fix: change LlmAgent.tools to covariant Sequence

[jokester]

recreated from #1804 which got closed as "stale"

Fixes #1803

(the type mismatch still happens in google-adk v1.15.1)

[gemini-code-assist]

Summary of Changes

Hello @jokester, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a type mismatch issue within the LlmAgent class by refining the type annotation for its tools attribute. By changing the type hint from a concrete list to the more general Sequence, the change improves type compatibility and addresses a previously reported bug, enhancing the overall robustness of the google-adk library.

Highlights

• Type Hint Correction: The type hint for the tools attribute within the LlmAgent class has been updated from list[ToolUnion] to Sequence[ToolUnion].
• Issue Resolution: This change directly addresses and fixes a reported type mismatch issue (issue Agent() doesn't accept tools in list[FunctionTool] #1803) that was observed in google-adk v1.15.1.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a typing issue by changing the type hint for LlmAgent.tools from list[ToolUnion] to Sequence[ToolUnion]. This change makes the type covariant, allowing for more flexible usage, such as assigning lists of tool subtypes without causing static analysis errors. The implementation is clean and effective. I have no further suggestions.

[adk-bot]

Response from ADK Triaging Agent

Hello @jokester, thank you for creating this PR!

Could you please include a testing plan section in your PR to talk about how you will test?

In addition, could you please provide logs or screenshot after the fix is applied?

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

[ryanaiagent]

Hi @jokester, Thanks for submitting this pull request!
To move this forward, could you please add a few unit tests to this PR? Having solid test coverage will significantly expedite the review and merging process.

[jokester]

@ryanaiagent hi, thanks for checking this. However I'm not sure if adding "unit test" is simple or possible.

The issue in question is about type annotation, not a runtime bug. It would require a type checker to "test" the change, but I don't see this repo has one (pyright or mypy) in CI.

I can confirm the fix works with the snippet pyright complained about. Do you think this will work too?