refactor: manage monitor via gateway hooks

plugin/core/managed-monitor.ts

@@ -0,0 +1,51 @@
+import { spawn, type ChildProcess } from 'child_process';
+import { existsSync } from 'fs';
+
+export interface ManagedMonitorConfig {
+  managedMonitor?: string;
+  monitor_port?: number;
+  logLevel?: string;
+}
+
+let monitorProcess: ChildProcess | null = null;
+
+export function startManagedMonitor(
+  logger: { info: (...args: any[]) => void; warn: (...args: any[]) => void; error: (...args: any[]) => void },
+  config: ManagedMonitorConfig,
+): void {
+  if (!config.managedMonitor) return;
+  if (monitorProcess) {
+    logger.info('HarborForge managed monitor already running');
+    return;
+  }
+  if (!existsSync(config.managedMonitor)) {
+    logger.warn(`HarborForge managed monitor path not found: ${config.managedMonitor}`);
+    return;
+  }
+
+  const args: string[] = [];
+  if (config.monitor_port) args.push('--port', String(config.monitor_port));
+  if (config.logLevel) args.push('--log-level', String(config.logLevel));
+
+  monitorProcess = spawn(config.managedMonitor, args, {
+    stdio: 'inherit',
+    detached: false,
+  });
+
+  monitorProcess.on('exit', (code, signal) => {
+    logger.warn(`HarborForge managed monitor exited code=${code ?? 'null'} signal=${signal ?? 'null'}`);
+    monitorProcess = null;
+  });
+
+  logger.info(`HarborForge managed monitor started: ${config.managedMonitor}`);
+}
+
+export function stopManagedMonitor(
+  logger: { info: (...args: any[]) => void; warn: (...args: any[]) => void },
+): void {
+  if (!monitorProcess) return;
+  const pid = monitorProcess.pid;
+  monitorProcess.kill('SIGTERM');
+  monitorProcess = null;
+  logger.info(`HarborForge managed monitor stopped pid=${pid ?? 'unknown'}`);
+}