How should we deal with interactions not from a “fundamental force”? Question
Should the cosmological constant and/or vacuum energy be listed as one of the fundamental interactions?
If not, how can we have actual energy and forces that are not assignable to one of the fundamental forces of the universe?
But If it should be added, how do we reconcile including the vacuum itself as one of the subtypes of quantum harmonic oscillation?
I simply do not understand the physics well enough to know which is the right view.

A Request
Hoping we don’t overcomplicate or divert. This much I gather: However we slice it, there are interactions that happen that cannot be assigned to one of the four fundamental interactions. Therefore, by logic alone, we are either

A. Incorrectly excluding a fifth that should be listed, perhaps with a caveat about how different it is. Or else we are


B. Incorrectly saying all real-world physical interactions come from fundamental forces. And therefore also either incorrectly calling them “the fundamental forces”, or at least incorrectly excluding their own caveat explaining how they are fundamental but don’t cover all fundamentals.

Please explain which one we are actually doing and the physics behind why that is the case. If you think part of it is opinion, please just touch on what the question of interpretation is.
If you’re following that and also see the dilemma cleanly, then you can probably skip the final section. Whether we are doing A or B, I then have two further questions below, as “If so..”.
Fundamental Interactions
We hear that our models have contained four fundamental forces for quite awhile: gravitational, electromagnetic, strong and weak nuclear.
For example even wikipedia has been telling us this for years:
https://en.m.wikipedia.org/wiki/Fundamental_interaction
Quantum Vacuum
It’s not so straightforward that $\Lambda$ is equivalent to dark energy, although some would say exactly this.
My understanding is that $\Lambda$ is a single added term for the quantum vacuum and not at all the same as the other fundamental forces that arise in the vacuum. Do you see that as a fair summary?
At a minimum we would need to say it is fundamentally different than the other four. And that’s if $\Lambda$ operates such that we should add it as fifth outright. If so, what’s a parsimonious phrase for capturing how it’s included but different? Would you go as far as saying $\Lambda$ is vacuum energy, and that it’s the basis of, and even more fundamental than, the fundamental four - and how so?
$\mathbf{\Lambda}$ Interactions
But we have the Casimir effect, and dark energy’s effects, i.e. $\Lambda$ affecting the rate of expansion.
At a minimum, we must say there is more than just a single set of four fundamental forces and all interactions can be boiled down to those. And that’s if $\Lambda$ operates such that we should continue to exclude it. If so, what do we call it if not a fundamental force, in a way that describes for me its ability to have effect but justifies its exclusion? And secondly, what should be said about the fundamental forces regarding the fact that they don’t explain every force while being identified as exhaustive?
-END-

What’s not being asked
Some but not all of this section is to motivate that this is not only not a repeat, but doesn’t have related answers that speak directly to only this question - not with any I have so far seen. Another motive is to avoid unnecessary diversions that miss the heart of the question.
Not asking:
How virtual particles cause Casimir (except in how it helps me understand whether and how the situation is more like A or B, if it does).
How similar quantum field theories explain both fundamental forces and Casimir, or and acceleration (except in how it helps us understand..).
What explains gravity or how gravity relates to quantum field theory. (Quantum gravity).
Anything at all about how the four forces relate to qft (except.. ).
Whether or in what sense $\Lambda$ is dark energy.
—
Other questions ask which fundamental force something that comes from vacuum energy is. And then say, “Oh I thought it was one of the four. How odd.” No question says please explain the physics of this and which of these two things is true. So overall they don’t even add to an answer to this question.
 A: 
However we slice it, there are interactions that happen that cannot be assigned to one of the four fundamental interactions.

It think this premise is wrong, or at least we don't know yet whether it is right. It is possible that the effects you mention (Casimir effect and the universe accelerated expansion) are both explained by the four fundamental interactions.
Casimir effect: along with spontaneous emission and Lamb shift. They are explained by quantum field theory, in particular by electromagnetic interaction, so no fifth force is required.
Accelerated expansion of the universe: recent Planck data (and we'll see what Euclid tells us) suggest that the accelerated expansion is due to a cosmological constant. In this case it may just be caused by gravity. It may be that the Einstein field equations contain a $\Lambda$ therm, just because the universe is like that. This would mean that the cosmological constant is just a feature of gravity. No fifth force required.
I'm playing the devil's advocate here, because few people would be satisfied by this explanation. Some theories would like to explain the expansion by postulating a scalar field whose effect is to provide a cosmological constant. Other theories talk about more general forms of dark energy, like a variable $\Lambda$ in time, quintessence, ghost models, modified Einstein gravity...
Many of these theories introduce one or more new fundamental fields, and so new interactions. If these theories are found to be correct, then we will add these interactions to the list.
Inflation: this also is often explained by introducing new scalar fields. New interactions? Possibly. But presently we are not even sure the inflation really took place.
My point is that, as of today, we are not sure whether there are other fundamental interactions, and we don't know how they might look like.
My answer is that we don't know yet whether it is A or B or even C (everything is explained by the four known interactions)
A: Whether you're talking about accelerating expansion of the universe due to a cosmological constant, or due to vacuum energy, this does involve one of the already-known fundamental forces - gravity, as described by general relativity.
