fix(eventing): make inbox idempotent, use no-op mail in integration tests

Root cause: all 68 integration tests pass, but the process hangs during
shutdown because:
1. EfCoreInboxStore.MarkProcessedAsync did a blind INSERT, causing
   PK_InboxMessages duplicate key violations when the same event was
   processed via both the direct publish and outbox retry paths concurrently.
   This caused outbox messages to never be marked as processed, leading to
   infinite retry loops.
2. UserRegisteredEmailHandler tried to send real emails in CI (no SMTP
   configured), failing with "Rate limited". Hangfire retried these jobs
   with exponential backoff (10 retries), keeping the process alive past
   the CI timeout.

Fixes:
- Make MarkProcessedAsync idempotent: check HasProcessedAsync before INSERT,
  and catch DbUpdateException for the concurrent race case
- Register a NoOpMailService in the test factory to prevent real SMTP calls

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: iammukeshm

src/BuildingBlocks/Eventing/Inbox/EfCoreInboxStore.cs

@@ -27,6 +27,16 @@ public async Task<bool> HasProcessedAsync(Guid eventId, string handlerName, Canc
 
     public async Task MarkProcessedAsync(Guid eventId, string handlerName, string? tenantId, string eventType, CancellationToken ct = default)
     {
+        // Idempotent: skip if already marked (race between direct publish and outbox retry)
+        bool alreadyProcessed = await _dbContext.Set<InboxMessage>()
+            .AnyAsync(i => i.Id == eventId && i.HandlerName == handlerName, ct)
+            .ConfigureAwait(false);
+
+        if (alreadyProcessed)
+        {
+            return;
+        }
+
         var message = new InboxMessage
         {
             Id = eventId,
@@ -36,7 +46,16 @@ public async Task MarkProcessedAsync(Guid eventId, string handlerName, string? t
             ProcessedOnUtc = _timeProvider.GetUtcNow().UtcDateTime
         };
 
-        await _dbContext.Set<InboxMessage>().AddAsync(message, ct).ConfigureAwait(false);
-        await _dbContext.SaveChangesAsync(ct).ConfigureAwait(false);
+        _dbContext.Set<InboxMessage>().Add(message);
+
+        try
+        {
+            await _dbContext.SaveChangesAsync(ct).ConfigureAwait(false);
+        }
+        catch (DbUpdateException) when (!ct.IsCancellationRequested)
+        {
+            // Concurrent insert won the race — treat as already processed.
+            _dbContext.ChangeTracker.Clear();
+        }
     }
 }

src/Tests/Integration.Tests/Infrastructure/FshWebApplicationFactory.cs

@@ -2,6 +2,8 @@
 using Finbuckle.MultiTenant;
 using Finbuckle.MultiTenant.Abstractions;
 using FSH.Framework.Jobs.Services;
+using FSH.Framework.Mailing;
+using FSH.Framework.Mailing.Services;
 using FSH.Framework.Persistence;
 using FSH.Framework.Shared.Multitenancy;
 using FSH.Framework.Web.Modules;
@@ -101,6 +103,10 @@ protected override void ConfigureWebHost(IWebHostBuilder builder)
                 JwtBearerDefaults.AuthenticationScheme,
                 options => options.RequireHttpsMetadata = false);
 
+            // Replace real mail service with a no-op to avoid SMTP errors and Hangfire retries
+            services.RemoveAll<IMailService>();
+            services.AddSingleton<IMailService, NoOpMailService>();
+
             // Detailed errors in tests instead of generic "An unexpected error occurred"
             var existingHandlers = services.Where(d =>
                 d.ServiceType == typeof(Microsoft.AspNetCore.Diagnostics.IExceptionHandler)).ToList();

src/Tests/Integration.Tests/Infrastructure/NoOpMailService.cs

@@ -0,0 +1,13 @@
+using FSH.Framework.Mailing;
+using FSH.Framework.Mailing.Services;
+
+namespace Integration.Tests.Infrastructure;
+
+/// <summary>
+/// No-op mail service for integration tests ��� prevents real SMTP calls
+/// and avoids Hangfire retry loops from email failures.
+/// </summary>
+internal sealed class NoOpMailService : IMailService
+{
+    public Task SendAsync(MailRequest request, CancellationToken ct) => Task.CompletedTask;
+}