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/workflows/state-management/state_with_agents.py

@@ -7,10 +7,10 @@ from typing import Any
 from uuid import uuid4
 
 from agent_framework import (
+    Agent,
     AgentExecutorRequest,
     AgentExecutorResponse,
-    ChatAgent,
-    ChatMessage,
+    Message,
     WorkflowBuilder,
     WorkflowContext,
     executor,
@@ -103,7 +103,7 @@ async def store_email(email_text: str, ctx: WorkflowContext[AgentExecutorRequest
     ctx.set_state(CURRENT_EMAIL_ID_KEY, new_email.email_id)
 
     await ctx.send_message(
-        AgentExecutorRequest(messages=[ChatMessage("user", text=new_email.email_content)], should_respond=True)
+        AgentExecutorRequest(messages=[Message("user", text=new_email.email_content)], should_respond=True)
     )
 
 
@@ -134,7 +134,7 @@ async def submit_to_email_assistant(detection: DetectionResult, ctx: WorkflowCon
     # Load the original content by id from workflow state and forward it to the assistant.
     email: Email = ctx.get_state(f"{EMAIL_STATE_PREFIX}{detection.email_id}")
     await ctx.send_message(
-        AgentExecutorRequest(messages=[ChatMessage("user", text=email.email_content)], should_respond=True)
+        AgentExecutorRequest(messages=[Message("user", text=email.email_content)], should_respond=True)
     )
 
 
@@ -154,7 +154,7 @@ async def handle_spam(detection: DetectionResult, ctx: WorkflowContext[Never, st
         raise RuntimeError("This executor should only handle spam messages.")
 
 
-def create_spam_detection_agent() -> ChatAgent:
+def create_spam_detection_agent() -> Agent:
     """Creates a spam detection agent."""
     return AzureOpenAIChatClient(credential=AzureCliCredential()).as_agent(
         instructions=(
@@ -167,7 +167,7 @@ def create_spam_detection_agent() -> ChatAgent:
     )
 
 
-def create_email_assistant_agent() -> ChatAgent:
+def create_email_assistant_agent() -> Agent:
     """Creates an email assistant agent."""
     return AzureOpenAIChatClient(credential=AzureCliCredential()).as_agent(
         instructions=(

python/samples/getting_started/workflows/state-management/workflow_kwargs.py

@@ -4,7 +4,7 @@ import asyncio
 import json
 from typing import Annotated, Any, cast
 
-from agent_framework import ChatMessage, tool
+from agent_framework import Message, tool
 from agent_framework.openai import OpenAIChatClient
 from agent_framework.orchestrations import SequentialBuilder
 from pydantic import Field
@@ -74,10 +74,10 @@ async def main() -> None:
     print("=" * 70)
 
     # Create chat client
-    chat_client = OpenAIChatClient()
+    client = OpenAIChatClient()
 
     # Create agent with tools that use kwargs
-    agent = chat_client.as_agent(
+    agent = client.as_agent(
         name="assistant",
         instructions=(
             "You are a helpful assistant. Use the available tools to help users. "
@@ -121,10 +121,10 @@ async def main() -> None:
         stream=True,
     ):
         if event.type == "output":
-            output_data = cast(list[ChatMessage], event.data)
+            output_data = cast(list[Message], event.data)
             if isinstance(output_data, list):
                 for item in output_data:
-                    if isinstance(item, ChatMessage) and item.text:
+                    if isinstance(item, Message) and item.text:
                         print(f"\n[Final Answer]: {item.text}")
 
     print("\n" + "=" * 70)