docs-only PRs pay the full two-OS build+test matrix — add a fail-closed inert-path skip gate

docs-only PRs pay the full two-OS build+test matrix — add a fail-closed inert-path skip gate

Evidence (2026-08-16, measured on PR #239 — a record-only change)

check (macos) 2m31s + check (ubuntu) 1m57s + smoke 20s + zizmor 10s + gitleaks 6s + record-lint 4s, all ruleset-required. For a docs-only PR the only strictly needed work is: gitleaks (docs can leak secrets), the reviews-charter record-lint, attribution, and the check job's last two steps — go run ./cmd/record-lint and go run ./cmd/abcd docs lint — which compile most of the module anyway (the gates ARE the binary; a zero-build docs lane is structurally impossible). Skippable on inert changes: the full test suite, race tests, vet, the entire macOS leg, smoke, and zizmor (unless .github/** changed).

Design constraints (settled or recorded)

• Fail-closed classifier only. The 2026-08-15 decision records that a "no source touched" test FAILS OPEN here: commands/*.md, hooks/hooks.json, .abcd/*.json, and the rules router are markdown/ JSON that change behaviour. Skip only when EVERY changed file matches a narrow inert allowlist (docs/**, .abcd/development/**, .abcd/work/**, root markdown); anything else runs the full matrix.
• All seven check contexts are ruleset-required, so workflow-level paths: filtering wedges PRs (never-reporting checks block). The viable shape is a changes classifier job + job-level if: on downstream jobs; skipped jobs report a skipped conclusion, documented as satisfying required checks — MUST be verified on a rehearsal PR before auto-merge relies on it (loud-staging: no assumed green).
• ci.yml is not scaffold-coupled (parity test pins release workflows only). Typed link: a proven skip gate refines what itd-106 (abcd scaffolds required CI per repo) would ship to managed repos.
• Repo is public — Actions minutes are free; the win is wall-clock / auto-merge latency (~2.5-3 min → ~1 min) and queue pressure, not money.
• CI config changes need explicit maintainer sign-off before landing.

Related: iss-233 (duplicate push+PR runs) is the cheaper, independent first fix — do it regardless of this one.