A 62-year-old man with a 3-year history of progressive lumbar spinal stenosis presents with neurogenic claudication. Imaging shows severe central stenosis at L4–L5 with ligamentum flavum hypertrophy and facet joint osteoarthritis. Conservative management (NSAIDs, physical therapy, epidural steroid injections) has failed over 6 months. He is now a candidate for surgical decompression. Which of the following surgical approaches would provide the most direct decompression of the ligamentum flavum and lateral recess stenosis while preserving segmental stability and minimizing iatrogenic instability?