prefixes: [ [ "dijit", "../../dijit" ], [ "dojox", "../../dojox" ], [ "esri", "../../esri"], [ "app", "../../app" ], [ "dbp", "../../dbp" ] ]
You can include esri code in your layer. You need to download the source code from the esri customers site (i think). It's kind of hard to find but it's on arcgis.com somewhere.
After that you need to do something like this, and then add the esri namespace to your deps.prefixes: [ [ "dijit", "../../dijit" ], [ "dojox", "../../dojox" ], [ "esri", "../../esri"], [ "app", "../../app" ], [ "dbp", "../../dbp" ] ]
It's not easy, but it can be done!
We don't provide an un-minified version of the API. You can download the API if you'd like to host locally here: http://help.arcgis.com/en/webapi/javascript/arcgis/help/jshelp/intro_accessapi.html
Which takes you here: http://resources.arcgis.com/content/web/arcgis-javascript-api-download
No, you can still do builds.
I haven not personally done it, but the two blog post links you originally posted are talking about doing dojo builds with our already built API.
To clarify, I'm looking for a way to produce a custom build that includes my app's dojo dependencies AND esri dependencies all bundled up in one or a few lean layer file(s).