In my design I'm modeling the LLM with access to untrusted information (emails, support tickets) as an adversary. And I'm saying that the adversarial LLM communicates with the rest of the system through structured messages, not English text.

It turns out Simon Willison has been saying this for some time now; he calls it the "dual LLM" design, I think? (For me, both terms are a little broken; you can have way more than 2, and it's "contexts" you're multiplying, not LLMs.)