I'm not sure this will ever be a solved problem. If it's in your threat model to worry about such things, you necessarily need to have your own servers, in a se

I'm not sure this will ever be a solved problem. If it's in your threat model to worry about such things, you necessarily need to have your own servers, in a secured physical location you control. No amount of attestation and auditing will allow you to overcome that sort of threat. For the most part, I believe audit logs and severely restricted permissions provided to employees greatly disincentive the chances of an inside job occurring successfully.