Preserve MCP tool input schema metadata

[almahfuz777]

Summary

• Convert MCP tool JSON input schemas to Zod schemas before passing them to LangChain tools
• Preserve argument descriptions, required fields, enums, arrays, nested objects, and union-like schemas
• Add regression coverage for MCP schema conversion and LangChain tool creation

Why

Custom MCP tools can expose parameter metadata through JSON Schema. Passing that schema through directly can drop useful tool argument metadata before it reaches the model/tool interface. Converting the schema into the Zod format expected by LangChain preserves that metadata and keeps validation behavior intact.

Fixes #6497.

Validation

• corepack pnpm --dir packages/components exec eslint nodes/tools/MCP/core.ts nodes/tools/MCP/core.test.ts --ext ts --report-unused-disable-directives --max-warnings 0
• $env:NODE_OPTIONS='--max-old-space-size=4096'; corepack pnpm --dir packages/components exec jest nodes/tools/MCP/core.test.ts --runInBand

[gemini-code-assist]

Code Review

This pull request introduces a JSON Schema to Zod converter (mcpInputSchemaToZodObject) to dynamically transform MCP input schemas into Zod schemas for validation within LangChain MCP tools, along with corresponding unit tests. Feedback highlights several limitations in the current converter implementation—such as lack of support for non-string enums, multi-type fields, implicit types, and default values—and suggests a robust refactoring that also throws errors on invalid input types to promote fail-fast behavior.

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[almahfuz777]

Thanks for the review. I addressed the schema converter gaps in packages/components/nodes/tools/MCP/core.ts:

• supports non-string and mixed enums
• supports array-based type definitions like ['string', 'null']
• infers object/array schemas from properties and items
• preserves schema default values
• throws on invalid or unsupported schema definitions instead of falling back to z.any()

I also added regression coverage in packages/components/nodes/tools/MCP/core.test.ts.

Verified with:
node --max-old-space-size=4096 .\node_modules\jest\bin\jest.js nodes/tools/MCP/core.test.ts --runInBand

Commit pushed: 6e596e0