Leave all servers in parallel on shutdown

Quitting tells every server goodbye at once, so leaving takes as long as
the slowest server rather than all of them together. Desktop and Android
both go through ServerSession.shutdownAll.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/java/com/ts3client/android/ServerController.kt

@@ -117,11 +117,10 @@ class ServerController internal constructor(
         session.disconnect()
     }
 
-    /** Leaves the server before returning, for when the app goes away with the connection. */
+    /** Before the app goes away with the connection, which [SessionController.leave] then ends. */
-    internal fun leave() {
+    internal fun leaving() {
         left = true
         network.leaving()
-        session.shutdown()
     }
 
     internal fun dispose() {

android/app/src/main/java/com/ts3client/android/SessionController.kt

@@ -21,6 +21,7 @@ import com.ts3client.myts.MyTeamSpeak
 import com.ts3client.net.HostButton
 import com.ts3client.myts.MyTeamSpeakLogin
 import com.ts3client.session.SelfState
+import com.ts3client.session.ServerSession
 import com.ts3client.session.Sessions
 import com.ts3client.sound.SoundNotifier
 import com.ts3client.sound.SoundPack
@@ -199,7 +200,9 @@ class SessionController(private val context: Context) {
 
     /** Leaves every server before returning, for when the app goes away with the connections. */
     fun leave() {
-        _servers.value.forEach(ServerController::leave)
+        val servers = _servers.value
+        servers.forEach(ServerController::leaving)
+        ServerSession.shutdownAll(servers.map { it.session })
         contactStore.flush()
     }
 

ts3-client/core/src/main/java/com/ts3client/session/ServerSession.java

@@ -208,6 +208,27 @@ public final class ServerSession {
         if (isBusy()) conn.disconnectBlocking("Leaving");
     }
 
+    /**
+     * {@link #shutdown()}s every session at once, so leaving takes as long as the slowest
+     * server rather than all of them together: a frontend may have little time left.
+     */
+    public static void shutdownAll(List<ServerSession> sessions) {
+        List<Thread> leaving = new ArrayList<>();
+        for (ServerSession s : sessions) {
+            Thread t = new Thread(s::shutdown, "ts3-leave");
+            t.start();
+            leaving.add(t);
+        }
+        for (Thread t : leaving) {
+            try {
+                t.join();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                return;
+            }
+        }
+    }
+
     /** Releases the background resources of a session that is being thrown away. */
     public void dispose() {
         conn.getIcons().shutdown();

ts3-client/core/src/main/java/com/ts3client/session/Sessions.java

@@ -153,7 +153,7 @@ public final class Sessions {
 
     /** Leaves every server, waiting until each has been told. */
     public void shutdown() {
-        for (ServerSession s : new ArrayList<>(sessions)) s.shutdown();
+        ServerSession.shutdownAll(new ArrayList<>(sessions));
         handover.shutdown();
     }
 }