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

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 @@ class AdkWebServer:
           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 @@ class AdkWebServerClient:
       )
       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,