Today we start a shard split operation with either a kUninitialized or kAborted state written to the durable state document, which can be problematic because a stepdown between initial state document insertion and transition to the first state (kBlocking) will result in trying to re-insert the state document when a secondary steps up. We should never write kUninitialized to disk, and instead make transition to kBlocking the first write (if not aborted).