This is a stop-gap solution and doesn't have to be pretty. Just for now, reject writes when:
- The collection has reshardingFields, and
- The collection is in the states:
- kMirroring, or
- kRenaming and the UUID is the original collection.
The above conditions are satisfied with the call to writesShouldRunInDistributedTransaction, which is the "blocking" state that's still named as the "distributed transaction" state.
Suggestion: for now, create a named error code "WriteRejectedForResharding" that's easy to verify in a test. In Milestone 3, a more robust solution will be designed to possibly queue writes.