Explanation
The default behavior for how the Salesforce B2B Commerce Global APIs transform Salesforce data is to return field names with a lowercase first letter, camelcase convention. For example, the field nameccrz__E_Product__c in Salesforce will be transformed to eProduct in the API. This is done to follow the JavaScript naming convention and to avoid conflicts with the standard Salesforce fields and relationships.
Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Query Transformation

The event that is triggered within Salesforce B2B Commerce whenever a cart's state changes is cartChange. This event is triggered by the updateCart method of the CCRZ.Cart class, which is responsible for updating the cart data and performing any actions that depend on the cart state, such as applying discounts, taxes, or shipping charges. The event can be used to notify all the components that are listening to it that the cart has changed and they should refresh their data accordingly. Salesforce Reference: B2B Commerce and D2C Commerce Developer Guide, Events, Cart Class

To introduce new screen behavior in a checkout flow step, a developer should clone the appropriate subflow and replace the Lightning web components in it. A subflow is a reusable flow that can be invoked from another flow as an element. A checkout flow is a flow that defines the steps and components for the checkout process in the storefront. A checkout flow consists of several subflows, each of which corresponds to a checkout step, such as Cart, Shipping Address, Payment, or Order Summary. To introduce new screen behavior in a checkout flow step, a developer should clone the subflow that matches the checkout step they want to modify and replace the Lightning web components in the cloned subflow with their custom components. The developer can then update the checkoutSteps.xml file to point to the cloned subflow instead of the original subflow. Modifying the property mappings in checkoutSteps.xml is not a valid way to introduce new screen behavior in a checkout flow step, as it only affects how data is passed between subflows, not how screens are displayed or rendered. Editing the default subflow directly is not a valid way either, as it can cause conflicts or errors with other stores or environments that use the same default subflow. Adjusting next-state in previous subflow configuration is not a valid way either, as it only affects how subflows are transitioned or navigated, not how screens are displayed or rendered. Salesforce References: B2B Commerce Developer Guide: Checkout Flow, B2B Commerce Developer Guide: Checkout Subflows, B2B Commerce Developer Guide: Customize Checkout Steps

A Lightning Message Channel can receive signaling from any component on a page (anywhere on it). A Lightning Message Channel is a service that allows components to communicate with each other across different Salesforce UI technologies, such as Aura, LWC, Visualforce, and Lightning web apps. A component can subscribe to a message channel and receive events that are published by another component on the same or different page. The message channel acts as a mediator that delivers the events to the subscribers. A Lightning Message Channel does not receive signaling only from descendants (i.e., children), only from direct siblings, or only from ancestors (i.e., parents), as these are limitations of event-based communication. Salesforce References: [Lightning Web Components Developer Guide: Communicate Across Salesforce UI Technologies], [Lightning Web Components Developer Guide: Communicate with Events]

Useful debugging information in Salesforce B2B Commerce implementation can be garnered in three ways:
* Enabling the logging token via Admin and subsequently inspecting the logs via the browser console.
This will enable logging messages and errors to the browser console, which can be viewed by opening the Developer Tools in the browser. The logging token can be enabled by setting the value of CO.logToken to true in CCAdmin.
* Enabling debugging options for the current user and visually inspecting the Salesforce debug logs. This will enable logging messages and errors to the Salesforce debug logs, which can be viewed by opening the Debug Logs page in Salesforce Setup. The debugging options can be enabled by creating a Debug Level and a Trace Flag for the current user in Salesforce Setup.
* Logging into the community as a system administrator to identify any potential permissions or Visualforce exceptions. This will allow viewing any errors or warnings that may occur on the community pages due to insufficient permissions or Visualforce issues. The system administrator can also access CCAdmin and other tools from within the community. Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Logging, Debug Your Code