"Hey Claude, can you please make a full matrix of tests according to the following pattern and parameters? Thanks." That's 15-20 minutes of work that can run in the background while I do something else.
What I mean by "talk to the agent in code" really is to code. Establish patterns. Then have the agent use those patterns as reference for other areas of the project.
If you're doing this, then why not just write the effing code?