I'm not sure this is a plausible brink. The initial "tariff board" situation was 10 times more severe than this, and additionally this is a repeat of the same playbook.

This won't be the start of (further) major decoupling unless it's what China wanted in the first place, and they needed another 6 months of preparation before committing to the path. If China says "Go ahead and tariff us 100%. All rare earth exports and re-experts to the US are banned", then that's when to expect changes that won't be reversed any time soon. Everyone knows that Trump will blindly auto-escalate in response, so China saying so would mean "this is the outcome we prefer" and all that follows from there.