Well the vehicle is new to me. Bought it knowing the timing belt had snapped, and would need at least the head done.
You think that valve failed causing the belt to snap, rather than the other way around? All the other valves and pistons have a smooth covering of carbon, like you'd expect, I can't see any signs of contact, though admittedly I was focused on getting the head off before the weather turned.
Only that one valve looked clean, it was very distinct.
I had awful luck changing thermostats on different VW diesel vehicles, sheared the bolt twice, tried EZ-outs etc. didn't want to do the pump, hindsight maybe should have, couldn't get it to seal right after changing etc.