In the taught future context, حَتَّى means “until” and points to the endpoint.
لَنْ أَجْلِسَ حَتَّى يَأْذَنَ الْمُعَلِّمُ
I will not sit until the teacher permits.
Not sitting continues up to the teacher's permission. The first-group verb يَأْذَنَ ends in fatḥah here. Do not turn this example into the claim that every use of حَتَّى has the same grammar.
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Kay, Idhan, Hatta and Purpose Li
In the taught future context, حَتَّى means “until” and points to the endpoint.
لَنْ أَجْلِسَ حَتَّى يَأْذَنَ الْمُعَلِّمُ
I will not sit until the teacher permits.
Not sitting continues up to the teacher's permission. The first-group verb يَأْذَنَ ends in fatḥah here. Do not turn this example into the claim that every use of حَتَّى has the same grammar.