Has ever any plans for the proposed Soviet campaign against Germany in the autumn of 1939 been published? The size of the force involved, how and when the attack was to be launched, estimates of the German forces etc.?
During the August 1939 talks with the Anglo-French military mission, the Soviet side put on the table precise details of the forces they were prepared to commit against Germany. Those details are in the Soviet record of the talks.
The Soviet side then asked the Anglo-French delegation to give equivalent details of the forces they were prepared to commit against Germany. The Anglo-French delegation could not give any such details, since it had not been authorised by the British and French Governments to make any specific offers.
It is impossible to tell whether the Soviet Government was genuinely proposing military action against Germany, or whether its offer to commit enormous forces against Germany was simply a bluff, designed to establish a case for going with Germany rather than the Anglo-French alliance. It appears to me that the different interpretations of the negotiations by various commentators depend essentially on the respective biases of those commentators, either pro-Soviet or anti-Soviet. We see examples of precisely those biases in some of the posts made on this thread.
With regard to Beck himself, I think there is no hard evidence that he was ever a German agent, if by that is meant a person working specifically to forward the interests of Germany. He always saw himself as working solely for the national interests of Poland.
Nevertheless, the way in which Beck interpreted the national interests. Beck was a disciple of PIlsudski, and as such a Polish nationalist of the Jagiellonian variety, seeing Russia as the arch-enemy of Poland, with Germany as a potential ally against the threat from the east, so long as it was not itself hostile to Poland.
Once Hitler had ended the anti-Polish policies of preceding German governments and sought detente with Poland, there was a basis for a close German-Polish relationship based on their common interests, such as hostility toward the Soviet Union and Czechoslovakia, and both Pilsudski and Beck seized the opening offered by Hitler.
According to a post-war statement by Rauschning, who late in 1933 carried out negotiations in Warsaw that led to the German-Polish Declaration of Non-Aggression of 28 Janaury 1934, Pilsudski hinted that he would be willing to enter into an alliance with Germany against the Soviet Union.
[I introduced that statement in a separate thread on this section of the Forum. Details can be found there].
The main obstacle to a German-Polish alliance was the strong anti-Pilsudski opposition within Poland, mainly from Endecja and the Peasant Parties, which PIlsudski was able to suppress only with difficulty. That same opposition, which was even stronger once the strong personality of PIlsudski had vanished from the scene, applied in 1938-39, and was probably the main factor that prevented Beck from responding more favourably to the German offer of a package deal in October 1938.
One issue on which Beck and Hitler had a common interest was that of hostility toward Czechoslovakia. The Polish Government had its own reasons for desiring the disintegration of Czechoslovakia, unrelated to those of Germany. The main reason was a desire to establish a common border with Hungary, which required the separation of Slovakia and Ruthenia from Czechia and their annexation by Poland or Hungary or both. Furthermore, Pilsudski and Beck considered Czechoslovakia to be aligned with the Soviet Union, and therefore equally an enemy of Poland.
That is the reason why in 1938 Beck co-operated with Germany in the moves toward the overthrow of Czechoslovakia. He was not acting as an agent of Germany, but rather rather according to the Pilsudskiite interpretation of Polish national interests, which in this case happened to coincide with those of Germany.