'Wolf' is the OS Platform Codename for Apple's realityOS or xrOS
Wolf will most likely be the name used by Apple for the platform prefix codename that appears in the name of app bundles. This is based on the latest changes to Apple’s OSS public repository. Mark Gurman has previously reported that realityOS’s codename is Oak. This could mean that the realityOS 2.0 could be another tree or more likely it is the case that Oak is similar to the codename for the original iPhone (Purple) and not change. Then xrOS 2.0 could be a constellation since Borealis is another xrOS codename. But in any case the codename for realityOS or xrOS will not change from Wolf since it is at the platform level and not the version level. Also it appears that there will be an Xcode simulator for xrOS.
One last note: this code could be as old as September 2020 which is why it references realityOS instead of xrOS.
h/t @riscv64 and @aaronp613.
+-------------------+---------------+----------------+-----------------+
| Device | OS | App Bundle | Code Names |
+-------------------+---------------+----------------+-----------------+
| Mac | OS X, macOS | Mail.app | Cats, landmarks |
| iPhone | iPhoneOS, iOS | MobileMail.app | Ski resorts |
| Apple Watch | watchOS | NanoMail.app | Beaches |
| Apple Reality Pro | xrOS | WolfMail.app | Constellations |
+-------------------+---------------+----------------+-----------------+