The thread installs the Montreal Protocol as a coupled machine — listed chemicals, air measurements that can catch cheating, substitute technology paid through the Multilateral Fund, and Article 4 trade bans — rather than as a morality play about cooperation. The unresolved question is which of those three was load-bearing, and therefore which repair a climate treaty would have to copy. Scott Barrett's club model says the trade bans; the substitute model says drop-in chemicals a handful of firms could already make; the measurement model says a target you can see in flasks and satellite maps. Those are not substitutes. Kigali copied the same three onto HFCs, which do not deplete ozone. If HFC production and consumption fall on that schedule, the coupling travels. If they do not, Montreal converted because the original problem was easy, and the climate comparison was always a category error.