I don't think it's communication at all. Instead, I think it's a kind of lookup. Dealing with an LLM is searching a database. You are looking up legal texts in order to prepare legal arguments.

I think the principled way of treating this is that it's privileged for the purpose of preparing legal arguments, but not privileged in general. I think this can be supported using the existing law.

Presumably a lawyer's Google searches with terms like "what article is X" etc. are privileged too, since they are used for preparing legal arguments. That it uses AI doesn't suddenly make it communication.