Tightens the over-broad heading-walk detection: removes heading-walk
entirely and narrows fence-regex to require a multiline body ([\s\S]),
so single-line tests like /^```/ and /^###\s+/ are no longer flagged.
Grandfathers the 10 genuine section-collect sites across state.cts,
milestone.cts, audit.cts, and phase-lifecycle.cts with concrete reasons.
Adds 12 RuleTester tests (3 positive, 9 negative) to eslint-rules.test.cjs.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
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