better 404 handling.

Wino.Core/Synchronizers/Errors/EntityNotFoundHandler.cs

@@ -8,26 +8,27 @@ using Wino.Core.Domain.Models.Synchronization;
 namespace Wino.Core.Synchronizers.Errors;
 
 /// <summary>
-/// Generic handler for 404 (Not Found) errors across all synchronizers.
-/// When a resource is already gone on the server, this handler applies
-/// the intended change locally instead of throwing.
-/// Works for all mail actions, folder actions, and batch operations.
+/// Handles errors that were explicitly classified as missing remote entities.
+/// This avoids swallowing unrelated HTTP 404 responses that should still surface
+/// to the user as real synchronization failures.
 /// </summary>
 public class EntityNotFoundHandler : ISynchronizerErrorHandler
 {
     private readonly ILogger _logger = Log.ForContext<EntityNotFoundHandler>();
     private readonly IMailService _mailService;
     private readonly IFolderService _folderService;
+    private readonly ICalendarService _calendarService;
 
-    public EntityNotFoundHandler(IMailService mailService, IFolderService folderService)
+    public EntityNotFoundHandler(IMailService mailService, IFolderService folderService, ICalendarService calendarService)
     {
         _mailService = mailService;
         _folderService = folderService;
+        _calendarService = calendarService;
     }
 
     public bool CanHandle(SynchronizerErrorContext error)
     {
-        if (error.ErrorCode != 404) return false;
+        if (!error.IsEntityNotFound) return false;
         if (error.RequestBundle == null) return false;
         return true;
     }
@@ -81,9 +82,30 @@ public class EntityNotFoundHandler : ISynchronizerErrorHandler
             return true;
         }
 
+        // --- Individual calendar actions ---
+        if (uiRequest is ICalendarActionRequest calendarAction)
+        {
+            _logger.Warning("Entity not found for calendar operation {Op} on {CalendarItemId}. Deleting locally.",
+                calendarAction.Operation, calendarAction.Item?.Id);
+
+            try
+            {
+                if (calendarAction.Item != null)
+                {
+                    await _calendarService.DeleteCalendarItemAsync(calendarAction.Item.Id).ConfigureAwait(false);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.Error(ex, "Failed to delete calendar item locally after entity-not-found.");
+            }
+
+            return true;
+        }
+
         // --- Batch requests (can't identify specific item) ---
         // Mark as recoverable. Next sync will clean up stale items.
-        _logger.Warning("Entity not found (404) for batch operation. Marking as recoverable.");
+        _logger.Warning("Entity not found for batch operation. Marking as recoverable.");
         return true;
     }
 }

Wino.Core/Synchronizers/GmailSynchronizer.cs

@@ -1665,6 +1665,8 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
     {
         if (error == null) return;
 
+        var isEntityNotFound = IsKnownGmailEntityNotFoundError(error, bundle);
+
         // Create error context
         var errorContext = new SynchronizerErrorContext
         {
@@ -1672,6 +1674,7 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
             ErrorCode = error.Code,
             ErrorMessage = error.Message,
             RequestBundle = bundle,
+            IsEntityNotFound = isEntityNotFound,
             AdditionalData = new Dictionary<string, object>
             {
                 { "Error", error }
@@ -1702,7 +1705,7 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
             }
 
             // Entity not found.
-            if (error.Code == 404)
+            if (isEntityNotFound)
             {
                 bundle?.UIChangeRequest?.RevertUIChanges();
                 throw new SynchronizerEntityNotFoundException(error.Message);
@@ -1718,6 +1721,50 @@ public class GmailSynchronizer : WinoSynchronizer<IClientServiceRequest, Message
         }
     }
 
+    private static bool IsKnownGmailEntityNotFoundError(
+        RequestError error,
+        IRequestBundle<IClientServiceRequest> bundle)
+    {
+        if (error?.Code != 404 || bundle?.UIChangeRequest == null)
+            return false;
+
+        if (!IsExistingEntityOperation(bundle.UIChangeRequest))
+            return false;
+
+        var message = error.Message?.Trim() ?? string.Empty;
+        if (string.IsNullOrWhiteSpace(message))
+            return false;
+
+        var normalizedMessage = message.ToLowerInvariant();
+        return normalizedMessage.Contains("requested entity")
+               || normalizedMessage.Contains("message not found")
+               || normalizedMessage.Contains("thread not found")
+               || normalizedMessage.Contains("draft not found")
+               || normalizedMessage.Contains("label not found")
+               || normalizedMessage.Contains("event not found")
+               || normalizedMessage.Contains("calendar not found");
+    }
+
+    private static bool IsExistingEntityOperation(IUIChangeRequest request)
+        => request is BatchDeleteRequest
+           || request is BatchMoveRequest
+           || request is BatchChangeFlagRequest
+           || request is BatchMarkReadRequest
+           || request is BatchArchiveRequest
+           || request is DeleteRequest
+           || request is MoveRequest
+           || request is ChangeFlagRequest
+           || request is MarkReadRequest
+           || request is ArchiveRequest
+           || request is RenameFolderRequest
+           || request is DeleteFolderRequest
+           || request is AcceptEventRequest
+           || request is DeclineEventRequest
+           || request is OutlookDeclineEventRequest
+           || request is TentativeEventRequest
+           || request is UpdateCalendarEventRequest
+           || request is DeleteCalendarEventRequest;
+
     private static bool ShouldRevertOptimisticMailStateChange(IUIChangeRequest request)
         => request is BatchMarkReadRequest
         || request is MarkReadRequest

Wino.Core/Synchronizers/ImapSynchronizer.cs

@@ -763,7 +763,8 @@ public class ImapSynchronizer : WinoSynchronizer<ImapRequest, ImapMessageCreatio
                     ErrorMessage = ex.Message,
                     Exception = ex,
                     RequestBundle = item,
-                    OperationType = "RequestExecution"
+                    OperationType = "RequestExecution",
+                    IsEntityNotFound = ex is FolderNotFoundException || ex is SynchronizerEntityNotFoundException
                 };
 
                 var handled = await _errorHandlerFactory.HandleErrorAsync(errorContext).ConfigureAwait(false);

Wino.Core/Synchronizers/OutlookSynchronizer.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Net;
 using System.Net.Http;
 using System.Text;
 using System.Text.Json;
@@ -1860,6 +1861,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
             ErrorCode = (int)response.StatusCode,
             ErrorMessage = errorMessage,
             RequestBundle = bundle,
+            IsEntityNotFound = IsKnownOutlookEntityNotFoundError(response.StatusCode, errorCode, errorMessage, bundle),
             AdditionalData = new Dictionary<string, object>
             {
                 { "ErrorCode", errorCode },
@@ -1880,6 +1882,49 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         }
     }
 
+    private static bool IsKnownOutlookEntityNotFoundError(
+        HttpStatusCode statusCode,
+        string errorCode,
+        string errorMessage,
+        IRequestBundle<RequestInformation> bundle)
+    {
+        if (statusCode != HttpStatusCode.NotFound || bundle?.UIChangeRequest == null)
+            return false;
+
+        if (!IsExistingEntityOperation(bundle.UIChangeRequest))
+            return false;
+
+        var normalizedErrorCode = errorCode?.Trim().ToLowerInvariant() ?? string.Empty;
+        var normalizedMessage = errorMessage?.Trim().ToLowerInvariant() ?? string.Empty;
+
+        return normalizedErrorCode.Contains("notfound")
+               || normalizedErrorCode.Contains("itemnotfound")
+               || normalizedErrorCode.Contains("resource")
+               || normalizedMessage.Contains("not found")
+               || normalizedMessage.Contains("does not exist")
+               || normalizedMessage.Contains("cannot be found");
+    }
+
+    private static bool IsExistingEntityOperation(IUIChangeRequest request)
+        => request is BatchDeleteRequest
+           || request is BatchMoveRequest
+           || request is BatchChangeFlagRequest
+           || request is BatchMarkReadRequest
+           || request is BatchArchiveRequest
+           || request is DeleteRequest
+           || request is MoveRequest
+           || request is ChangeFlagRequest
+           || request is MarkReadRequest
+           || request is ArchiveRequest
+           || request is RenameFolderRequest
+           || request is DeleteFolderRequest
+           || request is AcceptEventRequest
+           || request is DeclineEventRequest
+           || request is OutlookDeclineEventRequest
+           || request is TentativeEventRequest
+           || request is UpdateCalendarEventRequest
+           || request is DeleteCalendarEventRequest;
+
     private async Task HandleSuccessfulResponseAsync(IRequestBundle<RequestInformation> bundle, HttpResponseMessage response)
     {
         try