the tale of the silent alif in انا

There are already four places in the language where hamza and nun couple together:
اِنَّ اِنْ اَنْ اَنَّ

All four are used in different ways:

اَنْ - converts the مضاري verb into a مصدر and occurs in the middle of a sentence
اِنْ is for conditional, it's followed by two مضاري verbs, in the context of condition and reward/ consequence. For example, IF Zaid comes to you, honour him.

اِنَّ and اَنَّ are called حرف مشبه بلفيل Translated as indeed, they have a subject and predicate coming after it.

اِنَّ comes at the beginning of the sentence, followed by an ism.
اَنَّ comes in the middle of a sentence and followed by an ism

So, in a book without vowels if you see a hamza followed by a nun, based on what comes after it, you can distinguish the one from the other.

But fifth instance of hamza and nun ( انا ) -can be followed by a noun or a verb. And you won't be able to tell it's the pronoun. The silent alif was added at the end- to make a profound difference.