Function swapDirectoryContents

pkg/cmd/skills/update/update.go:470–508

swapDirectoryContents replaces the entries inside dest with the entries inside src, preserving dest's inode. It first moves every existing entry into a sibling backup directory, then moves the staged entries into dest. If any step fails, the original contents are restored from the backup. src and d

(dest, src string)

//
// src and dest must live on the same filesystem so renames are atomic.
func swapDirectoryContents(dest, src string) error {
	backup, err := os.MkdirTemp(filepath.Dir(dest), "."+filepath.Base(dest)+".gh-skill-backup-")
	if err != nil {
		return fmt.Errorf("could not create backup directory: %w", err)
	}

	existing, err := os.ReadDir(dest)
	if err != nil {
		_ = os.RemoveAll(backup)
		return fmt.Errorf("could not read skill directory %s: %w", dest, err)
	}
	var movedOut []string
	for _, entry := range existing {
		if err := os.Rename(filepath.Join(dest, entry.Name()), filepath.Join(backup, entry.Name())); err != nil {
			restoreBackup(dest, backup, movedOut, nil)
			return fmt.Errorf("could not move %s aside: %w", entry.Name(), err)
		}
		movedOut = append(movedOut, entry.Name())
	}

	staged, err := os.ReadDir(src)
	if err != nil {
		restoreBackup(dest, backup, movedOut, nil)
		return fmt.Errorf("could not read staged skill directory %s: %w", src, err)
	}
	var movedIn []string
	for _, entry := range staged {
		from := filepath.Join(src, entry.Name())
		to := filepath.Join(dest, entry.Name())
		if err := os.Rename(from, to); err != nil {
			restoreBackup(dest, backup, movedOut, movedIn)
			return fmt.Errorf("could not move %s into place: %w", entry.Name(), err)
		}
		movedIn = append(movedIn, entry.Name())
	}

	_ = os.RemoveAll(backup)
	return nil
}

// restoreBackup undoes a partial swap by removing any freshly installed
// entries and moving the original entries back from backup into dest.