gui: floating drop target, clipboard global shortcut, theming, UI watchdog

Continues the build order past Options/Scheduler/Speed Limiter/Batch/
Grabber/tray.

- DropTargetWidget: frameless always-on-top drop target (docs/03-gui-spec.md
  §5), position persisted, accepts a dropped http(s) URL or link text and
  opens FileInfoDialog directly (skipping Add URL, since the URL is already
  known). Shown/hidden from general.showDropTarget, live via
  event.settings.changed, same pattern MainWindow already used for
  general.minimizeToTray.
- Clipboard, explicit path #2 (docs/06-risks-and-spikes.md R2):
  GlobalShortcut wraps org.freedesktop.portal.GlobalShortcuts
  (CreateSession -> BindShortcuts -> Activated), triggering the same Add URL
  flow. Guarded end-to-end on `if(TARGET Qt6::DBus)` / VELOX_GUI_HAVE_DBUS
  so a build without the component degrades to "feature skipped," not
  broken (gui/docs/pkg-qa-requests-m1.md R4). Best-effort by design per the
  risk doc: fails silent, never advertised.

  Verified live against the real portal (a real Wayland session, not just
  offscreen): `CreateSession` refuses every caller with "An app id is
  required" — reproduced identically via a bare `busctl` call with no Qt
  involved at all, so this is the portal requiring a sandboxed caller
  identity, not something fixable from an unconfined process. Recorded as
  a partial Spike S2 answer in docs/06-risks-and-spikes.md: this explicit
  path likely doesn't work for Velox as a traditionally-packaged app on
  stock GNOME, only if/when it ships confined. Also fixed a real leak this
  verification caught: QDBusInterface's introspection cache reads as a
  LeakSanitizer leak the first time anything touches D-Bus (tst_rtl went
  red under ASan) — switched to QDBusMessage::createMethodCall, which
  needs no introspection.
- Theming (docs/03-gui-spec.md §7): gui/resources/qss/{idm-like,dark}.qss,
  each with a documented palette block up top (QSS itself has no variable
  syntax), applied by ThemeManager and kept live via
  QStyleHints::colorSchemeChanged. util/Theme.hpp gives the handful of
  inline C++ styles (status dot, offline banner, the eleven identical
  error-label styles across dialogs) named constants instead of a twelfth
  copy of the same hex.
- UiThreadWatchdog: the M1 DoD's 200 ms debug-build watchdog. A background
  std::thread pings the UI thread every 50 ms via a queued invokeMethod and
  warns once (not per-poll) if a ping goes unanswered past 200 ms; no
  QThread, no Qt event loop of its own, so the watchdog itself can never be
  what blocks the thread it watches. No-op in a release build. Proven both
  ways in tst_uithreadwatchdog: fires on a genuinely blocked UI thread
  (synchronous sleep, no processEvents) and stays silent on a responsive
  one.

Full non-conformance suite (55 tests across every lane, `ctest -LE
conformance`) passes clean at this point, including the whole gui label
under ASan+UBSan.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NSCdCWFXBTSBBK3MzWtJiC

gui/src/mainwindow/MainWindow.cpp

@@ -37,8 +37,14 @@
 #include "rpc/RpcClient.hpp"
 #include "tray/TrayIcon.hpp"
 #include "util/Format.hpp"
+#include "util/Theme.hpp"
+#include "widgets/DropTargetWidget.hpp"
 #include "widgets/ProgressDelegate.hpp"
 
+#ifdef VELOX_GUI_HAVE_DBUS
+#include "clipboard/GlobalShortcut.hpp"
+#endif
+
 namespace velox::gui {
 namespace {
 
@@ -88,7 +94,9 @@ MainWindow::MainWindow(rpc::RpcClient *client, QWidget *parent)
     bannerLabel->setObjectName(QStringLiteral("offlineBannerLabel"));
     bannerLayout->addWidget(bannerLabel);
     bannerLayout->addStretch();
-    offlineBanner_->setStyleSheet(QStringLiteral("background: #5a3a00; color: #ffd9a0;"));
+    offlineBanner_->setStyleSheet(
+        QStringLiteral("background: %1; color: %2;")
+            .arg(QLatin1String(theme::kOfflineBannerBg), QLatin1String(theme::kOfflineBannerText)));
     offlineBanner_->setVisible(false);
 
     auto *splitter = new QSplitter(Qt::Horizontal, this);
@@ -111,9 +119,10 @@ MainWindow::MainWindow(rpc::RpcClient *client, QWidget *parent)
     buildMenus();
     buildToolBar();
     buildTray();
+    buildDropTarget();
 
     // --- status bar -----------------------------------------------------------------
-    connDot_->setStyleSheet(dotStyle(QStringLiteral("#c0392b")));
+    connDot_->setStyleSheet(dotStyle(QLatin1String(theme::kDanger)));
     statusBar()->addPermanentWidget(countsLabel_, 1);
     statusBar()->addPermanentWidget(connText_);
     statusBar()->addPermanentWidget(connDot_);
@@ -261,6 +270,23 @@ void MainWindow::buildTray() {
     trayIcon_->show();
 }
 
+void MainWindow::buildDropTarget() {
+    // Qt::Tool + a parent keeps it grouped with the main window (no separate taskbar
+    // entry, destroyed when MainWindow is) while still floating independently per spec.
+    dropTarget_ = new DropTargetWidget(this);
+    connect(dropTarget_, &DropTargetWidget::urlDropped, this, &MainWindow::onUrlDropped);
+    connect(dropTarget_, &DropTargetWidget::addUrlRequested, this, &MainWindow::openAddUrlDialog);
+
+#ifdef VELOX_GUI_HAVE_DBUS
+    // docs/06-risks-and-spikes.md R2, explicit path #2. Best-effort: requestBinding() is
+    // silent and permanent-for-this-session on any desktop that lacks the portal or
+    // declines the prompt — see GlobalShortcut's own header for why that's by design.
+    globalShortcut_ = new GlobalShortcut(this);
+    connect(globalShortcut_, &GlobalShortcut::activated, this, &MainWindow::openAddUrlDialog);
+    globalShortcut_->requestBinding();
+#endif
+}
+
 void MainWindow::closeEvent(QCloseEvent *event) {
     if (minimizeToTrayEnabled_ && trayIcon_ && trayIcon_->isVisible()) {
         hide();
@@ -275,11 +301,11 @@ void MainWindow::closeEvent(QCloseEvent *event) {
 void MainWindow::onConnectionState(rpc::ConnectionState state) {
     connText_->setText(tr(rpc::toString(state)));
 
-    QString colour = QStringLiteral("#c0392b");  // red
+    QString colour = QLatin1String(theme::kDanger);
     if (state == rpc::ConnectionState::Connected) {
-        colour = QStringLiteral("#27ae60");  // green
+        colour = QLatin1String(theme::kSuccess);
     } else if (state != rpc::ConnectionState::Disconnected) {
-        colour = QStringLiteral("#e67e22");  // amber
+        colour = QLatin1String(theme::kWarning);
     }
     connDot_->setStyleSheet(dotStyle(colour));
 
@@ -299,7 +325,7 @@ void MainWindow::onConnectionState(rpc::ConnectionState state) {
 
     if (online) {
         fetchTree();
-        fetchMinimizeToTraySetting();
+        fetchGeneralUiSettings();
     }
 }
 
@@ -318,29 +344,40 @@ void MainWindow::fetchTree() {
     });
 }
 
-void MainWindow::fetchMinimizeToTraySetting() {
-    client_->call(QStringLiteral("settings.get"),
-                  QJsonObject{{"keys", QJsonArray{QStringLiteral("general.minimizeToTray")}}},
-                  [this](const rpc::RpcReply &reply) {
-                      if (reply.ok()) {
-                          minimizeToTrayEnabled_ = reply.result.toObject()
-                                                       .value("values")
-                                                       .toObject()
-                                                       .value("general.minimizeToTray")
-                                                       .toBool();
-                      }
-                  });
+void MainWindow::fetchGeneralUiSettings() {
+    client_->call(
+        QStringLiteral("settings.get"),
+        QJsonObject{{"keys", QJsonArray{QStringLiteral("general.minimizeToTray"),
+                                        QStringLiteral("general.showDropTarget")}}},
+        [this](const rpc::RpcReply &reply) {
+            if (!reply.ok()) {
+                return;
+            }
+            const QJsonObject values = reply.result.toObject().value("values").toObject();
+            minimizeToTrayEnabled_ = values.value("general.minimizeToTray").toBool();
+            if (dropTarget_) {
+                dropTarget_->setVisible(values.value("general.showDropTarget").toBool(true));
+            }
+        });
 }
 
 void MainWindow::onSettingsChanged(const QJsonObject &params) {
     for (const QJsonValue &key : params.value("keys").toArray()) {
-        if (key.toString() == QLatin1String("general.minimizeToTray")) {
-            fetchMinimizeToTraySetting();
+        const QString k = key.toString();
+        if (k == QLatin1String("general.minimizeToTray") ||
+            k == QLatin1String("general.showDropTarget")) {
+            fetchGeneralUiSettings();
             break;
         }
     }
 }
 
+void MainWindow::onUrlDropped(const QString &url) {
+    auto *info = new FileInfoDialog(client_, url, categoriesCache_, queuesCache_, this);
+    info->setAttribute(Qt::WA_DeleteOnClose);
+    info->show();
+}
+
 void MainWindow::openAddUrlDialog() {
     AddUrlDialog dlg(this);
     if (dlg.exec() != QDialog::Accepted) {

gui/src/mainwindow/MainWindow.hpp

@@ -26,6 +26,10 @@ namespace velox::gui {
 class DownloadTableModel;
 class CategoryPanel;
 class TrayIcon;
+class DropTargetWidget;
+#ifdef VELOX_GUI_HAVE_DBUS
+class GlobalShortcut;
+#endif
 namespace rpc {
 class RpcClient;
 }  // namespace rpc
@@ -64,14 +68,16 @@ class MainWindow : public QMainWindow {
     void openGrabberWizard();
     void showAndRaise();
     void onSettingsChanged(const QJsonObject &params);
+    void onUrlDropped(const QString &url);
 
   private:
     void buildActions();
     void buildMenus();
     void buildToolBar();
     void buildTray();
+    void buildDropTarget();
     void fetchTree();
-    void fetchMinimizeToTraySetting();
+    void fetchGeneralUiSettings();
     QStringList selectedTaskIds() const;
     QStringList allTaskIds() const;
     void actOnTasks(const char *methodName, const QStringList &ids);
@@ -102,7 +108,11 @@ class MainWindow : public QMainWindow {
     QJsonArray categoriesCache_;
     QJsonArray queuesCache_;
     TrayIcon *trayIcon_ = nullptr;
+    DropTargetWidget *dropTarget_ = nullptr;
     bool minimizeToTrayEnabled_ = false;
+#ifdef VELOX_GUI_HAVE_DBUS
+    GlobalShortcut *globalShortcut_ = nullptr;
+#endif
 
     QLabel *connDot_;
     QLabel *connText_;