With mode-compile, which is not core, but nevertheless the default in cperl-mode.

You may want to look into the perl menu in the top-bar after activating cperl-mode.

<menu-bar> <Perl> <Run> runs the command mode-compile, which is an
interactive autoloaded compiled Lisp function in `mode-compile.el'.
[download]

Auto flush was helpful yes, but input is still ignored.

Actually all input is considered compilation or error navigation commands, which makes sense in a buffer with start

Now I'm thinking about making my script automatically redirecting stdout and stdin to a spawned console /or buffer. This while still keeping stder in the compilation buffer...

I did this before in order to debug Term::ReadLine apps, have to dig that out again. I'm weak on tty Channel foo ...