I believe this is because getpath has hit its final fallback case of looking in ".\DLLs" and ".\Lib" for the standard library, and has not performed proper normalisation on these paths. So after removing the last segment, the result is "." which does not end in SEP.

So at least in this case, we can probably just ignore the assertion. However, I'm concerned that this would open up other cases where search paths may be added that are otherwise unintended.

The expected behaviour when the stdlib can't be found is a detailed error message, not a debug assertion/crash.