I ginned up a "wait for the internet to come back up" script that repeatedly pinged something with one packet, and used the Mac 'open' command to play an mp3 file once the ping succeeded. Unsexy, but when you can't google up a better solution...
I like this idea. Some company that I may or may not work for either does or does not install malware on our computers, extending the boot sequence and something in the network layer that makes it take MINUTES for anything http to be usable, even after the DE is loaded. Would love to add such a script to my login’s boot sequence
