refactor: replace Ardalis.Result with ErrorOr across the app

Ardalis Result<T> carried incoherent success sub-statuses and a clunky
generic converter; ErrorOr models success-or-errors cleanly.

- Application: all commands/queries/handlers now return ErrorOr<T>
  (non-generic Result -> ErrorOr<Success>); errors via Error.NotFound/
  Conflict/Validation/Unauthorized/Failure; success via value or new Success()
- Drop ResultExtensions.As<>(): error propagation is now just return .Errors
- Rewrite HTTP mapping (ErrorOrHttpExtensions) off Error.Type; success maps
  to 200 (value) or 204 (Success); Created still built in the endpoints
- Endpoints/gateway middleware: !IsSuccess -> IsError
- Swap Ardalis.Result package for ErrorOr 2.1.1 (remove unused ref from Worker)

Build: 0 warnings, 0 errors.

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

backend/Musify.Application/Tracks/Commands/CreateTrackCommand.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Tracks.Responses;
 
@@ -9,5 +9,5 @@ namespace Musify.Application.Tracks.Commands
         string Title,
         Guid PictureIntentId,
         Guid AudioIntentId)
-        : ICommand<Result<TrackApplicationResponse>>;
+        : ICommand<ErrorOr<TrackApplicationResponse>>;
 }

backend/Musify.Application/Tracks/Commands/DeleteTrackCommand.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 
 namespace Musify.Application.Tracks.Commands
@@ -6,5 +6,5 @@ namespace Musify.Application.Tracks.Commands
     public record DeleteTrackCommand(
         long UserId,
         Guid TrackId)
-        : ICommand<Result>;
+        : ICommand<ErrorOr<Success>>;
 }

backend/Musify.Application/Tracks/Commands/RequestTrackUploadUrlsCommand.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Tracks.Responses;
 
@@ -12,5 +12,5 @@ namespace Musify.Application.Tracks.Commands
         string AudioContentType,
         long? ExpectedPictureSizeBytes = null,
         long? ExpectedAudioSizeBytes = null)
-        : ICommand<Result<TrackUploadUrlsResponse>>;
+        : ICommand<ErrorOr<TrackUploadUrlsResponse>>;
 }

backend/Musify.Application/Tracks/Handlers/CreateTrackCommandHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
@@ -7,7 +7,6 @@ using Musify.Application.Shared;
 using Musify.Application.Events;
 using Musify.Application.Tracks.Commands;
 using Musify.Application.Tracks.Responses;
-using Musify.Application.Extensions;
 using Musify.Application.Services;
 using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
@@ -23,29 +22,29 @@ namespace Musify.Application.Tracks.Handlers
         ApplicationStorageConfiguration storageConfiguration,
         TrackConfiguration trackConfiguration,
         UploadIntentConfiguration uploadIntentConfiguration)
-        : ICommandHandler<CreateTrackCommand, Result<TrackApplicationResponse>>
+        : ICommandHandler<CreateTrackCommand, ErrorOr<TrackApplicationResponse>>
     {
-        public async ValueTask<Result<TrackApplicationResponse>> Handle(CreateTrackCommand request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<TrackApplicationResponse>> Handle(CreateTrackCommand request, CancellationToken cancellationToken)
         {
             var userExists = await database.Users.AsNoTracking()
                 .AnyAsync(u => u.Id == request.UserId, cancellationToken);
             if (!userExists)
             {
                 logger.LogWarning("User {UserId} not found", request.UserId);
-                return Result.NotFound($"User {request.UserId} not found");
+                return Error.NotFound(description: $"User {request.UserId} not found");
             }
 
             var pictureValidation = await uploadIntentValidator.ValidateAndLoadAsync(
                 uploadIntentConfiguration,
                 request.PictureIntentId, request.UserId, cancellationToken);
-            if (!pictureValidation.IsSuccess)
-                return pictureValidation.As<UploadIntent, TrackApplicationResponse>();
+            if (pictureValidation.IsError)
+                return pictureValidation.Errors;
 
             var audioValidation = await uploadIntentValidator.ValidateAndLoadAsync(
                 uploadIntentConfiguration,
                 request.AudioIntentId, request.UserId, cancellationToken);
-            if (!audioValidation.IsSuccess)
-                return audioValidation.As<UploadIntent, TrackApplicationResponse>();
+            if (audioValidation.IsError)
+                return audioValidation.Errors;
 
             var pictureIntent = pictureValidation.Value;
             var audioIntent = audioValidation.Value;
@@ -105,7 +104,7 @@ namespace Musify.Application.Tracks.Handlers
             catch (Exception exception)
             {
                 logger.LogError(exception, "Failed to publish create track event for track {TrackId}", trackEntity.Id);
-                return Result.Error($"Failed to create track for {request.Title}");
+                return Error.Failure(description: $"Failed to create track for {request.Title}");
             }
 
             try
@@ -115,10 +114,10 @@ namespace Musify.Application.Tracks.Handlers
             catch (Exception exception)
             {
                 logger.LogError(exception, "Failed to save track {Title}", request.Title);
-                return Result.Error($"Failed to create track for {request.Title}");
+                return Error.Failure(description: $"Failed to create track for {request.Title}");
             }
 
-            return Result.Created(TrackApplicationResponse.FromEntity(trackEntity));
+            return TrackApplicationResponse.FromEntity(trackEntity);
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/DeleteTrackCommandHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
@@ -13,15 +13,15 @@ namespace Musify.Application.Tracks.Handlers
         IDatabase database,
         IEventBus eventBus,
         ILogger<DeleteTrackCommandHandler> logger)
-        : ICommandHandler<DeleteTrackCommand, Result>
+        : ICommandHandler<DeleteTrackCommand, ErrorOr<Success>>
     {
-        public async ValueTask<Result> Handle(DeleteTrackCommand request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<Success>> Handle(DeleteTrackCommand request, CancellationToken cancellationToken)
         {
             var track = await database.Tracks.SingleOrDefaultAsync(t => t.Id == request.TrackId, cancellationToken);
             if (track is null)
             {
                 logger.LogInformation("Track {TrackId} not found", request.TrackId);
-                return Result.NotFound();
+                return Error.NotFound();
             }
 
             var isOwner = await database.UserHasTracks
@@ -30,14 +30,14 @@ namespace Musify.Application.Tracks.Handlers
             if (!isOwner)
             {
                 logger.LogWarning("User {UserId} unauthorized to delete track {TrackId}", request.UserId, request.TrackId);
-                return Result.Unauthorized();
+                return Error.Unauthorized();
             }
 
             if (track.AudioTranscodeProcessingStatus == ProcessingStatus.Processing
                 || track.AudioTranscodeProcessingStatus == ProcessingStatus.Pending)
             {
                 logger.LogWarning("Track {TrackId} is currently being processed and cannot be deleted", request.TrackId);
-                return Result.Conflict("Track is currently being processed and cannot be deleted");
+                return Error.Conflict(description: "Track is currently being processed and cannot be deleted");
             }
 
             track.LifeCycleStatus = LifeCycleStatus.Removing;
@@ -51,7 +51,7 @@ namespace Musify.Application.Tracks.Handlers
             catch (Exception exception)
             {
                 logger.LogError(exception, "Failed to publish delete track event for track {TrackId}", request.TrackId);
-                return Result.Error($"Failed to delete track {request.TrackId}");
+                return Error.Failure(description: $"Failed to delete track {request.TrackId}");
             }
 
             try
@@ -61,10 +61,10 @@ namespace Musify.Application.Tracks.Handlers
             catch (Exception exception)
             {
                 logger.LogError(exception, "Failed to mark track {TrackId} as processing before deletion", request.TrackId);
-                return Result.Error($"Failed to delete track {request.TrackId}");
+                return Error.Failure(description: $"Failed to delete track {request.TrackId}");
             }
 
-            return Result.NoContent();
+            return new Success();
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/GetTrackByIdQueryHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Contracts;
@@ -8,18 +8,19 @@ using Musify.Application.Tracks.Responses;
 namespace Musify.Application.Tracks.Handlers
 {
     public class GetTrackByIdQueryHandler(IDatabase database)
-        : IQueryHandler<GetTrackByIdQuery, Result<TrackApplicationResponse> >
+        : IQueryHandler<GetTrackByIdQuery, ErrorOr<TrackApplicationResponse> >
     {
-        public async ValueTask<Result<TrackApplicationResponse>> Handle(GetTrackByIdQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<TrackApplicationResponse>> Handle(GetTrackByIdQuery request, CancellationToken cancellationToken)
         {
             var track = await database.Tracks.AsNoTracking()
                 .Where(t => t.Id == request.TrackId)
                 .Select(t => TrackApplicationResponse.FromEntity(t))
                 .SingleOrDefaultAsync(cancellationToken);
 
-            return track is null
-                ? Result<TrackApplicationResponse>.NotFound()
-                : Result.Success(track);
+            if (track is null)
+                return Error.NotFound();
+
+            return track;
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/GetTrackStreamQueryHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
@@ -16,9 +16,9 @@ namespace Musify.Application.Tracks.Handlers
         TrackConfiguration trackConfiguration,
         StreamGatewayConfiguration streamGatewayConfiguration,
         ILogger<GetTrackStreamQueryHandler> logger)
-        : IQueryHandler<GetTrackStreamQuery, Result<TrackStreamResponse>>
+        : IQueryHandler<GetTrackStreamQuery, ErrorOr<TrackStreamResponse>>
     {
-        public async ValueTask<Result<TrackStreamResponse>> Handle(GetTrackStreamQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<TrackStreamResponse>> Handle(GetTrackStreamQuery request, CancellationToken cancellationToken)
         {
             var track = await database.Tracks.AsNoTracking()
                 .Where(t => t.Id == request.TrackId)
@@ -26,13 +26,13 @@ namespace Musify.Application.Tracks.Handlers
                 .SingleOrDefaultAsync(cancellationToken);
 
             if (track is null)
-                return Result<TrackStreamResponse>.NotFound();
+                return Error.NotFound();
 
             if (string.IsNullOrWhiteSpace(track.AudioFolderName)
                 || track.AudioTranscodeProcessingStatus != ProcessingStatus.Completed)
             {
                 logger.LogInformation("Stream requested for track {TrackId} but audio is not ready", request.TrackId);
-                return Result<TrackStreamResponse>.Conflict("Track audio is not available for streaming yet.");
+                return Error.Conflict(description: "Track audio is not available for streaming yet.");
             }
 
             var folderPath = trackConfiguration.Routes.BuildProcessedAudioPath(track.AudioFolderName);
@@ -48,7 +48,7 @@ namespace Musify.Application.Tracks.Handlers
 
             logger.LogInformation("Issued stream ticket for track {TrackId} to user {UserId}", request.TrackId, request.UserId);
 
-            return Result.Success(new TrackStreamResponse(manifestUrl, ticket.Token, ticket.ExpiresInSeconds));
+            return new TrackStreamResponse(manifestUrl, ticket.Token, ticket.ExpiresInSeconds);
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/GetTracksByUserIdQueryHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Pagination;
@@ -10,9 +10,9 @@ using Musify.Application.Contracts;
 namespace Musify.Application.Tracks.Handlers
 {
     public class GetTracksByUserIdQueryHandler(IDatabase database)
-        : IQueryHandler<GetTracksByUserIdQuery, Result<PaginatedResponse<TrackApplicationResponse>> >
+        : IQueryHandler<GetTracksByUserIdQuery, ErrorOr<PaginatedResponse<TrackApplicationResponse>> >
     {
-        public async ValueTask<Result<PaginatedResponse<TrackApplicationResponse> >> Handle(GetTracksByUserIdQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<PaginatedResponse<TrackApplicationResponse> >> Handle(GetTracksByUserIdQuery request, CancellationToken cancellationToken)
         {
             var pageNumber = request.PageNumber < 1 ? 1 : request.PageNumber;
             var pageSize = request.PageSize < 1 ? 10 : request.PageSize;
@@ -35,7 +35,7 @@ namespace Musify.Application.Tracks.Handlers
                 .Select(t => TrackApplicationResponse.FromEntity(t.Track))
                 .ToPagedListAsync(pageNumber, pageSize, totalCount, cancellationToken);
 
-            return Result.Success(PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks));
+            return PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks);
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/GetTracksQueryHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Pagination;
@@ -10,9 +10,9 @@ using Musify.Application.Contracts;
 namespace Musify.Application.Tracks.Handlers
 {
     public class GetTracksQueryHandler(IDatabase database)
-        : IQueryHandler<GetTracksQuery, Result<PaginatedResponse<TrackApplicationResponse>> >
+        : IQueryHandler<GetTracksQuery, ErrorOr<PaginatedResponse<TrackApplicationResponse>> >
     {
-        public async ValueTask<Result<PaginatedResponse<TrackApplicationResponse> >> Handle(GetTracksQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<PaginatedResponse<TrackApplicationResponse> >> Handle(GetTracksQuery request, CancellationToken cancellationToken)
         {
             var tracksQuery = database.UserHasTracks
                 .AsNoTracking()
@@ -23,7 +23,7 @@ namespace Musify.Application.Tracks.Handlers
             var totalCount = await tracksQuery.CountAsync(cancellationToken);
             var pagedTracks = await tracksQuery.ToPagedListAsync(request.PageNumber, request.PageSize, totalCount, cancellationToken);
 
-            return Result.Success(PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks));
+            return PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks);
         }
     }
 }

backend/Musify.Application/Tracks/Handlers/RequestTrackUploadUrlsCommandHandler.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
@@ -20,9 +20,9 @@ namespace Musify.Application.Tracks.Handlers
         ApplicationStorageConfiguration storageConfiguration,
         TrackConfiguration trackConfiguration,
         UploadIntentConfiguration uploadIntentConfiguration)
-        : ICommandHandler<RequestTrackUploadUrlsCommand, Result<TrackUploadUrlsResponse>>
+        : ICommandHandler<RequestTrackUploadUrlsCommand, ErrorOr<TrackUploadUrlsResponse>>
     {
-        public async ValueTask<Result<TrackUploadUrlsResponse>> Handle(RequestTrackUploadUrlsCommand request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<TrackUploadUrlsResponse>> Handle(RequestTrackUploadUrlsCommand request, CancellationToken cancellationToken)
         {
             var userExists = await database.Users
                 .AsNoTracking()
@@ -30,7 +30,7 @@ namespace Musify.Application.Tracks.Handlers
             if (!userExists)
             {
                 logger.LogWarning("User {UserId} not found", request.UserId);
-                return Result.NotFound($"User {request.UserId} not found");
+                return Error.NotFound(description: $"User {request.UserId} not found");
             }
 
             var effectivePictureSize = request.ExpectedPictureSizeBytes
@@ -72,10 +72,10 @@ namespace Musify.Application.Tracks.Handlers
                 var quotaCheck = await uploadIntentValidator.CheckQuotaAsync(
                     uploadIntentConfiguration,
                     request.UserId, effectivePictureSize + effectiveAudioSize, 2, cancellationToken);
-                if (!quotaCheck.IsSuccess)
+                if (quotaCheck.IsError)
                 {
                     logger.LogWarning("User {UserId} failed upload intent quota check", request.UserId);
-                    return quotaCheck;
+                    return quotaCheck.Errors;
                 }
 
                 var pictureIntent = new UploadIntent
@@ -110,7 +110,7 @@ namespace Musify.Application.Tracks.Handlers
                 logger.LogInformation("Issued upload intents {PictureIntentId}/{AudioIntentId} for user {UserId} (TrackPicture/TrackAudio)",
                     pictureIntent.Id, audioIntent.Id, request.UserId);
 
-                return Result.Success(new TrackUploadUrlsResponse(
+                return new TrackUploadUrlsResponse(
                     pictureIntent.Id,
                     audioIntent.Id,
                     storageConfiguration.Bucket,
@@ -122,12 +122,12 @@ namespace Musify.Application.Tracks.Handlers
                     audioObjectName,
                     request.AudioContentType,
                     audioUploadUrl,
-                    uploadIntentConfiguration.UploadUrlExpiresInSeconds));
+                    uploadIntentConfiguration.UploadUrlExpiresInSeconds);
             }
             catch (Exception exception)
             {
                 logger.LogError(exception, "Failed to generate track upload URLs for user {UserId}", request.UserId);
-                return Result.Error("Failed to generate upload URLs");
+                return Error.Failure(description: "Failed to generate upload URLs");
             }
         }
     }

backend/Musify.Application/Tracks/Queries/GetTrackByIdQuery.cs

@@ -1,9 +1,9 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Tracks.Responses;
 
 namespace Musify.Application.Tracks.Queries
 {
     public record GetTrackByIdQuery(Guid TrackId)
-        : IQuery<Result<TrackApplicationResponse>>;
+        : IQuery<ErrorOr<TrackApplicationResponse>>;
 }

backend/Musify.Application/Tracks/Queries/GetTrackStreamQuery.cs

@@ -1,9 +1,9 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Tracks.Responses;
 
 namespace Musify.Application.Tracks.Queries
 {
     public record GetTrackStreamQuery(Guid TrackId, long UserId)
-        : IQuery<Result<TrackStreamResponse>>;
+        : IQuery<ErrorOr<TrackStreamResponse>>;
 }

backend/Musify.Application/Tracks/Queries/GetTracksByUserIdQuery.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Pagination;
 using Musify.Application.Tracks.Responses;
@@ -10,5 +10,5 @@ namespace Musify.Application.Tracks.Queries
     string? Name = null,
         int PageNumber = 1,
         int PageSize = 10)
-        : IQuery<Result<PaginatedResponse<TrackApplicationResponse> > >;
+        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> > >;
 }

backend/Musify.Application/Tracks/Queries/GetTracksQuery.cs

@@ -1,4 +1,4 @@
-using Ardalis.Result;
+using ErrorOr;
 using Mediator;
 using Musify.Application.Pagination;
 using Musify.Application.Tracks.Responses;
@@ -6,5 +6,5 @@ using Musify.Application.Tracks.Responses;
 namespace Musify.Application.Tracks.Queries
 {
     public record GetTracksQuery(int PageNumber = 1, int PageSize = 10)
-        : IQuery<Result<PaginatedResponse<TrackApplicationResponse> >>;
+        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> >>;
 }