fix(db): add atomic collection creation RPC path with migration script

db/atomic_create_collection_with_owner.sql

@@ -0,0 +1,48 @@
+-- Atomic collection creation + owner membership insert
+-- Run this in Supabase SQL Editor.
+
+create or replace function public.create_collection_with_owner(
+  p_name text,
+  p_description text default null
+)
+returns public.collections
+language plpgsql
+security definer
+set search_path = public
+as $$
+declare
+  v_user_id uuid := auth.uid();
+  v_collection public.collections;
+begin
+  if v_user_id is null then
+    raise exception 'Not authenticated';
+  end if;
+
+  insert into public.collections (
+    name,
+    owner_id,
+    description
+  )
+  values (
+    p_name,
+    v_user_id,
+    nullif(trim(p_description), '')
+  )
+  returning * into v_collection;
+
+  insert into public.collection_members (
+    collection_id,
+    user_id,
+    role
+  )
+  values (
+    v_collection.id,
+    v_user_id,
+    'owner'
+  );
+
+  return v_collection;
+end;
+$$;
+
+grant execute on function public.create_collection_with_owner(text, text) to authenticated;

lib/services/collection_service.dart

@@ -263,13 +263,57 @@ class CollectionService {
   }) async {
     final userId = _requireUserId();
 
+    final trimmedDescription = description?.trim();
+    final normalizedDescription =
+        (trimmedDescription != null && trimmedDescription.isNotEmpty)
+            ? trimmedDescription
+            : null;
+
+    try {
+      final rpcResult = await supabase.rpc(
+        'create_collection_with_owner',
+        params: {
+          'p_name': name,
+          'p_description': normalizedDescription,
+        },
+      );
+
+      final row = rpcResult is List
+          ? (rpcResult.isNotEmpty
+              ? rpcResult.first as Map<String, dynamic>
+              : <String, dynamic>{})
+          : rpcResult as Map<String, dynamic>;
+
+      if (row.isNotEmpty) {
+        return Collection(
+          id: row['id'] as String,
+          name: row['name'] as String,
+          description: row['description'] as String?,
+          ownerId: row['owner_id'] as String,
+          createdAt: DateTime.parse(row['created_at'] as String),
+          role: 'owner',
+          itemCount: 0,
+          memberCount: 1,
+        );
+      }
+    } catch (e) {
+      final message = e.toString();
+      final rpcUnavailable = message.contains('create_collection_with_owner') &&
+          (message.contains('not found') ||
+              message.contains('does not exist') ||
+              message.contains('PGRST202'));
+      if (!rpcUnavailable) {
+        rethrow;
+      }
+      debugPrint('CollectionService.create RPC unavailable, using fallback: $e');
+    }
+
     final row = await supabase
         .from('collections')
         .insert({
           'name': name,
           'owner_id': userId,
-          if (description != null && description.isNotEmpty)
-            'description': description,
+          'description': normalizedDescription,
         })
         .select()
         .single();