MCP config source — either a file path string or an inline server definition.
Point at a JSON file of servers:
```json
".aether/mcp.json"
```
Reference a file with options:
```json
{ "type": "file", "path": ".aether/mcp.json", "optional": true }
```
Or define servers inline:
```json
{
"type": "inline",
"servers": {
}
}
```