Implement manual shipping method selection

app/controllers/concerns/checkout_callbacks.rb

@@ -27,6 +27,7 @@ module CheckoutCallbacks
 
   def load_order
     @order = current_order
+    @order.manual_shipping_selection = true
 
     redirect_to(main_app.shop_path) && return if redirect_to_shop?
     redirect_to_cart_path && return unless valid_order_line_items?

app/models/concerns/order_shipment.rb

@@ -13,6 +13,8 @@ require 'active_support/concern'
 module OrderShipment
   extend ActiveSupport::Concern
 
+  attr_accessor :manual_shipping_selection
+
   def shipment
     shipments.first
   end

engines/order_management/app/services/order_management/stock/estimator.rb

@@ -22,17 +22,8 @@ module OrderManagement
 
         shipping_rates.sort_by! { |r| r.cost || 0 }
 
-        unless shipping_rates.empty?
-          if frontend_only
-            shipping_rates.each do |rate|
-              if rate.shipping_method.frontend?
-                rate.selected = true
-                break
-              end
-            end
-          else
-            shipping_rates.first.selected = true
-          end
+        unless shipping_rates.empty? || order.manual_shipping_selection
+          select_first_shipping_method(shipping_rates, frontend_only)
         end
 
         shipping_rates
@@ -40,6 +31,21 @@ module OrderManagement
 
       private
 
+      # Sets the first available shipping method to "selected".
+      # Note: seems like a hangover from Spree, we can probably just remove this at some point.
+      def select_first_shipping_method(shipping_rates, frontend_only)
+        if frontend_only
+          shipping_rates.each do |rate|
+            if rate.shipping_method.frontend?
+              rate.selected = true
+              break
+            end
+          end
+        else
+          shipping_rates.first.selected = true
+        end
+      end
+
       def shipping_methods(package)
         shipping_methods = package.shipping_methods
         shipping_methods.delete_if { |ship_method| !ship_method.calculator.available?(package) }