feat: Support Standard Schema

[dannote]

• Ported schema handling to Standard Schema with parsing support and async JSON Schema conversion.
• Removed Zod as a required peer dependency so users can bring their own Standard Schema library.
• Added a Valibot compatibility test to verify parsing and JSON Schema conversion.
• Updated dependencies to include the Standard Schema converter and Valibot tooling.

Motivation and Context

• Makes the SDK vendor-agnostic by relying on the Standard Schema interface instead of requiring Zod.
• Confirms interoperability with another Standard Schema provider (Valibot) while maintaining JSON Schema export support.

How Has This Been Tested?

• Full npm test suite
• npm test -- src/server/valibot-compat.test.ts

Breaking Changes

Zod is no longer a required peer dependency; users need to install their preferred Standard Schema library (e.g., Zod, Valibot).

Types of Changes

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional Context

• Standard Schema JSON conversion now routes non-Zod vendors through @standard-community/standard-json (async).

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/sdk@1155

commit: 222d0c8

[KKonstantinov]

Thanks for your work! Will review and maintainers will discuss.

[fabian-hiller]

I recommend taking a look at our new Standard JSON Schema spec RFC: standard-schema/standard-schema#134

[rektide]

I've started playing around with converting this PR to Standard JSON Schema. There's a lot I don't understand in this code-base, but perhaps what I have might motivate others some or provoke some discussion: dannote#1

Is there a compelling reason to keep Zod v3? I realize v4 isn't even a year old yet. But the last PR in that stack removes v3 support & it feels like a lot of complexity is just gone, including our vendored Zod v3 instance. Would be a nice strong move towards #164.

[felixweinberger]

Thanks for this, superseded by #1689. Closing.