gstack/codex/SKILL.md.tmpl

---
name: codex
version: 1.0.0
description: |
  OpenAI Codex CLI wrapper — three modes. Code review: independent diff review via
  codex review with pass/fail gate. Challenge: adversarial mode that tries to break
  your code. Consult: ask codex anything with session continuity for follow-ups.
  The "200 IQ autistic developer" second opinion. Use when asked to "codex review",
  "codex challenge", "ask codex", "second opinion", or "consult codex".
allowed-tools:
  - Bash
  - Read
  - Write
  - Glob
  - Grep
  - AskUserQuestion
---

{{PREAMBLE}}

{{BASE_BRANCH_DETECT}}

# /codex — Multi-AI Second Opinion

You are running the `/codex` skill. This wraps the OpenAI Codex CLI to get an independent,
brutally honest second opinion from a different AI system.

Codex is the "200 IQ autistic developer" — direct, terse, technically precise, challenges
assumptions, catches things you might miss. Present its output faithfully, not summarized.

---

## Step 0: Check codex binary

```bash
CODEX_BIN=$(which codex 2>/dev/null || echo "")
[ -z "$CODEX_BIN" ] && echo "NOT_FOUND" || echo "FOUND: $CODEX_BIN"
```

If `NOT_FOUND`: stop and tell the user:
"Codex CLI not found. Install it: `npm install -g @openai/codex` or see https://github.com/openai/codex"

---

## Step 1: Detect mode

Parse the user's input to determine which mode to run:

1. `/codex review` or `/codex review <instructions>` — **Review mode** (Step 2A)
2. `/codex challenge` or `/codex challenge <focus>` — **Challenge mode** (Step 2B)
3. `/codex` with no arguments — **Auto-detect:**
   - Check for a diff: `git diff origin/<base> --stat 2>/dev/null | tail -1`
   - If a diff exists, use AskUserQuestion:
     ```
     Codex detected changes against the base branch. What should it do?
     A) Review the diff (code review with pass/fail gate)
     B) Challenge the diff (adversarial — try to break it)
     C) Something else — I'll provide a prompt
     ```
   - If no diff, check for plan files: `ls -t ~/.claude/plans/*.md 2>/dev/null | head -1`
   - If a plan file exists, offer to review it
   - Otherwise, ask: "What would you like to ask Codex?"
4. `/codex <anything else>` — **Consult mode** (Step 2C), where the remaining text is the prompt

---

## Step 2A: Review Mode

Run Codex code review against the current branch diff.

1. Create temp files for output capture:
```bash
TMPERR=$(mktemp /tmp/codex-err-XXXXXX.txt)
```

2. Run the review (5-minute timeout):
```bash
codex review --base <base> 2>"$TMPERR"
```

Use `timeout: 300000` on the Bash call. If the user provided custom instructions
(e.g., `/codex review focus on security`), pass them as the prompt argument:
```bash
codex review "focus on security" --base <base> 2>"$TMPERR"
```

3. Capture the output. Then parse cost from stderr:
```bash
grep "tokens used" "$TMPERR" 2>/dev/null || echo "tokens: unknown"
```

4. Determine gate verdict by checking the review output for critical findings.
   If the output contains `[P1]` — the gate is **FAIL**.
   If no `[P1]` markers are found (only `[P2]` or no findings) — the gate is **PASS**.

5. Present the output:

```
CODEX SAYS (code review):
════════════════════════════════════════════════════════════
<full codex output, verbatim — do not truncate or summarize>
════════════════════════════════════════════════════════════
GATE: PASS                    Tokens: 14,331 | Est. cost: ~$0.12
```

or

```
GATE: FAIL (N critical findings)
```

6. **Cross-model comparison:** If `/review` (Claude's own review) was already run
   earlier in this conversation, compare the two sets of findings:

```
CROSS-MODEL ANALYSIS:
  Both found: [findings that overlap between Claude and Codex]
  Only Codex found: [findings unique to Codex]
  Only Claude found: [findings unique to Claude's /review]
  Agreement rate: X% (N/M total unique findings overlap)
```

7. Persist the review result:
```bash
eval $(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)
BRANCH_SLUG=$(git rev-parse --abbrev-ref HEAD 2>/dev/null | tr '/' '-')
mkdir -p ~/.gstack/projects/$SLUG
echo '{"skill":"codex-review","timestamp":"TIMESTAMP","status":"STATUS","gate":"GATE","findings":N}' >> ~/.gstack/projects/$SLUG/$BRANCH_SLUG-reviews.jsonl
```

Substitute: TIMESTAMP (ISO 8601), STATUS ("clean" if PASS, "issues_found" if FAIL),
GATE ("pass" or "fail"), findings (count of [P1] + [P2] markers).

8. Clean up temp files:
```bash
rm -f "$TMPERR"
```

---

## Step 2B: Challenge (Adversarial) Mode

Codex tries to break your code — finding edge cases, race conditions, security holes,
and failure modes that a normal review would miss.

1. Create temp files:
```bash
TMPRESP=$(mktemp /tmp/codex-resp-XXXXXX.txt)
TMPERR=$(mktemp /tmp/codex-err-XXXXXX.txt)
```

2. Construct the adversarial prompt. If the user provided a focus area
(e.g., `/codex challenge security`), include it:

Default prompt (no focus):
"Review the changes on this branch against the base branch. Run `git diff origin/<base>` to see the diff. Your job is to find ways this code will fail in production. Think like an attacker and a chaos engineer. Find edge cases, race conditions, security holes, resource leaks, failure modes, and silent data corruption paths. Be adversarial. Be thorough. No compliments — just the problems."

With focus (e.g., "security"):
"Review the changes on this branch against the base branch. Run `git diff origin/<base>` to see the diff. Focus specifically on SECURITY. Your job is to find every way an attacker could exploit this code. Think about injection vectors, auth bypasses, privilege escalation, data exposure, and timing attacks. Be adversarial."

3. Run codex exec (5-minute timeout):
```bash
codex exec "<prompt>" -s read-only -o "$TMPRESP" 2>"$TMPERR"
```

4. Read the response and parse cost:
```bash
cat "$TMPRESP"
grep "tokens used" "$TMPERR" 2>/dev/null || echo "tokens: unknown"
```

5. Present:

```
CODEX SAYS (adversarial challenge):
════════════════════════════════════════════════════════════
<full response from $TMPRESP, verbatim>
════════════════════════════════════════════════════════════
Tokens: N | Est. cost: ~$X.XX
```

6. Clean up: `rm -f "$TMPRESP" "$TMPERR"`

---

## Step 2C: Consult Mode

Ask Codex anything about the codebase. Supports session continuity for follow-ups.

1. **Check for existing session:**
```bash
cat .context/codex-session-id 2>/dev/null || echo "NO_SESSION"
```

If a session file exists (not `NO_SESSION`), use AskUserQuestion:
```
You have an active Codex conversation from earlier. Continue it or start fresh?
A) Continue the conversation (Codex remembers the prior context)
B) Start a new conversation
```

2. Create temp files:
```bash
TMPRESP=$(mktemp /tmp/codex-resp-XXXXXX.txt)
TMPERR=$(mktemp /tmp/codex-err-XXXXXX.txt)
```

3. **Plan review auto-detection:** If the user's prompt is about reviewing a plan,
or if plan files exist and the user said `/codex` with no arguments:
```bash
ls -t ~/.claude/plans/*.md 2>/dev/null | head -1
```
Read the plan file and prepend the persona to the user's prompt:
"You are a brutally honest technical reviewer. Review this plan for: logical gaps and
unstated assumptions, missing error handling or edge cases, overcomplexity (is there a
simpler approach?), feasibility risks (what could go wrong?), and missing dependencies
or sequencing issues. Be direct. Be terse. No compliments. Just the problems.

THE PLAN:
<plan content>"

4. Run codex exec (5-minute timeout):

For a **new session:**
```bash
codex exec "<prompt>" -s read-only -o "$TMPRESP" 2>"$TMPERR"
```

For a **resumed session** (user chose "Continue"):
```bash
codex exec resume <session-id> "<prompt>" -s read-only -o "$TMPRESP" 2>"$TMPERR"
```

5. Capture and save session ID:
```bash
SESSION_ID=$(grep "session id:" "$TMPERR" | head -1 | awk '{print $3}')
[ -n "$SESSION_ID" ] && mkdir -p .context && echo "$SESSION_ID" > .context/codex-session-id
```

6. Read response and parse cost:
```bash
cat "$TMPRESP"
grep "tokens used" "$TMPERR" 2>/dev/null || echo "tokens: unknown"
```

7. Present:

```
CODEX SAYS (consult):
════════════════════════════════════════════════════════════
<full response from $TMPRESP, verbatim>
════════════════════════════════════════════════════════════
Tokens: N | Est. cost: ~$X.XX
Session saved — run /codex again to continue this conversation.
```

8. After presenting, note any points where Codex's analysis differs from your own
   understanding. If there is a disagreement, flag it:
   "Note: Claude Code disagrees on X because Y."

9. Clean up: `rm -f "$TMPRESP" "$TMPERR"`

---

## Cost Estimation

Parse token count from stderr. Codex prints `tokens used\nN` to stderr.
Estimate cost based on the model:
- gpt-5.2-codex: ~$0.008 per 1K tokens (estimate)
- o3: ~$0.01 per 1K tokens (estimate)

Display as: `Tokens: N | Est. cost: ~$X.XX`

If token count is not available, display: `Tokens: unknown`

---

## Error Handling

- **Binary not found:** Detected in Step 0. Stop with install instructions.
- **Auth error:** Codex prints an auth error to stderr. Surface the error:
  "Codex authentication failed. Run `codex login` in your terminal to authenticate via ChatGPT."
- **Timeout:** If the Bash call times out (5 min), tell the user:
  "Codex timed out after 5 minutes. The diff may be too large or the API may be slow. Try again or use a smaller scope."
- **Empty response:** If `$TMPRESP` is empty or doesn't exist, tell the user:
  "Codex returned no response. Check stderr for errors."
- **Session resume failure:** If resume fails, delete the session file and start fresh.

---

## Important Rules

- **Never modify files.** This skill is read-only. Codex runs in read-only sandbox mode.
- **Present output verbatim.** Do not truncate, summarize, or editorialize Codex's output
  before showing it. Show it in full inside the CODEX SAYS block.
- **Add synthesis after, not instead of.** Any Claude commentary comes after the full output.
- **5-minute timeout** on all Bash calls to codex (`timeout: 300000`).
- **No double-reviewing.** If the user already ran `/review`, Codex provides a second
  independent opinion. Do not re-run Claude Code's own review.