What are your main takeaways from the summit?

The bottom line is that the agreement was close to a non-agreement, at least in any concrete terms. I assume there was some preliminary skirmishing about denuclearisation and that both sides realized the North Koreans were only going to agree to something firm and binding if the US was willing to pay a high price. So they decided to paper over continuing the talks.

That said, the North Koreans gained a lot more than Trump. He desperately wants a deal, and in pursuit of that is willing to forego certain military maneuvers with South Korea and, more importantly, continue talks, which implies, at least for a while, an end to sabre rattling (which he apparently only does with US allies).

What will we see next?

Continued talks, something which other US presidents can tell Trump a lot about. Will this make the world or the Korean peninsula safer? In the short run, it will deescalate tensions, though it may lead to a future explosion if Trump gets pushed strongly by the various hard-liners he's appointed to the State Department and the National Security Council.

The real question will be if, down the road, Trump tries to compensate for his giving in on North Korea by engaging in military action, or rather by getting US allies to engage in military action, against Iran.

How would you sum up Donald Trump’s approach to international diplomacy?

I'm not sure he has one. He notoriously said he didn't feel the need to prepare for the summit, nor, as we know, does he ever read briefing papers over half a page in length; I can't imagine that he will be following the negotiations closely, especially given his "work" habits. His modus operandi is simply to alternate, almost randomly, between charm and blood-curdling threats, and to assume that if things don't work out someone will bail him out.