Re: Wasn't this handled last time?
Sure, Japan was ready to surrender just like Germany was when Hitler was already in the bunker - some people were trying to contact US - but they too didn't want to accept an unconditional surrender, thus were trying to obtain what was not possible, - and moreover they weren't those with much power to force the military to surrender. There was no warranty Japan would have surrendered. Remember that even after the bombs the emperor had to force the unconditional surrender, and the imperial palace was attacked to hinder it. And the Hirohito recording never said "surrender".
Add that Japanese naively tried contacts through Russia, and Stalin deliberately downplayed and dismissed the approaches because he wanted to gain as much as it could before Japan surrendered. Also, if US had been forced to invade Japan, it would have meant they would have needed to weaken the European front.
Japan had already plans to resist a US invasion on the main islands. It would have been a huge massacre on both sides.
Russia was already stealing US bomb secrets, it didn't built it because it was launched on Japan. It would have built it as soon as possible anyway - and how fast they could show how much they spied - and it had stolen already a much needed B-29 to copy.
The Hiroshima/Nagasaki bombs cut the war suddenly, and Stalin plans were broken, as he declared war on Japan "too late" - a fact that tells that even Stalin wasn't able to assess the situation and didn't believe Japan would have surrendered quickly, or would have declared war well before.They waited until August 8, which was the last available day - they were bound to declare war on Japan within three months after Germany surrender.
The Nagasaki bomb was the result of different events. Japan didn't understand quickly enough what really hit it, and on the other side, US military was eager to try the "other" bomb - remember the two bombs weren't identical - the first one used uranium, the second plutonium.