curl -X POST https://win.oneshotagent.com/v1/compute/goal_01HX8K3YZ/cancel \
  -H "Content-Type: application/json" \
  -H "X-Agent-ID: 0xYourWalletAddress" \
  -d '{ "reason": "Changed requirements" }'

{
  "success": true,
  "data": {
    "goal_id": "goal_01HX8K3YZ...",
    "status": "cancelled",
    "remaining_budget": "3.350000",
    "message": "Goal cancelled. Remaining budget will be credited."
  }
}