use-codex

name	use-codex
description	Run Codex CLI as a subagent with GPT-5.6 at low or medium effort.
disable-model-invocation	true

Use Codex

You have access to the Codex CLI, as a cheaper source of GPT-5.6 calls.

Available models:

• gpt-5.6-sol: biggest model, expensive but powerful
• gpt-5.6-terra: default; balanced for everyday work
• gpt-5.6-luna: fast and affordable
• gpt-5.4-mini: smallest and cheapest for simple tasks

Treat Codex as a subagent: hand it a prompt, wait for the result, report back.

Steps

1. Pick model, effort, and sandbox. Use the default model unless the task calls for another listed model. Effort is low or medium (default medium). Sandbox is read-only (default, review), workspace-write (edits), or danger-full-access (network/broad). Done when: model, effort, and sandbox are chosen.

2. Run codex exec synchronously using the command shape below. Repo-exploration tasks at medium routinely take 3–7 minutes; set the shell's block/wait time above the expected runtime (e.g. 540s for a task that reads code and writes a doc). Background only if required; then timeout is 150s (low) or 600s (medium). Done when: the process exits and stdout is captured. Killing early yields empty output — never treat that as success.

3. Report. Summarize stdout. On non-zero exit, stop and report; do not retry without direction. Mention the session can be resumed. Done when: the user has the outcome (summary on success, failure report on error).

Command shape

codex exec \
  --skip-git-repo-check \
  -m <model> \
  --config model_reasoning_effort="<low|medium>" \
  --sandbox <read-only|workspace-write|danger-full-access> \
  [-C <DIR>] \
  "prompt" \
  </dev/null 2>/tmp/codex-stderr.log

Always: --skip-git-repo-check, effort low|medium, </dev/null (stdin must be closed or Codex hangs), 2><file> (hides thinking tokens from output but keeps them diagnosable — on failure, tail the log instead of flying blind; 2>/dev/null is acceptable only for throwaway calls).

Running from Cursor's Shell tool

• Codex cannot start inside Cursor's command sandbox: it dies with failed to initialize in-process app-server client: Operation not permitted (exit 1, empty stdout). Requesting full_network is NOT enough. Always run the Shell tool with required_permissions: ["all"] on the first try.
• Codex has its own sandbox on top: with --sandbox workspace-write, network is still blocked inside Codex, so Gradle/npm downloads and build daemons fail (SocketException: Operation not permitted). Don't ask Codex to verify with networked builds or tests unless using danger-full-access; run the verification yourself afterward.
• After the command exits, verify the expected artifact exists (e.g. test -s <output-file>) rather than trusting exit code alone.

Resume

Inherits model, effort, and sandbox — do not re-pass config unless the user asks:

echo "follow-up" | codex exec --skip-git-repo-check resume --last 2>/dev/null

Any flags go between exec and resume.