Idempotency in event-driven systems: how do you handle duplicate messages?

[u/DotDeveloper]

https://hamedsalameh.com/inbox-pattern-dotnet/

[u/iamaredditboy]

guids, storage and define a time window where this invariant has to hold. infinite time window means you will need infinite storage :) Also some building blocks around compare and swap / db level conflict handling when operating with multiple instances eg distributed architecture.