Arvit: S'michat G'ulah Litfilah

See Kitzur SA 18:2

«Uvmaariv, keivan she'ein habrachah shlifnei sh'moneh esrai m'sayemet b'go'al Yisroel, Muttar l'hafsik...»

Maybe this explains how Baruch Hashem L'olam, Kaddish, and v'shamru etc. are not a hefseiq and are even attributed sometimes to "g'ullah arichta"

Michdi let's see

Given
We have established "hashkiveinu" as "g'ulah arichta"

Now the KSA is seeming to say
"Once we break the Go'al Yisroel <=> Amidah connection, therefore other tefillot may be legitimately added on, even though they are not literally g'ulah arichta. Just that g'ulah arichta has created a heter that may be further exploited - albeit on a limited basis

So
• Baruch Hashem
• V'shamru
• Kaddish

are not literally g'ulah arichta, rather they just are not hefseiq BECAUSE of g'ullah arichta.

Shalom
RRW