AI Companions in PoE is what I want

You wouldn't really need actual AI to accomplish something like this.

It's most commonly called an AiHelper. It's a global action sequence for NPCs which determines their actions based on conditions. They might not want such a thing because it can actually make summons too smart. Plenty of CRPGs use this like Divinity OS2 and BG3.

I've ever worked on the AiHelper for those specific games. They have things like projectile fallback, weighted skills under specific situations, priority targeting, surface danger awareness and more.

The limitation of such a system is that everything needs to be tabled.
If it's not in the table it won't take action.