UdpTransport sockets are non-blocking, so a momentarily-full kernel send buffer
makes socket.send return WouldBlock (EAGAIN). submit_frame propagated that as a
fatal error, tearing the whole punktfunk/1 session down — observed when attaching
to an already-running source (a headless Steam session) that emits frames at full
rate the instant capture connects: the first burst saturates the tx queue and the
session dies before a single frame reaches the client.
The data plane is lossy + Leopard-FEC-protected and runs infinite-GOP with RFI
keyframes, so the real-time-correct response to a full tx queue is to DROP the
packet (the next frame / FEC recovers) — exactly what the recv path already does
for WouldBlock. Blocking would queue stale frames and add latency. Loopback/M1
paths are unaffected (LoopbackTransport never blocks; M1 tests stay green).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
b6f4164454