Immidiate ui reflection for calendar events and some more error handling.

Wino.Calendar.ViewModels/CalendarPageViewModel.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.ObjectModel;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -14,11 +15,13 @@ using Wino.Calendar.ViewModels.Interfaces;
 using Wino.Calendar.ViewModels.Messages;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Calendar;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models;
 using Wino.Core.Domain.Models.Calendar;
 using Wino.Core.Domain.Models.Navigation;
+using Wino.Core.Services;
 using Wino.Core.ViewModels;
 using Wino.Messaging.Client.Calendar;
 using Wino.Messaging.UI;
@@ -119,7 +122,7 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
     public partial bool IsCalendarEnabled { get; set; } = true;
 
     [ObservableProperty]
-    public partial IReadOnlyList<CalendarItemViewModel> CalendarItems { get; set; } = [];
+    public partial ObservableCollection<CalendarItemViewModel> CalendarItems { get; set; } = new();
 
     #endregion
 
@@ -153,7 +156,7 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
     private bool _subscriptionsAttached;
     private CancellationTokenSource _pageLifetimeCts = new();
     private long _pageLifetimeVersion;
-    private List<CalendarItemViewModel> _loadedCalendarItems = [];
+    private Dictionary<Guid, CalendarItemViewModel> _loadedCalendarItems = new();
 
     [ObservableProperty]
     public partial CalendarSettings CurrentSettings { get; set; }
@@ -323,8 +326,8 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
         CurrentVisibleRange = null;
         VisibleDateRangeText = string.Empty;
         LoadedDateWindow = null;
-        _loadedCalendarItems = [];
-        CalendarItems = [];
+        _loadedCalendarItems = new();
+        CalendarItems = new();
     }
 
     public void Dispose()
@@ -594,8 +597,7 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
             {
                 if (loadedItems != null)
                 {
-                    _loadedCalendarItems = loadedItems;
-                    CalendarItems = loadedItems;
+                    ReplaceLoadedCalendarItems(loadedItems);
                 }
 
                 EnsureSelectedQuickEventAccountCalendar();
@@ -656,8 +658,10 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
     {
         var loadedItems = new Dictionary<Guid, CalendarItemViewModel>();
         var loadPeriod = new TimeRange(loadedDateWindow.StartDate, loadedDateWindow.EndDate);
+        var activeCalendars = AccountCalendarStateService.ActiveCalendars.ToList();
+        var pendingCalendarItemIds = await GetPendingCalendarItemIdsAsync(activeCalendars, lifetimeVersion).ConfigureAwait(false);
 
-        foreach (var calendarViewModel in AccountCalendarStateService.ActiveCalendars)
+        foreach (var calendarViewModel in activeCalendars)
         {
             if (!IsPageActive(lifetimeVersion))
                 return [];
@@ -672,12 +676,16 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
 
                 if (!loadedItems.ContainsKey(calendarItem.Id))
                 {
-                    loadedItems.Add(calendarItem.Id, new CalendarItemViewModel(calendarItem));
+                    loadedItems.Add(calendarItem.Id, CreateCalendarItemViewModel(calendarItem, pendingCalendarItemIds));
                 }
             }
         }
 
-        return loadedItems.Values.ToList();
+        return loadedItems.Values
+            .OrderBy(item => item.StartDate)
+            .ThenBy(item => item.EndDate)
+            .ThenBy(item => item.Id)
+            .ToList();
     }
 
     private static bool IsSameVisibleRange(VisibleDateRange current, VisibleDateRange next)
@@ -754,41 +762,12 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
         await ReloadCurrentVisibleRangeAsync().ConfigureAwait(false);
     }
 
-    protected override void OnCalendarItemDeleted(CalendarItem calendarItem)
+    protected override void OnCalendarItemDeleted(CalendarItem calendarItem, EntityUpdateSource source)
     {
-        base.OnCalendarItemDeleted(calendarItem);
+        base.OnCalendarItemDeleted(calendarItem, source);
 
-        if (DisplayDetailsCalendarItemViewModel?.Id == calendarItem.Id ||
-            DisplayDetailsCalendarItemViewModel?.CalendarItem?.RecurringCalendarItemId == calendarItem.Id)
-        {
-            DisplayDetailsCalendarItemViewModel = null;
-        }
-
-        if (ShouldReloadFor(calendarItem))
-        {
-            _ = ReloadCurrentVisibleRangeAsync();
-        }
-    }
-
-    protected override void OnCalendarItemUpdated(CalendarItem calendarItem, CalendarItemUpdateSource source)
-    {
-        base.OnCalendarItemUpdated(calendarItem, source);
-
-        if (DisplayDetailsCalendarItemViewModel?.Id == calendarItem.Id)
-        {
-            calendarItem.AssignedCalendar ??= DisplayDetailsCalendarItemViewModel.AssignedCalendar;
-            DisplayDetailsCalendarItemViewModel = new CalendarItemViewModel(calendarItem);
-        }
-
-        if (ShouldReloadFor(calendarItem))
-        {
-            _ = ReloadCurrentVisibleRangeAsync();
-        }
-    }
-
-    protected override void OnCalendarItemAdded(CalendarItem calendarItem)
-    {
-        base.OnCalendarItemAdded(calendarItem);
+        if (calendarItem == null)
+            return;
 
         if (calendarItem.IsRecurringParent)
         {
@@ -796,21 +775,272 @@ public partial class CalendarPageViewModel : CalendarBaseViewModel,
             return;
         }
 
-        if (ShouldReloadFor(calendarItem))
+        var existingItemId = FindLoadedCalendarItemId(calendarItem);
+        if (!existingItemId.HasValue)
+            return;
+
+        RemoveLoadedCalendarItem(existingItemId.Value, calendarItem);
+    }
+
+    protected override void OnCalendarItemUpdated(CalendarItem calendarItem, EntityUpdateSource source)
     {
-            _ = ReloadCurrentVisibleRangeAsync();
+        base.OnCalendarItemUpdated(calendarItem, source);
+        ApplyCalendarItemUpsert(calendarItem, source);
+    }
+
+    protected override void OnCalendarItemAdded(CalendarItem calendarItem, EntityUpdateSource source)
+    {
+        base.OnCalendarItemAdded(calendarItem, source);
+        ApplyCalendarItemUpsert(calendarItem, source);
+    }
+
+    private async Task<HashSet<Guid>> GetPendingCalendarItemIdsAsync(IEnumerable<AccountCalendarViewModel> activeCalendars, long lifetimeVersion)
+    {
+        var pendingCalendarItemIds = new HashSet<Guid>();
+        var accountIds = activeCalendars
+            .Select(calendar => calendar.Account.Id)
+            .Where(accountId => accountId != Guid.Empty)
+            .Distinct()
+            .ToList();
+
+        foreach (var accountId in accountIds)
+        {
+            if (!IsPageActive(lifetimeVersion))
+                return pendingCalendarItemIds;
+
+            IWinoSynchronizerBase synchronizer;
+            try
+            {
+                synchronizer = await SynchronizationManager.Instance.GetSynchronizerAsync(accountId).ConfigureAwait(false);
+            }
+            catch (InvalidOperationException)
+            {
+                return pendingCalendarItemIds;
+            }
+
+            if (synchronizer == null)
+                continue;
+
+            foreach (var pendingCalendarItemId in synchronizer.GetPendingCalendarOperationIds())
+            {
+                pendingCalendarItemIds.Add(pendingCalendarItemId);
             }
         }
 
-    private bool ShouldReloadFor(CalendarItem calendarItem)
+        return pendingCalendarItemIds;
+    }
+
+    private void ApplyCalendarItemUpsert(CalendarItem calendarItem, EntityUpdateSource source)
+    {
+        if (calendarItem == null)
+            return;
+
+        if (calendarItem.IsRecurringParent)
+        {
+            _ = ReloadCurrentVisibleRangeAsync();
+            return;
+        }
+
+        var existingItemId = FindLoadedCalendarItemId(calendarItem);
+        var shouldDisplay = ShouldDisplayCalendarItem(calendarItem);
+
+        if (!shouldDisplay)
+        {
+            if (existingItemId.HasValue)
+            {
+                RemoveLoadedCalendarItem(existingItemId.Value, calendarItem);
+            }
+
+            return;
+        }
+
+        var newViewModel = CreateCalendarItemViewModel(calendarItem, source);
+
+        if (existingItemId.HasValue)
+        {
+            ReplaceLoadedCalendarItem(existingItemId.Value, newViewModel);
+        }
+        else
+        {
+            InsertLoadedCalendarItem(newViewModel);
+        }
+    }
+
+    private CalendarItemViewModel CreateCalendarItemViewModel(CalendarItem calendarItem, EntityUpdateSource source)
+        => CreateCalendarItemViewModel(
+            calendarItem,
+            source == EntityUpdateSource.ClientUpdated ? new HashSet<Guid> { calendarItem.Id } : null,
+            source);
+
+    private CalendarItemViewModel CreateCalendarItemViewModel(CalendarItem calendarItem, ISet<Guid> pendingCalendarItemIds, EntityUpdateSource source = EntityUpdateSource.Server)
+    {
+        calendarItem.AssignedCalendar ??= ResolveAssignedCalendar(calendarItem.CalendarId);
+
+        return new CalendarItemViewModel(calendarItem)
+        {
+            IsBusy = source == EntityUpdateSource.ClientUpdated || HasPendingCalendarOperation(calendarItem, pendingCalendarItemIds)
+        };
+    }
+
+    private void ReplaceLoadedCalendarItems(IEnumerable<CalendarItemViewModel> loadedItems)
+    {
+        var loadedItemsList = loadedItems?.ToList() ?? [];
+        CalendarItems = new ObservableCollection<CalendarItemViewModel>(loadedItemsList);
+        _loadedCalendarItems = loadedItemsList.ToDictionary(item => item.Id);
+    }
+
+    private void InsertLoadedCalendarItem(CalendarItemViewModel calendarItemViewModel)
+    {
+        var insertionIndex = 0;
+
+        while (insertionIndex < CalendarItems.Count && CompareCalendarItems(CalendarItems[insertionIndex], calendarItemViewModel) <= 0)
+        {
+            insertionIndex++;
+        }
+
+        CalendarItems.Insert(insertionIndex, calendarItemViewModel);
+        _loadedCalendarItems[calendarItemViewModel.Id] = calendarItemViewModel;
+
+        if (IsDisplayDetailsMatch(calendarItemViewModel.CalendarItem))
+        {
+            DisplayDetailsCalendarItemViewModel = calendarItemViewModel;
+        }
+    }
+
+    private void ReplaceLoadedCalendarItem(Guid existingItemId, CalendarItemViewModel replacementViewModel)
+    {
+        if (!_loadedCalendarItems.TryGetValue(existingItemId, out var existingViewModel))
+        {
+            InsertLoadedCalendarItem(replacementViewModel);
+            return;
+        }
+
+        replacementViewModel.IsSelected = existingViewModel.IsSelected;
+
+        var existingIndex = CalendarItems.IndexOf(existingViewModel);
+        if (existingIndex >= 0)
+        {
+            CalendarItems[existingIndex] = replacementViewModel;
+        }
+
+        _loadedCalendarItems.Remove(existingItemId);
+        _loadedCalendarItems[replacementViewModel.Id] = replacementViewModel;
+
+        if (existingIndex >= 0)
+        {
+            MoveCalendarItemToSortedPosition(replacementViewModel, existingIndex);
+        }
+
+        if (IsDisplayDetailsMatch(replacementViewModel.CalendarItem, existingItemId))
+        {
+            DisplayDetailsCalendarItemViewModel = replacementViewModel;
+        }
+    }
+
+    private void RemoveLoadedCalendarItem(Guid existingItemId, CalendarItem calendarItem)
+    {
+        if (_loadedCalendarItems.TryGetValue(existingItemId, out var existingViewModel))
+        {
+            CalendarItems.Remove(existingViewModel);
+            _loadedCalendarItems.Remove(existingItemId);
+        }
+
+        if (IsDisplayDetailsMatch(calendarItem, existingItemId))
+        {
+            DisplayDetailsCalendarItemViewModel = null;
+        }
+    }
+
+    private void MoveCalendarItemToSortedPosition(CalendarItemViewModel calendarItemViewModel, int previousIndex)
+    {
+        if (previousIndex < 0)
+            return;
+
+        var targetIndex = 0;
+        while (targetIndex < CalendarItems.Count && CompareCalendarItems(CalendarItems[targetIndex], calendarItemViewModel) <= 0)
+        {
+            targetIndex++;
+        }
+
+        if (targetIndex > previousIndex)
+        {
+            targetIndex--;
+        }
+
+        if (targetIndex != previousIndex)
+        {
+            CalendarItems.Move(previousIndex, targetIndex);
+        }
+    }
+
+    private Guid? FindLoadedCalendarItemId(CalendarItem calendarItem)
+    {
+        if (calendarItem == null)
+            return null;
+
+        if (_loadedCalendarItems.ContainsKey(calendarItem.Id))
+            return calendarItem.Id;
+
+        var trackedLocalItemId = calendarItem.RemoteEventId.GetClientTrackingId();
+        if (trackedLocalItemId.HasValue && _loadedCalendarItems.ContainsKey(trackedLocalItemId.Value))
+            return trackedLocalItemId.Value;
+
+        return null;
+    }
+
+    private bool ShouldDisplayCalendarItem(CalendarItem calendarItem)
     {
         if (calendarItem == null || LoadedDateWindow == null)
             return false;
 
+        if (calendarItem.IsHidden || calendarItem.IsRecurringParent || !IsCalendarActive(calendarItem.CalendarId))
+            return false;
+
         var loadedWindow = new TimeRange(LoadedDateWindow.StartDate, LoadedDateWindow.EndDate);
         return loadedWindow.OverlapsWith(calendarItem.Period);
     }
 
+    private bool IsDisplayDetailsMatch(CalendarItem calendarItem, Guid? existingItemId = null)
+    {
+        if (DisplayDetailsCalendarItemViewModel == null || calendarItem == null)
+            return false;
+
+        var trackedLocalItemId = calendarItem.RemoteEventId.GetClientTrackingId();
+
+        return DisplayDetailsCalendarItemViewModel.Id == calendarItem.Id ||
+               (existingItemId.HasValue && DisplayDetailsCalendarItemViewModel.Id == existingItemId.Value) ||
+               (trackedLocalItemId.HasValue && DisplayDetailsCalendarItemViewModel.Id == trackedLocalItemId.Value) ||
+               DisplayDetailsCalendarItemViewModel.CalendarItem?.RecurringCalendarItemId == calendarItem.Id;
+    }
+
+    private bool HasPendingCalendarOperation(CalendarItem calendarItem, ISet<Guid> pendingCalendarItemIds)
+    {
+        if (calendarItem == null || pendingCalendarItemIds == null || pendingCalendarItemIds.Count == 0)
+            return false;
+
+        if (pendingCalendarItemIds.Contains(calendarItem.Id))
+            return true;
+
+        var trackedLocalItemId = calendarItem.RemoteEventId.GetClientTrackingId();
+        return trackedLocalItemId.HasValue && pendingCalendarItemIds.Contains(trackedLocalItemId.Value);
+    }
+
+    private AccountCalendarViewModel ResolveAssignedCalendar(Guid calendarId)
+        => AccountCalendarStateService.AllCalendars.FirstOrDefault(calendar => calendar.Id == calendarId);
+
+    private static int CompareCalendarItems(CalendarItemViewModel left, CalendarItemViewModel right)
+    {
+        var compareResult = DateTime.Compare(left?.StartDate ?? DateTime.MinValue, right?.StartDate ?? DateTime.MinValue);
+        if (compareResult != 0)
+            return compareResult;
+
+        compareResult = DateTime.Compare(left?.EndDate ?? DateTime.MinValue, right?.EndDate ?? DateTime.MinValue);
+        if (compareResult != 0)
+            return compareResult;
+
+        return Nullable.Compare(left?.Id, right?.Id);
+    }
+
     partial void OnIsAllDayChanged(bool value)
     {
         if (value)

Wino.Calendar.ViewModels/EventDetailsPageViewModel.cs

@@ -12,6 +12,7 @@ using Serilog;
 using Wino.Calendar.ViewModels.Data;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Calendar;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Calendar;
@@ -187,20 +188,20 @@ public partial class EventDetailsPageViewModel : CalendarBaseViewModel
         await LoadCalendarItemTargetAsync(args);
     }
 
-    protected override async void OnCalendarItemUpdated(CalendarItem calendarItem, CalendarItemUpdateSource source)
+    protected override async void OnCalendarItemUpdated(CalendarItem calendarItem, EntityUpdateSource source)
     {
         base.OnCalendarItemUpdated(calendarItem, source);
 
         // If the current event was updated, reload it
-        if (CurrentEvent?.CalendarItem?.Id == calendarItem.Id || CurrentEvent?.CalendarItem.RecurringCalendarItemId == calendarItem.Id)
+        if (IsCurrentEventMatch(calendarItem))
         {
             // Reflect client-side optimistic changes immediately; fallback to DB for server updates.
-            if (source == CalendarItemUpdateSource.ClientUpdated || source == CalendarItemUpdateSource.ClientReverted)
+            if (source == EntityUpdateSource.ClientUpdated || source == EntityUpdateSource.ClientReverted)
             {
                 var previousAttendees = CurrentEvent?.Attendees?.ToList() ?? [];
                 CurrentEvent = new CalendarItemViewModel(calendarItem)
                 {
-                    IsBusy = source == CalendarItemUpdateSource.ClientUpdated
+                    IsBusy = source == EntityUpdateSource.ClientUpdated
                 };
 
                 foreach (var attendee in previousAttendees)
@@ -221,17 +222,54 @@ public partial class EventDetailsPageViewModel : CalendarBaseViewModel
         }
     }
 
-    protected override void OnCalendarItemDeleted(CalendarItem calendarItem)
+    protected override async void OnCalendarItemAdded(CalendarItem calendarItem, EntityUpdateSource source)
     {
-        base.OnCalendarItemDeleted(calendarItem);
+        base.OnCalendarItemAdded(calendarItem, source);
+
+        if (!IsCurrentEventMatch(calendarItem))
+            return;
+
+        if (source == EntityUpdateSource.ClientUpdated || source == EntityUpdateSource.ClientReverted)
+        {
+            CurrentEvent = new CalendarItemViewModel(calendarItem)
+            {
+                IsBusy = source == EntityUpdateSource.ClientUpdated
+            };
+
+            return;
+        }
+
+        var refreshedEvent = await _calendarService.GetCalendarItemAsync(calendarItem.Id);
+        if (refreshedEvent != null)
+        {
+            CurrentEvent = new CalendarItemViewModel(refreshedEvent);
+            await LoadAttendeesAsync(refreshedEvent.Id, refreshedEvent);
+        }
+    }
+
+    protected override void OnCalendarItemDeleted(CalendarItem calendarItem, EntityUpdateSource source)
+    {
+        base.OnCalendarItemDeleted(calendarItem, source);
 
         // If the current event was deleted, navigate back
-        if (CurrentEvent?.CalendarItem?.Id == calendarItem.Id || CurrentEvent?.CalendarItem.RecurringCalendarItemId == calendarItem.Id)
+        if (IsCurrentEventMatch(calendarItem))
         {
             NavigateBackToCalendar(forceReload: true);
         }
     }
 
+    private bool IsCurrentEventMatch(CalendarItem calendarItem)
+    {
+        if (CurrentEvent?.CalendarItem == null || calendarItem == null)
+            return false;
+
+        var trackedLocalItemId = calendarItem.RemoteEventId.GetClientTrackingId();
+
+        return CurrentEvent.CalendarItem.Id == calendarItem.Id ||
+               (trackedLocalItemId.HasValue && CurrentEvent.CalendarItem.Id == trackedLocalItemId.Value) ||
+               CurrentEvent.CalendarItem.RecurringCalendarItemId == calendarItem.Id;
+    }
+
     private async Task LoadCalendarItemTargetAsync(CalendarItemTarget target)
     {
         try

Wino.Core.Domain/Enums/EntityUpdateSource.cs

@@ -1,17 +1,17 @@
 namespace Wino.Core.Domain.Enums;
 
 /// <summary>
-/// Indicates the source of a calendar item update.
+/// Indicates the source of an entity update.
 /// </summary>
-public enum CalendarItemUpdateSource
+public enum EntityUpdateSource
 {
     /// <summary>
-    /// Update originated from client-side UI changes (ApplyUIChanges).
+    /// Update originated from client-side optimistic UI changes (ApplyUIChanges).
     /// </summary>
     ClientUpdated,
 
     /// <summary>
-    /// Update originated from client-side UI revert (RevertUIChanges).
+    /// Update originated from reverting client-side optimistic UI changes (RevertUIChanges).
     /// </summary>
     ClientReverted,
 

Wino.Core.Domain/Enums/MailUpdateSource.cs

@@ -1,22 +0,0 @@
-namespace Wino.Core.Domain.Enums;
-
-/// <summary>
-/// Indicates the source of a mail update.
-/// </summary>
-public enum MailUpdateSource
-{
-    /// <summary>
-    /// Update originated from client-side UI changes (ApplyUIChanges).
-    /// </summary>
-    ClientUpdated,
-
-    /// <summary>
-    /// Update originated from client-side UI revert (RevertUIChanges).
-    /// </summary>
-    ClientReverted,
-
-    /// <summary>
-    /// Update originated from server synchronization or database operations.
-    /// </summary>
-    Server
-}

Wino.Core.Domain/Interfaces/IBaseSynchronizer.cs

@@ -42,6 +42,11 @@ public interface IBaseSynchronizer
     /// <param name="calendarItemId">Calendar item id to check.</param>
     bool HasPendingCalendarOperation(Guid calendarItemId);
 
+    /// <summary>
+    /// Returns calendar item ids that currently have queued or executing operations.
+    /// </summary>
+    IReadOnlyCollection<Guid> GetPendingCalendarOperationIds();
+
     /// <summary>
     /// Synchronizes profile information with the server.
     /// Sender name and Profile picture are updated.

Wino.Core.Domain/Models/Synchronization/CalendarSynchronizationResult.cs

@@ -1,4 +1,6 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Text.Json.Serialization;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
@@ -22,6 +24,13 @@ public class CalendarSynchronizationResult
 
     public SynchronizationCompletedState CompletedState { get; set; }
 
+    public Exception Exception { get; set; }
+
+    public List<SynchronizationIssue> Issues { get; set; } = [];
+
+    [JsonIgnore]
+    public IEnumerable<SynchronizationIssue> AllIssues => Issues;
+
     public static CalendarSynchronizationResult Empty => new() { CompletedState = SynchronizationCompletedState.Success };
 
     // Mail synchronization
@@ -41,5 +50,48 @@ public class CalendarSynchronizationResult
         };
 
     public static CalendarSynchronizationResult Canceled => new() { CompletedState = SynchronizationCompletedState.Canceled };
-    public static CalendarSynchronizationResult Failed => new() { CompletedState = SynchronizationCompletedState.Failed };
+    public static CalendarSynchronizationResult Failed(Exception exception = null) => new()
+    {
+        CompletedState = SynchronizationCompletedState.Failed,
+        Exception = exception
+    };
+
+    public CalendarSynchronizationResult MergeIssues(IEnumerable<SynchronizationIssue> issues)
+    {
+        if (issues == null)
+            return this;
+
+        foreach (var issue in issues.Where(issue => issue != null))
+        {
+            if (!Issues.Any(existing => AreEquivalent(existing, issue)))
+            {
+                Issues.Add(issue);
+            }
+        }
+
+        if (CompletedState == SynchronizationCompletedState.Success && Issues.Any())
+        {
+            CompletedState = SynchronizationCompletedState.PartiallyCompleted;
+        }
+
+        if (Exception == null)
+        {
+            Exception = Issues.FirstOrDefault(issue => !string.IsNullOrWhiteSpace(issue?.Message)) is { } issue
+                ? new Exception(issue.Message)
+                : null;
+        }
+
+        return this;
+    }
+
+    private static bool AreEquivalent(SynchronizationIssue left, SynchronizationIssue right)
+        => string.Equals(left?.Message, right?.Message, StringComparison.Ordinal)
+           && left?.ErrorCode == right?.ErrorCode
+           && left?.Severity == right?.Severity
+           && left?.Category == right?.Category
+           && string.Equals(left?.OperationType, right?.OperationType, StringComparison.Ordinal)
+           && string.Equals(left?.RequestType, right?.RequestType, StringComparison.Ordinal)
+           && left?.FolderId == right?.FolderId
+           && left?.CalendarId == right?.CalendarId
+           && string.Equals(left?.ScopeName, right?.ScopeName, StringComparison.Ordinal);
 }

Wino.Core.Domain/Models/Synchronization/MailSynchronizationResult.cs

@@ -26,6 +26,8 @@ public class MailSynchronizationResult
 
     public Exception Exception { get; set; }
 
+    public List<SynchronizationIssue> Issues { get; set; } = [];
+
     /// <summary>
     /// Gets or sets the results for each folder that was synchronized.
     /// Enables partial failure tracking - some folders may succeed while others fail.
@@ -75,6 +77,10 @@ public class MailSynchronizationResult
     [JsonIgnore]
     public IEnumerable<FolderSyncResult> FailedFolders => FolderResults.Where(f => !f.Success);
 
+    [JsonIgnore]
+    public IEnumerable<SynchronizationIssue> AllIssues
+        => Issues.Concat(FailedFolders.Select(SynchronizationIssue.FromFolderResult).Where(issue => issue != null));
+
     public static MailSynchronizationResult Empty => new() { CompletedState = SynchronizationCompletedState.Success };
 
     // Mail synchronization
@@ -121,4 +127,43 @@ public class MailSynchronizationResult
         CompletedState = SynchronizationCompletedState.Failed,
         Exception = exception
     };
+
+    public MailSynchronizationResult MergeIssues(IEnumerable<SynchronizationIssue> issues)
+    {
+        if (issues == null)
+            return this;
+
+        foreach (var issue in issues.Where(issue => issue != null))
+        {
+            if (!Issues.Any(existing => AreEquivalent(existing, issue)))
+            {
+                Issues.Add(issue);
+            }
+        }
+
+        if (CompletedState == SynchronizationCompletedState.Success && AllIssues.Any())
+        {
+            CompletedState = SynchronizationCompletedState.PartiallyCompleted;
+        }
+
+        if (Exception == null)
+        {
+            Exception = Issues.FirstOrDefault(issue => !string.IsNullOrWhiteSpace(issue?.Message)) is { } issue
+                ? new Exception(issue.Message)
+                : null;
+        }
+
+        return this;
+    }
+
+    private static bool AreEquivalent(SynchronizationIssue left, SynchronizationIssue right)
+        => string.Equals(left?.Message, right?.Message, StringComparison.Ordinal)
+           && left?.ErrorCode == right?.ErrorCode
+           && left?.Severity == right?.Severity
+           && left?.Category == right?.Category
+           && string.Equals(left?.OperationType, right?.OperationType, StringComparison.Ordinal)
+           && string.Equals(left?.RequestType, right?.RequestType, StringComparison.Ordinal)
+           && left?.FolderId == right?.FolderId
+           && left?.CalendarId == right?.CalendarId
+           && string.Equals(left?.ScopeName, right?.ScopeName, StringComparison.Ordinal);
 }

Wino.Core.Domain/Models/Synchronization/SynchronizationIssue.cs

@@ -0,0 +1,110 @@
+using System;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+
+namespace Wino.Core.Domain.Models.Synchronization;
+
+/// <summary>
+/// Represents a user-visible synchronization issue collected during request execution or provider synchronization.
+/// </summary>
+public class SynchronizationIssue
+{
+    public string Message { get; set; }
+    public int? ErrorCode { get; set; }
+    public SynchronizerErrorSeverity Severity { get; set; } = SynchronizerErrorSeverity.Fatal;
+    public SynchronizerErrorCategory Category { get; set; } = SynchronizerErrorCategory.Unknown;
+    public string OperationType { get; set; }
+    public string RequestType { get; set; }
+    public Guid? FolderId { get; set; }
+    public string FolderName { get; set; }
+    public Guid? CalendarId { get; set; }
+    public string CalendarName { get; set; }
+    public string ScopeName { get; set; }
+    public bool WasHandled { get; set; }
+    public string HandledBy { get; set; }
+    public bool CanContinueSync { get; set; }
+    public bool IsEntityNotFound { get; set; }
+    public string ExceptionType { get; set; }
+
+    public static SynchronizationIssue FromErrorContext(SynchronizerErrorContext errorContext)
+    {
+        if (errorContext == null)
+            return null;
+
+        return new SynchronizationIssue
+        {
+            Message = errorContext.ErrorMessage ?? errorContext.Exception?.Message,
+            ErrorCode = errorContext.ErrorCode,
+            Severity = errorContext.Severity,
+            Category = errorContext.Category,
+            OperationType = errorContext.OperationType,
+            RequestType = errorContext.Request?.GetType().Name,
+            FolderId = errorContext.FolderId,
+            FolderName = errorContext.FolderName,
+            CalendarId = errorContext.CalendarId,
+            CalendarName = errorContext.CalendarName,
+            ScopeName = GetScopeName(errorContext),
+            WasHandled = errorContext.WasHandled,
+            HandledBy = errorContext.HandledBy,
+            CanContinueSync = errorContext.CanContinueSync,
+            IsEntityNotFound = errorContext.IsEntityNotFound,
+            ExceptionType = errorContext.Exception?.GetType().Name
+        };
+    }
+
+    public static SynchronizationIssue FromException(
+        Exception exception,
+        string operationType = null,
+        SynchronizerErrorSeverity severity = SynchronizerErrorSeverity.Fatal,
+        SynchronizerErrorCategory category = SynchronizerErrorCategory.Unknown,
+        string scopeName = null)
+    {
+        if (exception == null)
+            return null;
+
+        return new SynchronizationIssue
+        {
+            Message = exception.Message,
+            Severity = severity,
+            Category = category,
+            OperationType = operationType,
+            ScopeName = scopeName,
+            CanContinueSync = severity == SynchronizerErrorSeverity.Recoverable,
+            ExceptionType = exception.GetType().Name
+        };
+    }
+
+    public static SynchronizationIssue FromFolderResult(FolderSyncResult folderResult)
+    {
+        if (folderResult == null || folderResult.Success)
+            return null;
+
+        return new SynchronizationIssue
+        {
+            Message = folderResult.ErrorMessage,
+            Severity = folderResult.ErrorSeverity ?? SynchronizerErrorSeverity.Fatal,
+            Category = folderResult.ErrorCategory ?? SynchronizerErrorCategory.Unknown,
+            OperationType = "FolderSync",
+            FolderId = folderResult.FolderId,
+            FolderName = folderResult.FolderName,
+            ScopeName = folderResult.FolderName
+        };
+    }
+
+    private static string GetScopeName(SynchronizerErrorContext errorContext)
+    {
+        if (!string.IsNullOrWhiteSpace(errorContext.CalendarName))
+            return errorContext.CalendarName;
+
+        if (!string.IsNullOrWhiteSpace(errorContext.FolderName))
+            return errorContext.FolderName;
+
+        return errorContext.Request switch
+        {
+            IFolderActionRequest folderRequest => folderRequest.Folder?.FolderName,
+            IMailActionRequest mailRequest => mailRequest.Item?.Subject,
+            ICalendarActionRequest calendarRequest => calendarRequest.Item?.Title,
+            _ => null
+        };
+    }
+}

Wino.Core.Domain/Models/Synchronization/SynchronizerErrorContext.cs

@@ -31,6 +31,11 @@ public class SynchronizerErrorContext
     /// </summary>
     public IRequestBundle RequestBundle { get; set; }
 
+    /// <summary>
+    /// Gets or sets the original request associated with the error when available.
+    /// </summary>
+    public IRequestBase Request { get; set; }
+
     /// <summary>
     /// Gets or sets additional data associated with the error
     /// </summary>
@@ -76,6 +81,16 @@ public class SynchronizerErrorContext
     /// </summary>
     public string FolderName { get; set; }
 
+    /// <summary>
+    /// Gets or sets the calendar ID associated with the error for calendar sync issue tracking.
+    /// </summary>
+    public Guid? CalendarId { get; set; }
+
+    /// <summary>
+    /// Gets or sets the calendar name for display purposes.
+    /// </summary>
+    public string CalendarName { get; set; }
+
     /// <summary>
     /// Gets or sets the type of operation that failed.
     /// Examples: "FolderSync", "MailSync", "RequestExecution", "Idle"
@@ -89,6 +104,16 @@ public class SynchronizerErrorContext
     /// </summary>
     public bool IsEntityNotFound { get; set; }
 
+    /// <summary>
+    /// Gets or sets whether a synchronizer error handler processed this error.
+    /// </summary>
+    public bool WasHandled { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler type that processed this error.
+    /// </summary>
+    public string HandledBy { get; set; }
+
     /// <summary>
     /// Gets whether this error should be retried based on severity and retry count.
     /// </summary>

Wino.Core.Domain/Translations/en_US/resources.json

@@ -989,6 +989,7 @@
     "StoreRatingDialog_MessageFirstLine": "All feedbacks are appreciated and they will make much Wino better in the future. Would you like to rate Wino in Microsoft Store?",
     "StoreRatingDialog_MessageSecondLine": "Would you like to rate Wino Mail in Microsoft Store?",
     "StoreRatingDialog_Title": "Enjoying Wino?",
+    "SynchronizationIssueFormat_WithScope": "{0}: {1}",
     "SynchronizationFolderReport_Failed": "synchronization is failed",
     "SynchronizationFolderReport_Success": "up to date",
     "SystemFolderConfigDialog_ArchiveFolderDescription": "Archived messages will be moved to here.",

Wino.Core.Tests/CalendarPageViewModelTests.cs

@@ -2,6 +2,7 @@ using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Globalization;
 using CommunityToolkit.Mvvm.Collections;
+using CommunityToolkit.Mvvm.Messaging;
 using FluentAssertions;
 using Itenso.TimePeriod;
 using Moq;
@@ -10,9 +11,12 @@ using Wino.Calendar.ViewModels.Data;
 using Wino.Calendar.ViewModels.Interfaces;
 using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Calendar;
+using Wino.Core.Domain.Models.Navigation;
+using Wino.Messaging.Client.Calendar;
 using Xunit;
 
 namespace Wino.Core.Tests;
@@ -155,19 +159,140 @@ public class CalendarPageViewModelTests
         calendarService.Verify(service => service.GetCalendarEventsAsync(It.Is<IAccountCalendar>(calendar => calendar.Id == hiddenCalendar.Id), It.IsAny<ITimePeriod>()), Times.Never);
     }
 
+    [Fact]
+    public async Task CalendarItemAddedMessage_AddsVisibleItemWithoutReloadAndMarksBusy()
+    {
+        var settings = CreateSettings();
+        var preferencesService = CreatePreferencesService(settings);
+        var calendarService = new Mock<ICalendarService>();
+
+        var account = CreateAccount();
+        var calendar = CreateCalendar(account, "Calendar");
+        var accountCalendarViewModel = new AccountCalendarViewModel(account, calendar);
+        var existingItem = CreateCalendarItem(calendar.Id, new DateTime(2026, 3, 20, 9, 0, 0), "Existing");
+
+        calendarService
+            .Setup(service => service.GetCalendarEventsAsync(It.IsAny<IAccountCalendar>(), It.IsAny<ITimePeriod>()))
+            .ReturnsAsync([existingItem]);
+
+        var viewModel = CreateViewModel(
+            calendarService.Object,
+            preferencesService.Object,
+            new DateOnly(2026, 3, 20),
+            new FakeAccountCalendarStateService([accountCalendarViewModel]));
+
+        viewModel.OnNavigatedTo(NavigationMode.New, null!);
+
+        try
+        {
+            await viewModel.ApplyDisplayRequestAsync(new CalendarDisplayRequest(CalendarDisplayType.Day, new DateOnly(2026, 3, 20)));
+
+            var optimisticItem = CreateCalendarItem(calendar.Id, new DateTime(2026, 3, 20, 10, 0, 0), "Optimistic");
+            optimisticItem.AssignedCalendar = accountCalendarViewModel;
+
+            WeakReferenceMessenger.Default.Send(new CalendarItemAdded(optimisticItem, EntityUpdateSource.ClientUpdated));
+
+            viewModel.CalendarItems.Should().HaveCount(2);
+            viewModel.CalendarItems.Should().Contain(item => item.Id == optimisticItem.Id && item.IsBusy);
+            calendarService.Verify(service => service.GetCalendarEventsAsync(It.IsAny<IAccountCalendar>(), It.IsAny<ITimePeriod>()), Times.Once);
+        }
+        finally
+        {
+            viewModel.OnNavigatedFrom(NavigationMode.Back, null!);
+        }
+    }
+
+    [Fact]
+    public async Task CalendarItemDeletedMessage_RemovesVisibleItemWithoutReload()
+    {
+        var settings = CreateSettings();
+        var preferencesService = CreatePreferencesService(settings);
+        var calendarService = new Mock<ICalendarService>();
+
+        var account = CreateAccount();
+        var calendar = CreateCalendar(account, "Calendar");
+        var accountCalendarViewModel = new AccountCalendarViewModel(account, calendar);
+        var existingItem = CreateCalendarItem(calendar.Id, new DateTime(2026, 3, 20, 9, 0, 0), "Existing");
+
+        calendarService
+            .Setup(service => service.GetCalendarEventsAsync(It.IsAny<IAccountCalendar>(), It.IsAny<ITimePeriod>()))
+            .ReturnsAsync([existingItem]);
+
+        var viewModel = CreateViewModel(
+            calendarService.Object,
+            preferencesService.Object,
+            new DateOnly(2026, 3, 20),
+            new FakeAccountCalendarStateService([accountCalendarViewModel]));
+
+        viewModel.OnNavigatedTo(NavigationMode.New, null!);
+
+        try
+        {
+            await viewModel.ApplyDisplayRequestAsync(new CalendarDisplayRequest(CalendarDisplayType.Day, new DateOnly(2026, 3, 20)));
+
+            WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(existingItem, EntityUpdateSource.ClientUpdated));
+
+            viewModel.CalendarItems.Should().BeEmpty();
+            calendarService.Verify(service => service.GetCalendarEventsAsync(It.IsAny<IAccountCalendar>(), It.IsAny<ITimePeriod>()), Times.Once);
+        }
+        finally
+        {
+            viewModel.OnNavigatedFrom(NavigationMode.Back, null!);
+        }
+    }
+
+    [Fact]
+    public async Task CalendarItemAddedMessage_ReconcilesTrackedLocalPreviewInPlace()
+    {
+        var settings = CreateSettings();
+        var preferencesService = CreatePreferencesService(settings);
+        var calendarService = new Mock<ICalendarService>();
+
+        var account = CreateAccount();
+        var calendar = CreateCalendar(account, "Calendar");
+        var accountCalendarViewModel = new AccountCalendarViewModel(account, calendar);
+        var localPreview = CreateCalendarItem(calendar.Id, new DateTime(2026, 3, 20, 9, 0, 0), "Local preview");
+
+        calendarService
+            .Setup(service => service.GetCalendarEventsAsync(It.IsAny<IAccountCalendar>(), It.IsAny<ITimePeriod>()))
+            .ReturnsAsync([localPreview]);
+
+        var viewModel = CreateViewModel(
+            calendarService.Object,
+            preferencesService.Object,
+            new DateOnly(2026, 3, 20),
+            new FakeAccountCalendarStateService([accountCalendarViewModel]));
+
+        viewModel.OnNavigatedTo(NavigationMode.New, null!);
+
+        try
+        {
+            await viewModel.ApplyDisplayRequestAsync(new CalendarDisplayRequest(CalendarDisplayType.Day, new DateOnly(2026, 3, 20)));
+
+            var syncedItem = CreateCalendarItem(calendar.Id, localPreview.StartDate, "Synced");
+            syncedItem.RemoteEventId = "remote-event-id".WithClientTrackingId(localPreview.Id);
+            syncedItem.AssignedCalendar = accountCalendarViewModel;
+
+            WeakReferenceMessenger.Default.Send(new CalendarItemAdded(syncedItem, EntityUpdateSource.Server));
+
+            viewModel.CalendarItems.Should().ContainSingle();
+            viewModel.CalendarItems[0].Id.Should().Be(syncedItem.Id);
+            viewModel.CalendarItems[0].Title.Should().Be("Synced");
+            viewModel.CalendarItems[0].IsBusy.Should().BeFalse();
+            viewModel.CalendarItems.Should().NotContain(item => item.Id == localPreview.Id);
+        }
+        finally
+        {
+            viewModel.OnNavigatedFrom(NavigationMode.Back, null!);
+        }
+    }
+
     private static CalendarPageViewModel CreateViewModel(
         ICalendarService calendarService,
         IPreferencesService preferencesService,
         DateOnly today)
     {
-        var account = new MailAccount
-        {
-            Id = Guid.NewGuid(),
-            Name = "Primary",
-            SenderName = "Primary",
-            Address = "primary@example.com",
-            ProviderType = MailProviderType.Outlook
-        };
+        var account = CreateAccount();
 
         var calendar = CreateCalendar(account, "Calendar");
         var accountCalendarViewModel = new AccountCalendarViewModel(account, calendar);
@@ -217,6 +342,26 @@ public class CalendarPageViewModelTests
             IsSynchronizationEnabled = true
         };
 
+    private static MailAccount CreateAccount()
+        => new()
+        {
+            Id = Guid.NewGuid(),
+            Name = "Primary",
+            SenderName = "Primary",
+            Address = "primary@example.com",
+            ProviderType = MailProviderType.Outlook
+        };
+
+    private static CalendarItem CreateCalendarItem(Guid calendarId, DateTime startDate, string title)
+        => new()
+        {
+            Id = Guid.NewGuid(),
+            CalendarId = calendarId,
+            StartDate = startDate,
+            DurationInSeconds = TimeSpan.FromMinutes(30).TotalSeconds,
+            Title = title
+        };
+
     private static Mock<IPreferencesService> CreatePreferencesService(CalendarSettings settings)
         => CreatePreferencesService(() => settings);
 

Wino.Core.Tests/Services/CreateCalendarEventRequestTests.cs

@@ -32,8 +32,10 @@ public sealed class CreateCalendarEventRequestTests
 
             recipient.Added.Should().ContainSingle();
             recipient.Deleted.Should().ContainSingle();
-            recipient.Added[0].Id.Should().Be(request.LocalCalendarItemId!.Value);
-            recipient.Deleted[0].Id.Should().Be(request.LocalCalendarItemId!.Value);
+            recipient.Added[0].CalendarItem.Id.Should().Be(request.LocalCalendarItemId!.Value);
+            recipient.Deleted[0].CalendarItem.Id.Should().Be(request.LocalCalendarItemId!.Value);
+            recipient.Added[0].Source.Should().Be(EntityUpdateSource.ClientUpdated);
+            recipient.Deleted[0].Source.Should().Be(EntityUpdateSource.ClientReverted);
         }
         finally
         {
@@ -117,11 +119,11 @@ public sealed class CreateCalendarEventRequestTests
         IRecipient<CalendarItemAdded>,
         IRecipient<CalendarItemDeleted>
     {
-        public List<CalendarItem> Added { get; } = [];
-        public List<CalendarItem> Deleted { get; } = [];
+        public List<CalendarItemAdded> Added { get; } = [];
+        public List<CalendarItemDeleted> Deleted { get; } = [];
 
-        public void Receive(CalendarItemAdded message) => Added.Add(message.CalendarItem);
+        public void Receive(CalendarItemAdded message) => Added.Add(message);
 
-        public void Receive(CalendarItemDeleted message) => Deleted.Add(message.CalendarItem);
+        public void Receive(CalendarItemDeleted message) => Deleted.Add(message);
     }
 }

Wino.Core.Tests/Services/MailRequestStateTests.cs

@@ -28,8 +28,8 @@ public sealed class MailRequestStateTests
 
             mailCopy.IsRead.Should().BeFalse();
             recipient.Updated.Should().HaveCount(2);
-            recipient.Updated[0].Source.Should().Be(MailUpdateSource.ClientUpdated);
-            recipient.Updated[1].Source.Should().Be(MailUpdateSource.ClientReverted);
+            recipient.Updated[0].Source.Should().Be(EntityUpdateSource.ClientUpdated);
+            recipient.Updated[1].Source.Should().Be(EntityUpdateSource.ClientReverted);
             recipient.Updated[1].UpdatedMail.IsRead.Should().BeFalse();
         }
         finally
@@ -56,8 +56,8 @@ public sealed class MailRequestStateTests
 
             mailCopy.IsFlagged.Should().BeFalse();
             recipient.Updated.Should().HaveCount(2);
-            recipient.Updated[0].Source.Should().Be(MailUpdateSource.ClientUpdated);
-            recipient.Updated[1].Source.Should().Be(MailUpdateSource.ClientReverted);
+            recipient.Updated[0].Source.Should().Be(EntityUpdateSource.ClientUpdated);
+            recipient.Updated[1].Source.Should().Be(EntityUpdateSource.ClientReverted);
             recipient.Updated[1].UpdatedMail.IsFlagged.Should().BeFalse();
         }
         finally

Wino.Core.Tests/Services/SynchronizationResultTests.cs

@@ -0,0 +1,80 @@
+using FluentAssertions;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Synchronization;
+using Wino.Core.Services;
+using Xunit;
+
+namespace Wino.Core.Tests.Services;
+
+public class SynchronizationResultTests
+{
+    [Fact]
+    public void Mail_result_merge_issues_should_mark_success_as_partial_and_set_exception()
+    {
+        var result = MailSynchronizationResult.Completed([]);
+        var issues = new[]
+        {
+            new SynchronizationIssue
+            {
+                Message = "Create event failed",
+                OperationType = "RequestExecution",
+                Severity = SynchronizerErrorSeverity.Fatal
+            }
+        };
+
+        result.MergeIssues(issues);
+
+        result.CompletedState.Should().Be(SynchronizationCompletedState.PartiallyCompleted);
+        result.Issues.Should().ContainSingle();
+        result.Exception.Should().NotBeNull();
+        result.Exception!.Message.Should().Be("Create event failed");
+    }
+
+    [Fact]
+    public void Calendar_result_merge_issues_should_mark_success_as_partial_and_preserve_issue()
+    {
+        var result = CalendarSynchronizationResult.Empty;
+        var issues = new[]
+        {
+            new SynchronizationIssue
+            {
+                Message = "Calendar API rate limit",
+                OperationType = "CalendarSync",
+                Severity = SynchronizerErrorSeverity.Transient
+            }
+        };
+
+        result.MergeIssues(issues);
+
+        result.CompletedState.Should().Be(SynchronizationCompletedState.PartiallyCompleted);
+        result.Issues.Should().ContainSingle(issue => issue.Message == "Calendar API rate limit");
+        result.Exception.Should().NotBeNull();
+        result.Exception!.Message.Should().Be("Calendar API rate limit");
+    }
+
+    [Fact]
+    public async Task Error_factory_should_record_handled_metadata_on_context()
+    {
+        var factory = new SynchronizerErrorHandlingFactory();
+        factory.RegisterHandler(new TestErrorHandler());
+
+        var context = new SynchronizerErrorContext
+        {
+            ErrorMessage = "Handled sync error"
+        };
+
+        var handled = await factory.HandleErrorAsync(context);
+
+        handled.Should().BeTrue();
+        context.WasHandled.Should().BeTrue();
+        context.HandledBy.Should().Be(nameof(TestErrorHandler));
+    }
+
+    private sealed class TestErrorHandler : ISynchronizerErrorHandler
+    {
+        public bool CanHandle(SynchronizerErrorContext error) => true;
+
+        public Task<bool> HandleAsync(SynchronizerErrorContext error) => Task.FromResult(true);
+    }
+}

Wino.Core.Tests/Synchronizers/WinoSynchronizerCalendarRequestTests.cs

@@ -0,0 +1,136 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.Messaging;
+using FluentAssertions;
+using Wino.Core.Domain.Entities.Calendar;
+using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.MailItem;
+using Wino.Core.Domain.Models.Synchronization;
+using Wino.Core.Requests.Calendar;
+using Wino.Core.Synchronizers;
+using Wino.Messaging.UI;
+using Xunit;
+
+namespace Wino.Core.Tests.Synchronizers;
+
+public sealed class WinoSynchronizerCalendarRequestTests
+{
+    [Fact]
+    public async Task Calendar_request_failure_should_complete_actions_and_reset_state()
+    {
+        var recipient = new SynchronizationActionsCompletedRecipient();
+        WeakReferenceMessenger.Default.RegisterAll(recipient);
+
+        try
+        {
+            var synchronizer = new TestCalendarSynchronizer(throwDuringRequestExecution: true);
+            var calendarItemId = Guid.NewGuid();
+
+            synchronizer.QueueRequest(new DeleteCalendarEventRequest(new CalendarItem { Id = calendarItemId }));
+
+            var result = await synchronizer.SynchronizeCalendarEventsAsync(new CalendarSynchronizationOptions
+            {
+                AccountId = synchronizer.Account.Id,
+                Type = CalendarSynchronizationType.ExecuteRequests
+            });
+
+            result.CompletedState.Should().Be(SynchronizationCompletedState.Failed);
+            synchronizer.State.Should().Be(AccountSynchronizerState.Idle);
+            synchronizer.GetPendingCalendarOperationIds().Should().BeEmpty();
+            recipient.CompletedAccountIds.Should().ContainSingle().Which.Should().Be(synchronizer.Account.Id);
+        }
+        finally
+        {
+            WeakReferenceMessenger.Default.UnregisterAll(recipient);
+        }
+    }
+
+    [Fact]
+    public async Task Calendar_request_success_should_complete_actions_and_reset_state()
+    {
+        var recipient = new SynchronizationActionsCompletedRecipient();
+        WeakReferenceMessenger.Default.RegisterAll(recipient);
+
+        try
+        {
+            var synchronizer = new TestCalendarSynchronizer(throwDuringRequestExecution: false);
+            var calendarItemId = Guid.NewGuid();
+
+            synchronizer.QueueRequest(new DeleteCalendarEventRequest(new CalendarItem { Id = calendarItemId }));
+
+            var result = await synchronizer.SynchronizeCalendarEventsAsync(new CalendarSynchronizationOptions
+            {
+                AccountId = synchronizer.Account.Id,
+                Type = CalendarSynchronizationType.ExecuteRequests
+            });
+
+            result.CompletedState.Should().Be(SynchronizationCompletedState.Success);
+            synchronizer.State.Should().Be(AccountSynchronizerState.Idle);
+            synchronizer.GetPendingCalendarOperationIds().Should().BeEmpty();
+            recipient.CompletedAccountIds.Should().ContainSingle().Which.Should().Be(synchronizer.Account.Id);
+        }
+        finally
+        {
+            WeakReferenceMessenger.Default.UnregisterAll(recipient);
+        }
+    }
+
+    public sealed class SynchronizationActionsCompletedRecipient : IRecipient<SynchronizationActionsCompleted>
+    {
+        public List<Guid> CompletedAccountIds { get; } = [];
+
+        public void Receive(SynchronizationActionsCompleted message) => CompletedAccountIds.Add(message.AccountId);
+    }
+
+    private sealed class TestCalendarSynchronizer : WinoSynchronizer<object, object, object>
+    {
+        private readonly bool _throwDuringRequestExecution;
+
+        public TestCalendarSynchronizer(bool throwDuringRequestExecution)
+            : base(new MailAccount { Id = Guid.NewGuid(), Name = "Test account" }, WeakReferenceMessenger.Default)
+        {
+            _throwDuringRequestExecution = throwDuringRequestExecution;
+        }
+
+        public override uint BatchModificationSize => 1;
+        public override uint InitialMessageDownloadCountPerFolder => 0;
+
+        public override Task ExecuteNativeRequestsAsync(List<IRequestBundle<object>> batchedRequests, CancellationToken cancellationToken = default)
+            => _throwDuringRequestExecution
+                ? Task.FromException(new InvalidOperationException("Calendar request execution failed."))
+                : Task.CompletedTask;
+
+        public override List<IRequestBundle<object>> DeleteCalendarEvent(DeleteCalendarEventRequest request)
+            => [new TestRequestBundle(new object(), request)];
+
+        public override Task<List<NewMailItemPackage>> CreateNewMailPackagesAsync(
+            object message,
+            Wino.Core.Domain.Entities.Mail.MailItemFolder assignedFolder,
+            CancellationToken cancellationToken = default)
+            => Task.FromResult(new List<NewMailItemPackage>());
+
+        protected override Task<MailSynchronizationResult> SynchronizeMailsInternalAsync(MailSynchronizationOptions options, CancellationToken cancellationToken = default)
+            => Task.FromResult(MailSynchronizationResult.Empty);
+
+        protected override Task<CalendarSynchronizationResult> SynchronizeCalendarEventsInternalAsync(CalendarSynchronizationOptions options, CancellationToken cancellationToken = default)
+            => Task.FromResult(CalendarSynchronizationResult.Empty);
+    }
+
+    private sealed class TestRequestBundle : IRequestBundle<object>
+    {
+        public TestRequestBundle(object nativeRequest, IRequestBase request)
+        {
+            NativeRequest = nativeRequest;
+            Request = request;
+        }
+
+        public string BundleId { get; set; } = Guid.NewGuid().ToString();
+        public IUIChangeRequest UIChangeRequest => Request;
+        public object NativeRequest { get; }
+        public IRequestBase Request { get; }
+    }
+}

Wino.Core.ViewModels/CalendarBaseViewModel.cs

@@ -11,13 +11,13 @@ public class CalendarBaseViewModel : CoreBaseViewModel,
     IRecipient<CalendarItemUpdated>,
     IRecipient<CalendarItemDeleted>
 {
-    public void Receive(CalendarItemAdded message) => DispatchToUIThread(() => OnCalendarItemAdded(message.CalendarItem));
+    public void Receive(CalendarItemAdded message) => DispatchToUIThread(() => OnCalendarItemAdded(message.CalendarItem, message.Source));
     public void Receive(CalendarItemUpdated message) => DispatchToUIThread(() => OnCalendarItemUpdated(message.CalendarItem, message.Source));
-    public void Receive(CalendarItemDeleted message) => DispatchToUIThread(() => OnCalendarItemDeleted(message.CalendarItem));
+    public void Receive(CalendarItemDeleted message) => DispatchToUIThread(() => OnCalendarItemDeleted(message.CalendarItem, message.Source));
 
-    protected virtual void OnCalendarItemAdded(CalendarItem calendarItem) { }
-    protected virtual void OnCalendarItemUpdated(CalendarItem calendarItem, CalendarItemUpdateSource source) { }
-    protected virtual void OnCalendarItemDeleted(CalendarItem calendarItem) { }
+    protected virtual void OnCalendarItemAdded(CalendarItem calendarItem, EntityUpdateSource source) { }
+    protected virtual void OnCalendarItemUpdated(CalendarItem calendarItem, EntityUpdateSource source) { }
+    protected virtual void OnCalendarItemDeleted(CalendarItem calendarItem, EntityUpdateSource source) { }
 
     private void DispatchToUIThread(Action action)
     {

Wino.Core/Requests/Calendar/AcceptEventRequest.cs

@@ -27,13 +27,13 @@ public record AcceptEventRequest(CalendarItem Item, string ResponseMessage = nul
         Item.Status = CalendarItemStatus.Accepted;
         
         // Notify UI that the event status was updated
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientUpdated));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
         // If acceptance fails, revert to the previous status
         Item.Status = _previousStatus;
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientReverted));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Requests/Calendar/CreateCalendarEventRequest.cs

@@ -47,7 +47,7 @@ public record CreateCalendarEventRequest : CalendarRequestBase
         if (Item == null)
             return;
 
-        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
@@ -55,7 +55,7 @@ public record CreateCalendarEventRequest : CalendarRequestBase
         if (Item == null)
             return;
 
-        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item, EntityUpdateSource.ClientReverted));
     }
 
     private static bool ShouldCreateOptimisticItem(CalendarEventComposeResult composeResult)

Wino.Core/Requests/Calendar/DeclineEventRequest.cs

@@ -27,13 +27,13 @@ public record DeclineEventRequest(CalendarItem Item, string ResponseMessage = nu
         Item.Status = CalendarItemStatus.Cancelled;
 
         // Notify UI that the event status was updated
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientUpdated));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
         // If decline fails, revert to the previous status
         Item.Status = _previousStatus;
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientReverted));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Requests/Calendar/DeleteCalendarEventRequest.cs

@@ -21,12 +21,12 @@ public record DeleteCalendarEventRequest(CalendarItem Item) : CalendarRequestBas
     public override void ApplyUIChanges()
     {
         // Notify UI that the event was deleted
-        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
         // If deletion fails, we should notify the UI to add it back
-        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Requests/Calendar/OutlookDeclineEventRequest.cs

@@ -26,13 +26,13 @@ public record OutlookDeclineEventRequest(CalendarItem Item, string ResponseMessa
     {
         // In Outlook, declined events are deleted from the calendar after sync
         // Send deleted message to remove from UI immediately
-        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
         // If decline fails, restore the previous status and re-add the event
         Item.Status = _previousStatus;
-        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item));
+        WeakReferenceMessenger.Default.Send(new CalendarItemAdded(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Requests/Calendar/TentativeEventRequest.cs

@@ -27,13 +27,13 @@ public record TentativeEventRequest(CalendarItem Item, string ResponseMessage =
         Item.Status = CalendarItemStatus.Tentative;
         
         // Notify UI that the event status was updated
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientUpdated));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
         // If tentative acceptance fails, revert to the previous status
         Item.Status = _previousStatus;
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientReverted));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Requests/Calendar/UpdateCalendarEventRequest.cs

@@ -33,7 +33,7 @@ public record UpdateCalendarEventRequest(CalendarItem Item, List<CalendarEventAt
     public override void ApplyUIChanges()
     {
         // Notify UI that the event was updated locally
-        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientUpdated));
+        WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
@@ -42,12 +42,12 @@ public record UpdateCalendarEventRequest(CalendarItem Item, List<CalendarEventAt
         if (OriginalItem != null && OriginalAttendees != null)
         {
             // Send the original item back to restore UI state
-            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(OriginalItem, CalendarItemUpdateSource.ClientReverted));
+            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(OriginalItem, EntityUpdateSource.ClientReverted));
         }
         else
         {
             // Fallback: just notify with current item to trigger refresh
-            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, CalendarItemUpdateSource.ClientReverted));
+            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(Item, EntityUpdateSource.ClientReverted));
         }
     }
 }

Wino.Core/Requests/Folder/EmptyFolderRequest.cs

@@ -16,7 +16,7 @@ public record EmptyFolderRequest(MailItemFolder Folder, List<MailCopy> MailsToDe
     {
         foreach (var item in MailsToDelete)
         {
-            WeakReferenceMessenger.Default.Send(new MailRemovedMessage(item));
+            WeakReferenceMessenger.Default.Send(new MailRemovedMessage(item, EntityUpdateSource.ClientUpdated));
         }
     }
 
@@ -24,7 +24,7 @@ public record EmptyFolderRequest(MailItemFolder Folder, List<MailCopy> MailsToDe
     {
         foreach (var item in MailsToDelete)
         {
-            WeakReferenceMessenger.Default.Send(new MailAddedMessage(item));
+            WeakReferenceMessenger.Default.Send(new MailAddedMessage(item, EntityUpdateSource.ClientReverted));
         }
     }
 

Wino.Core/Requests/Folder/MarkFolderAsReadRequest.cs

@@ -26,7 +26,7 @@ public record MarkFolderAsReadRequest(MailItemFolder Folder, List<MailCopy> Mail
 
             item.IsRead = true;
 
-            WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(item, MailUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead));
+            WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(item, EntityUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead));
         }
     }
 
@@ -41,7 +41,7 @@ public record MarkFolderAsReadRequest(MailItemFolder Folder, List<MailCopy> Mail
 
             item.IsRead = false;
 
-            WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(item, MailUpdateSource.ClientReverted, MailCopyChangeFlags.IsRead));
+            WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(item, EntityUpdateSource.ClientReverted, MailCopyChangeFlags.IsRead));
         }
     }
 }

Wino.Core/Requests/Mail/ArchiveRequest.cs

@@ -41,12 +41,12 @@ public record ArchiveRequest(bool IsArchiving, MailCopy Item, MailItemFolder Fro
 
     public override void ApplyUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item, EntityUpdateSource.ClientReverted));
     }
 }
 

Wino.Core/Requests/Mail/ChangeFlagRequest.cs

@@ -33,7 +33,7 @@ public record ChangeFlagRequest(MailCopy Item, bool IsFlagged) : MailRequestBase
 
         Item.IsFlagged = IsFlagged;
 
-        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, MailUpdateSource.ClientUpdated, MailCopyChangeFlags.IsFlagged));
+        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, EntityUpdateSource.ClientUpdated, MailCopyChangeFlags.IsFlagged));
     }
 
     public override void RevertUIChanges()
@@ -43,7 +43,7 @@ public record ChangeFlagRequest(MailCopy Item, bool IsFlagged) : MailRequestBase
 
         Item.IsFlagged = _originalIsFlagged;
 
-        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, MailUpdateSource.ClientReverted, MailCopyChangeFlags.IsFlagged));
+        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, EntityUpdateSource.ClientReverted, MailCopyChangeFlags.IsFlagged));
     }
 }
 

Wino.Core/Requests/Mail/DeleteRequest.cs

@@ -22,12 +22,12 @@ public record DeleteRequest(MailCopy MailItem) : MailRequestBase(MailItem),
 
     public override void ApplyUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item, EntityUpdateSource.ClientReverted));
     }
 }
 

Wino.Core/Requests/Mail/MarkReadRequest.cs

@@ -32,7 +32,7 @@ public record MarkReadRequest(MailCopy Item, bool IsRead) : MailRequestBase(Item
 
         Item.IsRead = IsRead;
 
-        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, MailUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead));
+        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, EntityUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead));
     }
 
     public override void RevertUIChanges()
@@ -42,7 +42,7 @@ public record MarkReadRequest(MailCopy Item, bool IsRead) : MailRequestBase(Item
 
         Item.IsRead = _originalIsRead;
 
-        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, MailUpdateSource.ClientReverted, MailCopyChangeFlags.IsRead));
+        WeakReferenceMessenger.Default.Send(new MailUpdatedMessage(Item, EntityUpdateSource.ClientReverted, MailCopyChangeFlags.IsRead));
     }
 }
 

Wino.Core/Requests/Mail/MoveRequest.cs

@@ -18,12 +18,12 @@ public record MoveRequest(MailCopy Item, MailItemFolder FromFolder, MailItemFold
 
     public override void ApplyUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item, EntityUpdateSource.ClientReverted));
     }
 }
 

Wino.Core/Requests/Mail/SendDraftRequest.cs

@@ -34,11 +34,11 @@ public record SendDraftRequest(SendDraftPreparationRequest Request)
 
     public override void ApplyUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailRemovedMessage(Item, EntityUpdateSource.ClientUpdated));
     }
 
     public override void RevertUIChanges()
     {
-        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item));
+        WeakReferenceMessenger.Default.Send(new MailAddedMessage(Item, EntityUpdateSource.ClientReverted));
     }
 }

Wino.Core/Services/SynchronizationManager.cs

@@ -146,7 +146,10 @@ public class SynchronizationManager : ISynchronizationManager
         {
             _logger.Error("Could not find or create synchronizer for account {AccountId}", options.AccountId);
 
-            return MailSynchronizationResult.Failed(new Exception("Can't create/get synchronizer."));
+            var exception = new InvalidOperationException("Can't create/get synchronizer.");
+            return MailSynchronizationResult
+                .Failed(exception)
+                .MergeIssues([SynchronizationIssue.FromException(exception, "MailSync")]);
         }
 
         _logger.Information("Starting mail synchronization for account {AccountId} with type {SyncType}",
@@ -185,12 +188,16 @@ public class SynchronizationManager : ISynchronizationManager
             // Create app notification for authentication attention
             _notificationBuilder.CreateAttentionRequiredNotification(authEx.Account);
 
-            return MailSynchronizationResult.Failed(authEx);
+            return MailSynchronizationResult
+                .Failed(authEx)
+                .MergeIssues([SynchronizationIssue.FromException(authEx, "MailSync", SynchronizerErrorSeverity.AuthRequired)]);
         }
         catch (Exception ex)
         {
             _logger.Error(ex, "Mail synchronization failed for account {AccountId}", options.AccountId);
-            return MailSynchronizationResult.Failed(ex);
+            return MailSynchronizationResult
+                .Failed(ex)
+                .MergeIssues([SynchronizationIssue.FromException(ex, "MailSync")]);
         }
     }
 
@@ -432,7 +439,10 @@ public class SynchronizationManager : ISynchronizationManager
         if (synchronizer == null)
         {
             _logger.Error("Could not find or create synchronizer for account {AccountId}", options.AccountId);
-            return CalendarSynchronizationResult.Failed;
+            var exception = new InvalidOperationException("Can't create/get synchronizer.");
+            return CalendarSynchronizationResult
+                .Failed(exception)
+                .MergeIssues([SynchronizationIssue.FromException(exception, "CalendarSync")]);
         }
 
         _logger.Information("Starting calendar synchronization for account {AccountId} with type {SyncType}",
@@ -478,12 +488,16 @@ public class SynchronizationManager : ISynchronizationManager
             // Create app notification for authentication attention
             _notificationBuilder.CreateAttentionRequiredNotification(authEx.Account);
 
-            return CalendarSynchronizationResult.Failed;
+            return CalendarSynchronizationResult
+                .Failed(authEx)
+                .MergeIssues([SynchronizationIssue.FromException(authEx, "CalendarSync", SynchronizerErrorSeverity.AuthRequired)]);
         }
         catch (Exception ex)
         {
             _logger.Error(ex, "Calendar synchronization failed for account {AccountId}", options.AccountId);
-            return CalendarSynchronizationResult.Failed;
+            return CalendarSynchronizationResult
+                .Failed(ex)
+                .MergeIssues([SynchronizationIssue.FromException(ex, "CalendarSync")]);
         }
         finally
         {

Wino.Core/Services/SynchronizerErrorHandlingFactory.cs

@@ -37,13 +37,20 @@ public class SynchronizerErrorHandlingFactory
                 _logger.Debug("Found handler {HandlerType} for error code {ErrorCode} message {ErrorMessage}",
                     handler.GetType().Name, error.ErrorCode, error.ErrorMessage);
 
-                return await handler.HandleAsync(error);
+                var handled = await handler.HandleAsync(error);
+                error.WasHandled = handled;
+                error.HandledBy = handled ? handler.GetType().Name : null;
+
+                return handled;
             }
         }
 
         _logger.Debug("No handler found for error code {ErrorCode} message {ErrorMessage}",
             error.ErrorCode, error.ErrorMessage);
 
+        error.WasHandled = false;
+        error.HandledBy = null;
+
         return false;
     }
 }

Wino.Core/Synchronizers/BaseSynchronizer.cs

@@ -11,6 +11,7 @@ using Wino.Core.Domain.Entities.Shared;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Accounts;
+using Wino.Core.Domain.Models.Synchronization;
 using Wino.Core.Requests.Bundles;
 using Wino.Messaging.UI;
 
@@ -24,6 +25,7 @@ public abstract partial class BaseSynchronizer<TBaseRequest> : ObservableObject,
     protected List<IRequestBase> changeRequestQueue = [];
     private readonly ConcurrentDictionary<Guid, byte> _pendingMailOperationIds = new();
     private readonly ConcurrentDictionary<Guid, byte> _pendingCalendarOperationIds = new();
+    private readonly ConcurrentQueue<SynchronizationIssue> _capturedSynchronizationIssues = new();
     protected readonly IMessenger Messenger;
     
     public MailAccount Account { get; }
@@ -135,6 +137,8 @@ public abstract partial class BaseSynchronizer<TBaseRequest> : ObservableObject,
 
     public bool HasPendingCalendarOperation(Guid calendarItemId) => _pendingCalendarOperationIds.ContainsKey(calendarItemId);
 
+    public IReadOnlyCollection<Guid> GetPendingCalendarOperationIds() => _pendingCalendarOperationIds.Keys.ToArray();
+
     protected void TrackQueuedRequest(IRequestBase request)
     {
         if (request is IMailActionRequest mailActionRequest)
@@ -173,6 +177,27 @@ public abstract partial class BaseSynchronizer<TBaseRequest> : ObservableObject,
             UntrackProcessedRequest(request);
     }
 
+    protected void ResetCapturedSynchronizationIssues()
+    {
+        while (_capturedSynchronizationIssues.TryDequeue(out _))
+        {
+        }
+    }
+
+    protected void CaptureSynchronizationIssue(SynchronizationIssue issue)
+    {
+        if (issue == null || string.IsNullOrWhiteSpace(issue.Message))
+            return;
+
+        _capturedSynchronizationIssues.Enqueue(issue);
+    }
+
+    protected void CaptureSynchronizationIssue(SynchronizerErrorContext errorContext)
+        => CaptureSynchronizationIssue(SynchronizationIssue.FromErrorContext(errorContext));
+
+    protected IReadOnlyList<SynchronizationIssue> GetCapturedSynchronizationIssues()
+        => _capturedSynchronizationIssues.ToArray();
+
     /// <summary>
     /// Runs existing queued requests in the queue.
     /// </summary>

Wino.Core/Synchronizers/GmailSynchronizer.cs

@@ -522,8 +522,9 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
             .Where(c => c.IsSynchronizationEnabled)
             .ToList();
 
-        // TODO: Better logging and exception handling.
         foreach (var calendar in localCalendars)
+        {
+            try
             {
                 var request = _calendarService.Events.List(calendar.RemoteCalendarId);
 
@@ -535,14 +536,10 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
 
                 if (!string.IsNullOrEmpty(calendar.SynchronizationDeltaToken))
                 {
-                // If a sync token is available, perform an incremental sync
                     request.SyncToken = calendar.SynchronizationDeltaToken;
                 }
                 else
                 {
-                // If no sync token, perform an initial sync
-                // Fetch events from the past year
-
                     request.TimeMinDateTimeOffset = DateTimeOffset.UtcNow.AddYears(-1);
                 }
 
@@ -553,29 +550,21 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
 
                 do
                 {
-                // Execute the request
-                var events = await request.ExecuteAsync();
+                    var events = await request.ExecuteAsync(cancellationToken).ConfigureAwait(false);
 
-                // Process the fetched events
                     if (events.Items != null)
                     {
                         allEvents.AddRange(events.Items);
                     }
 
-                // Get the next page token and sync token
                     nextPageToken = events.NextPageToken;
                     syncToken = events.NextSyncToken;
-
-                // Set the next page token for subsequent requests
                     request.PageToken = nextPageToken;
-
-            } while (!string.IsNullOrEmpty(nextPageToken));
+                }
+                while (!string.IsNullOrEmpty(nextPageToken));
 
                 calendar.SynchronizationDeltaToken = syncToken;
 
-            // allEvents contains new or updated events.
-            // Process them and create/update local calendar items.
-
                 var eventByRemoteId = allEvents
                     .Where(e => !string.IsNullOrWhiteSpace(e.Id))
                     .GroupBy(e => e.Id, StringComparer.Ordinal)
@@ -585,12 +574,59 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
                 {
                     cancellationToken.ThrowIfCancellationRequested();
 
+                    try
+                    {
                         await EnsureRecurringParentProcessedAsync(calendar, @event, eventByRemoteId, cancellationToken).ConfigureAwait(false);
                         await _gmailChangeProcessor.ManageCalendarEventAsync(@event, calendar, Account).ConfigureAwait(false);
                     }
+                    catch (OperationCanceledException)
+                    {
+                        throw;
+                    }
+                    catch (Exception ex)
+                    {
+                        var errorContext = new SynchronizerErrorContext
+                        {
+                            Account = Account,
+                            ErrorMessage = ex.Message,
+                            Exception = ex,
+                            CalendarId = calendar.Id,
+                            CalendarName = calendar.Name,
+                            OperationType = "CalendarEventSync",
+                            Severity = SynchronizerErrorSeverity.Recoverable
+                        };
+
+                        _ = await _gmailSynchronizerErrorHandlerFactory.HandleErrorAsync(errorContext).ConfigureAwait(false);
+                        CaptureSynchronizationIssue(errorContext);
+                        _logger.Error(ex, "Failed to process Gmail event {EventId} for calendar {CalendarName}", @event.Id, calendar.Name);
+                    }
+                }
 
                 await _gmailChangeProcessor.UpdateAccountCalendarAsync(calendar).ConfigureAwait(false);
             }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
+            catch (Exception ex)
+            {
+                var errorContext = new SynchronizerErrorContext
+                {
+                    Account = Account,
+                    ErrorMessage = ex.Message,
+                    Exception = ex,
+                    CalendarId = calendar.Id,
+                    CalendarName = calendar.Name,
+                    OperationType = "CalendarSync"
+                };
+
+                _ = await _gmailSynchronizerErrorHandlerFactory.HandleErrorAsync(errorContext).ConfigureAwait(false);
+                CaptureSynchronizationIssue(errorContext);
+
+                if (!errorContext.CanContinueSync)
+                    throw;
+            }
+        }
 
         return CalendarSynchronizationResult.Empty;
     }
@@ -1674,6 +1710,7 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
             ErrorCode = error.Code,
             ErrorMessage = error.Message,
             RequestBundle = bundle,
+            Request = bundle.Request,
             IsEntityNotFound = isEntityNotFound,
             AdditionalData = new Dictionary<string, object>
             {
@@ -1697,6 +1734,8 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
         // If not handled by any specific handler, apply default error handling
         if (!handled)
         {
+            CaptureSynchronizationIssue(errorContext);
+
             // OutOfMemoryException is a known bug in Gmail SDK.
             if (error.Code == 0)
             {

Wino.Core/Synchronizers/ImapSynchronizer.cs

@@ -763,6 +763,7 @@ public class ImapSynchronizer : WinoSynchronizer<ImapRequest, ImapMessageCreatio
                     ErrorMessage = ex.Message,
                     Exception = ex,
                     RequestBundle = item,
+                    Request = item.Request,
                     OperationType = "RequestExecution",
                     IsEntityNotFound = ex is FolderNotFoundException || ex is SynchronizerEntityNotFoundException
                 };
@@ -771,6 +772,8 @@ public class ImapSynchronizer : WinoSynchronizer<ImapRequest, ImapMessageCreatio
 
                 if (!handled)
                 {
+                    CaptureSynchronizationIssue(errorContext);
+
                     if (ShouldApplyOptimisticUIChanges(item.Request))
                     {
                         item.Request.RevertUIChanges();

Wino.Core/Synchronizers/OutlookSynchronizer.cs

@@ -1861,6 +1861,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
             ErrorCode = (int)response.StatusCode,
             ErrorMessage = errorMessage,
             RequestBundle = bundle,
+            Request = bundle.Request,
             IsEntityNotFound = IsKnownOutlookEntityNotFoundError(response.StatusCode, errorCode, errorMessage, bundle),
             AdditionalData = new Dictionary<string, object>
             {
@@ -1876,6 +1877,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         // Transient errors still need to bubble so the request can be retried or surfaced to the caller.
         if (!handled || errorContext.Severity == SynchronizerErrorSeverity.Transient)
         {
+            CaptureSynchronizationIssue(errorContext);
             bundle.UIChangeRequest?.RevertUIChanges();
             Debug.WriteLine(errorString);
             errors.Add(errorString);
@@ -2265,6 +2267,8 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         // TODO: Maybe we can batch each calendar?
 
         foreach (var calendar in localCalendars)
+        {
+            try
             {
                 bool isInitialSync = string.IsNullOrEmpty(calendar.SynchronizationDeltaToken);
 
@@ -2329,12 +2333,12 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                     if (IsResourceDeleted(item.AdditionalData))
                     {
                         await _outlookChangeProcessor.DeleteCalendarItemAsync(item.Id, calendar.Id).ConfigureAwait(false);
+                        continue;
                     }
-                else
-                {
+
                     try
                     {
-                        await _handleCalendarEventRetrievalSemaphore.WaitAsync();
+                        await _handleCalendarEventRetrievalSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
 
                         Event fullEvent = await _graphClient.Me.Calendars[calendar.RemoteCalendarId].Events[item.Id]
                             .GetAsync(requestConfiguration =>
@@ -2344,8 +2348,25 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                             }, cancellationToken: cancellationToken).ConfigureAwait(false);
                         await _outlookChangeProcessor.ManageCalendarEventAsync(fullEvent, calendar, Account).ConfigureAwait(false);
                     }
+                    catch (OperationCanceledException)
+                    {
+                        throw;
+                    }
                     catch (Exception ex)
                     {
+                        var errorContext = new SynchronizerErrorContext
+                        {
+                            Account = Account,
+                            ErrorMessage = ex.Message,
+                            Exception = ex,
+                            CalendarId = calendar.Id,
+                            CalendarName = calendar.Name,
+                            OperationType = "CalendarEventSync",
+                            Severity = SynchronizerErrorSeverity.Recoverable
+                        };
+
+                        _ = await _errorHandlingFactory.HandleErrorAsync(errorContext).ConfigureAwait(false);
+                        CaptureSynchronizationIssue(errorContext);
                         _logger.Error(ex, "Error occurred while handling item {Id} for calendar {Name}", item.Id, calendar.Name);
                     }
                     finally
@@ -2353,7 +2374,6 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                         _handleCalendarEventRetrievalSemaphore.Release();
                     }
                 }
-            }
 
                 var latestDeltaLink = messageIteratorAsync.Deltalink;
 
@@ -2367,6 +2387,29 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                     await _outlookChangeProcessor.UpdateCalendarDeltaSynchronizationToken(calendar.Id, deltaToken).ConfigureAwait(false);
                 }
             }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
+            catch (Exception ex)
+            {
+                var errorContext = new SynchronizerErrorContext
+                {
+                    Account = Account,
+                    ErrorMessage = ex.Message,
+                    Exception = ex,
+                    CalendarId = calendar.Id,
+                    CalendarName = calendar.Name,
+                    OperationType = "CalendarSync"
+                };
+
+                _ = await _errorHandlingFactory.HandleErrorAsync(errorContext).ConfigureAwait(false);
+                CaptureSynchronizationIssue(errorContext);
+
+                if (!errorContext.CanContinueSync)
+                    throw;
+            }
+        }
 
         // TODO: Return proper results.
         return CalendarSynchronizationResult.Empty;

Wino.Core/Synchronizers/WinoSynchronizer.cs

@@ -12,6 +12,7 @@ using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Mail;
 using Wino.Core.Domain.Entities.Shared;
 using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Exceptions;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Accounts;
 using Wino.Core.Domain.Models.Folders;
@@ -121,12 +122,15 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
     /// <returns>Synchronization result that contains summary of the sync.</returns>
     public async Task<MailSynchronizationResult> SynchronizeMailsAsync(MailSynchronizationOptions options, CancellationToken cancellationToken = default)
     {
+        ResetCapturedSynchronizationIssues();
+        List<IRequestBase> requestCopies = null;
+
         try
         {
             if (!ShouldQueueMailSynchronization(options))
             {
                 Log.Debug($"{options.Type} synchronization is ignored.");
-                return MailSynchronizationResult.Canceled;
+                return FinalizeMailResult(MailSynchronizationResult.Canceled);
             }
 
             var newCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
@@ -147,7 +151,7 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
 
                 List<IRequestBundle<TBaseRequest>> nativeRequests = new();
 
-                List<IRequestBase> requestCopies = new(changeRequestQueue);
+                requestCopies = new(changeRequestQueue);
 
                 var keys = changeRequestQueue.GroupBy(a => a.GroupingKey());
 
@@ -226,9 +230,8 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 finally
                 {
                     UntrackProcessedRequests(requestCopies);
-                }
-
                     Messenger.Send(new SynchronizationActionsCompleted(Account.Id));
+                }
 
                 PublishUnreadItemChanges();
 
@@ -275,14 +278,19 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 {
                     newProfileInformation = await SynchronizeProfileInformationInternalAsync();
                 }
+                catch (AuthenticationAttentionException)
+                {
+                    throw;
+                }
                 catch (Exception ex)
                 {
                     Log.Error(ex, "Failed to update profile information for {Name}", Account.Name);
 
-                    return MailSynchronizationResult.Failed(ex);
+                    CaptureSynchronizationIssue(SynchronizationIssue.FromException(ex, "ProfileSync"));
+                    return FinalizeMailResult(MailSynchronizationResult.Failed(ex));
                 }
 
-                return MailSynchronizationResult.Completed(newProfileInformation);
+                return FinalizeMailResult(MailSynchronizationResult.Completed(newProfileInformation));
             }
 
             // Alias sync.
@@ -294,13 +302,18 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 {
                     await SynchronizeAliasesAsync();
 
-                    return MailSynchronizationResult.Empty;
+                    return FinalizeMailResult(MailSynchronizationResult.Empty);
+                }
+                catch (AuthenticationAttentionException)
+                {
+                    throw;
                 }
                 catch (Exception ex)
                 {
                     Log.Error(ex, "Failed to update aliases for {Name}", Account.Name);
 
-                    return MailSynchronizationResult.Failed(ex);
+                    CaptureSynchronizationIssue(SynchronizationIssue.FromException(ex, "AliasSync"));
+                    return FinalizeMailResult(MailSynchronizationResult.Failed(ex));
                 }
             }
 
@@ -314,19 +327,23 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
 
             PublishUnreadItemChanges();
 
-            return synchronizationResult;
+            return FinalizeMailResult(synchronizationResult);
         }
         catch (OperationCanceledException)
         {
             Logger.Warning("Synchronization canceled.");
 
-            return MailSynchronizationResult.Canceled;
+            return FinalizeMailResult(MailSynchronizationResult.Canceled);
+        }
+        catch (AuthenticationAttentionException)
+        {
+            throw;
         }
         catch (Exception ex)
         {
             Logger.Error(ex, "Synchronization failed for {Name}", Account.Name);
-
-            throw;
+            CaptureSynchronizationIssue(SynchronizationIssue.FromException(ex, "MailSync"));
+            return FinalizeMailResult(MailSynchronizationResult.Failed(ex));
         }
         finally
         {
@@ -354,6 +371,12 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>Synchronization result that contains summary of the sync.</returns>
     public async Task<CalendarSynchronizationResult> SynchronizeCalendarEventsAsync(CalendarSynchronizationOptions options, CancellationToken cancellationToken = default)
+    {
+        ResetCapturedSynchronizationIssues();
+        List<IRequestBase> requestCopies = null;
+        var calendarRequestsWereExecuting = false;
+
+        try
         {
             bool shouldExecuteRequests = changeRequestQueue.Any(r => r is ICalendarActionRequest);
             bool shouldDelayExecution = false;
@@ -361,10 +384,11 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
 
             if (shouldExecuteRequests)
             {
+                calendarRequestsWereExecuting = true;
                 State = AccountSynchronizerState.ExecutingRequests;
 
                 List<IRequestBundle<TBaseRequest>> nativeRequests = new();
-            List<IRequestBase> requestCopies = new(changeRequestQueue.Where(r => r is ICalendarActionRequest));
+                requestCopies = new(changeRequestQueue.Where(r => r is ICalendarActionRequest));
 
                 var keys = requestCopies.GroupBy(a => a.GroupingKey());
 
@@ -433,9 +457,8 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 finally
                 {
                     UntrackProcessedRequests(requestCopies);
-            }
-
                     Messenger.Send(new SynchronizationActionsCompleted(Account.Id));
+                }
 
                 // Let servers to finish their job. Sometimes the servers don't respond immediately.
                 shouldDelayExecution = requestCopies.Any(a => a.ResynchronizationDelay > 0);
@@ -451,8 +474,30 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 await Task.Delay(maxExecutionDelay, cancellationToken);
             }
 
-        // Execute the actual synchronization
-        return await SynchronizeCalendarEventsInternalAsync(options, cancellationToken);
+            var synchronizationResult = await SynchronizeCalendarEventsInternalAsync(options, cancellationToken);
+            return FinalizeCalendarResult(synchronizationResult);
+        }
+        catch (OperationCanceledException)
+        {
+            return FinalizeCalendarResult(CalendarSynchronizationResult.Canceled);
+        }
+        catch (AuthenticationAttentionException)
+        {
+            throw;
+        }
+        catch (Exception ex)
+        {
+            CaptureSynchronizationIssue(SynchronizationIssue.FromException(ex, "CalendarSync"));
+            return FinalizeCalendarResult(CalendarSynchronizationResult.Failed(ex));
+        }
+        finally
+        {
+            if (calendarRequestsWereExecuting && State == AccountSynchronizerState.ExecutingRequests)
+            {
+                ResetSyncProgress();
+                State = AccountSynchronizerState.Idle;
+            }
+        }
     }
 
     /// <summary>
@@ -626,4 +671,10 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
             request.Value.Dispose();
         }
     }
+
+    private MailSynchronizationResult FinalizeMailResult(MailSynchronizationResult result)
+        => (result ?? MailSynchronizationResult.Empty).MergeIssues(GetCapturedSynchronizationIssues());
+
+    private CalendarSynchronizationResult FinalizeCalendarResult(CalendarSynchronizationResult result)
+        => (result ?? CalendarSynchronizationResult.Empty).MergeIssues(GetCapturedSynchronizationIssues());
 }

Wino.Mail.ViewModels.Tests/Collections/WinoMailCollectionTests.cs

@@ -181,7 +181,7 @@ public class WinoMailCollectionTests
         var updatedSecond = CloneMailCopy(second);
         updatedSecond.ThreadId = "shared-thread";
 
-        await sut.UpdateMailCopy(updatedSecond, MailUpdateSource.Server, MailCopyChangeFlags.ThreadId);
+        await sut.UpdateMailCopy(updatedSecond, EntityUpdateSource.Server, MailCopyChangeFlags.ThreadId);
 
         var items = FlattenItems(sut);
         var threadItem = items.Should().ContainSingle().Which.Should().BeOfType<ThreadMailItemViewModel>().Subject;
@@ -201,7 +201,7 @@ public class WinoMailCollectionTests
         var updatedExisting = CloneMailCopy(existing);
         updatedExisting.ThreadId = "shared-thread";
 
-        await sut.UpdateMailCopy(updatedExisting, MailUpdateSource.Server, MailCopyChangeFlags.ThreadId);
+        await sut.UpdateMailCopy(updatedExisting, EntityUpdateSource.Server, MailCopyChangeFlags.ThreadId);
         await sut.AddAsync(incoming);
 
         var items = FlattenItems(sut);

Wino.Mail.ViewModels.Tests/Data/MailItemViewModelUpdateTests.cs

@@ -102,7 +102,7 @@ public class MailItemViewModelUpdateTests
 
         latest.IsRead = true;
 
-        await collection.UpdateMailCopy(latest, MailUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead);
+        await collection.UpdateMailCopy(latest, EntityUpdateSource.ClientUpdated, MailCopyChangeFlags.IsRead);
 
         raisedProperties.Should().Equal(nameof(ThreadMailItemViewModel.IsRead));
     }

Wino.Mail.ViewModels/Collections/WinoMailCollection.cs

@@ -530,7 +530,7 @@ public class WinoMailCollection : ObservableRecipient, IRecipient<SelectedItemsC
 
     private async Task UpdateExistingItemAsync(MailItemContainer itemContainer,
                                                MailCopy updatedItem,
-                                               MailUpdateSource mailUpdateSource = MailUpdateSource.Server,
+                                               EntityUpdateSource mailUpdateSource = EntityUpdateSource.Server,
                                                MailCopyChangeFlags changeHint = MailCopyChangeFlags.None)
     {
         if (itemContainer?.ItemViewModel == null)
@@ -559,7 +559,7 @@ public class WinoMailCollection : ObservableRecipient, IRecipient<SelectedItemsC
                 itemContainer.ThreadViewModel?.ResumeChildPropertyNotifications();
             }
 
-            existingItem.IsBusy = mailUpdateSource == MailUpdateSource.ClientUpdated;
+            existingItem.IsBusy = mailUpdateSource == EntityUpdateSource.ClientUpdated;
 
             UpdateUniqueIdHashes(existingItem, true);
             UpdateThreadIdCache(threadOwner, true);
@@ -849,7 +849,7 @@ public class WinoMailCollection : ObservableRecipient, IRecipient<SelectedItemsC
     /// </summary>
     /// <param name="updatedMailCopy">Updated mail copy.</param>
     /// <returns></returns>
-    public Task UpdateMailCopy(MailCopy updatedMailCopy, MailUpdateSource mailUpdateSource, MailCopyChangeFlags changedProperties = MailCopyChangeFlags.None)
+    public Task UpdateMailCopy(MailCopy updatedMailCopy, EntityUpdateSource mailUpdateSource, MailCopyChangeFlags changedProperties = MailCopyChangeFlags.None)
         => RunSerializedAsync(() =>
         {
             var itemContainer = GetMailItemContainer(updatedMailCopy.UniqueId);

Wino.Mail.ViewModels/ComposePageViewModel.cs

@@ -874,7 +874,7 @@ public partial class ComposePageViewModel : MailBaseViewModel,
         _dialogService.InfoBarMessage(Translator.Info_InvalidAddressTitle, string.Format(Translator.Info_InvalidAddressMessage, address), InfoBarMessageType.Warning);
     }
 
-    protected override async void OnMailUpdated(MailCopy updatedMail, MailUpdateSource source, MailCopyChangeFlags changedProperties)
+    protected override async void OnMailUpdated(MailCopy updatedMail, EntityUpdateSource source, MailCopyChangeFlags changedProperties)
     {
         base.OnMailUpdated(updatedMail, source, changedProperties);
 

Wino.Mail.ViewModels/MailBaseViewModel.cs

@@ -20,9 +20,9 @@ public class MailBaseViewModel : CoreBaseViewModel,
     IRecipient<FolderDeleted>,
     IRecipient<FolderSynchronizationEnabled>
 {
-    protected virtual void OnMailAdded(MailCopy addedMail) { }
-    protected virtual void OnMailRemoved(MailCopy removedMail) { }
-    protected virtual void OnMailUpdated(MailCopy updatedMail, MailUpdateSource source, MailCopyChangeFlags changedProperties) { }
+    protected virtual void OnMailAdded(MailCopy addedMail, EntityUpdateSource source) { }
+    protected virtual void OnMailRemoved(MailCopy removedMail, EntityUpdateSource source) { }
+    protected virtual void OnMailUpdated(MailCopy updatedMail, EntityUpdateSource source, MailCopyChangeFlags changedProperties) { }
     protected virtual void OnMailDownloaded(MailCopy downloadedMail) { }
     protected virtual void OnDraftCreated(MailCopy draftMail, MailAccount account) { }
     protected virtual void OnDraftFailed(MailCopy draftMail, MailAccount account) { }
@@ -31,8 +31,8 @@ public class MailBaseViewModel : CoreBaseViewModel,
     protected virtual void OnFolderDeleted(MailItemFolder folder) { }
     protected virtual void OnFolderSynchronizationEnabled(IMailItemFolder mailItemFolder) { }
 
-    void IRecipient<MailAddedMessage>.Receive(MailAddedMessage message) => OnMailAdded(message.AddedMail);
-    void IRecipient<MailRemovedMessage>.Receive(MailRemovedMessage message) => OnMailRemoved(message.RemovedMail);
+    void IRecipient<MailAddedMessage>.Receive(MailAddedMessage message) => OnMailAdded(message.AddedMail, message.Source);
+    void IRecipient<MailRemovedMessage>.Receive(MailRemovedMessage message) => OnMailRemoved(message.RemovedMail, message.Source);
     void IRecipient<MailUpdatedMessage>.Receive(MailUpdatedMessage message) => OnMailUpdated(message.UpdatedMail, message.Source, message.ChangedProperties);
     void IRecipient<MailDownloadedMessage>.Receive(MailDownloadedMessage message) => OnMailDownloaded(message.DownloadedMail);
 

Wino.Mail.ViewModels/MailListPageViewModel.cs

@@ -745,7 +745,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         var fi = MailCollection.GetFirst();
         if (fi == null) return;
 
-        Messenger.Send(new MailRemovedMessage(fi.MailCopy));
+        Messenger.Send(new MailRemovedMessage(fi.MailCopy, EntityUpdateSource.Server));
     }
 
     /// <summary>
@@ -758,9 +758,9 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         return MailCollection.ContainsThreadId(mailItem.ThreadId);
     }
 
-    protected override async void OnMailAdded(MailCopy addedMail)
+    protected override async void OnMailAdded(MailCopy addedMail, EntityUpdateSource source)
     {
-        base.OnMailAdded(addedMail);
+        base.OnMailAdded(addedMail, source);
 
         if (addedMail.AssignedAccount == null || addedMail.AssignedFolder == null) return;
 
@@ -847,6 +847,15 @@ public partial class MailListPageViewModel : MailBaseViewModel,
             // AddAsync already handles UI threading internally, no need to wrap it
             await MailCollection.AddAsync(addedMail);
 
+            if (source == EntityUpdateSource.ClientUpdated)
+            {
+                var addedContainer = MailCollection.GetMailItemContainer(addedMail.UniqueId);
+                if (addedContainer?.ItemViewModel != null)
+                {
+                    addedContainer.ItemViewModel.IsBusy = true;
+                }
+            }
+
             await ExecuteUIThread(() =>
             {
                 NotifyItemFoundState();
@@ -862,7 +871,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         }
     }
 
-    protected override async void OnMailUpdated(MailCopy updatedMail, MailUpdateSource source, MailCopyChangeFlags changedProperties)
+    protected override async void OnMailUpdated(MailCopy updatedMail, EntityUpdateSource source, MailCopyChangeFlags changedProperties)
     {
         base.OnMailUpdated(updatedMail, source, changedProperties);
 
@@ -890,9 +899,9 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         await ExecuteUIThread(() => { SetupTopBarActions(); });
     }
 
-    protected override async void OnMailRemoved(MailCopy removedMail)
+    protected override async void OnMailRemoved(MailCopy removedMail, EntityUpdateSource source)
     {
-        base.OnMailRemoved(removedMail);
+        base.OnMailRemoved(removedMail, source);
 
         if (removedMail.AssignedAccount == null) return;
 

Wino.Mail.ViewModels/MailRenderingPageViewModel.cs

@@ -639,7 +639,7 @@ public partial class MailRenderingPageViewModel : MailBaseViewModel,
             MenuItems.Add(MailOperationMenuItem.Create(MailOperation.MarkAsRead, true, false));
     }
 
-    protected override async void OnMailUpdated(MailCopy updatedMail, MailUpdateSource source, MailCopyChangeFlags changedProperties)
+    protected override async void OnMailUpdated(MailCopy updatedMail, EntityUpdateSource source, MailCopyChangeFlags changedProperties)
     {
         base.OnMailUpdated(updatedMail, source, changedProperties);
 

Wino.Mail.WinUI/App.xaml.cs

@@ -910,7 +910,7 @@ public partial class App : WinoApplication,
             syncResult.CompletedState == SynchronizationCompletedState.PartiallyCompleted)
         {
             var dialogService = Services.GetRequiredService<IMailDialogService>();
-            var errorMessage = GetSynchronizationFailureMessage(message.Options.Type, syncResult.Exception?.Message);
+            var errorMessage = GetSynchronizationFailureMessage(message.Options.Type, syncResult.AllIssues, syncResult.Exception?.Message);
             var severity = syncResult.CompletedState == SynchronizationCompletedState.PartiallyCompleted
                 ? InfoBarMessageType.Warning
                 : InfoBarMessageType.Error;
@@ -925,18 +925,15 @@ public partial class App : WinoApplication,
 
         var calendarSyncResult = await _synchronizationManager.SynchronizeCalendarAsync(message.Options);
 
-        if (calendarSyncResult.CompletedState == SynchronizationCompletedState.Failed)
+        if (calendarSyncResult.CompletedState is SynchronizationCompletedState.Failed or SynchronizationCompletedState.PartiallyCompleted)
         {
             var dialogService = Services.GetRequiredService<IMailDialogService>();
             dialogService.InfoBarMessage(
                 Translator.Info_SyncFailedTitle,
-                message.Options.Type switch
-                {
-                    CalendarSynchronizationType.CalendarMetadata => Translator.Exception_FailedToSynchronizeCalendarMetadata,
-                    CalendarSynchronizationType.Strict => Translator.Exception_FailedToSynchronizeCalendarData,
-                    _ => Translator.Exception_FailedToSynchronizeCalendarEvents
-                },
-                InfoBarMessageType.Error);
+                GetCalendarSynchronizationFailureMessage(message.Options.Type, calendarSyncResult.AllIssues, calendarSyncResult.Exception?.Message),
+                calendarSyncResult.CompletedState == SynchronizationCompletedState.PartiallyCompleted
+                    ? InfoBarMessageType.Warning
+                    : InfoBarMessageType.Error);
         }
     }
 
@@ -1052,8 +1049,17 @@ public partial class App : WinoApplication,
         });
     }
 
-    private static string GetSynchronizationFailureMessage(MailSynchronizationType synchronizationType, string? exceptionMessage)
+    private static string GetSynchronizationFailureMessage(
+        MailSynchronizationType synchronizationType,
+        IEnumerable<SynchronizationIssue> issues,
+        string? exceptionMessage)
     {
+        var issueMessage = FormatSynchronizationIssues(issues);
+        if (!string.IsNullOrWhiteSpace(issueMessage))
+        {
+            return issueMessage;
+        }
+
         if (!string.IsNullOrWhiteSpace(exceptionMessage))
         {
             return exceptionMessage;
@@ -1067,6 +1073,49 @@ public partial class App : WinoApplication,
         };
     }
 
+    private static string GetCalendarSynchronizationFailureMessage(
+        CalendarSynchronizationType synchronizationType,
+        IEnumerable<SynchronizationIssue> issues,
+        string? exceptionMessage)
+    {
+        var issueMessage = FormatSynchronizationIssues(issues);
+        if (!string.IsNullOrWhiteSpace(issueMessage))
+        {
+            return issueMessage;
+        }
+
+        if (!string.IsNullOrWhiteSpace(exceptionMessage))
+        {
+            return exceptionMessage;
+        }
+
+        return synchronizationType switch
+        {
+            CalendarSynchronizationType.CalendarMetadata => Translator.Exception_FailedToSynchronizeCalendarMetadata,
+            CalendarSynchronizationType.Strict => Translator.Exception_FailedToSynchronizeCalendarData,
+            _ => Translator.Exception_FailedToSynchronizeCalendarEvents
+        };
+    }
+
+    private static string? FormatSynchronizationIssues(IEnumerable<SynchronizationIssue> issues)
+    {
+        if (issues == null)
+        {
+            return null;
+        }
+
+        var issueLines = issues
+            .Where(issue => issue != null && !string.IsNullOrWhiteSpace(issue.Message))
+            .Select(issue => string.IsNullOrWhiteSpace(issue.ScopeName)
+                ? issue.Message
+                : string.Format(Translator.SynchronizationIssueFormat_WithScope, issue.ScopeName, issue.Message))
+            .Distinct(StringComparer.Ordinal)
+            .Take(5)
+            .ToList();
+
+        return issueLines.Count == 0 ? null : string.Join(Environment.NewLine, issueLines);
+    }
+
     private void PreferencesServiceChanged(object? sender, string propertyName)
     {
         if (propertyName != nameof(IPreferencesService.EmailSyncIntervalMinutes))

Wino.Messages/Client/Calendar/CalendarItemEventMessages.cs

@@ -3,6 +3,6 @@ using Wino.Core.Domain.Enums;
 
 namespace Wino.Messaging.Client.Calendar;
 
-public record CalendarItemAdded(CalendarItem CalendarItem);
-public record CalendarItemUpdated(CalendarItem CalendarItem, CalendarItemUpdateSource Source);
-public record CalendarItemDeleted(CalendarItem CalendarItem);
+public record CalendarItemAdded(CalendarItem CalendarItem, EntityUpdateSource Source = EntityUpdateSource.Server);
+public record CalendarItemUpdated(CalendarItem CalendarItem, EntityUpdateSource Source);
+public record CalendarItemDeleted(CalendarItem CalendarItem, EntityUpdateSource Source = EntityUpdateSource.Server);

Wino.Messages/UI/MailAddedMessage.cs

@@ -1,5 +1,6 @@
 using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
 
 namespace Wino.Messaging.UI;
 
-public record MailAddedMessage(MailCopy AddedMail) : UIMessageBase<MailAddedMessage>;
+public record MailAddedMessage(MailCopy AddedMail, EntityUpdateSource Source = EntityUpdateSource.Server) : UIMessageBase<MailAddedMessage>;

Wino.Messages/UI/MailRemovedMessage.cs

@@ -1,5 +1,6 @@
 using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
 
 namespace Wino.Messaging.UI;
 
-public record MailRemovedMessage(MailCopy RemovedMail) : UIMessageBase<MailRemovedMessage>;
+public record MailRemovedMessage(MailCopy RemovedMail, EntityUpdateSource Source = EntityUpdateSource.Server) : UIMessageBase<MailRemovedMessage>;

Wino.Messages/UI/MailUpdatedMessage.cs

@@ -3,4 +3,4 @@ using Wino.Core.Domain.Enums;
 
 namespace Wino.Messaging.UI;
 
-public record MailUpdatedMessage(MailCopy UpdatedMail, MailUpdateSource Source, MailCopyChangeFlags ChangedProperties = MailCopyChangeFlags.None) : UIMessageBase<MailUpdatedMessage>;
+public record MailUpdatedMessage(MailCopy UpdatedMail, EntityUpdateSource Source, MailCopyChangeFlags ChangedProperties = MailCopyChangeFlags.None) : UIMessageBase<MailUpdatedMessage>;

Wino.Services/AccountService.cs

@@ -362,7 +362,7 @@ public class AccountService : BaseDatabaseService, IAccountService
 
         foreach (var calendarItem in deletedCalendarItems)
         {
-            WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(calendarItem));
+            WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(calendarItem, EntityUpdateSource.Server));
         }
 
         foreach (var accountCalendar in accountCalendars)

Wino.Services/CalendarService.cs

@@ -122,7 +122,7 @@ public class CalendarService : BaseDatabaseService, ICalendarService
             await Connection.Table<Reminder>().DeleteAsync(r => r.CalendarItemId == @event.Id).ConfigureAwait(false);
             await Connection.Table<CalendarAttachment>().DeleteAsync(a => a.CalendarItemId == @event.Id).ConfigureAwait(false);
 
-            WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(@event));
+            WeakReferenceMessenger.Default.Send(new CalendarItemDeleted(@event, EntityUpdateSource.Server));
         }
     }
 
@@ -149,7 +149,7 @@ public class CalendarService : BaseDatabaseService, ICalendarService
                 }
             });
 
-            WeakReferenceMessenger.Default.Send(new CalendarItemAdded(calendarItem));
+            WeakReferenceMessenger.Default.Send(new CalendarItemAdded(calendarItem, EntityUpdateSource.Server));
         }
         catch (Exception ex)
         {
@@ -174,7 +174,7 @@ public class CalendarService : BaseDatabaseService, ICalendarService
                 }
             });
 
-            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(calendarItem, CalendarItemUpdateSource.Server));
+            WeakReferenceMessenger.Default.Send(new CalendarItemUpdated(calendarItem, EntityUpdateSource.Server));
         }
         catch (Exception ex)
         {

Wino.Services/MailService.cs

@@ -659,7 +659,7 @@ public class MailService : BaseDatabaseService, IMailService
 
         await Connection.InsertAsync(mailCopy, typeof(MailCopy)).ConfigureAwait(false);
 
-        ReportUIChange(new MailAddedMessage(mailCopy));
+        ReportUIChange(new MailAddedMessage(mailCopy, EntityUpdateSource.Server));
     }
 
     public async Task UpdateMailAsync(MailCopy mailCopy)
@@ -675,7 +675,7 @@ public class MailService : BaseDatabaseService, IMailService
 
         await Connection.UpdateAsync(mailCopy, typeof(MailCopy)).ConfigureAwait(false);
 
-        ReportUIChange(new MailUpdatedMessage(mailCopy, MailUpdateSource.Server));
+        ReportUIChange(new MailUpdatedMessage(mailCopy, EntityUpdateSource.Server));
     }
 
     private async Task DeleteMailInternalAsync(MailCopy mailCopy, bool preserveMimeFile)
@@ -699,7 +699,7 @@ public class MailService : BaseDatabaseService, IMailService
             await _mimeFileService.DeleteMimeMessageAsync(mailCopy.AssignedAccount.Id, mailCopy.FileId).ConfigureAwait(false);
         }
 
-        ReportUIChange(new MailRemovedMessage(mailCopy));
+        ReportUIChange(new MailRemovedMessage(mailCopy, EntityUpdateSource.Server));
     }
 
     #endregion