In SERVER-92385, we made the ReplicaSetFixture wait until the keys for signing $clusterTime had landed in the db. However, there is still a lag between the keys appearing in the db and the keys getting picked up by the KeyCollectionCaches on each node in the replica set, and so the ReplicaSetFixture may still violate causal consistency guarantees if the keys do not appear in the cache in time.

Make the ReplicaSetFixture wait for the $operationTime field to show up in a command response to ensure that nodes are ready to sign.