CLI backend selection and PTY session management commands

[geoffjay]

Context

Part of #671 (PTY execution backend epic). Blocked by: #673 (PtyBackend implementation).

Update the CLI to support the new PTY backend and expose PTY-specific session management capabilities.

Problem

The CLI's wrap commands currently assume tmux sessions. With three backends (tmux, docker, pty), the CLI needs:

1. A way to specify or detect which backend is active
2. PTY-specific features (attach to session for interactive use)
3. Consistent behavior across backends

Changes

1. Backend-Aware Session Commands

The existing agent wrap commands should work transparently across backends. The CLI already communicates with the wrap/orchestrator service via REST, so most commands need no changes. However, new capabilities should be exposed:

# Existing commands (work unchanged)
agent wrap list
agent wrap kill <session>
agent wrap launch --agent-type claude-code ...
agent wrap health

# New: show backend info
agent wrap info                    # Shows active backend type, version, capabilities

# New: attach to PTY session (PTY backend only)
agent wrap attach <session>        # Opens interactive terminal to PTY session

2. Backend Configuration

# Environment variable (already exists for orchestrator)
AGENTD_BACKEND=pty   # or tmux (default), docker

# CLI flag override for wrap service
agent wrap launch --backend pty ...

3. Session Info Enhancement

The agent wrap list output should indicate the backend type and session capabilities:

NAME                    BACKEND  STATUS   CAPABILITIES
agentd-orch-abc123      pty      running  terminal,interactive
agentd-orch-def456      tmux     running  attach-tmux
agentd-orch-ghi789      docker   running  health-check,logs

4. PTY Attach Command

For PTY backend sessions, the attach command opens an interactive terminal:

• Connects to the orchestrator's /terminal/{agent_id} WebSocket endpoint
• Uses crossterm for raw terminal mode in the CLI
• Forwards all input/output between the local terminal and remote PTY
• Ctrl-D or special key sequence to detach

Implementation Steps

1. Add info subcommand to WrapCommand enum in crates/cli/src/commands/wrap.rs
2. Add attach subcommand with session name argument
3. Implement attach using crossterm raw mode + WebSocket client to /terminal/{agent_id}
4. Add --backend flag to launch subcommand
5. Update list output to include backend type
6. Add crossterm dependency to CLI crate

Relevant Files

• crates/cli/src/commands/wrap.rs — wrap subcommands
• crates/cli/src/commands/mod.rs — command registration
• crates/cli/Cargo.toml — dependencies
• crates/common/src/client.rs — service client base

Acceptance Criteria

• agent wrap info shows active backend type and capabilities
• agent wrap attach <session> opens interactive terminal for PTY sessions
• agent wrap attach returns clear error for non-PTY backends
• agent wrap list shows backend type per session
• Attach uses raw terminal mode, forwards I/O correctly
• Ctrl-D or escape sequence cleanly detaches
• Existing commands work unchanged for tmux/docker backends

Caution

All work for this issue must branch from feature/autonomous-pipeline and PR back into it — never directly to main.

[geoffjay]

Implemented in PR #766. All acceptance criteria met:

• agent wrap info shows active backend type and capabilities
• agent wrap attach <session> opens interactive PTY terminal (crossterm raw mode + WebSocket relay)
• Attach returns clear error for non-PTY backends
• agent wrap list shows BACKEND and CAPABILITIES columns
• agent wrap launch --backend pty forwards backend hint to service
• Ctrl-D cleanly detaches; initial terminal size sent on connect
• Existing tmux/docker commands work unchanged