I don't know how long the agent loop runs. Without a limit, the cost seemed likely to be higher than expected. Therefore, I decided to create a library to limit the cost. It's not complex as it blocks with purely simple code. I'm developing it little by little during my breaks.

  npm install budget-guard

  const ai = guard(openai.chat.completions, {project: 'app', dailyCapUSD: 50});
  await ai.create({ model: 'gpt-5.6', messages }, { feature: 'summarize' });

The current default behavior is blocking. I'm wondering if it would be better to use warning messages and callback functions. Any feedback is appreciated.