When the warning finally reached Esau — do not marry a Canaanite — he did what a man who has already lost tries to do. He went sideways to find a wife who might count.
The Targum Pseudo-Jonathan on Genesis 28:9 preserves an unusually precise genealogy. Esau went to Ishmael and took Mahalath, who is Besemath the daughter of Ishmael bar Abraham, the sister of Nebaioth from his mother, in addition to his other wives. Two names for one woman, because midrashic tradition records her renaming — Mahalath meaning "forgiven," since a groom's sins are forgiven on his wedding day. And the note that Nebaioth was her full brother, not merely a half-brother, to fix her lineage precisely within the house of Ishmael.
The Targum refuses to soften what is happening. Esau has taken a new wife besides his other wives. He is not replacing the Canaanite women. He is adding Mahalath on top of them. The Hittite wives still fill the tent, still embitter Isaac and Rebekah, still poison the inheritance Esau has already forfeited.
This is the portrait of a man who has learned part of a lesson. Esau understood that the daughters of Abraham's extended house counted for something. He did not understand that marrying one more wife does not cancel the two he already had. The covenant does not work by addition.
The takeaway: partial repentance is not repentance. You cannot patch a covenant violation by adding a correct marriage on top of two incorrect ones.