Validate and deduplicate custom difficulty presets

supabase/migrations/20261016064302_fix_difficulty_preset_names.sql

@@ -0,0 +1,32 @@
+-- The original U& expression doubled its Unicode escapes, so the regex
+-- interpreted code-point text as a character range and rejected normal names.
+alter table public.difficulty_presets
+  drop constraint difficulty_presets_name_check;
+alter table public.difficulty_presets
+  add constraint difficulty_presets_name_check check (
+    name = btrim(name)
+    and length(name) between 2 and 40
+    and name !~ U&'[\0001-\001F\007F-\009F\202A-\202E\2066-\2069]'
+  );
+
+-- A PL/pgSQL CASE without ELSE raises case_not_found for every saved UUID,
+-- before reaching the custom-preset lookup below it.
+create or replace function public.resolve_difficulty_preset(p_id text)
+returns jsonb language plpgsql stable security invoker set search_path = '' as $$
+declare preset jsonb;
+begin
+  case p_id
+    when 'easy' then
+      return jsonb_build_object('id', 'easy', 'name', 'Easy', 'seconds', 180, 'zoom', true);
+    when 'normal' then
+      return jsonb_build_object('id', 'normal', 'name', 'Normal', 'seconds', 90, 'zoom', true);
+    when 'hard' then
+      return jsonb_build_object('id', 'hard', 'name', 'Hard', 'seconds', 30, 'zoom', false);
+    else null;
+  end case;
+  select jsonb_build_object('id', p.id::text, 'name', p.name, 'seconds', p.seconds, 'zoom', p.zoom)
+  into preset from public.difficulty_presets p where p.id::text = lower(p_id);
+  if not found then raise exception 'Choose a saved difficulty'; end if;
+  return preset;
+end;
+$$;