Resumed sessions loaded message dicts from state.db WITHOUT the
_DB_PERSISTED_MARKER, so any flush that lost the identity boundary
(compression durable-snapshot adoption, incremental tool-call persists,
rotation preflight on cold resume) re-appended the ENTIRE loaded
transcript as new rows. Compression cycles then doubled the copies:
the incident session grew 998 -> 1995 -> 3990 -> 7981 rows across
three aborted rotations (15,962 active rows, only 472 distinct).
Fix at the architectural chokepoint: SessionDB._rows_to_conversation
(shared by get_messages_as_conversation and get_resume_conversations)
now stamps the marker at row materialization time - a dict built FROM
a durable row is persisted by construction, regardless of which caller
loads it or how the list is later handed to a flush.
Safety:
- Wire-safe: every transport strips underscore-prefixed keys before
the API request (chat_completion_helpers, anthropic_adapter), same
contract as the existing _row_id stamp in the same function.
- Rotation handoffs still write: compression's assembly copies strip
the marker (_fresh_compaction_message_copy + the terminal
_strip_persistence_markers sweep), so compacted transcripts still
flush to the child session (#57491 invariant preserved).
- Branch/seed copies unaffected: /branch and _persist_branch_seed
build fresh field-projected dicts and write via append_messages_batch
directly, not through the marker-gated flush.
Tests: new regression suite (marker sync, load stamping, 3-cycle
amplification repro, new-tail write guard, compaction-copy handoff);
updated the #68454 control test that asserted the old double-write
behavior and the ACP restore shape test.
kshitijk4poor
016ba66176