Appending services to an existing runtime in Effect Typescript

class A extends Context.Tag("A")<A, {}>() {
  static layer = Layer.succeed(this, {})
}
class B extends Context.Tag("B")<B, {}>() {
  static layer = Layer.succeed(this, {})
}
class C extends Context.Tag("C")<C, {}>() {}

const builder = (rt: Runtime.Runtime<A | B | C>) => {

  return () => Effect.gen(function*(){
    const a = yield* A
    const b = yield* B
    const c = yield* C

  }).pipe(rt.runPromise)
})

class TheService extends Effect.Service<TheService>()(
  "TheService",
  {
    dependencies: [
      A.layer,
      B.layer
    ],
    effect: Effect.gen(function*() {
      const runtime = yield* Effect.runtime<
        | A
        | B
      >()

      const buildThings = Effect.fn("buildThings")(function*() {
        // Here is where I need to build the C service
        return { x: builder(runtime) }
      })

      return { buildThings }
    })
  }
) {}