- Communists made peace with Germany in WW1 when defeat was inevitable. Food is more important than ideology.
Different situation, and players entirely
Firstly the soviets considered themselves new management and had little investment in continuing the fight it being seen as largely the previous management's folly. On top of that Russian foreign policy and other active choices played more of an active role in Russia being in WW1 and that was obvious to Russians. Compare that to WW2 which was a surprise attack by Germany. The new regime (naively) thought they could extricate themselves from the war by dint of just not being there. Brest-Litovsk actually shocked everyone in it's harshness and it's very unlikely the New government considered it to be the likely outcome prior to the "negotiations". It would have in fact severely destabilised the regime, and certainly would not have relieved Russian hunger. Luckily for the the new regime it didn't matter because of what happened next.
Secondly the Soviets had basically campaigned and promised an end to the war i.e in 1917 /18 their entire modus operandi is ending the war and seeking peace. They had largely come to power on the back of strong anti war feeling, civil and army revolts against it, None of this is true in 1942
Thirdly, Imperial Germany was not Nazi Germany, because....
- In a scenario where Germany beats the Soviets by mid 1942, nobody would be aware that the Germans were planning on exterminating them.
- ...
Show me the source where Stalin and Soviet leaders explicitly knew that the Germans were planning the Holocaust/General plan ost before 1941?
The first post you quoted by yourself, yes you'd be right. But that post was the last in a series that was arguing against the idea that the Soviet Union would never surrender because they knew from the very beginning that they were fighting for their very existence.
The deaths, and mass murder started pretty much instantly, the food being taken started pretty soon after that. There was a constant stream of refuges from occupied Russia fleeing east who told the rest of Russia exactly what was going on. On top of that there was active reporting back by Partisans and other soviet agents still present
They knew OTL and they'll know here as well. The Germans will leave the Russian little choice but to fight, in whatever capacity they can. As already mentioned imagine the largest insurgency action you can think of, likely backed by outside powers with a vested interest in keeping the Germany tied up in Russia)
If you think the killing were either just in the death camps, POW camps of planned after the war, you are wrong. The Germans made it very clear, very early on what they were all about in Russia (and elsewhere come to that).