I just finished reading your source, and I can't find the part which mentions the Curzon Line. Actually, I would find it very strange for Lenin & co. to decide to respect the Curzon Line, to be honest, given that by January 1919, they had already broached more-or-less all of the Entente's major decisions thus far in Eastern Europe (such as Latvia, Lithuania, Finland, Estonia's independence, et cetera). There was an attempt in 1920 to negotiate a ceasefire along the Curzon Line, which both the Polish and the Soviets wouldn't agree to, maybe you are thinking of that? The source that I am using (The Outbreak of the Polish-Soviet War: A Polish Perspective by Jerzy Borzecki) asserts the following:Trotsky claimed that he wanted the Soviets to stop at the Curzon line instead of advancing to Warsaw. It was already obvious by then that there would be no rekindling of the Spartacist revolt. There was a better source I've seen, but this is all I can find right now.
"Indeed, as a well-informed Soviet historian asserts, the Kremlin treated the military ‘operations in Lithuania, Belarus, and Poland as one strategic-political whole’. It is therefore hardly surprising that the Bolshevik leadership intended to capture territories on the Vistula, that is, so-called Congress Poland with its capital, Warsaw. Accordingly, Soviet military planners codenamed the operation ‘Target Vistula’, although the term ‘Operation against Warsaw’ was used as well. The task of implementing these plans was given to the Red Army. In mid-November 1918, the Soviets transformed the Western Defense Region into the Western Army with headquarters in Smolensk. It was to reach the border of East Prussia after first having taken Belarus and Lithuania. The next point on its itinerary was Poland."
And then it goes on to describe the minutiae. In your source, the only things I can find that corroborate what you're saying are two quotes by Lenin and Trotsky, each saying that they never intended war. I find that hard to believe due to the fact that they had already invaded territories considered integral to Poland (the Polish government had directly contacted Moscow warning them that they would consider the occupation of Wilno as an invasion; Moscow ignored this). We must remember that when Soviet forces occupied Wilno in January of 1919, they besieged and defeated troops from the Polish army. Not only that, but Lenin and Trotsky's statements were made after they had already lost the war. I think it would be naive to take these post-defeat statements at face value.
From Norman Davies' White Eagle, Red Star:
"The belief that Soviet Russia could not easily survive without a favourable end to the confrontation with Poland was universally accepted. Poland was the ‘Red Bridge’ to the west, Russia’s natural link with the advanced societies of Europe, with technical progress, with proletarian solidarity, with future revolution. Although the quiet on the Polish front in the autumn of 1919 was welcome, it was generally recognised that a solution of the Polish problem could not be postponed indefinitely. The debate in Russia was not whether the Polish bridge should be crossed, but how and when."
In regards to the Spartacist thing: admittedly, I was sort of spitballing as I haven't yet decided weather or not to include anything resembling a rekindling of a Spartacist Revolt (I haven't even decided how the Polish-Soviet War will pan out in this timeline yet), but I believe I am still correct in asserting that the Polish-Soviet War can be seen as part of a wider drive for revolution across Europe. Your source mentions that other than Karl Radek, the Soviet leaders saw victory in the Polish-Soviet War as key to exporting revolution. Admittedly, they did not seek to actually invade beyond Poland, and the source is ambiguous about what exactly they planned to do with Poland in the event of a victory. From your source, a quotation form Lenin: "During the Polish war, the Executive believed that revolutionary movements were maturing in Western Europe, that in the drive toward the West the aim was not to impose Bolshevism at bayonet point, but only to break through the crust of the military might of the ruling classes, since there were already sufficient internal forces unleashed in Germany to keep things under control". And, from the source's author: "The Soviet leaders regarded Germany as particularly ripe for a toppling of the regime".
Britain will be annoyed... But also, France! France is one of the most ardent supporters of an independent Poland, and in OTL, they even briefly considered a minor military involvement with the Polish against the Bolsheviks. We will see...Great timeline with an interesting idea behind it, I like the inclusion of art as well. I'm wondering how the Enetre powers are reacting to this mess. I get the feeling Britian is rather annoyed.
Also I get the feeling that by the end of this Soviet Russia will have mixed emotions about the Polish Adventure.
As for your nice comments about the art and the timeline, thank you! I think that the art of the interwar period is really unique and captures a very distinct vibe that I am trying to convey in my narrative. Also, much of the subject matter of the art is chosen with foreshadowing in mind...