diff --git a/app/lib/desktop/wrapper_server.dart b/app/lib/desktop/wrapper_server.dart
index 220f26f..25c9ddb 100644
--- a/app/lib/desktop/wrapper_server.dart
+++ b/app/lib/desktop/wrapper_server.dart
@@ -35,7 +35,20 @@ class WrapperServer {
     required this.webRoot,
     required this.dataDir,
     required this.gitHubProxy,
-  });
+    bool? serveSyncAccount,
+    String? syncConfigDir,
+  }) : serveSyncAccount =
+           serveSyncAccount ??
+           (Platform.environment[kSyncAccountEnvVar] ?? '').isNotEmpty,
+       syncConfigDir =
+           syncConfigDir ??
+           p.join(Platform.environment['HOME'] ?? '', '.config', 'crdt-sync');
+
+  /// Whether the sync-account route answers; off unless explicitly enabled.
+  final bool serveSyncAccount;
+
+  /// Directory holding `firebase.json` and `password`.
+  final String syncConfigDir;
 
   /// Directory holding the built Flutter web assets.
   final String webRoot;
@@ -114,17 +127,12 @@ class WrapperServer {
   /// the same reasoning that keeps the GitHub token in [gitHubProxy] instead
   /// of the browser.
   Future<void> _syncAccount(HttpRequest request) async {
-    if ((Platform.environment[kSyncAccountEnvVar] ?? '').isEmpty) {
+    if (!serveSyncAccount) {
       request.response.statusCode = HttpStatus.notFound;
       return;
     }
-    final configDir = p.join(
-      Platform.environment['HOME'] ?? '',
-      '.config',
-      'crdt-sync',
-    );
-    final configFile = File(p.join(configDir, 'firebase.json'));
-    final passwordFile = File(p.join(configDir, 'password'));
+    final configFile = File(p.join(syncConfigDir, 'firebase.json'));
+    final passwordFile = File(p.join(syncConfigDir, 'password'));
     if (!configFile.existsSync() || !passwordFile.existsSync()) {
       stderr.writeln(
         'Sync account requested but ~/.config/crdt-sync/ is incomplete — '
diff --git a/app/test/desktop/wrapper_server_test.dart b/app/test/desktop/wrapper_server_test.dart
index b2039bf..a083ca7 100644
--- a/app/test/desktop/wrapper_server_test.dart
+++ b/app/test/desktop/wrapper_server_test.dart
@@ -7,6 +7,7 @@ import 'dart:io';
 
 import 'package:diet_guard_app/desktop/github_proxy.dart';
 import 'package:diet_guard_app/desktop/wrapper_server.dart';
+import 'package:crdt_sync/crdt_sync.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:http/http.dart' as http;
 import 'package:http/testing.dart';
@@ -20,7 +21,10 @@ void main() {
   late List<http.Request> outbound;
   late Map<String, http.Response> canned;
 
-  Future<void> startServer() async {
+  Future<void> startServer({
+    bool serveSyncAccount = false,
+    String? syncConfigDir,
+  }) async {
     outbound = [];
     canned = {};
     final proxy = GitHubProxy(
@@ -36,6 +40,8 @@ void main() {
       webRoot: webRoot,
       dataDir: dataDir,
       gitHubProxy: proxy,
+      serveSyncAccount: serveSyncAccount,
+      syncConfigDir: syncConfigDir,
     );
     await server.start(0);
   }
@@ -285,4 +291,59 @@ void main() {
       expect(typeOf('data.bin').mimeType, 'application/octet-stream');
     });
   });
+
+  group('sync-account provisioning', () {
+    /// Writes [files] into a temp config dir and restarts with the route on.
+    Future<String> enableWith(Map<String, String> files) async {
+      final configDir = Directory(p.join(tempDir.path, 'crdt-sync'))
+        ..createSync(recursive: true);
+      files.forEach((name, contents) {
+        File(p.join(configDir.path, name)).writeAsStringSync(contents);
+      });
+      await server.stop();
+      await startServer(serveSyncAccount: true, syncConfigDir: configDir.path);
+      return 'http://localhost:${server.port}';
+    }
+
+    test('is 404 when not enabled', () async {
+      // The default, and the whole security posture: a credential route must
+      // not be reachable just because the wrapper is running.
+      final response = await http.get(url(kSyncAccountPath));
+
+      expect(response.statusCode, HttpStatus.notFound);
+    });
+
+    test('serves the account when enabled', () async {
+      final origin = await enableWith({
+        'firebase.json': '{"email":"a@b.c"}',
+        'password': 'pw\n',
+      });
+
+      final response = await http.get(Uri.parse('$origin$kSyncAccountPath'));
+      final account = FirebaseAccount.tryParse(response.body);
+
+      expect(response.statusCode, HttpStatus.ok);
+      expect(account?.email, 'a@b.c');
+      expect(account?.password, 'pw');
+    });
+
+    test('is 404 when the config files are absent', () async {
+      final origin = await enableWith({});
+
+      final response = await http.get(Uri.parse('$origin$kSyncAccountPath'));
+
+      expect(response.statusCode, HttpStatus.notFound);
+    });
+
+    test('is 404 when firebase.json has no usable email', () async {
+      final origin = await enableWith({
+        'firebase.json': '{"apiKey":"x"}',
+        'password': 'pw',
+      });
+
+      final response = await http.get(Uri.parse('$origin$kSyncAccountPath'));
+
+      expect(response.statusCode, HttpStatus.notFound);
+    });
+  });
 }