After a day of wondering why the microcontroller + crystal didn’t oscillate at all, it was discovered that the 4 pin crystal was wired backwards (4321 instead of 1234). Two methods of fixing this were attempted (rotating the part 90 degrees and shifting the part on the circuit were both found to connect the two leads that were crystal to the microcontroller’s xin and xout). Both failed. It is unknown why. Guesses include using the wrong capacitance crystal, or blowing up the oscillator inside the microcontroller in some way. My vote’s on the latter at the very least since the prototype used a crystal with the internal oscillator and worked fine since September until two days ago but doesn’t oscillate anymore with a crystal.
Then, after a couple days of worrying about why the crystal didn’t work, full-size oscillators were aquired instead because that’s all that could be found locally (parts kit + electronics supply store). Both the prototype and the circuit board now function with external oscillators. The circuit board looks a little funny with such a large, non-surface mount part hot-glued to it. Not really as elegant as I wanted, but it works.
The vectorboard pictured below is just for the temporary jtag header for programming.