> China needs the west to keep buying their stuff. China had a huge economic development thanks to the money from the west. They don't even have to care about their internal economy as long as billions and billions flow in from the west.

This seems... economically confused. Billions flowing in from the West reflect the fact that China's internal economy is strong. If it fell apart, no money would flow in.

It means that the productivity of the Chinese economy, and thus the ability of the CCP to siphon off some of that for things like building mass detention facilities, is dependent upon foreign demand. It is doubtful that China has enough domestic consumption demand to keep everyone gainfully employed if foreign demand dried up. But it’s hard to say what would actually happen.

> and thus the ability of the CCP to siphon off some of that for things like building mass detention facilities, is dependent upon foreign demand

Way off the mark. You could have an economy on par with North Korea and build those facilities. China's economy is 100+ times larger than it needs to be to build the facilities they're building in Xinjiang. If you rolled their economy back to 1990 on a GDP per capita basis, they could still get it done with zero problems. Concrete, barbed wire, guards, guns and slave labor are most of the necessary ingredients. The most primitive of nations have what's necessary to do it.