The _executePhase() method of ShardingDDLCoordinator is deceiving: it takes in a DDL Phase value and a callable object to implement the handling of such phase, but it does not actually invoke the received functor - instead, it returns a decorated version of it, and the caller of _executePhase() is then responsible to trigger the execution phase when appropriate.

This misleading name has caused some hard to diagnose issue in the past - and the problem may be fixed with a simple refactoring.