Why is there no mention of Rosh Chodesh after the Haftara?

Question

After the reading of the haftarah, a series of b'rachot is said. The final one, on Shabbat ends, "m'kadesh hashabbat." On the 3 r'galim, "m'kadesh yisra'el v'haz'manim" (and on Shabbat fo the holidays, add in "hashabbat"). On Rosh Hashana and Yom Kippur, there is a change to address the specific day, as well.

But on Shabbat which is Rosh Chodesh, my siddur (and the one used by the guy who read the Haftarah in my shul, apparently) has no text incorporating "Rosh Chodesh" even though the selection which we read was special for Shabbat-Rosh Chodesh.

In Musaf, we end the middle section with the closing "m'kadesh hashabbat v'yisra'el v'Roshei Chodashim" so the text can exist and be used on the day. Why isn't it employed after the haftarah?

Answer 1

Shabbos 24a

אֲמַר לֵיהּ אַבָּיֵי לְרַב יוֹסֵף: הָא דְּרַב הוּנָא וְרַב יְהוּדָה דְּרַב הוּא. דְּאָמַר רַב גִּידֵּל אָמַר רַב: רֹאשׁ חֹדֶשׁ שֶׁחָל לִהְיוֹת בְּשַׁבָּת —

הַמַּפְטִיר בַּנָּבִיא בְּשַׁבָּת אֵינוֹ צָרִיךְ לְהַזְכִּיר שֶׁל רֹאשׁ חֹדֶשׁ, שֶׁאִילְמָלֵא שַׁבָּת אֵין נָבִיא בְּרֹאשׁ חֹדֶשׁ

Abaye said to Rav Yosef: This opinion of Rav Huna and Rav Yehuda is Rav’s opinion, as Rav Giddel said that Rav said: In the case of the New Moon that occurs on Shabbat, the one who recites the portion from the Prophets [haftara] on Shabbat need not mention the New Moon in the blessing, as, if it were not Shabbat, there would be no reading from the Prophets on the New Moon. The haftara is unrelated to the New Moon, and therefore the New Moon is not mentioned in the blessing.

See further in the Gemara where there is a dispute.