Function process_pending_assign_material 

pub fn process_pending_assign_material(
    project_vfs: Option<&Arc<Mutex<ProjectVfs>>>,
    world: &mut GameWorld,
    editor_state: &Arc<Mutex<EditorState>>,
)

Drains [EditorState::pending_assign_material]: sets MaterialRef::Asset(uuid) on every selected entity, where uuid is derived from the chosen .kmat’s forward-slash relative path.