What the Old World Left Behind
None of what follows is the AI's work, and the AI does not tend any of it. The nanobots were set to erase technology and waste. Living things were never on that list, so everything the old world engineered alive is still here.
Why it was built alive
The old world engineered living things for three reasons: to feed people, to kill them, and to keep essential functions running once the power failed. Biology was not where it began. It had grids and machines that ran on them, built from rare minerals that came out of the mountains. As its wars went on the mountains were made unlivable and the minerals stopped coming, and when the pumping stations failed and the grids went dark there was nothing to rebuild them from. So everything that had to go on working was moved into living things — the water first, then the pumps, and in the end the thinking. A thing that is alive does not stop when the power does.
The crops
The old world had farmed its own native crops for as long as it had farmed, and Clearhold eats some of them still, having domesticated them from wild stock a second time without knowing it had been done before. But transfer testing had brought our world's plants and animals through long before the AI existed, and as the collapse deepened the old world was desperate and they were there; its people had watched us eat these things for decades, so they ate them too, then engineered them to yield more. Nearly every crop in the Known World outside Clearhold descends from that stock. See Cultivated Plants.
The weapons
Built from whatever would do the work. A thing meant to ruin a harvest was built from something that already eats the crops brought through. A thing meant to hunt people through Teraell's wilderness was often built from a native animal that already survived there. That is why the naturalist's tells never quite sort: native species carry bone in the skin and lay down mineral, and most engineered ones do not, but the weapons built on native stock kept the bone they started with, and the designers copied skin bone into the Dorath and the Vennek because it was what already survived. The correlation holds about four times in five — enough to notice and not enough to sort by. The weapons do not break off an attack the way a native animal does, because nothing built to kill people was built to care about surviving, and they do not vary from region to region, which the native species do. See Dangerous Fauna and Flora#What they have in common.
The working things
The Fraeska, the Kravoen, and the Eledh — water, pumps, and waste, moved into living things when the grids failed.
What the pattern still shows
The Waedhra are where the old world's collection points stood; the rigs are nine centuries gone and the Kravoen still keep the appointments engineered into them. Every Vespra sits where something once stood that was worth denying access to, and guards nothing. Clearhold's mountain carries more made things than anywhere, and two of them — the Kollgar and the Skrafna — exist only to make the place unlivable. Somebody wanted people off that mountain permanently; whatever it was denied for is still in the rock. Clearhold settled it anyway, never knowing it had been done, and has no use now for what lies there.
What nobody knows is there to reach
No expedition from any city has reached the polar interior, and nobody knows there is anything there to reach. Somebody has built an iron-hulled ship, and it is the only thing that could go further north than anyone has gone. Nobody aboard would know what they were sailing toward.