Set Stage Gate

{
  "success": true,
  "tool": {
    "id": "9a1b2c3d-0000-4000-8000-000000000001",
    "name": "check_availability",
    "available_in_statuses": ["qualified", "negotiating"]
  }
}

{
  "error": "Invalid input",
  "message": "available_in_statuses must be an array of status keys, or null to clear"
}

{
  "error": "Not found",
  "message": "Tool not found"
}