Module authoring 

Developer-facing effect-authoring helpers (design §4.1).

This is the second of the two real gaps the generalization closes (design §0): today the only HandlerFns that exist are buried in pokered’s #[cfg(test)] parity harness, with no ergonomic, documented way to author a move / ability / item / weather. This module is concept-free: it adds no new runtime type — it is pure constructors over the existing Effect / EventHook shape (plus the typed RelayVar accessors, which live on RelayVar itself). It introduces no game concept and no rand; a game authors a const Effect with zero-capture fn handlers.

The effect! macro

Builds the same &'static [EventHook] table the engine folds, in a const/static context, so registrations stay zero-alloc constants:

fn flamethrower<P: EffectProvider + ?Sized>() -> Effect<P> {
    effect!(EffectId(0x10), EffectType::Move, {
        DamagingHit       => my_hit::<P>,
        Residual(20)      => my_residual::<P>,  // explicit on<Event>Order
    })
}

The first form (Event => fn) defaults order to u32::MAX (fires last, matching the engine’s EventHook default); the second form (Event(order) => fn) sets on<Event>Order explicitly. priority defaults to 0 and sub_order to None (derive from the effect’s EffectType), exactly as a hand-written EventHook would.