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/devui/weather_agent_azure/agent.py

@@ -7,15 +7,16 @@ from collections.abc import AsyncIterable, Awaitable, Callable
 from typing import Annotated
 
 from agent_framework import (
-    ChatAgent,
+    Agent,
     ChatContext,
-    ChatMessage,
     ChatResponse,
     ChatResponseUpdate,
     Content,
     FunctionInvocationContext,
+    Message,
     MiddlewareTermination,
     ResponseStream,
+    Role,
     chat_middleware,
     function_middleware,
     tool,
@@ -44,7 +45,7 @@ async def security_filter_middleware(
 
     # Check only the last message (most recent user input)
     last_message = context.messages[-1] if context.messages else None
-    if last_message and last_message.role == "user" and last_message.text:
+    if last_message and last_message.role == Role.USER and last_message.text:
         message_lower = last_message.text.lower()
         for term in blocked_terms:
             if term in message_lower:
@@ -55,26 +56,29 @@ async def security_filter_middleware(
                 )
 
                 if context.stream:
-                    # Streaming mode: return async generator
+                    # Streaming mode: wrap in ResponseStream
                     async def blocked_stream(msg: str = error_message) -> AsyncIterable[ChatResponseUpdate]:
                         yield ChatResponseUpdate(
                             contents=[Content.from_text(text=msg)],
-                            role="assistant",
+                            role=Role.ASSISTANT,
                         )
 
-                    context.result = ResponseStream(blocked_stream(), finalizer=ChatResponse.from_updates)
+                    response = ChatResponse(
+                        messages=[Message(role=Role.ASSISTANT, text=error_message)]
+                    )
+                    context.result = ResponseStream(blocked_stream(), finalizer=lambda _, r=response: r)
                 else:
                     # Non-streaming mode: return complete response
                     context.result = ChatResponse(
                         messages=[
-                            ChatMessage(
-                                role="assistant",
+                            Message(
+                                role=Role.ASSISTANT,
                                 text=error_message,
                             )
                         ]
                     )
 
-                raise MiddlewareTermination
+                raise MiddlewareTermination(result=context.result)
 
     await call_next(context)
 
@@ -92,7 +96,7 @@ async def atlantis_location_filter_middleware(
             "Blocked! Hold up right there!! Tell the user that "
             "'Atlantis is a special place, we must never ask about the weather there!!'"
         )
-        raise MiddlewareTermination
+        raise MiddlewareTermination(result=context.result)
 
     await call_next(context)
 
@@ -136,7 +140,7 @@ def send_email(
 
 
 # Agent instance following Agent Framework conventions
-agent = ChatAgent(
+agent = Agent(
     name="AzureWeatherAgent",
     description="A helpful agent that provides weather information and forecasts",
     instructions="""
@@ -144,7 +148,7 @@ agent = ChatAgent(
     and forecasts for any location. Always be helpful and provide detailed
     weather information when asked.
     """,
-    chat_client=AzureOpenAIChatClient(
+    client=AzureOpenAIChatClient(
         api_key=os.environ.get("AZURE_OPENAI_API_KEY", ""),
     ),
     tools=[get_weather, get_forecast, send_email],