Fix push device registration

tests/QMax.Tests/ApiSmokeTests.cs

@@ -158,6 +158,45 @@ public sealed class ApiSmokeTests : IDisposable
         Assert.Contains(chats, x => x.Title == "\u0410\u043d\u044e\u0442\u0430");
     }
 
+    [Fact]
+    public async Task PushRegistrationUsesSingleExistingUserWhenTokenUserIsStale()
+    {
+        using var factory = _factory.WithWebHostBuilder(builder =>
+        {
+            builder.ConfigureTestServices(services =>
+            {
+                services.RemoveAll<IHostedService>();
+            });
+        });
+        using var client = factory.CreateClient();
+        await LoginAsync(client);
+
+        Guid currentUserId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<QMaxDbContext>();
+            db.UserSessions.RemoveRange(db.UserSessions);
+            db.Users.RemoveRange(db.Users);
+            var currentUser = new User { DisplayName = "QMAX Owner" };
+            db.Users.Add(currentUser);
+            await db.SaveChangesAsync();
+            currentUserId = currentUser.Id;
+        }
+
+        var response = await client.PostAsJsonAsync(
+            "/api/push/devices",
+            new { FirebaseToken = "stale-token-user-fcm-token", Platform = "android" });
+
+        await AssertStatusAsync(HttpStatusCode.NoContent, response);
+        using (var scope = factory.Services.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<QMaxDbContext>();
+            var device = await db.PushDevices.SingleAsync();
+            Assert.Equal(currentUserId, device.UserId);
+            Assert.Equal("stale-token-user-fcm-token", device.FirebaseToken);
+        }
+    }
+
     [Fact]
     public async Task SyncMergesLateDiscoveredAttachmentsIntoExistingMessage()
     {