security(editor): upgrade Tiptap past GHSA-cp6q-959q-f8rh #413

Problem

Trivy on licensing PR #270 exact head 210284bb30661294a86f413581c26731c25d4b8a reports MEDIUM GHSA-cp6q-959q-f8rh in pnpm-lock.yaml. The lockfile resolves @tiptap/core@2.27.2; the GitHub Reviewed advisory marks versions before 3.30.4 affected. Its attack path is an own JSON-origin __proto__ key passed through mergeAttributes(), followed by inherited DOM attributes being serialized, which can execute an event handler.

Authoritative advisory: GHSA-cp6q-959q-f8rh

Owner repair contract

1. Add a browser/runtime RED regression using a JSON-origin own __proto__ key at the product's actual imported-document/plugin/API attribute boundary.
2. Prove the result retains the intended prototype, exposes no inherited attacker attributes, and cannot emit or execute an inherited event-handler attribute through the active ProseMirror serializer.
3. Upgrade the full compatible Tiptap package family to a release containing @tiptap/core>=3.30.4; do not patch only the lockfile or suppress the advisory.
4. Re-run editor unit/integration/browser tests, production build, license/NOTICE artifact contract, SBOM/provenance, and exact-head Security/SAST/CodeQL/Trivy gates.
5. Close only after the fix is integrated into the protected branch and an immutable release/consumer path is evidenced where applicable.

Separation from #270

#270 remains the canonical MIT/OFL artifact-evidence lane and must not hide this runtime vulnerability. Its separate Office Python 3.14 failure belongs to the existing Office support-contract writer #405; that failure is tests/test_python_support_contract.py::test_python_support_range_matches_classifiers_and_ci_matrix because the workflow matrix could not be parsed.