Re-review follow-up (N1, N2) for the group room failed-turn fix.
- Stranded harvest: the retained error only counts as the stranded turn's
own when no user row follows the turn's prompt. When a later turn in the
same session (a gateway/CLI message, a later room turn) failed, its error
is not the stranded turn's, and the real late reply now posts instead of
being dropped and reported as a failure.
- Live poll: the pre-submit comparison keys the retained error on
`turn_started_at` plus the `inflight` snapshot. The snapshot alone carries
no start time, so a failure identical to the previous turn's read as the
leftover and the pre-tool text was posted as the reply.
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