act no longer acks. result acks through the highest answered seq of the
process, never past a delivery still told and unanswered (the retold batch or
a line written and not yet echoed), and only forward. Soul s1
retell-ack-passes-unanswered: a newer turn's ack passed a retold batch, so a
session ending first lost it and the retell's answer acked a lower seq.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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