Also reminder that China could have simply grabbed and intergrated HK straight up into the mainland after the colonial “lease” to the UK was over. And they had every right too.

That's not exactly true; the 'New Territories' of Hong Kong were on a 99 year lease, so for those lands (comprising nearly half the population of HK and the vast majority of the territory) China had the right to take them back in 1997, however for the remainder of Hong Kong - (consisting of Hong Kong island and Kowloon Peninsula), these territories were leased in perpetuity, so China didn't have a legal basis to go in and take them.

This is why mediation was needed - splitting the New Territories from Kowloon and Hong Kong Island would split the city's population nearly 50-50 into two, which would present huge logistic issues for both sides and wreck the economy of both parts, and would've left Britain, China, and the Hong Kongers unhappy.

I'm not going to comment on whether either side is keeping or breaking the agreement that was made, just pointing out that it wasn't some act of kindness or magnanimity that brought China to the negotiating table - the only other way they could've seized central Hong Kong in 1997 was through war.