Function decide 

pub const fn decide(
    response: DefenseResponse,
    class: DefenseInteractionClass,
) -> InteractionDecision

The monotonic, exhaustive mapping from a recommendation and an interaction class to a decision. This is the single place the mapping lives.

Monotonicity: for a fixed class, the decision never weakens as the recommendation escalates Proceed < Observe < Backoff < Reconsider < Halt. Defense never allows less than the response requires and never adds work.