I also want to briefly note that communicating, from the outset, "this is a significant incident, your keys are compromised, the attack is ongoing and you cannot enter new keys as _those too will be compromised_" is a better response than leaving people to figure out "my keys are compromised and oh surprise, I can't deploy".

I would rather know I should put a notice on my site, or my own social media, or notify my own customers ASAP and disable some functionality (or make my own choice about porting somewhere else as a mitigation) than get caught out like this after the horse has bolted and my key has been compromised for hours.