Function note_not_holder_since 

pub(crate) fn note_not_holder_since(
    agent_id: &str,
    body: &Value,
    started: Instant,
) -> Option<String>

[note_not_holder] for a request that started at started: None (nothing recorded, and the caller must not fence) when a Take over cleared the refusal after the request started — its 409 predates the holder letting go (Codex P1 on #3908). Pulls and acks don’t take the op lock, so ordering by start time is what keeps them from restoring it.