When my external build is built I end up with the hash nv2Kki for react/addons.
When my main bundle is built, it is referencing react/addons with the hash yutbdK.
This of course leads to an Uncaught Error: Cannot find module 'yutbdK' error emitted from my external.js bundle.
If I manually find and replace yutbdK in my main bundle with nv2Kki, then everything works.
Here is my gulpfile for building these two files.