When I bid 1S, I'd prepared my second bid and decided that it was borderline between 2H and 3H. So when west preempted diamonds, I decided to upgrade and bid 3H. I was answering the wrong question. The 3D had opened up the opportunity to show 3 suits with a takeout double. The opponents had given me a chance to improve my second bid, but I didn't take it.
Partner would have left the double in and decent defense would have 3D down at least 2. The full hand: