refector: SSE 유저 상태 완전 제거 로직 추가

Author: soheeGit

src/main/java/store/lastdance/service/notification/SSENotificationV2ServiceImpl.java

@@ -146,14 +146,12 @@ private void cleanupConnection(UUID userId, String connectionId, SseEmitter emit
     }
 
     private void cleanupSingleConnection(UUID userId, String connectionId) {
-        // heartbeat 취소
         ConcurrentHashMap<String, ScheduledFuture<?>> userTasks = heartbeatTasks.get(userId);
         if (userTasks != null) {
             ScheduledFuture<?> task = userTasks.remove(connectionId);
             if (task != null) task.cancel(true);
         }
 
-        // emitter 종료
         ConcurrentHashMap<String, SseEmitter> userConnections = connections.get(userId);
         if (userConnections != null) {
             SseEmitter emitter = userConnections.remove(connectionId);
@@ -166,6 +164,13 @@ private void cleanupSingleConnection(UUID userId, String connectionId) {
             }
         }
 
+        if (userConnections != null && userConnections.isEmpty()) {
+            connections.remove(userId);
+            heartbeatTasks.remove(userId);
+            userLocks.remove(userId);
+            log.debug("SSE 유저 상태 완전 제거 (마지막 연결 정리): userId={}", userId);
+        }
+
         log.debug("SSE 단일 연결 정리: userId={}, connectionId={}", userId, connectionId);
     }