Anthony Roth Costanzo on Glass, Handel and “putting it together.”

Opera singers aren’t brought up to be as enterprising as Anthony Roth Costanzo. But few have his resume: He’s a child Broadway star-turned Princeton student-turned countertenor. Was Stephen Sondheim’s great networking song, “Putting it Together,” playing in the background when David Patrick Stearns met up with Costanzo a few weeks ago? No, but it should’ve been.