Function pipe_control_mutating 

async fn pipe_control_mutating(
    recv: PeekedRecv,
    send: SendStream,
    side: ProxySide,
    key: StreamKey,
    requests: Receiver<StreamCommand>,
    ctx: &ForwardCtx,
) -> Result<(), ProxyError>

Parse-then-forward control stream pipe.

Bytes are withheld until a complete control message has been parsed, at which point the hook’s on_control_message is consulted and the Action it returns is executed — forwarded verbatim, replaced, dropped, or deferred behind the stream’s queue. This adds a per-frame latency cost; a hook that only observes should leave interest() without Interest::CONTROL and take the pass-through path instead.