fix(infra): repair TransferFiles compensation + tidy MassTransit consistency

Fix (recoverability bug):
- TransferFilesToBucketActivity returned Completed() with no log, so its
  compensation could never delete the transferred files (orphaned objects on
  fault). IStorageService.TransferFilesAsync now returns the real uploaded
  keys; the activity logs them so Compensate can remove them. Also drops the
  Path.Combine key recomputation (produced backslash keys on Windows).

Consistency / DRY:
- Normalize all courier activities to internal + folder-based namespaces
  (several were public and in the flat .Activities namespace)
- Extract the duplicated exponential retry into UseStandardRetry
- Unify endpoint-name logic into a single EndpointHelper (remove the parallel
  MassTransitEndpointNames helper)

Build: 0 warnings, 0 errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/Musify.Application/Contracts/IStorageService.cs

@@ -14,7 +14,7 @@ namespace Musify.Application.Contracts
 
         Task UploadFileAsync(Stream sourceStream, string contentType, string bucket, string key, CancellationToken cancellationToken);
 
-        Task TransferFilesAsync(string sourceDirectory, string bucket, string route, CancellationToken cancellationToken);
+        Task<IReadOnlyList<string>> TransferFilesAsync(string sourceDirectory, string bucket, string route, CancellationToken cancellationToken);
 
         Task RemoveFileAsync(string bucket, string key, CancellationToken cancellationToken);
 

backend/Musify.Infrastructure/MassTransit/Activities/Audio/GenerateAudioWorkflowPathsActivity.cs

@@ -6,7 +6,7 @@ using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 using Musify.Infrastructure.MassTransit.Arguments;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Audio
 {
     internal class GenerateAudioWorkflowPathsActivity(
         IDatabase database,

backend/Musify.Infrastructure/MassTransit/Activities/Audio/TranscodeAudioActivity.cs

@@ -7,7 +7,7 @@ using Musify.Domain.ValueObjects;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Logs;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Audio
 {
     internal class TranscodeAudioActivity(
         IDatabase database,

backend/Musify.Infrastructure/MassTransit/Activities/Files/TransferFilesToBucketActivity.cs

@@ -4,9 +4,9 @@ using Musify.Application.Contracts;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Logs;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Files
 {
-    public class TransferFilesToBucketActivity(
+    internal class TransferFilesToBucketActivity(
         IStorageService storageHandler,
         ILogger<TransferFilesToBucketActivity> logger)
         : IActivity<TransferFilesToBucketArguments, TransferFilesToBucketLog>
@@ -22,16 +22,15 @@ namespace Musify.Infrastructure.MassTransit.Activities
 
             try
             {
-                var uploadedKeys = Directory.GetFiles(folderPath)
+                var uploadedKeys = await storageHandler.TransferFilesAsync(
-                    .Select(file => Path.Combine(destinationKey, Path.GetFileName(file)))
-                    .ToArray();
-
-                await storageHandler.TransferFilesAsync(
                     folderPath,
                     executeContext.Arguments.DestinationBucket,
                     destinationKey,
                     executeContext.CancellationToken);
-                return executeContext.Completed();
+
+                return executeContext.Completed(new TransferFilesToBucketLog(
+                    executeContext.Arguments.DestinationBucket,
+                    uploadedKeys.ToArray()));
             }
             catch (Exception exception)
             {

backend/Musify.Infrastructure/MassTransit/Activities/Files/UploadFileToBucketActivity.cs

@@ -6,7 +6,7 @@ using Musify.Infrastructure.MassTransit.Logs;
 
 namespace Musify.Infrastructure.MassTransit.Activities.Files
 {
-    public class UploadFileToBucketActivity(IStorageService storageHandler,
+    internal class UploadFileToBucketActivity(IStorageService storageHandler,
         ILogger<UploadFileToBucketActivity> logger)
         : IActivity<UploadFileToBucketArguments, UploadFileToBucketLog>
     {

backend/Musify.Infrastructure/MassTransit/Activities/Pictures/GeneratePictureWorkflowPathsActivity.cs

@@ -2,9 +2,9 @@ using MassTransit;
 using Microsoft.Extensions.Logging;
 using Musify.Infrastructure.MassTransit.Arguments;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Pictures
 {
-    public class GeneratePictureWorkflowPathsActivity(
+    internal class GeneratePictureWorkflowPathsActivity(
         ILogger<GeneratePictureWorkflowPathsActivity> logger)
         : IExecuteActivity<GeneratePictureWorkflowPathsArguments>
     {

backend/Musify.Infrastructure/MassTransit/Activities/Pictures/ResizePictureActivity.cs

@@ -4,9 +4,9 @@ using Musify.Application.Contracts;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Logs;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Pictures
 {
-    public class ResizePictureActivity(
+    internal class ResizePictureActivity(
         IPictureService pictureHandler,
         ILogger<ResizePictureActivity> logger)
         : IActivity<ResizePictureLocalArguments, ResizePictureLog>

backend/Musify.Infrastructure/MassTransit/Activities/Pictures/UpdatePlayListPictureActivity.cs

@@ -4,9 +4,9 @@ using Musify.Application.Contracts;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Logs;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Pictures
 {
-    public class UpdatePlayListPictureActivity(
+    internal class UpdatePlayListPictureActivity(
         IDatabase database,
         ILogger<UpdatePlayListPictureActivity> logger)
         : IActivity<UpdatePlayListPictureArguments, UpdatePlayListPictureLog>

backend/Musify.Infrastructure/MassTransit/Activities/Pictures/UpdateTrackPictureActivity.cs

@@ -5,9 +5,9 @@ using Musify.Domain.ValueObjects;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Logs;
 
-namespace Musify.Infrastructure.MassTransit.Activities
+namespace Musify.Infrastructure.MassTransit.Activities.Pictures
 {
-    public class UpdateTrackPictureActivity(
+    internal class UpdateTrackPictureActivity(
         IDatabase database,
         ILogger<UpdateTrackPictureActivity> logger)
         : IActivity<UpdateTrackPictureArguments, UpdateTrackPictureLog>

backend/Musify.Infrastructure/MassTransit/Consumers/EndpointHelper.cs

@@ -2,9 +2,13 @@ namespace Musify.Infrastructure.MassTransit.Consumers
 {
     internal static class EndpointHelper
     {
-        internal static Uri BuildExecuteActivityUri(string endpointName) => new($"queue:{endpointName}_execute");
+        internal static string ExecuteQueueName(string endpointName) => $"{endpointName}_execute";
 
-        internal static Uri BuildCompensateActivityUri(string endpointName) => new($"queue:{endpointName}_compensate");
+        internal static string CompensateQueueName(string endpointName) => $"{endpointName}_compensate";
+
+        internal static Uri BuildExecuteActivityUri(string endpointName) => new($"queue:{ExecuteQueueName(endpointName)}");
+
+        internal static Uri BuildCompensateActivityUri(string endpointName) => new($"queue:{CompensateQueueName(endpointName)}");
 
         internal static Uri BuildConsumerUri(string endpointName) => new($"queue:{endpointName}");
     }

backend/Musify.Infrastructure/MassTransit/DependencyInjection/MassTransitDependencyInjection.Endpoints.cs

@@ -6,6 +6,14 @@ namespace Musify.Infrastructure.MassTransit
 {
     public static partial class MassTransitDependencyInjection
     {
+        static void UseStandardRetry(IReceiveEndpointConfigurator endpointConfigurator) =>
+            endpointConfigurator.UseMessageRetry(retryConfigurator =>
+                retryConfigurator.Exponential(
+                    retryLimit: 5,
+                    minInterval: TimeSpan.FromSeconds(1),
+                    maxInterval: TimeSpan.FromSeconds(30),
+                    intervalDelta: TimeSpan.FromSeconds(2)));
+
         static void ConfigureConsumerEndpoint<TConsumer>(
             IRabbitMqBusFactoryConfigurator busFactoryConfigurator,
             IBusRegistrationContext busRegistrationContext,
@@ -14,15 +22,8 @@ namespace Musify.Infrastructure.MassTransit
         {
             busFactoryConfigurator.ReceiveEndpoint(queueName, endpointConfigurator =>
             {
-                endpointConfigurator.UseMessageRetry(retryConfigurator =>
+                UseStandardRetry(endpointConfigurator);
-                    retryConfigurator.Exponential(
-                        retryLimit: 5,
-                        minInterval: TimeSpan.FromSeconds(1),
-                        maxInterval: TimeSpan.FromSeconds(30),
-                        intervalDelta: TimeSpan.FromSeconds(2)));
-
                 endpointConfigurator.UseEntityFrameworkOutbox<Database>(busRegistrationContext);
-
                 endpointConfigurator.ConfigureConsumer<TConsumer>(busRegistrationContext);
             });
         }
@@ -34,17 +35,10 @@ namespace Musify.Infrastructure.MassTransit
             where TActivity : class, IExecuteActivity<TArguments>
             where TArguments : class
         {
-            busFactoryConfigurator.ReceiveEndpoint(MassTransitEndpointNames.ExecuteQueue(endpointName), endpointConfigurator =>
+            busFactoryConfigurator.ReceiveEndpoint(EndpointHelper.ExecuteQueueName(endpointName), endpointConfigurator =>
             {
-                endpointConfigurator.UseMessageRetry(retryConfigurator =>
+                UseStandardRetry(endpointConfigurator);
-                    retryConfigurator.Exponential(
-                        retryLimit: 5,
-                        minInterval: TimeSpan.FromSeconds(1),
-                        maxInterval: TimeSpan.FromSeconds(30),
-                        intervalDelta: TimeSpan.FromSeconds(2)));
-
                 endpointConfigurator.UseEntityFrameworkOutbox<Database>(busRegistrationContext);
-
                 endpointConfigurator.ExecuteActivityHost<TActivity, TArguments>(busRegistrationContext);
             });
         }
@@ -57,33 +51,19 @@ namespace Musify.Infrastructure.MassTransit
             where TArguments : class
             where TLog : class
         {
-            busFactoryConfigurator.ReceiveEndpoint(MassTransitEndpointNames.ExecuteQueue(endpointName), endpointConfigurator =>
+            busFactoryConfigurator.ReceiveEndpoint(EndpointHelper.ExecuteQueueName(endpointName), endpointConfigurator =>
             {
-                endpointConfigurator.UseMessageRetry(retryConfigurator =>
+                UseStandardRetry(endpointConfigurator);
-                    retryConfigurator.Exponential(
-                        retryLimit: 5,
-                        minInterval: TimeSpan.FromSeconds(1),
-                        maxInterval: TimeSpan.FromSeconds(30),
-                        intervalDelta: TimeSpan.FromSeconds(2)));
-
                 endpointConfigurator.UseEntityFrameworkOutbox<Database>(busRegistrationContext);
-
                 endpointConfigurator.ExecuteActivityHost<TActivity, TArguments>(
                     EndpointHelper.BuildCompensateActivityUri(endpointName),
                     busRegistrationContext);
             });
 
-            busFactoryConfigurator.ReceiveEndpoint(MassTransitEndpointNames.CompensateQueue(endpointName), endpointConfigurator =>
+            busFactoryConfigurator.ReceiveEndpoint(EndpointHelper.CompensateQueueName(endpointName), endpointConfigurator =>
             {
-                endpointConfigurator.UseMessageRetry(retryConfigurator =>
+                UseStandardRetry(endpointConfigurator);
-                    retryConfigurator.Exponential(
-                        retryLimit: 5,
-                        minInterval: TimeSpan.FromSeconds(1),
-                        maxInterval: TimeSpan.FromSeconds(30),
-                        intervalDelta: TimeSpan.FromSeconds(2)));
-
                 endpointConfigurator.UseEntityFrameworkOutbox<Database>(busRegistrationContext);
-
                 endpointConfigurator.CompensateActivityHost<TActivity, TLog>(busRegistrationContext);
             });
         }

backend/Musify.Infrastructure/MassTransit/DependencyInjection/MassTransitDependencyInjection.Registration.cs

@@ -1,7 +1,7 @@
 using MassTransit;
 using Microsoft.Extensions.DependencyInjection;
 using Musify.Infrastructure.Configuration;
-using Musify.Infrastructure.MassTransit.Activities;
+using Musify.Infrastructure.MassTransit.Activities.Pictures;
 using Musify.Infrastructure.MassTransit.Activities.Audio;
 using Musify.Infrastructure.MassTransit.Activities.Files;
 using Musify.Infrastructure.MassTransit.Activities.PlayLists;

backend/Musify.Infrastructure/MassTransit/DependencyInjection/MassTransitEndpointNames.cs

@@ -1,9 +0,0 @@
-namespace Musify.Infrastructure.MassTransit
-{
-    internal static class MassTransitEndpointNames
-    {
-        internal static string ExecuteQueue(string endpointName) => $"{endpointName}_execute";
-
-        internal static string CompensateQueue(string endpointName) => $"{endpointName}_compensate";
-    }
-}

backend/Musify.Infrastructure/MassTransit/RoutingSlip/Builders/PictureWorkflowRoutingSlipBuilder.cs

@@ -3,7 +3,7 @@ using MassTransit.Courier.Contracts;
 using Musify.Application.Shared;
 using Musify.Application.Events;
 using Musify.Infrastructure.Configuration;
-using Musify.Infrastructure.MassTransit.Activities;
+using Musify.Infrastructure.MassTransit.Activities.Pictures;
 using Musify.Infrastructure.MassTransit.Activities.Files;
 using Musify.Infrastructure.MassTransit.Arguments;
 using Musify.Infrastructure.MassTransit.Consumers;

backend/Musify.Infrastructure/Services/StorageService.cs

@@ -105,12 +105,13 @@ namespace Musify.Infrastructure.Services
             await amazonS3.DeleteObjectAsync(request, cancellationToken);
         }
 
-        public async Task TransferFilesAsync(string sourceDirectory, string bucket, string route, CancellationToken cancellationToken)
+        public async Task<IReadOnlyList<string>> TransferFilesAsync(string sourceDirectory, string bucket, string route, CancellationToken cancellationToken)
         {
             var trasnsferUtility = new TransferUtility(amazonS3);
 
             var files = Directory.GetFiles(sourceDirectory, "*");
 
+            var uploadedKeys = new List<string>();
             var successCount = 0;
             var failedCount = 0;
 
@@ -144,6 +145,7 @@ namespace Musify.Infrastructure.Services
                         },
                         cancellationToken);
                     upload.State = UploadState.Successful;
+                    uploadedKeys.Add(key);
                     successCount++;
                     logger.LogDebug("Transferred file to S3 {Bucket}/{Key}", bucket, key);
                 }
@@ -158,6 +160,8 @@ namespace Musify.Infrastructure.Services
 
             await database.SaveChangesAsync(cancellationToken);
             logger.LogInformation("File transfer completed to {Bucket}/{Route}. Success: {SuccessCount}, Failed: {FailedCount}", bucket, route, successCount, failedCount);
+
+            return uploadedKeys;
         }
 
         public async Task UploadFileAsync(string filePath, string bucket, string key, CancellationToken cancellationToken)