Refresh-loss interrupt is cooperative, so a stalled writer could still flush after another process reclaimed the conversation. Carry the holder into append_message / append_messages_batch and reject the write in the same SQLite transaction when the lease row is missing, expired, or owned by someone else.
Presence-only _delegate_from/_branched_from checks stopped the lease walk on
continuations that copied a delegate's model_config, so the first refresh
after rotation missed the parent-key lease and hard-interrupted. A failed
get_session probe also skipped acquire entirely. Walk the lineage inside
the write transaction and treat a probe error as contended, not a fresh
session.
Honor interrupts while waiting for admission, stop the turn when refresh
loses the lease, poll once per second under contention, and test dead-PID
reclaim.
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