Function offered_gestures 

fn offered_gestures(
    interaction: &Interaction,
    authoring: Authoring,
) -> Interaction

The interaction a frame hands its tool. A read-only session keeps the pointer — selecting and navigating are free — but loses the two channels that exist only to author: the held press every add-affordance arms from (the new-pin markers, the route-start targets) and the Delete key. Taken away here rather than in each of the tools that read them, so a new tool cannot forget.