AcknowledgeAsync swallowed every non-cancellation transport failure (and returned
normally when the session was lost while the ack queued), so the host logged the
Part 9 ack as applied while upstream still showed it unacknowledged. Both now throw
(ServiceResultException with the transport status / BadNotConnected). A reply,
including per-ack refusals, still returns normally and counts as the server answering.
Refs #743
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty