fix: nesting of conditional branches causing streaming output error (#14065)

api/core/workflow/nodes/answer/base_stream_processor.py

@@ -57,11 +57,19 @@ class StreamProcessor(ABC):
 
                     # The branch_identify parameter is added to ensure that
                     # only nodes in the correct logical branch are included.
+                    reachable_node_ids.append(edge.target_node_id)
                     ids = self._fetch_node_ids_in_reachable_branch(edge.target_node_id, run_result.edge_source_handle)
                     reachable_node_ids.extend(ids)
                 else:
+                    # if the condition edge in parallel, and the target node is not in parallel, we should not remove it
+                    # Issues: #13626
+                    if (
+                        finished_node_id in self.graph.node_parallel_mapping
+                        and edge.target_node_id not in self.graph.parallel_mapping
+                    ):
+                        continue
                     unreachable_first_node_ids.append(edge.target_node_id)
-
+            unreachable_first_node_ids = list(set(unreachable_first_node_ids) - set(reachable_node_ids))
             for node_id in unreachable_first_node_ids:
                 self._remove_node_ids_in_unreachable_branch(node_id, reachable_node_ids)