A 68-year-old woman undergoes a routine chest CT for evaluation of persistent cough. The scan incidentally reveals a 3 cm mass in the posterior mediastinum at the level of T6–T8 vertebrae, with erosion of the vertebral body. The radiologist notes the lesion is posterior to the esophagus and anterior to the vertebral column. The patient is asymptomatic except for the cough. Based on the anatomical location and imaging findings, which of the following structures is most likely to be compressed or invaded by this lesion?