feat(infrastructure): add TriggerSync to EmailSyncWorker for on-demand immediate sync; fix cancellation propagation after delay

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/Background/EmailSyncWorker.cs

@@ -14,6 +14,20 @@ public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServicePro
 {
     private readonly string DefaultFolder = "INBOX";
 
+    /// <summary>
+    /// Signals the current <see cref="Task.Delay"/> to complete immediately,
+    /// causing the sync loop to start the next cycle without waiting.
+    /// A new TCS is created at the start of each delay so repeated triggers work correctly.
+    /// </summary>
+    private volatile TaskCompletionSource<bool> _syncTrigger = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+    /// <summary>
+    /// Triggers an immediate sync cycle by completing the current delay early.
+    /// Safe to call from any thread or HTTP request at any time.
+    /// If a sync is already running, the trigger is ignored — the next cycle starts normally.
+    /// </summary>
+    public void TriggerSync() => _syncTrigger.TrySetResult(true);
+
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         await UpsertSeedEmailAccount(stoppingToken);
@@ -33,7 +47,15 @@ public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServicePro
                 await SyncAccountAsync(account, imapService, pop3Service, stoppingToken);
             }
 
-            await Task.Delay(interval, stoppingToken).ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);
+            // Reset trigger before waiting so any TriggerSync() call during the delay is caught
+            _syncTrigger = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+            var delay = Task.Delay(interval, stoppingToken);
+            var triggered = _syncTrigger.Task;
+            await Task.WhenAny(delay, triggered).ConfigureAwait(false);
+
+            // Propagate cancellation if the host is stopping
+            stoppingToken.ThrowIfCancellationRequested();
         }
     }