Update.
Thread from 2011 explains a lot about general concept of operation.
ORVR Valve location: 2000 Boxster?
I haven't pulled liner yet, but after looking up a picture of the Porsche Fuel Tank Bleeder Valve Contact Sensor (99661322401), the connector with the "white thing" terminated in it may actually be the connector for the contact sensor itself. (yeah, I've worked on a lot of cars in my life -- stupid is as stupid does).
The wheel liner has definitely been off before so maybe the previous owner had just disconnected it? The vent/bleeder valve, if not original, looked to be in there for some time as the red-orange cap on one of the two hose connectors was quite faded (Texas heat will do that to plastic -- even if no direct UV).
If the contact sensor is disconnected, the valves on the system (at tank and behind headlight) shouldn't open, and I should have the refueling issue, (fuel goes in, displaced air has nowhere to go, pressure builds, fueling stops), which I don't?
Car up, wheel off, liner out again. Ugh.