All old is new again
Server Shows Attachment Angles
It’s a known fact that the GET_ATTACHMENT engine function doesn’t return attachment angles. This feature is simply absent from the original engine and model compiler.
Xash3D can partially correct this by returning the angle between the forward vector (running from the bone to the attachment) and the attachment vector (shown in any version of the Half-Life Model Viewer when the Show attachment option is selected). This feature may be useful for implementing things like a headcrab jumping off a dead zombie or realistic positioning of the laser sight on a viewmodel.
To enable this, set the sv_allow_studio_attachment_angles console cvar to 1. The value of this variable is saved in config.cfg, but does not affect clients.