SERVER-122099 implemented an infrastructure to mark the phases that are holding the critical section and in those phases the OperationContexts created by the DDL coordinator are marked as non-deprioritizable.
From the client side it's done via implementing the RecoverableTypedDocMixin::isInCriticalSection virtual function.
The task here is to

• mark the RecoverableTypedDocMixin::isInCriticalSection pure virtual
• implement the function in every coordinator by checking which phase holds the critical section