[BUG] MCP numeric parameters broken in v2.1.33 - Go-based MCP servers fail with float64 type assertion

Bug Description

After upgrading from Claude Code 2.1.32 to 2.1.33, all MCP tools that accept numeric parameters fail on Go-based MCP servers. The server expects float64 type (standard Go JSON unmarshaling behavior for interface{}), but Claude Code 2.1.33 appears to send the value in an incompatible format (likely as a string or different numeric type).

Error Messages

parameter pullNumber is not of type float64

or:

'PullNumber' expected type 'int32', got unconvertible type 'string'

Affected Versions

| Version | Status |
|---------|--------|
| 2.1.30 | ✅ Working |
| 2.1.32 | ✅ Working |
| 2.1.33 | ❌ Broken |

This is a regression introduced in 2.1.33.

Reproduction Steps

1. Set up a Go-based MCP server (e.g., github-mcp-server using mcp-go v0.32.0)
2. Configure it in Claude Code settings
3. Call any tool that requires a numeric parameter (e.g., get_pull_request with pullNumber: 17415)
4. On v2.1.32: works fine
5. On v2.1.33: fails with the error above

Scope of Impact

All MCP tools with numeric parameters are affected, including:

• get_pull_request (pullNumber)
• get_pull_request_reviews (pullNumber)
• get_pull_request_diff (pullNumber)
• get_pull_request_files (pullNumber)
• add_issue_comment (issue_number)
• get_issue_comments (issue_number)
• Any other tool accepting numeric parameters

String-only parameter tools work fine:

• search_pull_requests (query: string) → works
• list_pull_requests → works

Root Cause Analysis

The MCP server's Go code uses standard JSON unmarshaling where numbers in interface{} become float64:

// mcp-go server.go
func RequiredInt(r mcp.CallToolRequest, p string) (int, error) {
    v, err := RequiredParam[float64](r, p)  // expects float64 type assertion
    ...
}

The MCP server itself works correctly when called directly via JSON-RPC:

echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{...}}
{"jsonrpc":"2.0","method":"notifications/initialized"}
{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"get_pull_request","arguments":{"owner":"BAND","repo":"BAND_iOS","pullNumber":17415}}}' | docker run -i --rm server-image

This returns data correctly, confirming the issue is in how Claude Code 2.1.33 serializes numeric parameters before sending them to the MCP server.

Environment

• OS: macOS (Darwin 25.2.0)
• MCP Server: github-mcp-server (Go, mcp-go v0.32.0) running in Podman container
• Transport: stdio