Without an index.md in each folder, Claude has no map of your vault. It reads every file to find what it needs. On a vault with + notes, that burns through your token budget fast.
The fix is simple. Add an index.md to each main folder. Include the folder's purpose in sentence, then list key files with a -line description for each. This gives Claude a navigation structure so it can jump straight to the right file.
This single pattern handles about % of the context problem. Claude stops scanning everything and starts reading only what it needs.