OK, maybe I'm dumb/blind, but in the docs it says "rebuild and restart the server." But I don't see a button to do this anywhere. Or from any contextual menu. And I can't find anything in their docs explaining how to do it. If I just try to start the app again, it gets angry because I already have App Engine running on the needed port.
Only solution I've found is to restart Eclipse... any other ideas? A screenshot of a button would help if possible. :)
I might add that the "little red box" is not always visible. It drove me crazy reading that same instruction but not seeing the terminate button until I discovered that the Console windows has "layers" that you can select from using the drop-down button on the far right of the controls for the Console view. You just need to go "back" to the console screen that says the server is running and you will see the little red terminate button.
The previous answer wasn't cutting the cheese for me. Upon first starting App Engine, the red square would be available above the text entry area. If I then clicked the run button again, then red square would go away and the console for the previous launch would be replaced by the console for the new launch. To manually stop the App Engine server, you can kill it from the terminal: http://geekbrigade.wordpress.com/2009/02/26/how-to-find-and-kill-a-process-that-is-using-a-particular-port-in-ubuntu/ In short, "sudo netstat -lpn |grep :8888" and kill the service by process ID.
Strangely, adding Google Web Toolkit to the project made my App Engine launch show up in the Development Mode pane, where it could be easily be killed or restarted.