allow to set the recipe already for construction sites

src/lib/sim/Building.h

@@ -54,6 +54,11 @@ struct ConstructionSite
     std::string  recipeId;                      // may be configured before completion
     Tick         completesAt   = 0;             // 0 = queued but not yet started
     std::optional<ShipLayoutConfig> shipLayout;
+
+    // Splitter output filters configured before completion (REQ-BLD-SITE-CONFIG).
+    // Empty = accept all; applied to the BeltSystem when the splitter is built.
+    std::vector<ItemType> splitterFilterA;
+    std::vector<ItemType> splitterFilterB;
 };
 
 // A fully constructed, operational building.

src/lib/sim/BuildingSystem.cpp

@@ -479,6 +479,44 @@ void BuildingSystem::setShipLayout(BuildingId id, const ShipLayoutConfig& layout
     }
 }
 
+std::optional<BeltSystem::SplitterInfo>
+BuildingSystem::getSiteSplitterInfo(BuildingId id) const
+{
+    for (const ConstructionSite& site : m_constructionQueue)
+    {
+        if (site.id != id) { continue; }
+        if (site.type != BuildingType::Splitter) { return std::nullopt; }
+
+        const BuildingDef* def = findBuildingDef(site.type);
+        const ParsedSurfaceMask mask = parseSurfaceMask(
+            def ? def->surfaceMask : std::vector<std::string>{}, site.rotation);
+        if (mask.outputPorts.size() < 2) { return std::nullopt; }
+
+        BeltSystem::SplitterInfo info;
+        info.outputA = mask.outputPorts[0].direction;
+        info.outputB = mask.outputPorts[1].direction;
+        info.filterA = site.splitterFilterA;
+        info.filterB = site.splitterFilterB;
+        return info;
+    }
+    return std::nullopt;
+}
+
+void BuildingSystem::setSiteSplitterFilters(BuildingId id,
+                                            const std::vector<ItemType>& filterA,
+                                            const std::vector<ItemType>& filterB)
+{
+    for (ConstructionSite& site : m_constructionQueue)
+    {
+        if (site.id == id && site.type == BuildingType::Splitter)
+        {
+            site.splitterFilterA = filterA;
+            site.splitterFilterB = filterB;
+            return;
+        }
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Tick hooks
 // ---------------------------------------------------------------------------
@@ -564,6 +602,11 @@ void BuildingSystem::tickConstruction(Tick currentTick)
         m_belts.placeSplitter(front.anchor,
                               mask.outputPorts[0].direction,
                               mask.outputPorts[1].direction);
+        // Carry over any filters configured while under construction
+        // (REQ-BLD-SITE-CONFIG).
+        m_belts.setSplitterFilters(front.anchor,
+                                   front.splitterFilterA,
+                                   front.splitterFilterB);
     }
     else if (front.type == BuildingType::TunnelEntry)
     {

src/lib/sim/BuildingSystem.h

@@ -70,6 +70,18 @@ public:
     // (materials discarded) and reinitializes input buffers (REQ-BLD-SHIPYARD).
     void setShipLayout(BuildingId id, const ShipLayoutConfig& layout);
 
+    // Splitter filter configuration for a queued/under-construction Splitter
+    // site (REQ-BLD-SITE-CONFIG). Operational splitters are configured through
+    // BeltSystem by tile; these mirror that for sites, which are not yet
+    // registered with BeltSystem. getSiteSplitterInfo returns the site's two
+    // output directions (derived from its surface mask) and stored filters, or
+    // nullopt if the id is not a Splitter site. The stored filters are applied
+    // to BeltSystem when the splitter finishes building (tickConstruction).
+    std::optional<BeltSystem::SplitterInfo> getSiteSplitterInfo(BuildingId id) const;
+    void setSiteSplitterFilters(BuildingId id,
+                                const std::vector<ItemType>& filterA,
+                                const std::vector<ItemType>& filterB);
+
     // -- Tick hooks (called from Simulation::tick in the documented order) ---
     void tickConstruction(Tick currentTick);
     void tickBeltPull();