Add a /copy command to copy the latest assistant response to the clipboard

[Xander-299]

Motivation

Currently, users need to manually select assistant response text with the mouse and use terminal clipboard shortcuts to copy it.

Tools like OpenAI Codex CLI provide a convenient /copy command, allowing users to copy the latest assistant response directly.

Adding this feature would improve the user experience, especially when copying code snippets, technical explanations, and long responses.

Proposed Solution

Introduce a built-in /copy slash command.

• /copy — Copy the latest assistant response to the system clipboard.
• Copy plain response content without TUI decorations, timestamps, or status information.
• Preserve Markdown formatting, code blocks, and line breaks.
• Display a success or failure notification.
• Handle cases where no assistant response is available.

Implementation Considerations

• Reuse the existing conversation transcript as the source of truth.
• Reuse existing clipboard functionality where possible.
• Support macOS, Linux (Wayland/X11), and Windows.
• Avoid introducing unnecessary dependencies.

Scope

The initial implementation should focus on /copy without arguments.

Additional options, such as /copy 2 (copy the second-to-last assistant response) or /copy all (copy the entire conversation), can be considered in future improvements.

Expected Behavior

/copy

✓ Latest assistant response copied!

Acceptance Criteria

1. /copy copies the latest assistant response.
2. Markdown formatting and code blocks are preserved.
3. TUI decorations and unrelated tool output are excluded.
4. Clipboard errors are handled gracefully.
5. Existing commands and keyboard shortcuts remain unaffected.
6. Appropriate tests are added.