test: add regression test for frontmatter parse noise suppression

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/tests/frontmatter-parse-noise.test.ts

@@ -0,0 +1,42 @@
+/**
+ * Regression test for #3693 — suppress repeated frontmatter parse warnings
+ *
+ * parseFrontmatterBlock was logging a YAML parse warning on every call.
+ * The fix adds a _warnedFrontmatterParse flag so the warning only fires once.
+ */
+
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const prefsSrc = readFileSync(
+  join(__dirname, '..', 'preferences.ts'),
+  'utf-8',
+);
+
+describe('frontmatter parse noise suppression (#3693)', () => {
+  test('_warnedFrontmatterParse flag is defined', () => {
+    assert.match(prefsSrc, /_warnedFrontmatterParse/,
+      '_warnedFrontmatterParse flag should exist in preferences.ts');
+  });
+
+  test('parseFrontmatterBlock function exists', () => {
+    assert.match(prefsSrc, /function parseFrontmatterBlock\(/,
+      'parseFrontmatterBlock function should be defined');
+  });
+
+  test('flag is checked before warning', () => {
+    assert.match(prefsSrc, /if\s*\(\s*!_warnedFrontmatterParse\s*\)/,
+      'should check !_warnedFrontmatterParse before logging');
+  });
+
+  test('flag is set to true after first warning', () => {
+    assert.match(prefsSrc, /_warnedFrontmatterParse\s*=\s*true/,
+      'should set _warnedFrontmatterParse = true after warning');
+  });
+});