[21:03:07] <Reedy>	 woo, libup
[22:28:12] <Krinkle>	 milimetric: no, but there are indeed some Special: responses that result in the XAnalytics code not running.
[22:28:53] <Krinkle>	 One in particular I found in the webrequest stream is responses like HTTP 204 /wiki/Special:Watchlist ?action=render&peek=1&from=....&....
[22:28:59] <Krinkle>	 and I imagine there's an HTTP 200 variant of that as well.
[22:29:34] <Krinkle>	 which is a chunked HTML response as API for a client, similar to e.g. auto-login and Special:Export which also return something that isn't a skinned web page. 
[22:29:47] <Krinkle>	 and thus don't involve OutputPage and don't have XAnalytics call generateHeader()
[22:30:42] <Krinkle>	 I'll leave a comment, but my suggestion would be to ignore anything that doesn't have that response at all and treat them the same as e.g. /w/rest.php or /static/* requests or anything else that's irrelevant.