Follow-up correcting the salvaged fix's persistence approach to avoid a
duplicate user-message write (verified via E2E — the #860/#42039 bug class
the original diff aimed to avoid).
Root cause: in gateway mode the AIAgent is built WITH a session_db, so the
inbound user turn is already flushed at turn start (turn_context.
_persist_session). The original fix returned agent_persisted=False, making the
gateway re-write the whole new-message slice via append_to_transcript ->
append_message (a raw INSERT with no dedup), duplicating the already-flushed
user turn.
Corrected approach (single writer): run_codex_app_server_turn now flushes its
OWN projected assistant/tool messages via _flush_messages_to_session_db (which
dedups the already-persisted user turn through _DB_PERSISTED_MARKER) and
returns agent_persisted=True so the gateway skips its write. Net result:
session_search/distill see the full codex conversation, each message persisted
exactly once.
Adds regression coverage asserting exactly-once persistence on a real
SessionDB, agent_persisted=True, FTS visibility, and standard-runtime skip-db
behaviour preserved.
Co-authored-by: Lubos Buracinsky <lubos@komfi.health>
