As of SERVER-35707, if any batch write encounters a stale shard version error, the router can only continue the transaction if this was the first overall statement received from the client. This is to avoid double applying writes because currently batch writes in a transaction must be entirely retried, unlike outside of a transaction where only the individual writes that failed will be retried. This ticket is to track changing batch write behavior in a transaction to only retry the failed writes to avoid aborting more than necessary in the face of migrations.