Integration Procedure. This is the lowest-customization answer that still satisfies the business, security, and lifecycle requirements.
The Core Concept Explained: OmniStudio separates guided interaction, data mapping, orchestration, and UI presentation. That separation is critical for high-volume public-sector intake because each asset can be tested and reused independently.
Step-by-Step Technical Analysis: Design the user journey first, then decide which OmniStudio asset owns each responsibility. OmniScript captures guided input, DataRaptors map Salesforce data, Integration Procedures orchestrate server-side work, and FlexCards expose summarized context. After assembly, validate data payloads, error handling, security, and performance with realistic application records. Use an Integration Procedure because it can call external services, invoke DataRaptors, apply conditional logic, and shape a single response for an OmniScript or FlexCard.
Why the Incorrect Options Are Wrong: A may look related, but it does not place the logic in the correct declarative Public Sector or OmniStudio configuration layer. B may look related, but it does not place the logic in the correct declarative Public Sector or OmniStudio configuration layer. D may look related, but it does not place the logic in the correct declarative Public Sector or OmniStudio configuration layer.