Preserve nested REST attribute changes on save

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 Note: For changes to the API, see https://shopify.dev/changelog?filter=api
 ## Unreleased
+- Preserve in-place changes to nested REST attributes when saving resources.
 
 ## 16.3.0 (2026-08-04)
 - [#1443](https://github.com/Shopify/shopify-api-ruby/pull/1443) Add `ShopifyAPI::Utils::ShopValidator` with `sanitize_shop_domain` and `sanitize!`.

lib/shopify_api/rest/base.rb

@@ -3,6 +3,7 @@
 
 require "active_support/inflector"
 require "active_support/core_ext/hash/indifferent_access"
+require "active_support/core_ext/object/deep_dup"
 
 module ShopifyAPI
   module Rest
@@ -301,6 +302,7 @@ def create_instance(data:, session:, instance: nil)
             end
           end
 
+          instance.original_state = instance.original_state.deep_dup
           instance
         end
       end

test/clients/base_rest_resource_test.rb

@@ -315,6 +315,28 @@ def test_saves_removing_children
         assert_requested(stubbed_request)
       end
 
+      def test_saves_in_place_mutations_to_nested_attributes
+        resource = TestHelpers::FakeResource.create_instance(
+          session: @session,
+          data: {
+            "id" => 1,
+            "details" => { "address" => { "first_name" => "John" }, "tags" => ["original"] },
+          },
+        )
+        stubbed_request = stub_request(:put, "#{@prefix}/fake_resources/1.json")
+          .with(body: hash_including(
+            "fake_resource" => hash_including(
+              "details" => { "address" => { "first_name" => "Jane" } },
+            ),
+          ))
+          .to_return(status: 200)
+
+        resource.details["address"]["first_name"] = "Jane"
+        resource.save
+
+        assert_requested(stubbed_request)
+      end
+
       def test_loads_unknown_attribute_with_special_character
         body = { fake_resource: { id: 1, attribute: "attribute", "unknown?": "some-value" } }.to_json