Why is Hashkiveinu not considered a hefsek between Ga'al Yisra'el and the Amidah (Chabad)?

Question

Read this first: Veshameru in Chabad siddur

TL;DR

Many recite Veshamru (Shemot 31:16) before the Amidah in the Friday night Ma'ariv service. The custom in Chabad, however, is to not recite this paragraph. The reason is because the bracha of Ga'al Yisra'el and the Amidah ought to be connected, with no hefsek (interruption) between.

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If the bracha of Ga'al Yisra'el and the Amidah are supposed to be connected, why is the paragraph of Hashkiveinu between the two? Doesn't this undermine Chabad's reasoning for not reciting Veshamru? Perhaps Hashkiveinu is considered to be an extension of Ga'al Yisra'el and therefore not a hefsek?

Answer 1

As I wrote here, the Talmud states that Hashkiveinu is not an interruption between geulah and tefillah because since it was ordained by the Sages as part of the blessings for Keriat Shema it is as if it is an extended geulah.

Berachot 4b

דאי לא תימא הכי שחרית היכי מצי סמיך והא אמר רבי יוחנן בתחלה אומר ה׳ שפתי תפתח ולבסוף הוא אומר יהיו לרצון אמרי פי אלא התם כיון דתקינו רבנן למימר ה׳ שפתי תפתח כתפלה אריכתא דמיא הכא נמי כיון דתקינו רבנן למימר השכיבנו כגאולה אריכתא דמיא

For, if you do not admit that, how can he join in the morning, seeing that R. Johanan says: In the beginning [of the Tefillah] one has to say: O Lord, open Thou my lips [etc.], and at the end one has to say: Let the words of my mouth be acceptable? [The only explanation] there [is that] since the Rabbis ordained that O Lord, open Thou my lips should be said, it is like a long Tefillah. Here, too, since the Rabbis ordained that ‘Let us rest’ should be said, it is like a long Ge'ullah. (Soncino translation)