How do experienced Buddhists preserve their equanimity and well-being in unfavourable circumstances?

An example in the ancient texts of the termination of the life span is the monk Channa in MN 144, where his life was tortured by debilitating physical pain. This example appears related to if the rest of the life span has to be spent subjected to continuous violence (because such a life would be pointless). MN 144 says (my translation):

The mendicant Channa did indeed have such families. But this is not enough for me to call someone ‘blameworthy’. When someone lays down the burden (nikkhipati) if this group (of aggregates) and attaches to (upādiyati) another group (of aggregates), I call them ‘blameworthy’. But the mendicant Channa did no such thing. You should remember this: ‘The mendicant Channa slit his wrists blamelessly.’

Otherwise, if terminating the life span is not an option, only Dhamma can be practised, as taught in MN 21 and SN 35.101. There is no other choice.

As for 'forced isolation', well, as long as you are fed food, there is nothing challenging about this, even though spending the rest of your life in jhana or Nibbana is also meaningless or pointless; similar to the silent Buddhas in MN 116.

My opinion is an enlightened Buddhist does not live life for the sake of merely living. Even if not subjected to violence, I think the only reasons for an enlightened Buddhist to live is: (i) looking after their parents (DN 31); and (ii) teaching the Dhamma (MN 26). If there is nobody to teach Dhamma to, there is no point in living, in my opinion.

There are numerous stories in Tibetan Buddhism about Lamas getting imprisoned for years or decades by the Chinese and how they not only endured the hardships but became spiritual guides for other inmates and even their prison guards. If such a situation is possible then it would be practised. For example, the Chinese suffered very much under European & Japanese imperialism therefore some Chinese might be receptive to the Dhamma of a Tibetan Lama who renounced the Dalai Lama's allegiance to the American CIA. But if you were in a Bolshevik gulag run by that tribe who cannot be named then you might not fare so well.

First the stories as i remember them;

• In the commentary to Dhp there is a story of queen who hires a prostitute for the king because the queen is otherwise occupied attending to the monks. The prostitute later throws hot oil at the queen but the queen is established strongly in perception of sympathy and remains thus unharmed.

• In a Sutta, a lay disciple Mahanama is worried about getting mad at his servants and expresses these unholy bad qualities to the Tathagata. Buddha assures him that he isn't going to fall to lower realms and of having fruition of stream entry.

I don't recall anything else relevant which is a story and not an instruction nor a simile.

The general answer on the how-to is in dealing with the five hindrances, all and any one in particular.

One removes perception of aversion and perception of sensuality by establishing wholesome perceptions; of unattractiveness, inconstancy, death, dispassion for all worlds; and does not tolerate unwholesome thoughts.

As for suicide it is blameless only if one does not take another body. An Arahant is said to be using the knife blamessly.

Sāriputta, when one lays down this body and takes up another body, then I say one is blameworthy. This did not happen in the case of the bhikkhu Channa. The bhikkhu Channa used the knife blamelessly. Thus, Sāriputta, should you remember it.”https://suttacentral.net/sn35.87/en/bodhi

But this is not enough for me to call someone ‘blameworthy’. Na kho panāhaṃ, sāriputta, ettāvatā saupavajjoti vadāmi.

When someone lays down this body and takes up another body, I call them ‘blameworthy’. Yo kho, sāriputta, tañca kāyaṃ nikkhipati, aññañca kāyaṃ upādiyati, tamahaṃ https://suttacentral.net/sn35.87/en/sujato

Fwiw; some hold that an Arahant can't kill himself and that the people in the Sutta who are said to use the knife blamelessly kill themselves as worldlings and become Arahants at the moment of Death.

Which tools given in Dhamma do you think would be useful if one had to survive, for example, through the years in prison? Could it be possible to keep on the development of skilful qualities in places like this?

Would you consider suicide as a solution?

Look at it on the bright side, there're certain kinds of life outside of prison that are much much worse than inside. Imagine living in a war-torn region, working like a slave for at least 15 hours a day, witnessing the living hell going on all around you, seeing your parents killed, your sisters raped, your younger brothers forced to do child soldier's work, etc. Of course killing oneself would be the easy way out. But if you believe in the law of Kamma, you'd already knew that's the worst possible option, for bad Kamma is like a debt, and the collector is one cruel ruthless s.o.b who, like a terminator, will never ever ever stop hunting down his debtor until the debt's been paid in full, in this life or the next. So, make the best of what you've got. At least the inmate has an 8-hour/day(or more) advantage to cultivate the Dhamma, over the poor brothers outside of prison who have to work their behinds off every day to be able to afford little morsel of food to feed some hungry mouths and some money to keep a roof over their heads.

There are numerous stories in Tibetan Buddhism about Lamas getting imprisoned for years or decades by the Chinese and how they not only endured the hardships but became spiritual guides for other inmates and even their prison guards.

Tibetan Buddhism in general has a recurring theme of teachings about "putting all obstacles on the path" - meaning, using every real life problem as a practice aid, instead of seeing it negatively.

It's all about your perspective, and if your perspective is that your situation is a blessing, then you will perceive it as such.

Would you consider suicide as a solution?

A big NO...., suicide is not a solution, it creates more problems.

Which tools given in Dhamma do you think would be useful if one had to survive

Buddhism teaches us consequences for our each action,

For example if you hate someone, that person won't even know that you've hated him/her unless you told, but if you hating someone else and it isn't hurt them or do bad for them, it's really bad for the person who hate. Because hater's mind is impure, and it count as bad Karma.

When you collect bad Karma for long time, and suddenly die, while do the another bad Karma, there's high probability of being reincarnate in one of Four Hell(Animals, Pretha, Asura, Hell). And that's the danger of reincarnation. And those four places has lot more Pain, Suffering than human world, it's unimaginable.

" Imagine while four muscular guys hold your hands and legs and another two of'em rip your body apart with a saw, and no way to survive, And advice for the person who getting hurt is not to hate those six guys, being nice them. " And this is a allegory for Meththa.

So if someone think those accordingly and believe that's it truth, no one would do any bad things, And i think that is the best Motive for the survival of such situations.(If you follow and believe Lord Buddha).

I hope this would help.