C++20 provides symmetric transfer ([P0913R1](https://wg21.link/p0913r1)[1]) - a mechanism where `await_suspend` returns a `coroutine_handle<>` and the compiler resumes the designated coroutine as a tail call. Coroutine chains execute in constant stack space. `std::execution` ([P2300R10](https://wg21.link/p2300r10)[5]) composes asynchronous operations through sender algorithms. These algorithms create receivers that are structs, not coroutines. No `coroutine_handle<>` exists at any intermediate point in a sender pipeline. When a coroutine `co_await` s a sender that completes synchronously, the stack grows by one frame per completion. [P3552R3](https://wg21.link/p3552r3)[2]’s `std::execution::task` inherits this property. The sender model’s zero-allocation composition property and symmetric transfer’s constant-stack property cannot both be satisfied. One requires structs. The other requires coroutines. This paper describes the mechanism, provides implementation experience, and documents the tradeoff.