The hero of the opera was a dog. Samuel Weiser, a bass, wore a full-size dog costume, black-painted nose and all, to depict the eponymous hero of “Pepito,” a shelter dog dreaming of his old life and his new one. “Are you the right dog? Are you the one?” asks Camila, a harried lawyer in a frustrating marriage, arriving at the shelter to find a pet. “I don’t know,” responds the dog helpfully. “I love you.”