diff --git a/app/Console/Commands/BackfillArtworkPrimaryCategoryCommand.php b/app/Console/Commands/BackfillArtworkPrimaryCategoryCommand.php
new file mode 100644
index 00000000..720aac40
--- /dev/null
+++ b/app/Console/Commands/BackfillArtworkPrimaryCategoryCommand.php
@@ -0,0 +1,139 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Console\Commands;
+
+use App\Models\Artwork;
+use Illuminate\Console\Command;
+use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\DB;
+
+final class BackfillArtworkPrimaryCategoryCommand extends Command
+{
+    protected $signature = 'artworks:backfill-primary-category
+        {--dry-run : Report without writing (default unless --apply is passed)}
+        {--report : Print category-count distribution and conflicts}
+        {--apply : Write primary_category_id for artworks with exactly one category}
+        {--force : Overwrite existing primary_category_id values}';
+
+    protected $description = 'Backfill artworks.primary_category_id from unique artwork_category memberships';
+
+    public function handle(): int
+    {
+        $apply = (bool) $this->option('apply');
+        $force = (bool) $this->option('force');
+        $report = (bool) $this->option('report') || ! $apply;
+
+        if ($report) {
+            $this->printDistribution();
+        }
+
+        $conflicts = $this->conflictArtworkIds();
+        $zeros = $this->zeroCategoryArtworkIds();
+        $eligible = $this->eligibleArtworkIds($force);
+
+        $this->info('Zero-category artworks: '.$zeros->count());
+        $this->info('Single-category eligible for backfill: '.$eligible->count());
+        $this->info('Multi-category conflicts (not auto-resolved): '.$conflicts->count());
+
+        if ($conflicts->isNotEmpty()) {
+            $this->warn('Multi-category artwork IDs (first 50): '.$conflicts->take(50)->implode(', '));
+        }
+
+        if (! $apply) {
+            $this->comment('Dry run only. Re-run with --apply to write primary_category_id for single-category artworks.');
+
+            return self::SUCCESS;
+        }
+
+        $updated = 0;
+        foreach ($eligible->chunk(500) as $chunk) {
+            $rows = DB::table('artwork_category')
+                ->select('artwork_id', 'category_id')
+                ->whereIn('artwork_id', $chunk->all())
+                ->get()
+                ->groupBy('artwork_id');
+
+            foreach ($rows as $artworkId => $memberships) {
+                if ($memberships->count() !== 1) {
+                    continue;
+                }
+
+                $query = Artwork::query()->where('id', (int) $artworkId);
+                if (! $force) {
+                    $query->whereNull('primary_category_id');
+                }
+
+                $updated += $query->update([
+                    'primary_category_id' => (int) $memberships->first()->category_id,
+                ]);
+            }
+        }
+
+        $this->info("Updated {$updated} artwork(s).");
+
+        return self::SUCCESS;
+    }
+
+    private function printDistribution(): void
+    {
+        $distribution = DB::query()
+            ->fromSub(function ($query): void {
+                $query->from('artwork_category')
+                    ->select('artwork_id', DB::raw('COUNT(*) as category_count'))
+                    ->groupBy('artwork_id');
+            }, 'x')
+            ->select('category_count', DB::raw('COUNT(*) as artworks'))
+            ->groupBy('category_count')
+            ->orderBy('category_count')
+            ->get();
+
+        $this->table(['category_count', 'artworks'], $distribution->map(fn ($row): array => [
+            (int) $row->category_count,
+            (int) $row->artworks,
+        ])->all());
+    }
+
+    /**
+     * @return Collection<int, int>
+     */
+    private function eligibleArtworkIds(bool $force)
+    {
+        $query = DB::table('artwork_category')
+            ->select('artwork_id')
+            ->groupBy('artwork_id')
+            ->havingRaw('COUNT(*) = 1');
+
+        if (! $force) {
+            $query->whereIn('artwork_id', Artwork::query()->whereNull('primary_category_id')->select('id'));
+        }
+
+        return $query->pluck('artwork_id')->map(fn ($id): int => (int) $id);
+    }
+
+    /**
+     * @return Collection<int, int>
+     */
+    private function conflictArtworkIds()
+    {
+        return DB::table('artwork_category')
+            ->select('artwork_id')
+            ->groupBy('artwork_id')
+            ->havingRaw('COUNT(*) > 1')
+            ->orderByRaw('COUNT(*) DESC')
+            ->pluck('artwork_id')
+            ->map(fn ($id): int => (int) $id);
+    }
+
+    /**
+     * @return Collection<int, int>
+     */
+    private function zeroCategoryArtworkIds()
+    {
+        return Artwork::query()
+            ->whereDoesntHave('categories')
+            ->pluck('id')
+            ->map(fn ($id): int => (int) $id);
+    }
+}
diff --git a/app/Http/Controllers/Api/ArtworkController.php b/app/Http/Controllers/Api/ArtworkController.php
index 37b8a461..be85f312 100644
--- a/app/Http/Controllers/Api/ArtworkController.php
+++ b/app/Http/Controllers/Api/ArtworkController.php
@@ -1,13 +1,14 @@
 <?php
+
 namespace App\Http\Controllers\Api;
 
 use App\Http\Controllers\Controller;
 use App\Http\Requests\Artworks\ArtworkCreateRequest;
 use App\Http\Resources\ArtworkListResource;
 use App\Http\Resources\ArtworkResource;
-use App\Services\ArtworkService;
-use App\Services\Artworks\ArtworkDraftService;
 use App\Models\Category;
+use App\Services\Artworks\ArtworkDraftService;
+use App\Services\ArtworkService;
 use Illuminate\Http\Request;
 use Symfony\Component\HttpFoundation\Response;
 
@@ -29,9 +30,12 @@ class ArtworkController extends Controller
         $user = $request->user();
         $data = $request->validated();
 
-        $categoryId = isset($data['category']) && ctype_digit((string) $data['category'])
-            ? (int) $data['category']
-            : null;
+        $categoryId = isset($data['primary_category_id']) && ctype_digit((string) $data['primary_category_id'])
+            ? (int) $data['primary_category_id']
+            : (isset($data['category']) && ctype_digit((string) $data['category'])
+                ? (int) $data['category']
+                : null);
+        $secondaryCategoryIds = array_values(array_map('intval', $data['secondary_category_ids'] ?? []));
 
         $result = $drafts->createDraft(
             $user,
@@ -40,6 +44,7 @@ class ArtworkController extends Controller
             $categoryId,
             (bool) ($data['is_mature'] ?? false),
             $data['group'] ?? null,
+            $secondaryCategoryIds,
         );
 
         return response()->json([
diff --git a/app/Http/Controllers/Api/DiscoveryNegativeSignalController.php b/app/Http/Controllers/Api/DiscoveryNegativeSignalController.php
index 3dd5cc2c..fe2a8350 100644
--- a/app/Http/Controllers/Api/DiscoveryNegativeSignalController.php
+++ b/app/Http/Controllers/Api/DiscoveryNegativeSignalController.php
@@ -174,7 +174,7 @@ final class DiscoveryNegativeSignalController extends Controller
     }
 
     /**
-     * @param array<string, mixed> $meta
+     * @param  array<string, mixed>  $meta
      */
     private function recordFeedbackEvent(int $userId, int $artworkId, string $eventType, ?string $algoVersion = null, array $meta = []): void
     {
@@ -182,10 +182,9 @@ final class DiscoveryNegativeSignalController extends Controller
             return;
         }
 
-        $categoryId = DB::table('artwork_category')
-            ->where('artwork_id', $artworkId)
-            ->orderBy('category_id')
-            ->value('category_id');
+        $categoryId = DB::table('artworks')
+            ->where('id', $artworkId)
+            ->value('primary_category_id');
 
         DB::table('user_discovery_events')->insert([
             'event_id' => (string) Str::uuid(),
diff --git a/app/Http/Controllers/Api/UploadController.php b/app/Http/Controllers/Api/UploadController.php
index bdbed06e..c24c1121 100644
--- a/app/Http/Controllers/Api/UploadController.php
+++ b/app/Http/Controllers/Api/UploadController.php
@@ -5,52 +5,58 @@ declare(strict_types=1);
 namespace App\Http\Controllers\Api;
 
 use App\Http\Controllers\Controller;
+use App\Http\Requests\Uploads\UploadCancelRequest;
+use App\Http\Requests\Uploads\UploadChunkRequest;
 use App\Http\Requests\Uploads\UploadFinishRequest;
 use App\Http\Requests\Uploads\UploadInitRequest;
-use App\Http\Requests\Uploads\UploadChunkRequest;
-use App\Http\Requests\Uploads\UploadCancelRequest;
 use App\Http\Requests\Uploads\UploadStatusRequest;
-use App\Jobs\GenerateDerivativesJob;
 use App\Jobs\AnalyzeArtworkAiAssistJob;
-use App\Jobs\IndexArtworkJob;
 use App\Jobs\AutoTagArtworkJob;
 use App\Jobs\DetectArtworkMaturityJob;
 use App\Jobs\GenerateArtworkEmbeddingJob;
+use App\Jobs\GenerateDerivativesJob;
+use App\Jobs\IndexArtworkJob;
+use App\Models\ActivityEvent;
+use App\Models\Artwork;
+use App\Models\Group;
+use App\Models\Tag;
+use App\Notifications\NewArtworkReviewNotification;
 use App\Repositories\Uploads\UploadSessionRepository;
-use App\Services\Uploads\UploadChunkService;
-use App\Services\Uploads\UploadCancelService;
-use App\Services\Uploads\UploadAuditService;
-use App\Services\Uploads\UploadPipelineService;
-use App\Services\Uploads\UploadQuotaService;
-use App\Services\Uploads\UploadQueueService;
-use App\Services\Uploads\UploadSessionStatus;
-use App\Services\Uploads\UploadStatusService;
-use Illuminate\Support\Facades\DB;
-use Illuminate\Support\Facades\Log;
-use Symfony\Component\HttpFoundation\Response;
-use Throwable;
-use Illuminate\Http\Request;
-use Illuminate\Support\Facades\Validator;
-use App\Services\Upload\Contracts\UploadDraftServiceInterface;
-use Carbon\Carbon;
-use App\Uploads\Jobs\VirusScanJob;
-use App\Uploads\Services\PublishService;
 use App\Services\Activity\UserActivityService;
 use App\Services\ArtworkAttributionService;
+use App\Services\Artworks\ArtworkCategoryService;
+use App\Services\GroupArtworkReviewService;
 use App\Services\Maturity\ArtworkMaturityService;
+use App\Services\Moderation\ArtworkUploadPolicy;
+use App\Services\Upload\Contracts\UploadDraftServiceInterface;
+use App\Services\Uploads\UploadAuditService;
+use App\Services\Uploads\UploadCancelService;
+use App\Services\Uploads\UploadChunkService;
+use App\Services\Uploads\UploadPipelineService;
+use App\Services\Uploads\UploadQueueService;
+use App\Services\Uploads\UploadQuotaService;
+use App\Services\Uploads\UploadSessionStatus;
+use App\Services\Uploads\UploadStatusService;
+use App\Services\Worlds\WorldSubmissionService;
+use App\Support\ArtworkDescriptionContentValidator;
+use App\Uploads\Exceptions\DraftQuotaException;
 use App\Uploads\Exceptions\UploadNotFoundException;
 use App\Uploads\Exceptions\UploadOwnershipException;
 use App\Uploads\Exceptions\UploadPublishValidationException;
+use App\Uploads\Jobs\VirusScanJob;
 use App\Uploads\Services\ArchiveInspectorService;
 use App\Uploads\Services\DraftQuotaService;
-use App\Uploads\Exceptions\DraftQuotaException;
-use App\Models\Artwork;
-use App\Models\Group;
-use App\Services\GroupArtworkReviewService;
-use App\Support\ArtworkDescriptionContentValidator;
-use App\Services\Worlds\WorldSubmissionService;
-use Illuminate\Validation\ValidationException;
+use App\Uploads\Services\PublishService;
+use Carbon\Carbon;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+use Illuminate\Support\Facades\Notification;
+use Illuminate\Support\Facades\Validator;
 use Illuminate\Support\Str;
+use Illuminate\Validation\ValidationException;
+use Symfony\Component\HttpFoundation\Response;
+use Throwable;
 
 final class UploadController extends Controller
 {
@@ -59,8 +65,7 @@ final class UploadController extends Controller
         UploadPipelineService $pipeline,
         UploadQuotaService $quota,
         UploadAuditService $audit
-    )
-    {
+    ) {
         $user = $request->user();
 
         try {
@@ -251,6 +256,7 @@ final class UploadController extends Controller
                 if ((bool) config('vision.upload.ai_assist.enabled', false)) {
                     AnalyzeArtworkAiAssistJob::dispatch($artworkId)->afterCommit();
                 }
+
                 return UploadSessionStatus::PROCESSED;
             });
 
@@ -305,7 +311,7 @@ final class UploadController extends Controller
                     'realpath' => $chunkFile->getRealPath(),
                 ]);
             }
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             logger()->warning('Chunk upload debug logging failed', ['error' => $e->getMessage()]);
         }
 
@@ -333,7 +339,7 @@ final class UploadController extends Controller
                 'total_bytes' => $result->totalBytes,
                 'progress' => $result->progress,
             ], Response::HTTP_OK);
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             logger()->warning('Upload chunk failed', [
                 'session_id' => (string) $request->input('session_id'),
                 'error' => $e->getMessage(),
@@ -383,7 +389,7 @@ final class UploadController extends Controller
                 'session_id' => $result['session_id'],
                 'status' => $result['status'],
             ], Response::HTTP_OK);
-        } catch (\Throwable $e) {
+        } catch (Throwable $e) {
             logger()->warning('Upload cancel failed', [
                 'session_id' => (string) $request->input('session_id'),
                 'error' => $e->getMessage(),
@@ -512,6 +518,7 @@ final class UploadController extends Controller
             return response()->json($response, Response::HTTP_OK);
         } catch (Throwable $e) {
             logger()->error('Upload preload failed', ['error' => $e->getMessage()]);
+
             return response()->json(['message' => 'Preload failed.'], Response::HTTP_INTERNAL_SERVER_ERROR);
         }
     }
@@ -538,6 +545,8 @@ final class UploadController extends Controller
         $validated = $request->validate([
             'title' => ['nullable', 'string', 'max:255'],
             'category_id' => ['nullable', 'exists:categories,id'],
+            'secondary_category_ids' => ['nullable', 'array', 'max:'.(int) config('categories.max_secondary_categories', 5)],
+            'secondary_category_ids.*' => ['integer', 'exists:categories,id'],
             'description' => ['nullable', 'string'],
             'tags' => ['nullable', 'array'],
             'license' => ['nullable', 'string'],
@@ -547,7 +556,7 @@ final class UploadController extends Controller
         $this->ensureValidArtworkDescription($validated);
 
         $updates = [];
-        foreach (['title', 'category_id', 'description', 'tags', 'license', 'nsfw'] as $field) {
+        foreach (['title', 'category_id', 'secondary_category_ids', 'description', 'tags', 'license', 'nsfw'] as $field) {
             if (array_key_exists($field, $validated)) {
                 $updates[$field] = $validated[$field];
             }
@@ -557,7 +566,7 @@ final class UploadController extends Controller
         foreach ($updates as $field => $value) {
             $current = $upload->{$field} ?? null;
 
-            if ($field === 'tags') {
+            if ($field === 'tags' || $field === 'secondary_category_ids') {
                 $current = $current ? json_decode((string) $current, true) : null;
             }
 
@@ -575,6 +584,10 @@ final class UploadController extends Controller
             $dirty['tags'] = json_encode($dirty['tags']);
         }
 
+        if (array_key_exists('secondary_category_ids', $dirty)) {
+            $dirty['secondary_category_ids'] = json_encode($dirty['secondary_category_ids']);
+        }
+
         if (! empty($dirty)) {
             $dirty['updated_at'] = now();
             DB::table('uploads')->where('id', $id)->update($dirty);
@@ -616,23 +629,26 @@ final class UploadController extends Controller
         ], Response::HTTP_OK);
     }
 
-    public function publish(string $id, Request $request, PublishService $publishService, ArtworkAttributionService $attribution, ArtworkMaturityService $maturity, WorldSubmissionService $submissions)
+    public function publish(string $id, Request $request, PublishService $publishService, ArtworkAttributionService $attribution, ArtworkMaturityService $maturity, WorldSubmissionService $submissions, ArtworkUploadPolicy $uploadPolicy)
     {
         $user = $request->user();
 
         $validated = $request->validate([
-            'title'       => ['nullable', 'string', 'max:150'],
+            'title' => ['nullable', 'string', 'max:150'],
             'description' => ['nullable', 'string'],
-            'category'    => ['nullable', 'integer', 'exists:categories,id'],
-            'tags'        => ['nullable', 'array', 'max:' . (int) config('tags.max_user_tags', 30)],
-            'tags.*'      => ['string', 'max:64'],
-            'is_mature'   => ['nullable', 'boolean'],
-            'nsfw'        => ['nullable', 'boolean'],
+            'category' => ['nullable', 'integer', 'exists:categories,id'],
+            'primary_category_id' => ['nullable', 'integer', 'exists:categories,id'],
+            'secondary_category_ids' => ['nullable', 'array', 'max:'.(int) config('categories.max_secondary_categories', 5)],
+            'secondary_category_ids.*' => ['integer', 'exists:categories,id'],
+            'tags' => ['nullable', 'array', 'max:'.(int) config('tags.max_user_tags', 30)],
+            'tags.*' => ['string', 'max:64'],
+            'is_mature' => ['nullable', 'boolean'],
+            'nsfw' => ['nullable', 'boolean'],
             // Scheduled-publishing fields
-            'mode'        => ['nullable', 'string', 'in:now,schedule'],
-            'publish_at'  => ['nullable', 'string', 'date'],
-            'timezone'    => ['nullable', 'string', 'max:64'],
-            'visibility'  => ['nullable', 'string', 'in:public,unlisted,private'],
+            'mode' => ['nullable', 'string', 'in:now,schedule'],
+            'publish_at' => ['nullable', 'string', 'date'],
+            'timezone' => ['nullable', 'string', 'max:64'],
+            'visibility' => ['nullable', 'string', 'in:public,unlisted,private'],
             'group' => ['nullable', 'string', 'max:90'],
             'primary_author_user_id' => ['nullable', 'integer', 'min:1'],
             'contributor_user_ids' => ['nullable', 'array', 'max:20'],
@@ -649,21 +665,21 @@ final class UploadController extends Controller
 
         $this->ensureValidArtworkDescription($validated);
 
-        $mode       = $validated['mode'] ?? 'now';
+        $mode = $validated['mode'] ?? 'now';
         $visibility = $validated['visibility'] ?? 'public';
 
         // Resolve the UTC publish_at datetime for schedule mode
         $publishAt = null;
         if ($mode === 'schedule' && ! empty($validated['publish_at'])) {
             try {
-                $publishAt = \Carbon\Carbon::parse($validated['publish_at'])->utc();
+                $publishAt = Carbon::parse($validated['publish_at'])->utc();
                 // Must be at least 1 minute in the future (server-side guard)
                 if ($publishAt->lte(now()->addMinute())) {
                     return response()->json([
                         'message' => 'Scheduled publish time must be at least 1 minute in the future.',
                     ], Response::HTTP_UNPROCESSABLE_ENTITY);
                 }
-            } catch (\Throwable) {
+            } catch (Throwable) {
                 return response()->json(['message' => 'Invalid publish_at datetime.'], Response::HTTP_UNPROCESSABLE_ENTITY);
             }
         }
@@ -696,22 +712,25 @@ final class UploadController extends Controller
             if (array_key_exists('is_mature', $validated) || array_key_exists('nsfw', $validated)) {
                 $artwork->is_mature = (bool) ($validated['is_mature'] ?? $validated['nsfw'] ?? false);
             }
-            $artwork->slug             = Str::limit($slugBase, 160, '');
+            $artwork->slug = Str::limit($slugBase, 160, '');
             $artwork->artwork_timezone = $validated['timezone'] ?? null;
             $artwork->uploaded_by_user_id = $artwork->uploaded_by_user_id ?: (int) $user->id;
             $artwork->primary_author_user_id = $artwork->primary_author_user_id ?: (int) $user->id;
 
-            // Sync category if provided
-            $categoryId = isset($validated['category']) ? (int) $validated['category'] : null;
-            if ($categoryId && \App\Models\Category::where('id', $categoryId)->exists()) {
-                $artwork->categories()->sync([$categoryId]);
+            $categoryId = isset($validated['primary_category_id'])
+                ? (int) $validated['primary_category_id']
+                : (isset($validated['category']) ? (int) $validated['category'] : null);
+            $secondaryCategoryIds = array_values(array_map('intval', $validated['secondary_category_ids'] ?? []));
+            if ($categoryId) {
+                app(ArtworkCategoryService::class)
+                    ->sync($artwork, $categoryId, $secondaryCategoryIds, 'user', false);
             }
 
             // Sync tags if provided
-            if (!empty($validated['tags']) && is_array($validated['tags'])) {
+            if (! empty($validated['tags']) && is_array($validated['tags'])) {
                 $tagIds = [];
                 foreach ($validated['tags'] as $tagSlug) {
-                    $tag = \App\Models\Tag::firstOrCreate(
+                    $tag = Tag::firstOrCreate(
                         ['slug' => Str::slug($tagSlug)],
                         ['name' => $tagSlug, 'is_active' => true, 'usage_count' => 0]
                     );
@@ -727,56 +746,95 @@ final class UploadController extends Controller
 
             if ($mode === 'schedule' && $publishAt) {
                 // Scheduled: store publish_at but don't make public yet
-                $artwork->visibility     = $visibility;
-                $artwork->is_public      = false;
-                $artwork->is_approved    = true;
-                $artwork->publish_at     = $publishAt;
+                $artwork->visibility = $visibility;
+                $artwork->is_public = false;
+                $artwork->is_approved = true;
+                $artwork->publish_at = $publishAt;
                 $artwork->artwork_status = 'scheduled';
-                $artwork->published_at   = null;
+                $artwork->published_at = null;
                 $artwork->save();
 
                 IndexArtworkJob::dispatch((int) $artwork->id);
 
                 return response()->json([
-                    'success'      => true,
-                    'artwork_id'   => (int) $artwork->id,
-                    'status'       => 'scheduled',
-                    'slug'         => (string) $artwork->slug,
-                    'publish_at'   => $publishAt->toISOString(),
+                    'success' => true,
+                    'artwork_id' => (int) $artwork->id,
+                    'status' => 'scheduled',
+                    'slug' => (string) $artwork->slug,
+                    'publish_at' => $publishAt->toISOString(),
                     'published_at' => null,
                 ], Response::HTTP_OK);
             }
 
-            // Publish immediately
-            $artwork->visibility     = $visibility;
-            $artwork->is_public      = ($visibility !== 'private');
-            $artwork->is_approved    = true;
-            $artwork->published_at   = now();
+            // New and suspicious accounts are quarantined. Never let the client
+            // decide that an artwork is approved.
+            $policy = $uploadPolicy->assess($user, $artwork);
+            if ($policy['requires_review']) {
+                $artwork->visibility = $visibility;
+                $artwork->is_public = false;
+                $artwork->is_approved = false;
+                $artwork->approval_source = null;
+                $artwork->artwork_status = 'review';
+                $artwork->published_at = null;
+                $artwork->publish_at = null;
+                $artwork->moderated_at = null;
+                $artwork->moderated_by = null;
+                $artwork->moderation_note = implode(', ', $policy['reasons']);
+                $artwork->save();
+
+                $notifyEmail = trim((string) config('uploads.moderation.notify_email', ''));
+                if ($notifyEmail !== '') {
+                    try {
+                        Notification::route('mail', $notifyEmail)->notify(
+                            new NewArtworkReviewNotification($artwork, $user, $policy['reasons'])
+                        );
+                    } catch (Throwable) {
+                        // Email failure must not expose the artwork.
+                    }
+                }
+
+                return response()->json([
+                    'success' => true,
+                    'artwork_id' => (int) $artwork->id,
+                    'status' => 'submitted_for_review',
+                    'message' => 'Upload received and queued for moderation.',
+                    'review_reasons' => $policy['reasons'],
+                ], Response::HTTP_OK);
+            }
+
+            // Publish immediately for trusted users only.
+            $artwork->visibility = $visibility;
+            $artwork->is_public = ($visibility !== 'private');
+            $artwork->is_approved = true;
+            $artwork->approval_source = 'trusted_auto';
+            $artwork->published_at = now();
             $artwork->artwork_status = 'published';
-            $artwork->publish_at     = null;
+            $artwork->publish_at = null;
             $artwork->save();
 
             IndexArtworkJob::dispatch((int) $artwork->id);
 
             // Record upload activity event
             try {
-                \App\Models\ActivityEvent::record(
-                    actorId:    (int) $user->id,
-                    type:       \App\Models\ActivityEvent::TYPE_UPLOAD,
-                    targetType: \App\Models\ActivityEvent::TARGET_ARTWORK,
-                    targetId:   (int) $artwork->id,
+                ActivityEvent::record(
+                    actorId: (int) $user->id,
+                    type: ActivityEvent::TYPE_UPLOAD,
+                    targetType: ActivityEvent::TARGET_ARTWORK,
+                    targetId: (int) $artwork->id,
                 );
-            } catch (\Throwable) {}
+            } catch (Throwable) {
+            }
 
             try {
                 app(UserActivityService::class)->logUpload((int) $user->id, (int) $artwork->id);
-            } catch (\Throwable) {}
+            } catch (Throwable) {
+            }
 
             return response()->json([
-                'success'      => true,
-                'artwork_id'   => (int) $artwork->id,
-                'status'       => 'published',
-                'slug'         => (string) $artwork->slug,
+                'success' => true,
+                'artwork_id' => (int) $artwork->id,
+                'status' => 'published',
+                'slug' => (string) $artwork->slug,
                 'published_at' => optional($artwork->published_at)->toISOString(),
             ], Response::HTTP_OK);
         }
@@ -785,11 +843,11 @@ final class UploadController extends Controller
             $upload = $publishService->publish($id, $user);
 
             return response()->json([
-                'success'      => true,
-                'upload_id'    => (string) $upload->id,
-                'status'       => (string) $upload->status,
+                'success' => true,
+                'upload_id' => (string) $upload->id,
+                'status' => (string) $upload->status,
                 'published_at' => optional($upload->published_at)->toISOString(),
-                'final_path'   => (string) ($upload->final_path ?? ''),
+                'final_path' => (string) ($upload->final_path ?? ''),
             ], Response::HTTP_OK);
         } catch (UploadOwnershipException $e) {
             return response()->json(['message' => $e->getMessage()], Response::HTTP_FORBIDDEN);
@@ -808,7 +866,10 @@ final class UploadController extends Controller
             'title' => ['nullable', 'string', 'max:150'],
             'description' => ['nullable', 'string'],
             'category' => ['nullable', 'integer', 'exists:categories,id'],
-            'tags' => ['nullable', 'array', 'max:' . (int) config('tags.max_user_tags', 30)],
+            'primary_category_id' => ['nullable', 'integer', 'exists:categories,id'],
+            'secondary_category_ids' => ['nullable', 'array', 'max:'.(int) config('categories.max_secondary_categories', 5)],
+            'secondary_category_ids.*' => ['integer', 'exists:categories,id'],
+            'tags' => ['nullable', 'array', 'max:'.(int) config('tags.max_user_tags', 30)],
             'tags.*' => ['string', 'max:64'],
             'is_mature' => ['nullable', 'boolean'],
             'nsfw' => ['nullable', 'boolean'],
diff --git a/app/Http/Controllers/Dashboard/ManageController.php b/app/Http/Controllers/Dashboard/ManageController.php
index ef58bfd0..b371aa3d 100644
--- a/app/Http/Controllers/Dashboard/ManageController.php
+++ b/app/Http/Controllers/Dashboard/ManageController.php
@@ -3,12 +3,14 @@
 namespace App\Http\Controllers\Dashboard;
 
 use App\Http\Controllers\Controller;
+use App\Http\Requests\Manage\ManageArtworkDestroyRequest;
 use App\Http\Requests\Manage\ManageArtworkEditRequest;
 use App\Http\Requests\Manage\ManageArtworkUpdateRequest;
-use App\Http\Requests\Manage\ManageArtworkDestroyRequest;
+use App\Models\Artwork;
+use App\Services\Artworks\ArtworkCategoryService;
 use Illuminate\Http\Request;
-use Illuminate\Support\Facades\Storage;
 use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Storage;
 
 class ManageController extends Controller
 {
@@ -17,14 +19,12 @@ class ManageController extends Controller
         $userId = $request->user()->id;
         $perPage = 50;
 
-        $categorySub = DB::table('artwork_category as ac')
-            ->join('categories as c', 'ac.category_id', '=', 'c.id')
-            ->select('ac.artwork_id', DB::raw('MIN(c.name) as category_name'))
-            ->groupBy('ac.artwork_id');
+        $categorySub = DB::table('categories as c')
+            ->select('c.id as category_id', 'c.name as category_name');
 
         $query = DB::table('artworks as a')
             ->leftJoinSub($categorySub, 'cat', function ($join) {
-                $join->on('a.id', '=', 'cat.artwork_id');
+                $join->on('a.primary_category_id', '=', 'cat.category_id');
             })
             ->leftJoin('artwork_stats as s', 'a.id', '=', 's.artwork_id')
             ->where('a.user_id', $userId)
@@ -52,8 +52,8 @@ class ManageController extends Controller
     {
         $artwork = $request->artwork();
 
-        $selectedCategory = DB::table('artwork_category')->where('artwork_id', (int)$id)->value('category_id');
-        $artwork->category = $selectedCategory;
+        $selectedCategory = (int) ($artwork->primary_category_id ?: DB::table('artwork_category')->where('artwork_id', (int) $id)->value('category_id'));
+        $artwork->category = $selectedCategory ?: null;
 
         $categories = DB::table('categories')
             ->where('content_type_id', 0)
@@ -64,7 +64,7 @@ class ManageController extends Controller
         return view('manage.edit', [
             'artwork' => $artwork,
             'categories' => $categories,
-            'page_title' => 'Edit Artwork: ' . ($artwork->title ?? ''),
+            'page_title' => 'Edit Artwork: '.($artwork->title ?? ''),
         ]);
     }
 
@@ -91,14 +91,14 @@ class ManageController extends Controller
             $update['fname'] = basename($attPath);
         }
 
-        DB::table('artworks')->where('id', (int)$id)->update($update);
+        DB::table('artworks')->where('id', (int) $id)->update($update);
 
         if (isset($data['section'])) {
-            DB::table('artwork_category')->where('artwork_id', (int)$id)->delete();
-            DB::table('artwork_category')->insert([
-                'artwork_id' => (int)$id,
-                'category_id' => (int)$data['section'],
-            ]);
+            $model = Artwork::query()->find((int) $id);
+            if ($model) {
+                app(ArtworkCategoryService::class)
+                    ->sync($model, (int) $data['section'], [], 'moderator');
+            }
         }
 
         return redirect()->route('manage')->with('status', 'Artwork was successfully updated.');
@@ -108,14 +108,14 @@ class ManageController extends Controller
     {
         $artwork = $request->artwork();
 
-        if (!empty($artwork->fname)) {
-            Storage::delete('public/uploads/attachments/' . $artwork->fname);
+        if (! empty($artwork->fname)) {
+            Storage::delete('public/uploads/attachments/'.$artwork->fname);
         }
-        if (!empty($artwork->picture)) {
-            Storage::delete('public/uploads/artworks/' . $artwork->picture);
+        if (! empty($artwork->picture)) {
+            Storage::delete('public/uploads/artworks/'.$artwork->picture);
         }
 
-        DB::table('artworks')->where('id', (int)$id)->delete();
+        DB::table('artworks')->where('id', (int) $id)->delete();
 
         return redirect()->route('manage')->with('status', 'Artwork deleted.');
     }
diff --git a/app/Http/Controllers/Legacy/TodayDownloadsController.php b/app/Http/Controllers/Legacy/TodayDownloadsController.php
index 1743fb85..cdb8deef 100644
--- a/app/Http/Controllers/Legacy/TodayDownloadsController.php
+++ b/app/Http/Controllers/Legacy/TodayDownloadsController.php
@@ -3,11 +3,12 @@
 namespace App\Http\Controllers\Legacy;
 
 use App\Http\Controllers\Controller;
-use Illuminate\Http\Request;
+use App\Models\Artwork;
 use App\Models\ArtworkDownload;
-use Illuminate\Support\Facades\Storage;
-use Illuminate\Support\Str;
+use App\Services\ThumbnailPresenter;
 use Carbon\Carbon;
+use Illuminate\Http\Request;
+use Illuminate\Support\Str;
 
 class TodayDownloadsController extends Controller
 {
@@ -35,16 +36,16 @@ class TodayDownloadsController extends Controller
             $art = $row->artwork ?? null;
             // If Eloquent didn't eager load artwork (group queries sometimes don't), fetch it
             if (! $art && isset($row->artwork_id)) {
-                $art = \App\Models\Artwork::find($row->artwork_id);
+                $art = Artwork::find($row->artwork_id);
             }
 
             $name = $art->title ?? null;
             $picture = $art->file_name ?? null;
             $ext = pathinfo($picture ?? '', PATHINFO_EXTENSION) ?: 'jpg';
             $encoded = null; // legacy encoding unavailable; leave null
-            $present = $art ? \App\Services\ThumbnailPresenter::present($art, 'md') : null;
+            $present = $art ? ThumbnailPresenter::present($art, 'md') : null;
             $thumb = $present ? $present['url'] : 'https://files.skinbase.org/default/missing_md.webp';
-            $categoryId = $art->categories->first()->id ?? null;
+            $categoryId = $art->resolvedPrimaryCategory()?->id;
 
             return (object) [
                 'id' => $art->id ?? null,
diff --git a/app/Http/Controllers/Studio/StudioArtworksApiController.php b/app/Http/Controllers/Studio/StudioArtworksApiController.php
index b4bab332..e77b1821 100644
--- a/app/Http/Controllers/Studio/StudioArtworksApiController.php
+++ b/app/Http/Controllers/Studio/StudioArtworksApiController.php
@@ -6,27 +6,34 @@ namespace App\Http\Controllers\Studio;
 
 use App\Http\Controllers\Controller;
 use App\Models\Artwork;
+use App\Models\ArtworkVersion;
 use App\Models\Category;
 use App\Models\ContentType;
-use App\Models\ArtworkVersion;
-use App\Services\ArtworkEvolutionService;
-use App\Services\Cdn\ArtworkCdnPurgeService;
-use App\Services\ArtworkSearchIndexer;
+use App\Notifications\NewArtworkReviewNotification;
+use App\Repositories\Uploads\ArtworkFileRepository;
 use App\Services\ArtworkAttributionService;
+use App\Services\ArtworkEvolutionService;
+use App\Services\Artworks\ArtworkCategoryService;
 use App\Services\Artworks\ArtworkPublicationService;
-use App\Services\TagService;
+use App\Services\ArtworkSearchIndexer;
 use App\Services\ArtworkVersioningService;
+use App\Services\Cdn\ArtworkCdnPurgeService;
+use App\Services\Moderation\ArtworkUploadPolicy;
 use App\Services\Studio\StudioArtworkQueryService;
 use App\Services\Studio\StudioBulkActionService;
-use App\Support\ArtworkDescriptionContentValidator;
 use App\Services\Tags\TagDiscoveryService;
+use App\Services\TagService;
+use App\Services\Uploads\UploadDerivativesService;
+use App\Services\Uploads\UploadStorageService;
 use App\Services\Worlds\WorldSubmissionService;
+use App\Support\ArtworkDescriptionContentValidator;
 use Carbon\Carbon;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use Illuminate\Http\UploadedFile;
-use Illuminate\Support\Facades\Log;
 use Illuminate\Support\Facades\File;
+use Illuminate\Support\Facades\Log;
+use Illuminate\Support\Facades\Notification;
 use Illuminate\Support\Facades\Validator;
 use Illuminate\Validation\ValidationException;
 use Symfony\Component\HttpKernel\Exception\TooManyRequestsHttpException;
@@ -45,6 +52,7 @@ final class StudioArtworksApiController extends Controller
         private readonly TagService $tagService,
         private readonly ArtworkCdnPurgeService $cdnPurge,
         private readonly ArtworkPublicationService $artworkPublication,
+        private readonly ArtworkCategoryService $artworkCategories,
     ) {}
 
     /**
@@ -74,9 +82,9 @@ final class StudioArtworksApiController extends Controller
             'data' => $items,
             'meta' => [
                 'current_page' => $paginator->currentPage(),
-                'last_page'    => $paginator->lastPage(),
-                'per_page'     => $paginator->perPage(),
-                'total'        => $paginator->total(),
+                'last_page' => $paginator->lastPage(),
+                'per_page' => $paginator->perPage(),
+                'total' => $paginator->total(),
             ],
         ]);
     }
@@ -88,14 +96,14 @@ final class StudioArtworksApiController extends Controller
     public function bulk(Request $request): JsonResponse
     {
         $validator = Validator::make($request->all(), [
-            'action'      => 'required|string|in:publish,unpublish,archive,unarchive,delete,change_category,add_tags,remove_tags',
+            'action' => 'required|string|in:publish,unpublish,archive,unarchive,delete,change_category,add_tags,remove_tags',
             'artwork_ids' => 'required|array|min:1|max:200',
             'artwork_ids.*' => 'integer',
-            'params'      => 'sometimes|array',
+            'params' => 'sometimes|array',
             'params.category_id' => 'sometimes|integer|exists:categories,id',
-            'params.tag_ids'     => 'sometimes|array',
-            'params.tag_ids.*'   => 'integer|exists:tags,id',
-            'confirm'     => 'required_if:action,delete|string',
+            'params.tag_ids' => 'sometimes|array',
+            'params.tag_ids.*' => 'integer|exists:tags,id',
+            'confirm' => 'required_if:action,delete|string',
         ]);
 
         if ($validator->fails()) {
@@ -127,23 +135,26 @@ final class StudioArtworksApiController extends Controller
      * PUT /api/studio/artworks/{id}
      * Update artwork details (title, description, visibility).
      */
-    public function update(Request $request, int $id, ArtworkAttributionService $attribution, WorldSubmissionService $submissions): JsonResponse
+    public function update(Request $request, int $id, ArtworkAttributionService $attribution, WorldSubmissionService $submissions, ArtworkUploadPolicy $uploadPolicy): JsonResponse
     {
         $artwork = $request->user()->artworks()->findOrFail($id);
         $evolution = app(ArtworkEvolutionService::class);
 
         $validated = $request->validate([
-            'title'       => 'sometimes|string|max:255',
+            'title' => 'sometimes|string|max:255',
             'description' => 'sometimes|nullable|string|max:5000',
-            'is_public'   => 'sometimes|boolean',
-            'visibility'  => 'sometimes|string|in:public,unlisted,private',
-            'mode'        => 'sometimes|string|in:now,schedule',
-            'publish_at'  => 'sometimes|nullable|string|date',
-            'timezone'    => 'sometimes|nullable|string|max:64',
+            'is_public' => 'sometimes|boolean',
+            'visibility' => 'sometimes|string|in:public,unlisted,private',
+            'mode' => 'sometimes|string|in:now,schedule',
+            'publish_at' => 'sometimes|nullable|string|date',
+            'timezone' => 'sometimes|nullable|string|max:64',
             'category_id' => 'sometimes|nullable|integer|exists:categories,id',
+            'primary_category_id' => 'sometimes|nullable|integer|exists:categories,id',
+            'secondary_category_ids' => 'sometimes|array|max:'.(int) config('categories.max_secondary_categories', 5),
+            'secondary_category_ids.*' => 'integer|exists:categories,id',
             'content_type_id' => 'sometimes|nullable|integer|exists:content_types,id',
-            'tags'        => 'sometimes|array|max:' . (int) config('tags.max_user_tags', 30),
-            'tags.*'      => 'string|max:64',
+            'tags' => 'sometimes|array|max:'.(int) config('tags.max_user_tags', 30),
+            'tags.*' => 'string|max:64',
             'title_source' => 'sometimes|nullable|string|in:manual,ai_generated,ai_applied,mixed',
             'description_source' => 'sometimes|nullable|string|in:manual,ai_generated,ai_applied,mixed',
             'tags_source' => 'sometimes|nullable|string|in:manual,ai_generated,ai_applied,mixed',
@@ -210,14 +221,18 @@ final class StudioArtworksApiController extends Controller
 
         // Extract tags and category before updating core fields
         $tags = $validated['tags'] ?? null;
-        $categoryId = $validated['category_id'] ?? null;
+        $categoryId = $validated['primary_category_id'] ?? $validated['category_id'] ?? null;
+        $secondaryCategoryIds = array_key_exists('secondary_category_ids', $validated)
+            ? array_values(array_map('intval', $validated['secondary_category_ids'] ?? []))
+            : [];
+        $hasSecondaryCategoryUpdate = array_key_exists('secondary_category_ids', $validated);
         $contentTypeId = $validated['content_type_id'] ?? null;
         $evolutionPayload = [
             'target_artwork_id' => $validated['evolution_target_artwork_id'] ?? null,
             'relation_type' => $validated['evolution_relation_type'] ?? null,
             'note' => $validated['evolution_note'] ?? null,
         ];
-        unset($validated['tags'], $validated['category_id'], $validated['content_type_id'], $validated['visibility'], $validated['mode'], $validated['publish_at'], $validated['timezone'], $validated['group'], $validated['primary_author_user_id'], $validated['contributor_user_ids'], $validated['contributor_credits'], $validated['world_submissions']);
+        unset($validated['tags'], $validated['category_id'], $validated['primary_category_id'], $validated['secondary_category_ids'], $validated['content_type_id'], $validated['visibility'], $validated['mode'], $validated['publish_at'], $validated['timezone'], $validated['group'], $validated['primary_author_user_id'], $validated['contributor_user_ids'], $validated['contributor_credits'], $validated['world_submissions']);
         unset($validated['evolution_target_artwork_id'], $validated['evolution_relation_type'], $validated['evolution_note']);
 
         $validated['visibility'] = $visibility;
@@ -231,9 +246,17 @@ final class StudioArtworksApiController extends Controller
             $validated['artwork_status'] = 'scheduled';
         } else {
             $validated['is_public'] = $visibility !== Artwork::VISIBILITY_PRIVATE;
-            $validated['is_approved'] = true;
+            $policy = $uploadPolicy->assess($request->user(), $artwork);
+            $validated['is_approved'] = ! $policy['requires_review'];
+            $validated['approval_source'] = $policy['requires_review'] ? null : 'trusted_auto';
             $validated['publish_at'] = null;
-            $validated['artwork_status'] = 'published';
+            $validated['artwork_status'] = $policy['requires_review'] ? 'review' : 'published';
+
+            if ($policy['requires_review']) {
+                $validated['is_public'] = false;
+                $validated['published_at'] = null;
+                $validated['moderation_note'] = implode(', ', $policy['reasons']);
+            }
 
             if (($validated['is_public'] ?? false) && ! $artwork->published_at) {
                 $validated['published_at'] = now();
@@ -249,10 +272,19 @@ final class StudioArtworksApiController extends Controller
         }
 
         $artwork->update($validated);
+        $requiresReview = ($policy['requires_review'] ?? false) === true;
 
-        // Sync category
-        if ($categoryId !== null) {
-            $artwork->categories()->sync([(int) $categoryId]);
+        if ($categoryId !== null || $hasSecondaryCategoryUpdate) {
+            try {
+                $this->artworkCategories->sync(
+                    $artwork,
+                    $categoryId !== null ? (int) $categoryId : (int) $artwork->primary_category_id,
+                    $hasSecondaryCategoryUpdate ? $secondaryCategoryIds : ($categoryId !== null ? [] : null),
+                    (string) ($validated['category_source'] ?? $artwork->category_source ?? 'manual'),
+                );
+            } catch (ValidationException $exception) {
+                return response()->json(['errors' => $exception->errors()], 422);
+            }
         }
 
         // Sync tags through the shared tag service so pivot source/usage rules stay valid.
@@ -291,24 +323,40 @@ final class StudioArtworksApiController extends Controller
         // Reindex in Meilisearch — dispatches IndexArtworkJob which writes directly, no Scout hop.
         $this->searchIndexer->update($artwork);
 
+        if ($requiresReview) {
+            $notifyEmail = trim((string) config('uploads.moderation.notify_email', ''));
+            if ($notifyEmail !== '') {
+                try {
+                    Notification::route('mail', $notifyEmail)->notify(
+                        new NewArtworkReviewNotification($artwork, $request->user(), $policy['reasons'])
+                    );
+                } catch (\Throwable) {
+                    // Keep the artwork private if notification delivery fails.
+                }
+            }
+        }
+
         // Reload relationships for response
-        $artwork->load(['categories.contentType', 'tags', 'group', 'primaryAuthor.profile', 'contributors.user.profile']);
-        $primaryCategory = $artwork->categories->first();
+        $artwork->load(['categories.contentType', 'primaryCategory.contentType', 'tags', 'group', 'primaryAuthor.profile', 'contributors.user.profile']);
+        $primaryCategory = $artwork->resolvedPrimaryCategory();
 
         return response()->json([
             'success' => true,
+            'status' => $requiresReview ? 'submitted_for_review' : 'published',
+            'message' => $requiresReview ? 'Artwork saved and queued for moderation.' : 'Artwork updated successfully.',
+            'review_reasons' => $requiresReview ? $policy['reasons'] : [],
             'artwork' => [
-                'id'              => $artwork->id,
-                'title'           => $artwork->title,
-                'description'     => $artwork->description,
-                'is_public'       => (bool) $artwork->is_public,
-                'visibility'      => $artwork->visibility ?: ((bool) $artwork->is_public ? Artwork::VISIBILITY_PUBLIC : Artwork::VISIBILITY_PRIVATE),
-                'publish_mode'    => $artwork->artwork_status === 'scheduled' ? 'schedule' : 'now',
-                'publish_at'      => $artwork->publish_at?->toIso8601String(),
-                'artwork_status'  => $artwork->artwork_status,
+                'id' => $artwork->id,
+                'title' => $artwork->title,
+                'description' => $artwork->description,
+                'is_public' => (bool) $artwork->is_public,
+                'visibility' => $artwork->visibility ?: ((bool) $artwork->is_public ? Artwork::VISIBILITY_PUBLIC : Artwork::VISIBILITY_PRIVATE),
+                'publish_mode' => $artwork->artwork_status === 'scheduled' ? 'schedule' : 'now',
+                'publish_at' => $artwork->publish_at?->toIso8601String(),
+                'artwork_status' => $artwork->artwork_status,
                 'artwork_timezone' => $artwork->artwork_timezone,
-                'slug'            => $artwork->slug,
-                'group_slug'      => $artwork->group?->slug,
+                'slug' => $artwork->slug,
+                'group_slug' => $artwork->group?->slug,
                 'primary_author_user_id' => (int) ($artwork->primary_author_user_id ?: $artwork->user_id),
                 'contributor_user_ids' => $artwork->contributors->pluck('user_id')->map(fn ($contributorId): int => (int) $contributorId)->values()->all(),
                 'contributor_credits' => $artwork->contributors->map(fn ($contributor): array => [
@@ -317,11 +365,18 @@ final class StudioArtworksApiController extends Controller
                     'is_primary' => (bool) $contributor->is_primary,
                 ])->values()->all(),
                 'content_type_id' => $primaryCategory?->contentType?->id,
-                'category_id'     => $primaryCategory?->id,
-                'tags'            => $artwork->tags->map(fn ($t) => ['id' => $t->id, 'name' => $t->name, 'slug' => $t->slug])->values()->all(),
-                'title_source'    => $artwork->title_source ?: 'manual',
+                'category_id' => $primaryCategory?->id,
+                'primary_category_id' => $primaryCategory?->id,
+                'secondary_category_ids' => $artwork->categories
+                    ->reject(fn ($category): bool => (int) $category->id === (int) ($primaryCategory?->id ?? 0))
+                    ->pluck('id')
+                    ->map(fn ($id): int => (int) $id)
+                    ->values()
+                    ->all(),
+                'tags' => $artwork->tags->map(fn ($t) => ['id' => $t->id, 'name' => $t->name, 'slug' => $t->slug])->values()->all(),
+                'title_source' => $artwork->title_source ?: 'manual',
                 'description_source' => $artwork->description_source ?: 'manual',
-                'tags_source'     => $artwork->tags_source ?: 'manual',
+                'tags_source' => $artwork->tags_source ?: 'manual',
                 'category_source' => $artwork->category_source ?: 'manual',
                 'evolution_relation' => $evolution->editorRelation($artwork, $request->user()),
             ],
@@ -423,18 +478,18 @@ final class StudioArtworksApiController extends Controller
 
         return response()->json([
             'artwork' => [
-                'id'    => $artwork->id,
+                'id' => $artwork->id,
                 'title' => $artwork->title,
-                'slug'  => $artwork->slug,
+                'slug' => $artwork->slug,
             ],
             'analytics' => [
-                'views'               => (int) ($stats?->views ?? 0),
-                'favourites'          => (int) ($stats?->favorites ?? 0),
-                'shares'              => (int) ($stats?->shares_count ?? 0),
-                'comments'            => (int) ($stats?->comments_count ?? 0),
-                'downloads'           => (int) ($stats?->downloads ?? 0),
-                'ranking_score'       => (float) ($stats?->ranking_score ?? 0),
-                'heat_score'          => (float) ($stats?->heat_score ?? 0),
+                'views' => (int) ($stats?->views ?? 0),
+                'favourites' => (int) ($stats?->favorites ?? 0),
+                'shares' => (int) ($stats?->shares_count ?? 0),
+                'comments' => (int) ($stats?->comments_count ?? 0),
+                'downloads' => (int) ($stats?->downloads ?? 0),
+                'ranking_score' => (float) ($stats?->ranking_score ?? 0),
+                'heat_score' => (float) ($stats?->heat_score ?? 0),
                 'engagement_velocity' => (float) ($stats?->engagement_velocity ?? 0),
             ],
         ]);
@@ -449,28 +504,28 @@ final class StudioArtworksApiController extends Controller
         $stats = $artwork->stats ?? null;
 
         return [
-            'id'              => $artwork->id,
-            'title'           => $artwork->title,
-            'slug'            => $artwork->slug,
-            'thumb_url'       => $artwork->thumbUrl('md') ?? '/images/placeholder.jpg',
-            'is_public'       => (bool) $artwork->is_public,
-            'visibility'      => $artwork->visibility ?: ((bool) $artwork->is_public ? Artwork::VISIBILITY_PUBLIC : Artwork::VISIBILITY_PRIVATE),
-            'is_approved'     => (bool) $artwork->is_approved,
-            'published_at'    => $artwork->published_at?->toIso8601String(),
-            'publish_at'      => $artwork->publish_at?->toIso8601String(),
-            'artwork_status'  => $artwork->artwork_status,
-            'created_at'      => $artwork->created_at?->toIso8601String(),
-            'deleted_at'      => $artwork->deleted_at?->toIso8601String(),
-            'category'        => $artwork->categories->first()?->name,
-            'category_slug'   => $artwork->categories->first()?->slug,
-            'tags'            => $artwork->tags->pluck('slug')->values()->all(),
-            'views'           => (int) ($stats?->views ?? 0),
-            'favourites'      => (int) ($stats?->favorites ?? 0),
-            'shares'          => (int) ($stats?->shares_count ?? 0),
-            'comments'        => (int) ($stats?->comments_count ?? 0),
-            'downloads'       => (int) ($stats?->downloads ?? 0),
-            'ranking_score'   => (float) ($stats?->ranking_score ?? 0),
-            'heat_score'      => (float) ($stats?->heat_score ?? 0),
+            'id' => $artwork->id,
+            'title' => $artwork->title,
+            'slug' => $artwork->slug,
+            'thumb_url' => $artwork->thumbUrl('md') ?? '/images/placeholder.jpg',
+            'is_public' => (bool) $artwork->is_public,
+            'visibility' => $artwork->visibility ?: ((bool) $artwork->is_public ? Artwork::VISIBILITY_PUBLIC : Artwork::VISIBILITY_PRIVATE),
+            'is_approved' => (bool) $artwork->is_approved,
+            'published_at' => $artwork->published_at?->toIso8601String(),
+            'publish_at' => $artwork->publish_at?->toIso8601String(),
+            'artwork_status' => $artwork->artwork_status,
+            'created_at' => $artwork->created_at?->toIso8601String(),
+            'deleted_at' => $artwork->deleted_at?->toIso8601String(),
+            'category' => $artwork->resolvedPrimaryCategory()?->name,
+            'category_slug' => $artwork->resolvedPrimaryCategory()?->slug,
+            'tags' => $artwork->tags->pluck('slug')->values()->all(),
+            'views' => (int) ($stats?->views ?? 0),
+            'favourites' => (int) ($stats?->favorites ?? 0),
+            'shares' => (int) ($stats?->shares_count ?? 0),
+            'comments' => (int) ($stats?->comments_count ?? 0),
+            'downloads' => (int) ($stats?->downloads ?? 0),
+            'ranking_score' => (float) ($stats?->ranking_score ?? 0),
+            'heat_score' => (float) ($stats?->heat_score ?? 0),
         ];
     }
 
@@ -499,7 +554,7 @@ final class StudioArtworksApiController extends Controller
         $previousSnapshot = $this->versioningService->captureArtworkSnapshot($artwork);
 
         $request->validate([
-            'file'        => 'required|file|mimes:jpeg,jpg,png,webp|max:51200', // 50 MB
+            'file' => 'required|file|mimes:jpeg,jpg,png,webp|max:51200', // 50 MB
             'change_note' => 'sometimes|nullable|string|max:500',
         ]);
 
@@ -510,43 +565,43 @@ final class StudioArtworksApiController extends Controller
             return response()->json(['success' => false, 'error' => $e->getMessage()], 429);
         }
 
-        $file     = $request->file('file');
+        $file = $request->file('file');
         $tempPath = $file->getRealPath();
-        $hash     = hash_file('sha256', $tempPath);
+        $hash = hash_file('sha256', $tempPath);
 
         // Reject identical files early (before any disk writes)
         if ($artwork->hash === $hash) {
             return response()->json([
                 'success' => false,
-                'error'   => 'The uploaded file is identical to the current version.',
+                'error' => 'The uploaded file is identical to the current version.',
             ], 422);
         }
 
         try {
-            $derivatives  = app(\App\Services\Uploads\UploadDerivativesService::class);
-            $storage      = app(\App\Services\Uploads\UploadStorageService::class);
-            $artworkFiles = app(\App\Repositories\Uploads\ArtworkFileRepository::class);
+            $derivatives = app(UploadDerivativesService::class);
+            $storage = app(UploadStorageService::class);
+            $artworkFiles = app(ArtworkFileRepository::class);
 
             // 1. Store original on disk (preserve extension when possible)
-            $originalAsset    = $derivatives->storeOriginal($tempPath, $hash);
-            $originalPath     = $originalAsset['local_path'];
-            $origFilename     = basename($originalPath);
+            $originalAsset = $derivatives->storeOriginal($tempPath, $hash);
+            $originalPath = $originalAsset['local_path'];
+            $origFilename = basename($originalPath);
             $originalRelative = $storage->sectionRelativePath('original', $hash, $origFilename);
-            $origMime         = File::exists($originalPath) ? File::mimeType($originalPath) : 'application/octet-stream';
+            $origMime = File::exists($originalPath) ? File::mimeType($originalPath) : 'application/octet-stream';
             $artworkFiles->upsert($artwork->id, 'orig', $originalRelative, $origMime, (int) filesize($originalPath));
 
             // 2. Generate thumbnails (xs/sm/md/lg/xl)
             $publicAssets = $derivatives->generatePublicDerivatives($tempPath, $hash);
             foreach ($publicAssets as $variant => $asset) {
-                $relativePath = $storage->sectionRelativePath($variant, $hash, $hash . '.webp');
+                $relativePath = $storage->sectionRelativePath($variant, $hash, $hash.'.webp');
                 $artworkFiles->upsert($artwork->id, $variant, $relativePath, 'image/webp', (int) ($asset['size'] ?? 0));
             }
 
             // 3. Get new dimensions
-            $dims   = @getimagesize($tempPath);
-            $width  = is_array($dims) && isset($dims[0]) ? (int) $dims[0] : $artwork->width;
+            $dims = @getimagesize($tempPath);
+            $width = is_array($dims) && isset($dims[0]) ? (int) $dims[0] : $artwork->width;
             $height = is_array($dims) && isset($dims[1]) ? (int) $dims[1] : $artwork->height;
-            $size   = (int) filesize($originalPath);
+            $size = (int) filesize($originalPath);
 
             // 4. Update the artwork's file-serving fields (hash drives thumbnail URLs)
             $origExt = strtolower(pathinfo($originalPath, PATHINFO_EXTENSION) ?: '');
@@ -559,7 +614,7 @@ final class StudioArtworksApiController extends Controller
             if ($clientName !== '') {
                 $clientExt = strtolower((string) pathinfo($clientName, PATHINFO_EXTENSION));
                 if ($clientExt === '' && $origExt !== '') {
-                    $clientName .= '.' . $origExt;
+                    $clientName .= '.'.$origExt;
                 }
 
                 $displayFileName = $clientName;
@@ -570,11 +625,11 @@ final class StudioArtworksApiController extends Controller
                 'file_path' => '',
                 'file_size' => $size,
                 'mime_type' => $origMime,
-                'hash'      => $hash,
-                'file_ext'  => $origExt,
+                'hash' => $hash,
+                'file_ext' => $origExt,
                 'thumb_ext' => 'webp',
-                'width'     => max(1, $width),
-                'height'    => max(1, $height),
+                'width' => max(1, $width),
+                'height' => max(1, $height),
             ]);
 
             // 5. Create version record from the new full media snapshot.
@@ -593,7 +648,7 @@ final class StudioArtworksApiController extends Controller
             } catch (\Throwable $e) {
                 Log::warning('ArtworkVersioningService: Meilisearch reindex failed', [
                     'artwork_id' => $artwork->id,
-                    'error'      => $e->getMessage(),
+                    'error' => $e->getMessage(),
                 ]);
             }
 
@@ -601,16 +656,17 @@ final class StudioArtworksApiController extends Controller
             $this->purgeCdnCache($artwork, $hash);
 
             return response()->json([
-                'success'        => true,
+                'success' => true,
                 'version_number' => $version->version_number,
                 'requires_reapproval' => (bool) $artwork->requires_reapproval,
             ] + $this->mediaPayload($artwork));
         } catch (\Throwable $e) {
             Log::error('replaceFile: processing error', [
                 'artwork_id' => $artwork->id,
-                'error'      => $e->getMessage(),
+                'error' => $e->getMessage(),
             ]);
-            return response()->json(['success' => false, 'error' => 'File processing failed: ' . $e->getMessage()], 500);
+
+            return response()->json(['success' => false, 'error' => 'File processing failed: '.$e->getMessage()], 500);
         }
     }
 
@@ -678,8 +734,8 @@ final class StudioArtworksApiController extends Controller
             return response()->json(['success' => false, 'error' => $e->getMessage()], 429);
         }
 
-        $derivatives = app(\App\Services\Uploads\UploadDerivativesService::class);
-        $storage = app(\App\Services\Uploads\UploadStorageService::class);
+        $derivatives = app(UploadDerivativesService::class);
+        $storage = app(UploadStorageService::class);
         $cleanupLocalPaths = [];
         $cleanupObjectPaths = [];
 
@@ -766,7 +822,7 @@ final class StudioArtworksApiController extends Controller
 
             $allScreenshotDescriptors = [];
             foreach (array_values(array_merge($existingScreenshotDescriptors, $newScreenshotDescriptors)) as $index => $descriptor) {
-                $descriptor['variant'] = 'shot' . ($index + 1);
+                $descriptor['variant'] = 'shot'.($index + 1);
                 $allScreenshotDescriptors[] = $descriptor;
             }
 
@@ -862,7 +918,7 @@ final class StudioArtworksApiController extends Controller
 
             return response()->json([
                 'success' => false,
-                'error' => 'Revision update failed: ' . $exception->getMessage(),
+                'error' => 'Revision update failed: '.$exception->getMessage(),
             ], 500);
         }
     }
@@ -873,27 +929,27 @@ final class StudioArtworksApiController extends Controller
      */
     public function versions(Request $request, int $id): JsonResponse
     {
-        $artwork  = $request->user()->artworks()->findOrFail($id);
+        $artwork = $request->user()->artworks()->findOrFail($id);
         $versions = $artwork->versions()->reorder()->orderByDesc('version_number')->get();
 
         return response()->json([
             'artwork' => [
-                'id'            => $artwork->id,
-                'title'         => $artwork->title,
+                'id' => $artwork->id,
+                'title' => $artwork->title,
                 'version_count' => (int) ($artwork->version_count ?? 1),
             ],
             'versions' => $versions->map(fn (ArtworkVersion $v) => [
-                'id'             => $v->id,
+                'id' => $v->id,
                 'version_number' => $v->version_number,
-                'file_path'      => $v->file_path,
-                'file_hash'      => $v->file_hash,
-                'width'          => $v->width,
-                'height'         => $v->height,
-                'file_size'      => $v->file_size,
-                'file_name'      => (string) data_get($v->snapshot_json, 'artwork.file_name', ''),
-                'change_note'    => $v->change_note,
-                'is_current'     => $v->is_current,
-                'created_at'     => $v->created_at?->toIso8601String(),
+                'file_path' => $v->file_path,
+                'file_hash' => $v->file_hash,
+                'width' => $v->width,
+                'height' => $v->height,
+                'file_size' => $v->file_size,
+                'file_name' => (string) data_get($v->snapshot_json, 'artwork.file_name', ''),
+                'change_note' => $v->change_note,
+                'is_current' => $v->is_current,
+                'created_at' => $v->created_at?->toIso8601String(),
             ])->values(),
         ]);
     }
@@ -918,17 +974,18 @@ final class StudioArtworksApiController extends Controller
             // Reindex
             try {
                 $this->searchIndexer->update($artwork);
-            } catch (\Throwable) {}
+            } catch (\Throwable) {
+            }
 
             return response()->json([
-                'success'        => true,
+                'success' => true,
                 'version_number' => $newVersion->version_number,
-                'message'        => "Version {$version->version_number} has been restored as version {$newVersion->version_number}.",
+                'message' => "Version {$version->version_number} has been restored as version {$newVersion->version_number}.",
             ] + $this->mediaPayload($artwork));
         } catch (TooManyRequestsHttpException $e) {
             return response()->json(['success' => false, 'error' => $e->getMessage()], 429);
         } catch (\Throwable $e) {
-            return response()->json(['success' => false, 'error' => 'Restore failed: ' . $e->getMessage()], 500);
+            return response()->json(['success' => false, 'error' => 'Restore failed: '.$e->getMessage()], 500);
         }
     }
 
@@ -938,7 +995,7 @@ final class StudioArtworksApiController extends Controller
      * This is best-effort; failures are logged but never fatal.
      * Configure a CDN purge webhook via ARTWORK_CDN_PURGE_URL if needed.
      */
-    private function purgeCdnCache(\App\Models\Artwork $artwork, string $oldHash): void
+    private function purgeCdnCache(Artwork $artwork, string $oldHash): void
     {
         try {
             $this->cdnPurge->purgeArtworkHashVariants($oldHash, 'webp', ['xs', 'sm', 'md', 'lg', 'xl', 'sq'], [
@@ -951,7 +1008,7 @@ final class StudioArtworksApiController extends Controller
     }
 
     /**
-     * @param array<string, mixed> $snapshot
+     * @param  array<string, mixed>  $snapshot
      * @return array<string, array<string, mixed>>
      */
     private function snapshotFilesByVariant(array $snapshot): array
@@ -963,7 +1020,7 @@ final class StudioArtworksApiController extends Controller
     }
 
     /**
-     * @param array<string, mixed> $snapshot
+     * @param  array<string, mixed>  $snapshot
      * @return array<string, array{path: string, mime: string, size: int}>
      */
     private function currentPublicAssetsFromSnapshot(array $snapshot): array
@@ -981,7 +1038,7 @@ final class StudioArtworksApiController extends Controller
     }
 
     /**
-     * @param array<string, mixed>|null $file
+     * @param  array<string, mixed>|null  $file
      * @return array<string, mixed>|null
      */
     private function existingVariantDescriptor(?array $file, string $fallbackVariant): ?array
@@ -1002,7 +1059,7 @@ final class StudioArtworksApiController extends Controller
     }
 
     /**
-     * @param array<string, mixed> $stored
+     * @param  array<string, mixed>  $stored
      * @return array<string, mixed>
      */
     private function storedOriginalDescriptor(array $stored, string $variant): array
@@ -1028,7 +1085,7 @@ final class StudioArtworksApiController extends Controller
 
         $candidateExt = strtolower((string) pathinfo($candidate, PATHINFO_EXTENSION));
         if ($candidateExt === '' && $ext !== '') {
-            $candidate .= '.' . ltrim($ext, '.');
+            $candidate .= '.'.ltrim($ext, '.');
         }
 
         return $candidate;
@@ -1058,7 +1115,7 @@ final class StudioArtworksApiController extends Controller
     }
 
     /**
-     * @param array<string, mixed> $snapshot
+     * @param  array<string, mixed>  $snapshot
      * @return array<int, array<string, mixed>>
      */
     private function screenshotAssetsFromSnapshot(array $snapshot): array
@@ -1070,11 +1127,11 @@ final class StudioArtworksApiController extends Controller
             ->values()
             ->map(function (array $file, int $index) use ($base): array {
                 $path = trim((string) ($file['path'] ?? ''), '/');
-                $url = $base . '/' . $path;
+                $url = $base.'/'.$path;
 
                 return [
-                    'id' => (string) ($file['variant'] ?? ('shot' . ($index + 1))),
-                    'label' => 'Screenshot ' . ($index + 1),
+                    'id' => (string) ($file['variant'] ?? ('shot'.($index + 1))),
+                    'label' => 'Screenshot '.($index + 1),
                     'url' => $url,
                     'thumb_url' => $url,
                     'mime_type' => (string) ($file['mime'] ?? 'image/jpeg'),
diff --git a/app/Http/Controllers/Studio/StudioController.php b/app/Http/Controllers/Studio/StudioController.php
index 5e11bf30..10bf7e5c 100644
--- a/app/Http/Controllers/Studio/StudioController.php
+++ b/app/Http/Controllers/Studio/StudioController.php
@@ -5,26 +5,27 @@ declare(strict_types=1);
 namespace App\Http\Controllers\Studio;
 
 use App\Http\Controllers\Controller;
-use App\Models\Group;
 use App\Models\ContentType;
+use App\Models\Group;
 use App\Services\ArtworkEvolutionService;
 use App\Services\Artworks\ArtworkPublicationService;
 use App\Services\GroupMembershipService;
 use App\Services\GroupService;
+use App\Services\Studio\CreatorStudioActivityService;
 use App\Services\Studio\CreatorStudioAnalyticsService;
 use App\Services\Studio\CreatorStudioAssetService;
 use App\Services\Studio\CreatorStudioCalendarService;
+use App\Services\Studio\CreatorStudioChallengeService;
 use App\Services\Studio\CreatorStudioCommentService;
 use App\Services\Studio\CreatorStudioContentService;
 use App\Services\Studio\CreatorStudioFollowersService;
 use App\Services\Studio\CreatorStudioGrowthService;
-use App\Services\Studio\CreatorStudioActivityService;
 use App\Services\Studio\CreatorStudioInboxService;
 use App\Services\Studio\CreatorStudioOverviewService;
 use App\Services\Studio\CreatorStudioPreferenceService;
-use App\Services\Studio\CreatorStudioChallengeService;
-use App\Services\Studio\CreatorStudioSearchService;
 use App\Services\Studio\CreatorStudioScheduledService;
+use App\Services\Studio\CreatorStudioSearchService;
+use App\Services\Uploads\UploadQueueService;
 use App\Services\Worlds\WorldSubmissionService;
 use App\Support\CoverUrl;
 use Illuminate\Http\RedirectResponse;
@@ -132,7 +133,7 @@ final class StudioController extends Controller
 
     public function uploadQueue(Request $request): Response
     {
-        $queue = app(\App\Services\Uploads\UploadQueueService::class)->listPayload(
+        $queue = app(UploadQueueService::class)->listPayload(
             $request->user(),
             $request->only(['batch_id', 'status', 'sort'])
         );
@@ -361,7 +362,7 @@ final class StudioController extends Controller
                 'cover_url' => $user->cover_hash && $user->cover_ext ? CoverUrl::forUser($user->cover_hash, $user->cover_ext, time()) : null,
                 'cover_position' => (int) ($user->cover_position ?? 50),
                 'followers' => (int) ($user->statistics?->followers_count ?? 0),
-                'profile_url' => '/@' . strtolower((string) $user->username),
+                'profile_url' => '/@'.strtolower((string) $user->username),
                 'social_links' => $socialLinks,
             ],
             'moduleSummaries' => $this->content->moduleSummaries($user),
@@ -449,13 +450,13 @@ final class StudioController extends Controller
     {
         $user = $request->user();
         $artwork = $user->artworks()
-            ->with(['stats', 'categories.contentType', 'tags', 'artworkAiAssist', 'group.members', 'primaryAuthor.profile', 'contributors.user.profile'])
+            ->with(['stats', 'categories.contentType', 'primaryCategory.contentType', 'tags', 'artworkAiAssist', 'group.members', 'primaryAuthor.profile', 'contributors.user.profile'])
             ->findOrFail($id);
 
         $artwork = app(ArtworkPublicationService::class)->publishIfDue($artwork);
-        $artwork->loadMissing(['stats', 'categories.contentType', 'tags', 'artworkAiAssist', 'group.members', 'primaryAuthor.profile', 'contributors.user.profile']);
+        $artwork->loadMissing(['stats', 'categories.contentType', 'primaryCategory.contentType', 'tags', 'artworkAiAssist', 'group.members', 'primaryAuthor.profile', 'contributors.user.profile']);
 
-        $primaryCategory = $artwork->categories->first();
+        $primaryCategory = $artwork->resolvedPrimaryCategory();
         $availableGroups = app(GroupService::class)->studioOptionsForUser($user);
         $membershipService = app(GroupMembershipService::class);
         $contributorOptionsByGroup = [];
@@ -470,30 +471,30 @@ final class StudioController extends Controller
         }
 
         return Inertia::render('Studio/StudioArtworkEdit', [
-            'artwork'    => [
-                'id'              => $artwork->id,
-                'title'           => $artwork->title,
-                'slug'            => $artwork->slug,
-                'description'     => $artwork->description,
-                'is_public'       => (bool) $artwork->is_public,
-                'visibility'      => $artwork->visibility ?: ((bool) $artwork->is_public ? 'public' : 'private'),
-                'is_approved'     => (bool) $artwork->is_approved,
-                'publish_mode'    => $artwork->artwork_status === 'scheduled' ? 'schedule' : 'now',
-                'publish_at'      => $artwork->publish_at?->toIso8601String(),
-                'artwork_status'  => $artwork->artwork_status,
+            'artwork' => [
+                'id' => $artwork->id,
+                'title' => $artwork->title,
+                'slug' => $artwork->slug,
+                'description' => $artwork->description,
+                'is_public' => (bool) $artwork->is_public,
+                'visibility' => $artwork->visibility ?: ((bool) $artwork->is_public ? 'public' : 'private'),
+                'is_approved' => (bool) $artwork->is_approved,
+                'publish_mode' => $artwork->artwork_status === 'scheduled' ? 'schedule' : 'now',
+                'publish_at' => $artwork->publish_at?->toIso8601String(),
+                'artwork_status' => $artwork->artwork_status,
                 'artwork_timezone' => $artwork->artwork_timezone,
-                'thumb_url'       => $artwork->thumbUrl('md'),
-                'thumb_url_lg'    => $artwork->thumbUrl('lg'),
-                'download_url'    => route('art.download', ['id' => $artwork->id]),
-                'file_name'       => $artwork->file_name,
-                'file_ext'        => $artwork->file_ext,
-                'file_size'       => $artwork->file_size,
-                'width'           => $artwork->width,
-                'height'          => $artwork->height,
-                'mime_type'       => $artwork->mime_type,
+                'thumb_url' => $artwork->thumbUrl('md'),
+                'thumb_url_lg' => $artwork->thumbUrl('lg'),
+                'download_url' => route('art.download', ['id' => $artwork->id]),
+                'file_name' => $artwork->file_name,
+                'file_ext' => $artwork->file_ext,
+                'file_size' => $artwork->file_size,
+                'width' => $artwork->width,
+                'height' => $artwork->height,
+                'mime_type' => $artwork->mime_type,
                 'has_archive_file' => $this->artworkHasArchiveFile((int) $artwork->id),
-                'screenshots'     => $this->screenshotAssetsForArtwork((int) $artwork->id),
-                'group_slug'      => $artwork->group?->slug,
+                'screenshots' => $this->screenshotAssetsForArtwork((int) $artwork->id),
+                'group_slug' => $artwork->group?->slug,
                 'primary_author_user_id' => (int) ($artwork->primary_author_user_id ?: $artwork->user_id),
                 'contributor_user_ids' => $artwork->contributors->pluck('user_id')->map(fn ($id): int => (int) $id)->values()->all(),
                 'contributor_credits' => $artwork->contributors->map(fn ($contributor): array => [
@@ -502,19 +503,27 @@ final class StudioController extends Controller
                     'is_primary' => (bool) $contributor->is_primary,
                 ])->values()->all(),
                 'content_type_id' => $primaryCategory?->contentType?->id,
-                'category_id'     => $primaryCategory?->id,
+                'category_id' => $primaryCategory?->id,
+                'primary_category_id' => $primaryCategory?->id,
                 'parent_category_id' => $primaryCategory?->parent_id ? $primaryCategory->parent_id : $primaryCategory?->id,
-                'sub_category_id'    => $primaryCategory?->parent_id ? $primaryCategory->id : null,
-                'categories'      => $artwork->categories->map(fn ($c) => ['id' => $c->id, 'name' => $c->name, 'slug' => $c->slug])->values()->all(),
-                'tags'            => $artwork->tags->map(fn ($t) => ['id' => $t->id, 'name' => $t->name, 'slug' => $t->slug])->values()->all(),
-                'ai_status'       => $artwork->ai_status,
-                'title_source'    => $artwork->title_source ?: 'manual',
+                'sub_category_id' => $primaryCategory?->parent_id ? $primaryCategory->id : null,
+                'secondary_category_ids' => $artwork->categories
+                    ->reject(fn ($category): bool => (int) $category->id === (int) ($primaryCategory?->id ?? 0))
+                    ->pluck('id')
+                    ->map(fn ($id): int => (int) $id)
+                    ->values()
+                    ->all(),
+                'max_secondary_categories' => (int) config('categories.max_secondary_categories', 5),
+                'categories' => $artwork->categories->map(fn ($c) => ['id' => $c->id, 'name' => $c->name, 'slug' => $c->slug, 'is_primary' => (int) $c->id === (int) ($primaryCategory?->id ?? 0)])->values()->all(),
+                'tags' => $artwork->tags->map(fn ($t) => ['id' => $t->id, 'name' => $t->name, 'slug' => $t->slug])->values()->all(),
+                'ai_status' => $artwork->ai_status,
+                'title_source' => $artwork->title_source ?: 'manual',
                 'description_source' => $artwork->description_source ?: 'manual',
-                'tags_source'     => $artwork->tags_source ?: 'manual',
+                'tags_source' => $artwork->tags_source ?: 'manual',
                 'category_source' => $artwork->category_source ?: 'manual',
                 'evolution_relation' => app(ArtworkEvolutionService::class)->editorRelation($artwork, $user),
                 // Versioning
-                'version_count'       => (int) ($artwork->version_count ?? 1),
+                'version_count' => (int) ($artwork->version_count ?? 1),
                 'requires_reapproval' => (bool) $artwork->requires_reapproval,
             ],
             'worldSubmissionOptions' => app(WorldSubmissionService::class)->artworkSubmissionOptions($artwork, $user),
@@ -538,19 +547,19 @@ final class StudioController extends Controller
 
         return Inertia::render('Studio/StudioArtworkAnalytics', [
             'artwork' => [
-                'id'            => $artwork->id,
-                'title'         => $artwork->title,
-                'slug'          => $artwork->slug,
-                'thumb_url'     => $artwork->thumbUrl('md'),
+                'id' => $artwork->id,
+                'title' => $artwork->title,
+                'slug' => $artwork->slug,
+                'thumb_url' => $artwork->thumbUrl('md'),
             ],
             'analytics' => [
-                'views'           => (int) ($stats?->views ?? 0),
-                'favourites'      => (int) ($stats?->favorites ?? 0),
-                'shares'          => (int) ($stats?->shares_count ?? 0),
-                'comments'        => (int) ($stats?->comments_count ?? 0),
-                'downloads'       => (int) ($stats?->downloads ?? 0),
-                'ranking_score'   => (float) ($stats?->ranking_score ?? 0),
-                'heat_score'      => (float) ($stats?->heat_score ?? 0),
+                'views' => (int) ($stats?->views ?? 0),
+                'favourites' => (int) ($stats?->favorites ?? 0),
+                'shares' => (int) ($stats?->shares_count ?? 0),
+                'comments' => (int) ($stats?->comments_count ?? 0),
+                'downloads' => (int) ($stats?->downloads ?? 0),
+                'ranking_score' => (float) ($stats?->ranking_score ?? 0),
+                'heat_score' => (float) ($stats?->heat_score ?? 0),
                 'engagement_velocity' => (float) ($stats?->engagement_velocity ?? 0),
             ],
         ]);
@@ -569,16 +578,16 @@ final class StudioController extends Controller
         $data = $this->analytics->overview($user, $rangeDays);
 
         return Inertia::render('Studio/StudioAnalytics', [
-            'totals'           => $data['totals'],
-            'topContent'       => $data['top_content'],
-            'moduleBreakdown'  => $data['module_breakdown'],
-            'viewsTrend'       => $data['views_trend'],
-            'engagementTrend'  => $data['engagement_trend'],
+            'totals' => $data['totals'],
+            'topContent' => $data['top_content'],
+            'moduleBreakdown' => $data['module_breakdown'],
+            'viewsTrend' => $data['views_trend'],
+            'engagementTrend' => $data['engagement_trend'],
             'publishingTimeline' => $data['publishing_timeline'],
-            'comparison'       => $data['comparison'],
-            'insightBlocks'    => $data['insight_blocks'],
-            'rangeDays'        => $data['range_days'],
-            'recentComments'   => $this->overview->recentComments($user, 8),
+            'comparison' => $data['comparison'],
+            'insightBlocks' => $data['insight_blocks'],
+            'rangeDays' => $data['range_days'],
+            'recentComments' => $this->overview->recentComments($user, 8),
         ]);
     }
 
@@ -586,16 +595,16 @@ final class StudioController extends Controller
     {
         return ContentType::with(['rootCategories.children'])->ordered()->get()->map(function ($ct) {
             return [
-                'id'   => $ct->id,
+                'id' => $ct->id,
                 'name' => $ct->name,
                 'slug' => $ct->slug,
                 'categories' => $ct->rootCategories->map(function ($c) {
                     return [
-                        'id'       => $c->id,
-                        'name'     => $c->name,
-                        'slug'     => $c->slug,
+                        'id' => $c->id,
+                        'name' => $c->name,
+                        'slug' => $c->slug,
                         'children' => $c->children->map(fn ($ch) => [
-                            'id'   => $ch->id,
+                            'id' => $ch->id,
                             'name' => $ch->name,
                             'slug' => $ch->slug,
                         ])->values()->all(),
@@ -642,11 +651,11 @@ final class StudioController extends Controller
                     return null;
                 }
 
-                $url = $base . '/' . $path;
+                $url = $base.'/'.$path;
 
                 return [
-                    'id' => (string) ($row->variant ?? ('shot' . ($index + 1))),
-                    'label' => 'Screenshot ' . ($index + 1),
+                    'id' => (string) ($row->variant ?? ('shot'.($index + 1))),
+                    'label' => 'Screenshot '.($index + 1),
                     'url' => $url,
                     'thumb_url' => $url,
                     'mime_type' => (string) ($row->mime ?? 'image/jpeg'),
diff --git a/app/Http/Controllers/User/TodayDownloadsController.php b/app/Http/Controllers/User/TodayDownloadsController.php
index ec694fca..86562ce5 100644
--- a/app/Http/Controllers/User/TodayDownloadsController.php
+++ b/app/Http/Controllers/User/TodayDownloadsController.php
@@ -3,7 +3,10 @@
 namespace App\Http\Controllers\User;
 
 use App\Http\Controllers\Controller;
+use App\Models\Artwork;
 use App\Models\ArtworkDownload;
+use App\Services\ThumbnailPresenter;
+use App\Support\AvatarUrl;
 use Carbon\Carbon;
 use Illuminate\Http\Request;
 use Illuminate\Support\Str;
@@ -54,7 +57,7 @@ class TodayDownloadsController extends Controller
         $paginator->getCollection()->transform(function ($row) {
             $art = $row->artwork ?? null;
             if (! $art && isset($row->artwork_id)) {
-                $art = \App\Models\Artwork::find($row->artwork_id);
+                $art = Artwork::find($row->artwork_id);
             }
 
             if (! $art) {
@@ -75,9 +78,9 @@ class TodayDownloadsController extends Controller
             $picture = $art->file_name ?? null;
             $ext = pathinfo($picture ?? '', PATHINFO_EXTENSION) ?: 'jpg';
             $encoded = null;
-            $present = $art ? \App\Services\ThumbnailPresenter::present($art, 'md') : null;
+            $present = $art ? ThumbnailPresenter::present($art, 'md') : null;
             $thumb = $present ? $present['url'] : 'https://files.skinbase.org/default/missing_md.webp';
-            $primaryCategory = $art->categories->first();
+            $primaryCategory = $art->resolvedPrimaryCategory();
             $categoryId = $primaryCategory->id ?? null;
             $categoryName = $primaryCategory->name ?? '';
             $categorySlug = $primaryCategory->slug ?? '';
@@ -98,7 +101,7 @@ class TodayDownloadsController extends Controller
                 'category_slug' => $categorySlug,
                 'uname' => $art->user->name ?? 'Skinbase',
                 'username' => $art->user->username ?? '',
-                'avatar_url' => \App\Support\AvatarUrl::forUser((int) ($art->user->id ?? 0), $avatarHash, 64),
+                'avatar_url' => AvatarUrl::forUser((int) ($art->user->id ?? 0), $avatarHash, 64),
                 'width' => $art->width,
                 'height' => $art->height,
                 'published_at' => $art->published_at,
diff --git a/app/Http/Controllers/Web/ArtworkPageController.php b/app/Http/Controllers/Web/ArtworkPageController.php
index 15680f30..4ce7fd63 100644
--- a/app/Http/Controllers/Web/ArtworkPageController.php
+++ b/app/Http/Controllers/Web/ArtworkPageController.php
@@ -1,4 +1,5 @@
 <?php
+
 declare(strict_types=1);
 
 namespace App\Http\Controllers\Web;
@@ -7,17 +8,19 @@ use App\Enums\ReactionType;
 use App\Http\Controllers\Controller;
 use App\Http\Resources\ArtworkResource;
 use App\Models\Artwork;
-use Illuminate\Support\Facades\DB;
-use App\Services\ThumbnailPresenter;
+use App\Models\Category;
 use App\Services\ArtworkNavigationService;
+use App\Services\ArtworkRelatedService;
 use App\Services\ErrorSuggestionService;
 use App\Services\GroupService;
 use App\Services\Maturity\ArtworkMaturityService;
+use App\Services\ThumbnailPresenter;
 use App\Support\Seo\SeoFactory;
-use Illuminate\Support\Collection;
 use Illuminate\Http\RedirectResponse;
 use Illuminate\Http\Request;
 use Illuminate\Http\Response;
+use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Str;
 use Illuminate\View\View;
 use Inertia\Inertia;
@@ -29,6 +32,7 @@ final class ArtworkPageController extends Controller
         private readonly GroupService $groups,
         private readonly ArtworkMaturityService $maturity,
         private readonly ArtworkNavigationService $navigation,
+        private readonly ArtworkRelatedService $relatedArtworks,
     ) {}
 
     public function show(Request $request, int $id, ?string $slug = null): View|RedirectResponse|Response|InertiaResponse
@@ -39,6 +43,7 @@ final class ArtworkPageController extends Controller
         if (! $raw) {
             // Artwork never existed → contextual 404
             $suggestions = app(ErrorSuggestionService::class);
+
             return response(view('errors.contextual.artwork-not-found', [
                 'trendingArtworks' => $this->safeSuggestions(fn () => $suggestions->trendingArtworks()),
             ]), 404);
@@ -73,24 +78,25 @@ final class ArtworkPageController extends Controller
                         ->limit(6)
                         ->get()
                         ->map(function (Artwork $a) {
-                            $slug = \Illuminate\Support\Str::slug((string) ($a->slug ?: $a->title)) ?: (string) $a->id;
-                            $md   = \App\Services\ThumbnailPresenter::present($a, 'md');
+                            $slug = Str::slug((string) ($a->slug ?: $a->title)) ?: (string) $a->id;
+                            $md = ThumbnailPresenter::present($a, 'md');
+
                             return [
-                                'id'     => $a->id,
-                                'title'  => html_entity_decode((string) $a->title, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                                'id' => $a->id,
+                                'title' => html_entity_decode((string) $a->title, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
                                 'author' => html_entity_decode((string) ($a->user?->name ?: $a->user?->username ?: 'Artist'), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
-                                'url'    => route('art.show', ['id' => $a->id, 'slug' => $slug]),
-                                'thumb'  => $md['url'] ?? null,
+                                'url' => route('art.show', ['id' => $a->id, 'slug' => $slug]),
+                                'thumb' => $md['url'] ?? null,
                             ];
                         });
                 });
             }
 
             return response(view('errors.contextual.artwork-not-found', [
-                'message'          => 'This artwork is not publicly available.',
-                'isForbidden'      => true,
-                'creatorArtworks'  => $creatorArtworks,
-                'creatorUsername'  => $creatorUsername,
+                'message' => 'This artwork is not publicly available.',
+                'isForbidden' => true,
+                'creatorArtworks' => $creatorArtworks,
+                'creatorUsername' => $creatorUsername,
                 'trendingArtworks' => $this->safeSuggestions(fn () => $suggestions->trendingArtworks()),
             ]), 403);
         }
@@ -101,9 +107,15 @@ final class ArtworkPageController extends Controller
         // distinct responses. Reusing that model avoids a second identical
         // primary-key lookup on the public path.
         $artwork = $raw;
-        $artwork->load(['user.profile', 'group.owner.profile', 'uploadedBy.profile', 'primaryAuthor.profile', 'contributors.user.profile', 'categories.contentType', 'categories.parent.contentType', 'tags', 'stats', 'awardStat']);
+        $artwork->load(['user.profile', 'group.owner.profile', 'uploadedBy.profile', 'primaryAuthor.profile', 'contributors.user.profile', 'categories.contentType', 'categories.parent.contentType', 'primaryCategory.contentType', 'primaryCategory.parent.contentType', 'tags', 'stats', 'awardStat']);
 
-        $this->loadCategoryAncestors($artwork->categories);
+        $this->loadCategoryAncestors(
+            $artwork->categories
+                ->concat(collect([$artwork->resolvedPrimaryCategory()]))
+                ->filter()
+                ->unique('id')
+                ->values()
+        );
 
         $canonicalSlug = Str::slug((string) ($artwork->slug ?: $artwork->title));
         if ($canonicalSlug === '') {
@@ -152,37 +164,7 @@ final class ArtworkPageController extends Controller
             'xl' => $thumbXl,
         ], $canonical, $this->artworkBreadcrumbs($artwork, $canonical))->toArray();
 
-        $categoryIds = $artwork->categories->pluck('id')->filter()->values();
-        $tagIds = $artwork->tags->pluck('id')->filter()->values();
-
-        $related = Artwork::query()
-            ->with(['user', 'group', 'categories.contentType'])
-            ->whereKeyNot($artwork->id)
-            ->public()
-            ->published()
-            ->tap(fn ($builder) => $this->maturity->applyViewerFilter($builder, $request->user()))
-            ->where(function ($query) use ($artwork, $categoryIds, $tagIds): void {
-                $query->where('user_id', $artwork->user_id);
-
-                if ($artwork->group_id) {
-                    $query->orWhere('group_id', $artwork->group_id);
-                }
-
-                if ($categoryIds->isNotEmpty()) {
-                    $query->orWhereHas('categories', function ($categoryQuery) use ($categoryIds): void {
-                        $categoryQuery->whereIn('categories.id', $categoryIds->all());
-                    });
-                }
-
-                if ($tagIds->isNotEmpty()) {
-                    $query->orWhereHas('tags', function ($tagQuery) use ($tagIds): void {
-                        $tagQuery->whereIn('tags.id', $tagIds->all());
-                    });
-                }
-            })
-            ->latest('published_at')
-            ->limit(12)
-            ->get()
+        $related = $this->relatedArtworks->related($artwork, $request->user(), 12)
             ->map(function (Artwork $item): array {
                 $itemSlug = Str::slug((string) ($item->slug ?: $item->title));
                 if ($itemSlug === '') {
@@ -201,7 +183,7 @@ final class ArtworkPageController extends Controller
                     'publisher_id' => $item->group ? (int) $item->group->id : (int) ($item->user?->id ?? 0),
                     'url' => route('art.show', ['id' => $item->id, 'slug' => $itemSlug]),
                     'thumb' => $sm['url'] ?? null,
-                    'thumb_srcset' => ($sm['url'] ?? '') . ' 320w, ' . ($md['url'] ?? '') . ' 640w',
+                    'thumb_srcset' => ($sm['url'] ?? '').' 320w, '.($md['url'] ?? '').' 640w',
                 ], $item, request()->user());
             })
             ->values()
@@ -210,20 +192,19 @@ final class ArtworkPageController extends Controller
         $canReadSession = $request->hasSession() && ! $request->attributes->get('skinbase.session_skipped');
         $viewerId = ($canReadSession && $request->user() !== null) ? (int) $request->user()->id : null;
 
-
         return Inertia::render('ArtworkPage', [
-            'artwork'         => $artworkData,
-            'navigation'      => $navigationData,
-            'presentMd'       => $thumbMd,
-            'presentLg'       => $thumbLg,
-            'presentXl'       => $thumbXl,
-            'presentSq'       => $thumbSq,
-            'related'         => $related,
-            'canonicalUrl'    => $canonical,
-            'groupSummary'    => $groupSummary,
+            'artwork' => $artworkData,
+            'navigation' => $navigationData,
+            'presentMd' => $thumbMd,
+            'presentLg' => $thumbLg,
+            'presentXl' => $thumbXl,
+            'presentSq' => $thumbSq,
+            'related' => $related,
+            'canonicalUrl' => $canonical,
+            'groupSummary' => $groupSummary,
             'isAuthenticated' => $viewerId !== null,
-            'reactionTotals'  => $this->artworkReactionTotals((int) $artwork->id, $viewerId),
-            'seo'             => $seo,
+            'reactionTotals' => $this->artworkReactionTotals((int) $artwork->id, $viewerId),
+            'seo' => $seo,
         ])->rootView('artworks.show');
     }
 
@@ -245,7 +226,7 @@ final class ArtworkPageController extends Controller
 
         $totals = [];
         foreach (ReactionType::cases() as $type) {
-            $slug  = $type->value;
+            $slug = $type->value;
             $count = (int) ($rows[$slug]->total ?? 0);
 
             $mine = false;
@@ -261,7 +242,7 @@ final class ArtworkPageController extends Controller
                 'emoji' => $type->emoji(),
                 'label' => $type->label(),
                 'count' => $count,
-                'mine'  => $mine,
+                'mine' => $mine,
             ];
         }
 
@@ -282,7 +263,7 @@ final class ArtworkPageController extends Controller
                 ->values();
 
             if ($missingParentIds->isNotEmpty()) {
-                $fetchedParents = \App\Models\Category::query()
+                $fetchedParents = Category::query()
                     ->with('contentType')
                     ->whereIn('id', $missingParentIds->all())
                     ->get()
@@ -308,12 +289,7 @@ final class ArtworkPageController extends Controller
      */
     private function artworkBreadcrumbs(Artwork $artwork, string $canonical): array
     {
-        $primaryCategory = $artwork->categories
-            ->sortBy(fn ($category) => [
-                (int) ($category->sort_order ?? 0),
-                (string) ($category->name ?? ''),
-            ])
-            ->first();
+        $primaryCategory = $artwork->resolvedPrimaryCategory();
 
         if ($primaryCategory === null) {
             return [
@@ -338,7 +314,7 @@ final class ArtworkPageController extends Controller
         if ($contentTypeSlug !== '' && $contentTypeName !== '') {
             $breadcrumbs[] = [
                 'name' => $contentTypeName,
-                'url' => url('/' . $contentTypeSlug),
+                'url' => url('/'.$contentTypeSlug),
             ];
         }
 
@@ -355,7 +331,7 @@ final class ArtworkPageController extends Controller
             $pathSegments[] = $slug;
             $breadcrumbs[] = [
                 'name' => $name,
-                'url' => url('/' . $contentTypeSlug . '/' . implode('/', $pathSegments)),
+                'url' => url('/'.$contentTypeSlug.'/'.implode('/', $pathSegments)),
             ];
         }
 
diff --git a/app/Http/Requests/Artworks/ArtworkCreateRequest.php b/app/Http/Requests/Artworks/ArtworkCreateRequest.php
index ddfe0478..e412ad82 100644
--- a/app/Http/Requests/Artworks/ArtworkCreateRequest.php
+++ b/app/Http/Requests/Artworks/ArtworkCreateRequest.php
@@ -27,6 +27,9 @@ final class ArtworkCreateRequest extends FormRequest
             'title' => 'required|string|max:150',
             'description' => 'nullable|string',
             'category' => 'nullable|integer|exists:categories,id',
+            'primary_category_id' => 'nullable|integer|exists:categories,id',
+            'secondary_category_ids' => 'nullable|array|max:'.(int) config('categories.max_secondary_categories', 5),
+            'secondary_category_ids.*' => 'integer|exists:categories,id',
             'tags' => 'nullable|string|max:200',
             'license' => 'nullable|boolean',
             'is_mature' => 'nullable|boolean',
@@ -45,7 +48,7 @@ final class ArtworkCreateRequest extends FormRequest
 
     private function denyAsNotFound(): void
     {
-        throw new NotFoundHttpException();
+        throw new NotFoundHttpException;
     }
 
     private function logUnauthorized(string $reason): void
diff --git a/app/Http/Requests/Studio/ApplyArtworkAiAssistRequest.php b/app/Http/Requests/Studio/ApplyArtworkAiAssistRequest.php
index de16ee00..c0d06113 100644
--- a/app/Http/Requests/Studio/ApplyArtworkAiAssistRequest.php
+++ b/app/Http/Requests/Studio/ApplyArtworkAiAssistRequest.php
@@ -23,10 +23,13 @@ final class ApplyArtworkAiAssistRequest extends FormRequest
             'title_mode' => ['sometimes', Rule::in(['replace', 'insert'])],
             'description' => ['sometimes', 'nullable', 'string', 'max:5000'],
             'description_mode' => ['sometimes', Rule::in(['replace', 'append'])],
-            'tags' => ['sometimes', 'array', 'max:' . (int) config('tags.max_user_tags', 30)],
+            'tags' => ['sometimes', 'array', 'max:'.(int) config('tags.max_user_tags', 30)],
             'tags.*' => ['string', 'max:64'],
             'tag_mode' => ['sometimes', Rule::in(['add', 'replace', 'remove'])],
             'category_id' => ['sometimes', 'nullable', 'integer', 'exists:categories,id'],
+            'primary_category_id' => ['sometimes', 'nullable', 'integer', 'exists:categories,id'],
+            'secondary_category_ids' => ['sometimes', 'array', 'max:'.(int) config('categories.max_secondary_categories', 5)],
+            'secondary_category_ids.*' => ['integer', 'exists:categories,id'],
             'content_type_id' => ['sometimes', 'nullable', 'integer', 'exists:content_types,id'],
             'similar_actions' => ['sometimes', 'array', 'max:10'],
             'similar_actions.*.artwork_id' => ['required_with:similar_actions', 'integer'],
@@ -42,4 +45,4 @@ final class ApplyArtworkAiAssistRequest extends FormRequest
             }
         });
     }
-}
\ No newline at end of file
+}
diff --git a/app/Http/Resources/ArtworkResource.php b/app/Http/Resources/ArtworkResource.php
index 91a682a2..3a1532fe 100644
--- a/app/Http/Resources/ArtworkResource.php
+++ b/app/Http/Resources/ArtworkResource.php
@@ -1,9 +1,10 @@
 <?php
+
 namespace App\Http\Resources;
 
+use App\Models\World;
 use App\Models\WorldRelation;
 use App\Models\WorldSubmission;
-use App\Models\World;
 use App\Services\ArtworkEvolutionService;
 use App\Services\ContentSanitizer;
 use App\Services\Maturity\ArtworkMaturityService;
@@ -12,6 +13,7 @@ use App\Services\Worlds\WorldRewardService;
 use Illuminate\Http\Resources\Json\JsonResource;
 use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Str;
 
 class ArtworkResource extends JsonResource
 {
@@ -23,7 +25,7 @@ class ArtworkResource extends JsonResource
      */
     public function toArray($request): array
     {
-        $this->resource->loadMissing(['group', 'uploadedBy.profile', 'primaryAuthor.profile', 'contributors.user.profile', 'worldSubmissions.world', 'worldRewardGrants.world']);
+        $this->resource->loadMissing(['group', 'uploadedBy.profile', 'primaryAuthor.profile', 'contributors.user.profile', 'worldSubmissions.world']);
 
         $md = ThumbnailPresenter::present($this->resource, 'md');
         $lg = ThumbnailPresenter::present($this->resource, 'lg');
@@ -31,18 +33,16 @@ class ArtworkResource extends JsonResource
         $sq = ThumbnailPresenter::present($this->resource, 'sq');
         $screenshots = $this->resolveScreenshotAssets();
 
-        $canonicalSlug = \Illuminate\Support\Str::slug((string) ($this->slug ?: $this->title));
+        $canonicalSlug = Str::slug((string) ($this->slug ?: $this->title));
         if ($canonicalSlug === '') {
             $canonicalSlug = (string) $this->id;
         }
 
         $followerCount = 0;
-        if (!empty($this->user?->id)) {
-            if ($this->hasTable('user_statistics')) {
-                $followerCount = (int) DB::table('user_statistics')
-                    ->where('user_id', (int) $this->user->id)
-                    ->value('followers_count');
-            }
+        if (! empty($this->user?->id)) {
+            $followerCount = (int) DB::table('user_statistics')
+                ->where('user_id', (int) $this->user->id)
+                ->value('followers_count');
 
             // Legacy fallback for environments where new tables are unavailable.
             if (($followerCount <= 0) && $this->hasTable('friends_list')) {
@@ -61,9 +61,9 @@ class ArtworkResource extends JsonResource
         $viewerAward = null;
         $isOwner = $viewerId > 0 && $viewerId === (int) ($this->user?->id ?? 0);
 
-        $bookmarksCount = $this->hasTable('artwork_bookmarks')
-            ? (int) DB::table('artwork_bookmarks')->where('artwork_id', (int) $this->id)->count()
-            : 0;
+        $bookmarksCount = (int) DB::table('artwork_bookmarks')
+            ->where('artwork_id', (int) $this->id)
+            ->count();
 
         if ($viewerId > 0) {
             if ($this->hasTable('artwork_likes')) {
@@ -73,19 +73,17 @@ class ArtworkResource extends JsonResource
                     ->exists();
             }
 
-            if ($this->hasTable('artwork_bookmarks')) {
-                $isBookmarked = DB::table('artwork_bookmarks')
-                    ->where('user_id', $viewerId)
-                    ->where('artwork_id', (int) $this->id)
-                    ->exists();
-            }
+            $isBookmarked = DB::table('artwork_bookmarks')
+                ->where('user_id', $viewerId)
+                ->where('artwork_id', (int) $this->id)
+                ->exists();
 
             $isFavorited = DB::table('artwork_favourites')
                 ->where('user_id', $viewerId)
                 ->where('artwork_id', (int) $this->id)
                 ->exists();
 
-            if (!empty($this->user?->id)) {
+            if (! empty($this->user?->id)) {
                 if ($this->hasTable('user_followers')) {
                     $isFollowing = DB::table('user_followers')
                         ->where('user_id', (int) $this->user->id)
@@ -100,7 +98,7 @@ class ArtworkResource extends JsonResource
                 }
             }
 
-            if (!empty($this->group?->id) && $this->hasTable('group_follows')) {
+            if (! empty($this->group?->id) && $this->hasTable('group_follows')) {
                 $isFollowingGroup = DB::table('group_follows')
                     ->where('group_id', (int) $this->group->id)
                     ->where('user_id', $viewerId)
@@ -125,7 +123,7 @@ class ArtworkResource extends JsonResource
                 'id' => (int) ($user->id ?? 0),
                 'name' => html_entity_decode((string) ($user->name ?? ''), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
                 'username' => (string) ($user->username ?? ''),
-                'profile_url' => ! empty($user->username) ? '/@' . $user->username : null,
+                'profile_url' => ! empty($user->username) ? '/@'.$user->username : null,
                 'avatar_url' => $user->profile?->avatar_url,
             ];
         };
@@ -150,7 +148,7 @@ class ArtworkResource extends JsonResource
                 'slug' => (string) ($this->user?->username ?? ''),
                 'headline' => '',
                 'avatar_url' => $this->user?->profile?->avatar_url,
-                'profile_url' => $this->user?->username ? '/@' . $this->user->username : null,
+                'profile_url' => $this->user?->username ? '/@'.$this->user->username : null,
                 'followers_count' => $followerCount,
                 'follow_url' => null,
                 'unfollow_url' => null,
@@ -179,6 +177,8 @@ class ArtworkResource extends JsonResource
             'title' => $decode($this->title),
             'description' => $decode($this->description),
             'description_html' => $this->renderDescriptionHtml(),
+            'download_status' => (string) ($this->download_status ?? 'unknown'),
+            'download_source' => $this->download_source,
             'dimensions' => [
                 'width' => (int) ($this->width ?? 0),
                 'height' => (int) ($this->height ?? 0),
@@ -201,7 +201,7 @@ class ArtworkResource extends JsonResource
                 'id' => (int) ($this->user?->id ?? 0),
                 'name' => html_entity_decode((string) ($this->user?->name ?? ''), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
                 'username' => (string) ($this->user?->username ?? ''),
-                'profile_url' => $this->user?->username ? '/@' . $this->user->username : null,
+                'profile_url' => $this->user?->username ? '/@'.$this->user->username : null,
                 'avatar_url' => $this->user?->profile?->avatar_url,
                 'level' => (int) ($this->user?->level ?? 1),
                 'rank' => (string) ($this->user?->rank ?? 'Newbie'),
@@ -258,20 +258,40 @@ class ArtworkResource extends JsonResource
             'maturity' => app(ArtworkMaturityService::class)->presentation($this->resource, $request->user()),
             'evolution' => app(ArtworkEvolutionService::class)->publicPayload($this->resource, $request->user()),
             'world_participation' => $this->resolveWorldParticipation(),
-            'categories' => $this->categories->map(fn ($category) => [
-                'id' => (int) $category->id,
-                'slug' => (string) $category->slug,
-                'name' => html_entity_decode((string) $category->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
-                'content_type_slug' => (string) ($category->contentType?->slug ?? ''),
-                'url' => $category->contentType ? $category->url : null,
-                'parent' => $category->parent ? [
-                    'id' => (int) $category->parent->id,
-                    'slug' => (string) $category->parent->slug,
-                    'name' => html_entity_decode((string) $category->parent->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
-                    'content_type_slug' => (string) ($category->parent->contentType?->slug ?? ''),
-                    'url' => $category->parent->contentType ? $category->parent->url : null,
-                ] : null,
-            ])->values(),
+            'category' => ($primary = $this->resolvedPrimaryCategory()) ? [
+                'id' => (int) $primary->id,
+                'slug' => (string) $primary->slug,
+                'name' => html_entity_decode((string) $primary->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                'content_type_slug' => (string) ($primary->contentType?->slug ?? ''),
+                'url' => $primary->contentType ? $primary->url : null,
+                'is_primary' => true,
+            ] : null,
+            'primary_category' => ($primary = $this->resolvedPrimaryCategory()) ? [
+                'id' => (int) $primary->id,
+                'slug' => (string) $primary->slug,
+                'name' => html_entity_decode((string) $primary->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                'content_type_slug' => (string) ($primary->contentType?->slug ?? ''),
+                'url' => $primary->contentType ? $primary->url : null,
+            ] : null,
+            'categories' => $this->categories->map(function ($category) {
+                $primaryId = (int) ($this->primary_category_id ?? 0);
+
+                return [
+                    'id' => (int) $category->id,
+                    'slug' => (string) $category->slug,
+                    'name' => html_entity_decode((string) $category->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                    'content_type_slug' => (string) ($category->contentType?->slug ?? ''),
+                    'url' => $category->contentType ? $category->url : null,
+                    'is_primary' => $primaryId > 0 && (int) $category->id === $primaryId,
+                    'parent' => $category->parent ? [
+                        'id' => (int) $category->parent->id,
+                        'slug' => (string) $category->parent->slug,
+                        'name' => html_entity_decode((string) $category->parent->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                        'content_type_slug' => (string) ($category->parent->contentType?->slug ?? ''),
+                        'url' => $category->parent->contentType ? $category->parent->url : null,
+                    ] : null,
+                ];
+            })->values(),
             'tags' => $this->tags->map(fn ($tag) => [
                 'id' => (int) $tag->id,
                 'slug' => (string) $tag->slug,
@@ -282,10 +302,6 @@ class ArtworkResource extends JsonResource
 
     private function resolveScreenshotAssets(): array
     {
-        if (! $this->hasTable('artwork_files')) {
-            return [];
-        }
-
         return DB::table('artwork_files')
             ->where('artwork_id', (int) $this->id)
             ->where('variant', 'like', 'shot%')
@@ -296,9 +312,9 @@ class ArtworkResource extends JsonResource
                 $url = $this->objectUrl($path);
 
                 return [
-                    'id' => (string) ($row->variant ?? ('shot' . ($index + 1))),
+                    'id' => (string) ($row->variant ?? ('shot'.($index + 1))),
                     'variant' => (string) ($row->variant ?? ''),
-                    'label' => 'Screenshot ' . ($index + 1),
+                    'label' => 'Screenshot '.($index + 1),
                     'url' => $url,
                     'thumb_url' => $url,
                     'mime_type' => (string) ($row->mime ?? 'image/jpeg'),
@@ -319,7 +335,7 @@ class ArtworkResource extends JsonResource
 
         $base = rtrim((string) config('cdn.files_url', 'https://files.skinbase.org'), '/');
 
-        return $base . '/' . $trimmedPath;
+        return $base.'/'.$trimmedPath;
     }
 
     private function renderDescriptionHtml(): string
@@ -342,73 +358,75 @@ class ArtworkResource extends JsonResource
         $items = collect();
         $participationWorlds = collect();
 
-        if ($this->hasTable('world_relations') && $this->hasTable('worlds')) {
-            $relations = WorldRelation::query()
-                ->with('world')
-                ->where('related_type', WorldRelation::TYPE_ARTWORK)
-                ->where('related_id', (int) $this->id)
-                ->get()
-                ->filter(fn (WorldRelation $relation): bool => $relation->world !== null && $relation->world->isPubliclyVisible())
-                ->values();
+        $relations = WorldRelation::query()
+            ->with('world')
+            ->where('related_type', WorldRelation::TYPE_ARTWORK)
+            ->where('related_id', (int) $this->id)
+            ->get()
+            ->filter(fn (WorldRelation $relation): bool => $relation->world !== null && $relation->world->isPubliclyVisible())
+            ->values();
 
-            $participationWorlds = $participationWorlds->concat($relations->pluck('world')->filter());
+        $participationWorlds = $participationWorlds->concat(
+            $relations->pluck('world')->filter()
+        );
 
-            $items = $items->concat(
-                $relations->map(function (WorldRelation $relation): array {
-                    $world = $relation->world;
+        $items = $items->concat(
+            $relations->map(function (WorldRelation $relation): array {
+                $world = $relation->world;
 
-                    return [
-                        'world_id' => (int) $relation->world_id,
-                        'world_title' => (string) $world->title,
-                        'world_slug' => (string) $world->slug,
-                        'world_url' => $world->publicUrl(),
-                        'badge_label' => 'Part of ' . $world->title,
-                        'status' => 'curated',
-                        'status_label' => 'Curated',
-                        'tone' => 'curated',
-                        'sort_priority' => 1,
-                    ];
-                })
-            );
-        }
+                return [
+                    'world_id' => (int) $relation->world_id,
+                    'world_title' => (string) $world->title,
+                    'world_slug' => (string) $world->slug,
+                    'world_url' => $world->publicUrl(),
+                    'badge_label' => 'Part of '.$world->title,
+                    'status' => 'curated',
+                    'status_label' => 'Curated',
+                    'tone' => 'curated',
+                    'sort_priority' => 1,
+                ];
+            })
+        );
 
-        if ($this->hasTable('world_submissions')) {
-            $liveSubmissions = $this->worldSubmissions
-                ->filter(function (WorldSubmission $submission): bool {
-                    return (string) $submission->status === WorldSubmission::STATUS_LIVE
-                        && $submission->world !== null
-                        && $submission->world->isPubliclyVisible();
-                })
-                ->values();
+        $liveSubmissions = $this->worldSubmissions
+            ->filter(function (WorldSubmission $submission): bool {
+                return (string) $submission->status === WorldSubmission::STATUS_LIVE
+                    && $submission->world !== null
+                    && $submission->world->isPubliclyVisible();
+            })
+            ->values();
 
-            $participationWorlds = $participationWorlds->concat($liveSubmissions->pluck('world')->filter());
-            World::primeCanonicalEditionIds($participationWorlds->pluck('recurrence_key')->all());
+        $participationWorlds = $participationWorlds->concat(
+            $liveSubmissions->pluck('world')->filter()
+        );
 
-            $items = $items->concat(
-                $liveSubmissions->map(function (WorldSubmission $submission): array {
-                    $world = $submission->world;
-                    $isFeatured = (bool) $submission->is_featured;
+        World::primeCanonicalEditionIds(
+            $participationWorlds->pluck('recurrence_key')->all()
+        );
 
-                    return [
-                        'world_id' => (int) $submission->world_id,
-                        'world_title' => (string) $world->title,
-                        'world_slug' => (string) $world->slug,
-                        'world_url' => $world->publicUrl(),
-                        'badge_label' => ($isFeatured ? 'Featured in ' : 'Part of ') . $world->title,
-                        'status' => (string) $submission->status,
-                        'status_label' => $isFeatured ? 'Featured' : 'Community submission',
-                        'tone' => $isFeatured ? 'featured' : 'community',
-                        'sort_priority' => $isFeatured ? 0 : 2,
-                    ];
-                })
-            );
-        } elseif ($participationWorlds->isNotEmpty()) {
-            World::primeCanonicalEditionIds($participationWorlds->pluck('recurrence_key')->all());
-        }
+        $items = $items->concat(
+            $liveSubmissions->map(function (WorldSubmission $submission): array {
+                $world = $submission->world;
+                $isFeatured = (bool) $submission->is_featured;
 
-        if ($this->hasTable('world_reward_grants')) {
-            $items = $items->concat(app(WorldRewardService::class)->artworkRewardBadges($this->resource));
-        }
+                return [
+                    'world_id' => (int) $submission->world_id,
+                    'world_title' => (string) $world->title,
+                    'world_slug' => (string) $world->slug,
+                    'world_url' => $world->publicUrl(),
+                    'badge_label' => ($isFeatured ? 'Featured in ' : 'Part of ').$world->title,
+                    'status' => (string) $submission->status,
+                    'status_label' => $isFeatured ? 'Featured' : 'Community submission',
+                    'tone' => $isFeatured ? 'featured' : 'community',
+                    'sort_priority' => $isFeatured ? 0 : 2,
+                ];
+            })
+        );
+
+        $items = $items->concat(
+            app(WorldRewardService::class)
+                ->artworkRewardBadges($this->resource)
+        );
 
         return $items
             ->sortBy('sort_priority')
diff --git a/app/Jobs/IngestUserDiscoveryEventJob.php b/app/Jobs/IngestUserDiscoveryEventJob.php
index 4b10207c..8dfe9b84 100644
--- a/app/Jobs/IngestUserDiscoveryEventJob.php
+++ b/app/Jobs/IngestUserDiscoveryEventJob.php
@@ -4,8 +4,8 @@ declare(strict_types=1);
 
 namespace App\Jobs;
 
-use App\Services\Recommendations\UserInterestProfileService;
 use App\Services\Recommendations\SessionRecoService;
+use App\Services\Recommendations\UserInterestProfileService;
 use Carbon\CarbonImmutable;
 use Illuminate\Bus\Queueable;
 use Illuminate\Contracts\Queue\ShouldQueue;
@@ -30,7 +30,7 @@ final class IngestUserDiscoveryEventJob implements ShouldQueue
     public array $backoff = [5, 30, 120];
 
     /**
-     * @param array<string, mixed> $meta
+     * @param  array<string, mixed>  $meta
      */
     public function __construct(
         public readonly string $eventId,
@@ -40,8 +40,7 @@ final class IngestUserDiscoveryEventJob implements ShouldQueue
         public readonly string $algoVersion,
         public readonly string $occurredAt,
         public readonly array $meta = []
-    ) {
-    }
+    ) {}
 
     public function handle(UserInterestProfileService $profileService, SessionRecoService $sessionRecoService): void
     {
@@ -70,10 +69,9 @@ final class IngestUserDiscoveryEventJob implements ShouldQueue
             $eventVersion = (string) config('discovery.event_version', 'event-v1');
             $eventWeight = (float) ((array) config('discovery.weights', []))[$this->eventType] ?? 1.0;
 
-            $categoryId = DB::table('artwork_category')
-                ->where('artwork_id', $this->artworkId)
-                ->orderBy('category_id')
-                ->value('category_id');
+            $categoryId = DB::table('artworks')
+                ->where('id', $this->artworkId)
+                ->value('primary_category_id');
 
             $insertPayload = [
                 'event_id' => $this->eventId,
diff --git a/app/Models/Artwork.php b/app/Models/Artwork.php
index 14227620..761d5f87 100644
--- a/app/Models/Artwork.php
+++ b/app/Models/Artwork.php
@@ -66,6 +66,9 @@ class Artwork extends Model
         'description',
         'file_name',
         'file_path',
+        'download_status',
+        'download_source',
+        'download_checked_at',
         'hash',
         'file_ext',
         'thumb_ext',
@@ -81,6 +84,10 @@ class Artwork extends Model
         'is_public',
         'visibility',
         'is_approved',
+        'approval_source',
+        'moderated_at',
+        'moderated_by',
+        'moderation_note',
         'is_mature',
         'maturity_level',
         'maturity_source',
@@ -117,6 +124,7 @@ class Artwork extends Model
         'description_source',
         'tags_source',
         'category_source',
+        'primary_category_id',
         // Versioning
         'current_version_id',
         'version_count',
@@ -132,6 +140,7 @@ class Artwork extends Model
         'is_public' => 'boolean',
         'visibility' => 'string',
         'is_approved' => 'boolean',
+        'moderated_at' => 'datetime',
         'is_mature' => 'boolean',
         'maturity_level' => 'string',
         'maturity_source' => 'string',
@@ -171,6 +180,7 @@ class Artwork extends Model
         'category_source' => 'string',
         'version_updated_at' => 'datetime',
         'requires_reapproval' => 'boolean',
+        'download_checked_at' => 'datetime',
     ];
 
     /**
@@ -449,6 +459,32 @@ class Artwork extends Model
         return $this->belongsToMany(Category::class, 'artwork_category', 'artwork_id', 'category_id');
     }
 
+    public function primaryCategory(): BelongsTo
+    {
+        return $this->belongsTo(Category::class, 'primary_category_id');
+    }
+
+    public function resolvedPrimaryCategory(): ?Category
+    {
+        if ($this->relationLoaded('primaryCategory') && $this->getRelation('primaryCategory') instanceof Category) {
+            return $this->getRelation('primaryCategory');
+        }
+
+        $primaryId = $this->primary_category_id !== null ? (int) $this->primary_category_id : 0;
+        if ($primaryId > 0 && $this->relationLoaded('categories')) {
+            $match = $this->categories->firstWhere('id', $primaryId);
+            if ($match instanceof Category) {
+                return $match;
+            }
+        }
+
+        if ($primaryId > 0) {
+            return $this->primaryCategory;
+        }
+
+        return null;
+    }
+
     public function collections(): BelongsToMany
     {
         return $this->belongsToMany(Collection::class, 'collection_artwork', 'artwork_id', 'collection_id')
@@ -559,19 +595,25 @@ class Artwork extends Model
      */
     public function toSearchableArray(): array
     {
-        $this->loadMissing(['user', 'group', 'tags', 'categories.contentType', 'stats', 'awardStat']);
+        $this->loadMissing(['user', 'group', 'tags', 'categories.contentType', 'primaryCategory.contentType', 'stats', 'awardStat']);
 
         $stat = $this->stats;
         $awardStat = $this->awardStat;
         $publishedSortAt = $this->published_at ?? $this->created_at;
-        $sortedCategories = $this->categories->sortBy(
-            fn ($category) => sprintf(
-                '%010d|%s|%010d',
-                (int) ($category->sort_order ?? 999999999),
-                strtolower((string) ($category->name ?? '')),
-                (int) ($category->id ?? 0)
-            )
-        )->values();
+        $primaryCategory = $this->resolvedPrimaryCategory();
+        $sortedCategories = $this->categories
+            ->sortBy(function ($category) use ($primaryCategory) {
+                $isPrimary = $primaryCategory && (int) $category->id === (int) $primaryCategory->id;
+
+                return sprintf(
+                    '%d|%010d|%s|%010d',
+                    $isPrimary ? 0 : 1,
+                    (int) ($category->sort_order ?? 999999999),
+                    strtolower((string) ($category->name ?? '')),
+                    (int) ($category->id ?? 0)
+                );
+            })
+            ->values();
 
         // Orientation derived from pixel dimensions
         $orientation = 'square';
@@ -588,8 +630,6 @@ class Artwork extends Model
             ? $this->width.'x'.$this->height
             : '';
 
-        // Primary category slug follows the same sort_order-first semantics used by page presenters.
-        $primaryCategory = $sortedCategories->first();
         $categorySlugs = $sortedCategories
             ->pluck('slug')
             ->filter()
@@ -619,6 +659,13 @@ class Artwork extends Model
             'author_name' => $this->group?->name ?? $this->user?->name ?? 'Skinbase',
             'published_as_type' => $this->publishedAsType(),
             'category' => $category,
+            'primary_category_id' => $primaryCategory?->id ? (int) $primaryCategory->id : null,
+            'category_ids' => $this->categories
+                ->pluck('id')
+                ->map(static fn ($id): int => (int) $id)
+                ->unique()
+                ->values()
+                ->all(),
             'categories' => $categorySlugs,
             'content_type' => $content_type,
             'content_types' => $contentTypeSlugs,
diff --git a/app/Models/Upload.php b/app/Models/Upload.php
index 96fcf494..8c4d0171 100644
--- a/app/Models/Upload.php
+++ b/app/Models/Upload.php
@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 class Upload extends Model
 {
@@ -23,6 +24,7 @@ class Upload extends Model
         'title',
         'slug',
         'category_id',
+        'secondary_category_ids',
         'description',
         'tags',
         'license',
@@ -41,6 +43,7 @@ class Upload extends Model
 
     protected $casts = [
         'tags' => 'array',
+        'secondary_category_ids' => 'array',
         'nsfw' => 'boolean',
         'is_scanned' => 'boolean',
         'has_tags' => 'boolean',
@@ -48,4 +51,14 @@ class Upload extends Model
         'expires_at' => 'datetime',
         'moderated_at' => 'datetime',
     ];
+
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function category(): BelongsTo
+    {
+        return $this->belongsTo(Category::class);
+    }
 }
diff --git a/app/Services/Artworks/ArtworkCategoryService.php b/app/Services/Artworks/ArtworkCategoryService.php
new file mode 100644
index 00000000..0cc39e20
--- /dev/null
+++ b/app/Services/Artworks/ArtworkCategoryService.php
@@ -0,0 +1,201 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\Artworks;
+
+use App\Models\Artwork;
+use App\Models\Category;
+use App\Services\ArtworkSearchIndexer;
+use App\Services\ArtworkService;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Validation\ValidationException;
+
+final class ArtworkCategoryService
+{
+    public function __construct(
+        private readonly ArtworkSearchIndexer $searchIndexer,
+        private readonly ArtworkService $artworkService,
+    ) {}
+
+    public function maxSecondary(): int
+    {
+        return max(0, (int) config('categories.max_secondary_categories', 5));
+    }
+
+    /**
+     * @param  list<int|string>|null  $secondaryCategoryIds  null keeps existing secondaries that remain compatible
+     */
+    public function sync(
+        Artwork $artwork,
+        ?int $primaryCategoryId,
+        ?array $secondaryCategoryIds = [],
+        ?string $source = null,
+        bool $reindex = true,
+    ): void {
+        $primaryCategoryId = $primaryCategoryId !== null && $primaryCategoryId > 0 ? $primaryCategoryId : null;
+        $secondaryCategoryIds = $secondaryCategoryIds === null
+            ? $this->existingSecondaryIds($artwork, $primaryCategoryId)
+            : $this->normalizeIds($secondaryCategoryIds);
+
+        if ($primaryCategoryId === null) {
+            if ($secondaryCategoryIds !== []) {
+                throw ValidationException::withMessages([
+                    'primary_category_id' => ['A primary category is required when additional categories are selected.'],
+                ]);
+            }
+
+            $this->persist($artwork, null, [], $source, $reindex);
+
+            return;
+        }
+
+        $secondaryCategoryIds = array_values(array_filter(
+            $secondaryCategoryIds,
+            static fn (int $id): bool => $id !== $primaryCategoryId,
+        ));
+
+        if (count($secondaryCategoryIds) > $this->maxSecondary()) {
+            throw ValidationException::withMessages([
+                'secondary_category_ids' => [sprintf('You can add at most %d additional categories.', $this->maxSecondary())],
+            ]);
+        }
+
+        $requestedIds = array_values(array_unique([$primaryCategoryId, ...$secondaryCategoryIds]));
+        $categories = Category::query()
+            ->whereIn('id', $requestedIds)
+            ->get()
+            ->keyBy('id');
+
+        if ($categories->count() !== count($requestedIds)) {
+            throw ValidationException::withMessages([
+                'primary_category_id' => ['One or more selected categories do not exist.'],
+            ]);
+        }
+
+        $primary = $categories->get($primaryCategoryId);
+        if (! $primary) {
+            throw ValidationException::withMessages([
+                'primary_category_id' => ['Choose a valid primary category.'],
+            ]);
+        }
+
+        if (! $primary->is_active) {
+            throw ValidationException::withMessages([
+                'primary_category_id' => ['The primary category is not available.'],
+            ]);
+        }
+
+        $contentTypeId = (int) $primary->content_type_id;
+
+        foreach ($secondaryCategoryIds as $secondaryId) {
+            $category = $categories->get($secondaryId);
+            if (! $category || ! $category->is_active) {
+                throw ValidationException::withMessages([
+                    'secondary_category_ids' => ['One or more additional categories are not available.'],
+                ]);
+            }
+
+            if ((int) $category->content_type_id !== $contentTypeId) {
+                throw ValidationException::withMessages([
+                    'secondary_category_ids' => ['Additional categories must belong to the same content type as the primary category.'],
+                ]);
+            }
+        }
+
+        $this->persist($artwork, $primaryCategoryId, $secondaryCategoryIds, $source, $reindex);
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function presentCategory(Category $category, bool $isPrimary): array
+    {
+        return [
+            'id' => (int) $category->id,
+            'name' => html_entity_decode((string) $category->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+            'slug' => (string) $category->slug,
+            'content_type_slug' => (string) ($category->contentType?->slug ?? ''),
+            'url' => $category->contentType ? $category->url : null,
+            'is_primary' => $isPrimary,
+            'parent' => $category->parent ? [
+                'id' => (int) $category->parent->id,
+                'slug' => (string) $category->parent->slug,
+                'name' => html_entity_decode((string) $category->parent->name, ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+                'content_type_slug' => (string) ($category->parent->contentType?->slug ?? ''),
+                'url' => $category->parent->contentType ? $category->parent->url : null,
+            ] : null,
+        ];
+    }
+
+    /**
+     * @param  list<int|string>  $ids
+     * @return list<int>
+     */
+    private function normalizeIds(array $ids): array
+    {
+        $normalized = [];
+
+        foreach ($ids as $id) {
+            $value = (int) $id;
+            if ($value > 0 && ! in_array($value, $normalized, true)) {
+                $normalized[] = $value;
+            }
+        }
+
+        return $normalized;
+    }
+
+    /**
+     * @return list<int>
+     */
+    private function existingSecondaryIds(Artwork $artwork, ?int $primaryCategoryId): array
+    {
+        return $artwork->categories()
+            ->pluck('categories.id')
+            ->map(static fn ($id): int => (int) $id)
+            ->reject(static fn (int $id): bool => $primaryCategoryId !== null && $id === $primaryCategoryId)
+            ->values()
+            ->all();
+    }
+
+    /**
+     * @param  list<int>  $secondaryCategoryIds
+     */
+    private function persist(
+        Artwork $artwork,
+        ?int $primaryCategoryId,
+        array $secondaryCategoryIds,
+        ?string $source,
+        bool $reindex,
+    ): void {
+        $membershipIds = $primaryCategoryId === null
+            ? []
+            : array_values(array_unique([$primaryCategoryId, ...$secondaryCategoryIds]));
+
+        DB::transaction(function () use ($artwork, $primaryCategoryId, $membershipIds, $source): void {
+            $artwork->categories()->sync($membershipIds);
+            $artwork->primary_category_id = $primaryCategoryId;
+
+            if ($source !== null) {
+                $artwork->category_source = $source;
+            }
+
+            $artwork->save();
+        });
+
+        $artwork->unsetRelation('categories');
+        $artwork->unsetRelation('primaryCategory');
+
+        if (! $reindex) {
+            return;
+        }
+
+        DB::afterCommit(function () use ($artwork): void {
+            $this->artworkService->clearArtworkCache($artwork->fresh() ?? $artwork);
+            Cache::forget('categories.directory.v1');
+            $this->searchIndexer->update($artwork);
+        });
+    }
+}
diff --git a/app/Services/Artworks/ArtworkDraftService.php b/app/Services/Artworks/ArtworkDraftService.php
index 4496d483..441c85dd 100644
--- a/app/Services/Artworks/ArtworkDraftService.php
+++ b/app/Services/Artworks/ArtworkDraftService.php
@@ -17,12 +17,16 @@ final class ArtworkDraftService
 {
     public function __construct(
         private readonly GroupService $groups,
+        private readonly ArtworkCategoryService $categories,
     ) {
     }
 
-    public function createDraft(User $user, string $title, ?string $description, ?int $categoryId = null, bool $isMature = false, string|int|null $groupIdentifier = null): ArtworkDraftResult
+    /**
+     * @param  list<int>  $secondaryCategoryIds
+     */
+    public function createDraft(User $user, string $title, ?string $description, ?int $categoryId = null, bool $isMature = false, string|int|null $groupIdentifier = null, array $secondaryCategoryIds = []): ArtworkDraftResult
     {
-        return DB::transaction(function () use ($user, $title, $description, $categoryId, $isMature, $groupIdentifier) {
+        return DB::transaction(function () use ($user, $title, $description, $categoryId, $isMature, $groupIdentifier, $secondaryCategoryIds) {
             $slug = $this->makeSlug($title);
             $group = $this->resolveGroup($user, $groupIdentifier);
 
@@ -50,9 +54,8 @@ final class ArtworkDraftService
                 'artwork_status' => 'draft',
             ]);
 
-            // Attach the selected category to the artwork pivot table
-            if ($categoryId !== null && \App\Models\Category::where('id', $categoryId)->exists()) {
-                $artwork->categories()->sync([$categoryId]);
+            if ($categoryId !== null || $secondaryCategoryIds !== []) {
+                $this->categories->sync($artwork, $categoryId, $secondaryCategoryIds, 'user', false);
             }
 
             if ($group) {
diff --git a/app/Services/CollectionAiCurationService.php b/app/Services/CollectionAiCurationService.php
index bc4cacee..1fdbe1a7 100644
--- a/app/Services/CollectionAiCurationService.php
+++ b/app/Services/CollectionAiCurationService.php
@@ -140,7 +140,7 @@ class CollectionAiCurationService
                 ->first();
 
             $label = $tag?->name
-                ?: ($artwork->categories->first()?->name)
+                ?: ($artwork->resolvedPrimaryCategory()?->name)
                 ?: ($artwork->stats?->views ? 'Popular highlights' : 'Curated picks');
 
             if (! isset($themeBuckets[$label])) {
@@ -673,7 +673,7 @@ class CollectionAiCurationService
         $artworks = $this->candidateArtworks($collection, $draft, 36);
         $themes = $this->topThemes($artworks);
         $categories = $artworks
-            ->map(fn (Artwork $artwork) => $artwork->categories->first()?->name)
+            ->map(fn (Artwork $artwork) => $artwork->resolvedPrimaryCategory()?->name)
             ->filter()
             ->countBy()
             ->sortDesc();
diff --git a/app/Services/CollectionLinkService.php b/app/Services/CollectionLinkService.php
index 44677a2c..1a09042b 100644
--- a/app/Services/CollectionLinkService.php
+++ b/app/Services/CollectionLinkService.php
@@ -95,7 +95,7 @@ class CollectionLinkService
                 'label' => (string) $artwork->title,
                 'description' => collect([
                     $artwork->user?->username ? '@' . strtolower((string) $artwork->user->username) : null,
-                    $artwork->categories->first()?->contentType?->name,
+                    $artwork->resolvedPrimaryCategory()?->contentType?->name,
                 ])->filter()->join(' • ') ?: 'Published artwork',
             ])
             ->values()
@@ -343,7 +343,7 @@ class CollectionLinkService
                 'title' => (string) $entity->title,
                 'subtitle' => collect([
                     $entity->user?->username ? '@' . strtolower((string) $entity->user->username) : null,
-                    $entity->categories->first()?->contentType?->name,
+                    $entity->resolvedPrimaryCategory()?->contentType?->name,
                 ])->filter()->join(' • ') ?: 'Artwork',
                 'description' => $link->relationship_type ?: 'Linked artwork',
                 'url' => route('art.show', [
diff --git a/app/Services/CollectionService.php b/app/Services/CollectionService.php
index c46edc07..8bfadc2b 100644
--- a/app/Services/CollectionService.php
+++ b/app/Services/CollectionService.php
@@ -861,6 +861,14 @@ class CollectionService
             ? $collections
             : new EloquentCollection(is_array($collections) ? $collections : iterator_to_array($collections));
 
+        // The profile producer already eager-loads these relations. Keep the
+        // mapper safe for direct callers as well, so the card loop never
+        // triggers relation lazy-loading one collection at a time.
+        $collectionList->loadMissing([
+            'user:id,username,name',
+            'coverArtwork:id,user_id,title,slug,hash,thumb_ext,published_at,is_public,is_approved,deleted_at',
+        ]);
+
         $collectionIds = $collectionList->pluck('id')->map(static fn ($id) => (int) $id)->all();
         $hideMatureCovers = ! $ownerView && $this->viewerShouldHideMature($viewer);
 
@@ -879,12 +887,16 @@ class CollectionService
                 ->all()
             : [];
 
-        return $collectionList->map(function (Collection $collection) use ($ownerView, $viewer, $firstArtworkMap, $savedCollectionIds) {
+        return $collectionList->map(function (Collection $collection) use ($ownerView, $viewer, $firstArtworkMap, $savedCollectionIds, $hideMatureCovers) {
+            // Manual collections have their explicit cover eager-loaded. The
+            // already bulk-loaded first artwork map is the exact fallback
+            // used by resolvedCoverArtwork() when that cover is absent or not
+            // visible, so no per-card relation query is needed here.
             $resolvedCover = $collection->isSmart()
                 ? $this->smartCollections->firstArtwork($collection, $ownerView)
-                : $collection->resolvedCoverArtwork(! $ownerView, ! $ownerView && $this->viewerShouldHideMature($viewer));
+                : ($collection->relationLoaded('coverArtwork') ? $collection->coverArtwork : null);
             $fallbackCover = $firstArtworkMap->get((int) $collection->id);
-            $cover = $this->eligibleCoverArtwork($resolvedCover, ! $ownerView, ! $ownerView && $this->viewerShouldHideMature($viewer))
+            $cover = $this->eligibleCoverArtwork($resolvedCover, ! $ownerView, $hideMatureCovers)
                 ? $resolvedCover
                 : $fallbackCover;
             $summary = $collection->summary ?? $collection->description;
@@ -1264,7 +1276,7 @@ class CollectionService
 
     private function mapArtworkPayload(Artwork $artwork, array $extra = []): array
     {
-        $category = $artwork->categories->first();
+        $category = $artwork->resolvedPrimaryCategory();
         $contentType = $category?->contentType;
         $stats = $artwork->stats;
 
diff --git a/app/Services/GroupArtworkReviewService.php b/app/Services/GroupArtworkReviewService.php
index 63eef26a..905ae010 100644
--- a/app/Services/GroupArtworkReviewService.php
+++ b/app/Services/GroupArtworkReviewService.php
@@ -10,6 +10,7 @@ use App\Models\Group;
 use App\Jobs\IndexArtworkJob;
 use App\Models\Tag;
 use App\Models\User;
+use App\Services\Artworks\ArtworkCategoryService;
 use Illuminate\Pagination\LengthAwarePaginator;
 use Illuminate\Support\Facades\DB;
 use Illuminate\Support\Facades\Log;
@@ -23,6 +24,7 @@ class GroupArtworkReviewService
         private readonly GroupHistoryService $history,
         private readonly NotificationService $notifications,
         private readonly GroupMembershipService $memberships,
+        private readonly ArtworkCategoryService $artworkCategories,
     ) {
     }
 
@@ -108,6 +110,10 @@ class GroupArtworkReviewService
             'group_reviewed_at' => now(),
             'group_review_notes' => $notes,
             'is_approved' => true,
+            'approval_source' => 'moderator',
+            'moderated_at' => now(),
+            'moderated_by' => $actor->id,
+            'moderation_note' => $notes,
             'artwork_status' => 'published',
             'published_at' => now(),
             'publish_at' => null,
@@ -363,9 +369,20 @@ class GroupArtworkReviewService
         $artwork->uploaded_by_user_id = $artwork->uploaded_by_user_id ?: (int) $actor->id;
         $artwork->primary_author_user_id = $artwork->primary_author_user_id ?: (int) $actor->id;
 
-        $categoryId = isset($validated['category']) ? (int) $validated['category'] : null;
-        if ($categoryId > 0 && Category::query()->where('id', $categoryId)->exists()) {
-            $artwork->categories()->sync([$categoryId]);
+        $categoryId = isset($validated['primary_category_id'])
+            ? (int) $validated['primary_category_id']
+            : (isset($validated['category']) ? (int) $validated['category'] : null);
+        $secondaryCategoryIds = array_key_exists('secondary_category_ids', $validated)
+            ? array_values(array_map('intval', (array) $validated['secondary_category_ids']))
+            : [];
+        if ($categoryId > 0) {
+            $this->artworkCategories->sync(
+                $artwork,
+                $categoryId,
+                $secondaryCategoryIds,
+                'user',
+                false,
+            );
         }
 
         if (array_key_exists('tags', $validated) && is_array($validated['tags'])) {
@@ -395,4 +412,4 @@ class GroupArtworkReviewService
     {
         IndexArtworkJob::dispatch((int) $artwork->id);
     }
-}
\ No newline at end of file
+}
diff --git a/app/Services/RSS/RSSFeedBuilder.php b/app/Services/RSS/RSSFeedBuilder.php
index df356c01..b3d80634 100644
--- a/app/Services/RSS/RSSFeedBuilder.php
+++ b/app/Services/RSS/RSSFeedBuilder.php
@@ -87,7 +87,7 @@ final class RSSFeedBuilder
 
         // Primary category from eagerly loaded relation (avoid N+1)
         $primaryCategory = ($artwork->relationLoaded('categories'))
-            ? $artwork->categories->first()
+            ? $artwork->resolvedPrimaryCategory()
             : null;
 
         // Build HTML description embedded in CDATA
diff --git a/app/Services/Studio/Providers/ArtworkStudioProvider.php b/app/Services/Studio/Providers/ArtworkStudioProvider.php
index 2f657c06..2cdf26a0 100644
--- a/app/Services/Studio/Providers/ArtworkStudioProvider.php
+++ b/app/Services/Studio/Providers/ArtworkStudioProvider.php
@@ -201,7 +201,7 @@ final class ArtworkStudioProvider implements CreatorStudioProvider
                 ? 'scheduled'
                 : ((bool) $artwork->is_public ? 'published' : 'draft'));
 
-        $category = $artwork->categories->first();
+        $category = $artwork->resolvedPrimaryCategory();
         $visibility = $artwork->visibility ?: ((bool) $artwork->is_public ? Artwork::VISIBILITY_PUBLIC : Artwork::VISIBILITY_PRIVATE);
 
         return [
diff --git a/app/Services/Studio/StudioAiAssistService.php b/app/Services/Studio/StudioAiAssistService.php
index 72723199..b664d73f 100644
--- a/app/Services/Studio/StudioAiAssistService.php
+++ b/app/Services/Studio/StudioAiAssistService.php
@@ -211,9 +211,13 @@ final class StudioAiAssistService
             }
 
             $categoryId = $this->resolveCategoryId($payload);
+            $secondaryCategoryIds = array_key_exists('secondary_category_ids', $payload)
+                ? array_values(array_map('intval', (array) $payload['secondary_category_ids']))
+                : null;
 
             if ($categoryId !== null) {
-                $artwork->categories()->sync([$categoryId]);
+                app(\App\Services\Artworks\ArtworkCategoryService::class)
+                    ->sync($artwork, $categoryId, $secondaryCategoryIds, 'ai_applied', false);
                 $artwork->category_source = 'ai_applied';
                 $updated = true;
                 $applied[] = 'category';
@@ -294,10 +298,10 @@ final class StudioAiAssistService
      */
     public function payloadFor(Artwork $artwork): array
     {
-        $artwork->loadMissing(['artworkAiAssist', 'tags', 'categories.contentType']);
+        $artwork->loadMissing(['artworkAiAssist', 'tags', 'categories.contentType', 'primaryCategory.contentType']);
         $assist = $artwork->artworkAiAssist;
 
-        $primaryCategory = $artwork->categories->first();
+        $primaryCategory = $artwork->resolvedPrimaryCategory();
 
         if (! $assist) {
             return [
@@ -515,6 +519,13 @@ final class StudioAiAssistService
             'description' => (string) ($artwork->description ?? ''),
             'tags' => $artwork->tags->pluck('slug')->values()->all(),
             'category_id' => $primaryCategory?->id,
+            'primary_category_id' => $primaryCategory?->id,
+            'secondary_category_ids' => $artwork->categories
+                ->reject(fn ($category): bool => (int) $category->id === (int) ($primaryCategory?->id ?? 0))
+                ->pluck('id')
+                ->map(fn ($id): int => (int) $id)
+                ->values()
+                ->all(),
             'content_type_id' => $primaryCategory?->contentType?->id,
             'sources' => [
                 'title' => $artwork->title_source ?: 'manual',
@@ -530,6 +541,10 @@ final class StudioAiAssistService
      */
     private function resolveCategoryId(array $payload): ?int
     {
+        if (isset($payload['primary_category_id']) && $payload['primary_category_id'] !== null) {
+            return (int) $payload['primary_category_id'];
+        }
+
         if (isset($payload['category_id']) && $payload['category_id'] !== null) {
             return (int) $payload['category_id'];
         }
diff --git a/app/Services/Studio/StudioAiCategoryMapper.php b/app/Services/Studio/StudioAiCategoryMapper.php
index e59053d2..ca400a0b 100644
--- a/app/Services/Studio/StudioAiCategoryMapper.php
+++ b/app/Services/Studio/StudioAiCategoryMapper.php
@@ -49,8 +49,9 @@ final class StudioAiCategoryMapper
                 $selectedCategory,
                 $this->confidenceForModel($categoryScores, $selectedCategory->id),
                 $categoryScores
-                    ->reject(fn (array $row): bool => (int) $row['model']->id === (int) $selectedCategory->id)
-                    ->take(3)
+                    ->reject(fn (array $row): bool => (int) $row['model']->id === (int) $selectedCategory->id
+                        || (int) $row['model']->content_type_id !== (int) $selectedCategory->content_type_id)
+                    ->take(max(0, (int) config('categories.max_secondary_categories', 5)))
                     ->map(fn (array $row): array => $this->serializeCategory($row['model'], $row['confidence']))
                     ->all()
             ) : null,
@@ -245,6 +246,7 @@ final class StudioAiCategoryMapper
             'root_category_id' => (int) $rootCategory->id,
             'sub_category_id' => $category->parent_id ? (int) $category->id : null,
             'alternatives' => array_values($alternatives),
+            'secondary_categories' => array_values($alternatives),
         ];
     }
 }
\ No newline at end of file
diff --git a/app/Services/Studio/StudioBulkActionService.php b/app/Services/Studio/StudioBulkActionService.php
index d0f6e99c..d2dc105f 100644
--- a/app/Services/Studio/StudioBulkActionService.php
+++ b/app/Services/Studio/StudioBulkActionService.php
@@ -117,7 +117,8 @@ final class StudioBulkActionService
             throw new \InvalidArgumentException('category_id required for change_category');
         }
 
-        $artwork->categories()->sync([(int) $params['category_id']]);
+        app(\App\Services\Artworks\ArtworkCategoryService::class)
+            ->sync($artwork, (int) $params['category_id'], [], 'moderator');
     }
 
     private function addTags(Artwork $artwork, array $params): void
diff --git a/app/Services/Worlds/WorldSubmissionService.php b/app/Services/Worlds/WorldSubmissionService.php
index 1089bbc8..c0bc46a5 100644
--- a/app/Services/Worlds/WorldSubmissionService.php
+++ b/app/Services/Worlds/WorldSubmissionService.php
@@ -608,7 +608,7 @@ final class WorldSubmissionService
                 'thumbnail_url' => $artwork->thumbUrl('md'),
                 'creator_name' => (string) ($artwork->user?->name ?: $artwork->user?->username ?: ''),
                 'meta' => array_values(array_filter([
-                    $artwork->categories->first()?->name,
+                    $artwork->resolvedPrimaryCategory()?->name,
                     $views > 0 ? number_format($views) . ' views' : null,
                     $artwork->visibility ? Str::headline((string) $artwork->visibility) : null,
                 ])),
diff --git a/config/categories.php b/config/categories.php
new file mode 100644
index 00000000..4bc00cac
--- /dev/null
+++ b/config/categories.php
@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+return [
+    'max_secondary_categories' => max(0, (int) env('CATEGORIES_MAX_SECONDARY', 5)),
+];
diff --git a/database/migrations/2026_09_20_140000_add_primary_category_support_to_artworks.php b/database/migrations/2026_09_20_140000_add_primary_category_support_to_artworks.php
new file mode 100644
index 00000000..f2434233
--- /dev/null
+++ b/database/migrations/2026_09_20_140000_add_primary_category_support_to_artworks.php
@@ -0,0 +1,46 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        if (Schema::hasTable('artworks') && ! Schema::hasColumn('artworks', 'primary_category_id')) {
+            Schema::table('artworks', function (Blueprint $table): void {
+                $table->unsignedBigInteger('primary_category_id')->nullable()->after('user_id');
+                $table->index('primary_category_id');
+                $table->foreign('primary_category_id')
+                    ->references('id')
+                    ->on('categories')
+                    ->nullOnDelete();
+            });
+        }
+
+        if (Schema::hasTable('uploads') && ! Schema::hasColumn('uploads', 'secondary_category_ids')) {
+            Schema::table('uploads', function (Blueprint $table): void {
+                $table->json('secondary_category_ids')->nullable()->after('category_id');
+            });
+        }
+    }
+
+    public function down(): void
+    {
+        if (Schema::hasTable('artworks') && Schema::hasColumn('artworks', 'primary_category_id')) {
+            Schema::table('artworks', function (Blueprint $table): void {
+                $table->dropForeign(['primary_category_id']);
+                $table->dropColumn('primary_category_id');
+            });
+        }
+
+        if (Schema::hasTable('uploads') && Schema::hasColumn('uploads', 'secondary_category_ids')) {
+            Schema::table('uploads', function (Blueprint $table): void {
+                $table->dropColumn('secondary_category_ids');
+            });
+        }
+    }
+};
diff --git a/docs/SkinbaseNova_SN-CAT-001_Multi-Category_Artwork.md b/docs/SkinbaseNova_SN-CAT-001_Multi-Category_Artwork.md
new file mode 100644
index 00000000..1b8ea8dc
--- /dev/null
+++ b/docs/SkinbaseNova_SN-CAT-001_Multi-Category_Artwork.md
@@ -0,0 +1,1152 @@
+# SkinbaseNova — Multi-Category Artwork Classification
+
+**Milestone:** SN-CAT-001  
+**Status:** Implemented  
+**Scope:** Categories, artwork classification, upload flow, Nova AI suggestions, API, SEO, migration, tests  
+**Date:** 2026-09-20
+
+---
+
+## 1. Objective
+
+Upgrade SkinbaseNova so that an artwork can belong to more than one **category** while preserving one unambiguous **primary category**.
+
+The final model must support:
+
+- exactly one content type per artwork;
+- one primary category where a category is required;
+- zero to five secondary categories by default;
+- all selected categories belonging to the same content type as the artwork;
+- existing canonical artwork URLs;
+- deterministic breadcrumbs and SEO;
+- category browsing through all memberships;
+- Nova AI category suggestions;
+- backward-compatible migration from the current single-category application behavior.
+
+This feature must not turn categories into tags. Categories remain a curated taxonomy with strong semantic meaning. Tags continue to provide fine-grained descriptors.
+
+---
+
+## 2. Current State
+
+The existing database is already partly prepared for multi-category artwork classification.
+
+### Relevant tables
+
+#### `categories`
+
+The category taxonomy contains, among other fields:
+
+- `id`
+- `content_type_id`
+- `parent_id`
+- `name`
+- `slug`
+
+The taxonomy is scoped by content type.
+
+A category slug can therefore exist under different content types, for example:
+
+- `Wallpapers / Landscape`
+- `Photography / Landscape`
+
+These are distinct category records.
+
+#### `artwork_category`
+
+The existing pivot table already models an artwork-to-category many-to-many relationship.
+
+Conceptually:
+
+```text
+artworks
+    ↕
+artwork_category
+    ↕
+categories
+```
+
+The composite primary key prevents duplicate memberships:
+
+```sql
+PRIMARY KEY (artwork_id, category_id)
+```
+
+The current schema contains a foreign key for `category_id -> categories.id`, but the implementation should verify whether a matching FK exists for:
+
+```text
+artwork_category.artwork_id -> artworks.id
+```
+
+If missing, it must be added with `ON DELETE CASCADE`.
+
+#### `uploads`
+
+The current upload staging model contains a single:
+
+```text
+uploads.category_id
+```
+
+This reflects the current application's single-category behavior and must be adapted.
+
+#### `artwork_ai_assists`
+
+The existing AI-assist structure contains:
+
+```text
+category_suggestions_json
+```
+
+This is already suitable for multiple ranked category suggestions and should be reused rather than replaced unless the current code proves otherwise.
+
+---
+
+## 3. Terminology
+
+Do not call categories "groups" in this implementation.
+
+Skinbase has separate concepts and terminology.
+
+Use:
+
+```text
+Content Type
+Category
+Primary Category
+Secondary Category
+Tag
+```
+
+Example:
+
+```text
+Artwork: Morning Coffee in Venice
+
+Content Type:
+  Wallpapers
+
+Primary Category:
+  Cityscape
+
+Secondary Categories:
+  Architecture
+  Travel
+
+Tags:
+  Venice
+  Italy
+  Grand Canal
+  coffee
+  sunrise
+  golden hour
+```
+
+---
+
+## 4. Product Rules
+
+### 4.1 Content type
+
+An artwork belongs to one content type.
+
+Examples:
+
+- Wallpapers
+- Photography
+- Digital Art
+- Skins
+
+Multi-category classification must not implicitly make one artwork belong to multiple content types.
+
+### 4.2 Primary category
+
+An artwork has at most one primary category.
+
+The primary category is used for:
+
+- breadcrumb generation;
+- primary classification in artwork UI;
+- default SEO/category context;
+- legacy single-category compatibility;
+- admin/editor display;
+- any place that requires one deterministic category.
+
+### 4.3 Secondary categories
+
+An artwork may have multiple secondary categories.
+
+Default application rule:
+
+```text
+1 primary category
+0–5 secondary categories
+```
+
+The exact maximum should be configurable rather than hard-coded throughout the application.
+
+Suggested config:
+
+```php
+'max_secondary_categories' => 5,
+```
+
+Per-content-type overrides may be introduced if the existing architecture already has an appropriate configuration mechanism.
+
+For example, the application may eventually choose stricter rules for skin formats than for wallpapers or photography.
+
+### 4.4 Same-content-type invariant
+
+Every selected category must belong to the same content type as the artwork.
+
+Valid:
+
+```text
+Content Type: Wallpapers
+
+Primary:
+  Wallpapers / Cityscape
+
+Secondary:
+  Wallpapers / Architecture
+  Wallpapers / Sci-Fi
+```
+
+Invalid:
+
+```text
+Content Type: Wallpapers
+
+Primary:
+  Wallpapers / Cityscape
+
+Secondary:
+  Photography / Landscape
+  Digital Art / 3D
+```
+
+This invariant must be enforced server-side.
+
+Never rely only on frontend filtering.
+
+### 4.5 Categories are not tags
+
+Do not permit arbitrary category spam.
+
+Categories are broad curated browse/classification signals.
+
+Tags remain the detailed semantic descriptors.
+
+A category must not be automatically created merely because an AI suggestion contains an unknown label.
+
+---
+
+## 5. Target Data Model
+
+### 5.1 `artworks.primary_category_id`
+
+Add a nullable primary category reference:
+
+```sql
+ALTER TABLE artworks
+    ADD COLUMN primary_category_id BIGINT UNSIGNED NULL;
+```
+
+Add an indexed FK to `categories.id`.
+
+Expected behavior:
+
+```text
+artworks.primary_category_id
+    -> categories.id
+```
+
+Recommended deletion behavior:
+
+- prefer `ON DELETE SET NULL` for `artworks.primary_category_id`;
+- category deletion logic should separately remove the pivot membership through the existing pivot FK/cascade behavior.
+
+The implementation must follow existing project migration conventions.
+
+### Why store the primary category on `artworks`?
+
+The pivot remains the canonical set of memberships, while `primary_category_id` gives the application a deterministic and efficient answer to:
+
+> Which category represents this artwork in a single-category context?
+
+This avoids ordering-dependent behavior such as:
+
+```php
+$artwork->categories->first()
+```
+
+which is not a valid definition of "primary".
+
+### 5.2 `artwork_category`
+
+Keep the existing many-to-many table.
+
+Add or verify:
+
+```text
+FK artwork_id -> artworks.id ON DELETE CASCADE
+FK category_id -> categories.id ON DELETE CASCADE
+```
+
+Retain the composite uniqueness:
+
+```text
+PRIMARY KEY (artwork_id, category_id)
+```
+
+Consider adding metadata if it is consistent with existing project conventions:
+
+```text
+source
+confidence
+created_at
+updated_at
+```
+
+Suggested semantics:
+
+```text
+source:
+  user
+  ai
+  moderator
+  system
+  migration
+```
+
+`confidence` should be nullable and should only have meaning for machine-generated or machine-assisted classification.
+
+Do not add unnecessary metadata if the current application already stores equivalent provenance elsewhere.
+
+### 5.3 Membership invariant
+
+If:
+
+```text
+artworks.primary_category_id = X
+```
+
+then the row:
+
+```text
+(artwork_id, X)
+```
+
+must exist in `artwork_category`.
+
+All writes must preserve this invariant.
+
+### 5.4 Legacy `category_source`
+
+If `artworks.category_source` currently describes the single selected category, do not remove it in the first deployment unless all usages have been audited.
+
+Prefer a staged migration:
+
+1. support the new model;
+2. migrate provenance to the new relation if appropriate;
+3. update all readers/writers;
+4. deprecate the legacy field;
+5. remove it only in a later cleanup migration.
+
+---
+
+## 6. Central Domain Service
+
+Do not distribute category synchronization logic across controllers, jobs and model observers.
+
+Create or extend one domain/service-layer entry point, for example:
+
+```php
+ArtworkCategoryService
+```
+
+Suggested operation:
+
+```php
+sync(
+    Artwork $artwork,
+    int $primaryCategoryId,
+    array $secondaryCategoryIds = [],
+    ?string $source = null
+): void
+```
+
+The exact class/signature should follow current SkinbaseNova architecture.
+
+### The service must
+
+1. load all requested categories;
+2. reject nonexistent IDs;
+3. remove duplicates;
+4. verify the primary category is included exactly once;
+5. validate the category content type against the artwork;
+6. enforce the configured secondary-category limit;
+7. update the pivot and `primary_category_id` in one DB transaction;
+8. preserve or update provenance metadata correctly;
+9. leave the artwork in a valid state if any operation fails;
+10. emit existing domain events/cache invalidation/search-index updates if required by the codebase.
+
+Controllers, upload finalization, admin editing, imports and AI acceptance should call this service rather than implementing their own sync behavior.
+
+---
+
+## 7. Eloquent Model Changes
+
+Audit the existing models before changing them.
+
+The final `Artwork` model should conceptually support:
+
+```php
+public function categories(): BelongsToMany
+{
+    return $this->belongsToMany(Category::class);
+}
+
+public function primaryCategory(): BelongsTo
+{
+    return $this->belongsTo(Category::class, 'primary_category_id');
+}
+```
+
+The exact pivot configuration must match the existing schema.
+
+Audit for problematic patterns such as:
+
+```php
+$artwork->categories()->first();
+$artwork->categories->first();
+sync([$categoryId]);
+firstOrFail();
+```
+
+where the code assumes there can only be one category.
+
+Replace such assumptions only where they are category-related; do not make unrelated refactors.
+
+---
+
+## 8. Upload Flow
+
+### 8.1 UX
+
+The upload/edit UI should present:
+
+```text
+Primary category
+[ single select ]
+
+Additional categories
+[ multi-select, max 3 ]
+```
+
+Requirements:
+
+- secondary selection excludes the primary category;
+- only categories from the selected content type are available;
+- changing content type must revalidate/clear incompatible selections;
+- duplicate selections are impossible;
+- the UI displays the configured maximum;
+- server validation remains authoritative.
+
+Suggested copy:
+
+```text
+Primary category
+Choose the category that best represents the artwork.
+
+Additional categories
+Optional. Add up to 5 other relevant categories.
+```
+
+### 8.2 Upload staging schema
+
+Audit how the current `uploads.category_id` is used before changing it.
+
+Preferred target model:
+
+```text
+uploads.primary_category_id
+```
+
+plus either:
+
+```text
+upload_category
+---------------
+upload_id
+category_id
+```
+
+or another existing staging mechanism that cleanly supports multiple category IDs.
+
+Do not introduce a second competing staging architecture if the project already has reusable draft metadata storage.
+
+### 8.3 Safe migration strategy
+
+A staged approach is acceptable:
+
+**Phase A**
+
+- existing `uploads.category_id` continues to mean primary category;
+- add secondary-category staging support;
+- update finalization to use the central category service.
+
+**Phase B**
+
+- rename/deprecate `uploads.category_id` to `primary_category_id` if appropriate;
+- remove compatibility code after all writers/readers are migrated.
+
+Prefer deployability and rollback safety over a large destructive migration.
+
+---
+
+## 9. Nova AI Category Suggestions
+
+Reuse the existing AI-assist category suggestion facility where possible.
+
+Suggested normalized suggestion payload:
+
+```json
+[
+  {
+    "category_id": 123,
+    "name": "Cityscape",
+    "confidence": 0.96
+  },
+  {
+    "category_id": 456,
+    "name": "Architecture",
+    "confidence": 0.89
+  }
+]
+```
+
+The implementation should prefer IDs from the known taxonomy rather than free-form names.
+
+### AI rules
+
+Nova may:
+
+- rank existing categories;
+- suggest a likely primary category;
+- suggest secondary categories;
+- show confidence where available.
+
+Nova must not:
+
+- create new categories automatically;
+- silently replace a user's confirmed primary category;
+- attach categories from another content type;
+- exceed the configured maximum.
+
+Initial rollout should require explicit user/editor confirmation for AI category changes.
+
+Future auto-accept behavior can be added separately after measuring accuracy.
+
+---
+
+## 10. API Contract
+
+Audit current endpoints and serializers/resources.
+
+The API should expose both the deterministic primary category and all category memberships.
+
+Conceptual response:
+
+```json
+{
+  "primary_category": {
+    "id": 10,
+    "name": "Cityscape",
+    "slug": "cityscape"
+  },
+  "categories": [
+    {
+      "id": 10,
+      "name": "Cityscape",
+      "slug": "cityscape",
+      "is_primary": true
+    },
+    {
+      "id": 12,
+      "name": "Architecture",
+      "slug": "architecture",
+      "is_primary": false
+    }
+  ]
+}
+```
+
+If the current public API has a singular legacy `category` property:
+
+- keep it backward-compatible;
+- map it to the primary category;
+- add the plural structure additively;
+- document deprecation only if the project intends to remove the singular field later.
+
+For create/update operations, prefer an explicit contract such as:
+
+```json
+{
+  "primary_category_id": 10,
+  "secondary_category_ids": [12, 18]
+}
+```
+
+This is clearer than relying on array order.
+
+---
+
+## 11. Category Pages and Browsing
+
+A category page such as:
+
+```text
+/wallpapers/cityscape
+```
+
+must include every artwork attached to that category, regardless of whether it is the artwork's primary or secondary category.
+
+Conceptually query through:
+
+```text
+artwork_category
+```
+
+not only:
+
+```text
+artworks.primary_category_id
+```
+
+This is the main discovery benefit of the feature.
+
+Review:
+
+- pagination;
+- category counts;
+- sorting;
+- cache keys;
+- search indexing;
+- sitemap generation;
+- related-artwork queries;
+- category statistics.
+
+Any category count that currently assumes one category per artwork must be audited.
+
+---
+
+## 12. Artwork Page, Breadcrumbs and SEO
+
+### 12.1 Canonical artwork URL
+
+Do not change the canonical artwork URL.
+
+Keep the current model:
+
+```text
+/art/{id}/{slug}
+```
+
+An artwork must not gain a different canonical URL for every category.
+
+### 12.2 Breadcrumb
+
+Use the primary category only.
+
+Example:
+
+```text
+Home
+→ Wallpapers
+→ Cityscape
+→ Morning Coffee in Venice
+```
+
+Do not select the breadcrumb category by pivot ordering.
+
+### 12.3 Category display
+
+Artwork UI may display:
+
+```text
+Category
+Cityscape
+
+Also in
+Architecture
+Travel
+```
+
+or a combined component where the primary category is visibly distinguished.
+
+### 12.4 Structured data
+
+If the project emits `BreadcrumbList` or other structured data:
+
+- use the primary category path;
+- preserve one stable breadcrumb path;
+- avoid multiple competing breadcrumb definitions for the same artwork.
+
+### 12.5 Internal links
+
+Secondary category links are beneficial discovery links, but they must all point to their normal category pages.
+
+All category pages must link back to the same canonical artwork URL.
+
+---
+
+## 13. Parent Categories
+
+The schema supports `categories.parent_id`.
+
+Do not automatically duplicate membership into ancestor categories unless the existing taxonomy explicitly requires this.
+
+Example:
+
+```text
+Nature
+└── Flowers
+```
+
+If the artwork is directly classified as:
+
+```text
+Flowers
+```
+
+store the direct membership once.
+
+If the `Nature` category page is intended to include descendants, compute or query descendant membership rather than writing redundant pivot rows.
+
+Audit current category hierarchy behavior before changing it.
+
+---
+
+## 14. Existing Data Migration
+
+The migration must not make arbitrary semantic choices silently.
+
+### 14.1 Preflight report
+
+Before backfilling `primary_category_id`, inspect current production data.
+
+Required report:
+
+```sql
+SELECT
+    artwork_id,
+    COUNT(*) AS category_count
+FROM artwork_category
+GROUP BY artwork_id
+HAVING COUNT(*) > 1
+ORDER BY category_count DESC;
+```
+
+Distribution:
+
+```sql
+SELECT
+    category_count,
+    COUNT(*) AS artworks
+FROM (
+    SELECT
+        artwork_id,
+        COUNT(*) AS category_count
+    FROM artwork_category
+    GROUP BY artwork_id
+) x
+GROUP BY category_count
+ORDER BY category_count;
+```
+
+Also report artworks with no category if category membership is expected for their content type.
+
+### 14.2 Backfill rules
+
+For artwork with exactly one category:
+
+```text
+primary_category_id = that category
+```
+
+For artwork with zero categories:
+
+```text
+primary_category_id = NULL
+```
+
+and include it in an audit report if the content type normally requires a category.
+
+For artwork with more than one category:
+
+- do not silently use `MIN(category_id)`, `first()` or database row order as semantic truth;
+- first inspect whether existing application data provides a deterministic primary source;
+- if no reliable source exists, produce an actionable report for explicit resolution.
+
+An Artisan command is preferred for migration/preflight because it can support dry-run and reporting.
+
+Suggested capabilities:
+
+```text
+--dry-run
+--report
+--apply
+```
+
+Follow the project's command naming conventions.
+
+### 14.3 Idempotency
+
+The migration/backfill process must be safe to run more than once.
+
+Never overwrite an already-confirmed primary category unless explicitly requested.
+
+---
+
+## 15. Database Integrity
+
+Verify/add appropriate indexes.
+
+At minimum:
+
+```text
+artworks.primary_category_id
+artwork_category (artwork_id, category_id) PK/unique
+artwork_category category lookup index if not already covered
+```
+
+Verify both pivot FKs.
+
+Application-level validation must enforce:
+
+- primary is a member of the pivot;
+- same content type;
+- category-count limit.
+
+If project conventions use database constraints or triggers for these invariants, evaluate them, but avoid introducing database-specific complexity without a strong reason.
+
+---
+
+## 16. Search and Recommendation Systems
+
+Audit all consumers of artwork categories.
+
+Potential consumers include:
+
+- full-text/search indexing;
+- Meilisearch/Elasticsearch/OpenSearch if present;
+- recommendation scoring;
+- related artworks;
+- Nova embeddings/classification;
+- feeds;
+- filters;
+- analytics;
+- category statistics.
+
+Suggested representation in a search document:
+
+```json
+{
+  "primary_category_id": 10,
+  "category_ids": [10, 12, 18]
+}
+```
+
+Recommendation systems may weight primary and secondary membership differently, for example:
+
+```text
+primary category: strong signal
+secondary category: medium signal
+tags: fine-grained signal
+embeddings: semantic similarity signal
+```
+
+Do not introduce arbitrary scoring changes in this milestone unless the existing recommendation architecture clearly needs them. Make the data available first.
+
+---
+
+## 17. Admin / Moderation
+
+Admin/editor UI should clearly show:
+
+```text
+Primary
+Secondary
+Source
+AI confidence
+```
+
+where those metadata exist.
+
+Editors must be able to:
+
+- replace the primary category;
+- add/remove secondary categories;
+- promote a secondary category to primary;
+- see incompatible selections rejected;
+- save everything transactionally.
+
+When promoting a secondary category to primary, the previous primary may remain as a secondary category unless the editor removes it.
+
+---
+
+## 18. Caching and Invalidation
+
+Audit cached data related to:
+
+- artwork detail;
+- category pages;
+- category artwork counts;
+- breadcrumbs;
+- related artwork;
+- search documents.
+
+Changing category membership must invalidate/rebuild all affected representations.
+
+A change from:
+
+```text
+Cityscape
+```
+
+to:
+
+```text
+Primary: Architecture
+Secondary: Cityscape
+```
+
+must invalidate both relevant category views as well as the artwork detail/breadcrumb cache.
+
+Use existing cache/event patterns rather than creating a parallel mechanism.
+
+---
+
+## 19. Authorization and Security
+
+The new fields must use the same authorization rules as the current category edit action.
+
+Do not allow users to assign:
+
+- inaccessible/private taxonomy entries;
+- disabled categories;
+- categories belonging to another content type;
+- more than the allowed maximum.
+
+Validate IDs server-side.
+
+Avoid mass-assignment of unvalidated category arrays.
+
+---
+
+## 20. Tests
+
+Add tests at the level appropriate to the current project.
+
+### Database / model
+
+- artwork can have multiple categories;
+- duplicate pivot membership is rejected/prevented;
+- deleting an artwork removes pivot rows;
+- deleting a category handles pivot rows and primary reference safely;
+- primary category relationship works.
+
+### Domain service
+
+- one primary only;
+- primary is always in the pivot;
+- secondary categories sync correctly;
+- duplicate IDs are normalized/rejected consistently;
+- category from another content type is rejected;
+- more than configured secondary categories is rejected;
+- transaction rolls back on failure;
+- source/confidence metadata is preserved if implemented.
+
+### API
+
+- legacy singular category still maps to primary where required;
+- plural categories are returned;
+- create/update accepts primary + secondaries;
+- invalid cross-content-type categories return validation errors;
+- maximum is enforced.
+
+### Upload
+
+- primary category selection works;
+- multiple secondary categories persist through staging/finalization;
+- changing content type invalidates incompatible categories;
+- upload finalization uses central domain service.
+
+### Category pages
+
+- artwork appears on its primary category page;
+- artwork also appears on secondary category pages;
+- pagination/counts do not duplicate the same artwork;
+- category URL behavior remains unchanged.
+
+### Artwork page / SEO
+
+- canonical artwork URL remains unchanged;
+- breadcrumb uses the primary category;
+- changing secondary categories does not change breadcrumb;
+- promoting a secondary category updates breadcrumb;
+- structured data uses the primary path.
+
+### AI assist
+
+- suggestions are limited to known categories;
+- suggestions are filtered to matching content type;
+- AI cannot exceed the maximum;
+- confirmed user selection is not silently overwritten.
+
+### Migration
+
+- zero-category artwork is handled;
+- one-category artwork is backfilled deterministically;
+- multi-category legacy artwork is reported instead of arbitrarily resolved;
+- rerunning backfill is idempotent.
+
+---
+
+## 21. Backward Compatibility
+
+This implementation must not break existing public artwork/category URLs.
+
+Do not change:
+
+```text
+/art/{id}/{slug}
+```
+
+Do not change existing category route structure merely for this feature.
+
+If legacy API/UI code expects a singular category, map that concept to:
+
+```text
+primary_category
+```
+
+during the compatibility period.
+
+Prefer additive schema/API changes first, cleanup later.
+
+---
+
+## 22. Observability / Audit
+
+During rollout, log or report:
+
+- artwork with no primary category where one is required;
+- primary category missing from pivot;
+- cross-content-type memberships;
+- artwork exceeding the configured category limit;
+- migration conflicts;
+- failed AI suggestion mappings.
+
+If the project already has health/audit commands, integrate with them rather than creating unnecessary infrastructure.
+
+---
+
+## 23. Rollout Plan
+
+### Phase 1 — Audit
+
+- inspect current code paths;
+- inspect current data distribution;
+- identify all single-category assumptions;
+- confirm missing/existing foreign keys;
+- confirm API compatibility requirements.
+
+### Phase 2 — Additive database changes
+
+- add `artworks.primary_category_id`;
+- add/verify pivot integrity;
+- add pivot metadata only if needed;
+- add upload staging support.
+
+### Phase 3 — Domain logic
+
+- centralize category sync;
+- update models;
+- update validation;
+- update events/cache/search integration.
+
+### Phase 4 — Backfill
+
+- run dry-run report;
+- automatically backfill artworks with exactly one category;
+- explicitly resolve any legacy multi-category conflicts;
+- verify invariants.
+
+### Phase 5 — UI/API
+
+- upload editor;
+- artwork editor/admin;
+- API resources;
+- artwork display;
+- category pages;
+- breadcrumb/SEO.
+
+### Phase 6 — Nova integration
+
+- reuse ranked category suggestions;
+- support primary + secondary acceptance;
+- preserve explicit user control.
+
+### Phase 7 — Cleanup
+
+Only after production verification:
+
+- remove obsolete single-category assumptions;
+- deprecate/remove legacy fields where safe;
+- update documentation.
+
+---
+
+## 24. Acceptance Criteria
+
+The milestone is complete only when all of the following are true:
+
+- [ ] One artwork can belong to multiple categories.
+- [ ] Exactly one selected category can be marked as primary.
+- [ ] Primary category is always present in `artwork_category`.
+- [ ] Secondary category limit is enforced server-side.
+- [ ] Cross-content-type category assignment is impossible.
+- [ ] Existing artwork URLs remain unchanged.
+- [ ] Breadcrumb uses only the primary category.
+- [ ] Artwork is discoverable through every assigned category page.
+- [ ] Category pages do not duplicate an artwork.
+- [ ] Existing single-category API behavior remains compatible where required.
+- [ ] Upload/edit flow supports primary + secondary categories.
+- [ ] Nova category suggestions work with the new model.
+- [ ] Existing data can be migrated without arbitrary silent primary selection.
+- [ ] Missing `artwork_category.artwork_id` FK is fixed if confirmed absent.
+- [ ] Cache/search/index consumers are updated.
+- [ ] Automated tests cover the new invariants.
+- [ ] No unrelated refactors are included.
+- [ ] Documentation reflects the final implementation.
+
+---
+
+## 25. Definition of Done
+
+Before declaring the milestone finished:
+
+1. run the complete relevant automated test suite;
+2. run lint/static analysis/type checks used by the repository;
+3. run the migration/backfill in dry-run mode against representative data;
+4. verify at least one artwork with one primary and two secondary categories;
+5. verify that the artwork appears on all three category pages;
+6. verify its canonical URL is unchanged;
+7. verify breadcrumb follows only the primary category;
+8. verify a cross-content-type assignment is rejected;
+9. verify category deletion/artwork deletion preserves DB integrity;
+10. document migration evidence, test results and any compatibility decisions.
+
+Do not mark the feature complete if the database supports multiple categories but any main write path still collapses them back to one.
diff --git a/resources/js/Pages/Studio/StudioArtworkEdit.jsx b/resources/js/Pages/Studio/StudioArtworkEdit.jsx
index b8a16a03..f585a6ac 100644
--- a/resources/js/Pages/Studio/StudioArtworkEdit.jsx
+++ b/resources/js/Pages/Studio/StudioArtworkEdit.jsx
@@ -301,6 +301,8 @@ export default function StudioArtworkEdit() {
   const [contentTypeId, setContentTypeId] = useState(artwork?.content_type_id || null)
   const [categoryId, setCategoryId] = useState(artwork?.parent_category_id || null)
   const [subCategoryId, setSubCategoryId] = useState(artwork?.sub_category_id || null)
+  const [secondaryCategoryIds, setSecondaryCategoryIds] = useState(() => (Array.isArray(artwork?.secondary_category_ids) ? artwork.secondary_category_ids.map(Number).filter((id) => Number.isFinite(id) && id > 0) : []))
+  const maxSecondaryCategories = Number(artwork?.max_secondary_categories) > 0 ? Number(artwork.max_secondary_categories) : 5
   const [title, setTitle] = useState(artwork?.title || '')
   const [description, setDescription] = useState(() => normalizeMarkdownLiteContent(artwork?.description || ''))
   const [tagSlugs, setTagSlugs] = useState(() => (artwork?.tags || []).map((t) => t.slug || t.name))
@@ -415,6 +417,22 @@ export default function StudioArtworkEdit() {
   const aiStatus = aiData?.status || artwork?.ai_status || 'not_analyzed'
   const aiSuggestedTags = useMemo(() => (aiData?.tag_suggestions || []).map((item) => item.tag).filter(Boolean), [aiData])
   const selectedLeafCategoryId = subCategoryId || categoryId || null
+  const additionalCategoryOptions = useMemo(() => {
+    const options = []
+    const seen = new Set()
+    for (const root of rootCategories) {
+      const items = [root, ...(root.children || [])]
+      for (const item of items) {
+        const id = Number(item.id)
+        if (!Number.isFinite(id) || id === Number(selectedLeafCategoryId) || seen.has(id)) {
+          continue
+        }
+        seen.add(id)
+        options.push(item)
+      }
+    }
+    return options.sort((a, b) => String(a.name || '').localeCompare(String(b.name || ''), undefined, { numeric: true, sensitivity: 'base' }))
+  }, [rootCategories, selectedLeafCategoryId])
   const visibilitySummary = publishMode === 'schedule'
     ? `Scheduled as ${visibilityLabel(visibility)}`
     : visibilityLabel(visibility)
@@ -469,6 +487,7 @@ export default function StudioArtworkEdit() {
     setContentTypeId(id)
     setCategoryId(null)
     setSubCategoryId(null)
+    setSecondaryCategoryIds([])
     setIsCategoryChooserOpen(true)
     setCategorySource((current) => nextSourceForManualEdit(current))
   }
@@ -476,12 +495,14 @@ export default function StudioArtworkEdit() {
   const handleCategoryChange = (id) => {
     setCategoryId(id)
     setSubCategoryId(null)
+    setSecondaryCategoryIds((current) => current.filter((value) => Number(value) !== Number(id)))
     setIsCategoryChooserOpen(false)
     setCategorySource((current) => nextSourceForManualEdit(current))
   }
 
   const handleSubCategoryChange = (id) => {
     setSubCategoryId(id)
+    setSecondaryCategoryIds((current) => current.filter((value) => Number(value) !== Number(id)))
     setCategorySource((current) => nextSourceForManualEdit(current))
   }
 
@@ -781,6 +802,8 @@ export default function StudioArtworkEdit() {
           : [],
         content_type_id: contentTypeId,
         category_id: selectedLeafCategoryId,
+        primary_category_id: selectedLeafCategoryId,
+        secondary_category_ids: secondaryCategoryIds.filter((id) => Number(id) !== Number(selectedLeafCategoryId)),
         tags: tagSlugs,
         title_source: titleSource,
         description_source: descriptionSource,
@@ -834,7 +857,7 @@ export default function StudioArtworkEdit() {
     } finally {
       setSaving(false)
     }
-  }, [title, description, visibility, publishMode, scheduledAt, userTimezone, groupSlug, primaryAuthorUserId, contributorUserIds, contributorCredits, contentTypeId, selectedLeafCategoryId, tagSlugs, titleSource, descriptionSource, tagsSource, categorySource, worldSubmissionOptions, evolutionTarget, evolutionRelationType, evolutionNote, artwork?.id, evolutionRelationTypes])
+  }, [title, description, visibility, publishMode, scheduledAt, userTimezone, groupSlug, primaryAuthorUserId, contributorUserIds, contributorCredits, contentTypeId, selectedLeafCategoryId, secondaryCategoryIds, tagSlugs, titleSource, descriptionSource, tagsSource, categorySource, worldSubmissionOptions, evolutionTarget, evolutionRelationType, evolutionNote, artwork?.id, evolutionRelationTypes])
 
   const handleFileReplace = async (file) => {
     if (!file) return
@@ -1448,7 +1471,45 @@ export default function StudioArtworkEdit() {
                   </div>
                 )}
 
-                {errors.category_id && <p className="mt-4 text-xs text-red-400">{errors.category_id[0]}</p>}
+                {(errors.category_id || errors.primary_category_id) && <p className="mt-4 text-xs text-red-400">{(errors.category_id || errors.primary_category_id)[0]}</p>}
+                {errors.secondary_category_ids && <p className="mt-2 text-xs text-red-400">{errors.secondary_category_ids[0]}</p>}
+
+                {selectedLeafCategoryId && additionalCategoryOptions.length > 0 && (
+                  <div className="mt-6 rounded-2xl border border-white/10 bg-white/[0.03] p-4">
+                    <div className="text-[11px] font-semibold uppercase tracking-[0.18em] text-slate-400">Additional categories</div>
+                    <p className="mt-2 text-sm text-slate-400">Optional. Add up to {maxSecondaryCategories} other categories from this content type. They appear on those category pages but do not change the artwork URL or breadcrumb.</p>
+                    <div className="mt-3 flex flex-wrap gap-2">
+                      {additionalCategoryOptions.map((option) => {
+                        const selected = secondaryCategoryIds.includes(Number(option.id))
+                        const atLimit = !selected && secondaryCategoryIds.length >= maxSecondaryCategories
+                        return (
+                          <button
+                            key={`secondary-${option.id}`}
+                            type="button"
+                            disabled={atLimit}
+                            onClick={() => {
+                              setSecondaryCategoryIds((current) => (
+                                selected
+                                  ? current.filter((id) => Number(id) !== Number(option.id))
+                                  : [...current, Number(option.id)]
+                              ))
+                              setCategorySource((current) => nextSourceForManualEdit(current))
+                            }}
+                            className={[
+                              'rounded-full border px-3 py-1.5 text-sm transition',
+                              selected
+                                ? 'border-sky-400/40 bg-sky-400/15 text-sky-100'
+                                : 'border-white/10 bg-white/[0.03] text-slate-300 hover:border-white/20 disabled:opacity-40',
+                            ].join(' ')}
+                            aria-pressed={selected}
+                          >
+                            {option.name}
+                          </button>
+                        )
+                      })}
+                    </div>
+                  </div>
+                )}
               </div>
             </div>
           </Section>
diff --git a/resources/js/Pages/Upload/Index.jsx b/resources/js/Pages/Upload/Index.jsx
index 58c087f4..378b2c0b 100644
--- a/resources/js/Pages/Upload/Index.jsx
+++ b/resources/js/Pages/Upload/Index.jsx
@@ -3,6 +3,7 @@ import { usePage } from '@inertiajs/react'
 import SeoHead from '../../components/seo/SeoHead'
 import TagInput from '../../components/tags/TagInput'
 import UploadWizard from '../../components/upload/UploadWizard'
+import UploadReviewNotice from '../../components/upload/UploadReviewNotice'
 import UploadDescriptionEditor from '../../components/upload/UploadDescriptionEditor'
 import Checkbox from '../../Components/ui/Checkbox'
 import { mapUploadErrorNotice, mapUploadResultNotice } from '../../lib/uploadNotices'
@@ -52,6 +53,7 @@ const initialState = {
     title: '',
     type: '',
     category: '',
+    additionalCategories: [],
     tags: '',
     description: '',
     isMature: false,
@@ -320,6 +322,8 @@ function useUploadMachine({ draftId = null, filesCdnUrl = '', chunkSize, chunkRe
       const res = await window.axios.post('/api/artworks', {
         title: state.metadata.title,
         category: state.metadata.category,
+        primary_category_id: state.metadata.category ? Number(state.metadata.category) : null,
+        secondary_category_ids: (state.metadata.additionalCategories || []).map((id) => Number(id)).filter((id) => Number.isFinite(id) && id > 0),
         tags: state.metadata.tags,
         description: state.metadata.description,
         is_mature: state.metadata.isMature,
@@ -671,6 +675,8 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
                   contributorOptionsByGroup={props?.contributor_options_by_group && typeof props.contributor_options_by_group === 'object' ? props.contributor_options_by_group : {}}
                   initialGroupSlug={props?.initial_group || ''}
                   currentUserId={props?.auth?.user?.id ?? null}
+                  maxSecondaryCategories={Number(props?.max_secondary_categories) > 0 ? Number(props.max_secondary_categories) : 5}
+                  requiresUploadReview={Boolean(props?.requires_upload_review)}
                 />
               </div>
             </div>
@@ -841,6 +847,7 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
         <div className="grid gap-8 lg:grid-cols-[1.1fr,0.9fr]">
           <div className="space-y-6">
               <SeoHead seo={{ title: pageTitle, description: pageDescription, robots: 'noindex, nofollow' }} />
+            <UploadReviewNotice visible={Boolean(props?.requires_upload_review)} />
             <div className="rounded-2xl border border-white/10 bg-white/5 p-6 shadow-[0_0_50px_rgba(59,130,246,0.15)]">
               <div className="flex items-center justify-between">
                 <h1 className="text-3xl font-semibold tracking-tight">Upload artwork</h1>
@@ -911,7 +918,7 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
                         <button
                           key={ct.id}
                           type="button"
-                          onClick={() => dispatch({ type: 'SET_METADATA', payload: { type: String(ct.id), category: '' } })}
+                          onClick={() => dispatch({ type: 'SET_METADATA', payload: { type: String(ct.id), category: '', additionalCategories: [] } })}
                           className={`group rounded-2xl border px-4 py-3 text-left transition ${active
                             ? 'border-emerald-400/60 bg-emerald-500/10 shadow-[0_0_25px_rgba(16,185,129,0.25)]'
                             : 'border-white/10 bg-white/5 hover:border-sky-400/40 hover:bg-white/10'}`}
@@ -981,11 +988,11 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
                             onClick={() => {
                               if (hasChildren) {
                                 setSelectedParentCategory(String(cat.id))
-                                dispatch({ type: 'SET_METADATA', payload: { category: '' } })
+                                dispatch({ type: 'SET_METADATA', payload: { category: '', additionalCategories: state.metadata.additionalCategories || [] } })
                                 return
                               }
                               setSelectedParentCategory(null)
-                              dispatch({ type: 'SET_METADATA', payload: { category: String(cat.id) } })
+                              dispatch({ type: 'SET_METADATA', payload: { category: String(cat.id), additionalCategories: (state.metadata.additionalCategories || []).filter((id) => String(id) !== String(cat.id)) } })
                             }}
                             className={`rounded-full border px-4 py-2 text-sm transition ${isSelected || isExpanded
                               ? 'border-purple-300/60 bg-purple-400/20 text-purple-100'
@@ -1019,7 +1026,7 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
                                   type="button"
                                   onClick={() => {
                                     // Select child but keep parent expanded so the panel remains visible
-                                    dispatch({ type: 'SET_METADATA', payload: { category: String(child.id) } })
+                                    dispatch({ type: 'SET_METADATA', payload: { category: String(child.id), additionalCategories: (state.metadata.additionalCategories || []).filter((id) => String(id) !== String(child.id)) } })
                                   }}
                                   className={`rounded-full border px-4 py-2 text-sm transition ${activeChild
                                     ? 'border-purple-300/60 bg-purple-400/20 text-purple-100'
@@ -1038,6 +1045,43 @@ export default function UploadPage({ draftId = null, filesCdnUrl = '', chunkSize
                 )}
               </div>
 
+              {selectedType && state.metadata.category ? (
+                <div className="mt-4 rounded-2xl border border-white/10 bg-white/5 p-4 sm:p-5">
+                  <div className="text-sm font-semibold text-white">Additional categories</div>
+                  <div className="mt-1 text-xs text-white/60">Optional. Add up to 5 other relevant categories from the same type. They will not change the artwork URL or breadcrumb.</div>
+                  <div className="mt-3 flex flex-wrap gap-2">
+                    {categoryOptions.flatMap((cat) => [cat, ...(Array.isArray(cat.children) ? cat.children : [])])
+                      .filter((cat, index, all) => all.findIndex((item) => String(item.id) === String(cat.id)) === index)
+                      .filter((cat) => String(cat.id) !== String(state.metadata.category))
+                      .sort((a, b) => String(a.name || '').localeCompare(String(b.name || ''), undefined, { numeric: true, sensitivity: 'base' }))
+                      .map((cat) => {
+                        const selected = (state.metadata.additionalCategories || []).map(String).includes(String(cat.id))
+                        const atLimit = !selected && (state.metadata.additionalCategories || []).length >= 5
+                        return (
+                          <button
+                            key={`extra-${cat.id}`}
+                            type="button"
+                            disabled={atLimit}
+                            onClick={() => {
+                              const current = (state.metadata.additionalCategories || []).map(String)
+                              const next = selected
+                                ? current.filter((id) => id !== String(cat.id))
+                                : [...current, String(cat.id)]
+                              dispatch({ type: 'SET_METADATA', payload: { additionalCategories: next } })
+                            }}
+                            className={`rounded-full border px-4 py-2 text-sm transition ${selected
+                              ? 'border-sky-300/60 bg-sky-400/20 text-sky-100'
+                              : 'border-white/10 bg-white/5 text-white/70 hover:border-sky-300/50 hover:bg-sky-400/10 disabled:opacity-40'}`}
+                            aria-pressed={selected}
+                          >
+                            {cat.name}
+                          </button>
+                        )
+                      })}
+                  </div>
+                </div>
+              ) : null}
+
               <div className="mt-4">
                 <span className="text-sm text-white/80">Tags</span>
                 <div className="mt-2">
diff --git a/resources/js/components/artwork/ArtworkTags.jsx b/resources/js/components/artwork/ArtworkTags.jsx
index c7845b68..81bfa51e 100644
--- a/resources/js/components/artwork/ArtworkTags.jsx
+++ b/resources/js/components/artwork/ArtworkTags.jsx
@@ -35,9 +35,10 @@ export default function ArtworkTags({ artwork }) {
         seen.add(category.id)
         categoryPills.push({
           key: `cat-${category.id}`,
-          label: category.name,
+          label: category.is_primary ? category.name : category.name,
           href: category.url || `/${category.content_type_slug}/${category.slug}`,
           isCategory: true,
+          isPrimary: Boolean(category.is_primary),
         })
       }
     }
diff --git a/resources/js/components/upload/UploadWizard.jsx b/resources/js/components/upload/UploadWizard.jsx
index 486ca201..9880d8e6 100644
--- a/resources/js/components/upload/UploadWizard.jsx
+++ b/resources/js/components/upload/UploadWizard.jsx
@@ -28,6 +28,7 @@ import {
   getContentTypeValue,
   getProcessingTransparencyLabel,
 } from '../../lib/uploadUtils'
+import UploadReviewNotice from './UploadReviewNotice'
 import { validateMarkdownLiteContent } from '../../utils/contentValidation'
 
 // ─── Wizard step config ───────────────────────────────────────────────────────
@@ -55,6 +56,7 @@ function createInitialMetadata(initialGroupSlug = '', currentUserId = null, cont
     isMature: false,
     rightsAccepted: false,
     contentType: '',
+    additionalCategoryIds: [],
     group: normalizedGroupSlug,
     primaryAuthorUserId: defaultPrimaryAuthor,
     contributorUserIds: [],
@@ -116,6 +118,8 @@ export default function UploadWizard({
   contributorOptionsByGroup = {},
   initialGroupSlug = '',
   currentUserId = null,
+  maxSecondaryCategories = 5,
+  requiresUploadReview = false,
 }) {
   const [notices, setNotices] = useState([])
   // ── UI state ──────────────────────────────────────────────────────────────
@@ -589,9 +593,18 @@ export default function UploadWizard({
           filteredCategoryTree={filteredCategoryTree}
           allRootCategoryOptions={allRootCategoryOptions}
           requiresSubCategory={requiresSubCategory}
-          onContentTypeChange={(value) => setMeta({ contentType: value, rootCategoryId: '', subCategoryId: '' })}
-          onRootCategoryChange={(rootId) => setMeta({ rootCategoryId: rootId, subCategoryId: '' })}
-          onSubCategoryChange={(subId) => setMeta({ subCategoryId: subId })}
+          maxSecondaryCategories={maxSecondaryCategories}
+          onContentTypeChange={(value) => setMeta({ contentType: value, rootCategoryId: '', subCategoryId: '', additionalCategoryIds: [] })}
+          onRootCategoryChange={(rootId) => setMeta({
+            rootCategoryId: rootId,
+            subCategoryId: '',
+            additionalCategoryIds: (metadata.additionalCategoryIds || []).filter((id) => String(id) !== String(rootId)),
+          })}
+          onSubCategoryChange={(subId) => setMeta({
+            subCategoryId: subId,
+            additionalCategoryIds: (metadata.additionalCategoryIds || []).filter((id) => String(id) !== String(subId)),
+          })}
+          onAdditionalCategoriesChange={(ids) => setMeta({ additionalCategoryIds: ids })}
           groupOptions={groupOptions}
           currentContributorOptions={currentContributorOptions}
           onGroupChange={(groupSlug) => setMeta({ group: groupSlug })}
@@ -743,6 +756,8 @@ export default function UploadWizard({
         </div>
       )}
 
+      <UploadReviewNotice visible={requiresUploadReview} />
+
       {/* Restored draft banner */}
       {showRestoredBanner && (
         <div className="rounded-2xl border border-sky-300/20 bg-sky-500/10 px-4 py-3 text-sm text-sky-100 shadow-[0_14px_44px_rgba(14,165,233,0.10)]">
diff --git a/resources/js/components/upload/__tests__/UploadWizard.test.jsx b/resources/js/components/upload/__tests__/UploadWizard.test.jsx
index f1a4e46a..30640dab 100644
--- a/resources/js/components/upload/__tests__/UploadWizard.test.jsx
+++ b/resources/js/components/upload/__tests__/UploadWizard.test.jsx
@@ -347,6 +347,30 @@ describe('UploadWizard step flow', () => {
     expect(window.axios.post).not.toHaveBeenCalledWith('/api/uploads/session-1/publish', expect.anything(), expect.anything())
   })
 
+  it('shows additional categories alphabetically after the primary path is chosen', async () => {
+    installAxiosStubs({ statusValue: 'ready' })
+    await renderWizard({
+      initialDraftId: 318,
+      contentTypes: [{
+        id: 1,
+        name: 'Art',
+        categories: [
+          { id: 10, name: 'Root', children: [{ id: 11, name: 'Sub' }, { id: 14, name: 'Zebra' }] },
+          { id: 12, name: 'Apple', children: [{ id: 13, name: 'City' }] },
+        ],
+      }],
+    })
+
+    await completeStep1ToReady()
+    expect(await screen.findByText(/artwork details/i)).not.toBeNull()
+    await completeRequiredDetails({ title: 'My Art' })
+
+    const extraHeading = await screen.findByText(/additional categories/i)
+    const extraSection = extraHeading.closest('div')?.parentElement
+    const extraNames = Array.from(extraSection?.querySelectorAll('button') || []).map((button) => button.textContent?.trim())
+    expect(extraNames).toEqual(['Apple', 'City', 'Root', 'Zebra'])
+  })
+
   it('hides the mature content checkbox in the details step', async () => {
     installAxiosStubs({ statusValue: 'ready' })
     await renderWizard({ initialDraftId: 311, contentTypes: [{ id: 1, name: 'Art', categories: [{ id: 10, name: 'Root', children: [{ id: 11, name: 'Sub' }] }] }] })
diff --git a/resources/js/components/upload/steps/Step2Details.jsx b/resources/js/components/upload/steps/Step2Details.jsx
index ffc4c9d3..b67e7665 100644
--- a/resources/js/components/upload/steps/Step2Details.jsx
+++ b/resources/js/components/upload/steps/Step2Details.jsx
@@ -2,7 +2,7 @@ import React, { useEffect, useMemo, useState } from 'react'
 import ArchiveScreenshotPicker from '../ArchiveScreenshotPicker'
 import UploadSidebar from '../UploadSidebar'
 import { NovaSelect } from '../../ui'
-import { getContentTypeValue, getContentTypeVisualKey } from '../../../lib/uploadUtils'
+import { additionalCategoryOptions, getContentTypeValue, getContentTypeVisualKey } from '../../../lib/uploadUtils'
 
 /**
  * Step2Details
@@ -31,6 +31,8 @@ export default function Step2Details({
   onContentTypeChange,
   onRootCategoryChange,
   onSubCategoryChange,
+  onAdditionalCategoriesChange,
+  maxSecondaryCategories = 5,
   groupOptions,
   currentContributorOptions,
   onGroupChange,
@@ -100,6 +102,16 @@ export default function Step2Details({
     const q = subCategorySearch.trim().toLowerCase()
     return q ? sorted.filter((s) => s.name.toLowerCase().includes(q)) : sorted
   }, [subCategories, subCategorySearch])
+
+  const selectedLeafCategoryId = metadata.subCategoryId || (!requiresSubCategory ? metadata.rootCategoryId : '')
+  const extraCategoryOptions = useMemo(
+    () => additionalCategoryOptions(filteredCategoryTree, selectedLeafCategoryId),
+    [filteredCategoryTree, selectedLeafCategoryId]
+  )
+  const selectedAdditionalIds = useMemo(
+    () => (Array.isArray(metadata.additionalCategoryIds) ? metadata.additionalCategoryIds.map(String) : []),
+    [metadata.additionalCategoryIds]
+  )
   const contributorCredits = metadata.contributorCredits || {}
 
   useEffect(() => {
@@ -475,6 +487,50 @@ export default function Step2Details({
             <span className="font-medium text-slate-300">{selectedRoot.name}</span> has no subcategories — selecting it is enough.
           </div>
         )}
+
+        {selectedLeafCategoryId && extraCategoryOptions.length > 0 && (
+          <>
+            <div className="my-5 border-t border-white/8" />
+            <div>
+              <div className="mb-2 flex items-center justify-between gap-2">
+                <p className="text-[11px] font-semibold uppercase tracking-[0.16em] text-slate-500">Additional categories</p>
+                <span className="text-[11px] text-slate-600">{selectedAdditionalIds.length}/{maxSecondaryCategories}</span>
+              </div>
+              <p className="mb-3 text-sm text-slate-400">Optional. Add up to {maxSecondaryCategories} other categories from this content type. They appear on those category pages but do not change the artwork URL or breadcrumb.</p>
+              <div className="flex flex-wrap gap-2">
+                {extraCategoryOptions.map((option) => {
+                  const selected = selectedAdditionalIds.includes(String(option.id))
+                  const atLimit = !selected && selectedAdditionalIds.length >= maxSecondaryCategories
+                  return (
+                    <button
+                      key={`extra-${option.id}`}
+                      type="button"
+                      disabled={atLimit}
+                      onClick={() => {
+                        const next = selected
+                          ? selectedAdditionalIds.filter((id) => id !== String(option.id))
+                          : [...selectedAdditionalIds, String(option.id)]
+                        onAdditionalCategoriesChange?.(next)
+                      }}
+                      className={[
+                        'rounded-full border px-3 py-1.5 text-sm transition',
+                        selected
+                          ? 'border-sky-400/40 bg-sky-400/15 text-sky-100'
+                          : 'border-white/10 bg-white/[0.04] text-slate-300 hover:border-white/20 hover:bg-white/[0.08] disabled:cursor-not-allowed disabled:opacity-40',
+                      ].join(' ')}
+                      aria-pressed={selected}
+                    >
+                      {option.name}
+                    </button>
+                  )
+                })}
+              </div>
+              {metadataErrors.secondary_category_ids && (
+                <p className="mt-3 text-xs text-red-300">{metadataErrors.secondary_category_ids}</p>
+              )}
+            </div>
+          </>
+        )}
       </section>
 
       {Array.isArray(groupOptions) && groupOptions.length > 0 && (
diff --git a/resources/js/components/upload/steps/Step3Publish.jsx b/resources/js/components/upload/steps/Step3Publish.jsx
index 259c5181..ab063ae8 100644
--- a/resources/js/components/upload/steps/Step3Publish.jsx
+++ b/resources/js/components/upload/steps/Step3Publish.jsx
@@ -169,6 +169,9 @@ export default function Step3Publish({
               {subLabel && (
                 <span>Sub: <span className="text-white/75">{subLabel}</span></span>
               )}
+              {(metadata.additionalCategoryIds || []).length > 0 && (
+                <span>Also in: <span className="text-white/75">{metadata.additionalCategoryIds.length}</span></span>
+              )}
             </div>
 
             <div className="flex flex-wrap gap-x-4 gap-y-1 text-xs text-white/55">
diff --git a/resources/js/hooks/upload/useUploadMachine.js b/resources/js/hooks/upload/useUploadMachine.js
index 4474eea0..1fecd317 100644
--- a/resources/js/hooks/upload/useUploadMachine.js
+++ b/resources/js/hooks/upload/useUploadMachine.js
@@ -374,10 +374,17 @@ export default function useUploadMachine({
           String(titleSourceFile?.name || '').replace(/\.[^.]+$/, '') ||
           'Untitled upload'
 
+        const draftCategoryId = metadata.subCategoryId || metadata.rootCategoryId || null
+        const draftSecondaryIds = (Array.isArray(metadata.additionalCategoryIds) ? metadata.additionalCategoryIds : [])
+          .map((id) => Number(id))
+          .filter((id) => Number.isFinite(id) && id > 0 && String(id) !== String(draftCategoryId || ''))
+
         const draftResponse = await window.axios.post('/api/artworks', {
           title: derivedTitle,
           description: String(metadata.description || '').trim() || null,
-          category: metadata.subCategoryId || metadata.rootCategoryId || null,
+          category: draftCategoryId,
+          primary_category_id: draftCategoryId ? Number(draftCategoryId) : null,
+          secondary_category_ids: draftSecondaryIds,
           tags: Array.isArray(metadata.tags) ? metadata.tags.join(', ') : '',
           license: Boolean(metadata.rightsAccepted),
           is_mature: Boolean(metadata.isMature),
@@ -560,11 +567,16 @@ export default function useUploadMachine({
     const { mode = 'now', publishAt = null, timezone = null, visibility = 'public', action = 'publish' } = opts
 
     const resolvedCategoryId = metadata.subCategoryId || metadata.rootCategoryId || null
+    const secondaryCategoryIds = (Array.isArray(metadata.additionalCategoryIds) ? metadata.additionalCategoryIds : [])
+      .map((id) => Number(id))
+      .filter((id) => Number.isFinite(id) && id > 0 && String(id) !== String(resolvedCategoryId || ''))
 
     const buildPayload = () => ({
       title: String(metadata.title || '').trim() || undefined,
       description: String(metadata.description || '').trim() || null,
       category: resolvedCategoryId ? String(resolvedCategoryId) : null,
+      primary_category_id: resolvedCategoryId ? Number(resolvedCategoryId) : null,
+      secondary_category_ids: secondaryCategoryIds,
       tags: Array.isArray(metadata.tags) ? metadata.tags : [],
       is_mature: Boolean(metadata.isMature),
       group: String(metadata.group || '').trim() || null,
diff --git a/resources/js/lib/uploadUtils.additionalCategories.test.js b/resources/js/lib/uploadUtils.additionalCategories.test.js
new file mode 100644
index 00000000..614fc795
--- /dev/null
+++ b/resources/js/lib/uploadUtils.additionalCategories.test.js
@@ -0,0 +1,14 @@
+import { describe, expect, it } from 'vitest'
+import { additionalCategoryOptions } from './uploadUtils'
+
+describe('additionalCategoryOptions', () => {
+  it('excludes the primary leaf and sorts remaining names alphabetically', () => {
+    const options = additionalCategoryOptions([
+      { id: '10', name: 'Zebra', children: [{ id: '11', name: 'Moon' }] },
+      { id: '12', name: 'Apple', children: [{ id: '13', name: 'City' }] },
+    ], '11')
+
+    expect(options.map((option) => option.name)).toEqual(['Apple', 'City', 'Zebra'])
+    expect(options.map((option) => option.id)).not.toContain('11')
+  })
+})
diff --git a/resources/js/lib/uploadUtils.js b/resources/js/lib/uploadUtils.js
index 5f5f10d8..140f39e0 100644
--- a/resources/js/lib/uploadUtils.js
+++ b/resources/js/lib/uploadUtils.js
@@ -103,6 +103,33 @@ export function buildCategoryTree(contentTypes = []) {
   return Array.from(rootsById.values())
 }
 
+export function compareCategoryNames(a, b) {
+  return String(a?.name || '').localeCompare(String(b?.name || ''), undefined, {
+    numeric: true,
+    sensitivity: 'base',
+  })
+}
+
+export function additionalCategoryOptions(roots = [], primaryId = '') {
+  const options = []
+  const seen = new Set()
+  const primary = String(primaryId || '')
+
+  roots.forEach((root) => {
+    const items = [root, ...(Array.isArray(root.children) ? root.children : [])]
+    items.forEach((item) => {
+      const id = String(item?.id || '')
+      if (!id || id === primary || seen.has(id)) {
+        return
+      }
+      seen.add(id)
+      options.push({ id, name: item.name || `Category ${id}` })
+    })
+  })
+
+  return options.sort(compareCategoryNames)
+}
+
 // ─── Content type helpers ─────────────────────────────────────────────────────
 export function getContentTypeValue(type) {
   if (!type) return ''
diff --git a/tests/Feature/ArtworkSearchDocumentTest.php b/tests/Feature/ArtworkSearchDocumentTest.php
index 4d513094..55796f7c 100644
--- a/tests/Feature/ArtworkSearchDocumentTest.php
+++ b/tests/Feature/ArtworkSearchDocumentTest.php
@@ -13,7 +13,6 @@ function createSearchDocumentContentType(string $name, int $sortOrder = 0): int
         'description' => null,
         'created_at' => now(),
         'updated_at' => now(),
-        'sort_order' => $sortOrder,
     ]);
 }
 
@@ -48,14 +47,17 @@ it('indexes all attached categories and content types while preserving a primary
     $mattePaintingId = createSearchDocumentCategory($digitalArtId, 'Matte Painting', 20);
 
     $artwork->categories()->sync([$mattePaintingId, $fantasyId]);
+    $artwork->forceFill(['primary_category_id' => $fantasyId])->save();
 
-    $payload = $artwork->fresh(['categories.contentType'])->toSearchableArray();
+    $payload = $artwork->fresh(['categories.contentType', 'primaryCategory.contentType'])->toSearchableArray();
     $fantasySlug = (string) DB::table('categories')->where('id', $fantasyId)->value('slug');
     $mattePaintingSlug = (string) DB::table('categories')->where('id', $mattePaintingId)->value('slug');
     $wallpapersSlug = (string) DB::table('content_types')->where('id', $wallpapersId)->value('slug');
     $digitalArtSlug = (string) DB::table('content_types')->where('id', $digitalArtId)->value('slug');
 
     expect($payload['category'])->toBe($fantasySlug)
+        ->and($payload['primary_category_id'])->toBe($fantasyId)
+        ->and($payload['category_ids'])->toEqualCanonicalizing([$fantasyId, $mattePaintingId])
         ->and($payload['content_type'])->toBe($wallpapersSlug)
         ->and($payload['categories'])->toBe([$fantasySlug, $mattePaintingSlug])
         ->and($payload['content_types'])->toBe([$wallpapersSlug, $digitalArtSlug]);
diff --git a/tests/Feature/Artworks/ArtworkCategoryClassificationTest.php b/tests/Feature/Artworks/ArtworkCategoryClassificationTest.php
new file mode 100644
index 00000000..edd98867
--- /dev/null
+++ b/tests/Feature/Artworks/ArtworkCategoryClassificationTest.php
@@ -0,0 +1,284 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\Artwork;
+use App\Models\Category;
+use App\Models\ContentType;
+use App\Models\User;
+use App\Services\Artworks\ArtworkCategoryService;
+use App\Services\ArtworkService;
+use App\Services\Studio\StudioAiAssistService;
+use App\Services\Studio\StudioAiCategoryMapper;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Validation\ValidationException;
+use Inertia\Testing\AssertableInertia as Assert;
+
+use function Pest\Laravel\artisan;
+
+uses(RefreshDatabase::class);
+
+function snCatContentType(string $name = 'Wallpapers'): ContentType
+{
+    return ContentType::query()->create([
+        'name' => $name,
+        'slug' => strtolower($name).'-'.uniqid(),
+        'description' => $name,
+    ]);
+}
+
+function snCatCategory(ContentType $type, string $name, ?Category $parent = null): Category
+{
+    return Category::query()->create([
+        'content_type_id' => $type->id,
+        'parent_id' => $parent?->id,
+        'name' => $name,
+        'slug' => strtolower($name).'-'.uniqid(),
+        'description' => $name,
+        'is_active' => true,
+        'sort_order' => 0,
+    ]);
+}
+
+it('syncs a deterministic primary category into the pivot and rejects invalid combinations', function (): void {
+    $user = User::factory()->create();
+    $wallpapers = snCatContentType('Wallpapers');
+    $photography = snCatContentType('Photography');
+    $cityscape = snCatCategory($wallpapers, 'Cityscape');
+    $architecture = snCatCategory($wallpapers, 'Architecture');
+    $travel = snCatCategory($wallpapers, 'Travel');
+    $night = snCatCategory($wallpapers, 'Night');
+    $weather = snCatCategory($wallpapers, 'Weather');
+    $interior = snCatCategory($wallpapers, 'Interior');
+    $abstract = snCatCategory($wallpapers, 'Abstract');
+    $landscape = snCatCategory($photography, 'Landscape');
+    $artwork = Artwork::factory()->for($user)->create();
+
+    $service = app(ArtworkCategoryService::class);
+    $service->sync($artwork, $cityscape->id, [$architecture->id, $travel->id, $cityscape->id], 'user', false);
+
+    $artwork->refresh()->load('categories');
+
+    expect($artwork->primary_category_id)->toBe($cityscape->id)
+        ->and($artwork->categories->pluck('id')->sort()->values()->all())
+        ->toEqualCanonicalizing([$cityscape->id, $architecture->id, $travel->id])
+        ->and($artwork->resolvedPrimaryCategory()?->id)->toBe($cityscape->id);
+
+    $service->sync($artwork, $cityscape->id, [$architecture->id, $travel->id, $night->id, $weather->id, $interior->id], 'user', false);
+    expect($artwork->fresh()->categories()->count())->toBe(6);
+
+    expect(fn () => $service->sync($artwork, $cityscape->id, [$architecture->id, $travel->id, $night->id, $weather->id, $interior->id, $abstract->id], 'user', false))
+        ->toThrow(ValidationException::class);
+
+    expect(fn () => $service->sync($artwork, $cityscape->id, [$landscape->id], 'user', false))
+        ->toThrow(ValidationException::class);
+
+    $artwork->refresh();
+    expect($artwork->primary_category_id)->toBe($cityscape->id)
+        ->and($artwork->categories()->count())->toBe(6);
+});
+
+it('rolls back invalid category writes and keeps the previous membership', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $primary = snCatCategory($type, 'Primary');
+    $secondary = snCatCategory($type, 'Secondary');
+    $otherType = snCatContentType('Photography');
+    $invalid = snCatCategory($otherType, 'Invalid');
+    $artwork = Artwork::factory()->for($user)->create();
+    $service = app(ArtworkCategoryService::class);
+
+    $service->sync($artwork, $primary->id, [$secondary->id], 'user', false);
+
+    try {
+        $service->sync($artwork, $primary->id, [$invalid->id], 'user', false);
+        expect(false)->toBeTrue();
+    } catch (ValidationException) {
+        // expected
+    }
+
+    $artwork->refresh()->load('categories');
+    expect($artwork->primary_category_id)->toBe($primary->id)
+        ->and($artwork->categories->pluck('id')->all())->toEqualCanonicalizing([$primary->id, $secondary->id]);
+});
+
+it('promotes a secondary category to primary without dropping the previous primary', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $cityscape = snCatCategory($type, 'Cityscape');
+    $architecture = snCatCategory($type, 'Architecture');
+    $artwork = Artwork::factory()->for($user)->create();
+    $service = app(ArtworkCategoryService::class);
+
+    $service->sync($artwork, $cityscape->id, [$architecture->id], 'user', false);
+    $service->sync($artwork, $architecture->id, [$cityscape->id], 'user', false);
+
+    $artwork->refresh();
+    expect($artwork->primary_category_id)->toBe($architecture->id)
+        ->and($artwork->categories()->pluck('categories.id')->all())->toEqualCanonicalizing([$architecture->id, $cityscape->id]);
+});
+
+it('exposes primary category compatibly on the artwork API and category pages', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType('Wallpapers');
+    $cityscape = snCatCategory($type, 'Cityscape');
+    $architecture = snCatCategory($type, 'Architecture');
+    $artwork = Artwork::factory()->for($user)->create([
+        'is_public' => true,
+        'is_approved' => true,
+        'published_at' => now()->subMinute(),
+        'slug' => 'morning-coffee',
+        'title' => 'Morning Coffee',
+    ]);
+    app(ArtworkCategoryService::class)->sync($artwork, $cityscape->id, [$architecture->id], 'user', false);
+
+    $this->get(route('art.show', ['id' => $artwork->id, 'slug' => $artwork->slug]))
+        ->assertOk()
+        ->assertInertia(fn (Assert $page) => $page
+            ->component('ArtworkPage')
+            ->where('artwork.canonical_url', route('art.show', ['id' => $artwork->id, 'slug' => $artwork->slug]))
+            ->where('artwork.category.id', $cityscape->id)
+            ->where('artwork.primary_category.id', $cityscape->id)
+            ->where('artwork.categories.0.is_primary', true)
+            ->where('seo.json_ld', function ($schemas): bool {
+                $json = json_encode($schemas, JSON_UNESCAPED_SLASHES);
+
+                return str_contains($json, '"@type":"BreadcrumbList"')
+                    && str_contains($json, '"name":"Cityscape"')
+                    && ! str_contains($json, '"name":"Architecture"');
+            }));
+
+    $cityPage = app(ArtworkService::class)->getArtworksByCategoryPath([$type->slug, $cityscape->slug], 24);
+    $archPage = app(ArtworkService::class)->getArtworksByCategoryPath([$type->slug, $architecture->slug], 24);
+
+    expect($cityPage->pluck('id')->all())->toContain($artwork->id)
+        ->and($archPage->pluck('id')->all())->toContain($artwork->id)
+        ->and($cityPage->pluck('id')->filter(fn ($id) => (int) $id === (int) $artwork->id)->count())->toBe(1);
+});
+
+it('finalizes upload staging through the central category service', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $primary = snCatCategory($type, 'Cityscape');
+    $secondary = snCatCategory($type, 'Architecture');
+
+    $this->actingAs($user)
+        ->postJson('/api/artworks', [
+            'title' => 'Staged artwork',
+            'category' => $primary->id,
+            'secondary_category_ids' => [$secondary->id],
+            'description' => 'A valid description for the draft.',
+        ])
+        ->assertCreated();
+
+    $artwork = Artwork::query()->latest('id')->first();
+    expect($artwork?->primary_category_id)->toBe($primary->id)
+        ->and($artwork?->categories()->pluck('categories.id')->all())->toEqualCanonicalizing([$primary->id, $secondary->id]);
+});
+
+it('updates studio artwork categories with an explicit primary and secondary contract', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $primary = snCatCategory($type, 'Cityscape');
+    $secondary = snCatCategory($type, 'Architecture');
+    $promoted = snCatCategory($type, 'Travel');
+    $artwork = Artwork::factory()->for($user)->create([
+        'user_id' => $user->id,
+        'is_public' => false,
+        'visibility' => Artwork::VISIBILITY_PRIVATE,
+    ]);
+    app(ArtworkCategoryService::class)->sync($artwork, $primary->id, [$secondary->id], 'user', false);
+
+    $this->actingAs($user)
+        ->putJson('/api/studio/artworks/'.$artwork->id, [
+            'primary_category_id' => $promoted->id,
+            'secondary_category_ids' => [$primary->id],
+        ])
+        ->assertOk()
+        ->assertJsonPath('artwork.primary_category_id', $promoted->id)
+        ->assertJsonPath('artwork.category_id', $promoted->id);
+
+    $artwork->refresh();
+    expect($artwork->primary_category_id)->toBe($promoted->id)
+        ->and($artwork->categories()->pluck('categories.id')->all())->toEqualCanonicalizing([$promoted->id, $primary->id]);
+});
+
+it('does not let nova overwrite a confirmed primary unless the editor applies a category', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $confirmed = snCatCategory($type, 'Cityscape');
+    $suggested = snCatCategory($type, 'Architecture');
+    $artwork = Artwork::factory()->for($user)->create();
+    app(ArtworkCategoryService::class)->sync($artwork, $confirmed->id, [], 'manual', false);
+
+    $mapper = app(StudioAiCategoryMapper::class);
+    $payload = $mapper->map(['architecture', 'building'], $confirmed);
+
+    expect(count($payload['category']['secondary_categories'] ?? []))->toBeLessThanOrEqual((int) config('categories.max_secondary_categories', 5));
+    if (! empty($payload['category']['content_type_id'])) {
+        expect($payload['category']['content_type_id'])->toBe($type->id);
+    }
+
+    app(StudioAiAssistService::class)->applySuggestions($artwork->fresh(['tags', 'categories.contentType']), [
+        'title' => 'Keep my category',
+    ]);
+
+    expect($artwork->fresh()->primary_category_id)->toBe($confirmed->id);
+
+    app(StudioAiAssistService::class)->applySuggestions($artwork->fresh(['tags', 'categories.contentType']), [
+        'category_id' => $suggested->id,
+        'secondary_category_ids' => [$confirmed->id],
+    ]);
+
+    expect($artwork->fresh()->primary_category_id)->toBe($suggested->id);
+});
+
+it('backfills only unique memberships and stays idempotent', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $one = snCatCategory($type, 'One');
+    $two = snCatCategory($type, 'Two');
+    $single = Artwork::factory()->for($user)->create();
+    $conflict = Artwork::factory()->for($user)->create();
+    $empty = Artwork::factory()->for($user)->create();
+
+    $single->categories()->sync([$one->id]);
+    $conflict->categories()->sync([$one->id, $two->id]);
+
+    artisan('artworks:backfill-primary-category', ['--report' => true])
+        ->assertSuccessful()
+        ->expectsOutputToContain('Dry run only');
+
+    expect($single->fresh()->primary_category_id)->toBeNull()
+        ->and($conflict->fresh()->primary_category_id)->toBeNull();
+
+    artisan('artworks:backfill-primary-category', ['--apply' => true, '--report' => true])
+        ->assertSuccessful();
+
+    expect($single->fresh()->primary_category_id)->toBe($one->id)
+        ->and($conflict->fresh()->primary_category_id)->toBeNull()
+        ->and($empty->fresh()->primary_category_id)->toBeNull();
+
+    $single->forceFill(['primary_category_id' => $two->id])->save();
+    artisan('artworks:backfill-primary-category', ['--apply' => true])
+        ->assertSuccessful();
+    expect($single->fresh()->primary_category_id)->toBe($two->id);
+});
+
+it('clears the primary category reference when a category is deleted and cascades artwork deletion', function (): void {
+    $user = User::factory()->create();
+    $type = snCatContentType();
+    $category = snCatCategory($type, 'Temporary');
+    $artwork = Artwork::factory()->for($user)->create();
+    app(ArtworkCategoryService::class)->sync($artwork, $category->id, [], 'user', false);
+
+    $category->forceDelete();
+    expect($artwork->fresh()->primary_category_id)->toBeNull()
+        ->and(DB::table('artwork_category')->where('artwork_id', $artwork->id)->count())->toBe(0);
+
+    $other = snCatCategory($type, 'Kept');
+    app(ArtworkCategoryService::class)->sync($artwork->fresh(), $other->id, [], 'user', false);
+    $artwork->forceDelete();
+    expect(DB::table('artwork_category')->where('artwork_id', $artwork->id)->count())->toBe(0);
+});