Hook-file existence guard (settings.json ↔ disk integrity) — MC #103640

Hook-file existence guard (settings.json ↔ disk integrity)

Book: System Architecture Status: Implemented + self-verified — MC #103640 (2026-06-15) Commits: 7408f0170 (restore 22 hooks, ~/.claude) · 8f7b8e602 (existence guard, ~/system)

Incident that motivated this

On 2026-06-15 the CEO flagged that "someone did stupid things with skills/hooks." Tool-forensics found ~/.claude/settings.json registered 76 hook entries while 22 of the referenced gate FILES did not exist on disk (absent from ~/.claude, ~/system, and ~/backups). Every tool call was invoking non-existent gates → silently dead enforcement.

Root cause (per the CEO's own commit 568e9cee0 / MC #103627): a "previous session had left a no-op stub" — a prior session stubbed/deleted registered hooks. The files were never removed by a tracked commit (git log --diff-filter=D empty on the HEAD line); they lived only as working-tree files synced from [BACKUP] commits and vanished from disk.

Missing gates included critical security/claim enforcers: secret-scanner, git-author-guard, alai-claim-gate, evidence-contract-validator, pre-publish-claims-gate, john-determinism-gate, claim-auto-probe-gate, +15.

Why it went undetected

lint-hooks.sh verified that REQUIRED hooks were registered in settings.json (correct event / matcher / ordering, via substring match) — but it never checked that each registered hook's script file actually exists on disk. The daily com.john.hook-drift-detector-v2 runs lint-hooks.sh, so the same blind spot meant the daily drift detector also missed it.

The fix

Restore — all 22 missing gate hooks restored from canonical git history (5f7dc6ad5 MC#99730, 79f92e3f9 MC#99197, dated auto-backups) → commit 7408f0170. Audit went 22 → 0 missing.
Guard (lint-hooks.sh) — new EXISTENCE pass extracts every hook command's script path (/Users/* and ~/* .sh/.py/.js) and verifies os.path.exists. Missing → FAIL, counted into the summary and exit 2. Because the daily drift detector already runs lint-hooks.sh, this is enforced daily with no new schedule.
Boot surface (boot.sh) — SessionStart "Hook integrity" check prints EXISTENCE N present / N referenced and lists any MISSING-on-disk files via ok()/fail(), so the CEO sees it at every boot.

Verification

bash -n lint-hooks.sh / bash -n boot.sh → PASS.
Clean state: EXISTENCE 46 hook file(s) present / 46 referenced, 0 missing.
Regression: renamed secret-scanner.sh away → FAIL [file-exists:secret-scanner.sh] MISSING ON DISK + exit 2; file restored after test.
Closure passed restored gates live: mc-ready-gate.sh (evidence-json) → evidence-contract-validator.sh CONFIRMED → ZAKON #30 direct-probe gate.

Known separate drift (out of scope, logged)

userprompt-cost-guard.sh is not registered in UserPromptSubmit (a registration-drift, the inverse problem — file may exist but isn't wired). Surfaced by lint-hooks.sh as a pre-existing FAIL; tracked for follow-up.