How do I override a property (based on extended interface) in typescript class?

Question

I want to override property in Typescript class, which is also a constructor parameter. The property is shaped by the interface, which is also extended. Because of the verbal description is complicated, better see this minimal code example:

interface IA
{
  x: boolean;
}

class CA
{
  constructor(protected readonly o: IA)
  {    
  }
}

type Modify<T, R> = Omit<T, keyof R> & R;

interface IB extends Modify<IA, {x: number}>
{
  y: string;
}

class CB extends CA  // <--- Class 'CB' incorrectly extends base class 'CA'.
{
  constructor(protected readonly o: IB)
  {
    super(Object.assign(o, {x: !!o.x}));
  }
}

Playground Link

I read How do I override a property in typescript? but there are only interfaces involved, I need this for a class property.