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/devui/tests/devui/test_conversations.py

@@ -83,29 +83,29 @@ async def test_delete_conversation():
 
 
 @pytest.mark.asyncio
-async def test_get_thread():
-    """Test getting underlying AgentThread."""
+async def test_get_session():
+    """Test getting AgentSession for execution."""
     store = InMemoryConversationStore()
 
     # Create conversation
     conversation = store.create_conversation(metadata={"agent_id": "test_agent"})
 
-    # Get thread
-    thread = store.get_thread(conversation.id)
+    # Get session
+    session = store.get_session(conversation.id)
 
-    assert thread is not None
-    # AgentThread should have message_store
-    assert hasattr(thread, "message_store")
+    assert session is not None
+    # AgentSession should have session_id
+    assert hasattr(session, "session_id")
 
 
 @pytest.mark.asyncio
-async def test_get_thread_not_found():
-    """Test getting thread for non-existent conversation."""
+async def test_get_session_not_found():
+    """Test getting session for non-existent conversation."""
     store = InMemoryConversationStore()
 
-    thread = store.get_thread("conv_nonexistent")
+    session = store.get_session("conv_nonexistent")
 
-    assert thread is None
+    assert session is None
 
 
 @pytest.mark.asyncio
@@ -199,21 +199,13 @@ async def test_list_items_pagination():
 @pytest.mark.asyncio
 async def test_list_items_converts_function_calls():
     """Test that list_items properly converts function calls to ResponseFunctionToolCallItem."""
-    from agent_framework import ChatMessageStore, Message
+    from agent_framework import Message
 
     store = InMemoryConversationStore()
 
     # Create conversation
     conversation = store.create_conversation(metadata={"agent_id": "test_agent"})
 
-    # Get the underlying thread and set up message store
-    thread = store.get_thread(conversation.id)
-    assert thread is not None
-
-    # Initialize message store if not present
-    if thread.message_store is None:
-        thread.message_store = ChatMessageStore()
-
     # Simulate messages from agent execution with function calls
     messages = [
         Message(role="user", contents=[{"type": "text", "text": "What's the weather in SF?"}]),
@@ -241,8 +233,8 @@ async def test_list_items_converts_function_calls():
         Message(role="assistant", contents=[{"type": "text", "text": "The weather is sunny, 65°F"}]),
     ]
 
-    # Add messages to thread
-    await thread.on_new_messages(messages)
+    # Add messages to internal storage
+    store._conversations[conversation.id]["messages"].extend(messages)
 
     # List conversation items
     items, has_more = await store.list_items(conversation.id)
@@ -284,20 +276,13 @@ async def test_list_items_converts_function_calls():
 @pytest.mark.asyncio
 async def test_list_items_handles_images_and_files():
     """Test that list_items properly converts data content (images/files) to OpenAI types."""
-    from agent_framework import ChatMessageStore, Message
+    from agent_framework import Message
 
     store = InMemoryConversationStore()
 
     # Create conversation
     conversation = store.create_conversation(metadata={"agent_id": "test_agent"})
 
-    # Get the underlying thread
-    thread = store.get_thread(conversation.id)
-    assert thread is not None
-
-    if thread.message_store is None:
-        thread.message_store = ChatMessageStore()
-
     # Simulate message with image and file
     messages = [
         Message(
@@ -310,7 +295,8 @@ async def test_list_items_handles_images_and_files():
         ),
     ]
 
-    await thread.on_new_messages(messages)
+    # Add messages to internal storage
+    store._conversations[conversation.id]["messages"].extend(messages)
 
     # List items
     items, has_more = await store.list_items(conversation.id)