diff --git a/backend/internal/pkg/antigravity/client.go b/backend/internal/pkg/antigravity/client.go
index f24ff5a8..e2802535 100644
--- a/backend/internal/pkg/antigravity/client.go
+++ b/backend/internal/pkg/antigravity/client.go
@@ -257,6 +257,16 @@ func NewClient(proxyURL string) (*Client, error) {
 			return nil, fmt.Errorf("configure proxy: %w", err)
 		}
 		client.Transport = transport
+	} else {
+		// 无显式代理时，使用支持 HTTPS_PROXY 环境变量的 Transport
+		// 用于 OAuth token 交换等需要访问外部服务的场景
+		client.Transport = &http.Transport{
+			Proxy: http.ProxyFromEnvironment,
+			DialContext: (&net.Dialer{
+				Timeout: proxyDialTimeout,
+			}).DialContext,
+			TLSHandshakeTimeout: proxyTLSHandshakeTimeout,
+		}
 	}
 
 	return &Client{