Salesforce Shield. This is the packaged route that keeps the process supportable, auditable, and aligned to the data model.

The Core Concept Explained: Public-sector implementations must treat confidentiality, auditability, and legal retention as architecture requirements. The control must be applied at the platform layer that actually prevents unauthorized access or processing.

Step-by-Step Technical Analysis: Classify the protected data first, then apply the least-privilege control at the correct layer: object access, sharing, field security, encryption, event monitoring, or audit retention. Validate the design with a real external or internal user profile and confirm that reporting and integrations do not bypass the intended restriction. Recommend Salesforce Shield because it brings together Shield Platform Encryption, Event Monitoring, and Field Audit Trail.

Why the Incorrect Options Are Wrong: A does not meet the implementation-quality bar for security, scale, auditability, or maintainability in this scenario. C does not align with the Lightning-based managed package and Experience Cloud assumptions. D does not meet the implementation-quality bar for security, scale, auditability, or maintainability in this scenario.