fix(gitlab): keep persistent /improve thread stable when it has replies

pr_agent/tools/pr_code_suggestions.py

@@ -333,12 +333,26 @@ def _extract_link(comment_text: str):
                             pr_comment_updated += f"{prev_suggestion_table}\n"
 
                         get_logger().info(f"Persistent mode - updating comment {comment_url} to latest {name} message")
-                        if progress_response:  # publish to 'progress_response' comment, because it refreshes immediately
-                            git_provider.edit_comment(progress_response, pr_comment_updated)
-                            git_provider.remove_comment(comment)
-                            comment = progress_response
-                        else:
-                            git_provider.edit_comment(comment, pr_comment_updated)
+                        # Edit the previously-found persistent comment in place and remove the throwaway
+                        # progress note. Editing the persistent comment (rather than re-targeting to the
+                        # progress note and deleting the original) keeps the stable thread stable across
+                        # pushes on GitLab, where deleting a note with replies fails silently.
+                        git_provider.edit_comment(comment, pr_comment_updated)
+                        if progress_response:
+                            # Cleanup is best-effort: isolate it from the outer try/except so a failure
+                            # here does not trigger the "no previous comment" fallback below, which
+                            # would publish a duplicate suggestions thread despite the persistent
+                            # comment update having already succeeded.
+                            try:
+                                # Replace the WIP progress body with a benign final-state message
+                                # before deletion so that if remove_comment fails for any reason, the
+                                # leftover note does not keep displaying "Work in progress ...".
+                                git_provider.edit_comment(progress_response, "Code suggestions published in the persistent thread above.")
+                                git_provider.remove_comment(progress_response)
+                            except Exception as cleanup_error:
+                                get_logger().warning(
+                                    f"Failed to clean up progress note after persistent update, leaving it in place: {cleanup_error}"
+                                )
                         return comment
             except Exception as e:
                 get_logger().exception(f"Failed to update persistent review, error: {e}")