The developer can set up a subdomain for one of their websites by configuring the subdomain route in the
.magento/routes.yaml file. This file defines how incoming requests are routed to different applications or services on the Adobe Commerce Cloud platform. The developer needs to add a route for secondstore.example.com and map it to the same application as example.com. The developer also needs to specify the upstream variable for secondstore.example.com as MAGE_RUN_CODE and MAGE_RUN_TYPE. Verified References: [Magento 2.4 DevDocs] 3

According to the Plugins (Interceptors) guide for Magento 2 developers, plugins are class methods that modify the behavior of public class methods by intercepting them and running code before, after, or around them.
However, some classes in Magento 2 implement the NoninterceptableInterface interface, which prevents plugins from being generated for them. The Magento\Framework\App\cache\Proxy class is one of them, as it extends from Magento\Framework\ObjectManager\NoninterceptableInterface. Therefore, the plugin is not executing as expected because the target class implements NoninterceptableInterface. Verified References:
https://devdocs.magento.com/guides/v2.3/extension-dev-guide/plugins.html

The developer can test the new feature under the integration environment by deactivating one of the active integration environment branches, creating a new active branch from integration and installing the module, and pushing the changes. This is because Enhanced Integration Environments have a limit of four active branches at a time, and each branch has its own dedicated database and services. The developer can use the Cloud CLI for Commerce tool to manage the branches and deploy the code changes. Verified References:
[Magento 2.4 DevDocs] 1

The reason why there are records remaining in the inventory_reservation table is that only reservations no longer needed are removed by the cron job. The inventory_reservation table tracks the quantity of each product in each order and creates a reservation for each product when an order is placed, shipped, cancelled or refunded. The initial reservation has a negative quantity value and the subsequent reservations have positive values. When the order is complete, the sum of all reservations for the product is zero. The cron job removes only those reservations that have a zero sum from the table, leaving behind any reservations that are still needed for incomplete orders. Verified References: [Magento 2.4 DevDocs] [Magento Stack Exchange]

The developer can extend the existing CartltemPrices GraphQL schema to include a custom base_price field by adding the following code to the module's etc/schema.graphqls file:
extend type CartltemPrices { base_price: Money! @doc(description: "The base price of the cart item") } This code adds a new field called base_price to the CartltemPrices type and specifies that it is of type Money and it is not nullable. The @doc directive adds a description for the field that will be shown in the schema documentation. The developer also needs to create a custom resolver class for the base_price field and declare it in the di.xml file of the module. Verified References: [Magento 2.4 DevDocs] [Magento Stack Exchange]