Background-review forks share the live parent's session_id for prompt-cache
warmth but are _persist_disabled — they can never write to the transcript.
Without this, every review fork on an active session would (a) trip a false
cross-agent overlap warning against the parent's real turn, sending the
#64934 route investigation the wrong way, and (b) pop the parent's in-flight
slot at its own persist, making a real overlap right after a review go
unreported. Both legs now skip persist-disabled agents symmetrically.
+2 tests.
note_turn_start kept its in-flight marker on the agent object, but the
gateway caches agents per routing key (_agent_cache) while transcripts
are owned by session_id — and switch_session (/resume from a second
surface, CLI-continuity rebinding, async-delegation pinning,
topic-binding tip-walks) maps multiple routing keys onto one session_id
without any cross-key check. Two keys mapped to one session run
concurrent turns on two different agent objects, so the per-agent
tripwire could never fire for exactly the dispatch route #64934 is
waiting to identify.
Add a module-level session_id-keyed in-flight registry alongside the
per-agent marker. Same philosophy as the original tripwire: log-only,
takes ownership on overlap, under-reports rather than double-reports
(a same-agent overlap warns once, not twice). The persist-time clear
pops the session id stamped at turn start, so a mid-turn compression
rotation of agent.session_id cannot strand the slot.
Two turns interleaving on one session corrupt the durable transcript:
flushes race (user rows persist out of arrival order), the identity-marker
dedup over shared history dicts can swallow a row, and the second turn
runs on a history base that never saw the first turn's exchange. The
dispatch route that lets the second turn through the busy guard is not
yet identified.
Add note_turn_start (build_turn_context) / note_turn_persisted
(_persist_session funnel): one WARNING naming both turn_ids when a turn
starts before the previous turn's turn-end persist. Ownership transfer
keeps a crashed turn from warning more than once; the unconditional clear
makes the tripwire under-report rather than double-report under a real
overlap. Log-only, no behavior change.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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