The title is poor, but I don’t really know how to describe the problem better

Can someone please explain to me what the error is in this code:

  type Variants0 = {
    variant0: { v0: string };
    variant1: { v1: string };
  };

  const callAllVariants = <S extends { [P in keyof Variants0] }>(
    f: <V extends keyof S>(m: V) => S[V],
  ): { [V in keyof Variants0]: ReturnType<typeof f<V>> } => {
    return {
      variant0: f('variant0'),
      variant1: f('variant1'),
    };
  };

  const r0 = callAllVariants<Variants0>(<V extends keyof Variants0>(v: V) => {
    return {
      variant0: { v0: 'v0' },
      variant1: { v1: 'v1' },
    }[v];
  });

  type Variants1 = { [V in keyof Variants0]: Variants0[V] & { extra: number } };

  const r1 = callAllVariants<Variants1>(
    <V extends keyof Variants1>(vs: V): Variants1[V] => {
      const r = {
        variant0: { v0: 'v0', extra: 0 },
        variant1: { v1: 'v1', extra: 1 },
      }[vs];
      // Doesn't work:
      const r3: Variants0[V] & { extra: number } = r;
      const r2: Variants1[V] = r3;
      return r2;
      // Works:
      // return r;
    },
  );

The compile error is:

Type 'Variants0[V] & { extra: number; }' is not assignable to type 'Variants1[V]'.
  Type 'Variants0[V] & { extra: number; }' is not assignable to type '{ v0: string; } & { extra: number; } & { v1: string; }'.
    Type 'Variants0[V] & { extra: number; }' is not assignable to type '{ v0: string; }'

I don’t understand why Variants0[V] & { extra: number } isn’t the equivalent type of Variants1[V]

If I comment out the r2 and r3 lines and uncomment the return r then it compiles fine, but I don’t understand what the issue is… This is a simplified version of some code where I am having a similar issue but cant easily get rid of the intermediate types