As Renée Fleming, “America’s Diva,” introduced the third to last piece in a program that ranged from Handel to Cantaloube to Harold Arlen, the beloved singer sighed deeply. It was a testament to the magic and beauty she had spun singing one of the standout numbers of her concert, “O mio babbino caro” from Puccini’s “Gianni Schicchi.” She sang the {…}