Module stack 

Showdown-style effect-stack battle engine (Pattern C) — vertical-slice POC (design doc 06-battle-engine-effect-stack-design.md, §8).

This is an additive sibling to crate::battle::driver; the existing BattleDriver and every other game’s code keep compiling unchanged. The module is 100% game-agnostic: no game-specific concrete types, no rand (randomness only via the existing BattleRng).

Pieces

• event — the closed Event taxonomy, RelayVar/HandlerResult, the fn-pointer HandlerFn signature, and the Effect/EventHook registration shape.
• ctx — the EffectProvider trait, the typed EffectState arena, per-move scratch, and the split-borrow BattleCtx (battler_mut / pair_mut (both branches) / effect_mut).
• dispatch — the Showdown comparePriority comparator, the speed-tie draw, and the run_event fold.
• driver — the StackDriver firing the fixed §2 per-turn sequence with the per-mover residual + first-mover-faint short-circuit.

Re-exports

pub use ctx::BattleCtx;

pub use ctx::EffectHost;

pub use ctx::EffectProvider;

pub use ctx::EffectState;

pub use ctx::MoveContext;

pub use dispatch::collect_handlers;

pub use dispatch::compare;

pub use dispatch::run_event;

pub use dispatch::run_event_checked;

pub use dispatch::CollectedHandler;

pub use driver::FirstMover;

pub use driver::StackDriver;

pub use driver::StackTurnResult;

pub use log::HpChangeCause;

pub use log::TurnEvent;

pub use log::TurnLog;

pub use event::Effect;

pub use event::EffectId;

pub use event::EffectType;

pub use event::Event;

pub use event::EventHook;

pub use event::HandlerFn;

pub use event::HandlerResult;

pub use event::RelayVar;

Modules

authoring

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

ctx

The effect provider, per-effect state arena, per-move scratch, and the split-borrow BattleCtx (design §3).

dispatch

Handler collection, the Showdown comparePriority comparator, the speed-tie draw, and the run_event dispatch fold (design §1.3, §3.4).

driver

The StackDriver — the fixed per-turn firing sequence (design §2).

event

Event taxonomy, handler signature, and effect registration types for the Showdown-style effect-stack battle engine (design doc §1).

log

P6a — a generic, additive per-turn event log for stack-driven battles.