In SERVER-94144 we caught one edge case which had a somewhat accidental change in validation rules. We added some test coverage as part of that quick fix but we want to add more, allowing more time for a careful audit.

This ticket tracks the work to (a) enumerate interesting combinations of valid and invalid operators (e.g. $currentOp within a $unionWith, or $changeStream within a $lookup, etc.), (b) perform an audit to see how well covered each is, and (c) author new test cases to cover the difference, and possibly re-organize.