> Would we need to protect this against accidentally stepping into system
> processes?

Good question. First, the proposal always asks the user before opening a second debugger, which should reduce the chance of accidentally stepping. Second, currently only primitiveResume is monitored. Sempahores/critical sections are NOT covered at the moment because I believe this would fire up too often. I'm not aware of any place where a system process (by which I assure you mean high-level processes such as idle or timing) are manually resumed by normal processes. Were you having any concrete examples in mind?