1) Pakistan hasn't ceded any part of Kashmir to China, it has actually acquired 750 miles of territory previously administered by China.
2) Read provision 1 of Article XI of IWT. Nothing constitutes violaton of the treaty other than denying the use of waters of rivers and matters related to it. Even India abrogating article 370 is not a violation of IWT itself.
3) The Sino-Pak boundary agreement of 1963 does not change the status of Kashmir as it is 'provisional'.
The article 6 clearly states :
“The two parties have agreed that after the settlement of the Kashmir dispute between Pakistan and India, the sovereign authority concerned will reopen negotiations with the Government of the People’s Republic of China on the boundary, as described in Article Two of the present agreement, .."
And with the abrogation of Article 370, nor does India
Your point?