That's very useful! I can't decide if the architecture is more complicated or simpler because of that. It helps avoid stale data showing up in the UI, etc. It seems like you just need to store the idempotency key and the request data (in case the data changes, to catch bad requests using same key...), but not the response.

I think Amazon actually stores the response in a table for some amount of time (24 hours?), iirc https://aws.amazon.com/builders-library/making-retries-safe-... but I could be wrong.