[JS] Tool calls to tools registered by the MCP plugin don't always work.

[gspencergoog]

Describe the bug
Tool calls to tools registered by the MCP plugin don't always work.

Sometimes when calling a tool using Gemini 2.0-Flash, I get output similar to:

{
  "response": "```tool_code\nprint(default_api.search_nodes(query='Greg'))\n```"
}

Rather than an actual tool call. Sometimes it does actually call the tool correctly, though.

I think this is because Gemini is sometimes wrapping the tool call with the code markdown markers and/or just forgetting that the tool is registered.

I'm referring to the tool by its registered name in both the prompt header and the body of the prompt.

To Reproduce

Use this query:

{
  "prompt": "Hi, my name is Greg. Am I in your memory?"
}

on the mcpFlow for the genkit project in this .tar.gz file: genkit_issue.tar.gz

Expected behavior
I would expect the tool to be called and the result to be structured output from the tool.

The correct response would be something like "Yes, you are in my memory: you like Genkit".

Runtime (please complete the following information):

• OS: Linux
• Version 6.12.12-1rodete2-amd64

** Node version

• v20.18.1

[gspencergoog]

It appears that this might have to do with calling conventions for tools which take no arguments. When the example app attached to the original report above tries to call "read_graph" (which takes no arguments), it receives a MALFORMED_FUNCTION_CALL finish reason. When it tries to call "search_nodes", it succeeds. If I then change the definition of the read graph tool from:

      {
        name: 'read_graph',
        description: 'Read the entire knowledge graph',
        inputSchema: {
          type: 'object',
          properties: {},
          required: [],
        },
      },

to:

      {
        name: 'read_graph',
        description: 'Read the entire knowledge graph',
        inputSchema: {
          type: 'object',
          properties: {
            unused: {type: 'string', description: 'An unused optional parameter'},
          },
          required: [],
        },
      },

then calling "read_graph" works properly.