And you set up these permissions and groups for each individual task to be done? Do you tear them down after the task? Or maintain a lot of them for “LLM helps with house renovation” versus “LLM helps plan travel”?

I would if necessary but then again I’m not the one claiming it can’t be done am I? All the examples you gave would require just one llm group and one directory readable and writeable by the user and the llm group (and possibly making the directory setgid the llm group so files in that directory are group owned by the llm group by default). You don’t need a new group for every task just for every logical access role you need. And if you need something more granular than that then there are filesystem acls but I am yet (in 30 years of using unix) to come across a situation that genuinely required them as opposed to being doable just using groups.

I thought the claim was "It's annoying and difficult.", not "Can't be done.".