A team runs a customer-facing FAQ assistant built on Amazon Bedrock. During QA, testers notice that when users phrase the same underlying question in slightly different ways (e.g., 'How do I reset my password?' vs 'I forgot my login credentials, what now?'), the assistant sometimes returns correct answers and other times returns 'I don't have that information.' Accuracy on their fixed golden-dataset regression suite remains high (94%), so the issue is not caught before deployment. Which testing enhancement most directly addresses this observed inconsistency?