[macOS] Cmd+C copy broken after alt-screen enabled by default for --experimental users (v0.0.413)

[kevindesuyo]

Describe the bug

Since v0.0.413, alt-screen mode is enabled by default for users running with the --experimental flag. This causes Cmd+C text copy to stop working on macOS because the TUI's mouse reporting captures mouse drag events, preventing the terminal emulator from performing native text selection.

Before v0.0.413, alt-screen was opt-in, and Cmd+C worked normally for copying text. After the update, there is nothing to copy because text selection is intercepted by the TUI.

The relevant changelog entry from v0.0.413:

Enable alt-screen mode by default when running with --experimental flag

v0.0.414 added Ctrl+Insert for copying selected text in alt-screen, but this is not a standard macOS shortcut — most Mac keyboards do not have an Insert key.

Steps to reproduce the behavior

1. Run copilot with --experimental flag enabled (or with experimental features turned on in config)
2. Have Copilot generate some output
3. Try to select text with the mouse and press Cmd+C to copy
4. Text selection is captured by the TUI mouse reporting — nothing gets copied to clipboard

Expected behavior

Cmd+C should copy selected text to the system clipboard, consistent with macOS conventions. Possible solutions:

• Support Cmd+C as a native copy shortcut within the alt-screen TUI (macOS)
• Use OSC 52 escape sequences to programmatically write selections to the system clipboard
• Add a config option to disable mouse reporting so native terminal selection works
• Reconsider making alt-screen the default for --experimental users, or at least document the copy behavior change

Workaround

• Hold Shift (or Option in iTerm2) while dragging to bypass mouse reporting, then Cmd+C works
• Run copilot --no-alt-screen to disable alt-screen mode
• Use Ctrl+Insert to copy (v0.0.414+, but impractical on Mac keyboards)

Affected version

v0.0.413 ~ v0.0.414 (current)

Additional context

• OS: macOS (Apple Silicon)
• Copilot CLI version: 0.0.414
• Config: experimental features enabled, staff mode enabled
• The issue affects all macOS terminal emulators (Terminal.app, iTerm2, Ghostty, Kitty, etc.) since mouse reporting is handled at the TUI level before the terminal can process selections