Fantastic job isolating it like that!I posted here about how I can replicate.
I can now solve this (KP on reboot (Watchdogd))
My replication steps only work when my terminal emulator (iTerm/Terminal) was in added in "Developer Tools" section of Security & Privacy settings in macOS.
Removed them and I could not longer replicate.
This looks to be a bug in codesign/watchdogd/adhoc signatures. Where you remove the terminal from dev tools, you can see the signature check is performed and all is well.
If you have terminal in the "developer tools" category, certain tools (like the ones I describe in my post, ruby/pip), cause the OS to panic on reboot, as something ends up hanging.
Amazing but now solved...
Described further here: https://sigpipe.macromates.com/2020/macos-catalina-slow-by-design/
But still curios if that solves the problem for everyone that has it? It seems there can be different causes for ”watchdog timeout”, so I guess not…