What is the grammatical role of ṣadrī in the prayer?

Iṭnāb: Clarification after Ambiguity, Tawshīʿ, Repetition and Īghāl

• A nominative adjective of rabb
• The object of ishraḥ, specifying the request
• A substitute for the genitive governed by lī
• Emphasis of the imperative’s subject