Comment by your_fin

The way zod and arktype generally handle this is by providing treating the schema as the source of truth, rather than a type. They then provide a way to define the type in terms of the schema:

  // zod 3 syntax
  import { z } from 'zod'

  const RGB = z.schema({
    red: z.number(),
    green: z.number(),
    blue: z.number(),
  })
  type RGB = z.infer<typeof RGB>
  // same thing as:
  // type RGB = { red: number; green: number; blue: number };

For the initial migration, there are tools that can automatically convert types into the equivalent schema. A quick search turned up https://transform.tools/typesgcript-to-zodghl, but I've seen others too.

For what it's worth, I have come to prefer this deriving types from parsers approach to the other way around.