Great read and interesting implementation. I'm hoping for more like this from Alex in the future.
Unclear what makes this an atproto relay and not a websocket relay.
The only ATproto-specific part is how clients specify their starting position. They give a timestamp, which refers specifically to the `time_us` field in the messages, which I guess must be an ATproto thing. If jetrelay supported filtering, that would be ATproto-specific too. But you’re right: if you removed backfill support there’d be nothing ATproto- or even websocket-specific about it.
Bluesky's project name is 'Jetstream' and NATS.io persistence engine is `JetStream` (camel case), which can be confusing but name not exactly the same.