fix: ensure JSON Schema draft 2020-12 compliance for OpenAI-compatible providers

[roomote]

Related GitHub Issue

Closes: #10320

Description

This PR fixes the JSON Schema compatibility issue reported in #10320 where Claude models accessed through OpenAI-compatible proxies were failing with "JSON schema is invalid. It must match JSON Schema draft 2020-12" errors.

Root Cause:

• Several native tool definitions use type arrays like type: ["string", "null"] for nullable parameters
• This syntax is valid in JSON Schema draft-07 but NOT in draft 2020-12 (which requires anyOf format instead)
• The convertToolSchemaForOpenAI function in base-provider.ts was converting nullable types by simply removing null from the type array, rather than converting to the proper anyOf format

Implementation:

• Modified convertToolSchemaForOpenAI in src/api/providers/base-provider.ts to use the existing normalizeToolSchema function from src/utils/json-schema.ts
• The normalizeToolSchema function already properly handles:
  • Converting type: ["T", "null"] array syntax to anyOf: [{type: "T"}, {type: "null"}] format
  • Moving array-specific properties (items, minItems, etc.) inside the array variant when using anyOf
  • Setting additionalProperties: false for object types (OpenAI strict mode)
  • Stripping unsupported format values
• Updated Cerebras provider's stripUnsupportedSchemaFields to handle anyOf/oneOf/allOf arrays

Test Procedure

1. Added comprehensive tests in src/api/providers/__tests__/base-provider.spec.ts covering:

   • JSON Schema draft 2020-12 compliance (type array to anyOf conversion)
   • OpenAI strict mode compatibility (additionalProperties: false)
   • Format field handling
   • Edge cases (null input, deeply nested structures)

2. All existing tests continue to pass:

   • json-schema.spec.ts - 35 tests pass
   • cerebras.spec.ts - all tests pass
   • base-openai-compatible-provider.spec.ts - all tests pass

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

This fix reuses the existing, well-tested normalizeToolSchema function rather than implementing new conversion logic, ensuring consistency across all providers that use OpenAI-compatible format.

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Rooviewer   See task on Roo Cloud

Reviewed. No issues found.

The implementation correctly addresses the JSON Schema draft 2020-12 compliance issue by reusing the existing normalizeToolSchema function, which properly converts type arrays like ["string", "null"] to anyOf format. The Cerebras provider update to handle anyOf/oneOf/allOf arrays is also necessary and correct.

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