Using an acking system (like that in Storm or Heron) would move it to be physically at-least-once with a logical exactly-once by de-duping at the target. This

Using an acking system (like that in Storm or Heron) would move it to be physically at-least-once with a logical exactly-once by de-duping at the target. This means if you observe the inner system, you won't be seeing exactly-once semantics but looking at the system from the outside, the semantics would indeed be exactly-once at the target.