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/semantic-kernel-migration/openai_responses/01_basic_responses_agent.py

@@ -35,12 +35,12 @@ async def run_semantic_kernel() -> None:
 
 
 async def run_agent_framework() -> None:
-    from agent_framework import ChatAgent
+    from agent_framework import Agent
     from agent_framework.openai import OpenAIResponsesClient
 
-    # AF ChatAgent can swap in an OpenAIResponsesClient directly.
-    chat_agent = ChatAgent(
-        chat_client=OpenAIResponsesClient(),
+    # AF Agent can swap in an OpenAIResponsesClient directly.
+    chat_agent = Agent(
+        client=OpenAIResponsesClient(),
         instructions="Answer in one concise sentence.",
         name="Expert",
     )

python/samples/semantic-kernel-migration/openai_responses/02_responses_agent_with_tool.py

@@ -42,7 +42,7 @@ async def run_semantic_kernel() -> None:
 
 
 async def run_agent_framework() -> None:
-    from agent_framework import ChatAgent
+    from agent_framework import Agent
     from agent_framework._tools import tool
     from agent_framework.openai import OpenAIResponsesClient
 
@@ -50,8 +50,8 @@ async def run_agent_framework() -> None:
     async def add(a: float, b: float) -> float:
         return a + b
 
-    chat_agent = ChatAgent(
-        chat_client=OpenAIResponsesClient(),
+    chat_agent = Agent(
+        client=OpenAIResponsesClient(),
         instructions="Use the add tool when math is required.",
         name="MathExpert",
         # AF registers the async function as a tool at construction.

python/samples/semantic-kernel-migration/openai_responses/03_responses_agent_structured_output.py

@@ -47,11 +47,11 @@ async def run_semantic_kernel() -> None:
 
 
 async def run_agent_framework() -> None:
-    from agent_framework import ChatAgent
+    from agent_framework import Agent
     from agent_framework.openai import OpenAIResponsesClient
 
-    chat_agent = ChatAgent(
-        chat_client=OpenAIResponsesClient(),
+    chat_agent = Agent(
+        client=OpenAIResponsesClient(),
         instructions="Return launch briefs as structured JSON.",
         name="ProductMarketer",
     )