Thanks, Tom. If you ever encounter a link to something specific, I'd be interested in a (URL) pointer to the Japanese carpentry tools. I have a set of Japanese sharpening stones that are pretty amazing, I know that folks there have hand tools down to an impressive science.

Trench shelter that you didn't need to cover: my impression here is that you dug something deep enough to be out of the wind, but not so deep that you could have covered it and sat up inside?
I expect one that's covered would take more time and effort. An alternative to a trench for just blocking wind is to build a small (or large) snow wall on the appropriate side(s) of a tarp or tent. Heck, just stomping down a firm sleeping platform on snow tends to put a person at least a little below ground (okay "snow surface") level.

It is indeed nice to just cowboy camp on cold clear nights when you're pretty sure of no precipitation!

Back on the initial point, it occurred to me later today that I've been thinking of snow caves with a solo (or at least independent) hiker bias. Traveling in a group I could see a snow cave being a viable approach if one group member becomes sick or injured --- warmer for a group of two or three to share a small snow cave than to stick each person in individual trenches, plus if one were injured, a group shelter allows one or two others in there with them to monitor and help them out. But if time or energy were low, a "trench for two", where the two essentially embrace (regardless of gender or orientation) --- this might nevertheless be a good alternative.

The tough thing about emergency shelters is that we hopefully never get "real" practice at these, just designed practice at best under generally low pressure conditions. It's easy to sit back and make guesses as to what would be best. My hope here is that by sort of "thinking out loud" and getting feedback (here) that I'll be mentally prepared to make good decisions in an actual winter day hike emergency.