feat(infrastructure): implement IEmailSyncService on EmailSyncWorker with rate-limited ForceTriggerSync via IMemoryCache; register as singleton in DI

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -13,6 +13,7 @@ using Microsoft.AspNetCore.DataProtection;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
 
 namespace DigitalData.MessagingService.Infrastructure;
 
@@ -71,6 +72,13 @@ public static class DependencyInjection
         services.AddHostedService<AsyncInitWorker>();
         services.AddHostedService<EmailSyncWorker>();
 
+        services.AddSingleton<IEmailSyncService>(p =>
+        {
+            var hostedServices = p.GetRequiredService<IEnumerable<IHostedService>>();
+            var emailSyncWorkers = hostedServices.OfType<EmailSyncWorker>();
+            return emailSyncWorkers.FirstOrDefault() ?? throw new InvalidOperationException("EmailSyncWorker is not registered.");
+        });
+
         services.AddMemoryCache();
 
         // --- Database (InMemory) ---

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

@@ -3,6 +3,7 @@ using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
 using DigitalData.MessagingService.Application.Common.Options;
 using DigitalData.MessagingService.Domain.Entities;
 using DigitalData.MessagingService.Domain.Enums;
+using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
@@ -10,8 +11,10 @@ using Microsoft.Extensions.Options;
 
 namespace DigitalData.MessagingService.Infrastructure.Services.Background;
 
-public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServiceProvider Provider, ILogger<EmailSyncWorker> Logger) : BackgroundService
+public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServiceProvider Provider, ILogger<EmailSyncWorker> Logger, IMemoryCache Cache) : BackgroundService, IEmailSyncService
 {
+    private static string ForcedSyncDateCacheKey => $"{nameof(EmailSyncWorker)}_TriggerSync";
+
     private readonly string DefaultFolder = "INBOX";
 
     /// <summary>
@@ -26,7 +29,15 @@ public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServicePro
     /// 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);
+    public DateTime ForceTriggerSync()
+    {
+        return Cache.GetOrCreate(ForcedSyncDateCacheKey, e =>
+        {
+            e.SetAbsoluteExpiration(TimeSpan.FromSeconds(Options.Value.ForcedSyncIntervalSeconds));
+            _syncTrigger.TrySetResult(true);
+            return DateTime.UtcNow;
+        });
+    }
 
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
@@ -98,7 +109,7 @@ public class EmailSyncWorker(IOptions<EmailAccountsOptions> Options, IServicePro
         }
     }
 
-    public async Task UpsertSeedEmailAccount(CancellationToken stoppingToken)
+    private async Task UpsertSeedEmailAccount(CancellationToken stoppingToken)
     {
         await using var scope = Provider.CreateAsyncScope();