Cannot make _Adobe* script calls from HTML Widget

I have created a simple panel (with only a widget that loads an HTML page) and from within the HTML page I cannot call any of the _Adobe functions.

I determined that:

alert(typeof _AdobeInvokeScript);

shows "undefined"

So what am I doing wrong?

I am using Photoshop CS6, Windows 7 and the most recent version of Configurator.

Note: The HTML example included with Configurator DOES work, but I don't see how my code differs... other than it's vastly less complex.

My extension.html code is here: https://gist.github.com/hamstu/f74574b40644e5912b95#file-extension-htm l