fix(gate-46): resolve anchors the way GitHub actually publishes them

[rubenvdlinde]

What

spec-anchor-existence (gate-46) kebab-cased headings with one rule: every run of non-alphanumerics becomes a dash. GitHub does something different — it drops punctuation inside a word instead of replacing it.

heading   A subscription's retry/backoff policy MUST be independently configurable (REQ-009)
GitHub    #requirement-a-subscriptions-retrybackoff-policy-must-be-independently-configurable-req-009
gate-46   #requirement-a-subscription-s-retry-backoff-policy-must-be-independently-configurable-req-009

So a @spec tag written against the anchor a reader actually clicks was reported unresolved.

Why it matters

On openconnector this was 137 findings, none of them real, and it was failing on development — not just on branches. A gate that reports 137 non-issues is one nobody reads, which is the failure mode where a real broken anchor hides in the noise.

The tempting fix — retagging 137 call sites to match the gate — would have made every one of those links stop working on GitHub.

What changed

Headings are matched against both shapes. The old kebab form is still accepted so tags written to satisfy it keep resolving; either way the heading must exist, which is what the gate is actually for.

Verification

Fixture with both controls:

• resolve: GitHub-shaped anchor, old kebab-shaped anchor, punctuation-free anchor
• still fail: a fragment naming a heading that does not exist, and a near-miss of a real one

On openconnector: 137 → 46 findings, and those 46 are genuine (target file missing, or fragment names nothing).

Gate suite: 25 entry-point tests pass, 17 helper suites pass, 2 pre-existing quarantines unchanged.