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/05-end-to-end/chatkit-integration/app.py

@@ -141,7 +141,7 @@ async def stream_widget(
     yield ThreadItemDoneEvent(type="thread.item.done", item=widget_item)
 
 
-# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production; see samples/02-agents/tools/function_tool_with_approval.py and samples/02-agents/tools/function_tool_with_approval_and_threads.py.
+# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production; see samples/02-agents/tools/function_tool_with_approval.py and samples/02-agents/tools/function_tool_with_approval_and_sessions.py.
 @tool(approval_mode="never_require")
 def get_weather(
     location: Annotated[str, Field(description="The location to get the weather for.")],

python/samples/05-end-to-end/hosted_agents/agent_with_text_search_rag/main.py

@@ -2,11 +2,10 @@
 
 import json
 import sys
-from collections.abc import MutableSequence
 from dataclasses import dataclass
 from typing import Any
 
-from agent_framework import Context, ContextProvider, Message
+from agent_framework import AgentSession, BaseContextProvider, Message, SessionContext
 from agent_framework.azure import AzureOpenAIChatClient
 from azure.ai.agentserver.agentframework import from_agent_framework  # pyright: ignore[reportUnknownVariableType]
 from azure.identity import DefaultAzureCredential
@@ -24,19 +23,30 @@ class TextSearchResult:
     text: str
 
 
-class TextSearchContextProvider(ContextProvider):
+class TextSearchContextProvider(BaseContextProvider):
     """A simple context provider that simulates text search results based on keywords in the user's message."""
 
-    def _get_most_recent_message(self, messages: Message | MutableSequence[Message]) -> Message:
+    def __init__(self):
+        super().__init__("text-search")
+
+    def _get_most_recent_message(self, messages: list[Message]) -> Message:
         """Helper method to extract the most recent message from the input."""
-        if isinstance(messages, Message):
-            return messages
         if messages:
             return messages[-1]
         raise ValueError("No messages provided")
 
     @override
-    async def invoking(self, messages: Message | MutableSequence[Message], **kwargs: Any) -> Context:
+    async def before_run(
+        self,
+        *,
+        agent: Any,
+        session: AgentSession | None,
+        context: SessionContext,
+        state: dict[str, Any],
+    ) -> None:
+        messages = context.get_messages()
+        if not messages:
+            return
         message = self._get_most_recent_message(messages)
         query = message.text.lower()
 
@@ -80,14 +90,15 @@ class TextSearchContextProvider(ContextProvider):
             )
 
         if not results:
-            return Context()
+            return
 
-        return Context(
-            messages=[
+        context.extend_messages(
+            self.source_id,
+            [
                 Message(
                     role="user", text="\n\n".join(json.dumps(result.__dict__, indent=2) for result in results)
                 )
-            ]
+            ],
         )
 
 
@@ -99,7 +110,7 @@ def main():
             "You are a helpful support specialist for Contoso Outdoors. "
             "Answer questions using the provided context and cite the source document when available."
         ),
-        context_provider=TextSearchContextProvider(),
+        context_providers=[TextSearchContextProvider()],
     )
 
     # Run the agent as a hosted agent

python/samples/05-end-to-end/m365-agent/m365_agent_demo/app.py

@@ -79,7 +79,7 @@ def load_app_config() -> AppConfig:
     return AppConfig(use_anonymous_mode=use_anonymous_mode, port=port, agents_sdk_config=agents_sdk_config)
 
 
-# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production; see samples/02-agents/tools/function_tool_with_approval.py and samples/02-agents/tools/function_tool_with_approval_and_threads.py.
+# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production; see samples/02-agents/tools/function_tool_with_approval.py and samples/02-agents/tools/function_tool_with_approval_and_sessions.py.
 @tool(approval_mode="never_require")
 def get_weather(
     location: Annotated[str, Field(description="The location to get the weather for.")],