Production Agent Patterns: Queues, Retries, Idempotency

// Vercel Workflow DevKit — modern "use workflow" directive
// Models are addressed via the AI Gateway alias format.
import { step } from 'workflow';
import { generateText } from 'ai';

export async function researchAgent(goal: string) {
  'use workflow';

  const plan = await step('plan', async () => {
    const { text } = await generateText({
      model: 'anthropic/claude-opus-4.7',
      prompt: `Break into sub-questions:\n${goal}`,
    });
    return text.split('\n');
  });

  const findings = [];
  for (const q of plan) {
    const answer = await step(`research:${q.slice(0, 20)}`, async () => {
      return await searchAndSummarize(q);
    }, { retries: 3, timeout: '60s' });
    findings.push({ q, answer });
  }

  return await step('synthesize', async () => {
    const { text } = await generateText({
      model: 'anthropic/claude-opus-4.7',
      prompt: `Write a cited answer:\n${JSON.stringify(findings)}`,
    });
    return text;
  });
}

// Idempotent Stripe charge
const chargeId = `task:${taskId}:step:${stepName}`;
const charge = await stripe.paymentIntents.create(
  { amount: 5000, currency: 'usd', customer: custId },
  { idempotencyKey: chargeId }
);
// Same chargeId on retry returns the same charge — no double-billing.

const MAX_STEPS = 50;
const MAX_COST_USD = 2.00;

let stepCount = 0;
let costUsd = 0;

while (!isDone(state)) {
  if (++stepCount > MAX_STEPS) {
    throw new Error('Step cap exceeded — possible loop.');
  }
  const { result, usage } = await runOneStep(state);
  costUsd += usage.inputTokens * 3/1_000_000 + usage.outputTokens * 15/1_000_000;
  if (costUsd > MAX_COST_USD) {
    throw new Error(`Cost cap exceeded: $${costUsd.toFixed(2)}`);
  }
  state = applyResult(state, result);
}