Annie Clark, known as St. Vincent, launched her career as a guitar virtuoso—a real shredder—in indie rock, playing alongside artists like Sufjan Stevens. As a bandleader, she’s moved away from the explosive solos, telling David Remnick, “There’s a certain amount of guitar playing that is about pride, that isn’t about the song. . . . I’m not that interested in guitar being a means of poorly covered-up pride.” Her songs are dense, challenging, and not always easy, but catchy and seductive. Remnick caught up with Clark before the launch of her new album, “MASSEDUCTION.”  They talked about the clarity of purpose she needed in order to “clear a path” to write the “glamorously sad songs” she’s become known for.