Function connection_lost 

fn connection_lost(e: ConnectionError) -> TransportError

A lost connection, keeping the peer’s close code where it named one.

Both stream error enums render ConnectionLost as the two words “connection lost” and drop the cause, so a session a relay ended deliberately — with a MoQT error code, and often a reason phrase saying why — reaches a caller as a sentence carrying neither. This reads them off the value instead.

Only ApplicationClosed carries an application code. A timeout, a stateless reset or a local close have genuinely no such number, and those keep quinn’s own message.