feat: record existing terminal session

[dwmkerr]

Summary

Allow shellwright to attach to and record an existing terminal session, rather than spawning a new one.

Use Case

Currently shellwright spawns processes via shell_start. But often you're already running something (claude code, vim, htop) and want to start recording mid-session. This feature would let you attach shellwright to an existing PTY and capture what's happening.

Proposed Approach

New tool: shell_attach or shell_record_external

Options:

1. Attach by PID - attach to an existing process's PTY
2. Attach by TTY - attach to a specific TTY device (e.g., /dev/ttys001)
3. Pipe mode - shellwright reads from stdin, useful with script or tmux

Example Usage

{
  "tty": "/dev/ttys001",
  "cols": 80,
  "rows": 24
}

Or integration with tmux capture-pane / script command.

Technical Considerations

• Reading from existing PTY requires appropriate permissions
• May need to poll/capture the terminal buffer periodically
• Could leverage tmux or screen for easier capture
• Alternative: provide a CLI mode where shellwright wraps an existing command

Alternative: Wrapper Mode

shellwright wrap -- claude

This would be simpler - shellwright spawns the process but the user interacts with it directly in their terminal, while shellwright records in the background.