fix issue where construction sites could be placed outside of game world and add tests

src/lib/sim/BuildingSystem.cpp

@@ -235,12 +235,18 @@ std::vector<Item> BuildingSystem::rollReprocessingOutput(const RecipeDef& recipe
 BuildingId BuildingSystem::place(BuildingType type, QPoint anchor,
                                 Rotation rotation, Tick currentTick)
 {
-    const BuildingId id = m_allocateBuildingId();
-
     const BuildingDef* def = findBuildingDef(type);
     assert(def != nullptr);
     const ParsedSurfaceMask mask = parseSurfaceMask(def->surfaceMask, rotation);
 
+    // Reject placements that fall outside the world (REQ-BLD-PLACE-VALID).
+    if (!bodyCellsWithinWorldBounds(mask.bodyCells, anchor))
+    {
+        return kInvalidBuildingId;
+    }
+
+    const BuildingId id = m_allocateBuildingId();
+
     // Record tile occupancy for body cells.
     for (const QPoint& cell : mask.bodyCells)
     {
@@ -270,6 +276,70 @@ BuildingId BuildingSystem::place(BuildingType type, QPoint anchor,
     return id;
 }
 
+bool BuildingSystem::bodyCellsWithinWorldBounds(const std::vector<QPoint>& bodyCells,
+                                                QPoint anchor) const
+{
+    const int heightTiles = m_config.world.heightTiles;
+    const int leftEdgeX   = -m_config.world.regions.asteroidWidth_tiles;
+    for (const QPoint& cell : bodyCells)
+    {
+        const QPoint worldCell = anchor + cell;
+        if (worldCell.y() < 0 || worldCell.y() >= heightTiles)
+        {
+            return false;
+        }
+        if (worldCell.x() < leftEdgeX)
+        {
+            return false;
+        }
+    }
+    return true;
+}
+
+bool BuildingSystem::isPlacementValid(BuildingType type, QPoint anchor,
+                                      Rotation rotation) const
+{
+    const BuildingDef* def = findBuildingDef(type);
+    if (def == nullptr)
+    {
+        return false;
+    }
+    const ParsedSurfaceMask mask = parseSurfaceMask(def->surfaceMask, rotation);
+
+    if (!bodyCellsWithinWorldBounds(mask.bodyCells, anchor))
+    {
+        return false;
+    }
+
+    // Terrain: ship-dock (S) cells must sit in space (x >= 0); all other body
+    // (A) cells must sit on the asteroid (x < 0). (REQ-BLD-PLACE-VALID)
+    for (const QPoint& cell : mask.bodyCells)
+    {
+        const QPoint worldCell = anchor + cell;
+        bool isShipDock = false;
+        for (const QPoint& dock : mask.shipDockCells)
+        {
+            if (dock == cell)
+            {
+                isShipDock = true;
+                break;
+            }
+        }
+        if (isShipDock)
+        {
+            if (worldCell.x() < 0)
+            {
+                return false;
+            }
+        }
+        else if (worldCell.x() >= 0)
+        {
+            return false;
+        }
+    }
+    return true;
+}
+
 // ---------------------------------------------------------------------------
 // Demolish
 // ---------------------------------------------------------------------------