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Basically the sublime-workspace was just truncated, meaning the text ended up with lots of unclosed brackets/braces, etc.

I tried manually re-adding the missing brackets but then my SUblime Text just crashes on startup.

I have an error message when trying to leave Sublime text, I closed the window quite fast so I could not see, but it must have said there was an error while writing the file to the disk. I wish it had actually done NOTHING and preserve my previous working workspace. Not it seems like I have no other option but to remake my project manually...?