Yes, I refueled with diesel. ;-) In fact, I had refueled at this same station several days before, and I realized then that they have both the big-rig-style pumps and the smaller-diameter car pumps. This time, I made sure to use the smaller pump because the larger pump fills the tank and filler neck too quickly, overflowing the filler neck. What a mess.
And yes, I realize that 1 mile is not very far from a fuel up. However, during that mile I sat in line at a drive-thru food joint. Speaking of which, while in line I thought I heard a faint, tinny rattle, almost like a think piece of sheet metal that is loose and rattling around.
I did the 40k service myself, which included replacing the fuel filter. I do have a record of purchasing the filter from Keffer VW.
I have filed a preemptive claim with the fuel station (Wilco/Hess). They will retain a sample, and the dealership will retain a sample from my fuel tank, too. And since the drivetrain warranty is still active (thanks maxedtdi), I took it to the local dealer. We'll see how it goes with them first. Then I'll get VCDS and go my own route if need be.
The dash showed a Service Engine Soon notice right before it went dark.