“And they’re spread gossamer thin/ Pushed to the edge, frayed at the ends,” Conor Oberst sings over a folk-rock waltz, detailing one man’s spiral into substance abuse and infidelity. But the line feels relevant to the songwriter’s own career: In 2015, Oberst canceled his reunion tour with indie-punk band Desaparecidos, citing “laryngitis, anxiety and exhaustion.” In that fragile…