codex-mirror — the shared-canon mirror for Codex

The pain (found 2026-07-25): CLAUDE.md went through a v2 revision on 07-22, while ~/.codex/AGENTS.md quietly stayed on its June version — Codex worked off stale rules for a month, and the drift checker of that era was blind to the very same revision. The cure: the mirror is version-based (we compare versions, not shape), a watchdog shouts at night, and this skill is the cheap "rebuild" button so that the shouting doesn't turn into evening manual labour.

Roles (AK-47): the script moves the bytes and checks everything; I only write the text of the new rules. Do not retype the file by hand and do not eyeball the byte count.

Engine: python %USERPROFILE%\.claude\scripts\codex_mirror.py <check|backup|stamp|publish|selftest>

Step 0 — RECALL + the frame

• Memory: [[canon-versioning-and-drift-watchdog]] (the class "the watchdog died silently together with the thing it watched"), [[codex-cli-install]], [[any-llm-vault-actor]], [[claude-md-compression-contract]].
• The mirror = a canon edit → only the owner's machine in a live session; followers are receive-only ([[machine-governance-leader-follower]]).
• The 32 KiB cap is hard (DR 06-29: "lost in the middle" — a bloated file is WORSE than an empty one). The mirror = a distillation + pointers, NOT a copy of CLAUDE.md.

Step 1 — What exactly is stale

python %USERPROFILE%\.claude\scripts\codex_mirror.py check

Prints both versions, the headroom left before the cap and the delta from CLAUDE.CHANGELOG.md — exactly the entries that appeared after the mirror's version. That is the work list; you don't need to read all of CLAUDE.md.

• VERDICT: OK → leave, nothing to do.
• PATCH lag only → green by design; write it in only if the micro-edit changes BEHAVIOUR (thresholds, gates), not wording.
• REBUILD → carry on.

Step 2 — The safety net

python %USERPROFILE%\.claude\scripts\codex_mirror.py backup

Snapshot into ~/.codex/_backup/AGENTS.md.pre-<version>-<date-time>. Rollback = copy it back.

Step 3 — Write in the delta (the only step where I think)

For every delta entry:

1. Find the matching § in the mirror (the mirror's numbering mirrors CLAUDE.md's, so canon §8.4 lives in mirror §8.4).
2. Write the rule in the mirror's style: a bold **§X.Y ...** + the essence in 1-3 sentences + a pointer to the canon in the vault. Do not copy bodies.
3. A rule about people/the outside world (the house rulebook) — one line with a pointer; a rule about the Claude harness (skills/hooks) — translate into a principle, Codex has none of those mechanisms.
4. If the rule is entirely about Codex itself (the reviewer role, Windows pitfalls, protected zones) — its home is the CODEX BLOCK C1-C6, not the § part.

⚠️ Headroom before the cap is tiny (as of 07-26 — 37 bytes). New material fits only as a trade: squeeze the most bloated paragraph of the SAME § section, don't cut the TOP-20 and don't drop whole rules. Doesn't fit even then → that is the signal for a full mirror revision (as on 07-25: 137 KB → 32.7 KB), not for going "just a little" over the cap.

Step 4 — Stamp + publish

python %USERPROFILE%\.claude\scripts\codex_mirror.py stamp
python %USERPROFILE%\.claude\scripts\codex_mirror.py publish

stamp rewrites the > MIRRORS: ... line from the LIVE canon (version, date, md5, host) — never touch it by hand. publish runs the gates (cap · stamp vs canon · 17 anchors ## §0..§10 + ### C1..C6), then copies into $IMPORTS_ROOT\codex-canon\, verifies md5 and runs lint_agents_mirror.py. Any FAIL = nothing was copied; fix and repeat.

Step 5 — Proof and homes

• A live Codex run: codex exec -s read-only --skip-git-repo-check "quote §<new number> from your instructions" — does it actually read the new rule.
• External eyes per the /tt rule: secondop.py t3 --ritual tt (Codex itself as the breaker) — if the engine changed, not just the mirror text.
• A node that has Codex but is not the hub: run lint_agents_mirror.py locally there too (a line in codex-onboard-checklist.md).
• The rule changed the collaboration CONTRACT (what Codex may / may not do) → update ~/.codex/CODEX-COLLABORATION.md + the copy in the shared folder, not only the mirror.

Boundaries and accepted limitations

• ⛔ Don't edit CLAUDE.md with this skill (that is /intake for a rule and /canon-revision for structure); the mirror follows the canon, never leads it.
• ⛔ Don't run it on other people's machines: only the owner's hub rebuilds the canon.
• Accepted: an edit to the mirror body WITHOUT a stamp change is not caught by the watchdog (receive-only governance keeps that hole closed organisationally). We are not building a second watchdog — [[gate-implement-critical-only]].
• The cap and the anchors are the truth inside the engine's code (CAP, ANCHORS); a mismatch between code and this text is a bug in the code.
• Relatives: /arch (the nightly rail where the watchdog lives) · /secondop (Codex as reviewer) · /canon-revision (revising the canon itself) · /follower-onboard (a new node).

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