Add debug logging for empty-column-removal

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/grid_editor_api.py

@@ -1736,6 +1736,17 @@ async def _build_grid_core(
                 if fixed != text:
                     cell["text"] = fixed
 
+    # --- Debug: log cell counts per column before empty-column removal ---
+    for z in zones_data:
+        if z.get("zone_type") == "content":
+            from collections import Counter as _Counter
+            _cc = _Counter(c.get("col_index") for c in z.get("cells", []))
+            _cols = z.get("columns", [])
+            logger.info(
+                "pre-empty-col-removal zone %d: %d cols, cells_per_col=%s",
+                z.get("zone_index", 0), len(_cols), dict(sorted(_cc.items())),
+            )
+
     # --- Remove empty columns (no cells assigned) ---
     for z in zones_data:
         cells = z.get("cells", [])