Namespace egine routes

Issue summary

Before opening this issue, I have done the following:

• Upgraded to the latest version of the package
  • shopify_app version: 22.5.2
  • Ruby version: 3.3.0
  • Operating system: Arch Linux
• Set log_level: :debug in my configuration, if applicable
• Found a reliable way to reproduce the problem that indicates it's a problem with the package
• Looked for similar issues in this repository
• Checked that this isn't an issue with a Shopify API
  • If it is, please create a post in the Shopify community forums or report it to Shopify Partner Support

My shopify app needs to have a separate admin section where our admin will be able to handle our customers data, so I planned to namespace all the ShopifyApp with something like /shopify/ and leave the top level routes for our internal dashboard so I tried to wrap all the routes created by the rials template in a namespace like:

# frozen_string_literal: true

Rails.application.routes.draw do
  namespace :shopify do
    root to: "home#index"

    # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html

    scope path: :api, format: :json do
      # POST /api/products and GET /api/products/count
      resources :products, only: :create do
        collection do
          get :count
        end
      end
      namespace :webhooks do
        post "/app_uninstalled", to: "app_uninstalled#receive"
        post "/app_scopes_update", to: "app_scopes_update#receive"
        post "/customers_data_request", to: "customers_data_request#receive"
        post "/customers_redact", to: "customers_redact#receive"
        post "/shop_redact", to: "shop_redact#receive"
      end

      # Health check routes
    end

    mount ShopifyApp::Engine, at: "/api"
    get "/api", to: redirect(path: "/") # Needed because our engine root is /api but that breaks frontend routing

    # If you are adding routes outside of the /api path, remember to also add a proxy rule for
    # them in web/frontend/vite.config.js

    # Any other routes will just render the react app
    match "*path" => "shopify/home#index", via: %i[get post]
  end

  get "health", to: "health#index"
  get "health/detailed", to: "health#detailed"

  root to: "dashboard#index"
end

Checking the routes with rails route, I noticed that all the routes generated by the ShopifyApp engine are still not namespace. I spent several hours trying to set up the config.root_url and the at: "/api" in the engine mount to various properties in the engine initialisers, but this didn't help. Then I noticed that some of the paths are even hardcoded and not configurable.

https://github.com/Shopify/shopify_app/blob/bf3ab7ec710f7e2c7dbfd87411146742ff2937a7/config/routes.rb#L10-L11

Expected behavior

All the routes generated by the engine should be namespaced.

Actual behavior

all the routes are not namespaced

Steps to reproduce the problem

1. Add a namespace around the mount engine in the config/routes.rb
2. Run the command rails routes

Debug logs

// Paste any relevant logs here

The engine routes are defined in config/routes.rb at the linked lines; first reproduce the namespace setup and inspect the output from rails routes. Trace how the mounted engine's paths are built, then verify that every generated route carries the requested namespace without breaking the documented application routes.