Rav Nachman bar Yitzchak said 102a: Which Tanna laid down these principles on which the baraita is based? Ravi Yehudah, as it was taught in a baraita: Fellows who were reclining at a meal together, and they arose to their feet to go to the synagogue (beit knesset) or the study hall (beit midrash), when they go out, they do not require a blessing afterwards, and when they return, they do not require a blessing beforehand. Rabbi Yehudah said, about what matters are we talking? In a time when they leave in that place a few of their group, but if they do not leave behind a few of their group, then when they go out they require a blessing after the food, and when they return they require a blessing before resuming their food.
Rather, we should reason this way:
Specifically because these things require a blessing afterwards in their place, that when the people go out it does not require a blessing afterwards since they are bound to return to the same place to make the blessing eventually, and when they return it is not required to make a blessing before resuming, since it is considered a continuation of the same meal. But for food items which do not require a blessing afterwards in their place, even according to the rabbis, when the people go out, they are required to make a blessing after the food they have eaten, and when they return, they are required to make a blessing before eating again.
Shall we say this refutes Rabbi Yochanan? Why would we: Didn’t we already refute him one time? Well, shall we say that this, too, refutes him!
Rabbi Yochanan would say to you: this is the law even for items that do not require a blessing afterwards in their place; they too do not require a blessing before the people go out, and the reason they teach “they arose to their feet” is to acknowlege the strength of the position of Rabbi Yehudah, that even items that require a blessing aftwerwards in their place one is exempted from the blessing when going out for this reason: that a few of the company were left behind. But if they did not leave behind a few from the group, when they go out they are required to make a blessing after the food and when they return they are required to make a blessing before eating.
This teaching is consistent with Rav Chisdah: A group who recline together to drink wine and rise to their feet and return, it is not required to bless.
The Rabbis taught: members of fellowship that reclined together and the day became holy upon them i.e., Shabbat began while they were dining together, they bring to one of them a cup of wine, and he recites upon it the sanctification of the day, and a second person says upon it the same cup the blessing after the meal — the words of Rabbi Yehudah. Rabbi Yosei says, he eats and continues until it grows dark.
They finish the meal. The first cup — they bless upon it the blessing after the meal; and the second, he says upon it the sanctification of the day.
Why? Let them say both upon a single cup!
Rav Huna said that Rav Sheishet said: We do not say two sanctifications upon a single cup. What is the reason? Rav Nachman bar Yitzchak said: Because we don’t perform mitzvot in bulk.
No? But there’s this baraita: One who enters his house after Shabbat blesses on the wine, and on the light, and on spices, and after that he says Havdallah on the cup. And if he has naught except a single cup, he lets it rest until after the meal and makes all three afterwards. That is, he uses the same cup for the blessing of the wine and Havdallah and birkat hamazon.
If he doesn’t have except for a single cup, that’s different.
But hey: A festival that falls after Shabbat, and he has enough to not use the same cup for multiple blessings, and Rav said: יקנ’’ה! The mnemonic yayin-kiddush-ner-havdallah for the combined kiddush/havdallah which we recite on such occasions.
I say: Because he did not say “z’man” the codeword for Shehecheyanu in that mnemonic we must be dealing with the seventh day of Pesach, and everything that he had he has eaten, and he doesn’t have enough anymore for separate cups. But here, on the first day of the festival, when he has enough, and Abbaye says יקזנ’’ה, and Rabbah says יקנה’’ז. They include z’man, and argue over its placement, but what they agree on is that even when he has plenty of wine, at the start of the chag, he says it all over one cup.
There is no contradiction, rather, the resolution is thus: havdallah and kiddush — it is a single observance; the blessing after the meal and kiddush — they are two observances.