harden chat thread ownership

Author: dnywh

supabase/migrations/20260511044315_harden_chat_thread_owner_and_drop_duplicate_slug_indexes.sql

@@ -0,0 +1,67 @@
+-- Remove duplicate slug indexes covered by unique constraints, and ensure
+-- client-created chat threads point at the real visible listing owner.
+
+drop index if exists public.public_listings_slug_idx;
+drop index if exists public.listing_contact_cards_slug_idx;
+
+create or replace function private.enforce_chat_thread_insert()
+returns trigger
+language plpgsql
+security definer
+set search_path = ''
+as $$
+declare
+  jwt_role text;
+begin
+  jwt_role := nullif(current_setting('request.jwt.claim.role', true), '');
+
+  if jwt_role = 'service_role'
+    or ((select auth.uid()) is null and jwt_role is null)
+  then
+    return new;
+  end if;
+
+  if (select auth.uid()) is null or new.initiator_id is distinct from (select auth.uid()) then
+    raise exception 'Users can only start chat threads as themselves.'
+      using errcode = '42501';
+  end if;
+
+  if not exists (
+    select 1
+    from public.listings
+    where listings.id = new.listing_id
+      and listings.owner_id = new.owner_id
+      and listings.visibility = true
+  ) then
+    raise exception 'Users can only start chat threads for visible listings with the correct owner.'
+      using errcode = '42501';
+  end if;
+
+  if (
+    select count(*)
+    from public.chat_messages
+    where sender_id = new.initiator_id
+      and created_at >= now() - interval '1 hour'
+  ) >= 10 then
+    raise exception 'Too many messages sent recently to start a new chat thread.'
+      using errcode = '42501';
+  end if;
+
+  if (
+    select count(*)
+    from public.chat_threads
+    where initiator_id = new.initiator_id
+      and created_at >= now() - interval '1 hour'
+  ) >= 6 then
+    raise exception 'Too many chat threads started recently.'
+      using errcode = '42501';
+  end if;
+
+  return new;
+end;
+$$;
+
+alter function private.enforce_chat_thread_insert() owner to postgres;
+
+revoke all privileges on function private.enforce_chat_thread_insert()
+  from anon, authenticated, public;