> The existence of tools which demand time to make and primitive stone tool factories suggest abundance: division of labour is necessary to invest time in tool making for future benefit. There has to be a relative surplus, more food than not, less time for survival only, to make tools work.

I don't think that's really true. The species wasn't permanently on the brink of starvation such that they didn't have time to bend down and pick up a stick and use it to add to a shelter or throw at an animal, so in the very literal extreme sense we carry a surplus of energy with us. But the equation isn't necessarily much different between one person dividing their time between making tools and hunting, and a division over a slightly larger group. Efficiency improvements with primitive tools would have been large and quite immediate. Also people would have obvious and immediate specializations before any formal organization. Some would be faster, some stronger, some better climbers, some better at sharpening sticks. So there wouldn't have to be some significant build up of a surplus before pretty sophisticated tool making and division of labor would emerge, IMO.