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/packages/bedrock/tests/test_bedrock_client.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 from typing import Any
 
 import pytest
-from agent_framework import ChatMessage, Content
+from agent_framework import Content, Message
 from agent_framework.exceptions import ServiceInitializationError
 
 from agent_framework_bedrock import BedrockChatClient
@@ -41,8 +41,8 @@ async def test_get_response_invokes_bedrock_runtime() -> None:
     )
 
     messages = [
-        ChatMessage(role="system", contents=[Content.from_text(text="You are concise.")]),
-        ChatMessage(role="user", contents=[Content.from_text(text="hello")]),
+        Message(role="system", contents=[Content.from_text(text="You are concise.")]),
+        Message(role="user", contents=[Content.from_text(text="hello")]),
     ]
 
     response = await client.get_response(messages=messages, options={"max_tokens": 32})
@@ -62,7 +62,7 @@ def test_build_request_requires_non_system_messages() -> None:
         client=_StubBedrockRuntime(),
     )
 
-    messages = [ChatMessage(role="system", contents=[Content.from_text(text="Only system text")])]
+    messages = [Message(role="system", contents=[Content.from_text(text="Only system text")])]
 
     with pytest.raises(ServiceInitializationError):
         client._prepare_options(messages, {})

python/packages/bedrock/tests/test_bedrock_settings.py

@@ -6,10 +6,10 @@ from unittest.mock import MagicMock
 
 import pytest
 from agent_framework import (
-    ChatMessage,
     ChatOptions,
     Content,
     FunctionTool,
+    Message,
 )
 from pydantic import BaseModel
 
@@ -46,7 +46,7 @@ def test_build_request_includes_tool_config() -> None:
         "tools": [tool],
         "tool_choice": {"mode": "required", "required_function_name": "get_weather"},
     }
-    messages = [ChatMessage(role="user", contents=[Content.from_text(text="hi")])]
+    messages = [Message(role="user", contents=[Content.from_text(text="hi")])]
 
     request = client._prepare_options(messages, options)
 
@@ -58,14 +58,14 @@ def test_build_request_serializes_tool_history() -> None:
     client = _build_client()
     options: ChatOptions = {}
     messages = [
-        ChatMessage(role="user", contents=[Content.from_text(text="how's weather?")]),
-        ChatMessage(
+        Message(role="user", contents=[Content.from_text(text="how's weather?")]),
+        Message(
             role="assistant",
             contents=[
                 Content.from_function_call(call_id="call-1", name="get_weather", arguments='{"location": "SEA"}')
             ],
         ),
-        ChatMessage(
+        Message(
             role="tool",
             contents=[Content.from_function_result(call_id="call-1", result={"answer": "72F"})],
         ),