It would be nice to remove any mention of "migration" from TenantMigrationAccessBlocker method names.

For example:

• TenantMigrationAccessBlockerRegistry => TenantAccessBlockerRegistry
• getTenantMigrationAccessBlockerForDbName => getAccessBlockerForDbName
• getTenantMigrationAccessBlockerForTenantId => getAccessBlockerForTenantId

There's also a question about consistency of method names on this class. get is a global helper which returns the decorated value on a serviceContext, so we can't use that name to also return access blockers. On the other hand, we have add/remove/removeAll which don't reference access blockers. We should choose one of these names and make them consistent:

• addAccessBlockerForTenant
• addAccessBlockerForTenants
• addGlobalAccessBlocker
• getAccessBlockerForTenant
• removeAccessBlocker
  etc

Finally, we should investigate replacing DonorRecipientAccessBlockerPair with something simpler like:

using DonorRecipientAccessBlockerPair = std::pair<std::shared_ptr, std::shared_ptr>;