ifcviewer: load RocksDB-backed IFC models

The viewer can now open a .rdb directory (as produced by
RocksDbSerializer / convert_path_to_rocksdb) anywhere it accepts an
.ifc file. The full GUI gets an "Add Database..." File menu entry
that opens a directory chooser; the streamer lets the file
constructor autodetect the format and opens the store read-only so
multiple viewers can share a database without taking the exclusive
RocksDB lock.

Parallel mapping on RocksDB-backed files still produces
non-deterministic shape counts (the race is outside the instance
cache), so force num_threads=1 for the iterator when the storage is
RocksDB. Serial RocksDB (~2.6s) and parallel SPF (~0.7s) both
produce 107 shapes on AC20-FZK-Haus; @todo in-source points at the
remaining thread-safety work.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ifcviewer-full/MainWindow.cpp

@@ -132,6 +132,7 @@ void MainWindow::setupMenus() {
     auto* file_menu = menuBar()->addMenu("&File");
     auto* open_action = file_menu->addAction("&Add Files...", this, &MainWindow::onFileOpen);
     open_action->setShortcut(QKeySequence::Open);
+    file_menu->addAction("Add &Database...", this, &MainWindow::onDatabaseOpen);
     file_menu->addAction("&Settings...", this, &MainWindow::onFileSettings);
     file_menu->addSeparator();
     file_menu->addAction("&Quit", QKeySequence::Quit, qApp, &QApplication::quit);
@@ -146,6 +147,15 @@ void MainWindow::onFileOpen() {
     }
 }
 
+void MainWindow::onDatabaseOpen() {
+    QString path = QFileDialog::getExistingDirectory(
+        this, "Add IFC Database", QString(),
+        QFileDialog::ShowDirsOnly | QFileDialog::DontResolveSymlinks);
+    if (!path.isEmpty()) {
+        addFiles({ path });
+    }
+}
+
 void MainWindow::onFileSettings() {
     if (settings_ == nullptr) {
         settings_ = new SettingsWindow(this);

src/ifcviewer-full/MainWindow.h

@@ -48,6 +48,7 @@ public:
 
 private slots:
     void onFileOpen();
+    void onDatabaseOpen();
     void onFileSettings();
     void onObjectPicked(uint32_t object_id);
     void onTreeSelectionChanged();

src/ifcviewer/GeometryStreamer.cpp

@@ -263,7 +263,10 @@ static void worldAabbFromLocal(const float local_min[3],
 
 void GeometryStreamer::run(const std::string& path, int num_threads) {
     try {
-        ifc_file_ = std::make_unique<ifcopenshell::file>(path);
+        // read_only is a no-op for SPF; for RocksDB it allows concurrent
+        // readers and avoids acquiring the exclusive DB lock.
+        ifc_file_ = std::make_unique<ifcopenshell::file>(
+            path, ifcopenshell::FT_AUTODETECT, /*read_only=*/true);
     } catch (const std::exception& e) {
         emit errorOccurred(QString("Failed to parse IFC file: %1").arg(e.what()));
         return;
@@ -281,6 +284,12 @@ void GeometryStreamer::run(const std::string& path, int num_threads) {
     // time, but results are cached in the sidecar so it's a one-shot hit.
     settings.set("reorient-shells", true);
 
+    // @todo parallel mapping on RocksDB-backed files still races somewhere
+    // outside the instance cache, producing inconsistent shape counts. Force
+    // serial iteration for RocksDB until the read path is fully thread-safe.
+    const bool is_rocksdb = std::holds_alternative<ifcopenshell::impl::rocks_db_file_storage>(ifc_file_->storage_);
+    const int effective_threads = is_rocksdb ? 1 : num_threads;
+
     std::unique_ptr<IfcGeom::Iterator> iterator;
     try {
         const std::string geometry_library =
@@ -288,7 +297,8 @@ void GeometryStreamer::run(const std::string& path, int num_threads) {
         auto kernel = ifcopenshell::geometry::kernels::construct(
             ifc_file_.get(), geometry_library, settings);
         iterator = std::make_unique<IfcGeom::Iterator>(
-            std::move(kernel), settings, ifc_file_.get(), std::vector<ifcopenshell::geometry::filter_t>(), num_threads);
+            std::move(kernel), settings, ifc_file_.get(),
+            std::vector<ifcopenshell::geometry::filter_t>(), effective_threads);
     } catch (const std::exception& e) {
         emit errorOccurred(QString("Failed to create geometry iterator: %1").arg(e.what()));
         return;