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Read: SELECT quantity, reserved, version FROM inventory\nWHERE sku = 'SKU-BLK-001'; → qty=10, reserved=3, ver=42","originalText":"1. 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Check: available = 10 - 3 = 7 >= 1 (requested)","originalText":"2. 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Update:\nUPDATE inventory SET reserved = 4, version = 43\nWHERE sku = 'SKU-BLK-001'\nAND version = 42; ← CAS guard","originalText":"3. 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