Improving Cursor’s agent for OpenAI Codex models

This post details specific updates to Cursor's agent harness to better support OpenAI's Codex models, particularly `GPT-5.1-Codex-Max`. Key contributions include: adapting the harness for shell-oriented workflows by aligning tool definitions with shell equivalents (e.g., `rg`), adding explicit instructions to prefer tools over shell commands, refining preamble formatting for reasoning summaries to balance user visibility and avoid spam, improving the `read_lints` tool's effectiveness with literal instructions, implementing alerting to ensure preservation of reasoning traces (critical for Codex's performance), biasing the model towards autonomous action with stronger instructions, and tuning message ordering to prevent prompt contradictions with user messages.