{
    "data": list[dict],            # Records to aggregate (required)
    "group_by": str,               # Field to group by (required)
    "aggregations": dict           # Field → function mapping (required)
}

{
    "groups": list[dict],          # Grouped results
    "total_groups": int            # Number of groups
}

result = client.invoke("analytics-mcp", "aggregate", token, {
    "data": [
        {"region": "US", "sales": 100},
        {"region": "US", "sales": 150},
        {"region": "EU", "sales": 200}
    ],
    "group_by": "region",
    "aggregations": {
        "sales": "sum",
        "region": "count"
    }
})

for group in result["data"]["groups"]:
    print(f"{group['region']}: {group['sales_sum']} total sales")