fix(flows): terminate invocation at tool-level EUC

[doughayden]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: Tool-level auth continues invocation past the EUC event #5637

This change adds invocation_context.end_invocation = True after the auth event yield in _postprocess_handle_function_calls_async, mirroring the existing termination signal in _resolve_toolset_auth. Tool-level auth now terminates symmetrically with toolset-level auth at the EUC, instead of continuing for one more LLM call.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Three existing tests in test_functions_request_euc.py had assertions tied to the trailing post-EUC LLM call:

• test_function_request_euc: adds assert len(mock_model.requests) == 1 to anchor the new termination behavior.
• test_function_get_auth_response: events[-3] → events[-2] for the auth event lookup, since the auth event is now second-to-last.
• test_function_get_auth_response_partial: same events[-3] → events[-2] change, plus the two len(mock_model.requests) assertions drop by 1 (3 → 2 and 4 → 3).

$ pytest tests/unittests/flows/llm_flows/test_functions_request_euc.py
======================== 3 passed, 17 warnings in 1.31s ========================

$ pytest tests/unittests/
=============== 5695 passed, 2308 warnings in 122.89s (0:02:02) ================

Manual End-to-End (E2E) Tests:

A self-contained Runner-based reproduction is at https://github.com/doughayden/adk-issue-examples/tree/main/04-tool_level_auth_continuation. The agent definition (agent.py) wires up an OpenAPIToolset against a local OAuth2 test server. main.py constructs an InMemoryRunner, applies the workaround for #5327 (get_auth_config = lambda: None) at runtime to land on the tool-level auth path, and sends a tool-triggering prompt. The --apply-fix flag monkey-patches the proposed fix to demonstrate the resolution end-to-end.

Without the fix:

👤 User: What's the weather in San Francisco?
🌤️  Weather Assistant event stream:

    [function_call] get_weather by WeatherAssistant
    [auth_event] adk_request_credential by WeatherAssistant
    [function_response] get_weather by WeatherAssistant
    [post_euc_text] WeatherAssistant: "I'm sorry, I cannot retrieve the weather for San Francisco at the moment. It ..."

Event counts:
    function_calls: 1
    auth_events: 1
    function_responses: 1
    text_events: 1
    post_euc_text_events: 1

✅ Bug reproduced: 1 text event(s) after the EUC (agent loop continued past adk_request_credential).

With the fix:

👤 User: What's the weather in San Francisco?
🌤️  Weather Assistant event stream:

    [function_call] get_weather by WeatherAssistant
    [auth_event] adk_request_credential by WeatherAssistant
    [function_response] get_weather by WeatherAssistant

Event counts:
    function_calls: 1
    auth_events: 1
    function_responses: 1
    text_events: 0
    post_euc_text_events: 0

✅ Fix verified: no LLM events after the EUC.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

Alternative considered:

A reorder of the yields (yield auth_event last so last_event.is_final_response() returns True) would also fix the loop termination in a single iteration without needing the flag. I went with end_invocation = True to preserve the observable event order and to match the existing pattern in _resolve_toolset_auth. Happy to switch if maintainers prefer the reorder.

Related:

The same yield site at lines 1126-1130 also produces tool_confirmation_event for HITL with the same long_running_tool_ids shape and the same termination gap. This PR scopes to auth_event only. Happy to open a follow-up PR with the same fix for tool_confirmation_event if the team agrees with the approach here.

[rohityan]

Hi @doughayden , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[rohityan]

Hi @Jacksunwei , can you please review this.

[doughayden]

Gentle bump on this one. CI is green with one pending check. Happy to rebase or address any feedback.

[adk-bot]

Thank you @doughayden for your contribution! 🎉

Your changes have been successfully imported and merged via Copybara in commit 883ff98.

Closing this PR as the changes are now in the main branch.