feat: add in-memory rate limiter

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/utils/rateLimit.js

@@ -0,0 +1,42 @@
+import logger from './logger.js';
+
+const rateLimitMap = new Map();
+
+export const checkRateLimit = (key) => {
+  const now = Date.now();
+  const windowMs = parseInt(process.env.RATE_LIMIT_WINDOW_MS, 10) || 60000;
+  const maxRequests = parseInt(process.env.RATE_LIMIT_MAX_REQUESTS, 10) || 30;
+
+  if (!rateLimitMap.has(key)) {
+    rateLimitMap.set(key, { count: 0, reset: now + windowMs });
+  }
+
+  const record = rateLimitMap.get(key);
+
+  if (now > record.reset) {
+    record.count = 0;
+    record.reset = now + windowMs;
+  }
+
+  if (record.count >= maxRequests) {
+    logger.warn('Rate limit exceeded', { key, count: record.count, reset: record.reset });
+    return false;
+  }
+
+  record.count++;
+  return true;
+};
+
+export const cleanupRateLimitCache = () => {
+  const now = Date.now();
+  const windowMs = parseInt(process.env.RATE_LIMIT_WINDOW_MS, 10) || 60000;
+  const keysToDelete = [];
+
+  for (const [key, record] of rateLimitMap.entries()) {
+    if (now > record.reset) {
+      keysToDelete.push(key);
+    }
+  }
+
+  keysToDelete.forEach(key => rateLimitMap.delete(key));
+};