`std::execution` serves its domain well. Different asynchronous domains have different costs, and a single model cannot minimize all of them simultaneously. This paper identifies four structural gaps where the sender model meets coroutines: three at the boundary - error reporting, error returns, and frame allocator propagation - and one inside the composition mechanism - the symmetric transfer gap documented in [P2583R0](https://wg21.link/p2583r0)[63]. Each gap is the cost of a property the sender model requires for compile-time analysis ([P2300R10](https://wg21.link/p2300r10)[1], [P4014R0](https://wg21.link/p4014r0)[26]). They are not design defects, they are tradeoffs. Mandating that standard networking be built on the sender model would force coroutine I/O users to pay these costs. A coroutine-native I/O research report ([P4003R0](https://wg21.link/p4003r0)[25]) made the gaps visible by showing that partial results, error returns, cancellation, and frame allocator propagation emerge naturally when I/O is designed for coroutines. The findings hold regardless of that report’s specific design.