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/agents/custom/README.md

@@ -7,7 +7,7 @@ This folder contains examples demonstrating how to implement custom agents and c
 | File | Description |
 |------|-------------|
 | [`custom_agent.py`](custom_agent.py) | Shows how to create custom agents by extending the `BaseAgent` class. Demonstrates the `EchoAgent` implementation with both streaming and non-streaming responses, proper thread management, and message history handling. |
-| [`custom_chat_client.py`](../../chat_client/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`](../../chat_client/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. |
 
 ## Key Takeaways
 
@@ -20,7 +20,7 @@ This folder contains examples demonstrating how to implement custom agents and c
 ### Custom Chat Clients
 - Custom chat clients allow you to integrate any backend service or create new LLM providers
 - You must implement `_inner_get_response()` with a stream parameter to handle both streaming and non-streaming responses
-- Custom chat clients can be used with `ChatAgent` to leverage all agent framework features
+- Custom chat clients can be used with `Agent` to leverage all agent framework features
 - Use the `as_agent()` method to easily create agents from your custom chat clients
 
 Both approaches allow you to extend the framework for your specific use cases while maintaining compatibility with the broader Agent Framework ecosystem.

python/samples/getting_started/agents/custom/custom_agent.py

@@ -9,8 +9,8 @@ from agent_framework import (
     AgentResponseUpdate,
     AgentThread,
     BaseAgent,
-    ChatMessage,
     Content,
+    Message,
     Role,
     normalize_messages,
 )
@@ -57,7 +57,7 @@ class EchoAgent(BaseAgent):
 
     def run(
         self,
-        messages: str | ChatMessage | list[str] | list[ChatMessage] | None = None,
+        messages: str | Message | list[str] | list[Message] | None = None,
         *,
         stream: bool = False,
         thread: AgentThread | None = None,
@@ -81,7 +81,7 @@ class EchoAgent(BaseAgent):
 
     async def _run(
         self,
-        messages: str | ChatMessage | list[str] | list[ChatMessage] | None = None,
+        messages: str | Message | list[str] | list[Message] | None = None,
         *,
         thread: AgentThread | None = None,
         **kwargs: Any,
@@ -91,11 +91,9 @@ class EchoAgent(BaseAgent):
         normalized_messages = normalize_messages(messages)
 
         if not normalized_messages:
-            response_message = ChatMessage(
+            response_message = Message(
                 role=Role.ASSISTANT,
-                contents=[
-                    Content.from_text(text="Hello! I'm a custom echo agent. Send me a message and I'll echo it back.")
-                ],
+                contents=[Content.from_text(text="Hello! I'm a custom echo agent. Send me a message and I'll echo it back.")],
             )
         else:
             # For simplicity, echo the last user message
@@ -105,7 +103,7 @@ class EchoAgent(BaseAgent):
             else:
                 echo_text = f"{self.echo_prefix}[Non-text message received]"
 
-            response_message = ChatMessage(role=Role.ASSISTANT, contents=[Content.from_text(text=echo_text)])
+            response_message = Message(role=Role.ASSISTANT, contents=[Content.from_text(text=echo_text)])
 
         # Notify the thread of new messages if provided
         if thread is not None:
@@ -115,7 +113,7 @@ class EchoAgent(BaseAgent):
 
     async def _run_stream(
         self,
-        messages: str | ChatMessage | list[str] | list[ChatMessage] | None = None,
+        messages: str | Message | list[str] | list[Message] | None = None,
         *,
         thread: AgentThread | None = None,
         **kwargs: Any,
@@ -150,7 +148,7 @@ class EchoAgent(BaseAgent):
 
         # Notify the thread of the complete response if provided
         if thread is not None:
-            complete_response = ChatMessage(role=Role.ASSISTANT, contents=[Content.from_text(text=response_text)])
+            complete_response = Message(role=Role.ASSISTANT, contents=[Content.from_text(text=response_text)])
             await self._notify_thread_of_new_messages(thread, normalized_messages, complete_response)