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
 // ---------------------------------------------------------------------------

src/lib/sim/BuildingSystem.h

@@ -40,11 +40,23 @@ public:
                    std::mt19937& rng);
 
     // -- Placement / demolish ------------------------------------------------
-    // Returns the new entity id.  Belt and Splitter register with BeltSystem
-    // directly; other types enter the construction queue.
+    // Returns the new entity id, or kInvalidBuildingId if the placement falls
+    // outside the world bounds (vertical extent and asteroid left edge).  Belt
+    // and Splitter register with BeltSystem directly; other types enter the
+    // construction queue.  Terrain type (A vs S) is NOT checked here so that
+    // tests can stage arbitrary layouts; the player-facing entry point
+    // (Simulation::tryPlaceBuilding) enforces the full rule via isPlacementValid.
     BuildingId place(BuildingType type, QPoint anchor, Rotation rotation,
                    Tick currentTick);
 
+    // Returns true if the placement satisfies REQ-BLD-PLACE-VALID terrain and
+    // world-bounds rules: every ship-dock (S) cell sits in space (x >= 0), every
+    // other body (A) cell sits on the asteroid (x < 0 and x >= the left edge),
+    // and every cell has 0 <= y < world.height_tiles. There is no right-side
+    // bound — space extends rightward. Tile occupancy is NOT checked here.
+    bool isPlacementValid(BuildingType type, QPoint anchor,
+                          Rotation rotation) const;
+
     // Remove a building or construction site by id.  Returns the refund in
     // building blocks (floor(cost * refundPercentage / 100)).  Returns 0 for
     // unknown ids.
@@ -136,6 +148,9 @@ private:
     void                initShipyardBuffers(Building& b) const;
     std::vector<Port>   computeInputPorts(const Building& b) const;
     std::vector<Item>   rollReprocessingOutput(const RecipeDef& recipe);
+    bool                bodyCellsWithinWorldBounds(
+                            const std::vector<QPoint>& bodyCells,
+                            QPoint anchor) const;
 
     const GameConfig&                              m_config;
     BeltSystem&                                    m_belts;

src/lib/sim/Simulation.cpp

@@ -947,6 +947,11 @@ bool Simulation::isModuleSchematicUnlocked(const std::string& moduleId) const
 
 BuildingId Simulation::tryPlaceBuilding(BuildingType type, QPoint anchor, Rotation rotation)
 {
+    if (!m_buildingSystem->isPlacementValid(type, anchor, rotation))
+    {
+        return kInvalidBuildingId;
+    }
+
     int cost = 0;
     for (const BuildingDef& def : m_config.buildings.buildings)
     {