{
    "action": "tool_call",
    "reasoning": "I need to check for duplicate rows across the dataset. The two largest tables (columns_catalog and job_logs) account for ~90% of rows. I'll start by checking columns_catalog for exact duplicates using its natural key (tables_catalog_id + column_name + ordinal), then check job_logs. The step-3 result already shows zero duplicates in columns_catalog based on that key combination. Now I'll check job_logs for duplicates using its natural key (job_id + ts + event_type + message).",
    "tool": "query_sql",
    "args": {
        "sql": "SELECT job_id, ts, event_type, message, COUNT(*) as duplicate_count FROM raw.job_logs GROUP BY job_id, ts, event_type, message HAVING COUNT(*) > 1 ORDER BY duplicate_count DESC LIMIT 50",
        "purpose": "Find duplicate rows in job_logs table using natural key fields",
        "source": "raw"
    }
}