Return protocol errors for invalid tool arguments

[FU-max-boop]

Summary

Fixes #2162.

Invalid tool arguments are request-level validation failures, but McpServer was wrapping input schema validation failures in a CallToolResult with isError: true. This rethrows input validation ProtocolErrorCode.InvalidParams errors so clients receive a protocol error for malformed tool calls, while preserving tool execution errors as CallToolResult failures.

The tests update the existing Zod, union, ArkType, Valibot, and JSON Schema invalid-input cases to assert InvalidParams instead of tool error content.

Tests

• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server test -- mcp.test.ts standardSchema.test.ts
• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server lint
• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server typecheck
• npx -y pnpm@10.26.1 --filter @modelcontextprotocol/server build
• git diff --check HEAD~1..HEAD

Note: git push hit repeated network timeouts to github.com:443 from this environment, so I created the fork branch via the GitHub Git Data API after the local checks passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: eaf4444

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

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/server	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@2173

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/codemod@2173

@modelcontextprotocol/server

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@2173

@modelcontextprotocol/express

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@2173

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/fastify@2173

@modelcontextprotocol/hono

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@2173

@modelcontextprotocol/node

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@2173

commit: eaf4444

[FU-max-boop]

CI note: the Node 20/22 failures are both in test/server/cloudflareWorkers.test.ts with Miniflare reporting Network connection lost. The Node 24 job passed the same suite, and the local server-focused checks in the PR body passed. I tried to rerun failed jobs, but GitHub requires repository admin rights for reruns from this fork.

[FU-max-boop]

Closing this because it duplicates my earlier PR #2169 for the same issue (#2162). #2169 is already open and has the full check suite green, so keeping one thread should be easier for maintainers.