db: fix infinite RLS recursion on users table causing admin lockout

shop/supabase/migrations/20260709231500_fix_users_rls_recursion.sql

@@ -0,0 +1,22 @@
+-- Migration: Fix Users RLS Recursion and Admin Lockout
+-- Purpose: Implement a security definer function to check admin status, avoiding infinite recursion on public.users.
+
+-- 1. Create helper function to check admin role bypassing RLS (SECURITY DEFINER)
+CREATE OR REPLACE FUNCTION public.is_admin(user_id UUID)
+RETURNS BOOLEAN AS $$
+BEGIN
+    RETURN EXISTS (
+        SELECT 1 FROM public.users
+        WHERE id = user_id AND role = 'admin'
+    );
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;
+
+-- 2. Drop the recursive policy on public.users
+DROP POLICY IF EXISTS select_all_users_for_admin ON public.users;
+
+-- 3. Re-create the policy using the non-recursive helper function
+CREATE POLICY select_all_users_for_admin ON public.users
+    FOR SELECT
+    TO authenticated
+    USING (public.is_admin(auth.uid()));