It means anything which violates the social norms and laws that undergird a society, one of which is suicide. Another might be illicit drug use, including psychedelics. Any solution or help a state-linked therapist provides must necessarily steer away, if necessary by force, from anything that involves these. This even may be if something like psychedelics could help the individual, although psychedelics are likely to become legal in the future for this purpose. Suicide in most jurisdictions is entirely illegal not excepting euthanasia and in such jurisdictions, a therapist engaging with a rational terminally ill person as you describe would not be allowed in an official capacity to have an honest discussion about euthanasia as an option for their situation.
> There is no strong evidence that suicidal people have a genuinely held belief that they wish to stop living, as opposed to a psychiatric episode that once passed does not reflect their actual world view.
I would argue that there is an overwhelming amount of evidence that suicidal people have a genuine held belief that they wish to stop living, in the form of genuine and sometimes successful suicide attempts. To redescribe it as a "psychiatric episode that once passed does not reflect their actual world view" is to simply negate the validity of the belief by viewing it through a medical rubric which affirms suicidality as something pathological. This is a value judgement. Compound with the complication that, as described through the comments on this post, any discussion of intent towards suicide can have severe consequences and therefore suicidal people will necessarily be coerced into denying their true beliefs of things, and must acknowledge the consensus view that their desire to kill themselves was in fact not "a genuine beliefe". That they may come at some point (possibly much later on) to have genuinely changed their mind not to kill themselves or to have kill themselves may be great but does not invalidate their previous belief at the time they were suicidal.
For comparison, imagine a society in which intent towards abortion was viewed as a pathological state of mind, and any talk towards such was met by extreme force from the state similar to that which it is for suicide, to wit: forced imprisonment, pharmaceutical intervention and koshing of a person until they no longer expressed (openly) a desire to have an abortion. A statement like "There is no strong evidence that these women have a genuinely held belief that they wish to not have their baby, as opposed to a psychiatric episode that once passed does not reflect their actual world view." may sound valid to people living under such a value system but we might recognise something more going on here.