[claxman]

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Link to Issue or Description of Change

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

• Closes: RemoteA2aAgent(mode="task") closes a delegation on a nested peer's finish_task forwarded by A2aAgentExecutor #7745

Problem:
A task-mode RemoteA2aAgent treats any terminal finish_task response as the remote task completing. Both A2aAgentExecutor paths forward every event from runner.run_async, including a nested peer's finish_task. That nested event has branch set (inner@<run_id>), which is what the wire shows as adk_branch. The served agent's own finish_task leaves branch unset. The outer delegation then closes on the inner result.

Solution:
Skip a finish_task call or terminal response whose branch has a run id (name@run_id), in both executor loops, before conversion. That is what task delegation stamps, via override_branch on AgentTool and use_sub_branch on run_node. Other events on that branch are still forwarded. An unset branch is still forwarded, including a Workflow or SequentialAgent child whose author is not the served root. ParallelAgent stamps parent.child with no run id, and that child's finish_task is forwarded so a served parallel root still completes.

A client-side adk_branch check in RemoteA2aAgent is not in this change. The caller builds Event.branch from its own invocation context, not from the remote adk_branch metadata, so that check is a separate read of the A2A message.

Testing Plan

Unit Tests:

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

test_legacy_executor_forwards_finish_task_by_run_id and test_new_executor_forwards_finish_task_by_run_id each run four cases: a nested text event on inner@fc is forwarded while that hop's finish_task is dropped and the unset-branch finish_task is kept; author reporter against served root workflow with branch unset is kept; a chat root that ends in text keeps the text and drops the nested finish_task; par.child is kept. test_nested_branch_finish_task_requires_a_run_id checks the helper for unset branch, par.c, a text event on inner@fc, and a terminal finish_task on inner@fc.

pytest tests/unittests/a2a/executor/test_a2a_agent_executor.py::test_legacy_executor_forwards_finish_task_by_run_id tests/unittests/a2a/executor/test_a2a_agent_executor_impl.py::test_new_executor_forwards_finish_task_by_run_id tests/unittests/agents/llm/task/test_finish_task_tool.py::test_nested_branch_finish_task_requires_a_run_id

9 passed. mypy on _finish_task_tool.py, a2a_agent_executor.py, and a2a_agent_executor_impl.py: no issues.

Manual End-to-End (E2E) Tests:

Did not run the issue's three-agent ASGI script. The executor tests cover both _handle_request loops.

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

A non-terminal finish_task response on a sub-branch is still forwarded. It does not close the outer task.