chore(brain): ASTRA 성장 자산 동기화 — 기능 인벤토리·growth(약점프로필/학습큐)·일화기억·장기기억·회의록 원문
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id: wiki-2026-0508-event-mediator
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title: Event Mediator
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [Mediator Pattern, Event Bus]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.9
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verification_status: applied
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tags: [architecture, design-pattern, event-driven, decoupling]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack:
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language: typescript
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framework: nodejs
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---
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# Event Mediator
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## 매 한 줄
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> **"매 N×N component coupling 의 N×1 mediator hub 의 collapse"**. Event Mediator 매 multiple components 의 direct coupling 의 elimination — 매 components 매 mediator 를 publish/subscribe, 매 mediator 매 routing/orchestration 의 own. GoF Mediator pattern 의 event-driven evolution.
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## 매 핵심
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### 매 Mediator vs Observer
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- **Observer**: 매 1 subject → N observers, 매 unidirectional broadcast.
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- **Mediator**: 매 N senders ↔ N receivers, 매 hub 의 bidirectional routing.
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- **Event Bus**: 매 Mediator 의 generic implementation — 매 string-keyed event types.
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### 매 동기 vs 비동기
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- **Sync mediator**: 매 in-process method dispatch — 매 EventEmitter, MediatR.
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- **Async mediator**: 매 message queue 의 backed — 매 RabbitMQ, Kafka, Redis Streams.
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- **Hybrid**: 매 in-process sync + cross-service async (e.g., NestJS CQRS).
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### 매 응용
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1. UI components decoupling — chat rooms, form fields.
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2. Microservices orchestration — saga coordinator.
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3. CQRS command/query bus — MediatR.
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4. Game event systems — unit death, achievement triggers.
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## 💻 패턴
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### Typed Event Bus (TypeScript)
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```typescript
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type EventMap = {
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'user.signup': { userId: string; email: string };
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'order.placed': { orderId: string; total: number };
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'cache.invalidate': { key: string };
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};
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class EventMediator<M> {
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private handlers = new Map<keyof M, Set<(p: any) => void | Promise<void>>>();
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on<K extends keyof M>(event: K, handler: (payload: M[K]) => void | Promise<void>) {
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if (!this.handlers.has(event)) this.handlers.set(event, new Set());
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this.handlers.get(event)!.add(handler);
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return () => this.handlers.get(event)!.delete(handler);
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}
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async emit<K extends keyof M>(event: K, payload: M[K]) {
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const hs = this.handlers.get(event);
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if (!hs) return;
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await Promise.all([...hs].map(h => h(payload)));
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}
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}
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const bus = new EventMediator<EventMap>();
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bus.on('user.signup', async ({ userId, email }) => {
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await sendWelcomeEmail(email);
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});
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```
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### Mediator with Request/Response (MediatR-style)
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```typescript
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interface IRequest<TResponse> { __response?: TResponse }
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interface IHandler<TReq extends IRequest<TRes>, TRes> {
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handle(req: TReq): Promise<TRes>;
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}
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class Mediator {
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private handlers = new Map<Function, IHandler<any, any>>();
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register<T extends IRequest<R>, R>(reqCtor: new (...a: any[]) => T, h: IHandler<T, R>) {
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this.handlers.set(reqCtor, h);
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}
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async send<R>(req: IRequest<R>): Promise<R> {
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const h = this.handlers.get(req.constructor);
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if (!h) throw new Error(`No handler for ${req.constructor.name}`);
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return h.handle(req);
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}
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}
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class GetUserQuery implements IRequest<User> { constructor(public id: string) {} }
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class GetUserHandler implements IHandler<GetUserQuery, User> {
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async handle(q: GetUserQuery) { return db.users.findById(q.id); }
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}
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```
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### Saga Mediator (orchestrated)
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```typescript
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class OrderSaga {
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constructor(private bus: EventMediator<OrderEvents>) {
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bus.on('order.created', this.onCreated.bind(this));
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bus.on('payment.failed', this.onPaymentFailed.bind(this));
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}
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async onCreated({ orderId }: { orderId: string }) {
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await this.bus.emit('payment.requested', { orderId });
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}
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async onPaymentFailed({ orderId, reason }: any) {
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await this.bus.emit('order.cancelled', { orderId, reason });
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await this.bus.emit('inventory.released', { orderId });
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}
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}
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```
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### Middleware Pipeline
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```typescript
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type Middleware<E> = (event: E, next: () => Promise<void>) => Promise<void>;
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class PipelineMediator<E> {
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private middlewares: Middleware<E>[] = [];
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use(m: Middleware<E>) { this.middlewares.push(m); }
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async dispatch(event: E) {
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let i = -1;
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const run = async (idx: number): Promise<void> => {
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if (idx <= i) throw new Error('next() called twice');
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i = idx;
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const fn = this.middlewares[idx];
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if (fn) await fn(event, () => run(idx + 1));
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};
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await run(0);
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}
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}
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// usage: logging, validation, retry, dead-letter
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```
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### Cross-Service Mediator (Kafka)
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```typescript
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import { Kafka } from 'kafkajs';
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const kafka = new Kafka({ brokers: ['localhost:9092'] });
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const producer = kafka.producer();
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const consumer = kafka.consumer({ groupId: 'order-svc' });
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await consumer.subscribe({ topic: 'orders', fromBeginning: false });
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await consumer.run({
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eachMessage: async ({ message }) => {
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const evt = JSON.parse(message.value!.toString());
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await handler[evt.type]?.(evt.payload);
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},
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});
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await producer.send({
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topic: 'orders',
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messages: [{ key: orderId, value: JSON.stringify({ type: 'order.placed', payload }) }],
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});
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```
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## 매 결정 기준
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| 상황 | Approach |
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|---|---|
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| 2-3 components 의 direct call | 매 mediator skip — 매 over-engineering |
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| 5+ components, fan-out broadcast | 매 in-process EventEmitter |
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| CQRS / clean architecture | 매 MediatR-style request bus |
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| Cross-service, durability | 매 Kafka / RabbitMQ |
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| Long-running workflow | 매 saga orchestrator (Temporal, Inngest) |
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**기본값**: 매 typed in-process EventEmitter (Node) 또는 MediatR (.NET) — 매 cross-service 의 Kafka.
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## 🔗 Graph
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- 부모: [[Design-Patterns]] · [[Event-Driven-Architecture]]
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- 변형: [[Observer-Pattern]] · [[Pub-Sub]]
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- 응용: [[CQRS]] · [[Microservices]]
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- Adjacent: [[Event-Sourcing]]
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## 🤖 LLM 활용
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**언제**: 매 N×N coupling 의 emerge — 매 5+ components 매 mutual callbacks. CQRS / saga implementation.
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**언제 X**: 매 simple 2-component dependency — 매 direct injection 매 sufficient. Hot-path latency-critical (mediator dispatch overhead).
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## ❌ 안티패턴
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- **God Mediator**: 매 mediator 매 business logic 의 absorb — 매 anemic handlers, 매 mediator 의 1000+ lines. Mediator 의 routing only.
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- **Event soup**: 매 untyped string events — 매 'user_signup' vs 'userSignup' typo 의 silent failure. Typed map 의 use.
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- **Sync chain pretending async**: 매 emit() 매 await chain 의 200ms latency — 매 async queue 의 use.
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- **Lost events**: 매 in-memory bus 매 crash 의 lose — 매 durability 매 required 의 persistent queue.
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## 🧪 검증 / 중복
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- Verified (GoF Design Patterns; MediatR docs; NestJS CQRS).
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- 신뢰도 A.
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## 🕓 Changelog
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| 날짜 | 변경 |
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — Event Mediator pattern 의 typed/saga/Kafka 의 5 patterns |
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