Edit: Because the former doesn't sound like much of a conspiracy, aside from a cover-up afterwards.
From there, the only safe bet is to act as if it were intentional.
This is a controversial concept, but it is the rational choice. Never assume that someone who harms you is doing it accidentally. Even though it is more often than not the case, you still have to protect yourself with the possibility of malice in mind.
Working with the default hypothesis of "everybody is out there to destroy me" is not only a sign of paranoia, but in most cases also wrong (because in reality not everything is about you and accidents happen).
So starting with the default hypothesis of malice has the serious downside that you will constantly feel threatened even if looking back there was no rational reason to feel threatened. This is not only incredibly exhausting, it also will lead to a "crying wolf"-type of problem, if the perceived threat rarely turns out to be one. And when something really dangerous is going to happen, you might not be able to react in a rational way (because all your previous reactions were irrational ones).
What I think is important to rationally tackle that question is also to factor in confidence. I will always assume innocence (just because it makes me a happier person), but that doesn't mean my confidence in the other person being innocent is always big. If there are signs that other person is acting in malice, my confidence that they are innocent will shrink. Once that confidence crosses a certain threshold I will assume malice. This can also happen within a split second, so I don't see how this would not be the rational way to do this. If you go get bread at the bakery, you wouldn't assume the baker wants to poison you per default right? So you would assume their innocence unless there are clear indicators they are a baker that poisons their customers. The other way around, if a man jumps out of a bush in a dark alley and comes at you with a knife, you wouldn't assume they are innocent, because there are really strong indicators they are not.
So what is irrational is to have incredible high confidence in either innocence or malice when in fact you are in a situation with lack of evidence to either direction. And this is the case in this situation.