diff --git a/stronglift_replacement/workout_app/lib/screens/history_screen.dart b/stronglift_replacement/workout_app/lib/screens/history_screen.dart
index d1f15ef..2e82e39 100644
--- a/stronglift_replacement/workout_app/lib/screens/history_screen.dart
+++ b/stronglift_replacement/workout_app/lib/screens/history_screen.dart
@@ -8,6 +8,7 @@ library;
 import 'dart:async';
 import 'dart:convert';
 import 'dart:math';
+import 'package:crdt_sync/crdt_sync.dart';
 import 'package:flutter/material.dart';
 import 'package:http/http.dart' as http;
 import 'package:workout_app/models/exercise.dart';
@@ -29,11 +30,20 @@ class HistoryScreen extends StatefulWidget {
   ///
   /// [httpClient] is injected only by tests, so the synced-workout fetch can
   /// be driven without real network — same pattern as `SettingsScreen`.
-  const HistoryScreen({super.key, this.httpClient});
+  ///
+  /// [firebaseFactory] is likewise tests-only, and is NOT redundant with
+  /// [httpClient]: the sync guard short-circuits on "no backend configured",
+  /// and it asks Firebase that question directly. On a desktop that has a
+  /// cached refresh token the real factory answers yes, so the guard opens and
+  /// the fetch goes to the network even with the sync token faked away.
+  const HistoryScreen({super.key, this.httpClient, this.firebaseFactory});
 
   /// Overrides the HTTP client used to read synced workouts (tests only).
   final http.Client? httpClient;
 
+  /// Overrides how a Firebase account is discovered (tests only).
+  final Future<FirebaseRestClient?> Function()? firebaseFactory;
+
   @override
   State<HistoryScreen> createState() => _HistoryScreenState();
 }
@@ -106,6 +116,7 @@ class _HistoryScreenState extends State<HistoryScreen> {
   Future<List<Map<String, dynamic>>> _readSyncedPayloads() =>
       WorkoutSyncService(
         httpClient: widget.httpClient,
+        firebaseFactory: widget.firebaseFactory,
       ).readMergedWorkoutPayloads();
 
   Future<void> _pickExercise(String name) async {
diff --git a/stronglift_replacement/workout_app/test/screens/_history_test_fixtures.dart b/stronglift_replacement/workout_app/test/screens/_history_test_fixtures.dart
index 5478934..809ecce 100644
--- a/stronglift_replacement/workout_app/test/screens/_history_test_fixtures.dart
+++ b/stronglift_replacement/workout_app/test/screens/_history_test_fixtures.dart
@@ -23,9 +23,23 @@ Future<void> pumpHistory(WidgetTester tester, Widget w) async {
   await tester.pump();
 }
 
-Widget wrapHistory({http.Client? httpClient}) => MaterialApp(
+/// Wraps the history screen with sync pinned to a known state.
+///
+/// [firebaseFactory] defaults to "no account", which is what makes these
+/// tests independent of the machine they run on. Faking the sync token is not
+/// enough on its own: the guard also asks Firebase whether an account exists,
+/// and on a desktop holding a cached refresh token the real factory says yes,
+/// so the fetch escapes to the network and the test fails with a
+/// RemoteSyncError that has nothing to do with the screen.
+Widget wrapHistory({
+  http.Client? httpClient,
+  Future<FirebaseRestClient?> Function()? firebaseFactory,
+}) => MaterialApp(
   theme: buildAppTheme(),
-  home: HistoryScreen(httpClient: httpClient),
+  home: HistoryScreen(
+    httpClient: httpClient,
+    firebaseFactory: firebaseFactory ?? () async => null,
+  ),
 );
 
 /// A GitHub mock serving one PC device log holding a run and a manual.
diff --git a/stronglift_replacement/workout_app/test/services/workout_sync_read_test.dart b/stronglift_replacement/workout_app/test/services/workout_sync_read_test.dart
index b450685..694a707 100644
--- a/stronglift_replacement/workout_app/test/services/workout_sync_read_test.dart
+++ b/stronglift_replacement/workout_app/test/services/workout_sync_read_test.dart
@@ -75,6 +75,7 @@ void main() {
     );
     final payloads = await WorkoutSyncService(
       httpClient: httpClient,
+      firebaseFactory: () async => null,
     ).readMergedManualPayloads();
     expect(payloads, hasLength(1));
     expect(payloads.single['cost'], 'NEW');
@@ -148,6 +149,7 @@ void main() {
       );
       final manuals = await WorkoutSyncService(
         httpClient: httpClient,
+        firebaseFactory: () async => null,
       ).readMergedManualPayloads();
       expect(manuals, hasLength(1));
       expect(manuals.single['kind'], 'manual_workout');
@@ -207,6 +209,7 @@ void main() {
 
     final payloads = await WorkoutSyncService(
       httpClient: httpClient,
+      firebaseFactory: () async => null,
     ).readMergedManualPayloads();
 
     expect(payloads, hasLength(1));