Stone.js API
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    realtimeClientBlueprint: RealtimeClientBlueprint = ...

    Opt-in blueprint for the frontend: register it to enable the isomorphic realtime client.

    It contributes the RealtimeClientServiceProvider, which binds realtime to a RealtimeClient built from stone.realtime.url. stone.providers is an array, so this merges with the rest of the app configuration.