In a nutshell what Truss and KK have done is
1) put a cap that we will all spend on energy prices.
Which reduces inflation by 5% at a stroke.
2) and for doing so they have agreed that the government will pay the difference to the energy companies.
Current market projections are that there is a good chance that there will be no difference.
3) to do so they will add another £60bn on government borrowings so will be well above 100% of GDP. Taxpayers in the future will have to pay this.
£60 billion does not get the national debt from here to over 100% of GDP. You are of course assuming that GDP is unaffected by energy prices. A false assumption.
4) energy companies now effectively have free extraordinary profits which they return to shareholders as special dividends, and their directors get massive bonuses
To the extent that they do, the dividends are taxed at 20%, the directors are taxed at 40%, the shareholders are also taxed, the residual money left after this is also taxed, time and time again. The logical conclusion of your implicit argument is that it would be most desirable if all tax rates were 100% across the board, and the government distributed funds as it saw fit.
5) KK has reduced the tax take, so even more sovereign debt has to be sold.
It remains to be seen whether that is true. There is plentiful evidence to suggest that it won't be true.
6) this has pushed up the price of sovereign debt
So too, to a greater extent, has the response to COVID, the response to the financial crisis, the everyday cost of the NHS and welfare, etc.etc. etc. It is peculiar to pick out a single and fairly minor change as being pivotal against an established pattern across all parties of excess public spending.
7) this has crashed sterling. Given energy prices are in US$ this has made our energy even more expensive
Given energy prices are also falling rapidly, the claimed effects of this are overstated.
8) so government spend on energy has just got even higher which will lead to increase in government debt at an even higher price
Which places very great pressure on the government to reduce public spending, which would be a very healthy discipline and good for the long-term health of the country.
9) and repeat add infinitum.
It is this sort of fiscal policy that turns thriving countries into basket cases over night. Once countries loose the confidence of the markets it will happen very very quickly.
This isn't a thriving country. It, like the rest of Europe, is a stagnant country. You're right that once countries lose the confidence of the markets, things go downhill very very quickly. However, you do not recognise that market behaviour, in the short term, is often not rational. A rapid loss of confidence is not a rational reaction, which means that it moves the markets to a place which is not supported by the fundamentals and a reversion to the mean follows.
And markets don’t care - they just like to extract maximum pain.
Either markets care or they don't. If you say markets don't care, then you can't say that they like to extract maximum pain. They don't care.