The Nova+ even ships with a cautionary note tucked into the manual, saying not to tighten the valve closed too hard. I think that's what happened - the stove was hot and the metal expanded, and I closed it pretty hard when it suddenly shut down. It cooled, the metal contracted, and it was locked shut. Because the new valve design works by rotating a fuel line, rather than using a "handle" for the valve, it loses some torque to the rotation of the fuel line, and thus it's almost impossible to open it back up by rotating the line once it's stuck closed. That's why it took a pair of pliers.

It's a poor design, in my opinion. There are some things they could do to fix it, which I'll outline in my report (e.g., at least make sure the valve stem has flat sides that would allow the included tool to turn it in the field, rather than requiring pliers)...