Adds a repo-invariant check in the same 'Assert' block as the ADR-012 birpc guard. Anchored to YAML `uses:` lines so the inline self-test fixture does not false-positive. Fails with an actionable error referencing ADR-014 / #557. Guard is intentionally RED at this commit — the three v4 call sites are downgraded in the next commit. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>