About dusk I took a screwdriver and spoke wrench out to the garage in case my spokes needed tuning. The front ones sounded fine, but the back ones sounded a little loose. One sounded especially dull, and it curved where it crossed another spoke. Another spoke was the same way. Tightening the nipple didn't increase tension, and I saw the problem.
At the J end, the flare had worn or broken off, allowing it the slip through the hole in the hub. It was getting dark, so I didn't check them all. There may be more than two that have popped through. The sound of the others makes me wonder if they're all on their way to popping out.
Metal fatigue makes spokes fail, but I've ridden bicycles and motorcycles for decades without a spoke failure. I keep most of my weight on the pedals most of the time, which means the front wheel is loaded almost as heavily as the rear. Maybe the front has stood up better because the spokes are longer.
I seem to need 130mm 12 gauge J spokes. The ones I've seen are shipped from China. Not knowing how soon I could have a catastrophic failure, I'd like to replace bad spokes in the coming week. Where can I get replacements?