Review round fixes for the length continuation in Part A.
Before each continuation the runner now reads processing.status as well as
state. A halted, invalid or unreadable processing state starts no further
attempt; the message is left unread with no reply and no failure record, as
for a halt during any turn.
A failed state or processing read keeps the empty length classification, so
the sender gets no RESULT. The chief notice and the trail event name how many
attempts hit the limit.
usage.end for the message id now runs in a finally block, so it closes once
even when an attempt throws.
The library citation retry no longer starts continuations. They would run
outside the message's usage bracket, and the retry's own bracket is refused
(#1853). An empty length retry fails visibly instead, with no fixed RESULT.
Tests cover a halt between attempts, a failed continuation check on the plain
and library paths, a throwing attempt, a library continuation that succeeds,
and the retry path.
jason.woltje
3e03e123fe