Salesforce Public Sector Solutions provides a specific, pre-built Apex class, ContractEnvelopeStatusScheduler, designed to handle the polling of DocuSign for envelope status updates. Scheduling this Apex class is the standard, recommended, and most efficient method to automate the synchronization of e-signature statuses. This out-of-the-box functionality is part of the managed package and ensures proper integration and data handling without requiring custom development to call the DocuSign API directly.

A. ContractDocumentStatusScheduler is an incorrect class name. The correct, officially provided Apex class for this function is ContractEnvelopeStatusScheduler.

B. ContractStatusScheduler is an incorrect class name. The specific scheduler provided by the Public Sector Solutions package for this purpose is ContractEnvelopeStatusScheduler.

C. While using the DocuSign REST API is technically possible, it is not the "best way." It requires custom development, authentication handling, and maintenance, bypassing the standard, supported feature provided by the Salesforce Public Sector Solutions managed package.

1. Salesforce Help & Training, Public Sector Solutions Documentation: Set Up DocuSign for Signature Tasks. This official guide explicitly states the procedure for status polling. In the section "Schedule a Job to Get Envelope Statuses," it instructs administrators: "To get the status of envelopes submitted as part of the e-signature process, schedule the ContractEnvelopeStatusScheduler Apex class." This directly confirms that option D is the prescribed method.