Centralized schema stitching w/o using a gateway service

[gmanvel]

I was wondering if it's possible to use centralized schema stitching w/o using gateway. Using centralized stitching example as a reference, suppose we try to extend product type to include inventory, reviews service data.

Something like this. Define a Stitching.graphql in product service

extend type Product {
  inStock: Boolean
    @delegate(
      schema: "inventory",
      path: "inventoryInfo(upc: $fields:upc).isInStock")
  shippingEstimate: Int
    @delegate(
      schema: "inventory"
      path: "shippingEstimate(weight: $fields:weight price: $fields:price)")
  reviews: [Review] @delegate(schema: "reviews" path:"reviewsByProduct(upc: $fields:upc)")
}

Change registration in product service's Startup.cs to

services.AddHttpClient(Inventory, 
    c => c.BaseAddress = new Uri("http://localhost:64309/graphql"));
services.AddHttpClient(Reviews, 
    c => c.BaseAddress = new Uri("http://localhost:64317/graphql"));

services
    .AddSingleton<ProductRepository>()
    .AddGraphQLServer()
    .AddQueryType<Query>()
    .AddRemoteSchema(Inventory, ignoreRootTypes: true)
    .AddRemoteSchema(Reviews, ignoreRootTypes: true)
    .AddTypeExtensionsFromFile("./Stitching.graphql");

With this setup, trying to query extended product data fails with error

Is this supported, or am I doing it wrong ?

UPDATE

It seems that $fields:upc is not getting "resolved" to be passed to inventory. If I hard code upc value of 3

extend type Product {
  inStock: Boolean
    @delegate(
      schema: "inventory",
      path: "inventoryInfo(upc: 3).isInStock")
  shippingEstimate: Int
    @delegate(
      schema: "inventory"
      path: "shippingEstimate(weight: $fields:weight price: $fields:price)")
  reviews: [Review] @delegate(schema: "reviews" path:"reviewsByProduct(upc: $fields:upc)")
}

I can successfully query extended product data & get the expected results.

query {
  product(upc: 3) {
    upc
    name
    inStock
  }
}
{
  "data": {
    "product": {
      "upc": 3,
      "name": "Chair",
      "inStock": true
    }
  }
}