Zod transform types

Question

I have a zod type for our backend requirements that looks like this:
const ZCustomType = z.object({ 
  nameFirst: z.string(),
  nameLast: z.string(),
  dateOfBirth: z.string().transform((v) = {
        if (v) return dayjs(v, ['M/D/YYYY']).toDate();
        else return undefined;
  }),})

When I'm using that type through my code, it properly shows as a Date. When using that as a zod input on my trpc route, it's saying it's a string. I was assuming the transform isn't properly working since it's using dayjs but even just doing a straight transform to new Date() still shows as a string. Is there a way to make this work? (There are deeper problems that adjusting the type to z.date() wouldn't work because the API expects a Date but passes back 'M/D/YYYY' string)

Zod transform types

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