Deduplication

A dedup key decides what happens when a job's key is already queued:

-- IgnoreDuplicate: silently skip if key exists
job1 = Arb.defaultJob payload & Arb.setDedupKey (Just $ IgnoreDuplicate "order-123")

-- ReplaceDuplicate: replace the existing job and re-arm it for a fresh run
job2 = Arb.defaultJob payload & Arb.setDedupKey (Just $ ReplaceDuplicate "order-123")

Keys have queue scope. Jobs that have no key cannot cause a deduplication conflict.

ReplaceDuplicate copies each writable column from the new job: payload, priority, group key, attempt limit, admission keys, and retention. It clears the attempt count, last error, and active claim. The updated job is then ready for a new run.

Arbiter refuses replacement when the existing job is in flight, has a force-cancel flag, or has children in the queue or DLQ. For a refused replacement, insertJob returns Nothing and does not change the existing job. This return value states that the key existed. It does not state if replacement occurred.

See the Arbiter.Core.Job.Dedup haddocks for the key type.