There is currently no way to get the path to the resources you bundled using bundled_resources without using native code (see DefOS’s defos.get_bundle_root()). Sometimes this is the same as the current working directory (Linux and Windows if you double-click the executable), but it’s not always true (if the game is started from the terminal, or in case of macOS and iOS, apps start with their cwd set to / by default).
I think this should part of the engine because without it, another engine feature (bundled_resources) is really hard to use.