Function updateSkillInPlace

pkg/cmd/skills/update/update.go:418–462

updateSkillInPlace installs the resolved update into a staging directory alongside the existing skill directory and, on success, atomically swaps the staged contents into place via same-filesystem renames. This guarantees: - The skill directory's own inode is preserved, so symlinks, mounts, and ext

(opts *UpdateOptions, u pendingUpdate, apiClient *api.Client, gitRoot, homeDir string)

//     skill completely untouched: existing files are first moved aside into
//     a backup directory and restored if any subsequent step fails.
func updateSkillInPlace(opts *UpdateOptions, u pendingUpdate, apiClient *api.Client, gitRoot, homeDir string) error {
	if u.local.dir == "" {
		return fmt.Errorf("cannot update %s: no install location recorded", u.local.name)
	}

	parent := filepath.Dir(u.local.dir)
	if err := os.MkdirAll(parent, 0o755); err != nil {
		return fmt.Errorf("could not ensure parent directory %s: %w", parent, err)
	}

	// Stage as a sibling of the existing skill directory so the swap stays
	// on the same filesystem and every rename is atomic.
	staging, err := os.MkdirTemp(parent, "."+u.skill.Name+".gh-skill-update-")
	if err != nil {
		return fmt.Errorf("could not create staging directory: %w", err)
	}
	defer os.RemoveAll(staging)

	installOpts := &installer.Options{
		Host:    u.local.repoHost,
		Owner:   u.local.owner,
		Repo:    u.local.repo,
		Ref:     u.resolved.Ref,
		SHA:     u.resolved.SHA,
		Skills:  []discovery.Skill{u.skill},
		Dir:     staging,
		GitRoot: gitRoot,
		HomeDir: homeDir,
		Client:  apiClient,
	}
	if _, err := installer.Install(installOpts); err != nil {
		return err
	}

	stagedSkillDir := filepath.Join(staging, u.skill.Name)
	if _, err := os.Stat(stagedSkillDir); err != nil {
		return fmt.Errorf("installer did not produce %s: %w", stagedSkillDir, err)
	}

	if err := os.MkdirAll(u.local.dir, 0o755); err != nil {
		return fmt.Errorf("could not ensure skill directory %s: %w", u.local.dir, err)
	}

	return swapDirectoryContents(u.local.dir, stagedSkillDir)
}

// swapDirectoryContents replaces the entries inside dest with the entries
// inside src, preserving dest's inode. It first moves every existing entry