GOYANG, South Korea — There will be plenty to gawk at Friday when North Korean leader Kim Jong Un walks south across the world’s most heavily armed border and stands face-to-face with South Korean President Moon Jae-in. Two men who seemed on the verge of war months ago will take a pleasant walk, plant a commemorative tree, inspect an honor guard and belly-up to a lavish banquet. What’s less clear is whether the rivals can make any progress on the only thing the world really cares about: North Korea’s growing arsenal of nuclear weapons. The North likely still has work to do before it perfects the finer technological points on its long-range nukes, but there’s little question that it stands on the threshold of becoming what Kim says his nation already is: A nuclear weapons power. Friday’s summit will be the clearest sign yet of whether it’s possible to peacefully negotiate those weapons away from a country that has spent decades doggedly building its bombs despite crippling sanctions and near-constant international opprobrium. Expectations are generally low, given that past so-called breakthroughs on North Korea’s weapons have collapsed amid acrimonious charges of cheating and bad faith.