Fix: prevent generateCustomEndpointOptions from overriding headers (#3405)

* implement fix

* update changelog

* lint

Author: joeluong-sfcc

packages/commerce-sdk-react/CHANGELOG.md

@@ -1,10 +1,11 @@
 ## v4.2.0-dev (Sep 26, 2025)
+- Prevent headers from being overriden in `generateCustomEndpointOptions` [#3405](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/3405/)
 
 ## v4.1.0 (Sep 25, 2025)
 
 ## v4.0.0 (Sep 04, 2025)
 
-- [Breaking] Upgrade to commerce-sdk-isomorphic v4.0.0 [2879](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/2879)
+- [Breaking] Upgrade to commerce-sdk-isomorphic v4.0.0 [#2879](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/2879)
 - [Breaking] Remove deprecated properties from useDNT in commerce-sdk-react [#3177](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/3177)
 - Add support for environment level base paths on /mobify routes [#2892](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/2892)
 - Update USID expiry to match SLAS refresh token expiry [#2854](https://github.com/SalesforceCommerceCloud/pwa-kit/pull/2854)

packages/commerce-sdk-react/src/hooks/helpers.ts

@@ -53,6 +53,7 @@ export const generateCustomEndpointOptions = (
     return {
         ...options,
         options: {
+            ...options.options,
             method: options.options?.method || 'GET',
             headers: {
                 Authorization: `Bearer ${access_token}`,
@@ -61,8 +62,7 @@ export const generateCustomEndpointOptions = (
                 ...globalHeaders,
                 ...options.options?.headers,
                 ...(args?.headers ? args.headers : {})
-            },
-            ...options.options
+            }
         },
         clientConfig: {
             ...globalClientConfig,