feat(server): accept Standard Schemas for elicitation

[mattzcarey]

Fixes #662.

Allows Server.elicitInput() and ctx.mcpReq.elicitInput() to accept a Standard Schema/Zod object as requestedSchema, converts it to the existing JSON Schema wire shape, and keeps JSON Schema input working unchanged.

Verification:

• pnpm --filter @modelcontextprotocol/server test -- jsonSchemaValidatorOverride.test.ts
• pnpm --filter @modelcontextprotocol/core typecheck
• pnpm --filter @modelcontextprotocol/server typecheck
• pnpm --filter @modelcontextprotocol/core lint
• pnpm --filter @modelcontextprotocol/server lint
• pnpm --filter @modelcontextprotocol/server build
• pre-push hook: pnpm run typecheck:all, pnpm run build:all, pnpm run lint:all
• git diff --check

[changeset-bot]

🦋 Changeset detected

Latest commit: 12eb9e5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@modelcontextprotocol/core-internal	Minor
@modelcontextprotocol/server	Minor
@modelcontextprotocol/client	Minor
@modelcontextprotocol/express	Major
@modelcontextprotocol/fastify	Major
@modelcontextprotocol/hono	Major
@modelcontextprotocol/node	Major

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commit: 12eb9e5

[felixweinberger]

SGTM

[felixweinberger]

Mostly wondering if we should be updating the elicitInput API given we want people to use inputRequired for MRTR going forward.

[felixweinberger]

This is deprecated API, we don't really want people to continue you building on this, but consolidate on the inputRequired form - there's a backwards compatibility shim that allows people to write the MRTR based elicitation but still serve 2025-11-25 based servers with it.

Given that, I feel like we should instead mark this API @deprecated and not take on the effort of making it StandardSchema compatible.

[felixweinberger]

That would also remove the need for the overload introduced further down.

[felixweinberger]

Ah I see it's already marked deprecated here - rather than make it compatible with standard schema should we keep it simple and leave this out and push people to use inputRequired if they want to use standardSchema?

[felixweinberger]

I believe this could be cleaned up with something like this?

elicit(params: ElicitInputParams): InputRequest {
    try {
        const { params: normalizedParams } = normalizeElicitInputFormParams(params);
        return { method: 'elicitation/create', params: normalizedParams };
    } catch (error) {
        throw error instanceof ProtocolError ? new TypeError(error.message, { cause: error }) : error;
    }
},

Instead of the type assertions & Omit<...>s?