fix(transport): fail closed on unresolved endpoints

Author: loong10k

src/main/java/io/github/easy4j/hermes/util/EndpointGuard.java

@@ -93,10 +93,8 @@ public static void requireSafeHost(String host, String context) {
         try {
             addr = InetAddress.getByName(lookup);
         } catch (UnknownHostException e) {
-            // DNS 还无法解析该主机（内部域名、尚未就绪的服务、离线环境）。
-            // 约束只要求拦截 localhost/环回/私有/保留地址——未解析的主机不在
-            // 其列，且请求期 DNS 失败会由 OkHttp 自然报错。放行。
-            return;
+            throw new IllegalArgumentException(
+                    "Endpoint host could not be resolved: " + host + " (" + context + ")", e);
         }
         if (isUnsafe(addr)) {
             throw new IllegalArgumentException(