Fix: Human-in-the-Loop Not Resuming In ADK Python

Nov 15, 2025 by Alex Johnson 50 views

Human-in-the-Loop Not Resuming After Confirmation in ADK Python: A Troubleshooting Guide

Experiencing issues with Human-in-the-Loop (HITL) not resuming after confirmation in your ADK Python application can be frustrating. This comprehensive guide will walk you through the potential causes of this problem and provide step-by-step solutions to get your HITL workflows back on track. We'll explore common pitfalls, analyze error messages, and delve into code examples to ensure you have a clear understanding of how to resolve this issue. By the end of this article, you'll be equipped with the knowledge and tools necessary to diagnose and fix HITL resumption problems in your ADK Python projects.

Understanding the Issue: Why HITL Might Not Resume

When implementing Human-in-the-Loop (HITL) in your ADK Python applications, the goal is to seamlessly integrate human input into automated processes. A common scenario involves pausing the automated workflow, presenting a task or question to a human operator, and then resuming the workflow once the operator provides confirmation or input. However, sometimes the workflow fails to resume after the confirmation, leading to a standstill in the process. Several factors can contribute to this issue, and it's crucial to understand them to effectively troubleshoot the problem.

One primary cause is the improper handling of invocation IDs. In ADK, each interaction or session is assigned a unique invocation ID. This ID is essential for tracking the state of the workflow and ensuring that the system knows where to resume after human intervention. If the invocation ID is not correctly passed or stored during the confirmation process, the system may lose track of the session and fail to resume. Another potential issue is related to application resumability. The application needs to be designed to be resumable, meaning it can pick up where it left off after being paused. This typically involves saving the application's state before pausing and restoring it upon resumption. If the application is not properly configured for resumability, it may not be able to continue after confirmation.

Furthermore, errors in the event generator can also prevent HITL from resuming. The event generator is responsible for producing the events that drive the workflow. If an error occurs in this generator, it can halt the process and prevent the system from resuming. These errors can be caused by various factors, including incorrect code, missing dependencies, or unexpected data inputs. It's also important to consider session management issues. If the session is not properly managed, such as being terminated prematurely or encountering conflicts, it can disrupt the HITL workflow and prevent resumption. This can happen if the session times out, if there are multiple sessions trying to access the same resources, or if there are errors in the session handling logic. Finally, underlying code errors within the application's logic can also lead to HITL resumption failures. These errors can be subtle and difficult to track down, but they can have a significant impact on the workflow. Debugging the code and ensuring that it handles the confirmation process correctly is crucial for resolving these issues.

Diagnosing the "App is Not Resumable" Error

The error message "ValueError: invocation_id: [invocation_id] is provided but the app is not resumable" is a key indicator that your ADK Python application is encountering a problem related to resumability in the Human-in-the-Loop (HITL) workflow. This error typically arises when the system attempts to resume a paused session using an invocation ID, but the application has not been configured to handle resumption properly. To effectively diagnose and resolve this issue, it's essential to break down the error message and understand the underlying causes.

The core of the error message points to the fact that an invocation ID was provided, suggesting that the system is trying to resume a previously paused session. However, the crucial part of the message is the phrase "app is not resumable." This indicates that the application's code or configuration is lacking the necessary mechanisms to save its state before pausing and restore it upon resumption. In other words, the application is not designed to pick up where it left off after human intervention. This can happen for several reasons. One common reason is that the application's code does not include the logic to persist the state of the workflow. When an application pauses for human input, it needs to store information about its current state, such as variable values, progress markers, and any other relevant data. This stored state can then be used to restore the application to its previous condition when it resumes. If this state-saving mechanism is missing, the application will not be able to continue from where it paused.

Another potential cause is the absence of state restoration logic. Even if the application saves its state before pausing, it also needs to have the code to load and apply that state when resuming. This typically involves reading the stored state from a file or database and using it to initialize the application's variables and settings. If this restoration logic is not implemented correctly, the application may start from scratch instead of resuming from the correct point. Furthermore, incompatible changes in the code between pausing and resuming can also lead to this error. If the application's code is modified in a way that makes the saved state incompatible, the resumption process may fail. For example, if the data structure used to store the state is changed, the application may not be able to load the old state correctly. To diagnose this issue effectively, it's important to examine the application's code and configuration related to state management. Look for the mechanisms used to save and restore the application's state, and ensure that they are implemented correctly. Additionally, check for any code changes that might have introduced incompatibilities in the state format.

Step-by-Step Solutions to Resolve HITL Resumption Issues

Resolving Human-in-the-Loop (HITL) resumption issues in ADK Python requires a systematic approach. When encountering the "app is not resumable" error, it's essential to follow a series of steps to identify the root cause and implement the appropriate solution. These steps range from checking code for state management to verifying the ADK configuration and ensuring compatibility. Let's delve into each step in detail to guide you through the troubleshooting process.

1. Implement State Management: The first and most crucial step is to ensure that your application properly manages its state. This involves saving the application's state before pausing for human input and restoring it upon resumption. To achieve this, you need to identify the relevant data that represents the application's current state, such as variable values, progress markers, and any other contextual information. Once you've identified the state data, you can use various methods to store it, such as writing it to a file, saving it in a database, or using a dedicated state management library. When resuming the application, you'll need to read the stored state and use it to re-initialize the application's variables and settings. Here’s an example of how you might save and restore state using a simple file-based approach:

import json

def save_state(state, filename="state.json"):
    with open(filename, 'w') as f:
        json.dump(state, f)


def load_state(filename="state.json"):
    try:
        with open(filename, 'r') as f:
            return json.load(f)
    except FileNotFoundError:
        return None

2. Verify Invocation ID Handling: The invocation ID is a unique identifier that ADK uses to track sessions. Ensure that your application correctly handles the invocation ID throughout the HITL workflow. This means storing the invocation ID when the application pauses and using it to resume the session. If the invocation ID is lost or corrupted, the system will not be able to resume the workflow correctly. Double-check that the invocation ID is being passed correctly between different parts of your application and that it's being used in the resumption requests.

3. Review Event Generator Logic: The event generator is responsible for producing the events that drive the HITL workflow. If there's an error in the event generator, it can prevent the application from resuming. Carefully review the logic of your event generator to ensure that it's handling events correctly and that there are no exceptions or errors occurring. Use logging and debugging techniques to trace the flow of events and identify any potential issues. Ensure that the event generator is designed to handle the resumption process gracefully, meaning it can pick up where it left off after a pause.

4. Check for Code Incompatibilities: If you've made changes to your application's code between pausing and resuming, there's a possibility that these changes have introduced incompatibilities with the saved state. For example, if you've changed the structure of the data used to represent the application's state, the application may not be able to load the old state correctly. Review your code changes and ensure that they are compatible with the state management logic. If necessary, implement migration strategies to handle different versions of the state data.

5. Examine ADK Configuration: The ADK configuration plays a crucial role in the HITL workflow. Ensure that your ADK configuration is set up correctly to support resumption. This may involve checking settings related to session management, state persistence, and other HITL-specific parameters. Consult the ADK documentation for guidance on configuring your application for HITL and resumption. Make sure that all required dependencies and libraries are installed correctly and that there are no conflicts in the ADK environment.

6. Test and Debug Thoroughly: After implementing the above steps, it's essential to test your application thoroughly to ensure that HITL resumption is working correctly. Use a variety of test cases to simulate different scenarios and edge cases. Pay close attention to the error messages and logs to identify any remaining issues. Use debugging tools to step through the code and examine the application's state at different points in the workflow. This iterative process of testing and debugging will help you identify and fix any remaining problems.

Code Example: Implementing Resumability in ADK Python

To illustrate how to implement resumability in an ADK Python application, let's consider a simple example that involves executing commands on the filesystem. This example builds upon the code snippet provided in the original issue and demonstrates how to save and restore the application's state. The key to making an application resumable is to maintain a persistent state that can be loaded when the application restarts. This state might include variables, flags, or any data necessary to continue the process from where it was paused. Here’s a more detailed breakdown of the code and how it addresses the resumability issue:

import json
from google.adk.tools import AgentTool, FunctionTool
from google.adk import Agent

STATE_FILE = "agent_state.json"  # File to store the agent's state

def load_state():
    """Loads the agent state from a JSON file."""
    try:
        with open(STATE_FILE, 'r') as f:
            return json.load(f)
    except FileNotFoundError:
        return {}


def save_state(state):
    """Saves the agent state to a JSON file."""
    with open(STATE_FILE, 'w') as f:
        json.dump(state, f)


def execute_command(command: str, state=None) -> str:
    """Executes a command on the filesystem and updates the state."""
    if state is None:
        state = load_state()

    print(f"Executing command: {command}")
    output = f"Successfully executed: {command}"

    # Update state (example: track executed commands)
    if 'executed_commands' not in state:
        state['executed_commands'] = []
    state['executed_commands'].append(command)
    save_state(state)

    return {"output": output}


def confirmation_threshold(command: str) -> bool:
    """Determines if a command requires confirmation based on its type."""
    print(f"Checking if command needs confirmation: {command}")
    write_commands = ["write", "touch", "echo", "cat", "cp", "mv", "rm", "mkdir"]
    is_write = any(command.strip().startswith(cmd) for cmd in write_commands) or ">" in command
    print(f"Is write command: {is_write}")
    return is_write

# Load initial state
initial_state = load_state()

root_agent = Agent(
    name="filesystem_agent",
    description="This agent executes read/write commands on the filesystem",
    instruction="""You are a helpful assistant that executes read/write commands on the filesystem.\
    You will be given a command and you will need to execute it. \
    """,
    model="gemini-2.0-flash",
    tools=[
        FunctionTool(execute_command, require_confirmation=confirmation_threshold),
    ],
    state=initial_state  # Pass the loaded state to the agent
)

In this enhanced example, we introduce a STATE_FILE constant to specify the file where the agent's state will be stored. The load_state function attempts to load the state from this file, and if the file doesn't exist, it returns an empty dictionary. The save_state function writes the current state to the file as a JSON object. The execute_command function now accepts an optional state parameter. If no state is provided, it loads the state using load_state. After executing a command, it updates the state (in this example, by tracking the executed commands) and saves it using save_state. Finally, when creating the Agent, we pass the loaded initial_state to the state parameter. This ensures that the agent starts with the state from the previous session, enabling it to resume its operations seamlessly.

Conclusion

Successfully implementing Human-in-the-Loop (HITL) and ensuring smooth resumption in ADK Python applications requires careful attention to state management, invocation ID handling, event generator logic, and code compatibility. By following the steps outlined in this guide, you can effectively diagnose and resolve the "app is not resumable" error and other related issues. Remember to implement robust state management mechanisms, verify the correct handling of invocation IDs, review your event generator logic, check for code incompatibilities, and thoroughly test your application. By paying attention to these details, you can create resilient and efficient HITL workflows that seamlessly integrate human input into your automated processes. For more information on ADK Python and best practices, visit the official Google AI Developer Documentation.