Don't show stock for on-demand inventory items

app/controllers/admin/variant_overrides_controller.rb

@@ -71,6 +71,12 @@ def inventory_import_dates
 
     def load_collection
       collection_hash = Hash[variant_overrides_params.each_with_index.map { |vo, i| [i, vo] }]
+
+      # Reset count_on_hand when switching to producer settings:
+      collection_hash.each_value do |vo|
+        vo["count_on_hand"] = nil if vo.fetch("on_demand", :unchanged).nil?
+      end
+
       @vo_set = Sets::VariantOverrideSet.new(@variant_overrides,
                                              collection_attributes: collection_hash)
     end

app/serializers/api/admin/variant_override_serializer.rb

@@ -6,6 +6,12 @@ class VariantOverrideSerializer < ActiveModel::Serializer
       attributes :id, :hub_id, :variant_id, :sku, :price, :count_on_hand, :on_demand,
                  :default_stock, :resettable, :tag_list, :tags, :import_date
 
+      def count_on_hand
+        return if object.on_demand
+
+        object.count_on_hand
+      end
+
       def tag_list
         object.tag_list.join(",")
       end

app/serializers/api/admin/variant_simple_serializer.rb

@@ -19,6 +19,7 @@ def name
       end
 
       def on_hand
+        return if object.on_demand
         return 0 if object.on_hand.nil?
 
         object.on_hand

spec/system/admin/variant_overrides_spec.rb

@@ -254,9 +254,12 @@
 
         context "with overrides" do
           let!(:vo) {
-            create(:variant_override, :on_demand, variant:, hub:, price: 77.77,
-                                                  default_stock: 1000, resettable: true,
-                                                  tag_list: ["tag1", "tag2", "tag3"])
+            create(
+              :variant_override,
+              on_demand: true, count_on_hand: -5,
+              variant:, hub:, price: 77.77, default_stock: 1000, resettable: true,
+              tag_list: ["tag1", "tag2", "tag3"]
+            )
           }
           let!(:vo_no_auth) {
             create(:variant_override, variant:, hub: hub2, price: 1, count_on_hand: 2)