fix(tools): align analyze_descriptive required args + normalize Timestamp in aggregate

src/tools/analytics/aggregation.py

@@ -28,7 +28,13 @@ class UnsupportedAggregationError(ValueError):
 
 
 def _clean(value: object) -> object:
-    """Convert numpy scalars to plain Python so the output is JSON-clean."""
+    """Convert numpy/pandas scalars to plain Python so the output is JSON-clean.
+
+    A `group_by` over a datetime column yields `pandas.Timestamp` group keys,
+    which (like numpy scalars) are not JSON-serializable — normalise those too.
+    """
+    if isinstance(value, pd.Timestamp):
+        return value.isoformat()
     if hasattr(value, "item"):
         return value.item()
     return value

src/tools/registry.py

@@ -41,7 +41,7 @@ ANALYTICS_TOOLS: list[ToolSpec] = [
         name="analyze_descriptive",
         category="analytics.descriptive",
         input_schema={
-            "required": ["data"],
+            "required": ["data", "column_ids"],
             "properties": {
                 "data": {"type": "string"},
                 "column_ids": {"type": "array"},