How to automatically re-enable Fiddle as system proxy?

Reattaching Fiddler automatically is perilous for a bunch of reasons, but yes, it's technically possible to observe changes in the proxy setting for the current user and reattach if they change.

In CustomRules, add the following code:

static function DoReattach(o: Object, ea: EventArgs)
{
   ScheduledTasks.ScheduleWork("reattach", 1000, innerReattach);
}

static function innerReattach()
{
   FiddlerApplication.UI.actAttachProxy();
}

static function OnRetire()
{
   FiddlerApplication.oProxy.remove_DetachedUnexpectedly(DoReattach);
}

and inside the existing Main() function, add

  FiddlerApplication.oProxy.add_DetachedUnexpectedly(DoReattach);

Regards,
Eric Lawrence
Telerik