I've had a similar problem. I think the ideal shape of the solution depends on how you guys work and how in sync you want your AI context to be. Do you have shared rules that need to be followed? Markdown file in the git repo. Too many different places where information is stored? Only use tools that connect to the AI via MCP.

I built something to solve the "understand-the-conversation" problem for myself (chironmemory.com). I didn't want to worry about maintaining any sort of complex system where existing entries need to be updated, so it's basically an append-only self-organizing pile of info that your agents can throw whatever they want into and the recall does a good job of bringing it back later. I've got my whole git history and all my emails in there.