Data flow

This logic applies for both station view and single train view. Directly mutating the cache is not ideal, but works really well, because it can adapt to different types of queries (e.g. filtered trains) There have been some instances of the MQTT client not connecting (especially on Safari), so it should be treated as a progressive enhancement rather than a moving piece of the machine. The single point of failure is the trains query, which is acceptable, because without Digitraffic data the service is not expected to work. Stations are CacheFirst for 15 days (service worker) so the metadata endpoint not working is not a comparable concern.