fix: strip uniqueItems from Gemini function_declarations (#2123)

[Muran-prog]

Fixes #2123

Gemini API rejects uniqueItems in tool schemas:
400 Unknown name "uniqueItems" at 'request.tools0.function_declarations43.parameters.properties2.value'

Added uniqueItems to unsupportedConstraints in gemini_schema.go alongside minItems/maxItems - same approach as #1424 and #1531.

All existing schema sanitization tests pass.

[gemini-code-assist]

Summary of Changes

Hello, 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 addresses a compatibility issue with the Gemini API by ensuring that the uniqueItems schema constraint is properly handled. By adding this constraint to the list of unsupported items, the system prevents API rejections and ensures smooth integration, maintaining the integrity of existing schema sanitization processes.

Highlights

• Gemini API Compatibility: Resolved an issue where the Gemini API rejected uniqueItems in tool schemas by adding it to the list of unsupportedConstraints.
• Schema Sanitization: The uniqueItems constraint is now stripped from function declarations when interacting with the Gemini API, aligning with previous fixes for minItems and maxItems.

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Changelog

• internal/util/gemini_schema.go
  • Added 'uniqueItems' to the list of unsupported schema constraints.

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[gemini-code-assist]

Code Review

This pull request addresses an issue where the Gemini API rejects schemas containing the uniqueItems keyword. The fix correctly adds uniqueItems to the list of unsupported constraints, ensuring it's stripped from the schema before being sent to the API. The change is straightforward and follows the existing pattern for handling unsupported schema properties. I've suggested adding a test case to verify this new behavior and prevent future regressions.

[gemini-code-assist]

This change correctly adds uniqueItems to the list of unsupported constraints. To ensure this fix is robust and prevent future regressions, it would be beneficial to add a new test case to internal/util/gemini_schema_test.go. This test should verify that the uniqueItems keyword is removed from the schema and a corresponding hint is added to the description, similar to how other constraints like minItems are tested.

[Muran-prog]

Added a test in the follow-up commit - verifies uniqueItems is stripped and the description hint is added.

[luispater]

Summary

This change fixes the reported Gemini schema rejection by stripping uniqueItems alongside the other unsupported constraints and preserving it as a description hint. The implementation is consistent with the existing sanitizer flow, and the added regression test covers the shared constraint-to-description path.

Key findings

• No blocking issues found.
• Non-blocking: consider adding a CleanJSONSchemaForGemini regression test too, since that is the directly reported failing entry point.

Test plan

• Reviewed the diff for internal/util/gemini_schema.go and internal/util/gemini_schema_test.go
• Ran go test ./internal/util on the PR head
• Ignored translator-path-guard per instructions

This is an automated Codex review result and still requires manual verification by a human reviewer.