Export metadata edits (title, composer, source, encrypter) via patchScore

test-parser.mjs

@@ -403,6 +403,32 @@ ok('clean bar unchanged', barPatched.includes('beats_per_minute: 100'));
 ok('clean bar voice preserved', barPatched.includes('- D4 4'));
 ok('document separators preserved', (barPatched.match(/\n---\n/g) ?? []).length === 2);
 
+// ── patchScore metadata ────────────────────────────────────────────────────
+section('patchScore metadata');
+const META_SCORE = `title: Old Title
+composer: Old Composer
+source: Some Book
+
+instrument alpha:
+  character:
+    A: "1:0,10;1,0"
+`;
+const updatedInfo = { title: 'New Title', composer: 'New Composer', source: '', encrypter: 'Me' };
+const metaPatched = patchScore(META_SCORE, [], [], updatedInfo);
+ok('existing title replaced', metaPatched.includes('title: New Title'));
+ok('existing composer replaced', metaPatched.includes('composer: New Composer'));
+ok('empty value leaves existing line', metaPatched.includes('source: Some Book'));
+ok('new key prepended', metaPatched.includes('encrypter: Me'));
+ok('instrument block untouched', metaPatched.includes('instrument alpha:'));
+
+const META_SCORE_NO_TITLE = `composer: Bach\n\ninstrument ki:\n  character:\n`;
+const noTitlePatched = patchScore(META_SCORE_NO_TITLE, [], [], { title: 'Fugue', composer: 'Bach' });
+ok('missing title prepended', noTitlePatched.includes('title: Fugue'));
+ok('existing composer not duplicated', (noTitlePatched.match(/^composer:/mg) ?? []).length === 1);
+
+const nullInfoPatched = patchScore(META_SCORE, [], [], null);
+ok('null info leaves metadata unchanged', nullInfoPatched.includes('title: Old Title'));
+
 // ── Summary ────────────────────────────────────────────────────────────────
 console.log(`\n══ ${pass} passed, ${fail} failed ══\n`);
 process.exit(fail > 0 ? 1 : 0);