refactor: logging and improved multiplex handling

server/build.gradle.kts

@@ -16,6 +16,8 @@ repositories {
 
 dependencies {
     implementation("io.vertx:vertx-core:5.1.5")
+    implementation("org.apache.logging.log4j:log4j-core:2.26.0")
+    implementation("org.apache.logging.log4j:log4j-jul:2.26.0")   // route Netty/JUL fallback -> log4j2
     testImplementation("org.junit.jupiter:junit-jupiter:5.10.2")
     testRuntimeOnly("org.junit.platform:junit-platform-launcher:1.10.2")
 }
@@ -28,6 +30,11 @@ java {
 
 application {
     mainClass = "io.icybear.redapricot.Main"
+    // Route java.util.logging (Netty's fallback) through Log4j2 on the `run`/`installDist`
+    // launch paths. The `java -jar` shadow-jar path sets this programmatically in Main.
+    applicationDefaultJvmArgs = listOf(
+        "-Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager"
+    )
 }
 
 tasks.test {