implement belts are now added to the build queue

src/test/BuildingTest.cpp

@@ -92,7 +92,8 @@ TEST_CASE("BuildingSystem: place miner occupies expected body tiles", "[building
     REQUIRE_FALSE(bs.isTileOccupied(QPoint(1, 1)));
 }
 
-TEST_CASE("BuildingSystem: placing a belt registers it with BeltSystem", "[building]")
+TEST_CASE("BuildingSystem: placing a belt registers it with BeltSystem after construction",
+          "[building]")
 {
     const GameConfig cfg = loadConfig();
     BeltSystem belts(cfg.world.beltSpeedTilesPerSecond);
@@ -107,6 +108,13 @@ TEST_CASE("BuildingSystem: placing a belt registers it with BeltSystem", "[build
 
     bs.place(BuildingType::Belt, QPoint(5, 5), Rotation::East, 0);
 
+    // Belt is queued — not yet in BeltSystem.
+    REQUIRE_FALSE(belts.tryPutItem(QPoint(5, 5), makeItem("iron_ore")));
+
+    // Complete construction (1 s).
+    Tick tick = 0;
+    runTicks(bs, belts, static_cast<int>(secondsToTicks(1.0)) + 1, tick);
+
     REQUIRE(belts.tryPutItem(QPoint(5, 5), makeItem("iron_ore")));
     REQUIRE(bs.allBuildings().empty());  // belts do not create Building instances
 }