Backend returns an instance of the backend, either as a plugin if external or as a concrete implementation if builtin, casted as logical.Backend.
Factory returns a configured plugin logical.Backend.
PluginBackend is a thin wrapper around plugin.BackendPluginClient
HandleExistenceCheck is a thin wrapper implementation of HandleExistenceCheck that includes automatic plugin reload.
HandleRequest is a thin wrapper implementation of HandleRequest that includes automatic plugin reload.
Initialize is intentionally a no-op here, the backend will instead be initialized when it is lazily loaded.