Bug: Bash updater breaks/fails with symlinked ~/.copilot_here.sh

[GordonBeeming]

Summary

On macOS (at least), if ~/.copilot_here.sh is symlinked into a dotfiles repo (common setup), accepting the startup update prompt (or running --update) appears to succeed but the script content/version does not update. New terminal sessions then source the old script and continue to show the old version.

Environment

• OS: macOS
• Shell: zsh (or bash)
• Install style: ~/.copilot_here.sh symlinked to a dotfiles-managed file (e.g., ~/.copilot_here.sh -> ~/dotfiles/.copilot_here.sh)
• Update channel: cli-latest

Steps to reproduce

1. Create a symlink: ln -s ~/dotfiles/.copilot_here.sh ~/.copilot_here.sh
2. Start a new terminal that sources ~/.copilot_here.sh
3. Run copilot_here or yolo and accept the update prompt
4. Open a new terminal window

Expected behavior

• The update process updates the target file that ~/.copilot_here.sh points to (symlink is preserved).
• After update, new terminal sessions load the updated file and show the new version.

Actual behavior

• After update, the contents of the symlink target do not change (version remains old), so new terminals load the old content.
• In some cases the update may silently fail to persist the new script (leaving the old file unchanged).

Acceptance criteria

• With ~/.copilot_here.sh as a symlink, copilot_here --update updates the symlink target and does not break the symlink.
• With ~/.copilot_here.sh as a symlink, accepting the startup auto-update updates the target and a new terminal shows the new version.
• Non-symlink installs continue to work.
• Failure to persist the script produces a clear warning and does not claim success.

Notes

PowerShell update uses a content-write approach (Set-Content) already, so this bug is specific to the bash/zsh updater implementation.

[GordonBeeming]

• Bash updater should overwrite the script contents (write-through) rather than path-replacing (e.g., avoid mv tmp ~/.copilot_here.sh).