The replay-authority predicate accepted any non-empty assistant message,
but a new turn copies the full transcript into INFLIGHT.messages. In an
established conversation that content is the previous turn's reply, so
`canSeed` came back true with both stale cursor halves preserved and the
server kept skipping the range that rebuilds the body.
Message-based evidence now counts only from a current `_live` assistant
positioned after the latest user boundary; a historical assistant row
fails closed to floor 0 and an empty event id.
Refs #7640 (blocker on #7651)
webtecnica
4b791bd820
