Parameterized stateful property-based tests for the core job engine, using hedgehog. Works against any MonadArbiter backend via a passed runner and a raw-connection accessor.

Generates random sequences of engine operations against the real database (insert at varying priority, scheduled insert, claim, ack, cancel, suspend, resume, promote, retry, extend-lease, move-to-DLQ, retry-from-DLQ, batch insertcancelDLQ, dedup insert, and the reaper) and checks the core invariants after every step:

• at most one in-flight job per group (the serialization guarantee)
• no job exceeds its max_attempts
• no duplicate live dedup_key
• no concurrency key has more claimed-in-flight jobs than its effective cap
• every group summary column matches its recompute from the main table

Generated inserts also carry rate-limit keys and concurrency slots.

A second property (prop_concurrent) generates N independent branches of self-contained actions, runs them concurrently under a gap-free serialization detector (a row trigger that fires inside every claim), then quiesces with a reaper tick and asserts both the detector log and the full settled oracle are clean. All contention is in the generated, shrinkable model. Deterministic guards back the known-critical races.