bluememoExpiry
The point at which a memory stops being true, chosen by the model and computed by the runtime.
The model picks one of none, end_of_today, end_of_week, end_of_month, end_of_quarter, end_of_year, or on_date with an expiryDate. The runtime turns that choice into an instant from the note's arrival time in the configured Location, so "only this quarter" said on 21 September becomes 1 October 00:00. Date arithmetic stays out of the model because small models get it wrong far more often than they get the period wrong.