Alternatively, a weapon-AI builds a dyson sphere, preventing any light from the star from escaping, eliminating the risk of a more advanced outside AI (which it can reason about much better than we can) from destroying it.

Or a poor planet-local AI does the same thing.

You don't even have to abandon your friends; you have to take a forced 100 year break from them, after which you will all be eternally youthful

Voldemort also saves Harry from the Lethe Touch in Significant Digits, though how he knew of the spell was confusing to me (I suppose he may have learned from Salazar Slytherin's basilisk, or some other random place, and the Interdict of Merlin prevented him from actually casting it)

I think that they possibly evolved to have Untranslatable 2 whenever they disagreed which would perhaps resolve this.

Being unable to do so with another species, they expected a species which cannot have untranslatable 2 to be unable to come to a rational agreement.