I personally use a graph like format but organized like a simple text file, each node prefixed with [id] and inline referencing other nodes by [id], this works well with replace, diff, git and is navigable at larger scales without reading everything. Every time I start work I have the agent read it, and at the end update it. This ensures continuity over weeks and months of work. This is my take on file system as memory - make it a graph of nodes, but keep it simple - a flat text file, don't prescribe structure, just node size. It grows organically as needed, I once got one to 500 nodes.