debug: Add detailed logging to consolidation group buffering

Added logging to track:
- When groups are buffered at batch boundaries
- Group consolidation keys and row counts
- When buffered groups are resumed in next batch
- Final batch group yields

This will help diagnose why some nodes are being lost during consolidation
(observed: nodes 1-11 missing from consolidated group, only nodes 12-22 present).

🤖 Generated with Claude Code

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/connectors/mysql_connector.py

@@ -412,6 +412,10 @@ class MySQLConnector:
 
                         # If we have a buffered group, prepend it to continue
                         if buffered_group:
+                            logger.debug(
+                                f"Resuming buffered group: key={last_buffered_key}, "
+                                f"prev_buffered_rows={len(buffered_group)}, new_rows={len(rows)}"
+                            )
                             sorted_rows = buffered_group + sorted_rows
                             buffered_group = []
 
@@ -442,9 +446,17 @@ class MySQLConnector:
                             # Buffer incomplete group at boundary for next batch
                             buffered_group = current_group
                             last_buffered_key = last_key
+                            logger.debug(
+                                f"Buffering group at boundary: key={last_key}, "
+                                f"rows_in_group={len(current_group)}, total_rows_fetched={len(rows)}"
+                            )
                         else:
                             # This is the last batch, yield final group
                             if current_group:
+                                logger.debug(
+                                    f"Final batch: yielding group key={last_key}, "
+                                    f"rows_in_group={len(current_group)}, total_rows_fetched={len(rows)}"
+                                )
                                 yield current_group
 
                         last_id = rows[-1][id_column]