If the coordinator finishes transitioning to done before stepdown, the completion promise will be fulfilled with Status::OK instead of InterruptedDueToReplStateChange and cause this assert to fail.

kDone is different than the other state transitions since the coordinator doesn't actually persist its state of kDone to the ReshardingCoordinatorDocument on disk. Instead, if the in-memory state indicates kDone, the coordinator deletes the document altogether. 

Potential fix: remove kDone from the state guarded transitions and potentially add a new test case with an alternative approach if we want the test coverage.