{
    "action": "tool_call",
    "reasoning": "My previous reply was not valid JSON, and I can't see the tool results it quoted in the evidence. I'll re-run the per-surface summary so the claims are backed by a result that will render.",
    "tool": "query_sql",
    "args": {
        "sql": "SELECT Surface, COUNT(*) AS player_matches, ROUND(AVG(Aces),2) AS avg_aces, ROUND(AVG(Rk),1) AS mean_rank, MEDIAN(Rk) AS median_rank, MAX(Rk) AS max_rank FROM raw.raw_kaggle GROUP BY Surface ORDER BY player_matches DESC",
        "purpose": "Compare average aces and player ranking by surface to check whether surface and player quality are confounded",
        "source": "raw"
    }
}