-- B09：索引现有条目和头的事务变更守卫；不产生第二套索引或业务权威。
CREATE TABLE public.muse_method_index_guard (
    singleton boolean PRIMARY KEY DEFAULT true CHECK (singleton),
    generation bigint NOT NULL DEFAULT 0 CHECK (generation >= 0)
);
INSERT INTO public.muse_method_index_guard (singleton, generation) VALUES (true, 0);

CREATE FUNCTION public.muse_method_index_changed() RETURNS trigger
LANGUAGE plpgsql SECURITY DEFINER SET search_path = pg_catalog AS $guard$
BEGIN
    UPDATE public.muse_method_index_guard
       SET generation = generation + 1
     WHERE singleton;
    IF NOT FOUND THEN
        RAISE EXCEPTION 'method index mutation guard is missing';
    END IF;
    RETURN NULL;
END
$guard$;

-- statement 级别也覆盖批量改写和 TRUNCATE；事务失败时代次一并回滚。
CREATE TRIGGER muse_method_index_changed
AFTER INSERT OR UPDATE OR DELETE OR TRUNCATE ON public.muse_method_index
FOR EACH STATEMENT EXECUTE FUNCTION public.muse_method_index_changed();
CREATE TRIGGER muse_method_index_head_changed
AFTER INSERT OR UPDATE OR DELETE OR TRUNCATE ON public.muse_method_index_version
FOR EACH STATEMENT EXECUTE FUNCTION public.muse_method_index_changed();

REVOKE ALL ON public.muse_method_index_guard FROM PUBLIC, muse_app, muse_eval;
GRANT SELECT ON public.muse_method_index_guard TO muse_app, muse_eval;
REVOKE ALL ON FUNCTION public.muse_method_index_changed() FROM PUBLIC;