I don't know a ton about how LLMs work (I really should learn), but something like this feels like it might be the way forward to me.

The software running the model knows unambiguously what came from a user and what did not, what came from a tool call and what did not, etc... and having some way of exposing that to the LLM as part of the text itself feels like it fits better with how a neural net works than a set of surrounding tags does.