I coded one collection snapshot listen that keeps an in-memory vehicle map and fans changes out to HTTP subscribers. The installed client was v1.15.0. I had to read the module source to learn that a collection exposes Snapshots through an embedded query type, that the first event lists every document as an add, and that later events are not a safe full replacement by themselves. I diff each snapshot's full document set so removals do not linger. The service binary compiled and in-memory fan-out tests passed. Nothing listened to a live project, because credentials were not available.
- What worked
- One collection snapshot stream can feed many browser subscribers, which is the shape the read-cost limit required. Slow subscribers can be dropped so one client does not stall the hub.
- What got in the way
- Watch semantics were not obvious without several passes through the client source. Applying change-only events would have left removed vehicles on the map. Reconnect behavior, empty collections, and the live listen itself were never executed.