MCP server returns "Field required [type=missing, input_value={}, input_type=dict]" for valid convert_to_markdown input

Describe the bug

When calling the convert_to_markdown tool via HTTP with a valid uri (either a local file or a public internet PDF), the server responds with a validation error stating that the required field uri is missing, even though it is present in the request.

To Reproduce

1. Start the MCP server in HTTP mode (Docker or pip install, both tested).
2. Send the following JSON-RPC request (example with a public PDF):

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "convert_to_markdown",
    "input": {
      "uri": "https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf"
    }
  },
  "id": "2"
}

With headers:

Content-Type: application/json
Accept: application/json, text/event-stream

3. The response is:

{
  "jsonrpc": "2.0",
  "id": "2",
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Error executing tool convert_to_markdown: 1 validation error for convert_to_markdownArguments\nuri\n  Field required [type=missing, input_value={}, input_type=dict]\n    For further information visit https://errors.pydantic.dev/2.11/v/missing"
      }
    ],
    "isError": true
  }
}

Expected behavior

The server should recognize the uri field and process the file, returning the Markdown result or a relevant error if the file cannot be accessed.

Additional context

• The same error occurs for both local files (with correct Docker volume mount and file path) and public URLs.
• The request JSON matches the tool schema returned by tools/list.
• MCP server version: (please specify Docker image hash or pip version)
• Example debug output and full request/response attached.

Environment

• OS: [Windows 11]
• MCP server version: [Docker image hash or pip version]
• How you started the server: [docker run --rm -i -v C:\Example\Path\Stuff:/workdir -p 3001:3001 markitdown-mcp:latest --http --host 0.0.0.0 --port 3001]

Start by tracing the HTTP JSON-RPC tools/call handling for the convert_to_markdown entry point, then compare how its input is forwarded with the schema returned by tools/list. Done means the uri reaches validation and both local-file and public-URL requests return Markdown or a relevant access error.