Comment from mickey.winters@mongodb.com:
I think instead of calling ClusterAggregate::runAggregate() and the other runAggregate directly (which aren't part of the public API), we should try using something that is in the public API. if we use CommandHelpers::runCommandDirectly then the aggregate will run as if we sent a command to the mongod directly. IIUC we should be able to call that with {"clusterAggregate": ..., pipeline: [...], ...} for sharded clusters and {"aggregate": ..., pipeline: [...], ...}. then you can just pass a bool as a parameter to noDocumentsViolatingValidator.