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

Duplicate message processing is something every event-driven system eventually faces. With at-least-once delivery, retries and redeliveries are expected. The challenge is making sure processing the same message twice does not create side effects. I've been looking into the Inbox Pattern as a consumer-side solution: track processed messages keep message tracking and business changes in the same transaction scope the idempotency check per consumer One approach is using a MassTransit pipeline filte