I've cleaned out the plastic cable guide on the bottom bracket, and it doesn't appear to be worn. (The bike only has ~1100 miles on it.)

I think the cable has worked its way free of its normal route, since I don't see any fraying or broken strands. It doesn't help that I think I unseated the barrel adjuster and the threads aren't lining up properly. I think this may be beyond my skill to fix. (When it comes to mechanical stuff, I need someone to actually walk me through this, and since my resident 'mechanic' is in Arizona at the moment...)

I guess I needed to get acquainted with the LBS here anyway. And a full-on tuneup is probably best done now rather than in spring...