>  from everything I can tell, I think this is safe

OK. As an optional change to perhaps make the use case clearer:
```
String projectName = Iterables.get(Splitter.on("@").split(in.identity), 0);
if (projectName.indexOf("-") != -1) {
  // ID of the form project_id-extended_uid@developer.gserviceaccount.com
  projectName = Iterables.get(Splitter.on("-").split(projectName), 0);
}
...
```
? Also OK with leaving things as they are.