Effective Agentforce instructions must be explicit about the data format, the source of the data, and the requirements for the input. Option D is the best choice because it provides the most detail for the Large Language Model (LLM). It specifies the format (18 character ID / three-digit code), the source (conversation history or user input), and the logic/dependency (required only when the product ID is present). This level of detail prevents the agent from guessing or providing incomplete data to the underlying Salesforce action.
Options A and C are too vague and could lead to errors. Option B is better but lacks the explicit "Required" tag and format details found in Option D. High-quality instructions act as a contract between the agent's natural language understanding and the structured data requirements of the Salesforce system.