diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index eebde9c..a18ce77 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -34,3 +34,22 @@ add_library(diagscene STATIC
     scene/GridView.cpp
 )
 target_link_libraries(diagscene PUBLIC diagcore Qt6::Widgets Qt6::Svg)
+
+# App: main window and panels.
+add_library(diagapp STATIC
+    app/MainWindow.h
+    app/MainWindow.cpp
+    app/NodePalette.h
+    app/NodePalette.cpp
+    app/PropertyPanel.h
+    app/PropertyPanel.cpp
+    app/SettingsDialog.h
+    app/SettingsDialog.cpp
+)
+target_link_libraries(diagapp PUBLIC diagscene)
+
+# Resources live on the executable: a static lib would drop the unreferenced
+# resource-init object at link time.
+qt_add_resources(APP_RESOURCES ${CMAKE_CURRENT_SOURCE_DIR}/../resources/resources.qrc)
+qt_add_executable(pipediagram main.cpp ${APP_RESOURCES})
+target_link_libraries(pipediagram PRIVATE diagapp)
diff --git a/src/app/MainWindow.cpp b/src/app/MainWindow.cpp
new file mode 100644
index 0000000..bf57344
--- /dev/null
+++ b/src/app/MainWindow.cpp
@@ -0,0 +1,258 @@
+#include "MainWindow.h"
+
+#include "NodePalette.h"
+#include "PropertyPanel.h"
+#include "core/FlowSolver.h"
+#include "core/JsonIo.h"
+#include "scene/DiagramScene.h"
+#include "scene/GridView.h"
+
+#include <QApplication>
+#include <QCloseEvent>
+#include <QDockWidget>
+#include <QFileDialog>
+#include <QLabel>
+#include <QMenuBar>
+#include <QMessageBox>
+#include <QStatusBar>
+#include <QToolBar>
+
+namespace diag {
+
+MainWindow::MainWindow(QWidget* parent) : QMainWindow(parent)
+{
+    setWindowTitle(tr("PipeDiagram"));
+    resize(1280, 800);
+
+    TypeRegistry& registry = TypeRegistry::instance();
+    if (registry.nodeTypes().isEmpty()) {
+        QString err;
+        if (!registry.loadFromFile(QStringLiteral(":/config/nodetypes.json"), &err))
+            QMessageBox::warning(this, tr("Configuration"),
+                                 tr("Failed to load node types: %1").arg(err));
+    }
+
+    m_model = new NetworkModel(&registry, this);
+    m_undoStack = new QUndoStack(this);
+    m_scene = new DiagramScene(m_model, m_undoStack, this);
+    m_view = new GridView(m_scene, this);
+    setCentralWidget(m_view);
+
+    m_palette = new NodePalette(&registry, this);
+    auto* paletteDock = new QDockWidget(tr("Node palette"), this);
+    paletteDock->setObjectName(QStringLiteral("paletteDock"));
+    paletteDock->setWidget(m_palette);
+    addDockWidget(Qt::LeftDockWidgetArea, paletteDock);
+
+    m_properties = new PropertyPanel(this);
+    m_properties->setScene(m_scene);
+    auto* propsDock = new QDockWidget(tr("Properties"), this);
+    propsDock->setObjectName(QStringLiteral("propsDock"));
+    propsDock->setWidget(m_properties);
+    addDockWidget(Qt::RightDockWidgetArea, propsDock);
+
+    buildActions();
+
+    auto* cursorLabel = new QLabel;
+    auto* zoomLabel = new QLabel(QStringLiteral("100%"));
+    statusBar()->addPermanentWidget(cursorLabel);
+    statusBar()->addPermanentWidget(zoomLabel);
+    connect(m_view, &GridView::cursorMoved, this, [cursorLabel](QPointF p) {
+        cursorLabel->setText(QStringLiteral("x: %1  y: %2").arg(int(p.x())).arg(int(p.y())));
+    });
+    connect(m_view, &GridView::zoomChanged, this, [zoomLabel](double z) {
+        zoomLabel->setText(QStringLiteral("%1%").arg(int(z * 100)));
+    });
+    connect(m_scene, &DiagramScene::connectionMessage, this,
+            [this](const QString& text) { statusBar()->showMessage(text, 4000); });
+
+    m_settings.load();
+    applySettings(m_settings);
+}
+
+void MainWindow::buildActions()
+{
+    auto* fileMenu = menuBar()->addMenu(tr("&File"));
+    auto* toolbar = addToolBar(tr("Main"));
+    toolbar->setObjectName(QStringLiteral("mainToolbar"));
+
+    QAction* newAct = fileMenu->addAction(tr("&New"), QKeySequence::New, this,
+                                          &MainWindow::newDocument);
+    QAction* openAct = fileMenu->addAction(tr("&Open…"), QKeySequence::Open, this,
+                                           &MainWindow::openDocument);
+    QAction* saveAct = fileMenu->addAction(tr("&Save"), QKeySequence::Save, this,
+                                           &MainWindow::saveDocument);
+    fileMenu->addAction(tr("Save &As…"), QKeySequence::SaveAs, this,
+                        &MainWindow::saveDocumentAs);
+    fileMenu->addAction(tr("Load Sa&mple"), this, &MainWindow::loadSample);
+    fileMenu->addSeparator();
+    fileMenu->addAction(tr("&Quit"), QKeySequence::Quit, this, &QWidget::close);
+
+    auto* editMenu = menuBar()->addMenu(tr("&Edit"));
+    QAction* undoAct = m_undoStack->createUndoAction(this, tr("&Undo"));
+    undoAct->setShortcut(QKeySequence::Undo);
+    QAction* redoAct = m_undoStack->createRedoAction(this, tr("&Redo"));
+    redoAct->setShortcut(QKeySequence::Redo);
+    editMenu->addAction(undoAct);
+    editMenu->addAction(redoAct);
+    editMenu->addSeparator();
+    editMenu->addAction(tr("Cu&t"), QKeySequence::Cut, m_scene, &DiagramScene::cutSelection);
+    editMenu->addAction(tr("&Copy"), QKeySequence::Copy, m_scene,
+                        &DiagramScene::copySelection);
+    editMenu->addAction(tr("&Paste"), QKeySequence::Paste, m_scene, &DiagramScene::paste);
+    QAction* deleteAct = editMenu->addAction(tr("&Delete"), QKeySequence::Delete, m_scene,
+                                             &DiagramScene::deleteSelection);
+    editMenu->addAction(tr("Select &All"), QKeySequence::SelectAll, m_scene,
+                        &DiagramScene::selectAll);
+    editMenu->addSeparator();
+    editMenu->addAction(tr("Se&ttings…"), QKeySequence::Preferences, this,
+                        &MainWindow::showSettings);
+
+    auto* viewMenu = menuBar()->addMenu(tr("&View"));
+    viewMenu->addAction(tr("Zoom &In"), QKeySequence::ZoomIn, m_view, &GridView::zoomIn);
+    viewMenu->addAction(tr("Zoom &Out"), QKeySequence::ZoomOut, m_view, &GridView::zoomOut);
+    QAction* fitAct = viewMenu->addAction(tr("Zoom to &Fit"), QKeySequence(Qt::Key_F), m_view,
+                                          &GridView::zoomToFit);
+    viewMenu->addAction(tr("&Reset Zoom"), QKeySequence(Qt::CTRL | Qt::Key_0), m_view,
+                        &GridView::zoomReset);
+
+    auto* simMenu = menuBar()->addMenu(tr("&Simulation"));
+    m_simulateAction = simMenu->addAction(tr("&Run Flow Simulation"));
+    m_simulateAction->setCheckable(true);
+    m_simulateAction->setShortcut(QKeySequence(Qt::Key_F5));
+    connect(m_simulateAction, &QAction::toggled, this, &MainWindow::runSimulation);
+
+    toolbar->addAction(newAct);
+    toolbar->addAction(openAct);
+    toolbar->addAction(saveAct);
+    toolbar->addSeparator();
+    toolbar->addAction(undoAct);
+    toolbar->addAction(redoAct);
+    toolbar->addAction(deleteAct);
+    toolbar->addSeparator();
+    toolbar->addAction(fitAct);
+    toolbar->addAction(m_simulateAction);
+}
+
+void MainWindow::applySettings(const EditorSettings& settings)
+{
+    m_settings = settings;
+    m_scene->setRouteConfig(settings.route);
+    m_scene->setTheme(Theme::make(settings.scheme));
+    settings.save();
+}
+
+void MainWindow::showSettings()
+{
+    SettingsDialog dialog(m_settings, this);
+    if (dialog.exec() == QDialog::Accepted)
+        applySettings(dialog.settings());
+}
+
+bool MainWindow::maybeSave()
+{
+    if (m_undoStack->isClean())
+        return true;
+    const auto answer = QMessageBox::question(
+        this, tr("Unsaved changes"), tr("The diagram has unsaved changes. Save them?"),
+        QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel);
+    if (answer == QMessageBox::Save) {
+        saveDocument();
+        return m_undoStack->isClean();
+    }
+    return answer == QMessageBox::Discard;
+}
+
+void MainWindow::newDocument()
+{
+    if (!maybeSave())
+        return;
+    m_model->clear();
+    m_undoStack->clear();
+    m_currentFile.clear();
+    m_simulateAction->setChecked(false);
+}
+
+void MainWindow::openDocument()
+{
+    if (!maybeSave())
+        return;
+    const QString path = QFileDialog::getOpenFileName(this, tr("Open diagram"), {},
+                                                      tr("Diagrams (*.json)"));
+    if (path.isEmpty())
+        return;
+    QString err;
+    if (!JsonIo::load(m_model, path, &err)) {
+        QMessageBox::warning(this, tr("Open failed"), err);
+        return;
+    }
+    m_undoStack->clear();
+    m_currentFile = path;
+    m_simulateAction->setChecked(false);
+    m_view->zoomToFit();
+}
+
+void MainWindow::saveDocument()
+{
+    if (m_currentFile.isEmpty()) {
+        saveDocumentAs();
+        return;
+    }
+    QString err;
+    if (!JsonIo::save(*m_model, m_currentFile, &err))
+        QMessageBox::warning(this, tr("Save failed"), err);
+    else
+        m_undoStack->setClean();
+}
+
+void MainWindow::saveDocumentAs()
+{
+    const QString path = QFileDialog::getSaveFileName(this, tr("Save diagram"), {},
+                                                      tr("Diagrams (*.json)"));
+    if (path.isEmpty())
+        return;
+    m_currentFile = path;
+    saveDocument();
+}
+
+void MainWindow::loadSample()
+{
+    if (!maybeSave())
+        return;
+    QString err;
+    if (!JsonIo::load(m_model, QStringLiteral(":/samples/waterworks.json"), &err)) {
+        QMessageBox::warning(this, tr("Sample"), err);
+        return;
+    }
+    m_undoStack->clear();
+    m_currentFile.clear();
+    m_view->zoomToFit();
+}
+
+void MainWindow::runSimulation(bool enabled)
+{
+    if (enabled) {
+        // Mock calculation: distribute flow in every relation network, then
+        // publish rates to the read-only flowRate property and animate.
+        for (const Relation& rel : m_model->registry()->relations()) {
+            const FlowResult result = FlowSolver::solve(*m_model, rel.id);
+            if (!result.ok && !result.message.isEmpty())
+                statusBar()->showMessage(tr("%1: %2").arg(rel.name, result.message), 5000);
+            FlowSolver::apply(*m_model, result);
+        }
+        statusBar()->showMessage(tr("Flow simulation running"), 3000);
+    } else {
+        statusBar()->showMessage(tr("Flow simulation stopped"), 3000);
+    }
+    m_scene->setFlowAnimationEnabled(enabled);
+}
+
+void MainWindow::closeEvent(QCloseEvent* event)
+{
+    if (maybeSave())
+        event->accept();
+    else
+        event->ignore();
+}
+
+}  // namespace diag
diff --git a/src/app/MainWindow.h b/src/app/MainWindow.h
new file mode 100644
index 0000000..5058ab5
--- /dev/null
+++ b/src/app/MainWindow.h
@@ -0,0 +1,51 @@
+#pragma once
+
+#include "SettingsDialog.h"
+
+#include <QMainWindow>
+#include <QUndoStack>
+
+namespace diag {
+
+class DiagramScene;
+class GridView;
+class NetworkModel;
+class NodePalette;
+class PropertyPanel;
+
+class MainWindow : public QMainWindow {
+    Q_OBJECT
+public:
+    explicit MainWindow(QWidget* parent = nullptr);
+
+    DiagramScene* scene() const { return m_scene; }
+    NetworkModel* model() const { return m_model; }
+
+    void loadSample();
+
+protected:
+    void closeEvent(QCloseEvent* event) override;
+
+private:
+    void buildActions();
+    void applySettings(const EditorSettings& settings);
+    void newDocument();
+    void openDocument();
+    void saveDocument();
+    void saveDocumentAs();
+    bool maybeSave();
+    void runSimulation(bool enabled);
+    void showSettings();
+
+    NetworkModel* m_model;
+    QUndoStack* m_undoStack;
+    DiagramScene* m_scene;
+    GridView* m_view;
+    NodePalette* m_palette;
+    PropertyPanel* m_properties;
+    EditorSettings m_settings;
+    QString m_currentFile;
+    QAction* m_simulateAction = nullptr;
+};
+
+}  // namespace diag
diff --git a/src/app/NodePalette.cpp b/src/app/NodePalette.cpp
new file mode 100644
index 0000000..c6bbcaf
--- /dev/null
+++ b/src/app/NodePalette.cpp
@@ -0,0 +1,82 @@
+#include "NodePalette.h"
+
+#include "core/TypeRegistry.h"
+#include "scene/GridView.h"
+
+#include <QDrag>
+#include <QMimeData>
+#include <QPainter>
+#include <QSvgRenderer>
+
+namespace diag {
+
+namespace {
+
+QIcon iconFor(const NodeType* type)
+{
+    QSvgRenderer renderer(type->svgPath);
+    QPixmap pm(32, 32);
+    pm.fill(Qt::transparent);
+    if (renderer.isValid()) {
+        QPainter p(&pm);
+        renderer.render(&p, QRectF(0, 0, 32, 32));
+    }
+    return QIcon(pm);
+}
+
+}  // namespace
+
+NodePalette::NodePalette(TypeRegistry* registry, QWidget* parent)
+    : QTreeWidget(parent), m_registry(registry)
+{
+    setHeaderHidden(true);
+    setDragEnabled(true);
+    setIconSize({28, 28});
+    setRootIsDecorated(false);
+    setIndentation(12);
+    reload();
+}
+
+void NodePalette::reload()
+{
+    clear();
+    QHash<QString, QTreeWidgetItem*> groups;
+    for (const QString& group : m_registry->nodeGroups()) {
+        auto* item = new QTreeWidgetItem(this, {group});
+        item->setFlags(Qt::ItemIsEnabled);
+        QFont f = item->font(0);
+        f.setBold(true);
+        item->setFont(0, f);
+        groups.insert(group, item);
+    }
+    for (const NodeType* type : m_registry->nodeTypes()) {
+        auto* item = new QTreeWidgetItem(groups.value(type->group), {type->name});
+        item->setIcon(0, iconFor(type));
+        item->setData(0, Qt::UserRole, type->id);
+        item->setToolTip(0, QStringLiteral("%1 — %2 port(s). Drag onto the canvas.")
+                                .arg(type->name)
+                                .arg(type->ports.size()));
+    }
+    expandAll();
+}
+
+void NodePalette::startDrag(Qt::DropActions)
+{
+    QTreeWidgetItem* item = currentItem();
+    if (!item)
+        return;
+    const QString typeId = item->data(0, Qt::UserRole).toString();
+    if (typeId.isEmpty())
+        return;  // group header
+
+    auto* mime = new QMimeData();
+    mime->setData(QLatin1String(GridView::kNodeTypeMime), typeId.toUtf8());
+
+    auto* drag = new QDrag(this);
+    drag->setMimeData(mime);
+    drag->setPixmap(item->icon(0).pixmap(32, 32));
+    drag->setHotSpot({16, 16});
+    drag->exec(Qt::CopyAction);
+}
+
+}  // namespace diag
diff --git a/src/app/NodePalette.h b/src/app/NodePalette.h
new file mode 100644
index 0000000..75a7a8e
--- /dev/null
+++ b/src/app/NodePalette.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <QTreeWidget>
+
+namespace diag {
+
+class TypeRegistry;
+
+// Grouped list of node types with SVG icons; items are dragged onto the
+// canvas (mime: GridView::kNodeTypeMime carrying the type id).
+class NodePalette : public QTreeWidget {
+    Q_OBJECT
+public:
+    explicit NodePalette(TypeRegistry* registry, QWidget* parent = nullptr);
+
+    void reload();
+
+protected:
+    void startDrag(Qt::DropActions supportedActions) override;
+
+private:
+    TypeRegistry* m_registry;
+};
+
+}  // namespace diag
diff --git a/src/app/PropertyPanel.cpp b/src/app/PropertyPanel.cpp
new file mode 100644
index 0000000..3e9094d
--- /dev/null
+++ b/src/app/PropertyPanel.cpp
@@ -0,0 +1,303 @@
+#include "PropertyPanel.h"
+
+#include "scene/Commands.h"
+#include "scene/DiagramScene.h"
+#include "scene/EdgeItem.h"
+#include "scene/NodeItem.h"
+#include "core/NetworkModel.h"
+
+#include <QColorDialog>
+#include <QComboBox>
+#include <QDoubleSpinBox>
+#include <QFormLayout>
+#include <QGroupBox>
+#include <QLabel>
+#include <QLineEdit>
+#include <QListWidget>
+#include <QPushButton>
+#include <QSpinBox>
+#include <QToolButton>
+#include <QVBoxLayout>
+
+namespace diag {
+
+PropertyPanel::PropertyPanel(QWidget* parent) : QScrollArea(parent)
+{
+    setWidgetResizable(true);
+    setMinimumWidth(260);
+    showPlaceholder(tr("Select a node or an edge\nto edit its properties"));
+}
+
+void PropertyPanel::setScene(DiagramScene* scene)
+{
+    if (m_scene)
+        disconnect(m_scene, nullptr, this, nullptr);
+    m_scene = scene;
+    connect(scene, &DiagramScene::selectionChanged, this, &PropertyPanel::onSelectionChanged);
+    // Rebuild values (not widgets) when the selected element changes elsewhere
+    // (undo, solver run, ...).
+    connect(scene->model(), &NetworkModel::nodeChanged, this, [this](QUuid id) {
+        if (m_target == Target::Node && id == m_id && !m_updating)
+            rebuild();
+    });
+    connect(scene->model(), &NetworkModel::edgeChanged, this, [this](QUuid id) {
+        if (m_target == Target::Edge && id == m_id && !m_updating)
+            rebuild();
+    });
+    connect(scene->model(), &NetworkModel::flowChanged, this, [this](QUuid id) {
+        if (m_target == Target::Edge && id == m_id)
+            rebuild();
+    });
+    onSelectionChanged();
+}
+
+void PropertyPanel::onSelectionChanged()
+{
+    m_target = Target::None;
+    m_id = {};
+    if (m_scene) {
+        const auto items = m_scene->selectedItems();
+        if (items.size() == 1) {
+            if (auto* n = dynamic_cast<NodeItem*>(items.first())) {
+                m_target = Target::Node;
+                m_id = n->nodeId();
+            } else if (auto* e = dynamic_cast<EdgeItem*>(items.first())) {
+                m_target = Target::Edge;
+                m_id = e->edgeId();
+            }
+        } else if (items.size() > 1) {
+            showPlaceholder(tr("%1 elements selected").arg(items.size()));
+            return;
+        }
+    }
+    if (m_target == Target::None) {
+        showPlaceholder(tr("Select a node or an edge\nto edit its properties"));
+        return;
+    }
+    rebuild();
+}
+
+void PropertyPanel::showPlaceholder(const QString& text)
+{
+    auto* placeholder = new QLabel(text);
+    placeholder->setAlignment(Qt::AlignCenter);
+    placeholder->setWordWrap(true);
+    placeholder->setStyleSheet(QStringLiteral("color: gray;"));
+    setWidget(placeholder);
+    m_content = placeholder;
+}
+
+QVariant PropertyPanel::currentValue(const QString& key) const
+{
+    NetworkModel* model = m_scene->model();
+    if (m_target == Target::Node)
+        return model->nodeProperty(m_id, key);
+    // Solver result lives on the edge itself, exposed via the read-only spec.
+    if (key == QLatin1String("flowRate")) {
+        if (const Edge* e = model->edge(m_id))
+            return e->flowRate;
+    }
+    return model->edgeProperty(m_id, key);
+}
+
+void PropertyPanel::applyValue(const QString& key, const QVariant& value)
+{
+    if (m_updating)
+        return;
+    m_updating = true;
+    m_scene->undoStack()->push(new SetPropertyCommand(
+        m_scene->model(),
+        m_target == Target::Node ? SetPropertyCommand::NodeTarget : SetPropertyCommand::EdgeTarget,
+        m_id, key, value));
+    m_updating = false;
+}
+
+void PropertyPanel::rebuild()
+{
+    NetworkModel* model = m_scene->model();
+    QList<PropertySpec> specs;
+    QString header;
+    if (m_target == Target::Node) {
+        const Node* n = model->node(m_id);
+        if (!n)
+            return;
+        const NodeType* type = model->nodeTypeOf(m_id);
+        specs = model->registry()->nodeProperties(n->typeId);
+        header = tr("Node: %1").arg(type ? type->name : n->typeId);
+    } else {
+        const Edge* e = model->edge(m_id);
+        if (!e)
+            return;
+        const Relation* rel = model->registry()->relation(e->relation);
+        specs = model->registry()->edgeProperties(e->relation);
+        header = tr("Edge: %1 line").arg(rel ? rel->name : e->relation);
+    }
+
+    auto* content = new QWidget;
+    auto* layout = new QVBoxLayout(content);
+    layout->setContentsMargins(8, 8, 8, 8);
+
+    auto* title = new QLabel(header);
+    QFont f = title->font();
+    f.setBold(true);
+    title->setFont(f);
+    layout->addWidget(title);
+
+    // Group boxes in spec order, keeping first-seen group order.
+    QStringList groupOrder;
+    for (const auto& s : specs)
+        if (!groupOrder.contains(s.group))
+            groupOrder.append(s.group);
+    for (const QString& group : groupOrder) {
+        auto* box = new QGroupBox(group);
+        auto* form = new QFormLayout(box);
+        form->setLabelAlignment(Qt::AlignLeft);
+        for (const auto& spec : specs) {
+            if (spec.group != group)
+                continue;
+            QString label = spec.name;
+            if (!spec.unit.isEmpty())
+                label += QStringLiteral(", %1").arg(spec.unit);
+            form->addRow(label, createEditor(spec));
+        }
+        layout->addWidget(box);
+    }
+    layout->addStretch();
+
+    setWidget(content);
+    m_content = content;
+}
+
+QWidget* PropertyPanel::createEditor(const PropertySpec& spec)
+{
+    const QVariant value = currentValue(spec.id);
+    const bool unbounded = spec.min == spec.max;
+    QWidget* editor = nullptr;
+
+    switch (spec.type) {
+    case PropertyType::String: {
+        auto* w = new QLineEdit(value.toString());
+        connect(w, &QLineEdit::editingFinished, this,
+                [this, spec, w] { applyValue(spec.id, w->text()); });
+        editor = w;
+        break;
+    }
+    case PropertyType::Int: {
+        auto* w = new QSpinBox;
+        w->setRange(unbounded ? -1000000000 : int(spec.min), unbounded ? 1000000000 : int(spec.max));
+        w->setValue(value.toInt());
+        connect(w, &QSpinBox::editingFinished, this,
+                [this, spec, w] { applyValue(spec.id, w->value()); });
+        editor = w;
+        break;
+    }
+    case PropertyType::Float: {
+        auto* w = new QDoubleSpinBox;
+        w->setRange(unbounded ? -1e12 : spec.min, unbounded ? 1e12 : spec.max);
+        w->setDecimals(3);
+        w->setValue(value.toDouble());
+        connect(w, &QDoubleSpinBox::editingFinished, this,
+                [this, spec, w] { applyValue(spec.id, w->value()); });
+        editor = w;
+        break;
+    }
+    case PropertyType::Enum: {
+        auto* w = new QComboBox;
+        w->addItems(spec.enumValues);
+        w->setCurrentText(value.toString());
+        connect(w, &QComboBox::activated, this,
+                [this, spec, w] { applyValue(spec.id, w->currentText()); });
+        editor = w;
+        break;
+    }
+    case PropertyType::CatalogueItem: {
+        auto* w = new QComboBox;
+        w->addItem(tr("—"), QString());
+        if (const Catalogue* cat = m_scene->model()->registry()->catalogue(spec.catalogueId))
+            for (const auto& item : cat->items)
+                w->addItem(item.name, item.id);
+        const int idx = w->findData(value.toString());
+        w->setCurrentIndex(qMax(0, idx));
+        connect(w, &QComboBox::activated, this,
+                [this, spec, w] { applyValue(spec.id, w->currentData().toString()); });
+        editor = w;
+        break;
+    }
+    case PropertyType::CatalogueItems: {
+        auto* w = new QListWidget;
+        w->setMaximumHeight(96);
+        const QStringList selected = value.toStringList();
+        if (const Catalogue* cat = m_scene->model()->registry()->catalogue(spec.catalogueId)) {
+            for (const auto& item : cat->items) {
+                auto* li = new QListWidgetItem(item.name, w);
+                li->setData(Qt::UserRole, item.id);
+                li->setFlags(li->flags() | Qt::ItemIsUserCheckable);
+                li->setCheckState(selected.contains(item.id) ? Qt::Checked : Qt::Unchecked);
+            }
+        }
+        connect(w, &QListWidget::itemChanged, this, [this, spec, w] {
+            QStringList ids;
+            for (int i = 0; i < w->count(); ++i)
+                if (w->item(i)->checkState() == Qt::Checked)
+                    ids.append(w->item(i)->data(Qt::UserRole).toString());
+            applyValue(spec.id, ids);
+        });
+        editor = w;
+        break;
+    }
+    case PropertyType::Color: {
+        auto* row = new QWidget;
+        auto* layout = new QHBoxLayout(row);
+        layout->setContentsMargins(0, 0, 0, 0);
+        auto* button = new QPushButton;
+        auto* clear = new QToolButton;
+        clear->setText(QStringLiteral("✕"));
+        clear->setToolTip(tr("Reset to automatic color"));
+        auto sync = [button](const QString& name) {
+            const bool valid = QColor::isValidColorName(name);
+            button->setText(valid ? name : QObject::tr("Auto"));
+            button->setStyleSheet(valid
+                                      ? QStringLiteral("background-color: %1;").arg(name)
+                                      : QString());
+        };
+        sync(value.toString());
+        connect(button, &QPushButton::clicked, this, [this, spec, button, sync] {
+            const QColor initial(currentValue(spec.id).toString());
+            const QColor c = QColorDialog::getColor(initial.isValid() ? initial : Qt::gray,
+                                                    this, tr("Choose color"));
+            if (c.isValid()) {
+                applyValue(spec.id, c.name());
+                sync(c.name());
+            }
+        });
+        connect(clear, &QToolButton::clicked, this, [this, spec, sync] {
+            applyValue(spec.id, QString());
+            sync(QString());
+        });
+        layout->addWidget(button, 1);
+        layout->addWidget(clear);
+        editor = row;
+        break;
+    }
+    case PropertyType::ValueList: {
+        auto* w = new QLineEdit(value.toStringList().join(QStringLiteral(", ")));
+        w->setPlaceholderText(tr("value1, value2, …"));
+        w->setToolTip(tr("Comma-separated list of values"));
+        connect(w, &QLineEdit::editingFinished, this, [this, spec, w] {
+            QStringList values;
+            for (const QString& part : w->text().split(QLatin1Char(',')))
+                if (!part.trimmed().isEmpty())
+                    values.append(part.trimmed());
+            applyValue(spec.id, values);
+        });
+        editor = w;
+        break;
+    }
+    }
+
+    if (spec.readOnly)
+        editor->setEnabled(false);
+    return editor;
+}
+
+}  // namespace diag
diff --git a/src/app/PropertyPanel.h b/src/app/PropertyPanel.h
new file mode 100644
index 0000000..5863110
--- /dev/null
+++ b/src/app/PropertyPanel.h
@@ -0,0 +1,42 @@
+#pragma once
+
+#include "core/Types.h"
+
+#include <QScrollArea>
+#include <QUuid>
+
+class QVBoxLayout;
+
+namespace diag {
+
+class DiagramScene;
+
+// Right-side panel: grouped, typed editors for the selected node or edge.
+// Edits are pushed to the undo stack; values refresh on model changes.
+class PropertyPanel : public QScrollArea {
+    Q_OBJECT
+public:
+    explicit PropertyPanel(QWidget* parent = nullptr);
+
+    void setScene(DiagramScene* scene);
+
+public slots:
+    void onSelectionChanged();
+
+private:
+    enum class Target { None, Node, Edge };
+
+    void rebuild();
+    void showPlaceholder(const QString& text);
+    QVariant currentValue(const QString& key) const;
+    void applyValue(const QString& key, const QVariant& value);
+    QWidget* createEditor(const PropertySpec& spec);
+
+    DiagramScene* m_scene = nullptr;
+    Target m_target = Target::None;
+    QUuid m_id;
+    QWidget* m_content = nullptr;
+    bool m_updating = false;
+};
+
+}  // namespace diag
diff --git a/src/app/SettingsDialog.cpp b/src/app/SettingsDialog.cpp
new file mode 100644
index 0000000..80c6a98
--- /dev/null
+++ b/src/app/SettingsDialog.cpp
@@ -0,0 +1,82 @@
+#include "SettingsDialog.h"
+
+#include <QCheckBox>
+#include <QComboBox>
+#include <QDialogButtonBox>
+#include <QDoubleSpinBox>
+#include <QFormLayout>
+#include <QSettings>
+#include <QSpinBox>
+
+namespace diag {
+
+void EditorSettings::load()
+{
+    QSettings s;
+    route.gridStep = s.value(QStringLiteral("grid/step"), 20.0).toDouble();
+    route.snapToGrid = s.value(QStringLiteral("grid/snap"), true).toBool();
+    route.arcOnIntersection = s.value(QStringLiteral("edges/arcOnIntersection"), true).toBool();
+    route.arcRadius = s.value(QStringLiteral("edges/arcRadius"), 6.0).toDouble();
+    scheme = Theme::schemeFromName(
+        s.value(QStringLiteral("view/colorScheme"), QStringLiteral("Light")).toString());
+}
+
+void EditorSettings::save() const
+{
+    QSettings s;
+    s.setValue(QStringLiteral("grid/step"), route.gridStep);
+    s.setValue(QStringLiteral("grid/snap"), route.snapToGrid);
+    s.setValue(QStringLiteral("edges/arcOnIntersection"), route.arcOnIntersection);
+    s.setValue(QStringLiteral("edges/arcRadius"), route.arcRadius);
+    s.setValue(QStringLiteral("view/colorScheme"), Theme::schemeName(scheme));
+}
+
+SettingsDialog::SettingsDialog(const EditorSettings& settings, QWidget* parent)
+    : QDialog(parent)
+{
+    setWindowTitle(tr("Editor settings"));
+    auto* form = new QFormLayout(this);
+
+    m_gridStep = new QSpinBox;
+    m_gridStep->setRange(5, 200);
+    m_gridStep->setValue(int(settings.route.gridStep));
+    form->addRow(tr("Grid step, px"), m_gridStep);
+
+    m_snap = new QCheckBox(tr("Snap nodes to grid"));
+    m_snap->setChecked(settings.route.snapToGrid);
+    form->addRow(QString(), m_snap);
+
+    m_arcs = new QCheckBox(tr("Draw arcs where edges cross"));
+    m_arcs->setChecked(settings.route.arcOnIntersection);
+    form->addRow(QString(), m_arcs);
+
+    m_arcRadius = new QDoubleSpinBox;
+    m_arcRadius->setRange(3.0, 20.0);
+    m_arcRadius->setValue(settings.route.arcRadius);
+    form->addRow(tr("Arc radius, px"), m_arcRadius);
+
+    m_scheme = new QComboBox;
+    for (auto scheme : {ColorScheme::Light, ColorScheme::Dark, ColorScheme::HighContrast})
+        m_scheme->addItem(Theme::schemeName(scheme));
+    m_scheme->setCurrentText(Theme::schemeName(settings.scheme));
+    form->addRow(tr("Color scheme"), m_scheme);
+
+    auto* buttons =
+        new QDialogButtonBox(QDialogButtonBox::Ok | QDialogButtonBox::Cancel);
+    connect(buttons, &QDialogButtonBox::accepted, this, &QDialog::accept);
+    connect(buttons, &QDialogButtonBox::rejected, this, &QDialog::reject);
+    form->addRow(buttons);
+}
+
+EditorSettings SettingsDialog::settings() const
+{
+    EditorSettings s;
+    s.route.gridStep = m_gridStep->value();
+    s.route.snapToGrid = m_snap->isChecked();
+    s.route.arcOnIntersection = m_arcs->isChecked();
+    s.route.arcRadius = m_arcRadius->value();
+    s.scheme = Theme::schemeFromName(m_scheme->currentText());
+    return s;
+}
+
+}  // namespace diag
diff --git a/src/app/SettingsDialog.h b/src/app/SettingsDialog.h
new file mode 100644
index 0000000..7905e05
--- /dev/null
+++ b/src/app/SettingsDialog.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include "core/Router.h"
+#include "scene/Theme.h"
+
+#include <QDialog>
+
+class QCheckBox;
+class QComboBox;
+class QDoubleSpinBox;
+class QSpinBox;
+
+namespace diag {
+
+struct EditorSettings {
+    RouteConfig route;
+    ColorScheme scheme = ColorScheme::Light;
+
+    void load();  // from QSettings
+    void save() const;
+};
+
+// Editor configuration: grid step, snapping, intersection arcs, color scheme.
+class SettingsDialog : public QDialog {
+    Q_OBJECT
+public:
+    explicit SettingsDialog(const EditorSettings& settings, QWidget* parent = nullptr);
+
+    EditorSettings settings() const;
+
+private:
+    QSpinBox* m_gridStep;
+    QCheckBox* m_snap;
+    QCheckBox* m_arcs;
+    QDoubleSpinBox* m_arcRadius;
+    QComboBox* m_scheme;
+};
+
+}  // namespace diag
diff --git a/src/main.cpp b/src/main.cpp
new file mode 100644
index 0000000..ce7f293
--- /dev/null
+++ b/src/main.cpp
@@ -0,0 +1,28 @@
+#include "app/MainWindow.h"
+
+#include <QApplication>
+#include <QTimer>
+
+int main(int argc, char** argv)
+{
+    QApplication app(argc, argv);
+    QCoreApplication::setOrganizationName(QStringLiteral("PipeDiagram"));
+    QCoreApplication::setApplicationName(QStringLiteral("PipeDiagram"));
+
+    diag::MainWindow window;
+    window.show();
+    const QStringList args = app.arguments();
+    if (args.contains(QStringLiteral("--sample")))
+        window.loadSample();
+
+    // Headless smoke check: --screenshot <file.png> renders and exits.
+    const int shotIdx = args.indexOf(QStringLiteral("--screenshot"));
+    if (shotIdx >= 0 && shotIdx + 1 < args.size()) {
+        const QString path = args.at(shotIdx + 1);
+        QTimer::singleShot(300, &window, [&window, path] {
+            window.grab().save(path);
+            QApplication::quit();
+        });
+    }
+    return app.exec();
+}