anchor.diff:        const QueueCommand("buildPackage");
   }
   
  +/**
  + * Commands sent from a main isolate.
  + */
   class MainIsolateCommand<String> extends Enum<String> {
     const MainIsolateCommand(String val) : super (val);
     static const MainIsolateCommand PACKAGE_ADD =
         const MainIsolateCommand("packageAdd");
   }
   
  +/**
  + * Creates a message object to be sent over a `SendPort`
  + */
   Map createMessage(Enum e, dynamic message) =>
       {'command': e.value, 'message': message.toJson() };
   
  +/**
  + * Check data is a `Enum` command.
  + */
   bool isCommand(Enum e, Map data) => data['command'] == e.value;
  
positive.code:       const PackageValidationCommand("packageAddOutbox");
  }
  
  class GceLauncherCommand<String> extends Enum<String> {
    const GceLauncherCommand(String val) : super (val);
    static const GceLauncherCommand PACKAGE_BUILD_COMPLETE =
        const GceLauncherCommand("packageBuildComplete");
  }
  
  class QueueCommand<String> extends Enum<String> {
    const QueueCommand(String val) : super (val);
    static const QueueCommand CHECK_PACKAGE =
  
negative.code:   T get value => _value;
  }
  
  /**
   * Commands sent from a package validation isolate.
   */
  class PackageValidationCommand<String> extends Enum<String> {
    const PackageValidationCommand(String val) : super (val);
  
  