CREATE FUNCTION enforce_community_tombstone() RETURNS TRIGGER
LANGUAGE plpgsql AS $$
DECLARE
    executor_community TEXT := current_setting('buzz.deletion_executor_community', true);
    executor_generation TEXT := current_setting('buzz.deletion_fence_generation', true);
    expected_generation BIGINT;
BEGIN
    IF TG_OP = 'DELETE' THEN
        IF OLD.deletion_state <> 'active' OR OLD.deleted_at IS NOT NULL THEN
            RAISE EXCEPTION 'community tombstones are permanent'
                USING ERRCODE = 'object_not_in_prerequisite_state';
        END IF;
        RETURN OLD;
    END IF;
    expected_generation := CASE WHEN NEW.deletion_fence_generation > OLD.deletion_fence_generation
        THEN NEW.deletion_fence_generation ELSE OLD.deletion_fence_generation END;
    IF executor_community = OLD.id::text AND executor_generation ~ '^[0-9]+$'
       AND executor_generation::BIGINT = expected_generation THEN RETURN NEW; END IF;
    IF OLD.deletion_state <> 'active' OR NEW.deletion_state <> OLD.deletion_state
       OR NEW.deletion_fence_generation <> OLD.deletion_fence_generation
       OR NEW.deleted_at IS DISTINCT FROM OLD.deleted_at THEN
        RAISE EXCEPTION 'community tombstone mutation rejected: community % generation %',
            OLD.id, OLD.deletion_fence_generation
            USING ERRCODE = 'object_not_in_prerequisite_state';
    END IF;
    RETURN NEW;
END
$$;