I've run into this even with the modern million context length that 2.5 Pro offers, it kept trying one of a handful of failed approaches, realizing its failure,

I've run into this even with the modern million context length that 2.5 Pro offers, it kept trying one of a handful of failed approaches, realizing its failure, and looping without ending its train of thought until I yanked the tokens out of its mouth. Even though it has gotten drastically better and rarer, I think this is going to be one of the failure modes that's just fundamental to the technology.