"You're absolutely right!" The agent says it before it has looked at anything. You point out a bug, it tells you you're right. You suggest the opposite of what you asked for a minute ago, it tells you you're right again. That reflexive agreement, the little affirmation stapled to the front of every reply, is one of the most complained-about tics coding agents have right now, and once you notice it you cannot stop noticing it.
The obvious fix is to tell it to stop. Add a line to your instructions: do not open with placation, do not tell the user they are right before you have checked. Reasonable. But that line now rides in the model's context on every single turn, read again on the turns the agent was going to agree politely and the turns it was going to do real work, paid for whether or not it was ever about to placate. So the real question the title asks is how you actually stop it, and the answer turns out not to be an instruction at all.
Notice something about that line, though. It is not about any particular file. "Do not open with placation" applies whenever the agent is about to speak, which is every turn, in every file and in none of them. Set it beside a different rule you might add: production code under src/ must not import a mock library. That one has a home. It is about src/, a path you can name. Two kinds of rule end up on an instruction surface, the kind you can pin to a file path and the kind you cannot, because they are about behavior rather than location. Which kind a rule is decides where it can live and what it costs to keep it there. That split is what this piece is about.
