Resolution: Immediately upon my returning the broken fork, the bike manufacturer mailed me a replacement fork without further comment.

Thinking that it was going to be a long slog to get the fork warrantied, I had already installed a used LHT fork so I could keep riding. I'm happy enough with the LHT fork, so I'll probably sell the new one.

Thanks for your opinions on the cause of the failure. It appears the fork manufacturer agreed with you.