fix(cli): use Optional[List[str]] in cleanup_unused_files to fix parser error

[syzayd]

Problem

When the ADK web server runs and the LLM calls the cleanup_unused_files built-in tool, the automatic function calling system fails to parse its optional parameter type annotations on Python 3.10:

Error in event_generator: Failed to parse the parameter
file_patterns: List[str] | None = None of function
cleanup_unused_files for automatic function calling

The root cause is that file_patterns and exclude_patterns use the PEP 604 union syntax (list[str] | None) which ADK's _parse_schema_from_parameter cannot handle in all Python versions. list[str] | None evaluates to types.UnionType (Python 3.10+), while Optional[List[str]] evaluates to typing._GenericAlias — the latter has a well-tested path through the parser.

Fixes #3591

Fix

All sibling tools in src/google/adk/cli/built_in_agents/tools/ already use Optional[List[str]] from the typing module (see write_files.py, delete_files.py, read_files.py). This PR aligns cleanup_unused_files.py with that established pattern:

• Add from typing import List and from typing import Optional
• Replace list[str] | None with Optional[List[str]] on file_patterns and exclude_patterns
• Change used_files: list[str] to used_files: List[str] for style consistency

Testing Plan

• Manual reproduction (Python 3.10): Before the fix, from_function_with_options(cleanup_unused_files, variant) raises ValueError: Failed to parse the parameter file_patterns: list[str] | None = None. After the fix, it parses cleanly and returns nullable=True, type=ARRAY for both optional params.
• Consistency check: Confirmed that all sibling tools (write_files.py, delete_files.py, read_files.py) use Optional[List[str]] — this PR makes cleanup_unused_files.py consistent with the existing pattern.
• Existing tests: No test changes required. This is a type annotation change only; runtime behavior is identical.
• adk web smoke test: Launch adk web and invoke an agent that uses the cleanup_unused_files built-in tool. Confirm no parser warning appears in the console output.

Reproduction script

A minimal repro (repro_3591.py) is included in this branch. It calls from_function_with_options directly on both the old and new signatures to show the before/after behavior.

[google-cla]

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[adk-bot]

Response from ADK Triaging Agent

Hello @syzayd, thank you for creating this PR!

We appreciate your fix! It looks like there are a couple of things missing based on our contribution guidelines:

1. Contributor License Agreement (CLA): The CLA check is currently failing. Please sign the Google CLA at https://cla.developers.google.com/ to proceed.
2. Logs or Screenshots: Since this is a bug fix for a tool parse error, could you please provide a log or screenshot from adk web showing the tool runs successfully without the parser warning?
3. Testing Plan: Please include a formal testing plan section in your PR description.

This information will help reviewers to review your PR more efficiently. Thanks!

[rohityan]

Hi @syzayd, Thank you for your contribution! It appears you haven't yet signed the Contributor License Agreement (CLA). Please visit https://cla.developers.google.com/ to complete the signing process. Once the CLA is signed, we'll be able to proceed with the review of your PR. Thank you!

[syzayd]

Hi, I've addressed all the requested items:

• CLA: Signed: the cla/google check is now passing
• Testing plan: Added a formal testing plan section to the PR description
• Reproduction: Added repro_3591.py to the branch, which exercises from_function_with_options() directly on both the old and fixed signatures

Ready for review when you get a chance. Thanks!