Follow-up and thank you, especially to tsl and StephenH.
After thinking about these replies, it became very clear to me:
I needed to stop thinking about getting a bike and start thinking about becoming a cyclist.
That was... a lot more than I expected to bite off.
It took actually wobbling around the dirt yard of the Hub in Bellingham to really understand that, no matter what research I do, no matter what buying decisions I make, I'm not going to come home with a bike that I'll hop on first morning and take up that hill in traffic with no sweat.
Today I did ride a bike unsupervised for the first time in 25 years.
I learned that the more momentum you build up, the easier it is to keep going straight.
And that two good ideas-- like sitting up straighter and looking around more, and pedaling harder to get going faster-- may not be good together.
And that the best part of the path is the part that isn't paved.
At some point I realized that this was the first time I'd been alone on a bike since I was twelve years old, and had my first bike-car collision only two weeks after I learned to ride.
Same bike, too. My mom's.
I can't wait to get on it again.