I definitely wouldn't phrase it as an ultimatum in the hiring process.
I would say something like, "I'd like to understand what I'll be working with. Would you be up for letting me sign an NDA so that I can view the codebases on which you'll be having me contribute?"
If there's pushback on that and they are asking me to do a puzzle, I might then frame it as follows:
"I understand that you need a strong signal about the skill of engineers you hire. I also need a strong signal about the technical elements where I'll be spending the vast majority of my time. How can I gauge this without looking at some of your code?"
And just go from there, depending on their answer.
I definitely wouldn't phrase it as an ultimatum in the hiring process.
I would say something like, "I'd like to understand what I'll be working with. Would you be up for letting me sign an NDA so that I can view the codebases on which you'll be having me contribute?"
If there's pushback on that and they are asking me to do a puzzle, I might then frame it as follows:
"I understand that you need a strong signal about the skill of engineers you hire. I also need a strong signal about the technical elements where I'll be spending the vast majority of my time. How can I gauge this without looking at some of your code?"
And just go from there, depending on their answer.
Perhaps I'll edit to reflect that.