// core/bus.js (Lane F) — event bus. Event names are a contract: TECH.md §Bus.

export function createBus() {
  const map = new Map();
  return {
    on(name, fn) {
      if (!map.has(name)) map.set(name, new Set());
      map.get(name).add(fn);
      return () => map.get(name)?.delete(fn);
    },
    off(name, fn) { map.get(name)?.delete(fn); },
    emit(name, payload) {
      const set = map.get(name);
      if (set) for (const fn of [...set]) fn(payload);
    },
  };
}