Implement the SSH session to call protocol bridge:
- Add FrameFramedReader/FrameFramedWriter for async I/O of length-prefixed EventEnvelope frames
- SshSession::recv() reads InterfaceEvent frames from the alknet-control:0 channel via mpsc
- SshSession::send() writes EventEnvelope frames to the alknet-control:0 channel via mpsc
- Add ControlChannelBridge implementing ControlChannelHandler for routing channel data
- SshHandler::channel_open_direct_tcpip routes alknet-control:0 to the bridge task
- Session Identity attached to every InterfaceEvent produced by recv()
- ControlChannelRouter gains take_handler() for non-control alknet-* channel routing
Implement RawFramingSession with tokio::io::split for read/write halves,
BufReader/BufWriter for buffered I/O, and decode_with_remainder for
partial frame reassembly. Add first-frame authentication via
IdentityProvider::resolve_from_token(). Add RawFramingConfig.auth
field for IdentityProvider reference. Update SshInterface test for
new RawFramingConfig shape.
Per ADR-035: split Interface trait into StreamInterface (stream-based, SSH/RawFraming)
and MessageInterface (request/response, HTTP/DNS). Remove TransportKind::Dns (DNS is
a MessageInterface). Change WebTransport { host } to { server_name: Option<String> }.
Restructure ListenerConfig from flat struct to enum with Stream/Http/Dns variants.
Add doc comments and TODO markers to SshSession::recv() and send()
explicitly marking them as Phase 1 stubs. Notes that call protocol
event bridging from SSH channels is planned for Phase 2/3.
- SshInterface implements Interface trait with accept() method
- SshSession implements InterfaceSession trait (stub for call protocol events)
- RawFramingInterface is type-only stub (Phase 4+ for DNS, WebTransport)
- TransportKind consolidated into transport module with Display, PartialEq, Eq
- ListenerConfig gains interface_kind field for (Transport, Interface) pairs
- SshInterface wraps existing russh handler logic (SshHandler)
- Auth delegation through IdentityProvider (not embedded in SshInterface)
- Channel routing through session to Layer 3 (forwarding policy)
- Server accept loop uses (Transport, Interface) pairs
Per ADR-026: SSH is Layer 2, not Layer 1. This is the highest-risk Phase 1
task, implementing the Interface trait to separate transport from interface.
