how to ensure that the output of a function has the same type of one of the function parameter

typed-function.ts

import { z, ZodSchema } from 'zod';

function createAdapter<T extends ZodSchema, U extends ZodSchema>(
  options: {
    input: T;
    output: U;
  },
  fn: (a: z.infer<T>) => Promise<z.infer<U>>
) {
  return {
    a: options.input,
    b: options.output,
    fn,
  };
}

// demo

// define input and output
const input = z.object({
  title: z.string().nullish(),
});

const output = z.object({
  title: z.string().nullish(),
});

// create adapter implementation
const demo = createAdapter({ input: input, output: output }, async (args) => {
  return {
    title: args.title?.toUpperCase(),
  };
});

const test = async () => {
  const result = await demo.fn({ title: 'hello' });
  console.log(result);
};

test();