Python: [BREAKING] Simplify API: ChatAgent -> Agent, ChatMessage -> Message (#3747)

* [BREAKING] Rename ChatAgent -> Agent, ChatMessage -> Message, ChatClientProtocol -> SupportsChatGetResponse

Simplify the public API by removing redundant 'Chat' prefix from core types:
- ChatAgent -> Agent
- RawChatAgent -> RawAgent
- ChatMessage -> Message
- ChatClientProtocol -> SupportsChatGetResponse

Also renamed internal WorkflowMessage (was Message in _runner_context) to avoid collision.

No backward compatibility aliases - this is a clean breaking change.

* [BREAKING] Rename Agent chat_client parameter to client

* Fix rebase issues: WorkflowMessage references and broken markdown links

* Fix formatting and lint issues from code quality checks

* Fix import ordering in workflow sample files

* fixed rebase

* Fix test failures: use WorkflowMessage and A2AMessage after ChatMessage→Message rename

- Replace Message(data=..., source_id=...) with WorkflowMessage(...) in workflow tests
- Fix isinstance check in A2A agent to use A2AMessage instead of Message
- Fix import in test_workflow_observability.py (Message→WorkflowMessage)

* Fix lint, fmt, and sample errors after ChatMessage→Message rename

- Auto-fix 70+ ruff lint issues across samples (ChatMessage→Message refs)
- Fix HostedVectorStoreContent→Content.from_hosted_vector_store in file search sample
- Fix _normalize_messages→normalize_messages in custom agent sample
- Fix context.terminate→raise MiddlewareTermination in middleware samples
- Fix with_update_hook→with_transform_hook in override middleware sample
- Add TOptions_co import back to custom_chat_client sample
- Add noqa for FastAPI File() default in chatkit sample
- Fix B023 loop variable capture in weather agent sample

* fix: update Agent constructor calls from chat_client to client in declaration-only tool tests

* fix: add register_cleanup to devui lazy-loading proxy and type stub

* fixed tests and updated new pieces

* fix agui typevar

* fix merge errors

* fix merge conflicts

* fiux merge

* Remove unused links

---------

Co-authored-by: Evan Mattson <evan.mattson@microsoft.com>

python/samples/getting_started/chat_client/README.md

@@ -14,7 +14,7 @@ This folder contains simple examples demonstrating direct usage of various chat
 | [`openai_assistants_client.py`](openai_assistants_client.py) | Direct usage of OpenAI Assistants Client for basic chat interactions with OpenAI assistants. |
 | [`openai_chat_client.py`](openai_chat_client.py) | Direct usage of OpenAI Chat Client for chat interactions with OpenAI models. |
 | [`openai_responses_client.py`](openai_responses_client.py) | Direct usage of OpenAI Responses Client for structured response generation with OpenAI models. |
-| [`custom_chat_client.py`](custom_chat_client.py) | Demonstrates how to create custom chat clients by extending the `BaseChatClient` class. Shows a `EchoingChatClient` implementation and how to integrate it with `ChatAgent` using the `as_agent()` method. |
+| [`custom_chat_client.py`](custom_chat_client.py) | Demonstrates how to create custom chat clients by extending the `BaseChatClient` class. Shows a `EchoingChatClient` implementation and how to integrate it with `Agent` using the `as_agent()` method. |
 
 ## Environment Variables
 

python/samples/getting_started/chat_client/chat_response_cancellation.py

@@ -21,10 +21,10 @@ async def main() -> None:
     - OpenAI model ID: Use "model_id" parameter or "OPENAI_CHAT_MODEL_ID" environment variable
     - OpenAI API key: Use "api_key" parameter or "OPENAI_API_KEY" environment variable
     """
-    chat_client = OpenAIChatClient()
+    client = OpenAIChatClient()
 
     try:
-        task = asyncio.create_task(chat_client.get_response(messages=["Tell me a fantasy story."]))
+        task = asyncio.create_task(client.get_response(messages=["Tell me a fantasy story."]))
         await asyncio.sleep(1)
         task.cancel()
         await task

python/samples/getting_started/chat_client/custom_chat_client.py

@@ -8,12 +8,12 @@ from typing import Any, ClassVar, Generic
 
 from agent_framework import (
     BaseChatClient,
-    ChatMessage,
     ChatMiddlewareLayer,
     ChatResponse,
     ChatResponseUpdate,
     Content,
     FunctionInvocationLayer,
+    Message,
     ResponseStream,
     Role,
 )
@@ -61,7 +61,7 @@ class EchoingChatClient(BaseChatClient[OptionsCoT], Generic[OptionsCoT]):
     def _inner_get_response(
         self,
         *,
-        messages: Sequence[ChatMessage],
+        messages: Sequence[Message],
         stream: bool = False,
         options: Mapping[str, Any],
         **kwargs: Any,
@@ -82,7 +82,7 @@ class EchoingChatClient(BaseChatClient[OptionsCoT], Generic[OptionsCoT]):
             else:
                 response_text = f"{self.prefix} [No text message found]"
 
-        response_message = ChatMessage(role=Role.ASSISTANT, contents=[Content.from_text(response_text)])
+        response_message = Message(role=Role.ASSISTANT, contents=[Content.from_text(response_text)])
 
         response = ChatResponse(
             messages=[response_message],
@@ -124,7 +124,7 @@ class EchoingChatClientWithLayers(  # type: ignore[misc,type-var]
 
 
 async def main() -> None:
-    """Demonstrates how to implement and use a custom chat client with ChatAgent."""
+    """Demonstrates how to implement and use a custom chat client with Agent."""
     print("=== Custom Chat Client Example ===\n")
 
     # Create the custom chat client