diff --git a/volumes/db/cc/76-cabinet-memberships-rls-definer.sql b/volumes/db/cc/76-cabinet-memberships-rls-definer.sql
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+-- 76-cabinet-memberships-rls-definer.sql
+-- Fix cabinet_memberships/file_cabinets/files recursive RLS.
+--
+-- The original cabinet membership policies joined file_cabinets directly, while
+-- the file_cabinets/files membership policies joined cabinet_memberships
+-- directly. Under an authenticated as-user SELECT this creates an RLS cycle and
+-- PostgreSQL raises 42P17 (infinite recursion detected in policy for relation
+-- "cabinet_memberships").
+--
+-- SECURITY DEFINER helpers evaluate the ownership/membership checks as the
+-- function owner (bypassing the inner RLS checks) while still keying the result
+-- to auth.uid(), matching the class-management helper pattern in 71.
+--
+-- The existing public tables are owned by supabase_admin; Supabase migrations
+-- run as that table owner on dev/prod so the SECURITY DEFINER helpers are owned
+-- by a role that bypasses the inner RLS checks.
+
+create or replace function public.is_cabinet_owner(p_cabinet uuid)
+returns boolean
+language sql
+stable
+security definer
+set search_path = public
+as $$
+  select exists (
+    select 1
+    from public.file_cabinets c
+    where c.id = p_cabinet
+      and c.user_id = auth.uid()
+  )
+$$;
+
+create or replace function public.is_cabinet_member(p_cabinet uuid)
+returns boolean
+language sql
+stable
+security definer
+set search_path = public
+as $$
+  select exists (
+    select 1
+    from public.cabinet_memberships m
+    where m.cabinet_id = p_cabinet
+      and m.profile_id = auth.uid()
+  )
+$$;
+
+-- Keep function execution available to the roles used by RLS policies. The
+-- functions disclose only a boolean about the caller's own auth.uid() state.
+revoke all on function public.is_cabinet_owner(uuid) from public, anon;
+revoke all on function public.is_cabinet_member(uuid) from public, anon;
+grant execute on function public.is_cabinet_owner(uuid) to authenticated, service_role;
+grant execute on function public.is_cabinet_member(uuid) to authenticated, service_role;
+
+-- Re-declare cabinet_memberships policies without direct file_cabinets subqueries.
+drop policy if exists cm_read_self_or_owner on public.cabinet_memberships;
+create policy cm_read_self_or_owner on public.cabinet_memberships
+  for select to authenticated
+  using (profile_id = auth.uid() or public.is_cabinet_owner(cabinet_id));
+
+drop policy if exists cm_insert_by_owner on public.cabinet_memberships;
+create policy cm_insert_by_owner on public.cabinet_memberships
+  for insert to authenticated
+  with check (public.is_cabinet_owner(cabinet_id));
+
+drop policy if exists cm_update_by_owner on public.cabinet_memberships;
+create policy cm_update_by_owner on public.cabinet_memberships
+  for update to authenticated
+  using (public.is_cabinet_owner(cabinet_id))
+  with check (public.is_cabinet_owner(cabinet_id));
+
+drop policy if exists cm_delete_by_owner on public.cabinet_memberships;
+create policy cm_delete_by_owner on public.cabinet_memberships
+  for delete to authenticated
+  using (public.is_cabinet_owner(cabinet_id));
+
+-- Re-declare membership-based cabinet/file read policies without direct
+-- cabinet_memberships subqueries, so selecting cabinets/files does not recurse
+-- back through cabinet_memberships RLS.
+drop policy if exists "User can access cabinets via membership" on public.file_cabinets;
+create policy "User can access cabinets via membership" on public.file_cabinets
+  for select to authenticated
+  using (public.is_cabinet_member(id));
+
+drop policy if exists "User can access files via membership" on public.files;
+create policy "User can access files via membership" on public.files
+  for select to authenticated
+  using (public.is_cabinet_member(cabinet_id));