fix(sync): Ignore AsyncRequestNotUsableException in GlobalExceptionHandler

dap-was-lib/src/main/java/io/shinhanlife/dap/lib/mcp/exception/GlobalExceptionHandler.java

@@ -39,6 +39,12 @@ public class GlobalExceptionHandler {
         return buildErrorResponse(-32602, "Invalid params: " + e.getMessage());
     }
 
+    @ExceptionHandler(org.springframework.web.context.request.async.AsyncRequestNotUsableException.class)
+    public ResponseEntity<Void> handleAsyncRequestNotUsable(org.springframework.web.context.request.async.AsyncRequestNotUsableException e) {
+        log.debug(" [Gateway Info] 클라이언트가 비동기 연결을 종료했습니다 (정상): {}", e.getMessage());
+        return ResponseEntity.ok().build();
+    }
+
     @ExceptionHandler(RuntimeException.class)
     public ResponseEntity<JsonRpcResponse> handleRuntime(RuntimeException e) {
         log.error(" [Gateway Internal Error] 시스템 장애: {}", e.getMessage(), e);