When writing Row Level Security policies, never assume the column types referenced in older migration files are still correct. A single column-type drift — like swimmers.coach_id changing from text to uuid and gaining a coaches.auth_id uuid indirection — can break every policy that uses a text-cast pattern. The fix is mechanical: query information_schema.columns and pg_policies on the live database, then rewrite the USING expression against the actual join path (coach_id IN (SELECT id FROM coaches WHERE auth_id = auth.uid())) rather than the obsolete shorthand (coach_id = auth.uid()::text).
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