Update app/routers/datasources.py

app/routers/datasources.py

@@ -109,7 +109,16 @@ async def create_source_json(
         print(f"[api/json] 🎯 Industry detected: {industry} ({confidence:.1%})")
 
         # 3. 🎯 Prepare preview for real-time broadcast
-        preview_rows = df.head(3).to_dict("records") if not df.empty else []
+        
+        # Convert DataFrame to JSON-safe format
+        preview_df = df.head(3).copy()
+        for col in preview_df.columns:
+           if pd.api.types.is_datetime64_any_dtype(preview_df[col]):
+                preview_df[col] = preview_df[col].dt.strftime('%Y-%m-%d %H:%M:%S')
+           elif pd.api.types.is_timedelta64_dtype(preview_df[col]):
+               preview_df[col] = preview_df[col].astype(str)
+
+        preview_rows = preview_df.to_dict("records") if not preview_df.empty else []
         
         # 4. 📡 Broadcast to connected dashboards
         await sio.emit(