Jack O’Brien’s epic production of Puccini’s triple bill features first-class casting: tenor Marcelo Álvarez and soprano Amber Wagner are the illicit lovers of Il Tabarro; soprano Kristine Opolais sings the shattering title role of Suor Angelica; and the ageless Plácido Domingo takes an unusual comedic turn in the baritone title role of Gianni Schicchi. The performances mark the centennial of the work’s world premiere at the Met. Bertrand de Billy conducts.