Memes

But diplomatic cables reveal that the Germans would not have kept this part of Poland as they intended to uphold the pact with the Soviets

So if they didn't sign the pact or had left this request out of it as you seemingly desire they would have taken it wholesale? So again we're back to the Molotov-Ribbentrop saving eastern Poland (actually Western Ukraine Belarus and Lithuania that was simply occupied by Poland) from the Nazi scourge (for a time).

Whether you agree on that the Soviets should have signed

They absolutely should as the last power to do so allowing the time for them to build up the production capacity necessary cause 80% of the Nazi deaths of the war.

It really seems like you would have preferred the Soviets leave Western Belarus Lithuania and Ukraine for dead and do nothing to delay the inevitable war with the Nazis to actually recover to fighting strength post revolution. Maybe that would have been the more pure option but it also would have been suicidal idiocy.