struct test_domain {
    template <sender_expr_for<then_t> _Sender>
    static constexpr auto transform_sender(_Sender&& __sndr) noexcept {
      return just("goodbye"s);
    }
  };

  struct test_task_context {
    constexpr test_task_context(auto&&...) noexcept {
    }

    template <class _ThisPromise>
    using promise_context_t = test_task_context;

    template <class, class>
    using awaiter_context_t = test_task_context;

    static constexpr auto query(get_scheduler_t) noexcept {
      return basic_inline_scheduler<test_domain>{};
    }
  };

  template <class T>
  using test_task = exec::basic_task<T, test_task_context>;

auto msg = co_await stdexec::then([] { return "hello"s; });
assert(msg == "goodbye"s);