How to get output/debug isobuild

How can I debug the build system, or log info to the console from a build plugin, like a babel plugin in meteor?

It looks like we can console.log easily enough - but it only compiles once when the app starts, and then when a file has changed. To get it to recompile (and re-log) you have to restart the build system, and then modify a file.

I’m sure there’s a better way, and probably a way to use a debugger. That I still don’t know.