chore: Add session patch endpoint to api server for state update

This is allow user to update session state without running the agent. e.g. if I want to test some case when session has certain state on adk web.

PiperOrigin-RevId: 814252851

Author: seanzhougoogle

src/google/adk/cli/adk_web_server.py

@@ -220,6 +220,13 @@ class UpdateMemoryRequest(common.BaseModel):
   """The ID of the session to add to memory."""
 
 
+class UpdateSessionRequest(common.BaseModel):
+  """Request to update session state without running the agent."""
+
+  state_delta: dict[str, Any]
+  """The state changes to apply to the session."""
+
+
 class RunEvalResult(common.BaseModel):
   eval_set_file: str
   eval_set_id: str
@@ -767,6 +774,56 @@ async def delete_session(
           app_name=app_name, user_id=user_id, session_id=session_id
       )
 
+    @app.patch(
+        "/apps/{app_name}/users/{user_id}/sessions/{session_id}",
+        response_model_exclude_none=True,
+    )
+    async def update_session(
+        app_name: str,
+        user_id: str,
+        session_id: str,
+        req: UpdateSessionRequest,
+    ) -> Session:
+      """Updates session state without running the agent.
+
+      Args:
+          app_name: The name of the application.
+          user_id: The ID of the user.
+          session_id: The ID of the session to update.
+          req: The patch request containing state changes.
+
+      Returns:
+          The updated session.
+
+      Raises:
+          HTTPException: If the session is not found.
+      """
+      session = await self.session_service.get_session(
+          app_name=app_name, user_id=user_id, session_id=session_id
+      )
+      if not session:
+        raise HTTPException(status_code=404, detail="Session not found")
+
+      # Create an event to record the state change
+      import uuid
+
+      from ..events.event import Event
+      from ..events.event import EventActions
+
+      state_update_event = Event(
+          invocation_id="p-" + str(uuid.uuid4()),
+          author="user",
+          actions=EventActions(state_delta=req.state_delta),
+      )
+
+      # Append the event to the session
+      # This will automatically update the session state through __update_session_state
+      await self.session_service.append_event(
+          session=session, event=state_update_event
+      )
+
+      return session
+
     @app.post(
         "/apps/{app_name}/eval-sets",
         response_model_exclude_none=True,

src/google/adk/cli/conformance/adk_web_server_client.py

@@ -176,6 +176,36 @@ async def delete_session(
       )
       response.raise_for_status()
 
+  async def update_session(
+      self,
+      *,
+      app_name: str,
+      user_id: str,
+      session_id: str,
+      state_delta: Dict[str, Any],
+  ) -> Session:
+    """Update session state without running the agent.
+
+    Args:
+      app_name: Name of the application
+      user_id: User identifier
+      session_id: Session identifier to update
+      state_delta: The state changes to apply to the session
+
+    Returns:
+      The updated Session object
+
+    Raises:
+      httpx.HTTPStatusError: If the request fails or session not found
+    """
+    async with self._get_client() as client:
+      response = await client.patch(
+          f"/apps/{app_name}/users/{user_id}/sessions/{session_id}",
+          json={"state_delta": state_delta},
+      )
+      response.raise_for_status()
+      return Session.model_validate(response.json())
+
   async def run_agent(
       self,
       request: RunAgentRequest,

tests/unittests/cli/conformance/test_adk_web_server_client.py

@@ -127,6 +127,43 @@ async def test_delete_session():
     mock_response.raise_for_status.assert_called_once()
 
 
+@pytest.mark.asyncio
+async def test_update_session():
+  client = AdkWebServerClient()
+
+  # Mock the HTTP response
+  mock_response = MagicMock()
+  mock_response.json.return_value = {
+      "id": "test_session",
+      "app_name": "test_app",
+      "user_id": "test_user",
+      "events": [],
+      "state": {"key": "updated_value", "new_key": "new_value"},
+  }
+
+  with patch("httpx.AsyncClient") as mock_client_class:
+    mock_client = AsyncMock()
+    mock_client.patch.return_value = mock_response
+    mock_client_class.return_value = mock_client
+
+    state_delta = {"key": "updated_value", "new_key": "new_value"}
+    session = await client.update_session(
+        app_name="test_app",
+        user_id="test_user",
+        session_id="test_session",
+        state_delta=state_delta,
+    )
+
+    assert isinstance(session, Session)
+    assert session.id == "test_session"
+    assert session.state == {"key": "updated_value", "new_key": "new_value"}
+    mock_client.patch.assert_called_once_with(
+        "/apps/test_app/users/test_user/sessions/test_session",
+        json={"state_delta": state_delta},
+    )
+    mock_response.raise_for_status.assert_called_once()
+
+
 @pytest.mark.asyncio
 async def test_run_agent():
   client = AdkWebServerClient()

tests/unittests/cli/test_fast_api.py

@@ -288,6 +288,22 @@ async def delete_session(self, app_name, user_id, session_id):
       ):
         del session_data[app_name][user_id][session_id]
 
+    async def append_event(self, session, event):
+      """Append an event to a session."""
+      # Update session state if event has state_delta
+      if event.actions and event.actions.state_delta:
+        session["state"].update(event.actions.state_delta)
+
+      # Add event to session events
+      session["events"].append(event.model_dump())
+
+      # Update the session in storage
+      session_data[session["app_name"]][session["user_id"]][
+          session["id"]
+      ] = session
+
+      return event
+
   # Return an instance of our mock service
   return MockSessionService()
 
@@ -725,6 +741,80 @@ def test_delete_session(test_app, create_test_session):
   logger.info("Session deleted successfully")
 
 
+def test_update_session(test_app, create_test_session):
+  """Test patching a session state."""
+  info = create_test_session
+  url = f"/apps/{info['app_name']}/users/{info['user_id']}/sessions/{info['session_id']}"
+
+  # Get the original session
+  response = test_app.get(url)
+  assert response.status_code == 200
+  original_session = response.json()
+  original_state = original_session.get("state", {})
+
+  # Prepare state delta
+  state_delta = {"test_key": "test_value", "counter": 42}
+
+  # Patch the session
+  response = test_app.patch(url, json={"state_delta": state_delta})
+  assert response.status_code == 200
+
+  # Verify the response
+  patched_session = response.json()
+  assert patched_session["id"] == info["session_id"]
+
+  # Verify state was updated correctly
+  expected_state = {**original_state, **state_delta}
+  assert patched_session["state"] == expected_state
+
+  # Verify the session was actually updated in storage
+  response = test_app.get(url)
+  assert response.status_code == 200
+  retrieved_session = response.json()
+  assert retrieved_session["state"] == expected_state
+
+  # Verify an event was created for the state change
+  events = retrieved_session.get("events", [])
+  assert len(events) > len(original_session.get("events", []))
+
+  # Find the state patch event (looking for "p-" prefix pattern)
+  state_patch_events = [
+      event
+      for event in events
+      if (
+          event.get("invocationId") or event.get("invocation_id", "")
+      ).startswith("p-")
+  ]
+
+  assert len(state_patch_events) == 1, (
+      f"Expected 1 state_patch event, found {len(state_patch_events)}. Events:"
+      f" {events}"
+  )
+  state_patch_event = state_patch_events[0]
+  assert state_patch_event["author"] == "user"
+
+  # Check for actions in both camelCase and snake_case
+  actions = state_patch_event.get("actions") or state_patch_event.get("actions")
+  assert actions is not None, f"No actions found in event: {state_patch_event}"
+  state_delta_in_event = actions.get("state_delta") or actions.get("stateDelta")
+  assert state_delta_in_event == state_delta
+
+  logger.info("Session state patched successfully")
+
+
+def test_patch_session_not_found(test_app, test_session_info):
+  """Test patching a non-existent session."""
+  info = test_session_info
+  url = f"/apps/{info['app_name']}/users/{info['user_id']}/sessions/nonexistent"
+
+  state_delta = {"test_key": "test_value"}
+  response = test_app.patch(url, json={"state_delta": state_delta})
+
+  assert response.status_code == 404
+  assert "Session not found" in response.json()["detail"]
+  logger.info("Patch session not found test passed")
+
+
 def test_agent_run(test_app, create_test_session):
   """Test running an agent with a message."""
   info = create_test_session