Always show shipyard layout preview and Configure button, disabled until schematic selected

src/ui/SelectedBuildingPanel.cpp

@@ -566,11 +566,21 @@ void SelectedBuildingPanel::updateShipyardLayoutWidgets(
     const std::string& recipeId,
     const std::optional<ShipLayoutConfig>& shipLayout)
 {
-    const ShipDef* shipDef = (type == BuildingType::Shipyard)
-        ? findShipDef(recipeId)
-        : nullptr;
+    // The preview and Configure button are shipyard-only controls; hide them
+    // entirely for other building types.
+    if (type != BuildingType::Shipyard)
+    {
+        m_layoutPreview->hide();
+        m_configureLayoutBtn->hide();
+        return;
+    }
 
-    if (shipDef && !shipDef->layout.empty())
+    const ShipDef* shipDef = findShipDef(recipeId);
+    const bool hasSchematic = shipDef && !shipDef->layout.empty();
+
+    // Always show the preview and Configure button for a shipyard; they are only
+    // enabled once a schematic is selected (REQ-MOD-UI-PREVIEW).
+    if (hasSchematic)
     {
         ShipLayoutConfig layout;
         if (shipLayout.has_value())
@@ -579,14 +589,16 @@ void SelectedBuildingPanel::updateShipyardLayoutWidgets(
         }
         m_layoutPreview->setShipAndLayout(
             shipDef->layout, layout, &m_config->modules.modules);
-        m_layoutPreview->show();
-        m_configureLayoutBtn->show();
     }
     else
     {
-        m_layoutPreview->hide();
-        m_configureLayoutBtn->hide();
+        m_layoutPreview->showPlaceholder();
     }
+
+    m_layoutPreview->setEnabled(hasSchematic);
+    m_configureLayoutBtn->setEnabled(hasSchematic);
+    m_layoutPreview->show();
+    m_configureLayoutBtn->show();
 }
 
 const RecipeDef* SelectedBuildingPanel::findRecipe(const Building* b) const

src/ui/ShipLayoutPreview.cpp

@@ -8,6 +8,10 @@ namespace
 
 const int kCellSize = 8;
 
+// Size of the empty placeholder box shown when no schematic is selected.
+const int kPlaceholderWidth  = 64;
+const int kPlaceholderHeight = 40;
+
 const ModuleDef* findModuleDef(const std::vector<ModuleDef>& modules,
                                const std::string& id)
 {
@@ -90,14 +94,28 @@ void ShipLayoutPreview::clear()
     m_modules = nullptr;
     m_rows = 0;
     m_cols = 0;
+    m_placeholder = false;
     setFixedSize(0, 0);
     update();
 }
 
+void ShipLayoutPreview::showPlaceholder()
+{
+    m_grid.clear();
+    m_placedModules.clear();
+    m_modules = nullptr;
+    m_rows = 0;
+    m_cols = 0;
+    m_placeholder = true;
+    setFixedSize(kPlaceholderWidth, kPlaceholderHeight);
+    update();
+}
+
 void ShipLayoutPreview::setShipAndLayout(const std::vector<std::string>& shipLayout,
                                          const ShipLayoutConfig& layout,
                                          const std::vector<ModuleDef>* modules)
 {
+    m_placeholder = false;
     m_modules = modules;
     m_placedModules = layout.placedModules;
     m_rows = static_cast<int>(shipLayout.size());
@@ -156,6 +174,18 @@ void ShipLayoutPreview::setShipAndLayout(const std::vector<std::string>& shipLay
 
 void ShipLayoutPreview::paintEvent(QPaintEvent* /*event*/)
 {
+    if (m_placeholder)
+    {
+        QPainter painter(this);
+        painter.setRenderHint(QPainter::Antialiasing, false);
+        const QRect box = rect().adjusted(0, 0, -1, -1);
+        painter.fillRect(box, QColor(40, 40, 40));
+        painter.setPen(QColor(128, 128, 128));
+        painter.drawRect(box);
+        painter.drawText(box, Qt::AlignCenter, tr("No schematic"));
+        return;
+    }
+
     if (m_rows == 0 || m_cols == 0)
     {
         return;

src/ui/ShipLayoutPreview.h

@@ -20,6 +20,10 @@ public:
                           const std::vector<ModuleDef>* modules);
     void clear();
 
+    // Shows an empty placeholder box (no ship layout) so the preview stays
+    // visible while no schematic is selected (REQ-MOD-UI-PREVIEW).
+    void showPlaceholder();
+
 protected:
     void paintEvent(QPaintEvent* event) override;
 
@@ -35,4 +39,5 @@ private:
     const std::vector<ModuleDef>* m_modules;
     int m_rows;
     int m_cols;
+    bool m_placeholder = false;
 };