Fixing Supabase Row-Level Security Errors in Lovable and Bolt Apps

Apps built with Lovable or Bolt on Supabase often hit Postgres error 42501 when inserting rows, or see empty results when reading, because Row Level Security is blocking the action. These failures typically occur when RLS is enabled without a matching policy, the user is not logged in so auth.uid() is null, user_id is missing or mismatched, or an update policy lacks a with check clause. Reads fail silently by filtering out rows, while writes throw an explicit error. The recommended fix is to write per-operation policies that restrict access to rows where user_id matches auth.uid(), default user_id to auth.uid(), and keep the service_role key off the frontend. Public read access can be allowed only for genuinely public data.