revert(graph-engine): rollback stop-event unification (#32789)

api/core/workflow/graph_engine/graph_engine.py

@@ -9,7 +9,6 @@ from __future__ import annotations
 
 import logging
 import queue
-import threading
 from collections.abc import Generator
 from typing import TYPE_CHECKING, cast, final
 
@@ -77,13 +76,10 @@ class GraphEngine:
         config: GraphEngineConfig = _DEFAULT_CONFIG,
     ) -> None:
         """Initialize the graph engine with all subsystems and dependencies."""
-        # stop event
-        self._stop_event = threading.Event()
 
         # Bind runtime state to current workflow context
         self._graph = graph
         self._graph_runtime_state = graph_runtime_state
-        self._graph_runtime_state.stop_event = self._stop_event
         self._graph_runtime_state.configure(graph=cast("GraphProtocol", graph))
         self._command_channel = command_channel
         self._config = config
@@ -163,7 +159,6 @@ class GraphEngine:
             layers=self._layers,
             execution_context=execution_context,
             config=self._config,
-            stop_event=self._stop_event,
         )
 
         # === Orchestration ===
@@ -194,7 +189,6 @@ class GraphEngine:
             event_handler=self._event_handler_registry,
             execution_coordinator=self._execution_coordinator,
             event_emitter=self._event_manager,
-            stop_event=self._stop_event,
         )
 
         # === Validation ===
@@ -314,7 +308,6 @@ class GraphEngine:
 
     def _start_execution(self, *, resume: bool = False) -> None:
         """Start execution subsystems."""
-        self._stop_event.clear()
         paused_nodes: list[str] = []
         deferred_nodes: list[str] = []
         if resume:
@@ -348,7 +341,6 @@ class GraphEngine:
 
     def _stop_execution(self) -> None:
         """Stop execution subsystems."""
-        self._stop_event.set()
         self._dispatcher.stop()
         self._worker_pool.stop()
         # Don't mark complete here as the dispatcher already does it

api/core/workflow/graph_engine/orchestration/dispatcher.py

@@ -44,7 +44,6 @@ class Dispatcher:
         event_queue: queue.Queue[GraphNodeEventBase],
         event_handler: "EventHandler",
         execution_coordinator: ExecutionCoordinator,
-        stop_event: threading.Event,
         event_emitter: EventManager | None = None,
     ) -> None:
         """
@@ -62,7 +61,7 @@ class Dispatcher:
         self._event_emitter = event_emitter
 
         self._thread: threading.Thread | None = None
-        self._stop_event = stop_event
+        self._stop_event = threading.Event()
         self._start_time: float | None = None
 
     def start(self) -> None:
@@ -70,12 +69,14 @@ class Dispatcher:
         if self._thread and self._thread.is_alive():
             return
 
+        self._stop_event.clear()
         self._start_time = time.time()
         self._thread = threading.Thread(target=self._dispatcher_loop, name="GraphDispatcher", daemon=True)
         self._thread.start()
 
     def stop(self) -> None:
         """Stop the dispatcher thread."""
+        self._stop_event.set()
         if self._thread and self._thread.is_alive():
             self._thread.join(timeout=2.0)
 

api/core/workflow/graph_engine/worker.py

@@ -42,7 +42,6 @@ class Worker(threading.Thread):
         event_queue: queue.Queue[GraphNodeEventBase],
         graph: Graph,
         layers: Sequence[GraphEngineLayer],
-        stop_event: threading.Event,
         worker_id: int = 0,
         execution_context: IExecutionContext | None = None,
     ) -> None:
@@ -63,16 +62,13 @@ class Worker(threading.Thread):
         self._graph = graph
         self._worker_id = worker_id
         self._execution_context = execution_context
-        self._stop_event = stop_event
+        self._stop_event = threading.Event()
         self._layers = layers if layers is not None else []
         self._last_task_time = time.time()
 
     def stop(self) -> None:
-        """Worker is controlled via shared stop_event from GraphEngine.
+        """Signal the worker to stop processing."""
-
+        self._stop_event.set()
-        This method is a no-op retained for backward compatibility.
-        """
-        pass
 
     @property
     def is_idle(self) -> bool:

api/core/workflow/graph_engine/worker_management/worker_pool.py

@@ -37,7 +37,6 @@ class WorkerPool:
         event_queue: queue.Queue[GraphNodeEventBase],
         graph: Graph,
         layers: list[GraphEngineLayer],
-        stop_event: threading.Event,
         config: GraphEngineConfig,
         execution_context: IExecutionContext | None = None,
     ) -> None:
@@ -64,7 +63,6 @@ class WorkerPool:
         self._worker_counter = 0
         self._lock = threading.RLock()
         self._running = False
-        self._stop_event = stop_event
 
         # No longer tracking worker states with callbacks to avoid lock contention
 
@@ -135,7 +133,6 @@ class WorkerPool:
             layers=self._layers,
             worker_id=worker_id,
             execution_context=self._execution_context,
-            stop_event=self._stop_event,
         )
 
         worker.start()

api/core/workflow/nodes/base/node.py

@@ -302,10 +302,6 @@ class Node(Generic[NodeDataT]):
         """
         raise NotImplementedError
 
-    def _should_stop(self) -> bool:
-        """Check if execution should be stopped."""
-        return self.graph_runtime_state.stop_event.is_set()
-
     def run(self) -> Generator[GraphNodeEventBase, None, None]:
         execution_id = self.ensure_execution_id()
         self._start_at = naive_utc_now()
@@ -374,21 +370,6 @@ class Node(Generic[NodeDataT]):
                     yield event
                 else:
                     yield event
-
-                if self._should_stop():
-                    error_message = "Execution cancelled"
-                    yield NodeRunFailedEvent(
-                        id=self.execution_id,
-                        node_id=self._node_id,
-                        node_type=self.node_type,
-                        start_at=self._start_at,
-                        node_run_result=NodeRunResult(
-                            status=WorkflowNodeExecutionStatus.FAILED,
-                            error=error_message,
-                        ),
-                        error=error_message,
-                    )
-                    return
         except Exception as e:
             logger.exception("Node %s failed to run", self._node_id)
             result = NodeRunResult(

api/core/workflow/runtime/graph_runtime_state.py

@@ -2,7 +2,6 @@ from __future__ import annotations
 
 import importlib
 import json
-import threading
 from collections.abc import Mapping, Sequence
 from copy import deepcopy
 from dataclasses import dataclass
@@ -219,8 +218,6 @@ class GraphRuntimeState:
         self._pending_graph_node_states: dict[str, NodeState] | None = None
         self._pending_graph_edge_states: dict[str, NodeState] | None = None
 
-        self.stop_event: threading.Event = threading.Event()
-
         if graph is not None:
             self.attach_graph(graph)
 

api/tests/unit_tests/core/workflow/graph_engine/orchestration/test_dispatcher.py

@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 import queue
-import threading
 from unittest import mock
 
 from core.workflow.entities.pause_reason import SchedulingPause
@@ -37,7 +36,6 @@ def test_dispatcher_should_consume_remains_events_after_pause():
         event_queue=event_queue,
         event_handler=event_handler,
         execution_coordinator=execution_coordinator,
-        stop_event=threading.Event(),
     )
     dispatcher._dispatcher_loop()
     assert event_queue.empty()
@@ -98,7 +96,6 @@ def _run_dispatcher_for_event(event) -> int:
         event_queue=event_queue,
         event_handler=event_handler,
         execution_coordinator=coordinator,
-        stop_event=threading.Event(),
     )
 
     dispatcher._dispatcher_loop()
@@ -184,7 +181,6 @@ def test_dispatcher_drain_event_queue():
         event_queue=event_queue,
         event_handler=event_handler,
         execution_coordinator=coordinator,
-        stop_event=threading.Event(),
     )
 
     dispatcher._dispatcher_loop()

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

@@ -1,5 +1,4 @@
 import queue
-import threading
 from datetime import datetime
 
 from core.workflow.enums import NodeType, WorkflowNodeExecutionStatus
@@ -65,7 +64,6 @@ def test_dispatcher_drains_events_when_paused() -> None:
         event_handler=handler,
         execution_coordinator=coordinator,
         event_emitter=None,
-        stop_event=threading.Event(),
     )
 
     dispatcher._dispatcher_loop()

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

@@ -1,550 +0,0 @@
-"""
-Unit tests for stop_event functionality in GraphEngine.
-
-Tests the unified stop_event management by GraphEngine and its propagation
-to WorkerPool, Worker, Dispatcher, and Nodes.
-"""
-
-import threading
-import time
-from unittest.mock import MagicMock, Mock, patch
-
-from core.app.entities.app_invoke_entities import InvokeFrom
-from core.workflow.entities.graph_init_params import GraphInitParams
-from core.workflow.graph import Graph
-from core.workflow.graph_engine import GraphEngine, GraphEngineConfig
-from core.workflow.graph_engine.command_channels import InMemoryChannel
-from core.workflow.graph_events import (
-    GraphRunStartedEvent,
-    GraphRunSucceededEvent,
-    NodeRunStartedEvent,
-)
-from core.workflow.nodes.answer.answer_node import AnswerNode
-from core.workflow.nodes.start.start_node import StartNode
-from core.workflow.runtime import GraphRuntimeState, VariablePool
-from models.enums import UserFrom
-
-
-class TestStopEventPropagation:
-    """Test suite for stop_event propagation through GraphEngine components."""
-
-    def test_graph_engine_creates_stop_event(self):
-        """Test that GraphEngine creates a stop_event on initialization."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Verify stop_event was created
-        assert engine._stop_event is not None
-        assert isinstance(engine._stop_event, threading.Event)
-
-        # Verify it was set in graph_runtime_state
-        assert runtime_state.stop_event is not None
-        assert runtime_state.stop_event is engine._stop_event
-
-    def test_stop_event_cleared_on_start(self):
-        """Test that stop_event is cleared when execution starts."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-        mock_graph.root_node.id = "start"  # Set proper id
-
-        start_node = StartNode(
-            id="start",
-            config={"id": "start", "data": {"title": "start", "variables": []}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-        mock_graph.nodes["start"] = start_node
-        mock_graph.get_outgoing_edges = MagicMock(return_value=[])
-        mock_graph.get_incoming_edges = MagicMock(return_value=[])
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Set the stop_event before running
-        engine._stop_event.set()
-        assert engine._stop_event.is_set()
-
-        # Run the engine (should clear the stop_event)
-        events = list(engine.run())
-
-        # After running, stop_event should be set again (by _stop_execution)
-        # But during start it was cleared
-        assert any(isinstance(e, GraphRunStartedEvent) for e in events)
-        assert any(isinstance(e, GraphRunSucceededEvent) for e in events)
-
-    def test_stop_event_set_on_stop(self):
-        """Test that stop_event is set when execution stops."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-        mock_graph.root_node.id = "start"  # Set proper id
-
-        start_node = StartNode(
-            id="start",
-            config={"id": "start", "data": {"title": "start", "variables": []}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-        mock_graph.nodes["start"] = start_node
-        mock_graph.get_outgoing_edges = MagicMock(return_value=[])
-        mock_graph.get_incoming_edges = MagicMock(return_value=[])
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Initially not set
-        assert not engine._stop_event.is_set()
-
-        # Run the engine
-        list(engine.run())
-
-        # After execution completes, stop_event should be set
-        assert engine._stop_event.is_set()
-
-    def test_stop_event_passed_to_worker_pool(self):
-        """Test that stop_event is passed to WorkerPool."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Verify WorkerPool has the stop_event
-        assert engine._worker_pool._stop_event is not None
-        assert engine._worker_pool._stop_event is engine._stop_event
-
-    def test_stop_event_passed_to_dispatcher(self):
-        """Test that stop_event is passed to Dispatcher."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Verify Dispatcher has the stop_event
-        assert engine._dispatcher._stop_event is not None
-        assert engine._dispatcher._stop_event is engine._stop_event
-
-
-class TestNodeStopCheck:
-    """Test suite for Node._should_stop() functionality."""
-
-    def test_node_should_stop_checks_runtime_state(self):
-        """Test that Node._should_stop() checks GraphRuntimeState.stop_event."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-
-        answer_node = AnswerNode(
-            id="answer",
-            config={"id": "answer", "data": {"title": "answer", "answer": "{{#start.result#}}"}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-
-        # Initially stop_event is not set
-        assert not answer_node._should_stop()
-
-        # Set the stop_event
-        runtime_state.stop_event.set()
-
-        # Now _should_stop should return True
-        assert answer_node._should_stop()
-
-    def test_node_run_checks_stop_event_between_yields(self):
-        """Test that Node.run() checks stop_event between yielding events."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-
-        # Create a simple node
-        answer_node = AnswerNode(
-            id="answer",
-            config={"id": "answer", "data": {"title": "answer", "answer": "hello"}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-
-        # Set stop_event BEFORE running the node
-        runtime_state.stop_event.set()
-
-        # Run the node - should yield start event then detect stop
-        # The node should check stop_event before processing
-        assert answer_node._should_stop(), "stop_event should be set"
-
-        # Run and collect events
-        events = list(answer_node.run())
-
-        # Since stop_event is set at the start, we should get:
-        # 1. NodeRunStartedEvent (always yielded first)
-        # 2. Either NodeRunFailedEvent (if detected early) or NodeRunSucceededEvent (if too fast)
-        assert len(events) >= 2
-        assert isinstance(events[0], NodeRunStartedEvent)
-
-        # Note: AnswerNode is very simple and might complete before stop check
-        # The important thing is that _should_stop() returns True when stop_event is set
-        assert answer_node._should_stop()
-
-
-class TestStopEventIntegration:
-    """Integration tests for stop_event in workflow execution."""
-
-    def test_simple_workflow_respects_stop_event(self):
-        """Test that a simple workflow respects stop_event."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-        mock_graph.root_node.id = "start"
-
-        # Create start and answer nodes
-        start_node = StartNode(
-            id="start",
-            config={"id": "start", "data": {"title": "start", "variables": []}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-
-        answer_node = AnswerNode(
-            id="answer",
-            config={"id": "answer", "data": {"title": "answer", "answer": "hello"}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-
-        mock_graph.nodes["start"] = start_node
-        mock_graph.nodes["answer"] = answer_node
-        mock_graph.get_outgoing_edges = MagicMock(return_value=[])
-        mock_graph.get_incoming_edges = MagicMock(return_value=[])
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Set stop_event before running
-        runtime_state.stop_event.set()
-
-        # Run the engine
-        events = list(engine.run())
-
-        # Should get started event but not succeeded (due to stop)
-        assert any(isinstance(e, GraphRunStartedEvent) for e in events)
-        # The workflow should still complete (start node runs quickly)
-        # but answer node might be cancelled depending on timing
-
-    def test_stop_event_with_concurrent_nodes(self):
-        """Test stop_event behavior with multiple concurrent nodes."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        # Create multiple nodes
-        for i in range(3):
-            answer_node = AnswerNode(
-                id=f"answer_{i}",
-                config={"id": f"answer_{i}", "data": {"title": f"answer_{i}", "answer": f"test{i}"}},
-                graph_init_params=GraphInitParams(
-                    tenant_id="test_tenant",
-                    app_id="test_app",
-                    workflow_id="test_workflow",
-                    graph_config={},
-                    user_id="test_user",
-                    user_from=UserFrom.ACCOUNT,
-                    invoke_from=InvokeFrom.DEBUGGER,
-                    call_depth=0,
-                ),
-                graph_runtime_state=runtime_state,
-            )
-            mock_graph.nodes[f"answer_{i}"] = answer_node
-
-        mock_graph.get_outgoing_edges = MagicMock(return_value=[])
-        mock_graph.get_incoming_edges = MagicMock(return_value=[])
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # All nodes should share the same stop_event
-        for node in mock_graph.nodes.values():
-            assert node.graph_runtime_state.stop_event is runtime_state.stop_event
-            assert node.graph_runtime_state.stop_event is engine._stop_event
-
-
-class TestStopEventTimeoutBehavior:
-    """Test stop_event behavior with join timeouts."""
-
-    @patch("core.workflow.graph_engine.orchestration.dispatcher.threading.Thread", autospec=True)
-    def test_dispatcher_uses_shorter_timeout(self, mock_thread_cls: MagicMock):
-        """Test that Dispatcher uses 2s timeout instead of 10s."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        dispatcher = engine._dispatcher
-        dispatcher.start()  # This will create and start the mocked thread
-
-        mock_thread_instance = mock_thread_cls.return_value
-        mock_thread_instance.is_alive.return_value = True
-
-        dispatcher.stop()
-
-        mock_thread_instance.join.assert_called_once_with(timeout=2.0)
-
-    @patch("core.workflow.graph_engine.worker_management.worker_pool.Worker", autospec=True)
-    def test_worker_pool_uses_shorter_timeout(self, mock_worker_cls: MagicMock):
-        """Test that WorkerPool uses 2s timeout instead of 10s."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        worker_pool = engine._worker_pool
-        worker_pool.start(initial_count=1)  # Start with one worker
-
-        mock_worker_instance = mock_worker_cls.return_value
-        mock_worker_instance.is_alive.return_value = True
-
-        worker_pool.stop()
-
-        mock_worker_instance.join.assert_called_once_with(timeout=2.0)
-
-
-class TestStopEventResumeBehavior:
-    """Test stop_event behavior during workflow resume."""
-
-    def test_stop_event_cleared_on_resume(self):
-        """Test that stop_event is cleared when resuming a paused workflow."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-        mock_graph.root_node.id = "start"  # Set proper id
-
-        start_node = StartNode(
-            id="start",
-            config={"id": "start", "data": {"title": "start", "variables": []}},
-            graph_init_params=GraphInitParams(
-                tenant_id="test_tenant",
-                app_id="test_app",
-                workflow_id="test_workflow",
-                graph_config={},
-                user_id="test_user",
-                user_from=UserFrom.ACCOUNT,
-                invoke_from=InvokeFrom.DEBUGGER,
-                call_depth=0,
-            ),
-            graph_runtime_state=runtime_state,
-        )
-        mock_graph.nodes["start"] = start_node
-        mock_graph.get_outgoing_edges = MagicMock(return_value=[])
-        mock_graph.get_incoming_edges = MagicMock(return_value=[])
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Simulate a previous execution that set stop_event
-        engine._stop_event.set()
-        assert engine._stop_event.is_set()
-
-        # Run the engine (should clear stop_event in _start_execution)
-        events = list(engine.run())
-
-        # Execution should complete successfully
-        assert any(isinstance(e, GraphRunStartedEvent) for e in events)
-        assert any(isinstance(e, GraphRunSucceededEvent) for e in events)
-
-
-class TestWorkerStopBehavior:
-    """Test Worker behavior with shared stop_event."""
-
-    def test_worker_uses_shared_stop_event(self):
-        """Test that Worker uses shared stop_event from GraphEngine."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-        mock_graph = MagicMock(spec=Graph)
-        mock_graph.nodes = {}
-        mock_graph.edges = {}
-        mock_graph.root_node = MagicMock()
-
-        engine = GraphEngine(
-            workflow_id="test_workflow",
-            graph=mock_graph,
-            graph_runtime_state=runtime_state,
-            command_channel=InMemoryChannel(),
-            config=GraphEngineConfig(),
-        )
-
-        # Get the worker pool and check workers
-        worker_pool = engine._worker_pool
-
-        # Start the worker pool to create workers
-        worker_pool.start()
-
-        # Check that at least one worker was created
-        assert len(worker_pool._workers) > 0
-
-        # Verify workers use the shared stop_event
-        for worker in worker_pool._workers:
-            assert worker._stop_event is engine._stop_event
-
-        # Clean up
-        worker_pool.stop()
-
-    def test_worker_stop_is_noop(self):
-        """Test that Worker.stop() is now a no-op."""
-        runtime_state = GraphRuntimeState(variable_pool=VariablePool(), start_at=time.perf_counter())
-
-        # Create a mock worker
-        from core.workflow.graph_engine.ready_queue import InMemoryReadyQueue
-        from core.workflow.graph_engine.worker import Worker
-
-        ready_queue = InMemoryReadyQueue()
-        event_queue = MagicMock()
-
-        # Create a proper mock graph with real dict
-        mock_graph = Mock(spec=Graph)
-        mock_graph.nodes = {}  # Use real dict
-
-        stop_event = threading.Event()
-
-        worker = Worker(
-            ready_queue=ready_queue,
-            event_queue=event_queue,
-            graph=mock_graph,
-            layers=[],
-            stop_event=stop_event,
-        )
-
-        # Calling stop() should do nothing (no-op)
-        # and should NOT set the stop_event
-        worker.stop()
-        assert not stop_event.is_set()