How would you answer an interview scenario involving API idempotency?

In an interview, I would first define API idempotency and the problem it solves, then explain how I would use idempotency keys for suitable commands, persist the original outcome, define key scope and lifetime, and make downstream effects consistent with the same logical request. I would also call out the main failure mode: blindly retrying non-idempotent POST operations can create duplicate charges, orders, or messages even when the first request actually succeeded. Finally, I would describe how I would test, monitor, and safely roll back or recover the solution.