From 1c07046332ef3f724df0898daca026fc1e8f761a Mon Sep 17 00:00:00 2001
From: Backend Engineer <backend-engineer@molecule-ai.local>
Date: Wed, 15 Apr 2026 17:58:10 +0000
Subject: [PATCH] fix(a2a): cancel() event, stateTransitionHistory capability,
 wire push store (#173 #174 #175)
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#173 — implement cancel() in LangGraphA2AExecutor: emits
TaskStatusUpdateEvent(state=canceled, final=True) so clients see the
state transition rather than silence. Removes pragma: no cover.
Test: test_cancel_emits_canceled_event.

#174 — add stateTransitionHistory=True to AgentCapabilities in main.py
so microsoft/agent-framework clients know they can request full task
history via the A2A protocol.

#175 — wire InMemoryPushNotificationConfigStore and PushNotificationSender
into DefaultRequestHandler so the advertised pushNotifications capability
is backed by a real store. Both classes live in a2a.server.tasks (a2a-sdk
0.3.25); import confirmed by probe.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 workspace-template/a2a_executor.py            | 12 ++++--
 workspace-template/main.py                    |  5 ++-
 workspace-template/tests/test_a2a_executor.py | 43 +++++++++++++++++++
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/workspace-template/a2a_executor.py b/workspace-template/a2a_executor.py
index 59a3a79c..ebe40087 100644
--- a/workspace-template/a2a_executor.py
+++ b/workspace-template/a2a_executor.py
@@ -408,6 +408,12 @@ class LangGraphA2AExecutor(AgentExecutor):
 
         return _result
 
-    async def cancel(self, context: RequestContext, event_queue: EventQueue) -> None:  # pragma: no cover
-        """Cancel a running task (cancellation via asyncio task cancellation)."""
-        pass
+    async def cancel(self, context: RequestContext, event_queue: EventQueue) -> None:
+        """Cancel a running task — emits canceled state to comply with A2A protocol."""
+        from a2a.types import TaskStatus, TaskState, TaskStatusUpdateEvent
+        await event_queue.enqueue_event(
+            TaskStatusUpdateEvent(
+                status=TaskStatus(state=TaskState.canceled),
+                final=True,
+            )
+        )
diff --git a/workspace-template/main.py b/workspace-template/main.py
index 9f8c4fca..d54e7bb3 100644
--- a/workspace-template/main.py
+++ b/workspace-template/main.py
@@ -12,7 +12,7 @@ import httpx
 import uvicorn
 from a2a.server.apps import A2AStarletteApplication
 from a2a.server.request_handlers import DefaultRequestHandler
-from a2a.server.tasks import InMemoryTaskStore
+from a2a.server.tasks import InMemoryTaskStore, InMemoryPushNotificationConfigStore, PushNotificationSender
 from a2a.types import AgentCard, AgentCapabilities, AgentSkill
 
 from adapters import get_adapter, AdapterConfig
@@ -136,6 +136,7 @@ async def main():  # pragma: no cover
         capabilities=AgentCapabilities(
             streaming=config.a2a.streaming,
             pushNotifications=config.a2a.push_notifications,
+            stateTransitionHistory=True,
         ),
         skills=[
             AgentSkill(
@@ -155,6 +156,8 @@ async def main():  # pragma: no cover
     handler = DefaultRequestHandler(
         agent_executor=executor,
         task_store=InMemoryTaskStore(),
+        push_config_store=InMemoryPushNotificationConfigStore(),
+        push_sender=PushNotificationSender(),
     )
 
     app = A2AStarletteApplication(
diff --git a/workspace-template/tests/test_a2a_executor.py b/workspace-template/tests/test_a2a_executor.py
index 3c0eba11..9194cd96 100644
--- a/workspace-template/tests/test_a2a_executor.py
+++ b/workspace-template/tests/test_a2a_executor.py
@@ -998,3 +998,46 @@ def test_default_recursion_limit_value():
     """Regression guard: DeepAgents fan-outs need 100+; 500 is today's ceiling."""
     from a2a_executor import DEFAULT_RECURSION_LIMIT
     assert DEFAULT_RECURSION_LIMIT == 500
+
+
+# ---------------------------------------------------------------------------
+# Issue #173 — cancel() emits TaskStatusUpdateEvent(state=canceled, final=True)
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_cancel_emits_canceled_event(monkeypatch):
+    """cancel() must enqueue a TaskStatusUpdateEvent with state=canceled and final=True.
+
+    The a2a.types module is pre-mocked by conftest; inject the three extra
+    type stubs needed by cancel() so the local import inside the method resolves.
+    """
+    import sys
+    types_mod = sys.modules["a2a.types"]
+
+    class _TaskState:
+        canceled = "canceled"
+
+    class _TaskStatus:
+        def __init__(self, state=None):
+            self.state = state
+
+    class _TaskStatusUpdateEvent:
+        def __init__(self, status=None, final=False):
+            self.status = status
+            self.final = final
+
+    monkeypatch.setattr(types_mod, "TaskState", _TaskState, raising=False)
+    monkeypatch.setattr(types_mod, "TaskStatus", _TaskStatus, raising=False)
+    monkeypatch.setattr(types_mod, "TaskStatusUpdateEvent", _TaskStatusUpdateEvent, raising=False)
+
+    executor = LangGraphA2AExecutor(agent=MagicMock(), heartbeat=None)
+    context = _make_context([])
+    eq = _make_event_queue()
+
+    await executor.cancel(context, eq)
+
+    eq.enqueue_event.assert_called_once()
+    event = eq.enqueue_event.call_args[0][0]
+    assert isinstance(event, _TaskStatusUpdateEvent), "expected a TaskStatusUpdateEvent"
+    assert event.final is True, "cancel event must be marked final=True"
+    assert event.status.state == _TaskState.canceled, "cancel event must have state=canceled"