So, in short, I think I agree with the op:
> I don't see anything that indicates how spacetime solves the core problem CRDB does, which is guaranteeing that single node failures can be tolerated with zero data loss or loss of availability
how would a single node system survive the failure of its only node?
I'm not sure I follow. SpacetimeDB Cloud has the same exact behavior as CRDB in terms of tolerating single node failure and loss of availability.