[BUG] Bug: HTTP MCP server array parameters are serialized as strings instead of arrays

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug Description

When calling tools on an HTTP-type MCP server, array parameters are
sent as JSON strings instead of JSON arrays, causing validation errors.

Environment

• Claude Code version: 2.1.71
• OS: macOS
• MCP server type: HTTP (https://ai.todoist.net/mcp)

Steps to Reproduce

1. Configure an HTTP MCP server in .claude.json:

{
  "mcpServers": {
    "todoist": {
      "type": "http",
      "url": "https://ai.todoist.net/mcp",
      "headers": {
        "Authorization": "Bearer <token>"
      }
    }
  }
}


### What Should Happen?

Array parameters should be sent to HTTP MCP servers as proper JSON arrays, not as JSON strings.

Expected request body:
{"tasks": [{"id": "xxx", "content": "yyy"}]}

Currently sent as:
{"tasks": "[{\"id\": \"xxx\", \"content\": \"yyy\"}]"}


### Error Messages/Logs

```shell
Attempting to call update-tasks tool on Todoist HTTP MCP server 
(https://ai.todoist.net/mcp) resulted in the following error:

MCP error -32602: Input validation error: Invalid arguments for tool update-tasks: [
  {
    "expected": "array",
    "code": "invalid_type",
    "path": ["tasks"],
    "message": "Invalid input: expected array, received string"
  }
]

The same error occurs with all write tools that require array parameters:
- add-tasks (parameter: "tasks")
- update-tasks (parameter: "tasks")  
- complete-tasks (parameter: "ids")
- add-comments (parameter: "comments")

Steps to Reproduce

1. Configure an HTTP MCP server in .claude.json:

{
"mcpServers": {
"todoist": {
"type": "http",
"url": "https://ai.todoist.net/mcp",
"headers": {
"Authorization": "Bearer <YOUR_TOKEN>"
}
}
}
}

1. Ask Claude Code to update a task using the update-tasks tool:

"Please update task ID 'xxx' with content 'yyy'"

1. Claude Code calls the update-tasks tool with the following parameter:

tasks = [{"id": "xxx", "content": "yyy"}]

1. MCP server returns validation error:

"expected array, received string"

1. For comparison, calling the same MCP server directly via curl

with identical parameters succeeds:

curl -X POST https://ai.todoist.net/mcp \
-H "Content-Type: application/json" \
-H "Accept: application/json, text/event-stream" \
-H "Authorization: Bearer <YOUR_TOKEN>" \
-d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"update-tasks","arguments":{"tasks":[{"id":"xxx","content":"yyy"}]}}}'

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.71

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_