I have seen conflicting and unclear details in some of the SGZZ bio's
Jiang Wei's SGZ
However, Deng Ai had by then infiltrated through Yin Ping Gu Dao and proceeded to attack Zhuge Zhan at Mian Zhou. Subsequently, Deng Ai captured Cheng Du and Liu Shan accepted Deng Ai's proposal to surrender.
Liu Shan's bio(although Comprehensive, since SGZ is not available here)
After Zhuge Zhan died and Mian Zhu gate was lost, Liu Shan agreed to surrender to Deng Ai.
Deng Ai's SGZ
Subsequently, Deng Zhong and Shi Zuan led a second attack and managed to serve a crushing defeat to the Shu army. Zhuge Zhan and Zhuge Shang were executed. On hearing that, Liu Shan decided to surrender and he dispatched officials to Deng Ai’s camp bearing his Seal and documents.
In Jiang Wei's bio, it says it first says that Cheng Du was captured and Liu Shan's surrender is mentioned after that, implying that the capture of Cheng Du happened first. In Deng Ai's SGZ and in Liu Shan's comprehensive, Shan surrenders immediately after the defeat of Zhuge Zhan.
I guess the common sentiment seems to be that Liu Shan surrendered without a fight.
However, I note the discrepancies. In Jiang Wei's SGZ Deng Ai seems to propose the surrender, while in Deng Ai's SGZ, Shan surrenders without such influence from Ai. I thought to check a few of the bios of some of the others at Cheng Du at the fall of Shu, but Qiao Zhou, Huang Hao, and Chen Zhi, who immediately came to mind, do not have translated SGZs up yet.
So the questions I have are
-What actually happened? Where else could I look for clarification?
-Was Deng Ai in a position to quickly sieze Cheng Du, or could Shan have probably held out?(Regardless of whether it was a good idea or bad idea)
I tend to assume that Cheng Du, being the capital, was at least somewhat defended, and Deng Ai did not have a large force equipped for siege.