Message12302

> That this does not find the CPython available on the PATH may be a defect.

When I implemented that I felt like if it called into native CPython totally silently that would be too much magic under the hood. The message is also meant to let the user consciously acknowledge that it is invoking CPython now.
We can decide to add support for automatic CPython calls. Hoever I also wanted to let the user explicitly name the CPython to be used to ensure we won't get Python3 vs 2 bytecode incompatibility issues.

> If we like this answer, then it is a documentation (error message) change only.

Let's just fix the error message for now (i.e. for this release).