fix(api):LLM node losing Flask context during parallel iterations (#26098)

api/core/workflow/nodes/iteration/iteration_node.py

+import contextvars
 import logging
 from collections.abc import Generator, Mapping, Sequence
 from concurrent.futures import Future, ThreadPoolExecutor, as_completed
 from datetime import UTC, datetime
 from typing import TYPE_CHECKING, Any, NewType, cast
 
+from flask import Flask, current_app
 from typing_extensions import TypeIs
 
 from core.variables import IntegerVariable, NoneSegment
 from core.workflow.nodes.base.node import Node
 from core.workflow.nodes.iteration.entities import ErrorHandleMode, IterationNodeData
 from libs.datetime_utils import naive_utc_now
+from libs.flask_utils import preserve_flask_contexts
 
 from .exc import (
     InvalidIteratorValueError,
                     self._execute_single_iteration_parallel,
                     index=index,
                     item=item,
+                    flask_app=current_app._get_current_object(),  # type: ignore
+                    context_vars=contextvars.copy_context(),
                 )
                 future_to_index[future] = index
 
         self,
         index: int,
         item: object,
+        flask_app: Flask,
+        context_vars: contextvars.Context,
     ) -> tuple[datetime, list[GraphNodeEventBase], object | None, int]:
         """Execute a single iteration in parallel mode and return results."""
-        iter_start_at = datetime.now(UTC).replace(tzinfo=None)
-        events: list[GraphNodeEventBase] = []
-        outputs_temp: list[object] = []
+        with preserve_flask_contexts(flask_app=flask_app, context_vars=context_vars):
+            iter_start_at = datetime.now(UTC).replace(tzinfo=None)
+            events: list[GraphNodeEventBase] = []
+            outputs_temp: list[object] = []
 
-        graph_engine = self._create_graph_engine(index, item)
+            graph_engine = self._create_graph_engine(index, item)
 
-        # Collect events instead of yielding them directly
-        for event in self._run_single_iter(
-            variable_pool=graph_engine.graph_runtime_state.variable_pool,
-            outputs=outputs_temp,
-            graph_engine=graph_engine,
-        ):
-            events.append(event)
+            # Collect events instead of yielding them directly
+            for event in self._run_single_iter(
+                variable_pool=graph_engine.graph_runtime_state.variable_pool,
+                outputs=outputs_temp,
+                graph_engine=graph_engine,
+            ):
+                events.append(event)
 
-        # Get the output value from the temporary outputs list
-        output_value = outputs_temp[0] if outputs_temp else None
+            # Get the output value from the temporary outputs list
+            output_value = outputs_temp[0] if outputs_temp else None
 
-        return iter_start_at, events, output_value, graph_engine.graph_runtime_state.total_tokens
+            return iter_start_at, events, output_value, graph_engine.graph_runtime_state.total_tokens
 
     def _handle_iteration_success(
         self,