“It was my first visit to the Bayreuth Festival, and I was wrestling with conflicting emotions. There was the thrill of realizing my long-held dream of hearing Richard Wagner’s music in the opera house he built, where some of my favorite recordings were made. But there was queasiness, too, at the inescapable memories of old photos showing the theater defiled during the Nazi era, festooned with swastikas and visited regularly by Hitler. Then I stepped outside at intermission on Saturday evening and checked my phone.”