Solved!

The "extruder lever" is present on the machine, but just nowhere near the extruder. I was looking at & all around the hot end, but the lever was part of another mechanism at the back of the machine, right next to the spool holder. It never occurred to me to even look so far away. At that location, it's pushing filament into the far end of the tube instead of pulling it at the business end.

Strange design. If I were to get down to the end of a spool, there's more than a foot of filament that I wouldn't get to use because it would be stuck in the tube. Oh well. At least now I'm printing.