Function transient_capacity 

pub fn transient_capacity(
    initial: f32,
    elapsed: f32,
    rate: f32,
    threshold: f32,
) -> CapacityStatus

Capacity under a transient impairment: while the decayed level is at/above threshold the agent is Impaired; once it decays below, capacity self-clears to Intact. Distinct from durable incapacity (which does not decay).