There are no codes - checked that even though light not on.
Not in limp mode - drives ok-ish unless a lot of boost is called for.
It is possible there is a leak somewhere in the charge pipe, even though it looks ok. I should have mentioned that the reason the car was at the stealership to begin with was that I had a coolant leak at the oil-heater. One of the charge-pipe clamps had been put on clocked incorrectly by the factory and the screw actually wore through the body of the heater. So in replacing the oil-heater they DEFINITELY were messing with the charge-pipe.
My experience is that when a problem magically appears after something was messed with, it’s usually that thing. In this case, however, there was this and also the purge valve/flash, either of which could cause the problem...