There is only one thing missing from this tool to allow it to fully replace the built-in build system, making that functionality interactive, is the
file_regex function from there. Even if the double-click to jump to the error line is too hard to implement, the error phantoms and next/prev error navigation would be super useful.
Although most people might not see the benefit of interactively building via a terminal, I also use the error functionality for debug logging. So when I log something from my code it outputs the file name and source line as well and the log messages appear right in the code, which is a huge productivity boost.
You should be able to take the code pretty much verbatim from
exec.py in Default, but one thing I would request if you did this is an option to display message phantoms alongside the line instead of underneath. This reduces clutter substantially. It's a simple two-line change which I can give you.
Another argument for replacing the built-in build system, besides interactivity, is persistence and complex build environments.
Some people may want to launch build commands in a different CLI environment. For instance I could ssh into a remote server in the shell, log in once and then launch build commands as required. This is what I do when I'm building cross platform code, but I have to fiddle with slow and finicky tools that pass commands to the remote servers and capture the output.
In another scenario, there may be a lot of setup required in the environment before the build commands are executed and the setting up and tearing down of that could be avoided.