fn answer_delivery(
respond: Option<Sender<Result<(), String>>>,
outcome: Result<(), String>,
)Expand description
Answer a delivery’s respond channel, if the caller asked for one:
Ok(()) once the prompt was accepted - handed to the target’s session
queue, held for its turn end, or parked for its connect - and
Err(reason) when nothing could take it. The sender’s ack is built
from this answer alone, so it never claims a delivery that did not
happen.