Aqsama is a perfect verb, and rabbuhā is its subject; -hā refers to the arch. In la-tuktanafan(n)a, the initial lām and final heavy emphatic nūn express a strongly asserted oath.
In ḥattā tushāda, the imperfect verb after ḥattā appears in the subjunctive. The sequence is oath → firm enclosure → completed building. The poet invokes this construction process to illustrate an animal’s powerful, integrated form.