Python: Reduce Azure chat client import overhead (#4744)

* Reduce Azure chat client import overhead

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

* Fix Azure chat client type annotations and add _parse_text_from_openai tests

- Move Choice and ChunkChoice imports under TYPE_CHECKING to avoid
  runtime import cost (from __future__ annotations is already present)
- Restore proper typed signature (Choice | ChunkChoice) instead of Any
- Add direct unit tests for _parse_text_from_openai covering:
  - Choice with message content
  - ChunkChoice with delta content
  - Refusal branch for both Choice and ChunkChoice
  - No content/no refusal returning None
  - None delta (async content filtering) returning None

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

---------

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

python/packages/core/agent_framework/azure/_chat_client.py

@@ -8,9 +8,6 @@ import sys
 from collections.abc import Mapping, Sequence
 from typing import TYPE_CHECKING, Any, Generic, cast
 
-from openai.lib.azure import AsyncAzureOpenAI
-from openai.types.chat.chat_completion import Choice
-from openai.types.chat.chat_completion_chunk import Choice as ChunkChoice
 from pydantic import BaseModel
 
 from agent_framework import (
@@ -23,8 +20,7 @@ from agent_framework import (
     FunctionInvocationLayer,
 )
 from agent_framework.observability import ChatTelemetryLayer
-from agent_framework.openai import OpenAIChatOptions
-from agent_framework.openai._chat_client import RawOpenAIChatClient
+from agent_framework.openai._chat_client import OpenAIChatOptions, RawOpenAIChatClient
 
 from .._settings import load_settings
 from ._entra_id_authentication import AzureCredentialTypes, AzureTokenProvider
@@ -48,6 +44,10 @@ else:
     from typing_extensions import TypedDict  # type: ignore # pragma: no cover
 
 if TYPE_CHECKING:
+    from openai.lib.azure import AsyncAzureOpenAI
+    from openai.types.chat.chat_completion import Choice
+    from openai.types.chat.chat_completion_chunk import Choice as ChunkChoice
+
     from agent_framework._middleware import MiddlewareTypes
 
 logger: logging.Logger = logging.getLogger(__name__)
@@ -297,7 +297,9 @@ class AzureOpenAIChatClient(  # type: ignore[misc]
         For docs see:
         https://learn.microsoft.com/en-us/azure/ai-foundry/openai/references/on-your-data?tabs=python#context
         """
-        message = choice.message if isinstance(choice, Choice) else choice.delta
+        message = getattr(choice, "message", None)
+        if message is None:
+            message = getattr(choice, "delta", None)
         # When you enable asynchronous content filtering in Azure OpenAI, you may receive empty deltas
         if message is None:  # type: ignore
             return None

python/packages/core/tests/azure/test_azure_chat_client.py

@@ -652,6 +652,88 @@ async def test_streaming_with_none_delta(
     assert any(msg.contents for msg in results)
 
 
+# region _parse_text_from_openai direct unit tests
+
+
+def test_parse_text_from_openai_with_choice_message(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai correctly reads message from a Choice."""
+    client = AzureOpenAIChatClient()
+    choice = Choice(
+        index=0,
+        message=ChatCompletionMessage(content="hello", role="assistant"),
+        finish_reason="stop",
+    )
+    result = client._parse_text_from_openai(choice)
+    assert result is not None
+    assert result.type == "text"
+    assert result.text == "hello"
+
+
+def test_parse_text_from_openai_with_chunk_choice_delta(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai correctly reads delta from a ChunkChoice."""
+    client = AzureOpenAIChatClient()
+    choice = ChunkChoice(
+        index=0,
+        delta=ChunkChoiceDelta(content="streamed", role="assistant"),
+        finish_reason=None,
+    )
+    result = client._parse_text_from_openai(choice)
+    assert result is not None
+    assert result.type == "text"
+    assert result.text == "streamed"
+
+
+def test_parse_text_from_openai_refusal_choice(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai returns refusal text from a Choice."""
+    client = AzureOpenAIChatClient()
+    choice = Choice(
+        index=0,
+        message=ChatCompletionMessage(content=None, role="assistant", refusal="I cannot help with that"),
+        finish_reason="stop",
+    )
+    result = client._parse_text_from_openai(choice)
+    assert result is not None
+    assert result.type == "text"
+    assert result.text == "I cannot help with that"
+
+
+def test_parse_text_from_openai_refusal_chunk_choice(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai returns refusal text from a ChunkChoice."""
+    client = AzureOpenAIChatClient()
+    choice = ChunkChoice(
+        index=0,
+        delta=ChunkChoiceDelta(content=None, role="assistant", refusal="I cannot help with that"),
+        finish_reason=None,
+    )
+    result = client._parse_text_from_openai(choice)
+    assert result is not None
+    assert result.type == "text"
+    assert result.text == "I cannot help with that"
+
+
+def test_parse_text_from_openai_no_content_no_refusal(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai returns None when no content or refusal."""
+    client = AzureOpenAIChatClient()
+    choice = Choice(
+        index=0,
+        message=ChatCompletionMessage(content=None, role="assistant"),
+        finish_reason="stop",
+    )
+    result = client._parse_text_from_openai(choice)
+    assert result is None
+
+
+def test_parse_text_from_openai_none_delta(azure_openai_unit_test_env: dict[str, str]) -> None:
+    """Test _parse_text_from_openai returns None when delta is None (async content filtering)."""
+    client = AzureOpenAIChatClient()
+    choice = ChunkChoice.model_construct(index=0, delta=None, finish_reason=None)
+    result = client._parse_text_from_openai(choice)
+    assert result is None
+
+
+# endregion
+
+
 @patch.object(AsyncChatCompletions, "create", new_callable=AsyncMock)
 async def test_cmc_with_conversation_id(
     mock_create: AsyncMock,