[scanner] docs-threshold-parity guard does not pin the harness-floor flags — ratchets like #1319 drift AGENTS.md/CONTRIBUTING.md silently #1335

Finding

tests/docs-threshold-parity.test.mjs exists precisely to close the docs-drift class where a coverage-gate ratchet lands without updating contributor docs (#1037, #1169/#1189, #1193). But its enforcedThresholds() reads only four flags from test:unit:coverage:check — --check, --check-source, --check-regions, --check-source-regions — and its phrase regex only matches the "N% lines / N% source / N% regions / N% source regions" sentence.

The three harness-floor flags are outside its scope:

--check-harness 100 --check-harness-regions 99 --check-harness-file-regions 98

So when #1319 (commit 8766e9f) ratcheted --check-harness-regions 97→99 and --check-harness-file-regions 97→98, every test stayed green while AGENTS.md:54 and CONTRIBUTING.md:188 kept documenting the old 97/97 floors — the exact failure mode the parity test was built to prevent, one lane over. The stale docs are tracked in #1329; this issue is about the missing guard.

Steps to Reproduce / Evidence

• package.json:73 — gate enforces --check-harness 100 --check-harness-regions 99 --check-harness-file-regions 98
• tests/docs-threshold-parity.test.mjs — enforcedThresholds() maps only the four main flags; THRESHOLD_PHRASE matches only the four-number phrase
• tests/e2e-docs-threshold-parity.test.mjs — covers the e2e lane, also not the harness floors
• tests/coverage-report-harness-floor.test.mjs — pins harness-floor computation, not docs
• Verified no test references the harness flags alongside AGENTS.md/CONTRIBUTING.md at fb75c1a

Recommendation

Extend tests/docs-threshold-parity.test.mjs (or add a sibling harness-floor parity test) to:

1. Parse --check-harness, --check-harness-regions, and --check-harness-file-regions from test:unit:coverage:check.
2. Assert the tests/tools/ harness sentence in both AGENTS.md and CONTRIBUTING.md ("100% lines / N% regions, N% regions per harness file") matches those three values.

Then a future harness ratchet fails the suite until the docs move in the same commit. Best landed together with or immediately after the #1329 doc fix, since the new assertion would pin the corrected 99/98 text.

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