gstack/codex/SKILL.md.tmpl

---
name: codex
preamble-tier: 3
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". (gstack)
voice-triggers:
  - "code x"
  - "code ex"
  - "get another opinion"
triggers:
  - codex review
  - second opinion
  - outside voice challenge
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.

---

{{SECTION_INDEX:codex}}

---

## Step 0.4: Check codex binary

```bash
CODEX_BIN=$(command -v codex || echo "")
[ -z "$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"

If `NOT_FOUND`, also log the event:
```bash
_TEL=$(~/.claude/skills/gstack/bin/gstack-config get telemetry 2>/dev/null || echo off)
source ~/.claude/skills/gstack/bin/gstack-codex-probe 2>/dev/null && _gstack_codex_log_event "codex_cli_missing" 2>/dev/null || true
```

---

## Step 0.5: Auth probe + model probe + version check

Before building expensive prompts, verify Codex has valid auth, that the account
can actually USE gstack's selected model, AND the installed CLI version isn't in the
known-bad list. Sourcing `gstack-codex-probe` loads the shared helpers that both
`/codex` and `/autoplan` use.

If the user names a model for this request, set `GSTACK_CODEX_MODEL` to that model
before this probe and use it for every invocation in the request. The probe must
check the requested model, including when the frontier default is unavailable.

```bash
_TEL=$(~/.claude/skills/gstack/bin/gstack-config get telemetry 2>/dev/null || echo off)
source ~/.claude/skills/gstack/bin/gstack-codex-probe

# Running-under-Codex presence probe (#2519): a live Codex session exports
# CODEX_THREAD_ID / CODEX_SANDBOX into every shell it spawns.
if [ "${GSTACK_FORCE_CODEX_REVIEW:-0}" != "1" ] && { [ -n "${CODEX_THREAD_ID:-}" ] || [ -n "${CODEX_SANDBOX:-}" ]; }; then
  echo "UNDER_CODEX"
elif ! _gstack_codex_auth_probe >/dev/null; then
  _gstack_codex_log_event "codex_auth_failed"
  echo "AUTH_FAILED"
else
  _gstack_codex_model_probe   # ~10s round trip on first run, cached 1h (#2477)
fi
_gstack_codex_version_check   # warns if known-bad, non-blocking
```

If the output contains `UNDER_CODEX`, stop with exactly one line:
"[running under Codex — /codex would nest the same model at multiplied token
cost; skipped. Set `GSTACK_FORCE_CODEX_REVIEW=1` to force.]" The whole value
of this skill is a SECOND model's opinion; inside a Codex host it is the same
model reviewing itself, and nested spawns have burned 15M tokens in one
/review (#2519).

If the output contains `AUTH_FAILED`, stop and tell the user:
"No Codex authentication found. Run `codex login` or set `$CODEX_API_KEY` / `$OPENAI_API_KEY`, then re-run this skill."

If the output contains `MODEL_UNUSABLE`, stop — auth exists but the account
cannot use gstack's selected model (`GSTACK_CODEX_MODEL` or the `gpt-6-astra`
default). Relay the probe's HINT lines and
follow the "Model not supported (HTTP 400)" recovery steps in
`## Error Handling` below. Running the modes anyway just burns four
invocations on the same 400 (#2477).

`MODEL_PROBE_INCONCLUSIVE` is non-blocking (timeout/transient network): pass
the warning through and continue.

If the version check printed a `WARN:` line, pass it through to the user verbatim
(non-blocking — Codex may still work, but the user should upgrade).

The probe multi-signal auth logic accepts: `$CODEX_API_KEY` set, `$OPENAI_API_KEY`
set, or `${CODEX_HOME:-~/.codex}/auth.json` exists. Avoids false-negatives for
env-auth users (CI, platform engineers) that file-only checks would reject.

**Update the known-bad list** in `bin/gstack-codex-probe` when a new Codex CLI version
regresses. Current entries (`0.120.0`, `0.120.1`, `0.120.2`) trace to the stdin
deadlock fixed in #972.

---

## Step 0.6: Resolve portable roots

Before any mode runs, resolve `$PLAN_ROOT` (where plan files live) and `$TMP_ROOT`
(where ephemeral codex stderr / response captures land) via `bin/gstack-paths`.
This keeps the skill working whether installed as a Claude Code plugin
(`CLAUDE_PLANS_DIR` set), a global `~/.claude/skills/gstack/` install, or a CI
container where `HOME` may be unset and `/tmp` may be read-only.

```bash
eval "$(~/.claude/skills/gstack/bin/gstack-paths)"
```

After this, every subsequent bash block in this skill uses `"$PLAN_ROOT"` and
`"$TMP_ROOT"` rather than hardcoded `~/.claude/plans` or `/tmp/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 (with fallback if origin isn't available):
     `git diff origin/<base> --stat 2>/dev/null | tail -1 || git diff <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 scoped to the current project:
     `ls -t "$PLAN_ROOT"/*.md 2>/dev/null | xargs grep -l "$(basename $(pwd))" 2>/dev/null | head -1`
     If no project-scoped match, fall back to: `ls -t "$PLAN_ROOT"/*.md 2>/dev/null | head -1`
     but warn the user: "Note: this plan may be from a different project."
   - 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

The three modes are MUTUALLY EXCLUSIVE — at most one runs per invocation. Once
the mode is determined, read ONLY that mode's section (see the Section index
above); never read the other two mode sections.

**Reasoning effort override:** If the user's input contains `--xhigh` anywhere,
note it and remove it from the prompt text before passing to Codex. When `--xhigh`
is present, use `model_reasoning_effort="xhigh"` for all modes regardless of the
per-mode default below. Otherwise, use the per-mode defaults:
- Review (2A): `high` — bounded diff input, needs thoroughness
- Challenge (2B): `high` — adversarial but bounded by diff
- Consult (2C): `medium` — large context, interactive, needs speed

---

## Filesystem Boundary

Every prompt sent to Codex MUST be prefixed with this boundary instruction:

> IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. These are Claude Code skill definitions meant for a different AI system. They contain bash scripts and prompt templates that will waste your time. Ignore them completely. Do NOT modify agents/openai.yaml. Stay focused on the repository code only.

This applies to Challenge mode (prompt) and Consult mode (persona prompt), and to the
custom-instructions path of Review mode — all three use `codex exec`, which still takes
a free-form prompt argument. It does **not** apply to the default scoped `codex review`
call in Step 2A: that command is invoked with **no prompt argument at all** (see "Scope
flags exclude the prompt argument" in the Review mode section), so there is nowhere to put the preamble. That
is acceptable — `codex review --base` hands the model a pre-computed diff rather than
turning it loose on the filesystem, so the rabbit-hole risk the boundary guards against
is much lower on that path. Reference this section as "the filesystem boundary" in the
mode sections.

---

## Synthesis recommendation (REQUIRED) — all modes

Every mode ends by emitting ONE synthesis recommendation line after presenting
Codex's verbatim output, in the canonical format the AskUserQuestion judge grades:

```
Recommendation: <action> because <one-line reason that names the most actionable finding>
```

The reason must engage with a specific Codex finding or insight and compare
against an alternative (another finding, fix-vs-ship, fix order, or status-quo).
Boilerplate reasons ("because it's better", "because adversarial review found
things") fail the format. The recommendation is the ONE line a user reads when
they don't have time for the verbatim output. **Never silently auto-decide;
always emit the line.** Each mode section restates this rule with mode-specific
examples.

---

{{SECTION:review-mode}}

{{SECTION:challenge-mode}}

{{SECTION:consult-mode}}

{{PLAN_FILE_REVIEW_REPORT}}

{{EXIT_PLAN_MODE_GATE}}

---

## Model & Reasoning

**Model:** gstack defaults Codex invocations to the current frontier agentic coding
model via `{{CODEX_MODEL_CONFIG_FLAG}}` (currently `gpt-6-astra`). A user can override
the default for a shell with `GSTACK_CODEX_MODEL=<model>`, or for one request by naming a
model in the `/codex` prompt.
Native `codex review` also sets `review_model` to the selected model so a separate
review pin in the CLI config cannot override the request.

**Reasoning effort (per-mode defaults):**
- **Review (2A):** `high` — bounded diff input, needs thoroughness but not max tokens
- **Challenge (2B):** `high` — adversarial but bounded by diff size
- **Consult (2C):** `medium` — large context (plans, codebase), interactive, needs speed

`xhigh` uses ~23x more tokens than `high` and causes 50+ minute hangs on large context
tasks (OpenAI issues #8545, #8402, #6931). Users can override with `--xhigh` flag
(e.g., `/codex review --xhigh`) when they want maximum reasoning and are willing to wait.

**Web search:** All codex commands pass `{{CODEX_WEB_SEARCH_FLAG}}` so `codex exec`
invocations can look up docs and APIs during review. This is OpenAI's cached index —
fast, no extra cost. Unlike the legacy `--enable`-based spelling (deprecated by
codex >=0.144), the `-c` form explicitly overrides any top-level
`web_search` setting in `~/.codex/config.toml`. Note: native `codex review` disables
web search regardless of configuration, so on the default Review path the flag is a
harmless no-op — only exec-based modes actually search.

If the user specifies a model (e.g., `/codex review -m gpt-5.6-sol` or
`/codex challenge --model gpt-daybreak-blue-latest`), translate it to the same config
form and replace the default model flag with `-c "model=\"<model>\""`. Native review
also requires `-c "review_model=\"<model>\""`; replace both model values together.
Review mode runs `codex review`, which REJECTS `-m` (`error: unexpected argument '-m' found`,
verified on 0.147.0), while `-c model=...` is accepted by both `codex review` and
`codex exec`.

---

## Cost Estimation

Parse token count from stderr. Codex prints `tokens used\nN` to stderr.

Display as: `Tokens: N`

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 (Bash outer gate):** Every Bash gate sits ABOVE its inner wrapper (360s gate
  over the 330s review wrapper; 660s gate over the 600s challenge/consult wrappers), so
  the wrapper's exit-124 path normally fires first with its explicit message. If the Bash
  call itself times out anyway (wrapper unavailable AND codex hung), tell the user:
  "Codex timed out. The prompt may be too large or the API may be slow. Try again or use a smaller scope."
- **Timeout (inner `timeout` wrapper, exit 124):** If the shell `timeout 600` wrapper fires first, the skill's hang-detection block auto-logs a telemetry event + operational learning and prints: "Codex stalled past 10 minutes. Common causes: model API stall, long prompt, network issue. Try re-running. If persistent, split the prompt or check `~/.codex/logs/`." No extra action needed.
- **`the argument '[PROMPT]' cannot be used with '--base <BRANCH>'`:** a prompt argument
  leaked into a scoped `codex review`. This fails instantly, before any API call, so it
  looks like a hang-free "no output" — do not misread it as a model stall. Drop the
  prompt: the scope flags (`--base`, `--commit`, `--uncommitted`) carry the scope on
  their own. If the prompt was custom review instructions, run them through `codex exec`
  instead (Step 2A, custom-instructions path). Do **not** fix it by removing `--base` and
  keeping the prompt — that parses, but silently reviews the uncommitted working tree
  instead of the branch diff.
- **Review says "no changes" on a branch that clearly has changes:** the scope flag is
  missing or wrong. A prompt-only `codex review` defaults to uncommitted changes, so a
  clean working tree reads as an empty review even when `<base>...HEAD` is large. Confirm
  `--base <base>` is actually on the command line.
- **Model not supported (HTTP 400):** stderr shows
  `The '<model>' model is not supported when using Codex with a ChatGPT account`
  (a `status: 400` / `invalid_request_error` naming a model). This is a
  model-entitlement problem, not an auth or network failure, and the auth probe
  cannot catch it. Recovery, in order:
  1. Check whether `GSTACK_CODEX_MODEL` is set. If so, update it to a model the
     account can use.
  2. If no override is set, gstack defaults to `gpt-6-astra`. If the account cannot
     use it yet, set `GSTACK_CODEX_MODEL=<supported-model>` or replace the default
     flag with `-c "model=\"<supported-model>\""`.
  3. If Codex printed `[notice.model_migrations]`, use that replacement model.
  Never present this as a model stall or a PASS — it is a fail-closed gate result.
- **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.
- **Bash gate above the wrapper.** Every Bash call to codex sets its `timeout`
  parameter ABOVE the inner `_gstack_codex_timeout_wrapper` budget (Review:
  `timeout: 360000` over the 330s wrapper; Challenge/Consult: `timeout: 660000`
  over the 600s wrappers) so the wrapper fires first with a diagnosable exit 124.
- **No double-reviewing.** If the user already ran `/review`, Codex provides a second
  independent opinion. Do not re-run Claude Code's own review.
- **Detect skill-file rabbit holes.** After receiving Codex output, scan for signs
  that Codex got distracted by skill files: `gstack-config`, `gstack-update-check`,
  `SKILL.md`, or `skills/gstack`. If any of these appear in the output, append a
  warning: "Codex appears to have read gstack skill files instead of reviewing your
  code. Consider retrying."