The MCP server already provides an aggregate tool for the collection level - `mcp_plugin_mongodb_mongodb_aggregate` - a proxy for `aggregate(database: string, collection: string, pipeline?: Document[], options?: AggregateOptions & Abortable, dbOptions?: DbOptions): AggregationCursor;`.
The driver (and subsequently the service provider) has a separate method for db level aggregation which isn't exposed in the MCP server yet: `aggregateDb(database: string, pipeline?: Document[], options?: AggregateOptions & Abortable, dbOptions?: DbOptions): AggregationCursor;`