People who buy the USA-vs-China race to a specific goal - do they really believe if China gets "AGI" first, they will immediately try to conquer the USA? How exactly will that go?

It's more likely they will continue expansionist policy in Asia which counters several American diplomatic goals:

1. Democracy and freedom worldwide

2. Economic access+prosperity with Asia

3. Pro-American sentiment

(Not in order of importance, which shifts constantly)

I think assuming China would beat the US in conventional war if they reach 'AGI' first is a stretch, even if this actually grants them a force advantage it's not like the US can no longer reach AGI. The risk is really more that if they reach 'AGI' and subsequently a force advantage, that they would no longer be deterred and more decisively move on Taiwan next year. Taiwan is key to [1] and [2] above.