OVER THE COURSE of his career, Moses Sumney has earned a reputation as your favorite artist’s favorite artist. In 2014, Beck tapped Sumney to perform on his compilation album Beck Song Reader. Later that year, Karen O of the Yeah Yeah Yeahs hired him to open for her and play in her band on a solo tour. Sumney’s friend Solange Knowles had him sing backup on “Mad,” a track off her 2016 album A Seat at the Table. And that was Sumney playing guitar in Sufjan Stevens’s band at this year’s Academy Awards ceremony. All the while, he’s worked earnestly on his own music, including his new EP (untitled as of press time), which...