You step into the elevator of a pre-war building in Murray Hill on your way home from work. The doors close, the car lurches, and instead of climbing, it drops — three feet, six feet, maybe more — before slamming to a stop between floors. Your knees buckle, your back compresses against the steel cab, and when you finally crawl out, you can barely stand. Elevator free-fall injuries in New York City sound rare, but they happen often enough in older Manhattan walk-ups, mid-rise