Question about the new rewind feature

[lucasbarzotto-axonify]

Hi, could you please clarify some questions about the new "rewind to previous invocation" feature?

• Looking at the commit that added this feature (9dce06f) it looks like a rewind_async method was added to the runner but it's not being used anywhere. Could you please provide some examples on how to use it?
• What are the main use cases for this feature? Would enabling users to roll back session state if they’re unhappy with recent changes be a valid scenario?

Thank you!

[adk-bot]

Response from ADK Answering Agent (experimental, answer may be inaccurate)

TLDR: The rewind_async method is a developer-facing feature that allows you to revert a session to a state before a specific invocation. Your understanding of its use case for rolling back session state is spot on.

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Hi! Thank you for your questions about the "rewind to previous invocation" feature.

Use Cases

Your intuition is correct. The primary use case for rewind_async is to enable scenarios where a user might want to undo recent changes and roll back the session state. This provides a powerful way to manage the session's history and state.

How it Works

The rewind_async method works by identifying the specified invocation within the session's event log. It then calculates the necessary state and artifact adjustments to effectively reverse all changes that occurred after that particular invocation. Finally, it appends a "rewind" event to the session's history to record this action. [2]

Example Usage

You are correct that rewind_async is not used extensively within the ADK's internal code. This is because it is intended as a feature for developers to integrate into their applications. The unit tests for this feature provide a clear example of how to use it. Here’s a simplified example based on the tests: [1]

from google.adk import runners

# Assume 'runner' is an initialized ADK runner
# and we have a session with previous invocations
session = await runner.get_session_async(user_id, session_id)

# Choose an invocation ID to rewind to
invocation_to_rewind_before = "some_invocation_id"

# This will revert the session to the state it was in
# just before 'some_invocation_id' was processed
await runner.rewind_async(
    user_id=user_id,
    session_id=session_id,
    rewind_before_invocation_id=invocation_to_rewind_before
)

I hope this clarifies how the rewind feature works and how you can use it in your projects.

[1] https://github.com/google/adk-python/blob/main/tests/unittests/runners/test_runner_rewind.py
[2] https://github.com/google/adk-python/blob/main/src/google/adk/runners.py