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/declarative/tests/test_powerfx_safe.py

@@ -0,0 +1,59 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+"""Regression tests for ``_make_powerfx_safe``.
+
+PowerFx (via pythonnet) only accepts plain primitives, dicts, and lists.
+``Enum`` instances - especially ``str``- and ``int``-subclass enums like
+MAF's ``MessageRole`` - silently pass ``isinstance(v, str)`` /
+``isinstance(v, int)`` checks but blow up later inside pythonnet with
+``'<EnumName>' value cannot be converted to System.<X>``. These tests
+pin down the Enum coercion branch so we don't regress that interop fix.
+"""
+
+from enum import Enum, IntEnum
+
+from agent_framework_declarative._workflows._declarative_base import _make_powerfx_safe
+
+
+class _StrRole(str, Enum):
+    USER = "user"
+    SYSTEM = "system"
+
+
+class _IntCode(IntEnum):
+    ONE = 1
+    TWO = 2
+
+
+class _PlainEnum(Enum):
+    X = "x"
+    Y = 42
+
+
+def test_str_subclass_enum_reduces_to_str():
+    assert _make_powerfx_safe(_StrRole.USER) == "user"
+    assert type(_make_powerfx_safe(_StrRole.USER)) is str
+
+
+def test_int_subclass_enum_reduces_to_int():
+    assert _make_powerfx_safe(_IntCode.ONE) == 1
+    assert type(_make_powerfx_safe(_IntCode.ONE)) is int
+
+
+def test_plain_enum_reduces_to_underlying_value():
+    assert _make_powerfx_safe(_PlainEnum.X) == "x"
+    assert _make_powerfx_safe(_PlainEnum.Y) == 42
+
+
+def test_enum_inside_dict_is_coerced():
+    safe = _make_powerfx_safe({"role": _StrRole.USER, "code": _IntCode.TWO})
+    assert safe == {"role": "user", "code": 2}
+    assert type(safe["role"]) is str
+    assert type(safe["code"]) is int
+
+
+def test_enum_inside_list_is_coerced():
+    safe = _make_powerfx_safe([_StrRole.USER, _IntCode.ONE])
+    assert safe == ["user", 1]
+    assert type(safe[0]) is str
+    assert type(safe[1]) is int