LSP code actions don’t normally do file i/o, instead they perform editor actions that modify your editor buffers in the same way that a user writing the code by hand would. If regular LSP code actions work in your setup, then the stuff being worked on in Roadmap for actionable diagnostics should also work. Notebooks are an issue as always but I just saw that Jupyter[Lab] Language Server Protocol — Language Server Protocol integration for Jupyter[Lab] exists and seems to at least supports renaming, so maybe notebooks won’t be second-class citizens eventually!
Anyway, irrespective of the codegen proposal (which I’m not planning to spend more time on at this point), I encourage you to give feedback on Roadmap for actionable diagnostics since we’re still figuring out the details. Also if Databricks is interested in better integration between Databricks notebooks and LSP/BSP, perhaps it’s something the Scala Center could help with (the inability to run tools such as scalafix on notebooks has come up before and I think is something we’d all benefit from solving).