Follow KWin's layout service when it appears later

getLayout is asked asynchronously, and again whenever org.kde.keyboard
registers, so a late start or a KWin restart no longer leaves the globe
key switching only locally.

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

src/app/SystemLayouts.cpp

@@ -2,7 +2,9 @@
 
 #include <QDBusConnection>
 #include <QDBusMessage>
-#include <QDBusReply>
+#include <QDBusPendingCallWatcher>
+#include <QDBusPendingReply>
+#include <QDBusServiceWatcher>
 
 namespace {
 const QString Service = QStringLiteral("org.kde.keyboard");
@@ -21,12 +23,26 @@ SystemLayouts::SystemLayouts(QObject *parent)
     : QObject(parent)
 {
     QDBusConnection bus = QDBusConnection::sessionBus();
-    const QDBusReply<uint> reply = bus.call(call(QStringLiteral("getLayout")));
-    m_system = reply.isValid();
-    if (!m_system)
-        return;
-    m_current = reply.value();
+    // Follows the service's owner, so it survives KWin restarting.
     bus.connect(Service, Path, Interface, QStringLiteral("layoutChanged"), this, SLOT(setCurrent(uint)));
+    auto *watcher = new QDBusServiceWatcher(Service, bus, QDBusServiceWatcher::WatchForOwnerChange, this);
+    connect(watcher, &QDBusServiceWatcher::serviceRegistered, this, &SystemLayouts::fetchCurrent);
+    connect(watcher, &QDBusServiceWatcher::serviceUnregistered, this, [this] { m_system = false; });
+    fetchCurrent();
+}
+
+void SystemLayouts::fetchCurrent()
+{
+    auto *watcher = new QDBusPendingCallWatcher(
+        QDBusConnection::sessionBus().asyncCall(call(QStringLiteral("getLayout"))), this);
+    connect(watcher, &QDBusPendingCallWatcher::finished, this, [this](QDBusPendingCallWatcher *watcher) {
+        watcher->deleteLater();
+        const QDBusPendingReply<uint> reply = *watcher;
+        if (reply.isError())
+            return;
+        m_system = true;
+        setCurrent(reply.value());
+    });
 }
 
 void SystemLayouts::next(quint32 count)

src/app/SystemLayouts.h

@@ -4,7 +4,8 @@
 
 // Which of the system's keyboard layouts is active, followed and switched
 // over KWin's org.kde.keyboard D-Bus interface, so the on-screen and the
-// physical keyboard always agree. Without that service it switches locally.
+// physical keyboard always agree. Without that service it switches locally,
+// until the service appears (KWin starting late or restarting).
 class SystemLayouts : public QObject
 {
     Q_OBJECT
@@ -23,6 +24,8 @@ private Q_SLOTS:
     void setCurrent(uint index);
 
 private:
+    void fetchCurrent();
+
     bool m_system = false;
     quint32 m_current = 0;
 };