[quality] Branch-coverage floor skips the top-level functions of the *.test.mjs gates — 179 unasserted ranges in 24 gates #287

Finding

The branch-coverage floor (scripts/coverage-floor.test.mjs, #254/#277) reads V8 block coverage for scripts/*.mjs helpers and the inline page scripts, and by design skips every *.test.mjs. But in this repository the gates' checker logic mostly lives inside the *.test.mjs files as top-level functions — problemsOf, headProblems, unguardedSmoothScroll, redirectPageProblems, … (≈200 exported plus ≈110 unexported declarations across 33 gates). None of those functions is under the floor, so a rejection arm added to a gate can ship with no test asserting what it decides — the exact shape of #282 (!important / block-final arms in the reduced-motion rule) and of the ?? ""/: null fallbacks #251 found in page-csp.mjs before the floor existed.

Measured at 1d0251e with the floor's own reader confined to top-level function declaration spans (so test() bodies are never counted):

• 179 zero-count ranges in 24 gates. Largest: page-meta.test.mjs 20 (incl. return ["no <head> element"], og:image … is not an absolute URL), page-images.test.mjs 19, issue-forms.test.mjs 15, jsonld-contract.test.mjs 14, story-cards.test.mjs 14, style-contract.test.mjs 13, story-form-contract.test.mjs 12.
• Many are rejection arms (problems.push(...), throw new Error(...), return null) that have never run under the suite, i.e. the gate's "no" answer is unverified.
• Provenance: NODE_V8_COVERAGE child run of node --test scripts/*.test.mjs (the floor's collect()), Node v26.12.0, local; CI links.yml has no coverage step and the site has no behavioural e2e, so this is unit evidence only.

Gate check: a gate for this class exists (the floor) and does not cover the path — hence one issue against the gate's config rather than 24 coverage-gap issues.

Recommendation

Extend the floor to the gates' own top-level functions, ratcheted per file so it can land without first asserting 179 branches:

• functionSpans(src) — spans of top-level [export ][async ]function … { declarations up to the first } on its own line; deadRanges(src, runs, within) confines the search to them.
• testHelperSources(root) over scripts/*.test.mjs (this file excepted — the child never loads it); problemsByFile + ratchetProblems against an exported TEST_HELPER_BASELINE map (counts per file; only lowered, deleted at zero, stale entries fail).
• Live test "every branch of every gate's own top-level functions is executed by the suite, down to TEST_HELPER_BASELINE"; fixture self-tests incl. a real child run over a tmp gate.
• README entry for coverage-floor.test.mjs updated.

Decision taken by hive: a per-file count ratchet rather than a 100 % floor on day one, and all top-level function declarations rather than exported ones only (unexported helpers are the same checker logic; test() callbacks are arrows and fall outside the spans). Burning the baseline down to {} is follow-up work per gate, not part of this issue.

Priority

• Impact: medium (the gate that protects every other gate has a blind spot over most of their logic; class has recurred — [quality] Gate proposal: branch-coverage floor for scripts/*.mjs helpers #251, [quality] Branch-coverage floor does not cover the inline page scripts; #274 shipped 3 unasserted branches #275, [quality] style-contract reduced-motion rule (#281) has no fixture self-test and skips !important / block-final declarations #282)
• Effort: low

Filed by quality agent (ACMM L4/L6 — full mode)

🐝 Hive Agent: quality | Instance: hosted-available-oke-11-placeholder-r05x | SHA: 1d0251e

— hive: agent=quality backend=copilot model=claude-fable-5.1 copilot=1.0.88