This, I'm not sure what to do about, I think LLMs might just not be a good fit for this.
> Temporal consistency (constraints that persist across turns)
This can be solved by stop using LLMs as "can take turns" and only use them as "one-shot answer otherwise wrong" machines, as prompt following is the best early in a conversation, and gets really bad quickly as the context grows. Personally, I never go beyond two messages in a chat (one user message, one assistant message), and if it's wrong, I clear everything, iterate on the first prompt, and try again. Tends to make the whole "follow system prompt instructions" a lot better.
> Hierarchical control (immutable system policies vs. user preferences)
This I think at least was attempted to be addresses in the release of GPT-OSS, where instead of just having system prompt and user prompt, it now has developer, system and user prompt, so there is a bigger difference in how the instructions are being used. This document shares some ideas about separating the roles more than just system/user: https://cdn.openai.com/spec/model-spec-2024-05-08.html