A great result in Chile.
It will be interesting to watch Chile's new government. Boric belongs to the Salvador Allende tradition rather than the Castro tradition. Indeed he has been highly critical of Cuba (and Venezuela's) despotism and their human-rights abuses. He has an all-mighty task to replace the Chilean constitution which treats private enterprise as a sacred principle and has helped create one of the most unequal countries on earth. But he has a huge mandate. Good luck to them.
The constitution is certainly one very important battle.
However the Chilean constutional process will now be very hands off for Boric. Indeed, the hardest battle of actually winning the right to change the constitution is already over. The process is already in motion (via successful referendum - again with a very large mandate of over 70%), with it currently in the hands of an elected constitutional assembly, the outcome of which will be returned to the Chilean people next year for ratification in another referendum.
The big difference between him and Kast in terms of the constitutional process is that Kast and his supporters would have been doing everything in their power to disrupt both the constitutional assembly and the subsequent referendum.
You are also right that his brand of socialism is very much at odds with the strongmen of the continent who he has spoken out against (Indeed the likes of Cuba and Nicaragua are yet to send their well wishes...). That did not stop Kast getting this far by basically fear-mongering that Boric is a Communist-in-disguise, with millions still buying into it.
But Boric undoubtedly has a massive task ahead of him. The Chilean peso has already sank as foreign investors get their obligatory jitters (especially in the relation the massively damaging but highly profitable mining sector).
Their public healthcare system is practically non-existent, their state-education is an appalling mess, their entirely privatised pension system no where near fit for purpose, and the country is still reeling from the pandemic and the social upheavels of 2019.
This is all coupled with an incredibly powerful and very well entrenched ruling class who, if you visit, really do live in a completely paralell reality (Geographically, culturally, politically and socially). Many of whom still see Pinochet as a "necessary evil". Many of them also come from the very conservative Opus Dei branch of Catholicism (hence support for Chile´s punitive abortion laws). Also worth pointing out this ruling class seems to include some of the very worst kinds of "ex-pats" (Brits, American´s and Australian´s especially) - who are predictably already threatening to leave the country.
On the plus side the Cold War is over (although still being waged in the minds of the upper classes!) - which was enough to earn Allende a bullet in the head.
And what a bloody relief that Kast did not win. How depressing that would be!
Poll