diff --git a/crdt_sync_flutter/README.md b/crdt_sync_flutter/README.md
index c07997f..54d4808 100644
--- a/crdt_sync_flutter/README.md
+++ b/crdt_sync_flutter/README.md
@@ -26,7 +26,7 @@ dependencies:
   crdt_sync_flutter:
     git:
       url: https://github.com/kuhyx/utils
-      ref: crdt_sync_flutter-v0.2.0
+      ref: crdt_sync_flutter-v0.2.1
       path: crdt_sync_flutter
 ```
 
diff --git a/crdt_sync_flutter/lib/src/google_any_sign_in.dart b/crdt_sync_flutter/lib/src/google_any_sign_in.dart
index b890c31..0e61a08 100644
--- a/crdt_sync_flutter/lib/src/google_any_sign_in.dart
+++ b/crdt_sync_flutter/lib/src/google_any_sign_in.dart
@@ -22,10 +22,12 @@ import 'package:crdt_sync_flutter/src/google_sign_in.dart';
 ///
 /// [serverClientId] is the **Web** OAuth client id (the audience for the
 /// plugin's tokens); [desktopClientId] is a **Desktop**-type client, the only
-/// type permitted to redirect to loopback.
+/// type permitted to redirect to loopback. Both are required, and passing ''
+/// is how an app says it has not configured that half -- explicit, because a
+/// silently-defaulted '' is how a button that can never succeed gets shipped.
 bool googleAnySignInSupported({
   required String serverClientId,
-  String desktopClientId = '',
+  required String desktopClientId,
 }) =>
     googleSignInSupported(serverClientId) ||
     desktopSignInSupported(desktopClientId);
@@ -59,7 +61,7 @@ enum GoogleFlow {
 /// Picks the flow for this platform and configuration.
 GoogleFlow googleFlowFor({
   required String serverClientId,
-  String desktopClientId = '',
+  required String desktopClientId,
 }) {
   if (googleSignInSupported(serverClientId)) return GoogleFlow.plugin;
   if (desktopSignInSupported(desktopClientId)) return GoogleFlow.desktop;
@@ -72,7 +74,7 @@ GoogleFlow googleFlowFor({
 /// back to the password path either way.
 Future<String?> googleAnyIdToken({
   required String serverClientId,
-  String desktopClientId = '',
+  required String desktopClientId,
 }) async {
   switch (googleFlowFor(
     serverClientId: serverClientId,
diff --git a/crdt_sync_flutter/pubspec.yaml b/crdt_sync_flutter/pubspec.yaml
index 7f0881a..af83800 100644
--- a/crdt_sync_flutter/pubspec.yaml
+++ b/crdt_sync_flutter/pubspec.yaml
@@ -4,7 +4,7 @@ description: >-
   persisted per-install device id, and a one-call bootstrap. Removes the
   ~150 lines of firebase_backend.dart every consuming app was copying.
 publish_to: 'none'
-version: 0.2.0
+version: 0.2.1
 
 environment:
   sdk: ^3.12.2
diff --git a/crdt_sync_flutter/test/google_any_sign_in_test.dart b/crdt_sync_flutter/test/google_any_sign_in_test.dart
index eb6e96d..c7a5abd 100644
--- a/crdt_sync_flutter/test/google_any_sign_in_test.dart
+++ b/crdt_sync_flutter/test/google_any_sign_in_test.dart
@@ -29,13 +29,22 @@ void main() {
     });
 
     test('is false when neither half is configured', () {
-      expect(googleAnySignInSupported(serverClientId: ''), isFalse);
+      expect(
+        googleAnySignInSupported(serverClientId: '', desktopClientId: ''),
+        isFalse,
+      );
     });
 
     test('is false on this host when only the plugin half is configured', () {
       // The plugin does not run on Linux, so a Web client id alone buys
       // nothing here -- and the button must not appear.
-      expect(googleAnySignInSupported(serverClientId: 'web-cid'), isFalse);
+      expect(
+        googleAnySignInSupported(
+          serverClientId: 'web-cid',
+          desktopClientId: '',
+        ),
+        isFalse,
+      );
     });
   });
 
@@ -48,25 +57,37 @@ void main() {
     });
 
     test('picks nothing when neither half is configured', () {
-      expect(googleFlowFor(serverClientId: ''), GoogleFlow.none);
+      expect(
+        googleFlowFor(serverClientId: '', desktopClientId: ''),
+        GoogleFlow.none,
+      );
     });
 
     test('picks nothing when only the plugin half is configured here', () {
       // The plugin does not run on Linux, so a Web client id alone must not
       // route anywhere -- that would be a button that cannot succeed.
-      expect(googleFlowFor(serverClientId: 'web-cid'), GoogleFlow.none);
+      expect(
+        googleFlowFor(serverClientId: 'web-cid', desktopClientId: ''),
+        GoogleFlow.none,
+      );
     });
   });
 
   group('googleAnyIdToken', () {
     test('returns null when no flow is available', () async {
-      expect(await googleAnyIdToken(serverClientId: ''), isNull);
+      expect(
+        await googleAnyIdToken(serverClientId: '', desktopClientId: ''),
+        isNull,
+      );
     });
 
     test('returns null when the plugin half alone is configured', () async {
       // Would reach the plugin's platform channel if the gate were wrong,
       // which throws rather than returning null.
-      expect(await googleAnyIdToken(serverClientId: 'web-cid'), isNull);
+      expect(
+        await googleAnyIdToken(serverClientId: 'web-cid', desktopClientId: ''),
+        isNull,
+      );
     });
   });
 }