NoopRequestIdExistenceChecker

The existence checker of a node that has no event store, such as a gateway-only service.

It answers "absent": such a node cannot know, and the authoritative check runs where the command is processed, against the event store, before the command handler runs (DefaultCommandHandler), with the event store's unique request ID as the last guard at append. Since 9.3.0; it used to answer "exists", so a Bloom-filter false positive on a gateway-only service rejected a legitimate command, and a resent command was rejected on the gateway only.