This question is asked and answered by Ba'alei Brit Avram:
ויאמר בא אחיך במרמה ויקח ברכתך. יש לשאול שנראה לעין כל תימה גדול שיצחק
ע״ה שלח מדנים בין אחים שאמר
דברים שהעלה בהם חמת עשו. כאומרו ויהי כשמוע עשו אז דברי אביו ויצעק
וגו׳. והוא במה שאמר בא אחיך במרמה ויקח ברכתך ועוד במ״ש הן גביר שמתיו
לך וכיוצא. ויותר היה לו להמעיט הדברים ולהעלימם לשכך בהם חמתו והוא עשה
להיפך:
אמנם כשנתבונן נמצא שבכל זה היתה כוונת יצחק לטובת ולתועלת יעקב. והוא
אחר שראה שהענין היה בסייעתא דשמיא וידע שמאת ה׳ היתה זאת השתדל לקיים
בידו הברכות על כרחו של עשו ואע״ג שיקפיד שמוטב הוא שיתקיימו הברכות עתה
בידו אע״פ שתעלה חמתו של עשו וקיום הברכות לא יהיה כי אם בשישמע עשו
הברכות ויודה עליהם בעל כרחו. וג״כ אונסיה גמר ומקני ליה. וראיה לזה שהרי
הוצרך לומר לשרו של עשו שיודה לו על הברכות כאומרו לא אשלחך כי אם ברכתני
דמשמע שיצטרך מקום להודאתו ולזה פירש יצחק ואמר בא אחיך במרמה וגו׳. וכן
מ״ש הן גביר שמתיו לך וגו׳. הרס״ו זללה״ה:
A question arises that it appears, shockingly, that Yitzchak Alav
Hashalom caused contention between brothers when he said words that
aroused anger in Esav, as it says: "When Esav heard his father’s
words, he cried out...", and when he said "your brother came with
trickery and took your blessings" and furthermore when he said "I have
made him master over you...". Furthermore, it was incumbent upon him
to soften his words and abate Esav's anger, but he did the opposite!
Indeed, when we understand it properly, we find that Yitzchak's
intention all along (by telling Esav 'בא אחיך וגו) was for the benefit and sake of Yaacov. When he saw
that this matter was brought about by heaven and realised that it's from
Hashem, he endeavoured to keep the brachot firmly in his hands against Esav's will and despite his disagreement, because it is better that the brachot should be
fulfilled right now even though
this would end up angering Esav. But for the brachot to be fulfilled, they needed to be heard
and acknowledged by Esav by grudgingly (there is a
principle that you can force someone to agree to transfer ownership in
certain circumstances: אונסיה גמר ומקני ליה). Proof of this is that it
was necessary to tell Esav's angel to admit to the blessings as it is
written: "I will not let you go, unless you bless me" (Bereshit
32:27). It is clear he (Esav) needed a chance to admit, and that's why Yitzchak
deliberately told him that "your brother came deceitfully" and
"I have made him a master over you" etc.
In short: Yitzchak, upon figuring out what was going on (halevai we should also be able to immediately recognise the Will of Hashem in tense moments of things going wrong for us, and still keep our faculties and do the right thing!), proceeded to secure the bracha for Yaacov. He realised that for that to happen: Esav had to acknowledge and admit that Yaacov received his own bracha, (and he had to know exactly what happened including the trickery and his new status as Yaacov's subordinate), so that the "ownership" of the bracha could transfer effectively. All of this was l'toelet.
Trust me, Saba Yitzchak A"H knew how to give a bracha!