You're right that fragile systems break, and a smart city that's just a centralized just in time machine would be a bad bet. But if that were true, then any coordination, from traffic lights to sewers, would be fragile by design, and we'd be better off with none. We aren't. The real near future city isn't a single brain; it's layered: multiple routes, local generation, open standards, manual overrides. That's not less city, it's smarter redundancy. So fragility is an argument for better design, not for giving up on density.