When one makes kiddush friday night then has a meal afterwards, they don't make an al hagefen on the wine/grape juice that they drank by kiddush. This is because (from what I always heard/understood) that Bircas HaMazon will exempt the obligation of al hagefen.
Where does it say this in the poskim? (please provide the sources and actual text so others can easily see what it says.)
It's Shulchan Arukh OC 272:10
ברכת יין של קידוש פוטרת יין שבתוך הסעודה ואינו טעון ברכה לאחריו דברכת המזון פוטרתו בין שהוא על הכוס בין שאינו על הכוס.
The blessing on wine for Kiddush exempts wine during the meal [from needing a blessing before drinking] and the wine does not need a blessing afterwards for the blessings after bread exempt it, whether the blessings after bread were recited upon a cup [of wine] or not. (my translation)
See too ibid. 174:6, 208:17 and 299:8.
