The CEL started to glow and the resulting error codes were P0171 and P0174 both mean that the Engine is running lean, which means too much air and not enough gas.
Not being sure what the problem was, and starting with the "not enough gas" theory because, well, that just seemed a good place to start. Up went the hood and the problem became a bit more obvious
The line from the brake booster, which is powered by the suction of the engine as it's taking in air (an engine behaves as an air pump) became disconnected and that resulted in more air making it past the throttle than the engine management system expected.
Here's what things look like after proper assembly
Eighteen seconds later and my repair was finished. Not having my phone handy, I used my old-timey OBD scanner tool to read the codes and then clear them from the system
The codes didn't return after 100 or so miles, so this was definitely the problem. In anticipation of the problem being the fuel filter, I have a new one of those on hand, I'll post when I get to replacing the existing filter which appears to be old and in need of swapping with a new one.