Button Group

interface ButtonGroupButton {
  label: string;                  // Button label (required)
  variant?: 'default' | 'secondary' | 'destructive' | 'outline' | 'ghost' | 'link';
  size?: 'default' | 'sm' | 'lg' | 'icon';
  disabled?: boolean;             // Whether this button is disabled
  onClick?: never;                // RETIRED (objectui#6124) — author behaviour
                                  // as a node type, e.g. an action:button node
  className?: string;             // Per-button CSS class
}

interface ButtonGroupSchema {
  type: 'button-group';
  buttons?: ButtonGroupButton[];  // Button definitions

  // Defaults applied to every button that does not set its own
  variant?: 'default' | 'secondary' | 'destructive' | 'outline' | 'ghost' | 'link';
  size?: 'default' | 'sm' | 'lg' | 'icon';

  // States
  disabled?: boolean | string | { dialect?: string; source: string };   // boolean, predicate expression, or CEL envelope

  // Styling
  className?: string;
}