{
  "schema": "https://agent-atoms.com/schemas/atom-v1.json",
  "type": "tool-definition",
  "id": "send-message",
  "version": "1.0.0",
  "name": "send-message",
  "description": "Send a message to an external channel (Slack, email, etc.). External, side-effecting.",
  "tool_spec": {
    "function_name": "send_message",
    "summary": "Send a message to a channel.",
    "parameters": {
      "channel": { "type": "string", "description": "Channel identifier (slack://...; mailto:...)", "required": true },
      "subject": { "type": "string", "description": "Subject / title", "required": false },
      "body": { "type": "string", "description": "Message body", "required": true }
    },
    "returns": { "type": "object", "description": "{sent, message_id}." },
    "side_effects": ["network", "user-prompt"]
  }
}