Three layers of defense against the dtolnay-SHA-class bug reaching main
(today's incident: agent SHA-pinned dtolnay/rust-toolchain with a pin
that was real but semantically wrong — lost 'install current stable'
meaning, locked to rust 1.94.1 branch tip, broke CI).
Layer 1 — actionlint static lint
scripts/install-actionlint.sh (65 LOC) — installs rhysd/actionlint
v1.7.12 [VERIFIED] to ~/.local/bin or suggests brew install.
scripts/lint-workflows.sh (40 LOC) — runs actionlint on
.github/workflows/*.yml, exit 0 on clean, advisory when binary
missing.
Layer 2 — SHA existence check (today's bug class)
scripts/validate-workflow-shas.sh (98 LOC) — extracts every
'uses: <repo>@<40-hex>' from workflow files + dependabot.yml,
checks each via GitHub REST commits API (exit 200/404/422).
Supports 'validate-workflow-shas: skip=<reason>' trailing
comment for intentional exceptions. Falls back to anonymous
API (60/hr quota) if GITHUB_TOKEN probe fails.
DESIGN PIVOT from spec: spec said 'git ls-remote <repo> <sha>'
but that only resolves REFS (branch/tag tips), not arbitrary
commit SHAs — would have given false-positive 100% MISSING
report. Switched to REST API /commits/{sha} for unambiguous
200/404/422.
Layer 3 — CI gate
.github/workflows/ci.yml — new 'workflow-lint' job after
shell-lint. Installs actionlint + runs both scripts on every
push to main and PR. Blocks CI on any fabricated SHA.
Layer 4 — optional pre-commit hook
scripts/pre-commit-workflow-lint.sh (54 LOC) — detects staged
.github/workflows/*.{yml,yaml} + .github/dependabot.yml
changes, runs layers 1+2, blocks commit on failure.
Install via: ln -sf ../../scripts/pre-commit-workflow-lint.sh
.git/hooks/pre-commit
REAL EXECUTION VERIFIED (not claim-only):
- actionlint ran: zero findings on current workflows
- validate-workflow-shas.sh ran: 21 SHA pins checked, 21 OK,
0 MISSING (confirms all current v0.19.1+ pins resolve)
- bash -n on every new script: clean
- bash-3.2 parser bug workaround: case-in-subshell → grep -E
RULE 0.2 exception #6 (shell is external convention for git hooks
+ GH Actions runs — Rust rewrite would add zero value).
RULE 0.13 respected — no git invocations except read-only API calls.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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