alknet/tasks/client/channel-manager.md

id, name, status, depends_on, scope, risk, impact, level

id	name	status	depends_on	scope	risk	impact	level
client/channel-manager	Implement ChannelManager — SSH session management, channel opens, reconnection	done	auth/client-auth-handler transport/trait-and-types auth/error-types	moderate	high	component	implementation

Description

Implement the ChannelManager that owns the Arc<client::Handle<ClientHandler>> and provides the core client methods:

• open_direct_tcpip(host, port) — open a tunnel channel to a remote host
• open_streamlocal(socket_path) — open a tunnel to a Unix socket (stub for now)
• request_tcpip_forward(addr, port) — request remote listening
• cancel_tcpip_forward(addr, port) — cancel remote listening

Most importantly, the channel manager handles reconnection on transport failure:

1. Detect via handle.is_closed() or transport read error
2. Exponential backoff reconnect (1s, 2s, 4s, ... max 30s)
3. Re-establish transport connection (call transport.connect() again)
4. Re-authenticate SSH session
5. Notify SOCKS5 server and port forwards (in-flight connections fail, new connections work)

Reconnection is always enabled. The backoff caps at 30 seconds and continues indefinitely.

Acceptance Criteria

• crates/alknet-core/src/client/channel_manager.rs exports ChannelManager
• ChannelManager holds: Arc<Transport>, Arc<ClientAuthConfig>, Arc<client::Handle<ClientHandler>> (behind RwLock for reconnection)
• ChannelManager::new() establishes initial transport connection, authenticates, returns manager
• open_direct_tcpip(host, port) — opens SSH channel to target
• request_tcpip_forward(addr, port) — sends tcpip_forward request
• cancel_tcpip_forward(addr, port) — sends cancel_tcpip_forward request
• Reconnection detection: monitors handle.is_closed(), triggers reconnect on failure
• Exponential backoff: 1s, 2s, 4s, 8s, 16s, 30s (cap), continues indefinitely
• Full reconnect: new transport stream, new SSH session over it (ADR-004)
• After reconnect: port forward listeners (-L, -R) re-registered with new session
• In-flight connections on old session fail gracefully (channel errors, not session-wide)
• Unit tests: channel open, reconnection trigger, backoff timing, forward re-registration

References

• docs/architecture/client.md — Channel Manager section, Reconnection section
• docs/architecture/decisions/004-ssh-over-transport.md — full reconnect, not "SSH reconnects over same transport"

Notes

• Converted client.rs (single file) to directory module: client/mod.rs + client/channel_manager.rs
• Used russh::keys::PrivateKey and russh::keys::PublicKey (not the nonexistent russh::key::KeyPair)
• Reconnection monitor runs as a spawned tokio task that polls handle.is_closed() every 1s
• On reconnect: creates new transport stream + new SSH session (ADR-004 full reconnect)
• ForwardRequest struct tracks registered port forwards for re-registration after reconnect
• In-flight channels on old session naturally fail with ChannelError::ChannelClosed since the handle is replaced

Summary

Implemented ChannelManager in crates/alknet-core/src/client/channel_manager.rs with SSH session management, channel opens (open_direct_tcpip), port forward requests (request_tcpip_forward/cancel_tcpip_forward), and automatic reconnection with exponential backoff (1s→30s cap). Full reconnect per ADR-004 creates new transport stream + new SSH session. Port forwards are re-registered after successful reconnect. 8 unit tests covering backoff timing, forward tracking, transport failure, and reconnection detection.