question about the "taint" section of the "From 0 to Production" tutorial

import "server-only";

import { createHydrationHelpers } from "@trpc/react-query/rsc";
import { headers } from "next/headers";
import { cache } from "react";

import { createCaller, type AppRouter } from "@/server/api/root";
import { createTRPCContext } from "@/server/api/trpc";
import { createQueryClient } from "./query-client";

const createContext = cache(async () => {
  const heads = new Headers(await headers());
  heads.set("x-trpc-source", "rsc");

  return createTRPCContext({
    headers: heads,
  });
});

const getQueryClient = cache(createQueryClient);
const caller = createCaller(createContext);

export const { trpc: api, HydrateClient } = createHydrationHelpers<AppRouter>(
  caller,
  getQueryClient
);

import { z } from "zod";
import { createTRPCRouter, publicProcedure } from "@/server/api/trpc";
import { auth } from "@clerk/nextjs/server";


export const imageRouter = createTRPCRouter({

    getImages: publicProcedure.query(async ({ ctx }) => {

        const user = await auth();

        const userId = user.userId as string;

        if (!userId) return null;

        const images = await ctx.db.image.findMany({ 
            where: {
                userId: {
                    equals: userId
                } 
            }
        });

      return images ?? null;
    }),
})