allow to set the recipe already for construction sites

src/test/BuildingTest.cpp

@@ -984,3 +984,42 @@ TEST_CASE("BuildingSystem: rotateInPlace re-registers a belt tile with BeltSyste
     // Belt tile must still be registered after rotation — items can be placed on it.
     REQUIRE(belts.tryPutItem(QPoint(0, 0), makeItem("iron_ore")));
 }
+
+TEST_CASE("BuildingSystem: splitter filters configured on a construction site carry over "
+          "to the built splitter (REQ-BLD-SITE-CONFIG)", "[building]")
+{
+    PlacementFixture f;
+
+    const QPoint tile(5, 5);
+    const BuildingId id = f.bs.place(BuildingType::Splitter, tile, Rotation::East, 0);
+    REQUIRE(id != kInvalidBuildingId);
+    REQUIRE(f.bs.findSite(id) != nullptr);
+
+    // Configure an output filter on the still-queued splitter site.
+    const std::vector<ItemType> filterA{ ItemType{"iron_ore"} };
+    const std::vector<ItemType> filterB{};
+    f.bs.setSiteSplitterFilters(id, filterA, filterB);
+
+    // The site reports its two output directions and the stored filters before
+    // it is built; it is not yet registered with BeltSystem.
+    const std::optional<BeltSystem::SplitterInfo> siteInfo = f.bs.getSiteSplitterInfo(id);
+    REQUIRE(siteInfo.has_value());
+    REQUIRE(siteInfo->filterA == filterA);
+    REQUIRE(siteInfo->filterB.empty());
+    REQUIRE_FALSE(f.belts.getSplitterInfo(tile).has_value());
+
+    // Run until construction completes.
+    Tick tick = 0;
+    while (f.bs.allBuildings().empty() && tick < 100000)
+    {
+        runTicks(f.bs, f.belts, 1, tick);
+    }
+    REQUIRE(f.bs.allBuildings().size() == 1);
+    REQUIRE(f.bs.allBuildings()[0].type == BuildingType::Splitter);
+
+    // The built splitter is registered with BeltSystem carrying the filters.
+    const std::optional<BeltSystem::SplitterInfo> builtInfo = f.belts.getSplitterInfo(tile);
+    REQUIRE(builtInfo.has_value());
+    REQUIRE(builtInfo->filterA == filterA);
+    REQUIRE(builtInfo->filterB.empty());
+}