You might be interested in Tomasello’s “The Evolution of Agency” where he kind of addresses this very question. It really depends on how you define “making decisions” and “purely chemical reactions” doesn’t it - all life is chemical reactions, including when we make decisions, and it’s easy for us to apply decision-making language even to systems that are simple enough that we can see them as “purely chemical reactions”.
Tomasello defines the notion of “agents” as “feedback-control systems” that he distinguishes from pure stimulus-response systems. In his examples a nematode for example is “stimulus-response”; its behavior is very directly related to its immediate environment. If it runs into food it eats, otherwise it doesn’t, and there isn’t really a notion of it seeking out food when it’s hungry and not when it’s not. In contrast and “agent” is a feedback-control system with goals, a perceptual system that checks whether the goal is accomplished at any given time and a behavioral repertoire aimed at accomplishing the goal. In our lineage he sets the appearance of this agency around the evolution of vertebrates, and uses lizards as an example of the most basic level. (he doesn’t address other lineages other than to say that various levels of agency clearly evolved convergently a few times; so octopuses and social insects for example would also have these systems). So where a nematode has feeding behavior that’s triggered by running into food and other behaviors when food isn’t present, a lizard’s behavior depends not only on the immediate stimulus but on more abstract goals - in a given environment it might be currently hungry and looking for food, or sated and looking for shade or sun to rest or hide or thermoregulate, or looking to reproduce, etc, and its behavior will depend on and be directed towards accomplishing that goal.
It’s interesting that you say “thinks through and makes decisions” as if they’re on the same level but the book actually claims that human agency is actually the result of the evolution of several successive layers of feedback-control mechanisms that each allow more flexibility and responsiveness - so for example lizards have a feedback systems that adjusts behavior to achieve goals, and mammals have that and also a higher-level feedback system above that to adjust the goal-seeking behavior itself, mentally “playing out” different ways of accomplishing the goal in order to pick the best one. He describes four such levels for humans and it suggests a variety of ways we could define “think through and make decisions”, with different species qualifying or not depending on which we choose.
I think Feynman had a good answer to this question:
https://www.youtube.com/watch?v=Q1lL-hXO27Q
Essentially the issue with this question is that the usual ways you’d answer that question all seem unsatisfactory, and the key to “answering” the question is to understand not magnetism, but why magnetism seems mysterious and all the answers seem unsatisfactory. Like, actually understanding magnetism in the sense of having read and understood the Feynman lectures definitely helps but that’s no good to a layperson.
And the answer to that as I understand it is that we always understand things in terms of other things we understand. When you see a process you don’t understand and learn how it’s caused by a process you do understand, you will feel satisfied, like you understand the process. If you don’t understand a very weird thing but you find a good analogy to something you are familiar with, you will feel like you understand the thing. The thing is, that’s all a feeling. Hopefully the feeling correlates to having an internal model of the thing that’s closer to its nature than your previous internal model, and to being able to make better predictions about the thing’s interactions, and it usually does because the brain is well-made, but it’s still two different things and you can have a feeling of understanding without an improved model or predictions and vice-versa.
And the issue with magnetism is that unlike most other physical things we run into in daily life, it’s a fundamental force that has macroscopic effects our brain didn’t really evolve to be familiar with, and the best explanations for those effects require going directly to the fundamental force, and the fundamental forces is something that’s very very unfamiliar to anyone who hasn’t done university-level physics. If I say “electromagnetism explains how solid objects don’t just go through each other” your response won’t be “but I don’t understand electromagnetism!”, it will be “wait, did we need an explanation for why solid objects don’t go through each other?”. We have an innate sense of how solid objects interact at our scales that feels like it requires no extra explanation. And any behavior of solid objects that does require extra explanation usually involves explanations just one level deeper in the causal chain, which is close enough to what we are familiar with that we can understand it. And as explanations go deeper the causal chain things become weirder and weirder, but as a student of physics you go gradually, get used to each step and when a step becomes familiar enough it helps you “understand” the next one. So at some point you may end up feeling like you understand electromagnetism as a fundamental force, but it took a lot of work to get there (and that feeling my be fairly fleeing and changeable).
We don’t have an innate sense of how magnetism works, and the actual explanations for how it works aren’t just one step removed from things we do have an innate sense of. It’s legitimately the case that the answer to “Why do magnets work like that” is “electromagnetism”, and if you don’t understand electromagnetism (which, as a layperson, you don’t) you’re screwed. There is no phenomenon or analogy that you have an innate sense of that’s enough like magnetism to provide understanding. You straight-up have to do university-level physics until the concepts in question start becoming familiar.
In a way your question is even worse, because look:
You’re kind of asking “what component parts is the fundamental force of magnetism made of and how to they interact to make it behave that way”, aren’t you. And the issue with this is that in the current standard model, there are no such component parts and causes; that’s what “fundamental” means. Now, we know physics isn’t a solved field so in practice there may indeed be extra explanatory steps out there to be found. But 1) they’ll be even weirder than the current thing you’re asking about is. They won’t help you understand, they’ll just confuse you further and seem like worse ad-hoc gobbledlygook than “fields” and “force” do. They’d only help you understand if you’d studied enough quantum physics for it to feel familiar and maybe almost-understood. And 2) at some point we kind of do have to hit an explanation that has no further explanation, something that’s not made of something else. Maybe it’s worth it for you to think about what that might be like. You’ll probably still feel the urge to ask “but what is that basic thing made of, what explains that explanation?” but you’ll have to accept that this question is that of a brain that evolved in an environment where everything is made of something else and things have nigh-infinite causal chains explaining that they are what they are. It just might not be very good at thinking about a situation where that’s not the case.