I think you underestimate what a massive country China is and the scale of their military. Russia is already quite an adversary, but China is at an even higher level. By some metrics, they have already surpassed the US military.
So it is very unlikely that a neighbor will have the audacity to attack them, and even if this happens, i'd expect the war to be over rapidly. Just like if Canada or Mexico tried to attack the US.
I think the consensus is that Russia proved itself barely capable against just Ukraine. Also I didn't say someone has to attack prc, it's more likely to go the other way round and as many historic examples showed no matter how big you are people defending their home land will not make it easy.
The scenario we are all dancing around is if there is a war over reunification. That would be between the worlds two superpowers. No one would walk into a nuclear Holocaust on purpose I bthink, but miscommunication happens. Even if no other nations intervened, the reunification would definitely destroy all the worlds leading fabs, and even if it didn't, I read ASML can and would shut their machines down remotely. So those researchers would shift to figuring out what they can do at the 28nm node... Meanwhile the rest of us ponder why old powerful men can't let things be.
So it is very unlikely that a neighbor will have the audacity to attack them, and even if this happens, i'd expect the war to be over rapidly. Just like if Canada or Mexico tried to attack the US.