feat: add Executor Pool with concurrency control

server/scheduler/executor-pool.ts

@@ -0,0 +1,50 @@
+import log4js from "logger";
+
+const logger = log4js.getLogger("SCHEDULER");
+
+type QueuedTask = {
+  run: () => void;
+};
+
+export class ExecutorPool {
+  private running = 0;
+  private queue: QueuedTask[] = [];
+  private maxConcurrency: number;
+
+  constructor(maxConcurrency = 5) {
+    this.maxConcurrency = maxConcurrency;
+  }
+
+  get activeCount(): number {
+    return this.running;
+  }
+
+  get queuedCount(): number {
+    return this.queue.length;
+  }
+
+  async execute(fn: () => Promise<void>): Promise<void> {
+    if (this.running >= this.maxConcurrency) {
+      logger.info(
+        "Pool full (%d/%d), queuing task (%d in queue)",
+        this.running,
+        this.maxConcurrency,
+        this.queue.length + 1
+      );
+      await new Promise<void>((resolve) => {
+        this.queue.push({ run: resolve });
+      });
+    }
+
+    this.running++;
+    try {
+      await fn();
+    } finally {
+      this.running--;
+      const next = this.queue.shift();
+      if (next) {
+        next.run();
+      }
+    }
+  }
+}