Describe the feature or problem you'd like to solve

When crafting complex, multi-line prompts in Copilot CLI, the built-in line editing (Ctrl+a/e/w/u/) (Alt+f/b) is limited compared to a full text editor. In zsh edit-command-line (bound to Ctrl+X Ctrl+E) which opens the current command buffer in $EDITOR for more powerful editing.

Proposed solution

Proposed Solution:

Add a keybinding (e.g., Ctrl+x Ctrl+e, Ctrl+x+e) or (Ctrl+g - similar to claude code keybind) that:

 - Opens the current input buffer in the user's $EDITOR (or $VISUAL)
 - Allows full editor capabilities (syntax highlighting, multi-cursor, etc.)
 - On save and exit, replaces the input buffer with the edited content
 - On exit without save, leaves the buffer unchanged

Implementation Notes:

 - Respect $EDITOR then $VISUAL environment variables
 - Fallback to sensible defaults (nano/vi/vim)
 - Use temporary file, clean up after editing
 - Similar to how git commit opens editor for commit messages

Example prompts or workflows

On using copilot cli, there are several instances where I have copied a markdown file/code snippet that is fairly long from a read only file/website that I want to edit inline to fit my context. On this case, I would open up vim, edit it then either save it and make copilot refer to it OR I will yank it then put it on the cli text prompt.

For a specific instance, I am working on two projects (a migration) where the old project has features written in markdown. I normally would, open a new scratch buffer, make some necessary edits (with help of copilot-cli in vim it makes editing much easier!) then copy it and put it on the cli prompt.

Additional context

Benefits:

• Edit long prompts with familiar editor tools (Vim, Neovim, VSCode, etc.)
• Better support for complex multi-paragraph requests
• Leverage editor features: search/replace, macros, snippets
• Improves UX for users with extensive editor configurations