Rate limiting and backpressure

import { ConcurrencyLimiter, TokenRateLimiter, type Agent } from "@agentium/core";

export function createLimitedRunner(agent: Agent) {
  const tokens = new TokenRateLimiter({
    maxTokensPerMinute: 100_000,
    maxRequestsPerMinute: 60,
    perTenant: true,
    perUser: true,
  });
  const concurrency = new ConcurrencyLimiter(5, 30_000);
  return async function run(
    input: string,
    identity: { tenantId: string; userId: string },
    sessionId: string,
    estimatedTokens: number,
  ) {
    if (!Number.isSafeInteger(estimatedTokens) || estimatedTokens <= 0) {
      throw new Error("estimatedTokens must be a positive integer");
    }
    const release = await concurrency.acquire();
    try {
      const admission = tokens.acquire(estimatedTokens, identity);
      if (!admission.allowed) throw new Error(`Retry after ${admission.resetMs} ms`);
      // If the run throws without final usage, retain its reservation:
      // a failed request can still have incurred provider usage.
      const result = await agent.run(input, { ...identity, sessionId });
      tokens.record(result.usage.totalTokens, estimatedTokens, identity);
      return result;
    } finally {
      release();
    }
  };
}