infallible-scheduler(C++26)

template <class Sch, class Env>
concept infallible-scheduler =
  scheduler<Sch> &&
  (same_as<completion_signatures<set_value_t()>,
           completion_signatures_of_t<decltype(schedule(declval<Sch>())), Env>> ||
   (!unstoppable_token<stop_token_of_t<Env>> &&
    (same_as<completion_signatures<set_value_t(), set_stopped_t()>,
             completion_signatures_of_t<decltype(schedule(declval<Sch>())), Env>> ||
     same_as<completion_signatures<set_stopped_t(), set_value_t()>,
             completion_signatures_of_t<decltype(schedule(declval<Sch>())), Env>>)));