The LLM coding tool I have the most experience with is Windsurf IDE + Sonnet 3.5. In Windsurf you can define both global and project rules in .md files. I have found that managing those files very closely is key to success. They just tried to automate that with auto-generated "Memories" but they are generally slop, and I delete them. Managing the project rule file will save you so much pain. That is where I define the frameworks and APIs to use.