Five days ago, Kim Jung Un invited Vlad to a "conference." Three days later they sign this document. So what we can assume is the two countries were working this for some length of time before. Kim is basically "selling 3 or 4 of his seven brigades of construction engineers to Russia to use for infrastructure support in Ukraine. It's been known for years that DPRK government has been the "jobs center" for both Russia and China. This slave market provides anything either Russia or China need as far as unskilled labor and sex trafficking.
What this will do is to make money for the DPRK, which is has to have to keep up with it's offensive missile capabilities, which is part of an effort by Putin to bring together Russia, DPRK, Iran, Syria, and to a lessor extent, China into a single source of global offensive weapons systems. China on the other hand, is extremely active in Iran and Yemen as a surrogate. China feels they are the leader of this alliance, so there might be issues there. Or Vlad may have a "heart attack" from all the "stress" he's under.
In addition, on the 25th of June, DPRK fired a suspected solid fuel, multiple warhead missile which seems to have failed after launch. Solid fuel can be launched in a much shorter time than liquid, making it much harder to scan for in defense.
North Korea to send engineering troops to occupied territories of Ukraine – TV Chosun
North Korea will send military construction and engineering forces to participate in "reconstruction works" in occupied Donetsk Oblast as early as July 2024.
Source: South Korean TV network TV Chosun; Institute for the Study of War (ISW)
Details: TV Chosun reported on 21 June, citing a South Korean government official, that South Korea anticipates North Korea will deploy a large-scale engineering force to occupied Donetsk Oblast as early as July 2024 to assist in rebuilding infrastructure in the occupied city of Donetsk.
Background:
NATO Secretary General Jens Stoltenberg said that the agreement between Russia and the DPRK demonstrated the growing coherence between authoritarian states and underlined the importance of democracies speaking with one voice.
The Biden administration said that Putin's meeting with Kim Jong Un demonstrated Moscow's desire to build a coalition with North Korea, Iran, Syria and, to some extent, China.
The agreement signed by Putin and North Korean leader Kim Jong Un on Wednesday, 19 June obliges each side to provide immediate military assistance to the other in the event of armed aggression against one of them.
The Pentagon believes that the North Korean troops in Ukraine will become cannon fodder.