Implement deferred L-shaped belt drag placement

src/ui/GameWorldView.h

@@ -35,6 +35,7 @@
 #include "SpeedChangeRequestedEvent.h"
 
 #include "entt/entity/entity.hpp"
+#include "BeltDragPath.h"
 #include "CommandManager.h"
 #include "EntitySelectionChangedEvent.h"
 #include "GameConfig.h"
@@ -204,6 +205,24 @@ private:
     void                     stepSpeed(int delta);
     void                     placeAtTile(QPoint tile);
 
+    // Belt drag placement (REQ-BLD-BELT-DRAG).
+    // Per-path-tile decision, shared by ghost drawing and release-time placement.
+    enum class BeltTileAction { PlaceNew, RotateInPlace, Invalid };
+    struct BeltDragResolved
+    {
+        BeltTileAction            action;
+        bool                      affordable;   // meaningful only for PlaceNew
+        std::optional<BuildingId> rotateId;     // set only for RotateInPlace
+    };
+    // Recomputes m_beltDragPath from m_beltDragAnchor to cursorTile using the
+    // current ghost orientation.
+    void                          recomputeBeltDragPath(QPoint cursorTile);
+    // Classifies each path tile against the current sim state, applying cumulative
+    // affordability to the PlaceNew tiles.
+    std::vector<BeltDragResolved> resolveBeltDragPath() const;
+    // Enqueues placements and rotate-in-place commands for the resolved path.
+    void                          applyBeltDragPath();
+
     // Copy-settings gesture (REQ-BLD-COPY-CONFIG): Shift+right-click copies a
     // building's configuration into m_copiedConfig; Shift+left-click applies it to
     // another building of the same type via the existing configuration commands.
@@ -255,7 +274,11 @@ private:
     Rotation                             m_ghostRotation;
     QPoint                               m_ghostTile;
     bool                                 m_ghostValid;
-    std::set<QPoint, QPointCompare>      m_beltDragTiles;
+    // Deferred belt drag placement (REQ-BLD-BELT-DRAG): while dragging, the
+    // rectilinear anchor->cursor path is recomputed on each move and only applied
+    // on release. Empty unless a belt drag is in progress.
+    std::vector<BeltPathTile>            m_beltDragPath;
+    QPoint                               m_beltDragAnchor;
     bool                                 m_dragging;
 
     std::optional<Blueprint> m_blueprintMode;