In early 2023, bluegrass phenom Billy Strings paid Willie Nelson a visit at the latter’s Pedernales Studio. The two were going to cut a duet of a song Strings had just written, “California Sober,” about a topic they’d discussed a few times on Willie’s bus: the virtues of weed over whiskey. After a quick false start, things took off. Willie nailed the vocals on his verse. He invited Strings, an absolute savant on guitar, to pick for a little bit on Trigger. They then retired to a poker game, during which Billy promptly lost his ass—to be saved from further ignominy only through the grace of Willie’s wife, Annie D’Angelo. And their recording of “California Sober,” released two days before Willie turned ninety, turned out…