution has the same problem, no? deletes would mess it up as would updates, technicall

Yeah, solving this edge case properly can add a lot of complexity (your solution has the same problem, no? deletes would mess it up as would updates, technically). I've seen people using long-lived "idempotency tokens" point to an event log for this but it's a bit nuts. Definitely worth considering not solving it, which might be a more intuitive UX anyway (e.g. for leaderboards).