Phase 3.1: Implement RabbitMqConsumer

src/StarGate.Infrastructure/DependencyInjection.cs

@@ -8,9 +8,9 @@
 
 namespace StarGate.Infrastructure;
 
 public static partial class DependencyInjection
 {
     public static IServiceCollection AddMessageBroker(
         this IServiceCollection services,
         IConfiguration configuration)
     {
@@ -34,13 +34,15 @@
             // Register RabbitMQ options
             services.AddSingleton(options);
 
-            // Register RabbitMQ broker
+            // Register RabbitMQ broker and consumer
             services.AddSingleton<IMessageBroker, RabbitMqBroker>();
+            services.AddSingleton<IMessageConsumer, RabbitMqConsumer>();
         }
         else
         {
-            // Null object pattern - no-op broker when RabbitMQ is disabled
+            // Null object pattern - no-op broker and consumer when RabbitMQ is disabled
             services.AddSingleton<IMessageBroker, NullMessageBroker>();
+            services.AddSingleton<IMessageConsumer, NullMessageConsumer>();
         }
 
         return services;

src/StarGate.Infrastructure/Messaging/NullMessageConsumer.cs

@@ -0,0 +1,55 @@
+using Microsoft.Extensions.Logging;
+using StarGate.Core.Abstractions;
+
+namespace StarGate.Infrastructure.Messaging;
+
+/// <summary>
+/// Null object implementation of <see cref="IMessageConsumer"/>.
+/// Used when RabbitMQ is disabled or unavailable.
+/// Logs warnings and ignores all consumption requests.
+/// </summary>
+public sealed class NullMessageConsumer : IMessageConsumer
+{
+    private readonly ILogger<NullMessageConsumer> _logger;
+    private bool _disposed;
+
+    public NullMessageConsumer(ILogger<NullMessageConsumer> logger)
+    {
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _logger.LogWarning("NullMessageConsumer is active - no messages will be consumed");
+    }
+
+    public Task StartConsumingAsync<T>(
+        Func<T, MessageContext, Task> messageHandler,
+        CancellationToken ct = default)
+        where T : class
+    {
+        ArgumentNullException.ThrowIfNull(messageHandler);
+        ObjectDisposedException.ThrowIf(_disposed, this);
+
+        var queueName = $"stargate.{typeof(T).Name.ToLowerInvariant()}";
+
+        _logger.LogWarning(
+            "NullMessageConsumer: Ignoring consume request for queue {Queue}",
+            queueName);
+
+        return Task.CompletedTask;
+    }
+
+    public Task StopConsumingAsync()
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        return Task.CompletedTask;
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        if (!_disposed)
+        {
+            _logger.LogInformation("NullMessageConsumer disposed");
+            _disposed = true;
+        }
+
+        return ValueTask.CompletedTask;
+    }
+}