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/azure_ai_agent/README.md

@@ -8,7 +8,7 @@ All examples in this folder use the `AzureAIAgentsProvider` class which provides
 
 - **`create_agent()`** - Create a new agent on the Azure AI service
 - **`get_agent()`** - Retrieve an existing agent by ID or from a pre-fetched Agent object
-- **`as_agent()`** - Wrap an SDK Agent object as a ChatAgent without HTTP calls
+- **`as_agent()`** - Wrap an SDK Agent object as a Agent without HTTP calls
 
 ```python
 from agent_framework.azure import AzureAIAgentsProvider

python/samples/getting_started/agents/azure_ai_agent/azure_ai_with_hosted_mcp.py

@@ -17,7 +17,7 @@ servers, including user approval workflows for function call security.
 
 async def handle_approvals_with_thread(query: str, agent: "SupportsAgentRun", thread: "AgentThread") -> AgentResponse:
     """Here we let the thread deal with the previous responses, and we just rerun with the approval."""
-    from agent_framework import ChatMessage
+    from agent_framework import Message
 
     result = await agent.run(query, thread=thread, store=True)
     while len(result.user_input_requests) > 0:
@@ -29,7 +29,7 @@ async def handle_approvals_with_thread(query: str, agent: "SupportsAgentRun", th
             )
             user_approval = input("Approve function call? (y/n): ")
             new_input.append(
-                ChatMessage(
+                Message(
                     role="user",
                     contents=[user_input_needed.to_function_approval_response(user_approval.lower() == "y")],
                 )

python/samples/getting_started/agents/azure_ai_agent/azure_ai_with_local_mcp.py

@@ -51,7 +51,7 @@ async def mcp_tools_on_agent_level() -> None:
     print("=== Tools Defined on Agent Level ===")
 
     # Tools are provided when creating the agent
-    # The ChatAgent will connect to the MCP server through its context manager
+    # The Agent will connect to the MCP server through its context manager
     # and discover tools at runtime
     async with (
         AzureCliCredential() as credential,

python/samples/getting_started/agents/azure_ai_agent/azure_ai_with_multiple_tools.py

@@ -45,7 +45,7 @@ def get_time() -> str:
 
 async def handle_approvals_with_thread(query: str, agent: "SupportsAgentRun", thread: "AgentThread"):
     """Here we let the thread deal with the previous responses, and we just rerun with the approval."""
-    from agent_framework import ChatMessage
+    from agent_framework import Message
 
     result = await agent.run(query, thread=thread, store=True)
     while len(result.user_input_requests) > 0:
@@ -57,7 +57,7 @@ async def handle_approvals_with_thread(query: str, agent: "SupportsAgentRun", th
             )
             user_approval = input("Approve function call? (y/n): ")
             new_input.append(
-                ChatMessage(
+                Message(
                     role="user",
                     contents=[user_input_needed.to_function_approval_response(user_approval.lower() == "y")],
                 )