test: take Word re-saves of the corpus as a third author

corpus/word/ holds each document saved again by Word — rsids,
proofErr, separator notes, theme docDefaults — asserted to read like
the docx-lib original and survive our round trip. The formula fixture
is reauthored: a hand-wrapped MathNumerator doubled m:num/m:den, which
Word refuses to open, and the radical gets a visible degree.

CLAUDE.md

@@ -27,7 +27,7 @@ Tests live in `tests/` (outside `src/`, so `svelte-check` ignores them), jsdom v
 `roundtrip.test.ts` covers the ODF export↔import round trip + a foreign-doc/style-resolver leg;
 `lo-roundtrip.test.ts` re-saves through LibreOffice and **self-skips** without `soffice`, so
 `npm test`/CI stay green; `corpus.test.ts` round-trips the committed `tests/corpus/`
-documents (authored by `render-parity/make-fixtures.mjs`, never by our own exporter);
+documents (by `make-fixtures.mjs` + Word re-saves in `corpus/word/`, never our exporter);
 `fuzz-roundtrip.test.ts` round-trips seeded random documents (`fuzzDoc.ts` generator);
 `schema-validation.test.ts` validates the `kitchenSink.ts` exports against the vendored
 schemas in `tests/schemas/` (self-skips without `xmllint`); `package-lint.test.ts` checks the semantic invariants schemas can't express (unique ids, dangling references); `tests/unit/` holds fast helper tests. All test tooling stays a

tests/corpus.test.ts

@@ -58,6 +58,23 @@ describe.skipIf(!files.length)('the authored corpus', () => {
     });
   }
 
+  // Word re-saves of the same documents (tests/corpus/word/): Word rewrites the file
+  // in its own dialect — rsids, proofErr, separator notes, theme docDefaults — which
+  // neither the docx lib nor LibreOffice produce, so this is the third author here.
+  const WORD = join(FIX, 'word');
+  const wordFiles = existsSync(WORD)
+    ? readdirSync(WORD).filter((f) => /^\d\d-.+\.docx$/.test(f)).sort()
+    : [];
+  for (const f of wordFiles) {
+    it(`word/${f} reads like the original and survives the round trip`, async () => {
+      const doc = importDocx(new Uint8Array(readFileSync(join(WORD, f)))).content as N;
+      expect(outline(doc), 'matches the docx-lib original').toEqual(outline(importAny(f, load(f))));
+      const margins = { top: 2, bottom: 2, left: 2, right: 2 };
+      const again = importDocx(await buildDocx(doc, margins, 'portrait'));
+      expect(outline(again.content)).toEqual(outline(doc));
+    });
+  }
+
   // The same document in both formats, and each one exported as the other: the four
   // legs a document takes through this editor have to agree on what it says.
   for (const name of files.filter((f) => f.endsWith('.docx')).map((f) => f.slice(0, -5))) {

tests/render-parity/make-fixtures.mjs

@@ -12,7 +12,7 @@ import {
   Table, TableRow, TableCell, WidthType, convertMillimetersToTwip,
   Header, Footer, PageNumber, TabStopType,
   FootnoteReferenceRun, ImageRun, ExternalHyperlink, UnderlineType,
-  Math as DocxMath, MathRun, MathFraction, MathNumerator, MathDenominator, MathRadical,
+  Math as DocxMath, MathRun, MathFraction, MathRadical,
 } from 'docx';
 
 const OUT = join(dirname(fileURLToPath(import.meta.url)), '..', 'corpus');
@@ -265,9 +265,11 @@ await write('13-images.docx', [{
 }]);
 
 // 14. OMML formulas: one inline in the sentence, one alone on its line.
+// numerator/denominator take the runs directly — the lib mints m:num/m:den itself,
+// and a hand-wrapped MathNumerator doubles the element, which Word refuses to open.
 const frac = () => new MathFraction({
-  numerator: [new MathNumerator([new MathRun('a')])],
-  denominator: [new MathDenominator([new MathRun('b')])],
+  numerator: [new MathRun('a')],
+  denominator: [new MathRun('b')],
 });
 await write('14-formulas.docx', [{
   properties: { page },
@@ -278,7 +280,7 @@ await write('14-formulas.docx', [{
       new TextRun(' in the sentence.'),
     ] }),
     new Paragraph({ children: [new DocxMath({ children: [
-      new MathRadical({ children: [new MathRun('x')], degree: [] }), new MathRun('+1'),
+      new MathRadical({ children: [new MathRun('x')], degree: [new MathRun('3')] }), new MathRun('+1'),
     ] })] }),
     para(LOREM),
   ],