Checkpoint web-player design-system refactor and backend track genre tagging

Advances the ongoing token/componentization cleanup (anchored player dock,
border-based panels instead of floating shadows, corrected light-mode
accent/gradient tokens) alongside in-progress backend support for track
genre tags.

backend/Core/Musify.Application/Tracks/CreateTrack.cs

@@ -17,7 +17,8 @@ namespace Musify.Application.Tracks
         long UserId,
         string Title,
         Guid PictureIntentId,
-        Guid AudioIntentId)
+        Guid AudioIntentId,
+        IReadOnlyCollection<Genre> Tags)
         : ICommand<ErrorOr<TrackApplicationResponse>>;
 
     public class CreateTrackCommandHandler(
@@ -40,6 +41,23 @@ namespace Musify.Application.Tracks
                 return Error.NotFound(description: $"User {request.UserId} not found");
             }
 
+            var distinctTags = request.Tags.Distinct().ToList();
+            if (distinctTags.Count == 0)
+            {
+                logger.LogWarning("Track {Title} was submitted without any tags", request.Title);
+                return Error.Validation(description: "At least one tag is required.");
+            }
+
+            var tagConflicts = GenreCompatibility.FindConflicts(distinctTags);
+            if (tagConflicts.Count > 0)
+            {
+                var conflict = tagConflicts.First();
+                logger.LogWarning(
+                    "Track {Title} was submitted with incompatible tags {First} and {Second}",
+                    request.Title, conflict.First, conflict.Second);
+                return Error.Validation(description: $"Tags '{conflict.First}' and '{conflict.Second}' are not compatible.");
+            }
+
             var pictureValidation = await uploadIntentValidator.ValidateAndLoadAsync(
                 uploadIntentConfiguration,
                 request.PictureIntentId, request.UserId, cancellationToken);
@@ -80,6 +98,10 @@ namespace Musify.Application.Tracks
                 }
             };
 
+            trackEntity.Tags = distinctTags
+                .Select(tag => new TrackTag { TrackId = trackEntity.Id, Tag = tag })
+                .ToList();
+
             await database.Tracks.AddAsync(trackEntity, cancellationToken);
 
             await database.UserHasTracks.AddAsync(new UserHasTrack

backend/Core/Musify.Application/Tracks/GetListeningHistory.cs

@@ -25,6 +25,7 @@ namespace Musify.Application.Tracks
 
             var tracksById = await database.Tracks
                 .Include(t => t.Owner)
+                .Include(t => t.Tags)
                 .Where(t => recentTrackIds.Contains(t.Id))
                 .Select(t => new { t.Id, Track = t, ListensCount = t.ListeningHistories.Count } )
                 .ToDictionaryAsync(t => t.Id, cancellationToken);

backend/Core/Musify.Application/Tracks/GetTrackById.cs

@@ -16,6 +16,7 @@ namespace Musify.Application.Tracks
         {
             var entity = await database.Tracks.AsNoTracking()
                 .Include(t => t.Owner)
+                .Include(t => t.Tags)
                 .Where(t => t.Id == request.TrackId)
                 .Select(t => new { Track = t, ListensCount = t.ListeningHistories.Count })
                 .SingleOrDefaultAsync(cancellationToken);

backend/Core/Musify.Application/Tracks/GetTracks.cs

@@ -19,6 +19,7 @@ namespace Musify.Application.Tracks
             var tracksQuery = database.UserHasTracks
                 .AsNoTracking()
                 .Include(ut => ut.Track.Owner)
+                .Include(ut => ut.Track.Tags)
                 .AsQueryable();
 
             if (!string.IsNullOrEmpty(request.Name))

backend/Core/Musify.Application/Tracks/GetTracksByUserId.cs

@@ -27,6 +27,7 @@ namespace Musify.Application.Tracks
             var tracksQuery = database.UserHasTracks
                 .AsNoTracking()
                 .Include(ut => ut.Track.Owner)
+                .Include(ut => ut.Track.Tags)
                 .Where(p => p.UserId == request.UserId);
 
             if (!string.IsNullOrEmpty(request.Name))

backend/Core/Musify.Application/Tracks/Responses/TrackApplicationResponse.cs

@@ -14,7 +14,8 @@ namespace Musify.Application.Tracks.Responses
         int ListensCount,
         DateTime CreatedAt,
         DateTime UpdatedAt,
-        [property: JsonConverter(typeof(LongAsStringConverter))] long OwnerUserId)
+        [property: JsonConverter(typeof(LongAsStringConverter))] long OwnerUserId,
+        IReadOnlyCollection<Genre> Tags)
     {
         public static TrackApplicationResponse FromEntity(Track track, int listensCount) =>
             new(
@@ -26,6 +27,7 @@ namespace Musify.Application.Tracks.Responses
                 listensCount,
                 track.CreatedAt,
                 track.UpdatedAt,
-                track.OwnerUserId);
+                track.OwnerUserId,
+                track.Tags.Select(tag => tag.Tag).ToList());
     }
 }