fix(docx-compare): filter header/footer relationships from sectPrChange snapshots

[stevenobiajulu]

Consequence first

The sole tagged comparison spine emits schema-invalid section-property change snapshots when the prior section has header/footer relationships. A conforming consumer sees w:headerReference or w:footerReference inside the historical w:sectPr nested under w:sectPrChange, but that inner element is CT_SectPrBase and cannot contain relationship-bearing header/footer references.

This is not an ordering defect and is not part of #941's paragraph-move markup scope.

Reproduction on current main

Reproduced at 6a7bb7a35178153cc0e971285b2dc7421a8478df using only the repository's public ILPA fixtures:

• tests/test_documents/redline/ILPA-Model-Limited-Partnership-Agreement-WOF_v2.docx
  • SHA-256 7880ad250513d23be064a5c71ef79aecb2bf3d870c45fa070256d5388ac74455
• tests/test_documents/redline/ILPA-Model-Limited-Parnership-Agreement-Deal-By-Deal_v1.docx
  • SHA-256 46be28b42853da50eba3e24df944d04dd34893f56539258d53bd69b4b33547d7

Compare those files with compareDocuments() using a fixed author/date, extract word/document.xml, apply the repository's MCE preprocessing, and validate with:

xmllint --noout --nonet \
  --schema spec-compliance/ecma-376/validation/wml-document-transitional.xsd \
  document.xml

There are exactly 6 first-failure schema diagnostics in this class. One representative emitted shape is:

<w:sectPrChange w:id="1480" w:author="Public Investigation" w:date="2026-08-23T00:00:00Z">
  <w:sectPr>
    <w:footerReference w:type="even" r:id="rId56"/>
    <w:footerReference w:type="default" r:id="rId50"/>
    <w:pgSz w:w="12240" w:h="15840"/>
  </w:sectPr>
</w:sectPrChange>

The other first failures are in comparison-authored w:sectPrChange revisions 1915, 20075, 20161, 20446, and 20485.

Schema premise

The vendored Transitional WML schema establishes:

• CT_SectPrChange contains an optional w:sectPr of type CT_SectPrBase (wml.xsd:959-967).
• CT_SectPrBase contains only EG_SectPrContents (wml.xsd:1636-1641).
• Only live CT_SectPr adds EG_HdrFtrReferences before those contents (wml.xsd:1642-1649).

So header/footer references are legal in the live outer w:sectPr, not in its prior-state snapshot.

Root-cause localization

packages/docx-compare/src/tagged/taggedTreeSerializer.ts clones every original section child except a prior sectPrChange in both snapshot paths:

• section-scope applyPropertyDelta (~552-570)
• paragraph-property sectPr delta (~653-668)

By contrast, packages/docx-core/src/primitives/track-changes-emitter.ts already excludes w:headerReference, w:footerReference, and nested w:sectPrChange from buildSectPrChangeElement snapshots (~16-20, ~245-285). The tagged path has drifted from that typed helper/policy.

Acceptance criteria

• Both tagged section-delta paths use one schema-derived/shared CT_SectPrBase snapshot policy.
• Inner w:sectPrChange/w:sectPr snapshots exclude w:headerReference, w:footerReference, and nested w:sectPrChange; live outer section references remain correctly relationship-bound.
• Header/footer relationship differences that cannot be represented by w:sectPrChange are explicitly surfaced as unrepresented rather than silently discarded.
• Minimized section fixtures plus the public ILPA pair validate against the vendored schema for this class.
• Accept All and Reject All preserve the intended section/header/footer projections and every retained relationship resolves to the correct part.
• Tests use the shared OOXML fixture helpers and carry the required ECMA-376 conformance citations.

Non-duplicates / related

• fix(docx-compare): emit schema-valid paragraph move markup #941 covers invalid paragraph move-range attributes and block paragraphs inside move wrappers; it does not cover CT_SectPrChange snapshots.
• docx-compare: section-break and header/footer differences are silently dropped — success with 0 insertions and 0 deletions #648 addressed previously invisible section/header/footer changes and was closed by fix(docx-comparison): expose inserted-section footer stories #744; this is a schema-invalid representation in the surviving tagged implementation.
• No editing surface for section properties (w:sectPr): cannot restart page numbering, change page setup, or insert a section break #654's core primitive is evidence for the correct snapshot filtering, not coverage of this comparison path.

No private or purchased-template document was accessed for this reproduction. Microsoft Word was not touched.

[stevenobiajulu]

Fresh public-fixture characterization September17: this remains reproducible on built main ca61878 and the separate #979 branch efa602b. Both source ILPA DOCX files validate against the vendored schema; comparison-emitted tracked and native Reject packages fail on historical section header/footer references, while native Accept validates. Baseline and #979 have the same failing class; the note repair does not introduce or fix it. All23 note bindings on Accept/Reject independently match corresponding sources through both native complete-package and AST projections. No full ILPA XSD-clean claim is made. Local proof: /private/tmp/979-ilpa-baseline-source-schema-20260917.log (2/5 invalid, baseline tracked/rejected only), /private/tmp/979-ilpa-manifest-schema-20260917.log (2/3 invalid, new tracked/rejected only), and /private/tmp/979-ilpa-note-manifest-audit-20260917.log. Replay script retained at /private/tmp/safe-docx-979-note-reader-20260917/.peer-review/ilpa-note-manifest-audit.mjs; ILPA_BASELINE_ROOT=/private/tmp/automerge-smoke-988-20260917 selects separately built main producer. This is the CT_SectPrBase type restriction already described above, not permission to fix it by silently dropping relationship projections. Word remains UNVERIFIED; no private fixtures used.