Let a session reconnect to where it was

ServerSession.reconnect() connects again to the last server with the
same identity and returns to the channel the client was in: what a
dropped connection or a changed network (Android moving from Wi-Fi to
mobile data) needs.

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

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

@@ -56,6 +56,13 @@ public final class ServerSession {
     private volatile boolean connecting;
     /** Identity used for the current connection, so it can be saved into a bookmark. */
     private volatile String identityId = "";
+    /** How the last connect was made, for {@link #reconnect}; null before the first one. */
+    private volatile Target lastTarget;
+    /** The channel we were in when the connection last went, to return to on a reconnect. */
+    private volatile String lastChannelPath = "";
+
+    private record Target(String address, int port, String nickname, String password, String channelPassword) {
+    }
 
     private volatile boolean micMuted;
     private volatile boolean micLocalMuted;
@@ -120,6 +127,8 @@ public final class ServerSession {
             if (isBusy()) return;
             connecting = true;
         }
+        lastTarget = new Target(address, port, nickname, password, channelPassword);
+        lastChannelPath = channel == null ? "" : channel;
         title = address + ":" + port;
         listener.onSystemMessage("Connecting to " + address + ":" + port
                 + (channel == null || channel.isBlank() ? "" : " (channel \"" + channel + "\")") + " …");
@@ -158,6 +167,19 @@ public final class ServerSession {
         }, "ts3j-switch-server").start();
     }
 
+    /**
+     * Connects again to the server of the last connect, with the same identity, returning to
+     * the channel we were in — for a connection that dropped, or a network that changed.
+     * Leaves the server first if still on it. Does nothing before a first connect.
+     */
+    public void reconnect() {
+        Target target = lastTarget;
+        if (target == null) return;
+        String channel = conn.isConnected() ? currentChannelPath() : lastChannelPath;
+        switchTo(target.address(), target.port(), target.nickname(), target.password(), identityId,
+                channel, target.channelPassword());
+    }
+
     public void disconnect() {
         if (conn.isConnected()) conn.disconnect();
     }
@@ -393,6 +415,9 @@ public final class ServerSession {
 
         @Override
         public void onModelChanged() {
+            // By the time a connection is reported gone, it no longer knows where we were.
+            String channel = currentChannelPath();
+            if (!channel.isEmpty()) lastChannelPath = channel;
             String name = conn.getModel().getServerName();
             if (conn.isConnected() && name != null && !name.isBlank() && !name.equals(title)) {
                 title = name;