EEG — Slow Spike-and-Wave 1.5-2.5 Hz (Lennox-Gastaut Syndrome)

A 4-year-old boy with a 2-year history of multiple seizure types presents with recurrent episodes of sudden falls causing head injuries, incomplete loss of awareness lasting 10–20 seconds, and nocturnal stiffening of the trunk and extremities lasting 5–10 seconds. His parents report progressive cognitive decline. EEG shows the pattern marked **A** in the diagram. Which of the following is the MOST appropriate first-line antiepileptic drug combination for this patient, given the specific EEG finding?