The pipeline's answer before admission (FX-001), named by what the caller actually knows.
:overloaded and :unavailable are definite refusals — the owner
itself returned them (capacity; settling or expired at dequeue): no
permit was taken, nothing of this submission will execute.
:unacknowledged is NOT a refusal: the caller learned the outcome by
its acknowledgment timing out, and the submission may have been
admitted in the last instant before the reply was lost. request_ref
identifies it. Check FlowExtra.Admission.report/1's :refs — a live
view of unresolved reservations, not an admission history: the ref's
presence means admitted-and-unresolved; its absence means
released-or-never-admitted and proves nothing. These are policy
outcomes, not pipeline failures.