Okay, here's what I know. As of yesterday I was running on KoLMafia v16171, and Harvest could call EatDrink as normal. Today, I loaded up Mafia, updated my SVN scripts, and canadv.ash complained about a missing adventure location when I tried to run Harvest. Having run across this sort of thing before, I proceeded to update Mafia to the latest (v16214). Once I ran Harvest with the latest Mafia, it exhibited the behavior unponderable described, and his suggested fix worked.
I suppose it's possible that a change to EatDrink.ash or one of my other scripts caused this, but Harvest.ash didn't change at any point throughout this process.