Function run_stream_end 

fn run_stream_end(
    end: StreamEnd,
    st: &mut StreamState<'_>,
    side: ProxySide,
    ctx: &ForwardCtx,
    report: &Reporter<'_>,
) -> Plan

Call ProxyHook::on_stream_end and execute what it returns.

Fires only when the hook declared Interest::STREAMS. The plan is returned so the caller can honour a queued terminal (Action::ResetStream, the one non-Pass action admitted at a data stream’s end) or a session close, which is honoured at a control stream’s end too, because a close is session-scoped.