I know another att variant guy captured the newest pie zip URL and I downloaded it. The recovery lives in the boot.img right?
Were AT&T the ones that sent you the THX model? Or did you buy it straight from Razer?
I'll find that URL and past it here. I've extracted the previous Oreo update from the att build prior to moving to the global version. I had to capture the URL from a log, then downloaded it, then extracted it then I had to use python to fully extract pieces of the payload. Which included the boot.img.
Not a developer but I think I can help here.
Here's the URL for pie July security for att:
https://android.googleapis.com/pack.../2965f0fadb65852413dba10a4fed1029ecce838f.zip
This will help you extract the payload.bin in the zip:
https://shorturl.at/ABEMW