When a relay opens a SUBSCRIBE bidi for a track this session doesn't
publish (e.g. a watcher subscribes to `video/data` against a broadcast
that only declares `audio/data` + `catalog.json`), the session was
silently FINing the bidi without writing any reply. The peer's wait
on its receive side resolves to end-of-stream with no indication WHY —
indistinguishable from "publisher disappeared mid-subscribe."
Reply with [MoqLiteSubscribeDrop] carrying
[MoqLiteSubscribeDropCode.TRACK_DOES_NOT_EXIST] (0x04, mirroring the
IETF-MoQ `ErrorCode.TRACK_DOES_NOT_EXIST` convention) and an
informational reason phrase listing the tracks we DO publish, then
FIN. Matches what kixelated's `rs/moq-lite/src/lite/subscribe.rs`
expects on this path.
Doesn't change the happy path — every track NestsUI-v2 subscribes to
(`audio/data` + `catalog.json`) is now published — but is the
spec-correct behaviour for any future watcher that prospectively
subscribes to a track our publisher hasn't declared.
https://claude.ai/code/session_014JfZJHSTvyYYWJbC9VbB47
Claude
79c76d5831