Summary

A positioned layered cursor on a disaggregated follower can return stale data after a write through another cursor in the same transaction. This violates read-your-own-writes.

Impact

• remove(): iteration returns the deleted key.
• update() / insert() / modify(): iteration returns the old value or skips the new key.
• Range truncate: iteration returns a key deleted by the same transaction.
• Both next() and prev() affected. No on-disk corruption observed.

Root cause

__clayered_update_state() invalidates cached iteration state on snapshot or read-timestamp changes. Writes through another cursor in the same transaction change neither, so WTI_CLAYERED_ITERATE_NEXT/PREV reuse a stale alternate position.

Reproducer

See attached test_layered_cursor29.py. Minimal case: three keys, follower cursor A parked on key 550, cursor B removes 550 in the same transaction – A.prev() returns 550.