fix(linux): a session logout should hand the peer to the login screen (#15905)

* fix(linux): a session logout should hand the peer to the login screen

Logging out closes every window in the session, the connection manager's
included, and its close handler kicks every peer with the reason a person
gets when they disconnect one by hand. That reason is the one thing the
client never retries on, so the remote session dies on a frozen frame
instead of reconnecting to the greeter that is already there.

The close carries nothing to tell the two apart: measured on KDE, the CM
receives no signal and logind still reports the session active at that
instant, and the server is killed within a few hundred ms either way, so
neither a state check nor a grace period can decide it. What is
distinguishable is the ACTION: disconnecting a peer is not the same event
as this window going away. So the window-close path now says so, and the
server ends the session without poisoning the retry; the Disconnect
button and the app's own close control keep kicking exactly as before.
Linux only, since that is where a logout closes the window.

Verified on plasma/sddm with a client attached: a logout now reconnects
to the greeter with no dialog, while closing the manager window still
shows Closed manually by the peer.

* fix(linux): close the tunnel too, and keep the web build compiling

Three seams the first pass missed. The web bridge is hand written, not
generated, so the new call needs its stub there or flutter build web
stops compiling - and that job is disabled in CI, so it would have gone
green. try_port_forward_loop is a second consumer of the same channel
and only knew Close, so a forwarded tunnel outlived the window it was
supposed to die with. And the variant had landed inside the DRM section,
whose comment says everything below it is drm-gated.

flutter/lib/desktop/pages/server_page.dart

@@ -22,6 +22,14 @@ import '../../models/file_model.dart';
 import '../../models/platform_model.dart';
 import '../../models/server_model.dart';
 
+/// Set only by this window's own close control, and only once the user has confirmed. Any other
+/// way the window can go - a session logout closing every window, the window manager, a native
+/// title-bar button this app does not draw - leaves it false, which is the honest answer:
+/// nothing in that close says who asked for it. It lives at file scope because the control that
+/// sets it (`ConnectionManagerState`) and the handler that reads it (`_DesktopServerPageState`)
+/// are different widgets.
+bool _cmClosedByOperator = false;
+
 class DesktopServerPage extends StatefulWidget {
   const DesktopServerPage({Key? key}) : super(key: key);
 
@@ -55,7 +63,10 @@ class _DesktopServerPageState extends State<DesktopServerPage>
 
   @override
   void onWindowClose() {
-    Future.wait([gFFI.serverModel.closeAll(), gFFI.close()]).then((_) {
+    // Other platforms keep the old behaviour exactly: the ambiguity this guards against is a
+    // Linux session logout, which closes every window in the session.
+    final byOperator = _cmClosedByOperator || !isLinux;
+    Future.wait([gFFI.serverModel.closeAll(byOperator: byOperator), gFFI.close()]).then((_) {
       if (isMacOS) {
         RdPlatformChannel.instance.terminate();
       } else {
@@ -327,6 +338,7 @@ class ConnectionManagerState extends State<ConnectionManager>
     var tabController = gFFI.serverModel.tabController;
     final connLength = tabController.length;
     if (connLength <= 1) {
+      _cmClosedByOperator = true;
       windowManager.close();
       return true;
     } else {
@@ -338,6 +350,9 @@ class ConnectionManagerState extends State<ConnectionManager>
         res = await closeConfirmDialog();
       }
       if (res) {
+        // After the dialog, never before it: an external close while it is open must not
+        // inherit an intent the user had not expressed yet.
+        _cmClosedByOperator = true;
         windowManager.close();
       }
       return res;

flutter/lib/models/server_model.dart

@@ -738,9 +738,13 @@ class ServerModel with ChangeNotifier {
     }
   }
 
-  Future<void> closeAll() async {
-    await Future.wait(
-        _clients.map((client) => bind.cmCloseConnection(connId: client.id)));
+  /// `byOperator` false means the CM's window went away rather than a person asking for the
+  /// peers to go. The sessions end either way; only the close reason differs, and with it
+  /// whether the peer is allowed to reconnect. See `ipc::Data::CmWindowClosed`.
+  Future<void> closeAll({bool byOperator = true}) async {
+    await Future.wait(_clients.map((client) => byOperator
+        ? bind.cmCloseConnection(connId: client.id)
+        : bind.cmCloseConnectionWindow(connId: client.id)));
     _clients.clear();
     tabController.state.value.tabs.clear();
     if (isAndroid) androidUpdatekeepScreenOn();

flutter/lib/web/bridge.dart

@@ -1373,6 +1373,10 @@ class RustdeskImpl {
     throw UnimplementedError("cmLoginRes");
   }
 
+  Future<void> cmCloseConnectionWindow({required int connId, dynamic hint}) {
+    throw UnimplementedError("cmCloseConnectionWindow");
+  }
+
   Future<void> cmCloseConnection({required int connId, dynamic hint}) {
     throw UnimplementedError("cmCloseConnection");
   }