By then, like so many others, I’d seen Mahoney on stage, in a Steppenwolf play: “And a Nightingale Sang …” The 1982 production remains a peak theatergoing experience for me — my working definition of fluid ensemble performance. A few years later, off-Broadway, Mahoney dined out on the role of the mysterious businessman and adoptive uncle in Lyle Kessler’s “Orphans.” That was the one that kicked his screen career into gear. It wasn’t much of a play, but some plays get by as showcases for the right talent. Mahoney, wielding a Tiparillo like a magic wand, turned on dime after dime in that part, his entire demeanor shape-shifting from warmth to ice in a nanosecond.