Validate typescript union type on runtime

Context:

type NonFeline = 'Mouse' | 'Sheep';
type Feline = 'Lion' | 'Cat' ;

type AnimalInfo = {
    Category: NonFeline;
    Age: number;
} | {
   Category: Feline;
   Age: number;   
   Owner:string;
};

let x: AnimalInfo = getAnimal(1);
if(x.Category === 'Lion' || x.Category === 'Cat'){
  console.log(x.Owner);
}

function getAnimal(i: number): AnimalInfo{
  return i % 2 ? {
    Category: "Lion",
    Age: 10,
    Owner: "Y"
  } : {
    Category: "Mouse",
    Age: 1,
  };
}

How can I be sure when later I added "Tiger" to Animal type, no need to change to if, or at least if gives me a compile time typescript error?

To solve the runtime check use a set, extract values from it as a type and use a type predicate function (Set#has() doesn't narrow unfortunately) to check whether AnimalInfo is Feline:

Playground

type SetValues<T extends Set<unknown>> = T extends Set<infer I> ? I : never;

const felineCategories = new Set(['Lion', 'Cat'] as const); // you add any new types here
const isFeline = (animal: AnimalInfo): animal is Feline => felineCategories.has(animal.Category as FelineCategory);
type FelineCategory = SetValues<typeof felineCategories>;
type AnimalCategory = 'Mouse' | 'Sheep';

type Animal = {
    Category: AnimalCategory;
    Age: number;
}

type Feline = {
   Category: FelineCategory;
   Age: number;   
   Owner:string;
}

type AnimalInfo = Animal | Feline;

declare const x: AnimalInfo;
if(isFeline(x)){
  console.log(x.Owner);
}

An array version:

Playground

const felineCategories = ['Lion', 'Cat'] as const; // you add any new types here
const isFeline = (animal: AnimalInfo): animal is Feline => felineCategories.includes(animal.Category as FelineCategory);
type FelineCategory = typeof felineCategories[number];
type AnimalCategory = 'Mouse' | 'Sheep';

type Animal = {
    Category: AnimalCategory;
    Age: number;
}

type Feline = {
   Category: FelineCategory;
   Age: number;   
   Owner:string;
}

type AnimalInfo = Animal | Feline;

declare const x: AnimalInfo;
if(isFeline(x)){
  console.log(x.Owner);
}