The pasuk (Tehillim 146:10)
יִמְלֹ֤ךְ יְהוָ֨ה ׀ לְעוֹלָ֗ם אֱלֹהַ֣יִךְ צִ֭יּוֹן לְדֹ֥ר וָדֹ֗ר הַֽלְלוּ־יָֽהּ
Is used at the conclusion of the Kedusha. However, in most iterations, it is introduced with the statement:
וּבְדִבְרֵי קָדְשְׁךָ כָּתוּב לֵאמר
referring to Tehillim as "divrei kodshecha" in a manner parallel to the references to the p'sukei k'tuvim cited in the Rosh Hashana musaf.
However, in Shacharit for Shabbat, the same pasuk, in the same place in Kedusha is introduced with
כַּדָּבָר הָאָמוּר בְּשִׁירֵי עֻזֶּֽךָ עַל יְדֵי דָוִד מְשִֽׁיחַ צִדְקֶֽךָ
[I recall reading the Artscroll notes which said that the pasuk was added in the construction of the prayer to ensure that there is a mention of the future redemption/temple in each prayer, so the use seems to be the same -- added to the song of the angels]
Why in one particular form of Kedusha is David mentioned by name as the author of this pasuk while everywhere else, it is simply introduced as a quote from "divrei kodshecha"?