There's a lot of agency in heart attacks too, but we still say that the heart attack killed them, not that they killed themselves with a heart attack.

There is agency, but it's equally irresponsible and unhelpful to act like outside factors are not part of the equation, and that someone who drives a person to suicide is blameless.

Let's say someone jumps out of a burning building and they're killed by the fall. Did they have agency? Responsibility? Should we describe that as "committed suicide"?

Heart attacks can and do happen regardless of optimal diet and lifestyle, but notwithstanding, indeed CVd can be likened to a slow-motion suicide, like cigarettes, given modern knowledge most people are aware of.

No one is saying outside factors aren't part of it. But you cannot negate or mitigate the fact that people make a choice with suicide that is not inevitable.

Your last questions are irrelevant and pointless

How are questions about someone committing suicide irrelevant and pointless in a conversation about that exact topic?

Because its obvious. The margin case of escaping certain and imminent painful death in favour of another kind is not working in your favor. Yes they are responsible for their actions, yes they have agency. It is still suicide but that is a moot point when you are choosing between deaths. Here too, jumping is not something that invariably happens. That doesnt make it a bad thing. That is a value judgment that depends on the circumstance of the alternative being factually and irreparably worse.