RLS says yes and Postgres still says permission denied: the 403 family I only understood on the second one

A developer recently encountered a persistent 'permission denied' error in a PostgreSQL/Supabase environment despite having correct Row Level Security (RLS) policies. The issue stemmed from a misunderstanding of how Postgres handles permissions: RLS governs row access, but column-level GRANTs govern whether a role can interact with specific fields at all. The developer discovered that their 'SECURITY INVOKER' functions were failing because the 'authenticated' role lacked explicit column-level permissions. The solution involved wrapping privileged operations in 'SECURITY DEFINER' functions, ensuring an administrative check occurs before any data modification. After identifying a pattern of similar bugs, the author implemented a system catalog scanner to audit 'INVOKER' functions, allowing for proactive identification of potential security gaps. This experience highlights the importance of distinguishing between row-level and column-level security gates and suggests using automated tools to manage complex permission structures in production databases.