Understanding Effect's Dependency Injection with `provideSystem` and Context Tags

const extractShoppingList = (message: string) =>
      Effect.gen(function*() {
        const result = yield* completions.structured({
          input: message,
          schema: ShoppingList,
        });
        return yield* result.value;
      }).pipe(
        AiInput.provideSystem(`Extract the shopping list from the provided message.`),
      );

export class SystemInstruction extends Context.Tag("@effect/ai/AiInput/SystemInstruction")<
  SystemInstruction,
  string
>() {}

export const provideSystem = 
  <A, E, R>(effect: Effect.Effect<...>, input: string): Effect.Effect<A, E, Exclude<R, SystemInstruction>> =>
    Effect.provideService(effect, SystemInstruction, input)
)