diff --git a/skill/scripts/hook-admin.mjs b/skill/scripts/hook-admin.mjs
index ac3363d27..5a0c29abd 100644
--- a/skill/scripts/hook-admin.mjs
+++ b/skill/scripts/hook-admin.mjs
@@ -223,7 +223,11 @@ function writeHookConfig(cwd, hookConfig, opts = {}) {
   // (consent, quiet, auditLog) survive an Impeccable hooks edit.
   const next = { ...existing, hook: { ...existingHook, ...hookConfig } };
   if (Object.keys(legacyDetector).length > 0) {
-    next.detector = mergeDetectorConfig(detectorSection(existing), mergeDetectorConfig(legacyDetector));
+    const existingDetector = detectorSection(existing) || {};
+    next.detector = {
+      ...existingDetector,
+      ...mergeDetectorConfig(existingDetector, mergeDetectorConfig(legacyDetector)),
+    };
   }
   fs.mkdirSync(path.dirname(filePath), { recursive: true });
   fs.writeFileSync(filePath, JSON.stringify(next, null, 2) + '\n');
diff --git a/tests/hook.test.mjs b/tests/hook.test.mjs
index 87c55183a..18012f5c7 100644
--- a/tests/hook.test.mjs
+++ b/tests/hook.test.mjs
@@ -1026,7 +1026,10 @@ describe('hook-admin.mjs', () => {
     fs.mkdirSync(path.dirname(getConfigPath(cwd)), { recursive: true });
     fs.writeFileSync(getConfigPath(cwd), JSON.stringify({
       hook: { advisoryRules: 'include' },
-      detector: { advisoryRules: 'exclude' },
+      detector: {
+        advisoryRules: 'exclude',
+        extensions: [{ ext: '.blade.php', engine: 'html' }],
+      },
     }));
 
     runAdmin(['on']);
@@ -1034,6 +1037,7 @@ describe('hook-admin.mjs', () => {
     const config = JSON.parse(fs.readFileSync(getConfigPath(cwd), 'utf-8'));
     assert.equal(config.hook.advisoryRules, undefined);
     assert.equal(config.detector.advisoryRules, 'exclude');
+    assert.deepEqual(config.detector.extensions, [{ ext: '.blade.php', engine: 'html' }]);
   });
 
   it('ignore-file refuses unsupported reasons and unknown flags', () => {