The salvaged drift check compared durable rows to the in-memory snapshot
by content and ran in both modes. Two problems:
1. In-place compaction (the default) archives non-destructively — drift
cannot lose data there, and the strict-prefix content comparison
failed against seeded histories, aborting every in-place compaction
(5 test failures in test_in_place_compaction.py).
2. Content equality wedges on sessions with legal in-memory mutation of
past turns (multimodal compression, retry replacement) — the same
permanent-abort shape as #14694.
Now rotation-only and length-based: abort only when the durable parent
has MORE rows than the snapshot (a writer committed in the lease window).
Dead helper _durable_history_matches_snapshot removed.
c54fe5b33f