make kestrel a tak server, so that it can send and receive pois as cots data

server/utils/asyncLock.js

@@ -0,0 +1,39 @@
+/**
+ * Async lock utility - Promise-based mutex per key.
+ * Ensures only one async operation executes per key at a time.
+ */
+
+const locks = new Map()
+
+/**
+ * Acquire a lock for a key and execute callback.
+ * Only one callback per key executes at a time.
+ * @param {string} key - Lock key
+ * @param {Function} callback - Async function to execute
+ * @returns {Promise<any>} Result of callback
+ */
+export async function acquire(key, callback) {
+  const lockKey = String(key)
+  let queue = locks.get(lockKey)
+
+  if (!queue) {
+    queue = Promise.resolve()
+    locks.set(lockKey, queue)
+  }
+
+  const next = queue.then(() => callback()).finally(() => {
+    if (locks.get(lockKey) === next) {
+      locks.delete(lockKey)
+    }
+  })
+
+  locks.set(lockKey, next)
+  return next
+}
+
+/**
+ * Clear all locks (for testing).
+ */
+export function clearLocks() {
+  locks.clear()
+}