> it hallucinated a missing brace (my code parsed fine), "helpfully" inserted it, and then proceeded to break everything.
Your tone is rather hyperbolic here, making it sound like an extra brace resulted in a disaster. It didn't. It was easy to detect and easy to fix. Not a big deal.
It's not a big deal in the sense that it's easily reversed, but it is a big deal in that it means the tool is unpredictably unhelpful. Of the properties that good tools in my workflow possess, "unpredictably unhelpful" does not make the top 100.
When a tool starts confidently inserting random wrong code into my 100% correct code, there's not much more I need to see to know it's not a tool for me. That's less like a tool and more like a vandal. That's not something I need in my toolbox, and I'm certainly not going to replace my other tools with it.