With SPM-4048, a snapshot of the FCV will be taken during coordinator instantiation when the snapshotFCVInDDLCoordinators feature flag is enabled. This snapshot will be used for all checks of FCV gated feature flags during the DDL operation. To ensure that the on-disk FCV cannot change while the coordinator is being spawned, the ShardingDDLCoordiantorService::getOrCreateInstance() method always takes a FIxedFCVRegion as a parameter.

In some cases FCV gated feature flags must be checked already in the DDL entry point, prior to coordinator instantiation (example). Moreover, DDL implementors must make sure that the acquired FixedFCVRegion is manually released after creating the coordinator. All of this adds additional complexity, which might lead to subtle bugs if not done correctly. Therefore, we should explore ways to ensure that the FixedFCVRegion is acquired and released implicitly.