fix(kosong): strip JSON Schema metadata from Google GenAI tool parameters

[xiaoju111a]

Related Issue

Resolves #734

Description

This PR fixes a compatibility issue between Google GenAI provider and MCP tools that include standard JSON Schema metadata fields.

Problem

When using MCP tools (like Exa MCP) with Google GenAI provider, the following validation error occurs:

1 validation error for FunctionDeclaration
parameters.$schema
  Extra inputs are not permitted [type=extra_forbidden, input_value='http://json-schema.org/draft-07/schema#', input_type=str]

Root cause:

• MCP tools' inputSchema includes standard JSON Schema metadata fields
• Google GenAI SDK's Pydantic model has extra='forbid', which rejects these additional fields
• Kimi CLI was passing the complete schema without filtering metadata

Solution

Strip JSON Schema metadata fields in tool_to_google_genai() function before passing to Google GenAI SDK. We filter 4 fields that are rejected by the SDK:

• $schema, $id, $comment - JSON Schema metadata
• examples - Example values (not part of validation schema)

Note: $defs and definitions are already removed by kosong's deref_json_schema() function, so we don't need to filter them here.

def tool_to_google_genai(tool: KosongTool) -> Tool:
    # Strip JSON Schema metadata fields (google-genai SDK has extra='forbid')
    # Note: $defs/definitions are already removed by kosong's deref_json_schema()
    parameters = {
        k: v
        for k, v in tool.parameters.items()
        if k not in ("$schema", "$id", "$comment", "examples")
    }
    
    return Tool(
        function_declarations=[
            FunctionDeclaration(
                name=tool.name,
                description=tool.description,
                parameters=parameters,
            )
        ]
    )

Impact

• ✅ Only affects Google GenAI provider
• ✅ Backward compatible (tools without metadata work as before)
• ✅ No performance impact (simple dict filtering)
• ✅ Follows JSON Schema best practices (metadata fields are not parameter definitions)

Testing

Manually verified the 4 rejected fields with Google GenAI SDK:

# Tested fields that cause ValidationError:
# ❌ $schema, $id, $comment, examples

# After fix: ✅ All metadata stripped automatically
# Tools work correctly with Google GenAI provider

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any.
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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