fix: Fix issue with MCP tools throwing an error.

[nickvander]

Problem

When an MCP tool is resolved using _gemini_schema_util.py, if it has an array it wasn't correctly resolving them and showing an error:

GenerateContentRequest.tools[0].function_declarations[1].parameters.properties[segmentation_classes].items: missing field

Root Cause

The error "parameters.properties[segmentation_classes].items: missing field" indicates _to_gemini_schema isn't correctly handling array types.

Implementation Details

Correctly handle array types by adding a default items field of {"type": "string"} to schemas with type: array but no items field.

Fixes: #3082

[gemini-code-assist]

Summary of Changes

Hello @nickvander, 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 critical bug that prevented MCP tools from correctly processing schemas containing array types. Previously, if an array was defined without an explicit items field, the system would fail with a 'missing field' error. The change introduces logic to automatically assign a default {"type": "string"} to the items field for any array type lacking this definition, thereby ensuring proper schema resolution and preventing runtime errors.

Highlights

• Error Resolution: Fixes an issue where MCP tools would throw an error when resolving schemas containing array types that lacked an explicit 'items' field.
• Schema Handling for Arrays: Ensures that schemas with type: array but no items field are correctly processed by automatically assigning a default {"type": "string"} to the items field.
• Targeted Change: The modification is implemented within the _sanitize_schema_type function in _gemini_schema_util.py to address both inferred and directly specified array types.

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[adk-bot]

Response from ADK Triaging Agent

Hello @nickvander, thank you for creating this PR!

To help us review this bug fix efficiently, could you please provide the following information based on our contribution guidelines?

• Associated Issue: Please create and link a GitHub issue that this PR addresses.
• Testing Plan: Could you add a testing plan section to your PR description explaining how you've tested these changes?
• Verification: It would be helpful to include logs or screenshots demonstrating the fix in action.

You can find more details in our contribution guidelines. Thanks!

[gemini-code-assist]

Code Review

This pull request fixes an issue where MCP tools would error on schemas with array types that were missing an items field. The change correctly adds a default items field. However, the implementation introduces some code duplication. My review includes a suggestion to refactor the code to remove this duplication, which will improve the long-term maintainability of this function.