Function seed_from_transcript 

async fn seed_from_transcript(
    state: &TransportState,
    slot: &SessionSlot,
    timings: &mut OpenTimings,
) -> Option<Arc<Held>>

The conversation the seat’s transcript holds, for a seat this transport holds nothing for.

This is the read a resume performs (session_history), so what it seeds is what a Connected would bring - only sooner, because the file is already written. None when the seat records no session at all, or its file holds nothing yet: a seat that has never run has no history, and an empty conversation would claim exactly that.