From Copilot's thirteenth pass of #1962. This PR added `verify:dep-lockstep`
to the vouch loop in `verify-format-coverage.mjs` without a test for it. The
existing tests exercise `rootReachesScript` in isolation and the opposite
direction (dep-lockstep vouching for format-coverage), so a typo in a sibling's
name here would have left `test:scripts` green while that guard silently
stopped being enforced — the same "a gate that stops gating" failure the
vouch cycle exists to prevent, one level up.
Three cases, reusing the fixture-repo approach: dropping either sibling from
`validate` exits 1 naming that sibling, and with both wired no sibling is
reported missing. The last asserts on the *reason* rather than the exit
status, since the fixture has no client manifests to harvest globs from and
so fails later for an unrelated reason.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HDdo1rNRVQnVRRdsqSrvG3
8a2035c4d1