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/durabletask/tests/test_shim.py

@@ -13,7 +13,7 @@ import pytest
 from agent_framework import Message, SupportsAgentRun
 from pydantic import BaseModel
 
-from agent_framework_durabletask import DurableAgentThread
+from agent_framework_durabletask import DurableAgentSession
 from agent_framework_durabletask._executors import DurableAgentExecutor
 from agent_framework_durabletask._models import RunRequest
 from agent_framework_durabletask._shim import DurableAgentProvider, DurableAIAgent
@@ -30,7 +30,7 @@ def mock_executor() -> Mock:
     """Create a mock executor for testing."""
     mock = Mock(spec=DurableAgentExecutor)
     mock.run_durable_agent = Mock(return_value=None)
-    mock.get_new_thread = Mock(return_value=DurableAgentThread())
+    mock.get_new_session = Mock(return_value=DurableAgentSession())
 
     # Mock get_run_request to create actual RunRequest objects
     def create_run_request(
@@ -124,14 +124,14 @@ class TestDurableAIAgentMessageNormalization:
 class TestDurableAIAgentParameterFlow:
     """Test that parameters flow correctly through the shim to executor."""
 
-    def test_run_forwards_thread_parameter(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
-        """Verify run forwards thread parameter to executor."""
-        thread = DurableAgentThread(service_thread_id="test-thread")
-        test_agent.run("message", thread=thread)
+    def test_run_forwards_session_parameter(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
+        """Verify run forwards session parameter to executor."""
+        session = DurableAgentSession(service_session_id="test-session")
+        test_agent.run("message", session=session)
 
         mock_executor.run_durable_agent.assert_called_once()
         _, kwargs = mock_executor.run_durable_agent.call_args
-        assert kwargs["thread"] == thread
+        assert kwargs["session"] == session
 
     def test_run_forwards_response_format(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
         """Verify run forwards response_format parameter to executor."""
@@ -171,29 +171,29 @@ class TestDurableAISupportsAgentRunCompliance:
         assert agent.name == "my_agent"
 
 
-class TestDurableAIAgentThreadManagement:
-    """Test thread creation and management."""
+class TestDurableAIAgentSessionManagement:
+    """Test session creation and management."""
 
-    def test_get_new_thread_delegates_to_executor(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
-        """Verify get_new_thread delegates to executor."""
-        mock_thread = DurableAgentThread()
-        mock_executor.get_new_thread.return_value = mock_thread
+    def test_create_session_delegates_to_executor(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
+        """Verify create_session delegates to executor."""
+        mock_session = DurableAgentSession()
+        mock_executor.get_new_session.return_value = mock_session
 
-        thread = test_agent.get_new_thread()
+        session = test_agent.create_session()
 
-        mock_executor.get_new_thread.assert_called_once_with("test_agent")
-        assert thread == mock_thread
+        mock_executor.get_new_session.assert_called_once_with("test_agent")
+        assert session == mock_session
 
-    def test_get_new_thread_forwards_kwargs(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
-        """Verify get_new_thread forwards kwargs to executor."""
-        mock_thread = DurableAgentThread(service_thread_id="thread-123")
-        mock_executor.get_new_thread.return_value = mock_thread
+    def test_create_session_forwards_kwargs(self, test_agent: DurableAIAgent[Any], mock_executor: Mock) -> None:
+        """Verify create_session forwards kwargs to executor."""
+        mock_session = DurableAgentSession(service_session_id="session-123")
+        mock_executor.get_new_session.return_value = mock_session
 
-        test_agent.get_new_thread(service_thread_id="thread-123")
+        test_agent.create_session(service_session_id="session-123")
 
-        mock_executor.get_new_thread.assert_called_once()
-        _, kwargs = mock_executor.get_new_thread.call_args
-        assert kwargs["service_thread_id"] == "thread-123"
+        mock_executor.get_new_session.assert_called_once()
+        _, kwargs = mock_executor.get_new_session.call_args
+        assert kwargs["service_session_id"] == "session-123"
 
 
 class TestDurableAgentProviderInterface: