A single MCP server. The `type` field selects the transport; `stdio` is the
default and may be omitted.
A local stdio server launched as a subprocess:
```json
{
"type": "stdio",
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-github"],
"env": { "GITHUB_TOKEN": "ghp_..." }
}
```
A remote streamable-HTTP server:
```json
{
"type": "http",
"url": "https://mcp.example.com",
"headers": { "Authorization": "Bearer ..." }
}
```