Add a Python stress test for the async step-down. One thread walks the connection through every phase of the transition: setting the step-down timestamp, advancing stable to it, taking the final leader checkpoint, and demoting to a follower. A workload thread hammers layered table creates, drops, timestamped inserts and removes, and verifying reads the whole way through, with varied transaction shapes so operations land on every phase boundary in flight.

The workload records its own ground truth and tolerates only the errors the transition is allowed to inflict, checking the reason of each. The step-down checkpoint is verified from a fresh follower before the node steps back up, and after a step-up every surviving table must serve its exact contents, both current and at the step-down timestamp, to the leader and to a fresh follower. The test runs in both the schema-epoch and the epoch-less world, and scales up under the long-test flag.