I had my first PR merged into Medley Interlisp.
Although I worked on other PRs related to documentation and the project site, this is the first involving actual system code. The change was absolutely trivial, removing a duplicate line of code, but helped me get familiar with the setup and workflow of tracking and compiling modified files.
It turns out working on system code is pretty much the same as user code. You use the same tools and go through similar steps.
I guess now I'm a hotshot core kernel developer or something.