Channel 0 is not a special control plane with its own framing. It is
simply the alknet/call ALPN, pre-negotiated so both sides route it to
the CallAdapter without an explicit channel/open exchange. Every channel
works the same way: reassemble chunks into a stream, look up the ALPN
in the HandlerRegistry, hand off to the handler. Channel open is
bidirectional — either side can initiate.
Generalizes TTY's chunk format into a universal channel multiplexer
(alknet-channels) that serves as a transparent proxy between the call
protocol (control plane) and data-plane protocols (TTY, SSH, tunnels).
Key design: 9-byte chunk header (channel_id + stream_type + length),
ChannelConnection implementing the existing Connection interface, and
ACL inherited from the call protocol's OperationContext.
deepseek-v4-pro