Pure-reference catalog of row-level security for tenant isolation, Postgres-first. Covers enabling RLS (ALTER TABLE ... ENABLE ROW LEVEL SECURITY, default-deny semantics), CREATE POLICY syntax (USING vs WITH CHECK clauses, FOR SELECT/INSERT/UPDATE/DELETE/ALL, permissive vs restrictive, TO role_name), bypassing RLS (superuser / BYPASSRLS / table owner / FORCE ROW LEVEL SECURITY), tenant context patterns (current_user, current_setting, JWT claims via Supabase auth.uid() / auth.jwt()), and performance discipline (wrapping auth functions in SELECT, index on policy-referenced columns). Row/tenant isolation on the non-Postgres engines - MySQL / MariaDB invoker views, CockroachDB native RLS, Vitess vindex sharding, SQL Server security policies - lives in references/other-engines.md. Use as the RLS-pattern reference for tenant isolation on any of these engines. Consumed by cross-tenant-data-leak-tests.