A 58-year-old woman from Delhi presents with progressive ptosis and diplopia for 3 weeks. She reports worsening of symptoms toward the end of the day and improvement after rest. On examination, she has bilateral ptosis, ophthalmoplegia affecting extraocular movements, and mild proximal muscle weakness in the lower limbs. Repetitive nerve stimulation shows a decremental response. Serology is positive for anti-acetylcholine receptor (AChR) antibodies. Which of the following best explains the pathophysiology of her muscle weakness?