It is quite annoying, but there is not much I can do about it as it's based on the JUCE code editor component. I just a large file into the JUCE demo editor and it suffers the same fate. The text editor in Cabbage is the weakest aspect of the whole project. it drives me mad, which is why I created CabbageLite for those who wish to use an external editor instead. The other thing would be to split the file into small fragments and use includes. While it's never a bad idea to modularise one's code, I'm not sure the error reporting from Csound will still work well when dealing with multiple files.
For what's it worth, I did look into using a JS based editor within Cabbage, but an issue with how JUCE runs web pages is preventing me from using such a thing. At times like this one is reminded that JUCE is first and foremost an audio library