fix: preserve worker fallback start time

api/core/app/apps/common/workflow_response_converter.py

@@ -502,7 +502,7 @@ class WorkflowResponseConverter:
         snapshot = self._pop_snapshot(event.node_execution_id)
 
         start_at = snapshot.start_at if snapshot else event.start_at
-        finished_at = naive_utc_now()
+        finished_at = event.finished_at or naive_utc_now()
         elapsed_time = (finished_at - start_at).total_seconds()
 
         inputs, inputs_truncated = self._truncate_mapping(event.inputs)

api/core/app/apps/workflow_app_runner.py

@@ -436,6 +436,7 @@ class WorkflowBasedAppRunner:
                     node_id=event.node_id,
                     node_type=event.node_type,
                     start_at=event.start_at,
+                    finished_at=event.finished_at,
                     inputs=inputs,
                     process_data=process_data,
                     outputs=outputs,
@@ -451,6 +452,7 @@ class WorkflowBasedAppRunner:
                     node_id=event.node_id,
                     node_type=event.node_type,
                     start_at=event.start_at,
+                    finished_at=event.finished_at,
                     inputs=event.node_run_result.inputs,
                     process_data=event.node_run_result.process_data,
                     outputs=event.node_run_result.outputs,
@@ -467,6 +469,7 @@ class WorkflowBasedAppRunner:
                     node_id=event.node_id,
                     node_type=event.node_type,
                     start_at=event.start_at,
+                    finished_at=event.finished_at,
                     inputs=event.node_run_result.inputs,
                     process_data=event.node_run_result.process_data,
                     outputs=event.node_run_result.outputs,

api/core/app/entities/queue_entities.py

@@ -336,6 +336,7 @@ class QueueNodeSucceededEvent(AppQueueEvent):
     in_loop_id: str | None = None
     """loop id if node is in loop"""
     start_at: datetime
+    finished_at: datetime | None = None
 
     inputs: Mapping[str, object] = Field(default_factory=dict)
     process_data: Mapping[str, object] = Field(default_factory=dict)
@@ -391,6 +392,7 @@ class QueueNodeExceptionEvent(AppQueueEvent):
     in_loop_id: str | None = None
     """loop id if node is in loop"""
     start_at: datetime
+    finished_at: datetime | None = None
 
     inputs: Mapping[str, object] = Field(default_factory=dict)
     process_data: Mapping[str, object] = Field(default_factory=dict)
@@ -415,6 +417,7 @@ class QueueNodeFailedEvent(AppQueueEvent):
     in_loop_id: str | None = None
     """loop id if node is in loop"""
     start_at: datetime
+    finished_at: datetime | None = None
 
     inputs: Mapping[str, object] = Field(default_factory=dict)
     process_data: Mapping[str, object] = Field(default_factory=dict)

api/core/app/workflow/layers/persistence.py

@@ -268,7 +268,12 @@ class WorkflowPersistenceLayer(GraphEngineLayer):
 
     def _handle_node_succeeded(self, event: NodeRunSucceededEvent) -> None:
         domain_execution = self._get_node_execution(event.id)
-        self._update_node_execution(domain_execution, event.node_run_result, WorkflowNodeExecutionStatus.SUCCEEDED)
+        self._update_node_execution(
+            domain_execution,
+            event.node_run_result,
+            WorkflowNodeExecutionStatus.SUCCEEDED,
+            finished_at=event.finished_at,
+        )
 
     def _handle_node_failed(self, event: NodeRunFailedEvent) -> None:
         domain_execution = self._get_node_execution(event.id)
@@ -277,6 +282,7 @@ class WorkflowPersistenceLayer(GraphEngineLayer):
             event.node_run_result,
             WorkflowNodeExecutionStatus.FAILED,
             error=event.error,
+            finished_at=event.finished_at,
         )
 
     def _handle_node_exception(self, event: NodeRunExceptionEvent) -> None:
@@ -286,6 +292,7 @@ class WorkflowPersistenceLayer(GraphEngineLayer):
             event.node_run_result,
             WorkflowNodeExecutionStatus.EXCEPTION,
             error=event.error,
+            finished_at=event.finished_at,
         )
 
     def _handle_node_pause_requested(self, event: NodeRunPauseRequestedEvent) -> None:
@@ -352,13 +359,14 @@ class WorkflowPersistenceLayer(GraphEngineLayer):
         *,
         error: str | None = None,
         update_outputs: bool = True,
+        finished_at: datetime | None = None,
     ) -> None:
-        finished_at = naive_utc_now()
+        actual_finished_at = finished_at or naive_utc_now()
         snapshot = self._node_snapshots.get(domain_execution.id)
         start_at = snapshot.created_at if snapshot else domain_execution.created_at
         domain_execution.status = status
-        domain_execution.finished_at = finished_at
-        domain_execution.elapsed_time = max((finished_at - start_at).total_seconds(), 0.0)
+        domain_execution.finished_at = actual_finished_at
+        domain_execution.elapsed_time = max((actual_finished_at - start_at).total_seconds(), 0.0)
 
         if error:
             domain_execution.error = error

api/dify_graph/graph_engine/error_handler.py

@@ -159,6 +159,7 @@ class ErrorHandler:
             node_id=event.node_id,
             node_type=event.node_type,
             start_at=event.start_at,
+            finished_at=event.finished_at,
             node_run_result=NodeRunResult(
                 status=WorkflowNodeExecutionStatus.EXCEPTION,
                 inputs=event.node_run_result.inputs,
@@ -198,6 +199,7 @@ class ErrorHandler:
             node_id=event.node_id,
             node_type=event.node_type,
             start_at=event.start_at,
+            finished_at=event.finished_at,
             node_run_result=NodeRunResult(
                 status=WorkflowNodeExecutionStatus.EXCEPTION,
                 inputs=event.node_run_result.inputs,

api/dify_graph/graph_engine/worker.py

@@ -15,10 +15,13 @@ from typing import TYPE_CHECKING, final
 from typing_extensions import override
 
 from dify_graph.context import IExecutionContext
+from dify_graph.enums import WorkflowNodeExecutionStatus
 from dify_graph.graph import Graph
 from dify_graph.graph_engine.layers.base import GraphEngineLayer
-from dify_graph.graph_events import GraphNodeEventBase, NodeRunFailedEvent, is_node_result_event
+from dify_graph.graph_events import GraphNodeEventBase, NodeRunFailedEvent, NodeRunStartedEvent, is_node_result_event
+from dify_graph.node_events import NodeRunResult
 from dify_graph.nodes.base.node import Node
+from libs.datetime_utils import naive_utc_now
 
 from .ready_queue import ReadyQueue
 
@@ -65,6 +68,7 @@ class Worker(threading.Thread):
         self._stop_event = threading.Event()
         self._layers = layers if layers is not None else []
         self._last_task_time = time.time()
+        self._current_node_started_at: datetime | None = None
 
     def stop(self) -> None:
         """Signal the worker to stop processing."""
@@ -104,18 +108,15 @@ class Worker(threading.Thread):
             self._last_task_time = time.time()
             node = self._graph.nodes[node_id]
             try:
+                self._current_node_started_at = None
                 self._execute_node(node)
                 self._ready_queue.task_done()
             except Exception as e:
-                error_event = NodeRunFailedEvent(
-                    id=node.execution_id,
-                    node_id=node.id,
-                    node_type=node.node_type,
-                    in_iteration_id=None,
-                    error=str(e),
-                    start_at=datetime.now(),
+                self._event_queue.put(
+                    self._build_fallback_failure_event(node, e, started_at=self._current_node_started_at)
                 )
-                self._event_queue.put(error_event)
+            finally:
+                self._current_node_started_at = None
 
     def _execute_node(self, node: Node) -> None:
         """
@@ -136,6 +137,8 @@ class Worker(threading.Thread):
                 try:
                     node_events = node.run()
                     for event in node_events:
+                        if isinstance(event, NodeRunStartedEvent):
+                            self._current_node_started_at = event.start_at
                         self._event_queue.put(event)
                         if is_node_result_event(event):
                             result_event = event
@@ -149,6 +152,8 @@ class Worker(threading.Thread):
             try:
                 node_events = node.run()
                 for event in node_events:
+                    if isinstance(event, NodeRunStartedEvent):
+                        self._current_node_started_at = event.start_at
                     self._event_queue.put(event)
                     if is_node_result_event(event):
                         result_event = event
@@ -177,3 +182,24 @@ class Worker(threading.Thread):
             except Exception:
                 # Silently ignore layer errors to prevent disrupting node execution
                 continue
+
+    def _build_fallback_failure_event(
+        self, node: Node, error: Exception, *, started_at: datetime | None = None
+    ) -> NodeRunFailedEvent:
+        """Build a failed event when worker-level execution aborts before a node emits its own result event."""
+        failure_time = naive_utc_now()
+        error_message = str(error)
+        return NodeRunFailedEvent(
+            id=node.execution_id,
+            node_id=node.id,
+            node_type=node.node_type,
+            in_iteration_id=None,
+            error=error_message,
+            start_at=started_at or failure_time,
+            finished_at=failure_time,
+            node_run_result=NodeRunResult(
+                status=WorkflowNodeExecutionStatus.FAILED,
+                error=error_message,
+                error_type=type(error).__name__,
+            ),
+        )

api/dify_graph/graph_events/node.py

@@ -37,16 +37,19 @@ class NodeRunRetrieverResourceEvent(GraphNodeEventBase):
 
 class NodeRunSucceededEvent(GraphNodeEventBase):
     start_at: datetime = Field(..., description="node start time")
+    finished_at: datetime | None = Field(default=None, description="node finish time")
 
 
 class NodeRunFailedEvent(GraphNodeEventBase):
     error: str = Field(..., description="error")
     start_at: datetime = Field(..., description="node start time")
+    finished_at: datetime | None = Field(default=None, description="node finish time")
 
 
 class NodeRunExceptionEvent(GraphNodeEventBase):
     error: str = Field(..., description="error")
     start_at: datetime = Field(..., description="node start time")
+    finished_at: datetime | None = Field(default=None, description="node finish time")
 
 
 class NodeRunRetryEvent(NodeRunStartedEvent):

api/dify_graph/nodes/base/node.py

@@ -428,11 +428,13 @@ class Node(Generic[NodeDataT]):
                 error=str(e),
                 error_type="WorkflowNodeError",
             )
+            finished_at = naive_utc_now()
             yield NodeRunFailedEvent(
                 id=self.execution_id,
                 node_id=self._node_id,
                 node_type=self.node_type,
                 start_at=self._start_at,
+                finished_at=finished_at,
                 node_run_result=result,
                 error=str(e),
             )
@@ -601,6 +603,7 @@ class Node(Generic[NodeDataT]):
         return self._node_data
 
     def _convert_node_run_result_to_graph_node_event(self, result: NodeRunResult) -> GraphNodeEventBase:
+        finished_at = naive_utc_now()
         match result.status:
             case WorkflowNodeExecutionStatus.FAILED:
                 return NodeRunFailedEvent(
@@ -608,6 +611,7 @@ class Node(Generic[NodeDataT]):
                     node_id=self.id,
                     node_type=self.node_type,
                     start_at=self._start_at,
+                    finished_at=finished_at,
                     node_run_result=result,
                     error=result.error,
                 )
@@ -617,6 +621,7 @@ class Node(Generic[NodeDataT]):
                     node_id=self.id,
                     node_type=self.node_type,
                     start_at=self._start_at,
+                    finished_at=finished_at,
                     node_run_result=result,
                 )
             case _:
@@ -639,6 +644,7 @@ class Node(Generic[NodeDataT]):
 
     @_dispatch.register
     def _(self, event: StreamCompletedEvent) -> NodeRunSucceededEvent | NodeRunFailedEvent:
+        finished_at = naive_utc_now()
         match event.node_run_result.status:
             case WorkflowNodeExecutionStatus.SUCCEEDED:
                 return NodeRunSucceededEvent(
@@ -646,6 +652,7 @@ class Node(Generic[NodeDataT]):
                     node_id=self._node_id,
                     node_type=self.node_type,
                     start_at=self._start_at,
+                    finished_at=finished_at,
                     node_run_result=event.node_run_result,
                 )
             case WorkflowNodeExecutionStatus.FAILED:
@@ -654,6 +661,7 @@ class Node(Generic[NodeDataT]):
                     node_id=self._node_id,
                     node_type=self.node_type,
                     start_at=self._start_at,
+                    finished_at=finished_at,
                     node_run_result=event.node_run_result,
                     error=event.node_run_result.error,
                 )

api/dify_graph/nodes/iteration/iteration_node.py

@@ -235,7 +235,7 @@ class IterationNode(LLMUsageTrackingMixin, Node[IterationNodeData]):
             future_to_index: dict[
                 Future[
                     tuple[
-                        datetime,
+                        float,
                         list[GraphNodeEventBase],
                         object | None,
                         dict[str, Variable],
@@ -260,7 +260,7 @@ class IterationNode(LLMUsageTrackingMixin, Node[IterationNodeData]):
                 try:
                     result = future.result()
                     (
-                        iter_start_at,
+                        iteration_duration,
                         events,
                         output_value,
                         conversation_snapshot,
@@ -273,8 +273,9 @@ class IterationNode(LLMUsageTrackingMixin, Node[IterationNodeData]):
                     # Yield all events from this iteration
                     yield from events
 
-                    # Update tokens and timing
-                    iter_run_map[str(index)] = (datetime.now(UTC).replace(tzinfo=None) - iter_start_at).total_seconds()
+                    # The worker computes duration before we replay buffered events here,
+                    # so slow downstream consumers don't inflate per-iteration timing.
+                    iter_run_map[str(index)] = iteration_duration
 
                     usage_accumulator[0] = self._merge_usage(usage_accumulator[0], iteration_usage)
 
@@ -304,7 +305,7 @@ class IterationNode(LLMUsageTrackingMixin, Node[IterationNodeData]):
         index: int,
         item: object,
         execution_context: "IExecutionContext",
-    ) -> tuple[datetime, list[GraphNodeEventBase], object | None, dict[str, Variable], LLMUsage]:
+    ) -> tuple[float, list[GraphNodeEventBase], object | None, dict[str, Variable], LLMUsage]:
         """Execute a single iteration in parallel mode and return results."""
         with execution_context:
             iter_start_at = datetime.now(UTC).replace(tzinfo=None)
@@ -326,9 +327,10 @@ class IterationNode(LLMUsageTrackingMixin, Node[IterationNodeData]):
             conversation_snapshot = self._extract_conversation_variable_snapshot(
                 variable_pool=graph_engine.graph_runtime_state.variable_pool
             )
+            iteration_duration = (datetime.now(UTC).replace(tzinfo=None) - iter_start_at).total_seconds()
 
             return (
-                iter_start_at,
+                iteration_duration,
                 events,
                 output_value,
                 conversation_snapshot,

api/tests/unit_tests/core/app/apps/common/test_workflow_response_converter_truncation.py

@@ -5,6 +5,7 @@ Unit tests for WorkflowResponseConverter focusing on process_data truncation fun
 import uuid
 from collections.abc import Mapping
 from dataclasses import dataclass
+from datetime import UTC, datetime
 from typing import Any
 from unittest.mock import Mock
 
@@ -234,6 +235,50 @@ class TestWorkflowResponseConverter:
         assert response.data.process_data == {}
         assert response.data.process_data_truncated is False
 
+    def test_workflow_node_finish_response_prefers_event_finished_at(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Finished timestamps should come from the event, not delayed queue processing time."""
+        converter = self.create_workflow_response_converter()
+        start_at = datetime(2024, 1, 1, 0, 0, 0, tzinfo=UTC).replace(tzinfo=None)
+        finished_at = datetime(2024, 1, 1, 0, 0, 2, tzinfo=UTC).replace(tzinfo=None)
+        delayed_processing_time = datetime(2024, 1, 1, 0, 0, 10, tzinfo=UTC).replace(tzinfo=None)
+
+        monkeypatch.setattr(
+            "core.app.apps.common.workflow_response_converter.naive_utc_now",
+            lambda: delayed_processing_time,
+        )
+        converter.workflow_start_to_stream_response(
+            task_id="bootstrap",
+            workflow_run_id="run-id",
+            workflow_id="wf-id",
+            reason=WorkflowStartReason.INITIAL,
+        )
+
+        event = QueueNodeSucceededEvent(
+            node_id="test-node-id",
+            node_type=NodeType.CODE,
+            node_execution_id="node-exec-1",
+            start_at=start_at,
+            finished_at=finished_at,
+            in_iteration_id=None,
+            in_loop_id=None,
+            inputs={},
+            process_data={},
+            outputs={},
+            execution_metadata={},
+        )
+
+        response = converter.workflow_node_finish_to_stream_response(
+            event=event,
+            task_id="test-task-id",
+        )
+
+        assert response is not None
+        assert response.data.elapsed_time == 2.0
+        assert response.data.finished_at == int(finished_at.timestamp())
+
     def test_workflow_node_retry_response_uses_truncated_process_data(self):
         """Test that node retry response uses get_response_process_data()."""
         converter = self.create_workflow_response_converter()

api/tests/unit_tests/core/app/workflow/layers/test_persistence.py

@@ -0,0 +1,60 @@
+from datetime import UTC, datetime
+from unittest.mock import Mock
+
+import pytest
+
+from core.app.workflow.layers.persistence import (
+    PersistenceWorkflowInfo,
+    WorkflowPersistenceLayer,
+    _NodeRuntimeSnapshot,
+)
+from dify_graph.enums import WorkflowNodeExecutionStatus, WorkflowType
+from dify_graph.node_events import NodeRunResult
+
+
+def _build_layer() -> WorkflowPersistenceLayer:
+    application_generate_entity = Mock()
+    application_generate_entity.inputs = {}
+
+    return WorkflowPersistenceLayer(
+        application_generate_entity=application_generate_entity,
+        workflow_info=PersistenceWorkflowInfo(
+            workflow_id="workflow-id",
+            workflow_type=WorkflowType.WORKFLOW,
+            version="1",
+            graph_data={},
+        ),
+        workflow_execution_repository=Mock(),
+        workflow_node_execution_repository=Mock(),
+    )
+
+
+def test_update_node_execution_prefers_event_finished_at(monkeypatch: pytest.MonkeyPatch) -> None:
+    layer = _build_layer()
+    node_execution = Mock()
+    node_execution.id = "node-exec-1"
+    node_execution.created_at = datetime(2024, 1, 1, 0, 0, 0, tzinfo=UTC).replace(tzinfo=None)
+    node_execution.update_from_mapping = Mock()
+
+    layer._node_snapshots[node_execution.id] = _NodeRuntimeSnapshot(
+        node_id="node-id",
+        title="LLM",
+        predecessor_node_id=None,
+        iteration_id="iter-1",
+        loop_id=None,
+        created_at=node_execution.created_at,
+    )
+
+    event_finished_at = datetime(2024, 1, 1, 0, 0, 2, tzinfo=UTC).replace(tzinfo=None)
+    delayed_processing_time = datetime(2024, 1, 1, 0, 0, 10, tzinfo=UTC).replace(tzinfo=None)
+    monkeypatch.setattr("core.app.workflow.layers.persistence.naive_utc_now", lambda: delayed_processing_time)
+
+    layer._update_node_execution(
+        node_execution,
+        NodeRunResult(status=WorkflowNodeExecutionStatus.SUCCEEDED),
+        WorkflowNodeExecutionStatus.SUCCEEDED,
+        finished_at=event_finished_at,
+    )
+
+    assert node_execution.finished_at == event_finished_at
+    assert node_execution.elapsed_time == 2.0

api/tests/unit_tests/core/workflow/graph_engine/test_worker.py

@@ -0,0 +1,87 @@
+import queue
+from collections.abc import Generator
+from datetime import UTC, datetime, timedelta
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+from dify_graph.enums import NodeType, WorkflowNodeExecutionStatus
+from dify_graph.graph_engine.ready_queue import InMemoryReadyQueue
+from dify_graph.graph_engine.worker import Worker
+from dify_graph.graph_events import NodeRunFailedEvent, NodeRunStartedEvent
+
+
+def test_build_fallback_failure_event_uses_naive_utc_and_failed_node_run_result(mocker) -> None:
+    fixed_time = datetime(2024, 1, 1, 12, 0, 0, tzinfo=UTC).replace(tzinfo=None)
+    mocker.patch("dify_graph.graph_engine.worker.naive_utc_now", return_value=fixed_time)
+
+    worker = Worker(
+        ready_queue=InMemoryReadyQueue(),
+        event_queue=queue.Queue(),
+        graph=MagicMock(),
+        layers=[],
+    )
+    node = SimpleNamespace(
+        execution_id="exec-1",
+        id="node-1",
+        node_type=NodeType.LLM,
+    )
+
+    event = worker._build_fallback_failure_event(node, RuntimeError("boom"))
+
+    assert event.start_at == fixed_time
+    assert event.finished_at == fixed_time
+    assert event.error == "boom"
+    assert event.node_run_result.status == WorkflowNodeExecutionStatus.FAILED
+    assert event.node_run_result.error == "boom"
+    assert event.node_run_result.error_type == "RuntimeError"
+
+
+def test_worker_fallback_failure_event_reuses_observed_start_time() -> None:
+    start_at = datetime(2024, 1, 1, 12, 0, 0, tzinfo=UTC).replace(tzinfo=None)
+    failure_time = start_at + timedelta(seconds=5)
+    captured_events: list[NodeRunFailedEvent | NodeRunStartedEvent] = []
+
+    class FakeNode:
+        execution_id = "exec-1"
+        id = "node-1"
+        node_type = NodeType.LLM
+
+        def ensure_execution_id(self) -> str:
+            return self.execution_id
+
+        def run(self) -> Generator[NodeRunStartedEvent, None, None]:
+            yield NodeRunStartedEvent(
+                id=self.execution_id,
+                node_id=self.id,
+                node_type=self.node_type,
+                node_title="LLM",
+                start_at=start_at,
+            )
+
+    worker = Worker(
+        ready_queue=MagicMock(),
+        event_queue=MagicMock(),
+        graph=MagicMock(nodes={"node-1": FakeNode()}),
+        layers=[],
+    )
+
+    worker._ready_queue.get.side_effect = ["node-1"]
+
+    def put_side_effect(event: NodeRunFailedEvent | NodeRunStartedEvent) -> None:
+        captured_events.append(event)
+        if len(captured_events) == 1:
+            raise RuntimeError("queue boom")
+        worker.stop()
+
+    worker._event_queue.put.side_effect = put_side_effect
+
+    with patch("dify_graph.graph_engine.worker.naive_utc_now", return_value=failure_time):
+        worker.run()
+
+    fallback_event = captured_events[-1]
+
+    assert isinstance(fallback_event, NodeRunFailedEvent)
+    assert fallback_event.start_at == start_at
+    assert fallback_event.finished_at == failure_time
+    assert fallback_event.error == "queue boom"
+    assert fallback_event.node_run_result.status == WorkflowNodeExecutionStatus.FAILED

api/tests/unit_tests/core/workflow/nodes/iteration/test_parallel_iteration_duration.py

@@ -0,0 +1,63 @@
+import time
+from contextlib import nullcontext
+from datetime import UTC, datetime
+
+import pytest
+
+from dify_graph.enums import NodeType
+from dify_graph.graph_events import NodeRunSucceededEvent
+from dify_graph.model_runtime.entities.llm_entities import LLMUsage
+from dify_graph.nodes.iteration.entities import ErrorHandleMode, IterationNodeData
+from dify_graph.nodes.iteration.iteration_node import IterationNode
+
+
+def test_parallel_iteration_duration_map_uses_worker_measured_time() -> None:
+    node = IterationNode.__new__(IterationNode)
+    node._node_data = IterationNodeData(
+        title="Parallel Iteration",
+        iterator_selector=["start", "items"],
+        output_selector=["iteration", "output"],
+        is_parallel=True,
+        parallel_nums=2,
+        error_handle_mode=ErrorHandleMode.TERMINATED,
+    )
+    node._capture_execution_context = lambda: nullcontext()
+    node._sync_conversation_variables_from_snapshot = lambda snapshot: None
+    node._merge_usage = lambda current, new: new if current.total_tokens == 0 else current.plus(new)
+
+    def fake_execute_single_iteration_parallel(*, index: int, item: object, execution_context: object):
+        return (
+            0.1 + (index * 0.1),
+            [
+                NodeRunSucceededEvent(
+                    id=f"exec-{index}",
+                    node_id=f"llm-{index}",
+                    node_type=NodeType.LLM,
+                    start_at=datetime.now(UTC).replace(tzinfo=None),
+                ),
+            ],
+            f"output-{item}",
+            {},
+            LLMUsage.empty_usage(),
+        )
+
+    node._execute_single_iteration_parallel = fake_execute_single_iteration_parallel
+
+    outputs: list[object] = []
+    iter_run_map: dict[str, float] = {}
+    usage_accumulator = [LLMUsage.empty_usage()]
+
+    generator = node._execute_parallel_iterations(
+        iterator_list_value=["a", "b"],
+        outputs=outputs,
+        iter_run_map=iter_run_map,
+        usage_accumulator=usage_accumulator,
+    )
+
+    for _ in generator:
+        # Simulate a slow consumer replaying buffered events.
+        time.sleep(0.02)
+
+    assert outputs == ["output-a", "output-b"]
+    assert iter_run_map["0"] == pytest.approx(0.1)
+    assert iter_run_map["1"] == pytest.approx(0.2)