fix: load artifacts from workflow text responses

[he-yufeng]

Summary

• support load_artifacts results that were converted into workflow context text
• scan all parts in the latest content turn instead of assuming the first part is the function response
• add regressions for workflow text responses and non-first function responses

Fixes #5967.

Verified

• $env:PYTHONPATH=(Resolve-Path src).Path; python -m pytest tests\unittests\tools\test_load_artifacts_tool.py -q -> 9 passed, 5 warnings
• python -m pyink --check src\google\adk\tools\load_artifacts_tool.py tests\unittests\tools\test_load_artifacts_tool.py -> 2 files would be left unchanged
• $env:PYTHONPATH=(Resolve-Path src).Path; python -m py_compile src\google\adk\tools\load_artifacts_tool.py tests\unittests\tools\test_load_artifacts_tool.py -> passed
• git diff --check upstream/main..HEAD -> passed

Regression exercised

The new tests cover a workflow text response such as [workflow_node] `load_artifacts` tool returned result: {'artifact_names': ['invoice.txt'], 'status': 'ok'} and a turn where the load_artifacts function response is not the first part. In both cases the request receives a new artifact content turn before the model answers.

[adk-bot]

Response from ADK Triaging Agent

Hello @he-yufeng, thank you for creating this PR!

We noticed that a few requirements from our contribution guidelines are missing:

1. Summary of passed unit tests: Please run your tests and include a summary of the passed pytest results in your PR description.
2. Logs or screenshots: Please provide execution logs or screenshots showing the tool in action after applying the fix to help reviewers better understand the change.

Providing these details will help the maintainers review and merge your PR more efficiently. Thank you!

[adk-bot]

I have completed the read-only triage and analysis workflow for PR #5969 resolving workflow tool loops as requested.

The detailed findings, architectural audit, and compliance evaluation have been compiled into a premium pull request analysis report which you can access directly here:

📄 PR Analysis Report

• Report Location: analysis_results.md

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Key Summary & Next Steps

1. Google CLA Verification: Verified successfully. The contributor's signature check has been completed and marked as SUCCESS.
2. Technical Quality: Excellent code quality. The solution securely uses ast.literal_eval to safely parse workflow stringified representations without invoking code. Correctly handles multiple function response parts through recursive matching of isinstance.
3. Recommendation: Approve.
4. Action Needed: If you are satisfied with this analysis, you can proceed to merge the PR or let me know if you would like me to trigger integration tasks or further workspace steps.

[he-yufeng]

Rechecked the branch locally on current main. The PR description already includes the regression and verification details; current local validation is:

• python -m py_compile src/google/adk/tools/load_artifacts_tool.py tests/unittests/tools/test_load_artifacts_tool.py
• PYTHONPATH=src C:\dev\GITHUB-clean\adk-python\.venv\Scripts\python.exe -m pytest -q tests/unittests/tools/test_load_artifacts_tool.py --basetemp .tmp\pytest-5969 -p no:cacheprovider (9 passed)
• uv run pyink --check src/google/adk/tools/load_artifacts_tool.py tests/unittests/tools/test_load_artifacts_tool.py
• git diff --check upstream/main..HEAD

[he-yufeng]

I rechecked the current red checks on this branch.

They do not look caused by this PR diff:

• pre-commit --all-files is touching upstream files outside this PR's diff. The same .github/workflows/release-update-adk-web.yaml on google:main currently has name: Release: Update ADk Web, which check-yaml rejects at line 1, column 14; the generated browser chunk whitespace is also present on google:main.
• The failing unit tests are in tests/unittests/cli/test_fast_api.py and fail with missing Google Application Default Credentials, unrelated to the artifact loading fix.
• pr-analyze, check-changes, check-file-contents, mypy-diff, CLA, and header-check are green.

I am leaving the PR code unchanged for now to avoid mixing unrelated main-branch CI cleanup into this focused fix.