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Skillscodex-task

codex-task

Coding & development

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Updated 10-15 23:32

About this skill

Codex Task

Forward a coding task to Codex CLI in one shot. Codex writes the code; Claude verifies after.

Why not just use codex:rescue? rescue routes through a 1000-line Node companion (background mode, session persistence, status/result polling). For straightforward tasks, calling codex exec directly skips ~10s of wrapper overhead and avoids any chance of session-state confusion.

Prerequisites

  • codex CLI on PATH (npm install -g @openai/codex)
  • OpenAI credentials configured

Verify: codex --version. If missing, tell the user npm install -g @openai/codex and stop.

Working Directory

Codex runs in Claude's current cwd by default. Before invoking, sanity-check that cwd is the right repo for the task. If the user's task implies a different directory (e.g., "fix the bug in agentic_umm"), pass -C /absolute/path to codex or cd first. Don't assume.

Defaults

  • Model: gpt-5.5
  • Reasoning effort: xhigh
  • Sandbox: --dangerously-bypass-approvals-and-sandbox — Codex has full filesystem + network access, no approval prompts. Required so it can install packages, hit the internet, and run arbitrary commands.
  • Session: --ephemeral (no persistence, clean each run)

⚠️ The default sandbox is intentionally permissive. Codex can read/write anywhere on disk, install global packages, call external APIs, and modify files outside the repo. Only invoke this skill for tasks where you're OK with that. Pass --safe to drop back to workspace-write (cwd-only, no network).

Step 1: Parse Routing Flags

Parsing rules:

  • Routing flags must appear at the start of the user's task text, immediately after /codex-task or the trigger phrase. Once non-flag content is seen, stop parsing — the rest is task text, even if it looks like a flag (e.g., "add support for --safe" is task content, not a routing flag).
  • Treat -- as an explicit end-of-flags marker. Anything after -- is task text.
  • If a token at the head looks like a flag but is ambiguous (e.g., the user says "implement --read-only"), ask once before stripping.

Recognized flags (each consumed once at the head):

Flag Effect Precedence
--read-only Sandbox becomes read-only (Codex can only read, no edits, no network) overrides --safe and default
--safe Sandbox becomes workspace-write (Codex edits cwd only, no network) overrides default
--model <name> Override model (e.g. gpt-5.4, gpt-5.3-codex-spark) —
--effort <level> Override effort: low / medium / high / xhigh —
-C <dir> Run Codex with this cwd (alternative: cd first) —

If both --read-only and --safe are present, --read-only wins. Whatever's left is TASK_TEXT. Pass it through as-is — don't rewrite it. Codex prefers raw intent over Claude-mediated prompts.

Step 2: Confirm (Only If Truly Ambiguous)

Each codex round-trip is ~25s. Spending 5s to clarify is cheap, but don't over-clarify. Ask only if you genuinely can't tell:

  • Which file/module to touch
  • What "done" looks like
  • What's explicitly out of scope

Skip clarification for tasks that are already concrete. Trust Codex to ask if it needs more.

Step 3: Preflight Check

Before invoking Codex (especially in default danger mode), do a quick sanity check and surface anything risky:

echo "cwd: $(pwd)"
git rev-parse --show-toplevel 2>/dev/null || echo "WARNING: not in a git repo — codex changes will be hard to inspect/revert"
git status --short > /tmp/codex-task-pre-status-${TASK_ID}.txt
test -s /tmp/codex-task-pre-status-${TASK_ID}.txt && echo "WARNING: dirty worktree — codex's changes will mix with yours"

If any warning fires, surface it to the user and ask whether to continue. Default --dangerously-bypass-approvals-and-sandbox outside a git repo is high-risk: codex can change anything on disk and you'll have no diff to inspect.

If the user explicitly chose --safe or --read-only, you can skip the dirty-worktree warning (sandbox limits the damage).

Step 4: Invoke Codex

After Step 1, you have these resolved values. Default to substituting them inline below; only fall back to the variable form if you need to call codex multiple times in one session.

Variable Default Source
MODEL gpt-5.5 --model <name>
EFFORT xhigh --effort <level>
SANDBOX_FLAG --dangerously-bypass-approvals-and-sandbox --safe → -s workspace-write; --read-only → -s read-only
CD_FLAG empty -C <dir> if user passed it
TASK_TEXT — user input minus stripped routing flags

Critical: pass TASK_TEXT via stdin, not as a quoted argument. Raw user text in a shell-quoted argument is a command-injection risk under the default danger-mode sandbox (e.g., a task containing $(rm -rf ~) would execute). Always feed the prompt through stdin with a <<'PROMPT' heredoc (single-quoted delimiter prevents shell expansion):

TASK_ID=$(uuidgen | tr '[:upper:]' '[:lower:]' | head -c 8)
ERR_LOG=/tmp/codex-task-error-${TASK_ID}.log
OUT_FILE=/tmp/codex-task-output-${TASK_ID}.md

export https_proxy=http://127.0.0.1:7890 http_proxy=http://127.0.0.1:7890 all_proxy=socks5://127.0.0.1:7890

codex exec \
  -m "${MODEL}" \
  ${SANDBOX_FLAG} \
  -c "model_reasoning_effort=\"${EFFORT}\"" \
  ${CD_FLAG} \
  --ephemeral \
  -o "${OUT_FILE}" \
  - <<'PROMPT' 2>"${ERR_LOG}"
<TASK_TEXT goes here verbatim — no escaping needed because heredoc is single-quoted>

After making changes, end your response with one line:
STATUS: DONE  -- task complete and verified (tests run, build passes, etc.)
STATUS: PARTIAL  -- partially complete; list what's left
STATUS: BLOCKED  -- couldn't proceed; explain why
PROMPT

EXIT=$?
if [ $EXIT -ne 0 ] || [ ! -s "${OUT_FILE}" ]; then
  echo "Codex invocation failed (exit=$EXIT). stderr tail:"
  tail -30 "${ERR_LOG}"
  exit 1
fi

Note on the heredoc: because the delimiter is 'PROMPT' (single-quoted), the shell does no expansion inside the body — $(), backticks, ${...} are all preserved literally. This is what makes the user's task text safe to embed verbatim.

The trailing STATUS protocol is the only thing appended to the user's task text — everything else is forwarded as-is.

CLI notes:

  • Default sandbox --dangerously-bypass-approvals-and-sandbox — full network + filesystem.
  • -c 'model_reasoning_effort="xhigh"' is the official way to set effort.
  • --ephemeral keeps each task self-contained.
  • UUID-scoped temp files support concurrent invocations.
  • Don't add --background — this skill is single-shot foreground.
  • Don't pass --file — it doesn't exist on codex exec. Reference file paths inside the task text; Codex will read them itself.

Step 5: Verify Independently

Read ${OUT_FILE} AND inspect what changed. Don't trust Codex's self-reported STATUS alone.

git status --short > /tmp/codex-task-post-status-${TASK_ID}.txt
diff /tmp/codex-task-pre-status-${TASK_ID}.txt /tmp/codex-task-post-status-${TASK_ID}.txt
git diff --stat

Verification checklist:

  • Files changed match the task scope?
  • Any new files Codex created — necessary or scope creep?
  • Any edits outside the stated scope?
  • Run the project's test command on affected modules.
  • In default danger mode: also check whether codex touched anything outside the repo (run find ~/.config -newer /tmp/codex-task-pre-status-${TASK_ID}.txt 2>/dev/null or similar if you have reason to suspect global writes).

Special case: BLOCKED with no changes. git diff will be empty; verification reduces to reading codex's BLOCKED reason and judging whether it's plausible.

Step 6: Present Result

## Codex Task Result (${MODEL} · ${EFFORT})

**Status:** DONE / PARTIAL / BLOCKED

### What Codex did
[1-paragraph from Codex output]

### Files changed
[git diff --stat output]

### Verification
- Codex reported: [its claim]
- Claude verified: [what Claude ran independently + result]

### Concerns
[Anything off — out-of-scope edits, missing tests, suspicious changes, files touched outside cwd. Empty if none.]

Step 7: Decide Next Action

Result Action
DONE + verification clean Tell user it's ready. Ask if they want to commit.
DONE + Claude found issues Show issues. Options: (a) Claude fixes manually, (b) re-run codex with refined task text, (c) revert Codex's changes (see below).
PARTIAL Show what's left. Ask: continue with codex, switch to Claude, or stop.
BLOCKED Show blocker. Likely needs user input.

Reverting Codex's changes safely. Don't blindly run git checkout -- <file> — that can destroy unrelated edits the user had in the same files before the task started. Instead:

  1. If pre-status was clean for that file (compare /tmp/codex-task-pre-status-${TASK_ID}.txt), git checkout -- <file> is safe.
  2. If the file was already dirty pre-task, generate a reverse patch of just Codex's hunks: git diff <file> | git apply -R --check first to confirm it applies cleanly, and explicitly ask the user before applying.
  3. For files Codex created that didn't exist before, rm <file> is safe.

Step 8: Cleanup

rm -f /tmp/codex-task-output-${TASK_ID}.md \
      /tmp/codex-task-error-${TASK_ID}.log \
      /tmp/codex-task-pre-status-${TASK_ID}.txt \
      /tmp/codex-task-post-status-${TASK_ID}.txt

Examples

Example 1 — Bug fix in cwd:

  • User: "/codex-task have codex fix the N+1 query in src/api.py "
  • Step 1: no routing flags. TASK_TEXT = "have codex fix the N+1 query in src/api.py "
  • Step 3: cwd is the right repo, worktree clean. Proceed.
  • Step 4: codex runs in danger mode (default), edits src/api.py, returns STATUS: DONE.
  • Step 5: git diff src/api.py shows N+1 fix; pytest tests/api/ passes.
  • Step 6: present diff + test result.

Example 2 — Safe mode with new dependency:

  • User: "/codex-task --safe add a --dry-run flag to scripts/migrate.py and a unit test for it"
  • Step 1: --safe → SANDBOX_FLAG="-s workspace-write". TASK_TEXT = "add a --dry-run flag to scripts/migrate.py and a unit test for it"
  • Step 3: clean worktree. Proceed.
  • Step 4: codex runs sandboxed, edits scripts/migrate.py and tests/test_migrate.py.
  • Step 5: verify both files; run the new test.

Example 3 — Cwd mismatch:

  • User (in ~/workspace/sjh-skills): "/codex-task have codex change the lr scheduler in agentic_umm train.py to cosine"
  • Step 3 preflight: cwd is wrong repo. Either cd ~/workspace/agentic_umm/agentic_umm first, or pass -C ~/workspace/agentic_umm/agentic_umm.
  • Then proceed normally.

Ground Rules

  • Single shot. No multi-round loop. If the result is wrong, surface to user — don't auto-retry.
  • Forward, don't preprocess. Pass TASK_TEXT raw. Don't rewrite into "better" prompts unless the user asks.
  • Always feed prompt via stdin heredoc. Never embed user text in a quoted shell argument under default danger mode.
  • Verify independently. Codex saying "tests pass" ≠ tests passed. Run them.
  • Default sandbox is intentionally permissive. User opted in by choosing this skill. Mention it briefly at start of run so they remember.
  • Don't auto-commit. Even on clean DONE, wait for user.
  • Don't auto-revert with git checkout --. Generate reverse patches when the file was pre-dirty.
  • No background mode. That's codex:rescue's job.

When to use this vs alternatives

Situation Use
Concrete coding task, want it done fast codex-task (this skill)
Long-running task, want async + status polling codex:rescue agent
Want second opinion on plan/diff (no edits) codex-review skill
Task is small enough for Claude itself Just do it in Claude