And then how does public wifi work? Stand outside a Weatherspoons, or just walk down a highstreet with free internet, back to square one

seems dead simple to me: if you host public wifi, you are responsible for the people that use it. easy!

just like you already are responsible for what happens on your free public network (torrenting, hacking, CSAM, etc.) in most jurisdictions

(for what its worth, i think age verification is dumb. but it looks like we're getting it one way or the other)