codex-ab

Codex Panel A/B (contributor instrument — verdict decided)

Answer one question with evidence: do dimension-focused codex passes find real issues that one holistic codex exec review misses? Runs both on the same diff, then classifies every focused finding against the holistic pass.

DECIDED 2026-07-10 after 4 runs (2 fresh): panel KILLED. Fresh-only 1 real miss / 1 false positive plus one zero-value run at 4× cost — real misses did not outnumber FPs. Kept as contributor tooling (NOT distributed) for one possible retest: a UI-heavy diff with a single extra liveview-focused pass (2× cost). Scoreboard: .claude/research/2026-07-03-codex-review-integration.md §7.

Usage

/codex-ab            # A/B against main (~5 min, 4 codex runs)
/codex-ab develop    # explicit base branch

Iron Laws

1. FRESH DIFF ONLY — ask the user to confirm this branch has NOT been codex-reviewed yet (cloud or /phx:codex-loop). A drained diff returns NO FINDINGS everywhere and proves nothing — wasted quota
2. Verify every REAL MISS in the code before counting it — a focused finding only scores if the issue actually exists at that file:line
3. Read ONLY the findings .md files — streams are diverted to .log files; never cat a log into context (10k+ lines each)
4. Exactly 4 codex runs, never re-run dimensions — bounded quota
5. Persist the verdict — an unrecorded experiment is wasted quota

Workflow

Step 1: Preflight

Run command -v codex — missing → STOP with install hint. Then:

• git status --short dirty → warn (codex flags local dirt as findings)
• Ask: "Has codex already reviewed this branch (PR review or codex-loop)?" If yes → STOP, explain the fresh-diff requirement (Iron Law 1)

Step 2: Run the A/B (background, ~5 min)

bash ${CLAUDE_SKILL_DIR}/scripts/codex-panel-ab.sh {base} \
  .claude/reviews/codex-ab-$(date +%Y-%m-%d-%H%M)

Use run_in_background — it runs 1 holistic codex exec review + 3 focused codex exec workers (security / ecto / liveview) in parallel, all streams redirected. Do other work or wait; never poll.

Step 3: Classify

Read the 4 findings files (holistic.md, security.md, ecto.md, liveview.md — small). For EACH focused finding:

Class	Meaning	Test
DUPLICATE	Holistic already found it	Same file + same defect
REAL MISS	Genuine issue holistic missed	Read the code at file:line — defect confirmed (Iron Law 2)
FALSE POSITIVE	Manufactured, pre-existing, or wrong	Code check fails, or issue exists on base branch too

Step 4: Verdict

Present:

## Codex Panel A/B — {branch} vs {base}
| dimension | findings | duplicate | real miss | false positive |
Holistic-only findings: {n}
Verdict this run: {REAL MISS count} real miss vs {FP count} false positive
Decision rule: build --codex-panel only if real misses outnumber false
positives across 2-3 fresh branches.

Write the verdict table to .claude/reviews/codex-ab-{date}/VERDICT.md. Suggest repeating on the next 1–2 fresh branches before deciding.

Integration

fresh branch → /codex-ab (YOU ARE HERE) → verdict logged
   ├─ real misses win across runs → build /phx:review --codex-panel
   └─ duplicates/FPs win → keep holistic /phx:codex-loop, drop panel idea
       └─ OUTCOME 2026-07-10: this branch won — panel dropped

References

• ${CLAUDE_SKILL_DIR}/scripts/codex-panel-ab.sh — the 4-run harness
• Related: /phx:codex-loop (holistic fix loop), /phx:review --codex