> None of this makes any logical sense whatsoever.
It doesn't make any logical sense to set the bar as as you have, either. I mean if someone could provide the roadmap you're asking for, it's probably already too late.
And while we're talking about sci-fi, it seems fairly likely that an AI that could "kill us all" could fail to build a "entire self-assembly food chain from raw ore to von Neumann replicators." I'd be a civilizational collapse [1] without even birthing something new.
But it makes far more sense to worry about the AI x Late Capitalism crossover story or the havok that could be caused by some immature tech nerd amplified by AI, than far out sci-fi stuff.
[1] IMHO, even a genocidal plague probably wouldn't render humanity extinct, something like uncontacted tribe in a rainforest somewhere would probably survive and humanity would carry on (from square one, in a resource-depleted world).