fix(minimald): plumb errors for spawning/attaching to session shells - #383

Walkthrough

Threads attach errors through the session actor by introducing a public AttachError, returning Result from SessionHandle::attach and Session::attach, minting hosts with Result propagation, and having the connection handler report attach failures to SSH channels and close them.

Changes

SSH Channel Attach Error Handling

Sequence Diagram(s)

sequenceDiagram
  participant SSHClient
  participant ConnectionHandler
  participant SessionHandle
  participant SessionActor
  participant SessionHost
  SSHClient->>ConnectionHandler: open channel and shell request
  ConnectionHandler->>SessionHandle: attach(channel, config)
  SessionHandle->>SessionActor: send SessionMessage::Attach with oneshot
  SessionActor->>SessionHost: attempt attach with WinSize
  alt attach succeeds
    SessionHost-->>SessionActor: Ok
    SessionActor-->>SessionHandle: Ok
    SessionHandle-->>ConnectionHandler: Ok
  else attach fails
    SessionHost-->>SessionActor: Err(AttachError)
    SessionActor-->>SessionHandle: Err(AttachError)
    SessionHandle-->>ConnectionHandler: Err(AttachError)
    ConnectionHandler-->>SSHClient: write error to channel and close channel
  end

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• gominimal/minimal#375: Related work on the attach flow and earlier attachable-session scaffolding.
• gominimal/minimal#281: Related changes routing SSH channels into sessions for exec/shell handling.

Suggested reviewers

• 0chroma
• evanspearman
• norrietaylor

Poem

🐰 A rabbit hops through async lanes,
Threads of Result in tidy chains,
Where AttachError speaks its name,
Channels close and logs reclaim,
Hops done — the session stays humane.

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