I've been doing similar work since Claude code updated their "slash command"(later merge to skills), first 3-4 long content docs, gradually split to modular groups. I designed it for loading the docs based on what agent is actually doing. The maintenance part is honestly not that hard, for me, I created some CI jobs that diffs the docs against the codebase and flags drift handles of it.

The pattern works.

But I keep catching myself spending more time on how to organize context than on what the agent is actually supposed to accomplish.

Feels like the whole space has that problem right now.