I have a thing called Memento (https://rcarmo.github.io/projects/memento) that all my agents use to share skills and some cross-project notes, but in general most project-related context lives on SQLite someplace with some FTS. I built a little CRM skill that handles most project interactions just fine, and you can go a long way with well organized Markdown (or a shared Obsidian vault) before you start over-complicating things.