Python: [BREAKING] PR2 — Wire context provider pipeline, remove old types, update all consumers (#3850)

* PR2: Wire context provider pipeline and update all internal consumers

- Replace AgentThread with AgentSession across all packages
- Replace ContextProvider with BaseContextProvider across all packages
- Replace context_provider param with context_providers (Sequence)
- Replace thread= with session= in run() signatures
- Replace get_new_thread() with create_session()
- Add get_session(service_session_id) to agent interface
- DurableAgentThread -> DurableAgentSession
- Remove _notify_thread_of_new_messages from WorkflowAgent
- Wire before_run/after_run context provider pipeline in RawAgent
- Auto-inject InMemoryHistoryProvider when no providers configured

* fix: update all tests for context provider pipeline, fix lazy-loaders, remove old test files

* refactor: update all sample files for context provider pipeline (AgentThread→AgentSession, ContextProvider→BaseContextProvider)

* fix: update remaining ag-ui references (client docstring, getting_started sample)

* fix: make get_session service_session_id keyword-only to avoid confusion with session_id

* refactor: rename _RunContext.thread_messages to session_messages

* refactor: remove _threads.py, _memory.py, and old provider files; migrate devui to use plain message lists

* rename: remove _new_ prefix from test files

* refactor: rewrite SlidingWindowChatMessageStore as SlidingWindowHistoryProvider(InMemoryHistoryProvider)

* fix: read full history from session state directly instead of reaching into provider internals

* fix: update stale .pyi stubs, sample imports, and README references for new provider types

* fix: remove stale message_store, _notify_thread_of_new_messages, and session_id.key references in samples

* refactor: merge context_providers and sessions sample folders into sessions, remove aggregate_context_provider

* refactor: UserInfoMemory stores state in session.state instead of instance attributes

* feat: add Pydantic BaseModel support to session state serialization

Pydantic models stored in session.state are now automatically serialized
via model_dump() and restored via model_validate() during to_dict()/from_dict()
round-trips. Models are auto-registered on first serialization; use
register_state_type() for cold-start deserialization.

Also export register_state_type as a public API.

* fix mem0

* Update sample README links and descriptions for session terminology

- Replace 'thread' with 'session' in sample descriptions across all READMEs
- Update file links for renamed samples (mem0_sessions, redis_sessions, etc.)
- Fix Threads section → Sessions section in main samples/README.md
- Update tools, middleware, workflows, durabletask, azure_functions READMEs
- Update architecture diagrams in concepts/tools/README.md
- Update migration guides (autogen, semantic-kernel)

* Fix broken Redis README link to renamed sample

* Fix Mem0 OSS client search: pass scoping params as direct kwargs

AsyncMemory (OSS) expects user_id/agent_id/run_id as direct kwargs,
while AsyncMemoryClient (Platform) expects them in a filters dict.
Adds tests for both client types.

Port of fix from #3844 to new Mem0ContextProvider.

* Fix rebase issues: restore missing _conversation_state.py and checkpoint decode logic

- Add back _conversation_state.py (encode/decode_chat_messages) lost in rebase
- Fix on_checkpoint_restore to decode cache/conversation with decode_chat_messages
- Fix on_checkpoint_restore to use decode_checkpoint_value for pending requests
- Add tests/workflow/__init__.py for relative import support
- Fix test_agent_executor checkpoint selection (checkpoints[1] not superstep)

* Add STORES_BY_DEFAULT ClassVar to skip redundant InMemoryHistoryProvider injection

Chat clients that store history server-side by default (OpenAI Responses API,
Azure AI Agent) now declare STORES_BY_DEFAULT = True. The agent checks this
during auto-injection and skips InMemoryHistoryProvider unless the user
explicitly sets store=False.

* Fix broken markdown links in azure_ai and redis READMEs

* Fix getting-started samples to use session API instead of removed thread/ContextProvider API

* updates to workflow as agent

* fix group chat import

* Rename Thread→Session throughout, fix service_session_id propagation, remove stale AGUIThread

- Fix: Propagate conversation_id from ChatResponse back to session.service_session_id
  in both streaming and non-streaming paths in _agents.py
- Rename AgentThreadException → AgentSessionException
- Remove stale AGUIThread from ag_ui lazy-loader
- Rename use_service_thread → use_service_session in ag-ui package
- Rename test functions from *_thread_* to *_session_*
- Rename sample files from *_thread* to *_session*
- Update docstrings and comments: thread → session
- Update _mcp.py kwargs filter: add 'session' alongside 'thread'
- Fix ContinuationToken docstring example: thread=thread → session=session
- Fix _clients.py docstring: 'Agent threads' → 'Agent sessions'

* Fix broken markdown links after thread→session file renames

* fix azure ai test

python/packages/copilotstudio/tests/test_copilot_agent.py

@@ -4,7 +4,7 @@ from typing import Any
 from unittest.mock import MagicMock, patch
 
 import pytest
-from agent_framework import AgentResponse, AgentResponseUpdate, AgentThread, Content, Message
+from agent_framework import AgentResponse, AgentResponseUpdate, AgentSession, Content, Message
 from agent_framework.exceptions import ServiceException, ServiceInitializationError
 from microsoft_agents.copilotstudio.client import CopilotClient
 
@@ -165,10 +165,10 @@ class TestCopilotStudioAgent:
         assert content.text == "Test response"
         assert response.messages[0].role == "assistant"
 
-    async def test_run_with_thread(self, mock_copilot_client: MagicMock, mock_activity: MagicMock) -> None:
-        """Test run method with existing thread."""
+    async def test_run_with_session(self, mock_copilot_client: MagicMock, mock_activity: MagicMock) -> None:
+        """Test run method with existing session."""
         agent = CopilotStudioAgent(client=mock_copilot_client)
-        thread = AgentThread()
+        session = AgentSession()
 
         conversation_activity = MagicMock()
         conversation_activity.conversation.id = "test-conversation-id"
@@ -176,11 +176,11 @@ class TestCopilotStudioAgent:
         mock_copilot_client.start_conversation.return_value = create_async_generator([conversation_activity])
         mock_copilot_client.ask_question.return_value = create_async_generator([mock_activity])
 
-        response = await agent.run("test message", thread=thread)
+        response = await agent.run("test message", session=session)
 
         assert isinstance(response, AgentResponse)
         assert len(response.messages) == 1
-        assert thread.service_thread_id == "test-conversation-id"
+        assert session.service_session_id == "test-conversation-id"
 
     async def test_run_start_conversation_failure(self, mock_copilot_client: MagicMock) -> None:
         """Test run method when conversation start fails."""
@@ -217,10 +217,10 @@ class TestCopilotStudioAgent:
 
         assert response_count == 1
 
-    async def test_run_streaming_with_thread(self, mock_copilot_client: MagicMock) -> None:
-        """Test run(stream=True) method with existing thread."""
+    async def test_run_streaming_with_session(self, mock_copilot_client: MagicMock) -> None:
+        """Test run(stream=True) method with existing session."""
         agent = CopilotStudioAgent(client=mock_copilot_client)
-        thread = AgentThread()
+        session = AgentSession()
 
         conversation_activity = MagicMock()
         conversation_activity.conversation.id = "test-conversation-id"
@@ -235,7 +235,7 @@ class TestCopilotStudioAgent:
         mock_copilot_client.ask_question.return_value = create_async_generator([typing_activity])
 
         response_count = 0
-        async for response in agent.run("test message", thread=thread, stream=True):
+        async for response in agent.run("test message", session=session, stream=True):
             assert isinstance(response, AgentResponseUpdate)
             content = response.contents[0]
             assert content.type == "text"
@@ -243,7 +243,7 @@ class TestCopilotStudioAgent:
             response_count += 1
 
         assert response_count == 1
-        assert thread.service_thread_id == "test-conversation-id"
+        assert session.service_session_id == "test-conversation-id"
 
     async def test_run_streaming_no_typing_activity(self, mock_copilot_client: MagicMock) -> None:
         """Test run(stream=True) method with non-typing activity."""