feat: auto-run host doctor when hosting fails to start at boot

Prints the full diagnosis checklist to the server log via
HostDoctor.logReport, so admins get the exact config fix without
having to know the doctor command exists.

Author: Skidamek

core/src/main/java/pl/skidam/automodpack_core/protocol/HostDoctor.java

@@ -27,6 +27,19 @@ public enum Status { OK, INFO, WARN, FAIL }
 
     public record CheckResult(Status status, String name, String detail) {}
 
+    // Logs the checklist - used when hosting fails at boot, where no command source exists.
+    // Pass minecraftPort -1 when unknown.
+    public static void logReport(int minecraftPort) {
+        for (CheckResult result : run(minecraftPort)) {
+            String line = "[" + result.status() + "] " + result.name() + (result.detail().isEmpty() ? "" : " - " + result.detail());
+            switch (result.status()) {
+                case FAIL -> LOGGER.error(line);
+                case WARN -> LOGGER.warn(line);
+                default -> LOGGER.info(line);
+            }
+        }
+    }
+
     public static List<CheckResult> run(int minecraftPort) {
         List<CheckResult> results = new ArrayList<>();
 
@@ -101,8 +114,9 @@ private static void checkTls(List<CheckResult> results) {
 
     private static void checkPorts(List<CheckResult> results, int minecraftPort) {
         if (serverConfig.bindPort == -1) {
+            String mcPort = minecraftPort > 0 ? String.valueOf(minecraftPort) : "?";
             results.add(new CheckResult(Status.INFO, "Port setup",
-                    "sharing the Minecraft port (" + minecraftPort + ") using magic packets - proxies and DDoS protection (Velocity, BungeeCord, TCPShield...) usually break this; if clients get connection errors, set bindPort to a free port and portToSend to how it is reachable from outside"));
+                    "sharing the Minecraft port (" + mcPort + ") using magic packets - proxies and DDoS protection (Velocity, BungeeCord, TCPShield...) usually break this; if clients get connection errors, set bindPort to a free port and portToSend to how it is reachable from outside"));
         } else if (serverConfig.portToSend == -1) {
             results.add(new CheckResult(Status.FAIL, "Port setup",
                     "bindPort is " + serverConfig.bindPort + " but portToSend is -1, so clients will try the Minecraft port and fail - set portToSend to " + serverConfig.bindPort + " (or to the externally forwarded port)"));

src/main/java/pl/skidam/automodpack/init/Common.java

@@ -6,6 +6,7 @@
 import pl.skidam.automodpack.networking.ModPackets;
 import pl.skidam.automodpack_core.modpack.ModpackExecutor;
 import pl.skidam.automodpack_core.loader.LoaderManagerService;
+import pl.skidam.automodpack_core.protocol.HostDoctor;
 import pl.skidam.automodpack_core.protocol.netty.NettyServer;
 
 import java.util.HashMap;
@@ -52,6 +53,11 @@ public static void afterSetupServer() {
         }
 
         hostServer.start();
+
+        if (serverConfig.modpackHost && !hostServer.isRunning()) {
+            LOGGER.error("Modpack host failed to start - running diagnosis:");
+            HostDoctor.logReport(-1);
+        }
     }
 
     public static void beforeShutdownServer() {