When building prompt templates within the Prompt Builder, the most direct way to inject specific record data into the AI's instructions is through Merge Fields. Much like an email template or a mail merge, merge fields allow the administrator to reference specific fields from the object in context-in this case, the Case object.
For example, an administrator might use {!$Input:Case.Subject} or {!$Input:Case.Description} within the prompt template. When the agent runs, it replaces these placeholders with the actual data from the specific case record being viewed. This ensures that the AI has the "grounding" information it needs to generate an accurate and relevant summary. While Flows (Option A) can be used for more complex data retrieval, Merge Fields are the standard, low-code tool for simple record-to-prompt data population. Agent Instructions (Option C) provide the "how-to" logic for the AI but do not themselves represent the dynamic data points from the Salesforce database.