fix(OpenAi Node): Allow additionalProperties: {} in tools

[yehorkardash]

Summary

This PR fixes a bug when OpenAi node couldn't call some tools that passed additionalProperties: {} together with strict: true.

In that case it OpenAi throws Invalid schema for function 'function_name': In context=('additionalProperties',), schema must have a 'type' key.

This fix replaces empty objects when strict is true to false.

The simplest reproduction is to use MCP trigger workflow and call it in OpenAI node
When only url can be defined by AI, and it's the only required property, strict is true which caused this error.

{
  "nodes": [
    {
      "parameters": {
        "path": "c79b11d9-3cda-41fa-b61e-3dcbbbaf23a0"
      },
      "type": "@n8n/n8n-nodes-langchain.mcpTrigger",
      "typeVersion": 2,
      "position": [
        0,
        0
      ],
      "id": "09943e91-2637-410e-8906-90d1ec83df5d",
      "name": "MCP Server Trigger",
      "webhookId": "c79b11d9-3cda-41fa-b61e-3dcbbbaf23a0"
    },
    {
      "parameters": {
        "toolDescription": "Makes http POST request using provided url and json",
        "method": "POST",
        "url": "={{ /*n8n-auto-generated-fromAI-override*/ $fromAI('URL', ``, 'string') }}",
        "options": {}
      },
      "type": "n8n-nodes-base.httpRequestTool",
      "typeVersion": 4.3,
      "position": [
        96,
        240
      ],
      "id": "05e2bb28-d517-41f3-9b1d-869aae3bd794",
      "name": "make_http_request"
    }
  ],
  "connections": {
    "make_http_request": {
      "ai_tool": [
        [
          {
            "node": "MCP Server Trigger",
            "type": "ai_tool",
            "index": 0
          }
        ]
      ]
    }
  },
  "pinData": {},
  "meta": {
    "instanceId": "869de6ef8ff5644147e5589ff5c9f86171de90b2c3bb7db31c1025ea70eaa896"
  }
}

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/NODE-3828/community-issue-openai-node-built-in-mcp-eliminated-but-n8n-mcps-are
closes #21272

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[codecov]

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✅ All modified and coverable lines are covered by tests.

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[cubic-dev-ai]

No issues found across 2 files