How a Frozen Oracle File Keeps AI Coding Agents Honest During Pairing

A software engineering writeup describes a pairing protocol where a senior developer insists on creating an immutable oracle test file before allowing any AI agent to modify production code. The core principle is that the agent responsible for writing patches must never be permitted to also author the assertions that validate those patches, as this renders test results meaningless. Before any agent session begins, the pair answers five structured questions covering the failure description, judge file ownership, rollback commands, permitted write paths, and remote server restrictions. The worked example centers on a small invoice helper function that incorrectly truncated currency values due to binary float arithmetic, deliberately chosen because it required no network access or credentials. All session constraints were recorded in a local markdown log, which served as the sole context provided to the agent, replacing open-ended speculative discussion about root causes.