Turns out Raspberry Pi boards have provision for a Reset switch, but you gotta dig for it. On the Model B+, it’s labeled RUN:
Soldering in that 2-pin header and plugging a pushbutton switch on a short cable will suffice until I get around to thinking of / scrounging a suitable case.
Poking the button forces a power-on reset, which you shouldn’t do with the RPi running, lest you trash the filesystem. After shutting down with
sudo halt, however, the switch does exactly what’s needed: restarts the CPU from scratch.
The RPi draws little enough power that there’s no point in actually pulling the plug; stressing that Micro-B connector is definitely a Bad Idea.