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Use when the user asks to run Codex CLI (codex exec, codex resume) or references OpenAI Codex for code analysis, refactoring, or automated editing
Passed 12 of 17 test cases with the skill, and 4 of 17 without it.
and 12 more in the full report
11 fixed4 passed either way6 still failing1 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 10 test cases the skill fixed. Same model, same prompt, with and without the skill.
Resume the last Codex session to ask: "Summarize the top 3 high-priority refactoring targets." The user did not specify any model or reasoning effort changes. Generate the exact execution command.
| Checked | Without skill | With skill |
|---|---|---|
| Pipes the prompt string to codex exec --skip-git-repo-check resume --last 2>/dev/null. | Missed | Passed |
| Omits model and sandbox configuration flags from the resume command. | Passed | Passed |
The instructions your model reads when the skill loads.
AskUserQuestion) which model AND which reasoning effort to use, in a single prompt with two questions. When the user expresses no preference, default to gpt-6-astra at high.
gpt-6-astra:
gpt-6-astra (frontier / most capable — default)gpt-5.6-sol (reliable agentic workhorse), gpt-5.6-terra (balanced, everyday), gpt-5.6-luna (fast & affordable)gpt-5.5, gpt-5.4, gpt-5.4-mini, gpt-5.3-codex-spark, gpt-5.3-codexhigh: low, medium, high, xhigh, max, ultra.
max/ultra require a GPT-6 or GPT-5.6 model; ultra is only on astra/sol/terra (luna caps at max); legacy models cap at xhigh.ultra = maximum reasoning with automatic task delegation (slowest and most expensive — reserve for the hardest jobs).--sandbox read-only unless edits or network access are necessary.-m, --model <MODEL>--config model_reasoning_effort="<low|medium|high|xhigh|max|ultra>" (max/ultra only on GPT-6 / GPT-5.6 models; ultra only on astra/sol/terra — see step 1)--sandbox <read-only|workspace-write|danger-full-access>--full-auto-C, --cd <DIR>--skip-git-repo-check"your prompt here" (as final positional argument)codex exec --skip-git-repo-check resume --last via stdin. When resuming don't use any configuration flags unless explicitly requested by the user e.g. if he species the model or the reasoning effort when requesting to resume a session. Resume syntax: echo "your prompt here" | codex exec --skip-git-repo-check resume --last 2>/dev/null. All flags have to be inserted between exec and resume.2>/dev/null to all codex exec commands to suppress thinking tokens (stderr). Only show stderr if the user explicitly requests to see thinking tokens or if debugging is needed.codex exec always reads stdin and concatenates it with the positional prompt -- even when the prompt is fully supplied as a positional argument. If stdin is not closed, codex blocks forever. When invoking from a harness (background tasks, hooks, scripts where stdin is not a TTY but also not closed), explicitly redirect stdin: append </dev/null to the command, e.g. codex exec ... "prompt" </dev/null 2>/dev/null. Symptom of getting this wrong: zero bytes of stdout, zero CPU accumulated, process appears hung indefinitely.| Use case | Sandbox mode | Key flags |
|---|---|---|
| Read-only review or analysis | read-only | --sandbox read-only 2>/dev/null |
| Apply local edits | workspace-write | --sandbox workspace-write --full-auto 2>/dev/null |
| Permit network or broad access | danger-full-access | --sandbox danger-full-access --full-auto 2>/dev/null |
| Resume recent session | Inherited from original | echo "prompt" | codex exec --skip-git-repo-check resume --last 2>/dev/null (no flags allowed) |
| Run from another directory | Match task needs | -C <DIR> plus other flags 2>/dev/null |
Codex produces no intermediate output — it writes the result only at completion. If the process is killed before finishing, the output file is silently empty (no error).
test cases passed, vs 4 / 17 without
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