Conclusion: the voltage divider in the proximity circuit in the handle is failed.
Process to get this conclusion: I took the versicharge handle apart for diagnosis. There are 2 #10 torx tamper resistant screws under the rubber cover, then pry open starting on the latch end--there are 6 latching tabs which popped without too much effort--have care with the gasket.
The mechanical operation of the latch and the microswitch were all normal. Microswitch appears to be switching normally using a continuity tester . There are some spade terminals which had light corrosion; cleaned those. Put it back together, still "three flashing blue lights, 3 beeps"
Verified I could hear the microswitch clicking on and off inside the handle while the trigger is being operated. Cleaned some bug bits out the L2. Still "three flashing blue lights, 3 beeps".
Working on the assumption that the proximity circuit has failed, I borrowed one of those J1772 extension cables, connected the versicharge handle to it, plugged into the car, and charging commenced normally. The proximity circuit starts and ends in the handle (more or less, please don't mind my moderate understanding of electronics terminology), so the j1772 extension cable was reasonable diagnostic.
The voltage divider in the versicharge handle is molded into an off white plastic component about 1.5" long, 0.75" wide, and 0.5" thick. I feel confident that a) I wont find that part online, and b) some resistors in some potting compound would work if it was worth my time to repair it.
2013 Pearl White SV man 09/13 58k purchased new 12/13
2013 Ocean Blue SV man 07/13 18k purchased used 12/19