fix: add rpc-backed member removal migration

VIEWER_ROLE_MIGRATION.sql

@@ -1,7 +1,64 @@
--- Run this in Supabase SQL Editor to allow a read-only viewer role.
+-- Run in Supabase SQL Editor.
+-- 1) Allow viewer role
 alter table public.collection_members
   drop constraint if exists collection_members_role_check;
 
 alter table public.collection_members
   add constraint collection_members_role_check
   check (role in ('owner', 'member', 'viewer'));
+
+-- 2) Ensure owners can delete members from their collections
+--    (and users can still remove themselves for leave flow).
+drop policy if exists "Owner can remove members" on public.collection_members;
+
+create policy "Owner can remove members"
+on public.collection_members
+for delete
+to authenticated
+using (
+  collection_id in (
+    select c.id
+    from public.collections c
+    where c.owner_id = auth.uid()
+  )
+  or user_id = auth.uid()
+);
+
+-- 3) Stable, policy-safe removal RPC for app use
+create or replace function public.remove_collection_member(
+  p_collection_id uuid,
+  p_member_user_id uuid
+)
+returns void
+language plpgsql
+security definer
+set search_path = public
+as $$
+declare
+  v_owner_id uuid;
+begin
+  select c.owner_id
+    into v_owner_id
+  from public.collections c
+  where c.id = p_collection_id;
+
+  if v_owner_id is null then
+    raise exception 'Collection not found.';
+  end if;
+
+  if v_owner_id <> auth.uid() then
+    raise exception 'Only the collection owner can remove members.';
+  end if;
+
+  if p_member_user_id = v_owner_id then
+    raise exception 'Collection owner cannot be removed.';
+  end if;
+
+  delete from public.collection_members cm
+  where cm.collection_id = p_collection_id
+    and cm.user_id = p_member_user_id
+    and cm.role <> 'owner';
+end;
+$$;
+
+grant execute on function public.remove_collection_member(uuid, uuid) to authenticated;

lib/services/collection_service.dart

@@ -386,17 +386,43 @@ class CollectionService {
       throw Exception('Collection owner cannot be removed.');
     }
 
-    await supabase
-        .from('collection_members')
-        .delete()
-      .eq('collection_id', collectionId)
-        .eq('user_id', memberUserId);
+    var deleted = false;
+    try {
+      await supabase.rpc('remove_collection_member', params: {
+        'p_collection_id': collectionId,
+        'p_member_user_id': memberUserId,
+      });
+      deleted = true;
+    } catch (e) {
+      final message = e.toString();
+      final rpcUnavailable = message.contains('remove_collection_member') &&
+          (message.contains('not found') ||
+              message.contains('does not exist') ||
+              message.contains('PGRST202'));
+
+      if (!rpcUnavailable) {
+        rethrow;
+      }
+
+      await supabase
+          .from('collection_members')
+          .delete()
+          .eq('collection_id', collectionId)
+          .eq('user_id', memberUserId);
+      deleted = true;
+    }
+
+    if (!deleted) {
+      throw Exception('Member removal failed.');
+    }
 
     final membersAfter = await getMembers(collectionId);
     final stillExists =
         membersAfter.any((member) => member.userId == memberUserId);
     if (stillExists) {
-      throw Exception('Member removal did not persist. Please check RLS delete policy.');
+      throw Exception(
+        'Member removal did not persist. Run VIEWER_ROLE_MIGRATION.sql to update policies/functions.',
+      );
     }
   }