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/lab/gaia/samples/azure_ai_agent.py

@@ -26,13 +26,13 @@ Example:
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
 
-from agent_framework import ChatAgent, HostedCodeInterpreterTool, HostedWebSearchTool
+from agent_framework import Agent, HostedCodeInterpreterTool, HostedWebSearchTool
 from agent_framework.azure import AzureAIAgentClient
 from azure.identity.aio import AzureCliCredential
 
 
 @asynccontextmanager
-async def create_gaia_agent() -> AsyncIterator[ChatAgent]:
+async def create_gaia_agent() -> AsyncIterator[Agent]:
     """Create an Azure AI agent configured for GAIA benchmark tasks.
 
     The agent is configured with:
@@ -40,7 +40,7 @@ async def create_gaia_agent() -> AsyncIterator[ChatAgent]:
     - Code Interpreter tool for calculations and data analysis
 
     Yields:
-        ChatAgent: A configured agent ready to run GAIA tasks.
+        Agent: A configured agent ready to run GAIA tasks.
 
     Example:
         async with create_gaia_agent() as agent:

python/packages/lab/gaia/samples/openai_agent.py

@@ -25,12 +25,12 @@ Example:
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
 
-from agent_framework import ChatAgent, HostedCodeInterpreterTool, HostedWebSearchTool
+from agent_framework import Agent, HostedCodeInterpreterTool, HostedWebSearchTool
 from agent_framework.openai import OpenAIResponsesClient
 
 
 @asynccontextmanager
-async def create_gaia_agent() -> AsyncIterator[ChatAgent]:
+async def create_gaia_agent() -> AsyncIterator[Agent]:
     """Create an OpenAI agent configured for GAIA benchmark tasks.
 
     Uses OpenAI Responses API for enhanced capabilities.
@@ -40,16 +40,16 @@ async def create_gaia_agent() -> AsyncIterator[ChatAgent]:
     - Code Interpreter tool for calculations and data analysis
 
     Yields:
-        ChatAgent: A configured agent ready to run GAIA tasks.
+        Agent: A configured agent ready to run GAIA tasks.
 
     Example:
         async with create_gaia_agent() as agent:
             result = await agent.run("What is the capital of France?")
             print(result.text)
     """
-    chat_client = OpenAIResponsesClient()
+    client = OpenAIResponsesClient()
 
-    async with chat_client.as_agent(
+    async with client.as_agent(
         name="GaiaAgent",
         instructions="Solve tasks to your best ability. Use Web Search to find "
         "information and Code Interpreter to perform calculations and data analysis.",