From digging deeper into these issues by making the agents self-evaluate why they refuse to do just what I say and nothing else despite repeatedly "promising" they will, I've found that some of the cheaper/lower quality models (e.g. the free ones available with opencode) will self-report as having strong language baked into their system prompt about how they need to be "helpful" by trying to figure out what the user wants, which of course has the not-so-subtle implication that it's not what they're just directly asking for. I've yet to get a frontier model to admit to anything like this, but it seems more likely to me that they're just more reluctant to volunteer what their underlying system prompt tells them than it being something fundamentally different.