In the Christian scriptures, Acts 10:28 portrays association between Jews and Gentiles as being unlawful while Acts 11:3 portrays criticism for a Jew eating with the uncircumcised. Is there a Rabbinic law or a known pre-Rabbinic custom that supports a prohibition of Jews eating with Gentiles even if the meals are kosher?
Yes there is a special reason for Jews not to eat at an idolator's house even if the food is completely Kosher. This however is only binding when the idolator has invited the Jew to his house, or there was an assumed invitation. This is a law in the Talmud as seen here which expounds a passage in Exodus.
Here is the relevant discussion starting from a Baraita
It has been taught: R. Ishmael says, Israelites who reside outside Palestine serve idols though in pure innocence. If, for example, an idolater gives a banquet for his son and invites all the Jews i n his town, then, even though they eat of their own and drink of their own and their own attendant waits on them, Scripture regards them as if they had eaten of the sacrifices to dead idols, as it is said, And he will call thee and thou wilt eat of his sacrifice ( Ex. XXXIV, 15). But does not this apply to actual eating? — Said Raba: If that were so, the verse would have only said, And thou shalt eat of his sacrifice; why then say, And he will call thee? That extends the prohibition to the time of the participation. Hence during the entire thirty days [following a marriage celebration] whether it is or it is not mentioned that the banquet is connected with the wedding, [participation in it] is forbidden; from that time onward, however, if it is stated that it is connected with the wedding, it is forbidden, but if its connection with the wedding is not mentioned, it is permitted. And how long [is it forbidden] if it is connected with the wedding? — Said R. Papa: For a twelvemonth thereafter. And how long is it forbidden beforehand? — Said R. Papa in the name of Raba: From the time when the barley is placed in the tub.1 Is it, then, permitted [to partake of food in the house] after the twelvemonth? Yet R. Isaac the son of R. Mesharsheya, who happened to be in the house of a certain idolater more than a year after a marriage, when he heard that they were feasting [because of that event] abstained from eating there! It is different with R. Isaac the son of R. Mesharsheya who was a highly esteemed man.
This law is codified in Shulchan Aruch Yoreh Deah 152.
It would seem from the sources you bring that there was a definite invitation, even though this does not seem so significant from the ensuing discussion there.
Note that in the examples below, even if the food is kosher, one is still forbidden to accept food cooked by a non-Jew. Another example is the banquet produced by Achashveros where the food given to the Jews was completely kosher yet it was wrong of them to participate in the way that they did.
There is a prohibition of food cooked by a gentile (bishul Akum) and bread of a gentile (Pas Akum) in order to prevent mingling that can lead to intermarriage. These laws are similar but have differences in the details. Similarly the issur of stam yaynam (wine touched or moved by a gentile) is similar to these halachos. The chachamim stated that all of these halachos are based on the idea that one must not socialize with gentiles in order to prevent the possibility of intermarriage or becoming close to them.
Additionally, cooking for a gentile on Yom Tov is forbidden because it is considered a melacha such as cooking on Shabbos. A Jew is allowed to cook food for himself or other Jews on Yom Tov as an explicit leniency given in the Torah. This leniency does not apply to non-Jews. Thus, it would be forbidden (except under certain specific circumstances and with caveats) to invite a nonJew for Yom Tov even if it would be allowed for Shabbos. This is because one is cooking food for the guest on Yom Tov which is asur.
By forbidding Jews from eating food cooked by non-Jews, our sages intended to create a social barrier between Jews and non-Jews in order to prevent intermarriage. An example of social dining which led Jews to intermarry is found in the Torah3: "Israel settled in Shittim, and the people began to commit harlotry with the daughters of the Moabites. The [daughters of Moab] invited the people to the sacrifices of their gods, and the people ate and prostrated themselves to their gods."
Some say that the reason for this prohibition is also to prevent a Jew from becoming accustomed to eating food prepared by non-Jews, which could eventually lead to eating non-kosher food.4
The prohibition is called bishul akum, which literally means: "cooking of a pagan." Yet the prohibition applies to all non-Jews, even if they are not pagans, as the prohibition against intermarriage applies to all non-Jews.5 Food that was cooked by a Jewish person (see the details of this below) is called bishul yisrael ("cooking of a Jew").
The prohibition applies even if all of the ingredients used and the manner of preparation are kosher.6
Background: The Gezairah
The Chachomim enacted a gezairah forbidding bread that was baked by a non-Jew so as to avoid intermingling with them too much, which could lead to intermarriage. However, the bread of a non-Jew is prohibited even if there's no possibility of intermarriage, and doesn't depend on whether or not the non-Jew is an idolater
It is permitted to derive benefit from bread baked by a non-Jew without eating it.
While the Bavli's conclusion is somewhat ambiguous, most Rishonim understand that the prohibition of eating pas akum was revoked to some degree. According to some, the prohibition was revoked by the sages entirely. Another opinion, which is followed by Ashkenazim, is that the rabbis allowed bread baked only by a non-Jewish baker ("pas paltar", as opposed to "pas baal habayis"), whether or not there is bread baked by a Jew available. The third, and most stringent opinion, is that bread of a baker was permitted only in cases where bread baked by a Jew is not available. This appears to be the opinion of the Shulchan Aruch.
Although Ashkenazi practice is to usually follow the Rama, several poskim indicate that it is still proper to be stringent in this manner and not eat pas paltar where pas yisroel is available. Others are not concerned with this for most of the year. Someone whose practice was to be careful not to eat pas paltar and wants to change this practice must be mattir neder.
The Tur writes that even those who are not careful about pas paltar during the year are careful to only eat pas yisrael during Aseres Yemei Teshuvah. Several reasons are given for this custom. Some say that this is true of Shabbos and Yom Tov as well, as part of kavod shabbos.