A loop that refactors code until a check passes is a few lines of shell. Most guardrails beside such a loop only watch what an agent already wrote; the one worth building refuses a bad edit before it lands, and that is what this piece constructs.
The rule it enforces: production code under src/ must not import a mock library. That rule can live in two places. Put it in the prompt, do not import mock, and it is clear and still only a request: text loaded into a model is a lever on probability, not a switch, so it leaves the model free to write the import anyway. Put it in a gate that fires before a write lands, and it refuses the edit outright. Both state the same rule; only one can make it hold every time.
The ask channel has a ceiling: a prompt pushes the odds up, never to one. How close a prompt gets to that ceiling is measurable work. Reporails reads the asking channel and shows you, with measured evidence, which instructions pull the lever and which are text the model is free to ignore, so you can write the ask against evidence instead of on faith. Even a well-measured prompt tops out below certainty, because the model underneath stays probabilistic. Closing that last gap is what the gate is for.
