In a synchronous Request-Reply scenario where a bank agent is waiting "on the spot" for a credit check, the error-handling strategy must balance immediate feedback with system resilience.

Option A is the recommended architectural approach for enterprise resiliency. By placing a Middleware layer (like MuleSoft) between Salesforce and the credit agencies, the architect can implement sophisticated error-handling patterns that are invisible to the user but critical for success. If a credit agency's API is momentarily unreachable, the middleware can perform automated retries (e.g., three attempts with 500ms intervals). If the retries still fail, the middleware sends a clean, structured error response back to Salesforce.

Option B (Fire and Forget) is fundamentally unsuitable for this use case because the agent needs the result immediately to open the account; they cannot wait for a callback that might arrive hours later. Option C (Mock service) is only a testing tool and provides no value in a production environment where real financial data is required. By delegating the retry logic to the middleware, the architect protects Salesforce's concurrent request limits (since the agent only occupies a thread for the duration of the final response) and ensures that transient network issues do not result in a "failed" bank account application for the customer.