add_autoload
Register a new autoload in a project. autoloadPath accepts "res://..." or a project-relative path (auto-prefixed). singleton defaults true (accessible globally by name). No Godot process required. Warning: autoloads initialize in headless mode — a broken script will crash every subsequent headless op; validate before adding. Returns plain-text confirmation with the registered name, path, and singleton flag. Errors if an autoload with the same name already exists; use update_autoload to modify.