How would you answer an interview scenario involving message ordering and idempotent consumers?

In an interview, I would first define message ordering and idempotent consumers and the problem it solves, then explain how I would partition messages by an ordering key where order matters, track processed message or business keys, make handlers safe to repeat, and design for out-of-order events when strict ordering is not guaranteed. I would also call out the main failure mode: assuming exactly-once delivery from the broker alone can lead to duplicate writes or incorrect state when a consumer crashes after committing work but before acknowledging the message. Finally, I would describe how I would test, monitor, and safely roll back or recover the solution.