What is China's policy? After all, that's what really matters.
From what little I have gathered.
No, China and US policy is critical. A host of issues are linked.
China is concerned about Regime stability. If NK retains and or expands nuke capabilities, China worries that Japan will go Nuke and possibly the US may deploy Nukes to SK. In SK, many want the country to build their own nukes.
So, China would, if all went Nuke be facing Nukes from India, NK, SK???, Japan and the US.
China has taken the public line that there is little they can do to change NK policy. Partly true, sanctions on specific products have caused an impact, significant at that on industry, farming, transportation due to the lack of refined oil products. That said, there are tons of gaps, well known to the Chinese, who allow these to operate.
Neither do they want a war.
A US pre-emptive is loaded with substantial risk. At a minimum, the Regime craters, mass migration from NK to China. China presently has 300 K, on the border, up from 100 K.
China does not want the NK Regime to crater as that would result in reunification and the US on the Chinese border.
Some may or may not be surprises, but NK has no love for China. Both use the other
If you look to Chinese/Korean history, and they both have unsolved border disputes. The 1st leader of NK purged Russian supporters from the Regime, followed a few years later by Chinese supports as well.
NK sees that in the long term, China is more of a threat to security, economically & militarily than the US.
So, to be truthful, I really do not know what China's policy will be in these negotiations