sequence-checking

Preventing out-of-order event processing requires an inline sequence validation guard that returns false for detected gaps, forcing the handler to abandon the message until the missing events arrive and are processed in sequence.

The best way to add idempotency to event sourcing handlers is using an inline guard pattern that checks existence for creation handlers and validates the integer sequence for update handlers to complete or abandon service bus messages reliably.

Service bus listeners retry out-of-order messages and risk data corruption when missing an inline sequence guard to abandon gaps and complete duplicates, which ensures the entity behavior updates the sequence only after successful processing.

You do not need an external helper class to validate event sequences, because the inline sequence guard pattern performs a single in-handler check that directly evaluates the integer sequence and manages duplicates and gaps.

You can use inline sequence validation for both handler types, where creation handlers use existence checks and update handlers apply the sequence guard, requiring the entity behavior to update the sequence after successful processing.