Codex Code Review now supports custom review rules in AGENTS.md

OpenAI has added custom repository rules to Codex Code Review: you can put review guidelines in AGENTS.md, and Codex applies them during review and cites where each one came from in its findings. In OpenAI's own evaluation, the rule-guided version caught 98% of the required custom issues, versus 58.3% for the baseline. The guidance is to start with non-obvious invariants like compatibility requirements and data boundaries, put repo-level rules in the root directory and service-level rules in the corresponding directory, and leave formatting and mechanical checks to CI.