The ajax feature is not addressing much of it but anyway, the question is how to get an URL that is not pointing at a window or page but at the server itself, allowing to build a servlet url to whatever context is needed.
The only way I found is to compute it
{
PortalNodeURL url = response.createRenderURL(request.getPortalNode());
url.setRelative(false);
String portalURL= url.toString();
String context = request.getContextPath();
int contextPathIndex = portalURL.indexOf(context);
return portalURL.substring(0, contextPathIndex);
}