The most maintainable and performant approach is to model the necessary customer data as fields on the Order object. The Order object serves as the central record for the transaction and naturally holds contextual information. During the Order Management fulfillment process, integration logic (such as an Integration Procedure) can easily retrieve these fields from the Order record and include them in the payload sent to the legacy application. This avoids polluting the product catalog with non-product data and simplifies the integration design, making it easier to configure and maintain.

A. This describes the implementation mechanism (an adapter) but not the recommended data modeling strategy, which is the core of the question.

C. Modeling customer data as Technical Products is incorrect data architecture. Customer information is not a product or service being sold.

D. Using multi-picklist attributes on the cart is not a scalable or appropriate way to store structured customer data like names, IDs, or addresses.

1. Salesforce Help, Industries Order Management Developer Guide, "Order Management Data Model". The documentation shows the Order object as the central object, linked to Account and other contextual information, making it the logical place to source data for fulfillment callouts.

2. Salesforce Architects, "Salesforce Industries (Vlocity) Order Management" design patterns often emphasize using the Order as the context for fulfillment, from which related data (like Account details) can be easily queried.