Any person/mind should have the right to suicide

There's a lot of details to work out here, and this post doesn't really acknowledge any contention between principles that would make it non-absolute.  In one sense, it's an absolute right of any agent to make any decision they are able to execute unilaterally.  But that's kind of trivial, and you might prefer the term "capability" over "right".  I expect you mean that others have some duty to enable this decision in some (all?) circumstances, which is the normal smuggling of demands on others into a declaration of rights.

The biggest question is "how can a guardian (who has to decide whether to prevent the suicide) or friend (who has to decide whether to assist or impede the suicide) know that the agent is making a rational long-term decision, rather than over-indexing on a temporary suffering or depression?"

The problem with death is its finality. No redos. I generally agree that the right to die should be protected. But I reckon that most people who want to die, really just want to live better. In that they prefer death to their current life, but would prefer a better life to dying. And as Slider notes, knowledge is very important - there are lots of cases of people killing themselves because of a misunderstanding. Those deaths would be better prevented, seeing as they're conditional on something that turns out to be false.

We do not have a good handle on the concept of suffering, beyond that of human first-person experience and descriptions, and progress in that area seems essential in order to decide if a computer crash counts as a suicide attempt due to unbearable suffering.

It maybe better first to force person to undergo a course with psychologist and psychiatrist and only after that allow a suicide..

Something along these lines seems essential. It may be better to talk of the right to informed suicide. Arguably being informed is what makes it truly voluntary.

Forcing X to live will be morally better than forcing Y to die in circumstances where X's desire for suicide is ill-informed (let's assume Y's desire to live is not). X's life could in fact be worth living - perhaps because of a potential for future happiness, rather than current experiences - but X might be unable to recognise that fact. 

It may be that a significant portion of humanity has been psychologically 'forced' to live by an instinct of self-preservation, since if they stopped to reflect they would not immediately find their lives to be worth living. That would be a very good thing if their lives were in fact worth living in ways that they could not intellectually recognise.

I would see some Romeo wanting death for romantic purposes and utilising an unconditional right to suicide for it to be a tragedy scenario.

I have gotten to the part of the Cheliax story where Keltham starts to think that Dath Ilani are problematically fragile against negative emotions that they need superelaborate dances to not provoke even slight shades of despair in each other. This is presented as being causally connected for citizens being encouraged to end their lives based on unanalysed unhappiness.

Even in Cheliax terms death is not Evil as you do not get to experience it (modulo some outer plane stuff). What is Evil is being selfish about catering to your current structure over facing your circumstances. You should not create torment, to yourself or others, but dismissing existing torment creates new torment. Thus both the forceful resurrectionist and the kamikaze patient are antiproductive.

There is only one good; Knowledge, and one evil; Ignorance. You don't get to be ignorant of your pain. While an unexamined life might not be worth living, I would demand the examination before I will accept to take the life.