A 32-year-old male labourer in Delhi is brought to the emergency department with altered mental status, severe metabolic acidosis (pH 7.18, HCO₃⁻ 8 mEq/L), and an anion gap of 22. He consumed approximately 100 mL of a clear liquid from an unlabeled bottle 6 hours ago, thinking it was ethanol. On examination, he has visual blurring, photophobia, and fundoscopy reveals optic disc hyperaemia. His serum osmolality is elevated at 320 mOsm/kg. What is the most likely toxic agent he ingested?