Session is prematurely closed when using documented sync method

[jeff-got]

Prerequisites

• I've searched the current open issues
• I've updated to the latest version of Toolbox
• I've updated to the latest version of the SDK

Toolbox version

us-central1-docker.pkg.dev/database-toolbox/toolbox/toolbox:latest

Environment

1. OS type and version: Linux penguin 6.6.76-08174-g2f3b34fb3650
2. How are you running Toolbox:

• As a container (e.g. us-central1-docker.pkg.dev/database-toolbox/toolbox/toolbox:latest)

3. Python version :Python 3.11.2
4. pip version :pip 23.0.1

Client

1. Client: google-adk~=1.14.1.
2. Version:

• toolbox-core version 0.5.0
• google-adk~=1.14.1

Expected Behavior

That when asking an agent multiple questions that the session remains

Current Behavior

The first question an answer is provided however when asking a second question I get an error message that the session is closed

Steps to reproduce?

1. Follow ADK Quickstart
2. Update agent.py to the following

from google.adk.agents import Agent

from toolbox_core import ToolboxSyncClient, auth_methods
from datetime import datetime
from .prompt import agent_instruction

URL = "https://************.app"

auth_token_provider = auth_methods.get_google_id_token(URL, 10)

with ToolboxSyncClient(
    URL,
    client_headers={"Authorization": auth_token_provider},
) as toolbox:

    toolbox_tools = toolbox.load_toolset("project_toolset")

# ----- Example of a Function tool -----
def get_current_date() -> dict:
    """
    Get the current date in the format YYYY-MM-DD
    """
    return {"current_date": datetime.now().strftime("%Y-%m-%d")}

root_agent = Agent(
    model="gemini-2.0-flash-001",
    name="test_agent",
    instruction=agent_instruction,
    tools=[*toolbox_tools,get_current_date]
)

3. Run adk web
4. Ask to list tools
5. Ask a question that will use one of the tools provided by MCPToolbox and you get the following error

INFO: 127.0.0.1:60816 - "POST /run_sse HTTP/1.1" 200 OK
INFO:/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/cli/utils/envs.py:Loaded .env file for test_agent at /home/jeff/Agents/project-manager-assist/.env
INFO:google_adk.google.adk.models.google_llm:Sending out request, model: gemini-2.0-flash-001, backend: GoogleLLMVariant.VERTEX_AI, stream: False
INFO:google_genai.models:AFC is enabled with max remote calls: 10.
INFO:google_adk.google.adk.models.google_llm:Response received from the model.
WARNING:google_genai.types:Warning: there are non-text parts in the response: ['function_call'], returning concatenated text result from text parts. Check the full candidates.content.parts accessor to get the full model response.
ERROR:google_adk.google.adk.cli.adk_web_server:Error in event_generator: Session is closed
Traceback (most recent call last):
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/cli/adk_web_server.py", line 1066, in event_generator
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/runners.py", line 314, in run_async
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/runners.py", line 310, in _run_with_trace
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/runners.py", line 354, in _exec_with_plugin
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/runners.py", line 304, in execute
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/agents/base_agent.py", line 248, in run_async
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/agents/base_agent.py", line 238, in _run_with_trace
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/agents/llm_agent.py", line 288, in _run_async_impl
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 401, in run_async
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 447, in _run_one_step_async
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 539, in _postprocess_async
async for event in agen:
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 632, in _postprocess_handle_function_calls_async
if function_response_event := await functions.handle_function_calls_async(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/functions.py", line 198, in handle_function_calls_async
return await handle_function_call_list_async(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/functions.py", line 246, in handle_function_call_list_async
function_response_events = await asyncio.gather(*tasks)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/functions.py", line 333, in _execute_single_function_call_async
raise tool_error
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/functions.py", line 318, in _execute_single_function_call_async
function_response = await __call_tool_async(
^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/flows/llm_flows/functions.py", line 690, in __call_tool_async
return await tool.run_async(args=args, tool_context=tool_context)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/tools/function_tool.py", line 157, in run_async
return await self._invoke_callable(self.func, args_to_call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/google/adk/tools/function_tool.py", line 174, in _invoke_callable
return target(**args_to_call)
^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/toolbox_core/sync_tool.py", line 145, in call
return asyncio.run_coroutine_threadsafe(coro, self.__loop).result()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/concurrent/futures/_base.py", line 456, in result
return self.__get_result()
^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/concurrent/futures/_base.py", line 401, in __get_result
raise self._exception
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/toolbox_core/tool.py", line 307, in call
async with self.__session.post(
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/aiohttp/client.py", line 1482, in aenter
self._resp: _RetType = await self._coro
^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/project-manager-assist/venv/lib/python3.11/site-packages/aiohttp/client.py", line 527, in _request
raise RuntimeError("Session is closed")
RuntimeError: Session is closed

Additional Details

When using it in the following manner the session remains open

toolbox = ToolboxSyncClient(
    URL,
    client_headers={"Authorization": auth_token_provider},
)

toolbox_tools = toolbox.load_toolset("project_toolset")

[anubhav756]

Hello @jeff-got , thanks for filing this issue.

This is completely expected behaviour. The context manager (the with syntax) is designed to acquire a resource, run the code inside the block, and then automatically release or clean up the resource when the block ends.

In this case, the with ToolboxSyncClient(...) as toolbox: block creates the client instance and its internal session. As soon as your program exits that with block, the client's close() method is called automatically, which destroys the ToolboxSyncClient instance and, critically, closes the internally managed session.

Your root_agent is defined outside of this block. When the agent later tries to execute one of the toolbox_tools (which were loaded from the client), it attempts to use the session that has already been closed, leading to the RuntimeError: Session is closed.

Recommended Solution

The simplest solution is to ensure that all code that needs to use the toolbox or its tools is kept inside the with statement. This ensures the client and its session are active for the entire duration they are needed.

Something like this should work:

...

# Keep all dependent code inside the 'with' block
with ToolboxSyncClient(
    URL,
    client_headers={"Authorization": auth_token_provider},
) as toolbox:

    toolbox_tools = toolbox.load_toolset("project_toolset")

    # ----- Example of a Function tool -----
    def get_current_date() -> dict:
        ...

    root_agent = Agent(
        ...
    )

Regarding your second example

With the second example you provided (which worked), you did not use the with syntax:

In this case, since the session was not automatically closed by a context manager, it remained open, and you didn't get the error. However, it's a best practice to explicitly destroy the session and free up resources after the program ends. If you choose to manage the client manually like this, you should optionally add a toolbox.close() call at the very end of your program to properly clean up the session.

Let me know if you have any other questions!

Thanks :)

[jeff-got]

Cheers thank you @anubhav756

While my code examples have the tools and agent as a single file this isn't how I am planning for production, these I have created for ease of testing and troubleshooting these issues

I am using the following software bug assistant ADK samples as the base

The Agent and get_current_date tool I don't believe should be run inside the toolbox block

I have no issues when the with block closing the session with the MCP server however within the same ADK Agent session if we then try to use that tool again shouldn't it then create a new session?

[anubhav756]

By ADK session I assume you mean the Session. No the triggering of a tool doesn't create a new session. In fact all the tool triggers within the same chat thread use the same ADK session. Moreover, in case by session you mean the client network session, then that is also shared across all the tools from the same ToolboxClient.

In this scenario, instead of using the with statement, can you try initializing the ToolboxClient (or ToolboxSyncClient) in ADK's startup() and close it in the shutdown() callback? Something like the following for your Agent Engine (agent.py) file:

import os
from toolbox_core import ToolboxClient
from adk.agents import Agent

URL = "https://************.app"

app_state = {}

def get_current_date() -> dict:
    ...


async def startup():
    toolbox = ToolboxClient(URL, client_headers={"Authorization": auth_token_provider})
    app_state["toolbox_client"] = toolbox

async def shutdown():
    if client := app_state.get("toolbox_client"):
        await client.close()

async def create_agent() -> Agent:
    toolbox = app_state["toolbox_client"]
    toolbox_tools = toolbox.load_toolset("project_toolset")
    
    root_agent = Agent(
        model="gemini-2.0-flash-001",
        name="test_agent",
        instruction=agent_instruction,
        tools=[*toolbox_tools,get_current_date]
    )

Please do let me know if the issue still persists.

Thanks!

[jeff-got]

Hi @anubhav756

Unfortunately this doesn't work. When asking a question I get the following error
{"error": "Fail to load 'app' module. cannot import name 'root_agent' from 'app.agent' (/home/jeff/Agents/agent-starter-kit-test/app/agent.py)"}

With the below stack trace

2025-10-08 08:22:31,724 - ERROR - adk_web_server.py:1284 - Error in event_generator: Fail to load 'app' module. cannot import name 'root_agent' from 'app.agent' (/home/jeff/Agents/agent-starter-kit-test/app/agent.py)
Traceback (most recent call last):
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/adk_web_server.py", line 1264, in event_generator
runner = await self.get_runner_async(req.app_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/adk_web_server.py", line 444, in get_runner_async
agent_or_app = self.agent_loader.load_agent(app_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 234, in load_agent
agent_or_app = self._perform_load(agent_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 207, in _perform_load
if root_agent := self._load_from_module_or_package(actual_agent_name):
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 104, in _load_from_module_or_package
raise e
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 70, in _load_from_module_or_package
module_candidate = importlib.import_module(agent_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/importlib/init.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "", line 1206, in _gcd_import
File "", line 1178, in _find_and_load
File "", line 1149, in _find_and_load_unlocked
File "", line 690, in _load_unlocked
File "", line 940, in exec_module
File "", line 241, in _call_with_frames_removed
File "/home/jeff/Agents/agent-starter-kit-test/app/init.py", line 1, in
from app.agent import root_agent
ImportError: Fail to load 'app' module. cannot import name 'root_agent' from 'app.agent' (/home/jeff/Agents/agent-starter-kit-test/app/agent.py)

[anubhav756]

Can you change the create_agent() function to the following, along with initializing the root_agent outside the function as follows:

...

async def create_agent() -> Agent:
    toolbox = app_state["toolbox_client"]
    toolbox_tools = toolbox.load_toolset("project_toolset")
    
    return Agent(
        model="gemini-2.0-flash-001",
        name="test_agent",
        instruction=agent_instruction,
        tools=[*toolbox_tools,get_current_date]
    )

root_agent = create_agent()

[jeff-got]

Sorry @anubhav756 new error

{"error": "No root_agent found for 'app'. Searched in 'app.agent.root_agent', 'app.root_agent' and 'app/root_agent.yaml'. Ensure '/home/jeff/Agents/agent-starter-kit-test/app' is structured correctly, an .env file can be loaded if present, and a root_agent is exposed."}

2025-10-14 08:06:30,595 - INFO - envs.py:54 - No .env file found for app
2025-10-14 08:06:30,596 - INFO - envs.py:54 - No .env file found for app
2025-10-14 08:06:32,163 - WARNING - agent_loader.py:83 - Root agent found is not an instance of BaseAgent. But a type <class 'coroutine'>
2025-10-14 08:06:32,164 - INFO - agent_loader.py:126 - Found root_agent in app.agent
2025-10-14 08:06:32,164 - WARNING - agent_loader.py:130 - Root agent found is not an instance of BaseAgent. But a type <class 'coroutine'>
/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py:213: UserWarning: [EXPERIMENTAL] _load_from_yaml_config: This feature is experimental and may change or be removed in future versions without notice. It may introduce breaking changes at any time.
if root_agent := self._load_from_yaml_config(actual_agent_name, agents_dir):
/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py:169: UserWarning: [EXPERIMENTAL] from_config: This feature is experimental and may change or be removed in future versions without notice. It may introduce breaking changes at any time.
agent = config_agent_utils.from_config(config_path)
2025-10-14 08:06:32,180 - ERROR - adk_web_server.py:1284 - Error in event_generator: No root_agent found for 'app'. Searched in 'app.agent.root_agent', 'app.root_agent' and 'app/root_agent.yaml'. Ensure '/home/jeff/Agents/agent-starter-kit-test/app' is structured correctly, an .env file can be loaded if present, and a root_agent is exposed.
Traceback (most recent call last):
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/adk_web_server.py", line 1264, in event_generator
runner = await self.get_runner_async(req.app_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/adk_web_server.py", line 444, in get_runner_async
agent_or_app = self.agent_loader.load_agent(app_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 234, in load_agent
agent_or_app = self._perform_load(agent_name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/jeff/Agents/agent-starter-kit-test/.venv/lib/python3.11/site-packages/google/adk/cli/utils/agent_loader.py", line 217, in _perform_load
raise ValueError(
ValueError: No root_agent found for 'app'. Searched in 'app.agent.root_agent', 'app.root_agent' and 'app/root_agent.yaml'. Ensure '/home/jeff/Agents/agent-starter-kit-test/app' is structured correctly, an .env file can be loaded if present, and a root_agent is exposed.

[anubhav756]

Oops, I think I missed the await keywords. Can you update:

From

...

async def create_agent() -> Agent:
    toolbox = app_state["toolbox_client"]
    toolbox_tools = toolbox.load_toolset("project_toolset")
    
    return Agent(
        model="gemini-2.0-flash-001",
        name="test_agent",
        instruction=agent_instruction,
        tools=[*toolbox_tools,get_current_date]
    )

root_agent = create_agent()

To

...

async def create_agent() -> Agent:
    toolbox = app_state["toolbox_client"]
    toolbox_tools = await toolbox.load_toolset("project_toolset")
    
    return Agent(
        model="gemini-2.0-flash-001",
        name="test_agent",
        instruction=agent_instruction,
        tools=[*toolbox_tools,get_current_date]
    )

root_agent = await create_agent()