Ah-ha, the Wi-Fi controller needed to update the version of MongoDB that my server had installed, and the old version's repository was no longer signed, so apt-get update was failing silently, and that led to my weather graph generator library being linked against an old version of glibc.
@futzle@ThermiteBeGiants I ran the controller on the home server for a little while. Closest I’ve ever come to administering Mongo for any reason. Guess what? Update -> corrupted. Lucky I didn’t care about restoring from scratch.