How does one reconcile Abraham's seeking forgiveness for his father with his disavowal of him, his promises to him, and his attempt to intercede for him on the Day of Resurrection, knowing that Allah does not forgive polytheists?

Ibrahim's plea for forgiveness for his father was based on a promise he had made to him, and Allah did not rebuke him for it but rather clarified his excuse. Ibrahim disavowed his father when it became clear to him that his father was an enemy of Allah, by dying as a disbeliever. Ibrahim continued to seek forgiveness for his father during his lifetime, hoping for his faith, and this is what is permissible for Ibn Abbas and others, as it is permissible to seek forgiveness for a living disbeliever with the intention of guiding him. As for the Day of Judgment, his intercession stems from compassion for the situation and from invoking Allah's promise to him that He would not disgrace him, similar to Noah's invocation of Allah's promise to save his family. Ibrahim did not oppose revelation with his intellect, but rather with an understanding of a previous revelation, and this is a legitimate ijtihad (independent reasoning).