fix: filter stale hooks check to gsd-prefixed files only (#1200)

gsd-check-update.js scanned ALL .js files in the hooks directory and
flagged any without a gsd-hook-version header as stale. This incorrectly
flagged user-created hooks (e.g. guard-edits-outside-project.js),
producing a persistent 'stale hooks' warning that /gsd:update couldn't
resolve.

Fix: filter hookFiles to f.startsWith('gsd-') && f.endsWith('.js')
since all GSD hooks follow the gsd-* naming convention.

Includes regression test validating the filter excludes user hooks.

Closes #1200

hooks/gsd-check-update.js

@@ -70,7 +70,7 @@ const child = spawn(process.execPath, ['-e', `
     const hooksDir = path.join(configDir, 'hooks');
     try {
       if (fs.existsSync(hooksDir)) {
-        const hookFiles = fs.readdirSync(hooksDir).filter(f => f.endsWith('.js'));
+        const hookFiles = fs.readdirSync(hooksDir).filter(f => f.startsWith('gsd-') && f.endsWith('.js'));
         for (const hookFile of hookFiles) {
           try {
             const content = fs.readFileSync(path.join(hooksDir, hookFile), 'utf8');

tests/core.test.cjs

@@ -867,3 +867,33 @@ describe('normalizeMd', () => {
     assert.ok(result.includes('\n\n- Decision 1'), 'list needs blank line before');
   });
 });
+
+// ─── Stale hook filter regression (#1200) ─────────────────────────────────────
+
+describe('stale hook filter', () => {
+  test('filter should only match gsd-prefixed .js files', () => {
+    const files = [
+      'gsd-check-update.js',
+      'gsd-context-monitor.js',
+      'gsd-statusline.js',
+      'gsd-workflow-guard.js',
+      'guard-edits-outside-project.js',  // user hook
+      'my-custom-hook.js',               // user hook
+      'gsd-check-update.js.bak',         // backup file
+      'README.md',                       // non-js file
+    ];
+
+    const gsdFilter = f => f.startsWith('gsd-') && f.endsWith('.js');
+    const filtered = files.filter(gsdFilter);
+
+    assert.deepStrictEqual(filtered, [
+      'gsd-check-update.js',
+      'gsd-context-monitor.js',
+      'gsd-statusline.js',
+      'gsd-workflow-guard.js',
+    ], 'should only include gsd-prefixed .js files');
+
+    assert.ok(!filtered.includes('guard-edits-outside-project.js'), 'must not include user hooks');
+    assert.ok(!filtered.includes('my-custom-hook.js'), 'must not include non-gsd hooks');
+  });
+});