refactor: Seat WebSocket debug로깅 추가

* refactor: websocket동작 info로깅으로 테스트완료, 프로덕션에서는 debug레벨로 설정해서 로그가 남지 않도록 설정

* refactor: seat 웹소켓 이벤트 발행시점 AFTER_COMMIT으로 트랜잭션 종료 이후시점으로 보장

* chore: paymentService TODO 주석 추가

Author: gksdud1109

backend/src/main/java/com/back/api/payment/payment/service/PaymentService.java

@@ -21,7 +21,15 @@
 
 /**
  * Payment 관련 비즈니스 로직 처리
- * 큐,좌석,티켓의 상태변화 과도하게 책임 -> 추후 리팩토링 필요
+ * TODO: PG 연동 시 트랜잭션 경계 재설정 필요
+ *
+ * [설계 방향]
+ * 1. PG API 호출: 트랜잭션 밖으로 이동
+ * 2. 핵심 DB 변경만 @Transactional
+ * 3. Queue/Notification: @TransactionalEventListener(AFTER_COMMIT)
+ *
+ * [리팩토링 시점]
+ * - 실제 PG 연동 구현 시 (TossPaymentClient 등)
  */
 @Service
 @RequiredArgsConstructor

backend/src/main/java/com/back/api/seat/event/SeatEventHandler.java

@@ -1,20 +1,24 @@
 package com.back.api.seat.event;
 
-import org.springframework.context.event.EventListener;
 import org.springframework.stereotype.Component;
+import org.springframework.transaction.event.TransactionPhase;
+import org.springframework.transaction.event.TransactionalEventListener;
 
 import com.back.api.seat.dto.response.SeatStatusMessage;
 
 import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
 
+@Slf4j
 @Component
 @RequiredArgsConstructor
 public class SeatEventHandler {
 
 	private final SeatWebSocketPublisher publisher;
 
-	@EventListener
+	@TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
 	public void handleSeatStatus(SeatStatusMessage msg) {
+		log.debug("SEAT_EVENT_RECEIVED eventId={} seatId={} status={}", msg.eventId(), msg.seatId(), msg.status());
 		publisher.publish(msg);
 	}
 }

backend/src/main/java/com/back/api/seat/event/SeatWebSocketPublisher.java

@@ -6,17 +6,20 @@
 import com.back.api.seat.dto.response.SeatStatusMessage;
 
 import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
 
+@Slf4j
 @Service
 @RequiredArgsConstructor
 public class SeatWebSocketPublisher {
 
 	private final SimpMessagingTemplate messagingTemplate;
 
 	public void publish(SeatStatusMessage msg) {
-		messagingTemplate.convertAndSend(
-			"/topic/events/" + msg.eventId() + "/seats",
-			msg
-		);
+		String destination = "/topic/events/" + msg.eventId() + "/seats";
+		log.debug("WS_PUBLISH destination={} eventId={} seatId={} status={}", destination, msg.eventId(), msg.seatId(),
+			msg.status());
+		messagingTemplate.convertAndSend(destination, msg);
+		log.debug("WS_PUBLISH_COMPLETE destination={}", destination);
 	}
 }