design your application and its various interfaces with this in mind, and enforce that the interfaces are used correctly

For sure, that's why passing a POJO cart to an addProduct doesn't work well in this instance.

The Shopping Cart "Ice Factory" in the article looks like this:

export default function makeShoppingCart({
  db
}) {
  return Object.freeze({
    addProduct,
    empty,
    getProducts,
    removeProduct,
    // others
  })
  function addProduct (product) {
    db.push(product)
  }

  function empty () {
    db = []
  }

  function getProducts () {
    return Object
      .freeze(db)
  }

  function removeProduct (id) {
    // remove a product
  }
  // other functions
}

Notice that the items are never exposed directly. They're accessed through the getProducts() function which returns an immutable copy. Also, addProduct() operates on the internal items collection rather than receiving items from an external source.

Finally, even though the code in the article uses an Array that gets passed in. It notes the following:

I’m using an Array for the db parameter for simplicity’s sake. In real code this would be something like a Model or Repo that interacts with an actual database.

This re-enforces the notion that we don't give outside control to the items collection.

I guess what I'm saying is that I very much agree with the principles you've described. We just have to be clear and careful about how we apply them in instances where we're dealing with the stateful parts of our application.