apollo-rate-limits

# Apollo Rate Limits

## Overview
Implement robust rate limiting and backoff strategies for Apollo.io API to maximize throughput while avoiding 429 errors.

## Apollo Rate Limits

| Endpoint Category | Rate Limit | Window | Burst Limit |
|-------------------|------------|--------|-------------|
| People Search | 100/min | 1 minute | 10/sec |
| Person Enrichment | 100/min | 1 minute | 10/sec |
| Organization Enrichment | 100/min | 1 minute | 10/sec |
| Sequences/Campaigns | 50/min | 1 minute | 5/sec |
| Bulk Operations | 10/min | 1 minute | 2/sec |
| General API | 100/min | 1 minute | 10/sec |

## Rate Limit Headers

```bash
# Check current rate limit status
curl -I -X POST "https://api.apollo.io/v1/people/search" \
  -H "Content-Type: application/json" \
  -d '{"api_key": "'$APOLLO_API_KEY'", "per_page": 1}'

# Response headers:
# X-RateLimit-Limit: 100
# X-RateLimit-Remaining: 95
# X-RateLimit-Reset: 1640000000
# Retry-After: 60  (only when rate limited)
```

## Implementation: Rate Limiter Class

```typescript
// src/lib/apollo/rate-limiter.ts
interface RateLimiterConfig {
  maxRequests: number;
  windowMs: number;
  minSpacingMs: number;
}

class RateLimiter {
  private queue: Array<{
    resolve: (value: void) => void;
    reject: (error: Error) => void;
  }> = [];
  private requestTimestamps: number[] = [];
  private lastRequestTime = 0;
  private processing = false;

  constructor(private config: RateLimiterConfig) {}

  async acquire(): Promise<void> {
    return new Promise((resolve, reject) => {
      this.queue.push({ resolve, reject });
      this.processQueue();
    });
  }

  private async processQueue() {
    if (this.processing || this.queue.length === 0) return;
    this.processing = true;

    while (this.queue.length > 0) {
      // Clean old timestamps outside window
      const now = Date.now();
      this.requestTimestamps = this.requestTimestamps.filter(
        (ts) => now - ts < this.config.windowMs
      );

      // Check if we're at capaci