If you’re living in a country with reasonably low levels of corruption and a somewhat functional judiciary, why not use your country’s TLD? It also helps when verbally relaying your mail address.

Also, you're familiar with whatever laws govern that TLD already, and your local registrars will be by most familiar with them when any issues come up and likely have the quickest turnaround for solving issues. I'd probably avoid using one of the huge registrars (because big companies invariably have poor and slow support that's unable to account for exceptional cases), and of course avoid resellers.

This all seems too vague. Is there no registrar making more specifc availability and stability guarantees backed by law or at least believable rationale? Or is there some technical solution that bypasses the entire registrar system altogether?

>what is the safest registrar?

Nominet (.uk)

Whilst not entirely without controversy[1], they do allow any man or his dog to become a member[2], you only need to have "an interest in the operation of the .UK domain".

Nominet membership gives you the ability to maintain your names directly and bypass the middlemen.

The alternative (as others have already pointed out) is to write out a (very big) cheque to ICANN and setup your own TLD where you are the registrar.

    [1]https://publicbenefit.uk/
    [2]https://www.nominet.uk/corporate-governance/members/