Anthropic LLM failed to generate agent: Tool 'json' not found in provided tools

[atomicpages]

Description

Tested with Sonnet 4.5 and Opus 4.5 + 4.6. I pulled the latest from dev on github and have the full error detailed below. I see the JSON tools id efined

{
  "name": "AI_APICallError",
  "url": "https://api.anthropic.com/v1/messages",
  "requestBodyValues": {
    "model": "claude-sonnet-4-5-20250929",
    "max_tokens": 64000,
    "temperature": 0.3,
    "system": [
      {
        "type": "text",
        "text": "You are Claude Code, Anthropic's official CLI for Claude."
      },
      {
        "type": "text",
        "text": "...."
      }
    ],
    "messages": [
      {
        "role": "user",
        "content": [
          {
            "type": "text",
            "text": "..."
          }
        ]
      }
    ],
    "tools": [
      {
        "name": "json",
        "description": "Respond with a JSON object.",
        "input_schema": {
          "$schema": "http://json-schema.org/draft-07/schema#",
          "type": "object",
          "properties": {
            "identifier": {
              "type": "string"
            },
            "whenToUse": {
              "type": "string"
            },
            "systemPrompt": {
              "type": "string"
            }
          },
          "required": ["identifier", "whenToUse", "systemPrompt"],
          "additionalProperties": false
        }
      }
    ],
    "tool_choice": {
      "type": "tool",
      "name": "json",
      "disable_parallel_tool_use": true
    }
  },
  "statusCode": 400,
  "responseBody": "{\"type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"Tool 'json' not found in provided tools\"},\"request_id\":\"****\"}",
  "isRetryable": false,
  "data": {
    "type": "error",
    "error": {
      "type": "invalid_request_error",
      "message": "Tool 'json' not found in provided tools"
    }
  }
}

I had Opus take a crack at fixing it and the problem seems to be resolved. Here's a copy of my session: session-ses_37bf.md I'm happy to make a PR with this fix if it's fine. LMK!

Plugins

None

OpenCode version

1.2.10

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

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Terminal

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