Function cron_names_of 

pub fn cron_names_of(
    surface: &ViewSurface,
    slot: &SessionSlot,
    turns: &[TurnWire],
) -> BTreeMap<String, CronName>

The schedules the fired prompts in turns came from, keyed by the prompt’s own id.

Only a delivery row is looked up: its prompt id is the pairing’s key, and the map holds nothing for a row no schedule produced.