Kacey Musgraves’s third taping for Austin City Limits, which took place in June for an episode that will be the show’s fiftieth-season premiere when it airs Saturday, was a looser affair than most, despite the Golden, Texas, native complaining about the difficulty of sitting down in her restrictive, sequined minidress. Though her episode is one of the few to feature a single artist for the show’s full hour, Musgraves and her band took more than two hours to get through their set, retaking songs, retuning guitars, and generally revealing, as the singer put it at one point, “how the sausage gets made.”From another artist, the process might have come off as sloppy. But from Musgraves, especially at this point in her career, it played less…