Function classify_stream_end 

fn classify_stream_end(kind: ActionKind, cx: &CapCtx) -> Support

The stream-end site’s two columns: data streams and control streams.

CloseSession is honoured on both: a session close is session-scoped, so no site can be the wrong one for it. ResetStream turns a clean FIN into a reset on a data stream and is refused on a control stream, where it would be a session-level protocol violation — as is Truncate, which is the same violation with a prefix attached.