Previous status note speculated about a per-subscriber forwarding ceiling.
This pins it down with file:line citations from the production version of
kixelated/moq so the upstream issue we file (or the next person to debug
this) has the exact code paths in hand:
1. Unbounded per-track group queue (moq-lite/src/model/track.rs:69-90),
evicted only by 30 s age (track.rs:29).
2. serve_group's session.open_uni().await has no timeout
(moq-lite/src/lite/publisher.rs:317-379) — blocks forever when the
subscriber's CWND collapses.
3. Publisher's FuturesUnordered task pool is unbounded
(publisher.rs:325, 346) — keeps spawning blocked tasks with no
backpressure to upstream.
4. max_concurrent_uni_streams = 10000 (moq-native/src/quinn.rs:30-33)
so the symptom is NOT the QUIC stream-id cap; it's the cascade
above.
5. No lagging-consumer RESET/STOP_SENDING anywhere; the relay never
gives up on a stuck subscriber.
The framesPerGroup=5 mitigation we shipped sidesteps the cascade by
keeping upstream rate (10 streams/sec) below the threshold any of those
gaps would accumulate at. It doesn't fix the underlying issues — those
are upstream to address.
Claude
9841e3ca2c