Not a OS X developer but I will have a go at answering. To open a file that isn't in the application's private space the user must select it through the defaul

Not a OS X developer but I will have a go at answering. To open a file that isn't in the application's private space the user must select it through the default OS X file picker dialogue (the app then gets permanent access to the file). This will work well for apps working on single user selected files but doesn't work well when major parts of an app are file navigation, management and generation(which is typically the case for an IDE). I'm not sure whether full access can be granted to whole directories or what the rules on running/debugging generated binaries are. Sand boxing is a good thing that combined with the Apple review process means little utilities from providers you have never heard of trustable as local apps that aren't going to read your contacts and documents without your permission but it does make life hard for an IDE. It sounds like Coda haven't given up on supporting the sandbox yet but they did not want to delay product release for it.