test(coverage): score and enumerate the tests/helpers*.mjs harness modules

[hivecommons-hive]

Test Improvement

tests/tools/coverage-report.mjs treated tests/tools/ as the whole of the harness. SOURCE_ROOTS is a list of trees, so the shared helper modules that sit directly in tests/ could be named by neither --require-source-files nor the --check-harness* floors — 1,348 lines of the measuring apparatus (the script and gh sandboxes, the fetch mock, the JSX driver, the JSONC reader) enumerated and scored by nothing. A helper nothing imports produced no coverage record, and a file with no record is absent from the report rather than 0%.

What this changes

• isHarnessModule() — the file-level companion SOURCE_ROOTS cannot be: /^tests\/helpers[\w.-]*\.mjs$/, minus .test.mjs. The suite's own tests are what the harness is measured against, not part of it.
• isHarnessFile() matches it as well as HARNESS_ROOTS, so the helpers enter the harness files row and its three floors.
• enumerateSourceFiles() lists them one level deep beside the walked trees — guarded against symlinks and a missing tests/ exactly as the walk is — so --require-source-files fails on a helper nothing imports.
• The two comment blocks the issue names are updated so the stated scope and the code still agree.

Contract

New tests/coverage-report-harness-modules.test.mjs (6 tests): what the predicate matches and does not, that a helper is harness but never source, that the enumeration lists helpers and skips .test.mjs/nested/non-module/symlinked paths, that a missing tests/ is an absence rather than a throw, that an unimported helper is a missing source file, and that the predicate is not vacuous in this repository.

tests/coverage-report-source-files.test.mjs asserted that nothing under tests/ outside tests/tools/ was enumerated. That assertion is narrowed to its actual intent — no *.test.mjs, nothing that is not harness — and gains a positive check that a helper module is listed.

Arithmetic, which is why this landed now

Issue #1258 deferred itself because the then-minimum per-file harness region percentage (96.67%) would have gone red against #1250's ratchet to 97. #1250 is merged, and at 4184f33 the minimum is tests/helpers-script-sandbox.mjs at 97.06, which clears --check-harness-file-regions 97. No floor in package.json is changed by this PR.

Verified locally at 4184f33, node v26.10.0, TZ=UTC, npm ci:

• npm run test:unit:coverage:check → exit 0.
  • src files | 100.00 | 100.00 | 9135/9135 lines | 2753/2753 regions (unchanged)
  • harness files | 100.00 | 99.41 | 5315/5315 lines | 1869/1880 regions (was 3911/3911 lines, 1471/1481 regions — the helper tree is now scored)
• npm run check:format → All matched files use Prettier code style!

Related Issue

Closes #1258 — all three boxes in that issue's task list are implemented here, and nothing in it is left for the issue to track.

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Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88

[hivecommons-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will keep the hold label until a human removes it. Operators can make a deliberate one-off release during an ACMM level change with release_level_holds=true, but level changes never release this hold automatically.