Python: [BREAKING] update context provider APIs, middleware, and per-service-call history persistence (#4992)

* Rename provider base APIs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Allow provider-added chat and function middleware

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Simulate service-stored history per model call

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix typing regressions in CI

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix response ID suppression review feedback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Rename per-service-call history persistence APIs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address context persistence review feedback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Stabilize markdown sample docs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Persist service continuation state per call

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/a2a/agent_framework_a2a/_agent.py

@@ -35,9 +35,9 @@ from agent_framework import (
     AgentResponseUpdate,
     AgentSession,
     BaseAgent,
-    BaseHistoryProvider,
     Content,
     ContinuationToken,
+    HistoryProvider,
     Message,
     ResponseStream,
     SessionContext,
@@ -353,7 +353,7 @@ class A2AAgent(AgentTelemetryLayer, BaseAgent):
 
         # Run before_run providers (forward order)
         for provider in self.context_providers:
-            if isinstance(provider, BaseHistoryProvider) and not provider.load_messages:
+            if isinstance(provider, HistoryProvider) and not provider.load_messages:
                 continue
             if session is None:
                 raise RuntimeError("Provider session must be available when context providers are configured.")

python/packages/a2a/tests/test_a2a_agent.py

@@ -24,8 +24,8 @@ from agent_framework import (
     AgentResponse,
     AgentResponseUpdate,
     AgentSession,
-    BaseContextProvider,
     Content,
+    ContextProvider,
     Message,
     SessionContext,
 )
@@ -869,7 +869,7 @@ async def test_poll_task_completed(a2a_agent: A2AAgent, mock_a2a_client: MockA2A
 # region Context Provider Tests
 
 
-class TrackingContextProvider(BaseContextProvider):
+class TrackingContextProvider(ContextProvider):
     """A context provider that records when before_run and after_run are called."""
 
     def __init__(self) -> None: