Address Copilot review batch: tests + Workflow.reset escape hatch

* Add Workflow.reset() public method as recovery escape hatch when an
  in-flight run aborted (e.g. WorkflowConvergenceException) and the
  workflow is not checkpointed. Update the in-flight messages guard's
  error message to point callers at it.

* Add test_workflow_run_inflight_messages_guard exercising both the
  guard (sync + streaming) and the reset() recovery path.
* Add test_workflow_reset_rejects_concurrent_runs to lock down the
  in-progress guard on reset.

* Add test_as_agent_continuation_preserves_prior_state covering the
  is_continuation branch in _ensure_state_initialized: stamps a marker
  between calls and asserts it survives, while Inputs.input and
  System.LastMessageText refresh to the new turn.

* Add test_powerfx_safe.py regression tests for the Enum branch in
  _make_powerfx_safe (str-subclass, int-subclass, plain Enum, and
  Enums nested in dict/list).

* Drop redundant @pytest.mark.asyncio on
  test_as_agent_round_trip_with_last_message_text (asyncio_mode='auto').

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/core/tests/workflow/test_workflow.py

@@ -953,6 +953,50 @@ async def test_agent_streaming_vs_non_streaming() -> None:
     assert accumulated_text == "Hello World", f"Expected 'Hello World', got '{accumulated_text}'"
 
 
+async def test_workflow_run_inflight_messages_guard(simple_executor: Executor) -> None:
+    """``run(message=...)`` must reject in-flight executor messages from a prior run.
+
+    Workflows preserve state and pending messages across :meth:`Workflow.run`
+    calls. If a prior run aborted before the runner drained those pending
+    messages (e.g. it raised :class:`WorkflowConvergenceException`), the next
+    fresh-message call should fail loudly instead of silently mixing the
+    leftover messages with the new turn. Callers can recover via
+    :meth:`Workflow.reset`.
+    """
+    workflow = WorkflowBuilder(start_executor=simple_executor).add_edge(simple_executor, simple_executor).build()
+    test_message = WorkflowMessage(data="test", source_id="test", target_id=None)
+
+    # Simulate an aborted prior run by leaving a message in the runner context.
+    workflow._runner.context._messages["test"] = [test_message]
+    assert await workflow._runner.context.has_messages()
+
+    with pytest.raises(RuntimeError, match="in-flight executor messages"):
+        await workflow.run(test_message)
+
+    with pytest.raises(RuntimeError, match="in-flight executor messages"):
+        async for _ in workflow.run(test_message, stream=True):
+            pass
+
+    # ``Workflow.reset`` is the documented escape hatch.
+    await workflow.reset()
+    assert not await workflow._runner.context.has_messages()
+
+    # After reset, a new run is accepted again.
+    result = await workflow.run(test_message)
+    assert result.get_final_state() == WorkflowRunState.IDLE
+
+
+async def test_workflow_reset_rejects_concurrent_runs(simple_executor: Executor) -> None:
+    """``Workflow.reset`` must not stomp on an in-progress run."""
+    workflow = WorkflowBuilder(start_executor=simple_executor).add_edge(simple_executor, simple_executor).build()
+    workflow._is_running = True
+    try:
+        with pytest.raises(RuntimeError, match="run is in progress"):
+            await workflow.reset()
+    finally:
+        workflow._is_running = False
+
+
 async def test_workflow_run_parameter_validation(simple_executor: Executor) -> None:
     """Test that stream properly validate parameter combinations."""
     workflow = WorkflowBuilder(start_executor=simple_executor).add_edge(simple_executor, simple_executor).build()