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/samples/04-hosting/durabletask/02_multi_agent/README.md

@@ -6,7 +6,7 @@ This sample demonstrates how to host multiple AI agents with different tools in
 
 - Hosting multiple agents (WeatherAgent and MathAgent) in a single worker process.
 - Each agent with its own specialized tools and instructions.
-- Interacting with different agents using separate conversation threads.
+- Interacting with different agents using separate conversation sessions.
 - Worker-client architecture for multi-agent systems.
 
 ## Environment Setup
@@ -49,7 +49,7 @@ Using endpoint: http://localhost:8080
 Testing WeatherAgent
 ================================================================================
 
-Created weather conversation thread: <guid>
+Created weather conversation session: <guid>
 User: What is the weather in Seattle?
 
 🔧 [TOOL CALLED] get_weather(location=Seattle)
@@ -61,7 +61,7 @@ WeatherAgent: The current weather in Seattle is sunny with a temperature of 72°
 Testing MathAgent
 ================================================================================
 
-Created math conversation thread: <guid>
+Created math conversation session: <guid>
 User: Calculate a 20% tip on a $50 bill
 
 🔧 [TOOL CALLED] calculate_tip(bill_amount=50.0, tip_percentage=20.0)

python/samples/04-hosting/durabletask/02_multi_agent/client.py

@@ -70,30 +70,30 @@ def run_client(agent_client: DurableAIAgentClient) -> None:
 
     # Get reference to WeatherAgent
     weather_agent = agent_client.get_agent("WeatherAgent")
-    weather_thread = weather_agent.get_new_thread()
+    weather_session = weather_agent.create_session()
 
-    logger.debug(f"Created weather conversation thread: {weather_thread.session_id}")
+    logger.debug(f"Created weather conversation session: {weather_session.session_id}")
 
     # Test WeatherAgent
     weather_message = "What is the weather in Seattle?"
     logger.info(f"User: {weather_message}")
 
-    weather_response = weather_agent.run(weather_message, thread=weather_thread)
+    weather_response = weather_agent.run(weather_message, session=weather_session)
     logger.info(f"WeatherAgent: {weather_response.text} \n")
 
     logger.debug("Testing MathAgent")
 
     # Get reference to MathAgent
     math_agent = agent_client.get_agent("MathAgent")
-    math_thread = math_agent.get_new_thread()
+    math_session = math_agent.create_session()
 
-    logger.debug(f"Created math conversation thread: {math_thread.session_id}")
+    logger.debug(f"Created math conversation session: {math_session.session_id}")
 
     # Test MathAgent
     math_message = "Calculate a 20% tip on a $50 bill"
     logger.info(f"User: {math_message}")
 
-    math_response = math_agent.run(math_message, thread=math_thread)
+    math_response = math_agent.run(math_message, session=math_session)
     logger.info(f"MathAgent: {math_response.text} \n")
 
     logger.debug("Both agents completed successfully!")