A 17-year-old competitive swimmer presents with chest tightness, wheezing, and dyspnea that consistently begins 5–15 minutes after starting strenuous exercise and resolves within 30–60 minutes of rest. Baseline office spirometry is normal (FEV₁ 3.8 L, 98% predicted). An eucapnic voluntary hyperventilation (EVH) challenge is performed, and the flow-volume loop shown demonstrates the finding marked **A** — a post-challenge FEV₁ fall of 17% from baseline (3.8 L to 3.15 L). Inhaled albuterol reverses the obstruction within 15 minutes. According to American Thoracic Society criteria, which of the following best describes the diagnostic significance of the finding marked **A**?
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