Adding a heartbeat, avoiding dying cause of one failure.

src/main.rb

@@ -59,6 +59,7 @@ def main
   grace_deadline = Time.now + INITIAL_GRACE
   while Time.now < grace_deadline
     sleep 5
+    SystemdNotifier.notify('WATCHDOG=1')
     next unless ServerStatusDetector::MinecraftServer.self_diag[:type]
 
     MethodExecutor.record('info', 'mainloop',

src/systemd_notifier.rb

@@ -52,7 +52,6 @@ class SystemdNotifier
       MethodExecutor.record('debug', 'heartbeat', "Heartbeat sent: #{message}")
     rescue StandardError => e
       MethodExecutor.record('error', 'heartbeat', "Failed to send heartbeat: #{e}")
-      @enable_heartbeat = false
     end
   end
 end