Review of inner and outer context with express

import { initTRPC } from '@trpc/server';
import type * as trpcExpress from '@trpc/server/adapters/express';
import superjson from 'superjson';
import type { OpenApiMeta } from 'trpc-openapi';

// Fake prisma
const prisma = 'prisma';

export interface CreateInnerTRPCContextOptions
  extends Partial<trpcExpress.CreateExpressContextOptions> {}

export interface AppInnerContext
  extends Partial<trpcExpress.CreateExpressContextOptions> {
  prisma: string;
}

export async function createInnerTRPCContext(
  _opts: CreateInnerTRPCContextOptions,
): Promise<AppInnerContext> {
  return {
    prisma,
  };
}

type CreateTRPCContextOptions = CreateInnerTRPCContextOptions &
  trpcExpress.CreateExpressContextOptions;

export type AppContext = AppInnerContext &
  trpcExpress.CreateExpressContextOptions;

export async function createTRPCContext(
  opts: CreateTRPCContextOptions,
): Promise<AppContext> {
  const innerContext = await createInnerTRPCContext(opts);

  return {
    ...innerContext,
    req: opts.req,
    res: opts.res,
  };
}

const t = initTRPC.meta<OpenApiMeta>().context<AppInnerContext>().create({
  transformer: superjson,
});

export const createTRPCRouter = t.router;

export const publicProcedure = t.procedure;