Options for RealtimeBackplanePlugin, which fans WebSocket rooms and SSE channels out across replicas. Present → the plugin is registered at PLUGIN_PRIORITY.HIGH, so it precedes both consumers.

Absent → the WebSocket and SSE plugins emit their scaling notice, because their broadcast membership stays in-process.

{} selects the 'memory' transport, whose discriminant is optional. { transport: 'messaging' } requires a MessagingPlugin in the same application — the microservice and full-stack tiers supply one; on the REST tier the backplane's own register() throws naming it.