fix(tools): handle missing 'request' key in AgentTool.run_async fallb…

[phinglaspure123]

Problem

When AgentTool wraps an agent with no input_schema, run_async falls back to:

parts=[types.Part.from_text(text=args['request'])]

If the orchestrating LLM passes arguments under any key other than request (which is common — LLMs infer argument names from agent descriptions), 
this crashes:

ERROR - Error in event_generator: 'request'
Traceback (most recent call last):
  File "google/adk/tools/agent_tool.py", line 218, in run_async
    parts=[types.Part.from_text(text=args['request'])],
KeyError: 'request'

Full crash path:
runners.py → base_agent.py → llm_agent.py → base_llm_flow.py
  → functions.py: handle_function_calls_async
  → functions.py: __call_tool_async
  → agent_tool.py: run_async  ← CRASH HERE

This is the second bug reported in #1084. The AttributeError: 'AgentTool' object has no attribute 'func' half was fixed in November 2025, but     
args['request'] on line 218 was never addressed. Issue #1084 was closed after the first fix but this crash path remains in main.

Solution

# Before (broken)
else:
    content = types.Content(
        role='user',
        parts=[types.Part.from_text(text=args['request'])],
    )

# After (fixed)
else:
    request_text = args.get('request') or json.dumps(args, ensure_ascii=False)
    content = types.Content(
        role='user',
        parts=[types.Part.from_text(text=request_text)],
    )

- If LLM passed {"request": "do the task"} → use value as-is (backward compatible)
- If LLM passed {"brand": "Nike", "product": "shoes"} → serialize all args as JSON string → sub-agent receives '{"brand": "Nike", "product":      
"shoes"}'

Also adds import json to the stdlib imports at the top of the file.

Testing Plan

Unit Tests:
- Added test_no_schema_non_request_args_serialized_as_json — verifies non-request args are JSON-serialized and passed to sub-agent without        
crashing
- Added test_no_schema_request_key_backward_compat — verifies existing request key behavior is unchanged
- All 30 existing tests pass

============================= test session starts =============================
platform win32 -- Python 3.12.12, pytest-9.0.3, pluggy-1.6.0 -- D:\coding\adk-python\.venv\Scripts\python.exe
cachedir: .pytest_cache
rootdir: D:\coding\adk-python
configfile: pyproject.toml
plugins: anyio-4.13.0, langsmith-0.8.3, asyncio-1.3.0, mock-3.15.1, xdist-3.8.0
asyncio: mode=Mode.AUTO, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collecting ... collected 30 items

tests/unittests/tools/test_agent_tool.py::test_agent_tool_inherits_parent_app_name PASSED [  3%]
tests/unittests/tools/test_agent_tool.py::test_no_schema PASSED          [  6%]
tests/unittests/tools/test_agent_tool.py::test_use_plugins PASSED        [ 10%]
tests/unittests/tools/test_agent_tool.py::test_update_state PASSED       [ 13%]
tests/unittests/tools/test_agent_tool.py::test_update_artifacts PASSED   [ 16%]
tests/unittests/tools/test_agent_tool.py::test_custom_schema[GOOGLE_AI] PASSED [ 20%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_schema_no_output_schema_vertex_ai[VERTEX] PASSED [ 23%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_schema_with_output_schema_vertex_ai[VERTEX] PASSED [ 26%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_schema_gemini_api[GOOGLE_AI] PASSED [ 30%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_schema_with_input_schema_vertex_ai[VERTEX] PASSED [ 33%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_schema_with_input_schema_no_output_vertex_ai[VERTEX] PASSED [ 36%]
tests/unittests/tools/test_agent_tool.py::test_include_plugins_default_true PASSED [ 40%]
tests/unittests/tools/test_agent_tool.py::test_include_plugins_explicit_true PASSED [ 43%]
tests/unittests/tools/test_agent_tool.py::test_include_plugins_false PASSED [ 46%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_description_with_input_schema PASSED [ 50%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_no_schema_with_json_schema_feature PASSED [ 53%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_json_schema_no_output_schema_vertex_ai[VERTEX] PASSED [ 56%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_response_json_schema_with_output_schema_vertex_ai[VERTEX] PASSED [ 60%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_no_response_json_schema_gemini_api[GOOGLE_AI] PASSED [ 63%]
tests/unittests/tools/test_agent_tool.py::test_agent_tool_with_input_schema_uses_json_schema_feature[VERTEX] PASSED [ 66%]
tests/unittests/tools/test_agent_tool.py::test_run_async_handles_none_parts_in_response PASSED [ 70%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_sequential_agent_with_first_sub_agent_input_schema PASSED [ 73%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_sequential_agent_without_input_schema_falls_back_to_request PASSED [ 76%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_sequential_agent_with_last_sub_agent_output_schema[VERTEX] PASSED [ 80%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_nested_sequential_agent_input_schema PASSED [ 83%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_sequential_agent_custom_schema_end_to_end[GOOGLE_AI] PASSED [ 86%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_sequential_agent_custom_schema_end_to_end[VERTEX] PASSED [ 90%]
tests/unittests/tools/test_agent_tool.py::TestAgentToolWithCompositeAgents::test_empty_sequential_agent_falls_back_to_request PASSED [ 93%]
tests/unittests/tools/test_agent_tool.py::test_no_schema_non_request_args_serialized_as_json PASSED [ 96%]
tests/unittests/tools/test_agent_tool.py::test_no_schema_request_key_backward_compat PASSED [100%]

============================== warnings summary ===============================
tests/unittests/tools/test_agent_tool.py: 20 warnings
D:\coding\adk-python\src\google\adk\runners.py:250: DeprecationWarning: The `plugins` argument is deprecated. Please use the `app` argument to provide plugins instead.
  warnings.warn(

tests/unittests/tools/test_agent_tool.py::test_agent_tool_no_schema_with_json_schema_feature
D:\coding\adk-python\tests\unittests\tools\test_agent_tool.py:769: UserWarning: [WIP] feature FeatureName.JSON_SCHEMA_FOR_FUNC_DECL is enabled.
  declaration = agent_tool._get_declaration()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================= 30 passed, 21 warnings in 5.44s =======================


Manual E2E Test:

Orchestrator agent (LiteLLM) called sub-agent via AgentTool with {"brand": "Nike", "product": "running shoes"}. After fix, pipeline completed     
successfully:

[orchestrator]: Here's a concise synthesis of Nike running shoes based on
the latest brand/product research...

No KeyError. Before fix, same call crashed at agent_tool.py:218.

Checklist

- I have read the CONTRIBUTING.md document.
- I have performed a self-review of my own code.
- 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.

Closes #1084 (KeyError half — the AttributeError half was fixed Nov 2025)