Gate C18 r1 quality [Low, unverified -> reproduced]: on the
durable-carrier path `truncated` is the physical durable_prefix, so
`len(history) - len(truncated)` mixed live and physical rows. A probe
with target row 101 absorbed into a repaired live carrier reported
archived_messages=5 for a cut that drops all 6 live rows (the carrier
and everything after it). The refusal now counts from the live cut
index on that path; the plain path is unchanged.
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