The contributor's empty-sidecar recovery uses the persisted truncation_boundary
to distinguish a legitimate prefix from a deleted suffix, but two production
call sites still passed only truncation_watermark — the default /api/session
full reload (routes.py ~9504) and _merged_session_messages_for_display
(routes.py ~6098) — so a normal full reload fell back to the old 'drop one
turn pair' heuristic and resurrected deleted suffix turns when an OLDER message
was edited leaving >=2 later turns. Thread truncation_boundary through both.
Co-authored-by: AlexeyDsov <alexeydsov@gmail.com>
