The textbook gives a further, specialized reading. Where neither literal extension nor simple purpose adequately fits, hatta can link the acts with a consequential relation resembling fa.
«عبدي حر إن لم آتك حتى أتغدى عندك اليوم»
My servant is free if I do not come to you and have lunch with you today.
“Today” confines the setting. The text treats the meal as a linked consequence of coming and analyzes a distinct case in which arrival occurs but the meal does not occur as required. This is a contextual reading, not the meaning of every hatta.