Optionalid: stringReturns a defensive copy of accumulated sentences. Attempt sentences still held — read mid-stage, before the stage's outcome — come last, so nothing the run did is ever missing from the copy.
One sentence per attempt of a retried stage (10.1) — its outcome, duration, cause and decision. It replaces
the 9.15 retry sentence (onStageRetry is no longer narrated here): the attempt line already says
"retrying", and says it for the attempt that stopped the series too. Held until the stage's outcome is
known (heldAttempts); an event with no runtimeStageId has nothing to hold it by, so it is told now.
Clears accumulated sentences. Useful for reuse across runs.