i couldn't find any information about it but i still see an AGENTS.md file at the root of the source tree so: how much AI was used in the making of this? how was it used?

Since early 2026 it's mixed AI and handwritten. Before that it was mostly written by hand. Quite a lot of the code goes back to 2018 even. Typically, I do back and forth with Claude Code agents on new features and bug fixes, reading and editing code along with it.