Function find_scene_pck_path_for_append 

pub fn find_scene_pck_path_for_append(
    project_dir: &Path,
    append_dir: &str,
) -> Result<PathBuf>

Resolve the one active Scene.pck used by the original lexer.

The C++ path is Gp_dir->exe_dir + "\\" + Gp_dir->append_dir + "\\Scene.pck"; it does not scan later append entries when a scene name is missing. Keeping the active append explicit is important because save/load and return-to-menu can legitimately switch Scene.pck.