The harness kills shells mid-command, and the master releases the dead
session's lock only when it notices the connection is gone. That cleanup
lands after the harness has already re-acquired the lock, so it can clear
the lock this run holds and the next command refuses with
need to run "lock" first to continue
recoverInterruptedBalance answered that the way an operator would -- run
lock again and retry -- but the encode and decode recoveries called
shellCommand once and required success, so the same reap failed the run
outright. Move the retry into shellCommand: the reap can land during any
command that follows a kill, not only a balance.