Allow artworks to have one primary category and extra secondaries.

Keep artwork_category as membership, store a deterministic primary_category_id, and let upload plus studio pick up to five additional same-type categories without changing canonical URLs.

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'];
         }