I've developed a maven plugin that integrates a bunch of compilers and now I'm working on IDE support.
The sisu build API  seems to provide a way to abstract out the set of changed files since last compile run from a maven plugin.
Your external builder API  seems to provide roughly equivalent book-keeping via Timestamps.
Has the problem of bridging these already been solved?
If you're interested, https://github.com/mikesamuel/closure-maven-plugin is the plugin I want to integrate.