The attached -tu already supplies the subject. Ana is emphasis, not a second independent subject.
In the book’s treatment, the explicit emphasis permits a following noun to be coordinated with the subject pronoun; that creates a distinct analysis from the accusative accompaniment form.
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Al-Mafʿūl Maʿahu: Accompaniment and Coordination
The attached -tu already supplies the subject. Ana is emphasis, not a second independent subject.
In the book’s treatment, the explicit emphasis permits a following noun to be coordinated with the subject pronoun; that creates a distinct analysis from the accusative accompaniment form.