Allow direct output-to-input port coupling between adjacent buildings

src/test/BuildingTest.cpp

@@ -807,6 +807,84 @@ TEST_CASE("BuildingSystem: miner output buffer drains onto adjacent belt", "[bui
     REQUIRE(item->type.id == "iron_ore");
 }
 
+// Two directly adjacent buildings whose ports meet transfer items with no belt in
+// between: a miner's iron_ore output feeds straight into a smelter, which smelts it
+// (REQ-MAT-DIRECT-COUPLE).
+TEST_CASE("BuildingSystem: output port couples directly into an adjacent input port",
+          "[building]")
+{
+    const GameConfig cfg = loadConfig();
+    BeltSystem belts(cfg.world.beltSpeed_tps);
+    int stock = 0;
+    std::mt19937 rng(0);
+    BuildingId nextBuildingId = 1;
+    BuildingSystem bs(cfg, belts,
+                      [&nextBuildingId]() { return nextBuildingId++; },
+                      [&stock](int n) { stock += n; },
+                      [](const std::string&, QVector2D, const std::optional<ShipLayoutConfig>&) {},
+                      [](const std::string&) -> bool { return true; },
+                      rng);
+
+    // Miner at (0,0): body (0,0),(1,0),(0,1); output port tile (1,1) flowing East.
+    const BuildingId minerId = bs.place(BuildingType::Miner, QPoint(0, 0), Rotation::East, 0);
+    bs.setRecipe(minerId, "mine_iron_ore");
+    // Smelter anchored at (1,1): body (1,1),(2,1),(1,2),(2,2). Its body cell (1,1) is
+    // the miner's output-port tile, and its west input edge there faces East, so the
+    // two ports meet — no belt placed anywhere.
+    const BuildingId smelterId = bs.place(BuildingType::Smelter, QPoint(1, 1), Rotation::East, 0);
+
+    Tick tick = 0;
+    // Smelter build (15s) + margin for coupling and a smelt cycle.
+    runTicks(bs, belts, static_cast<int>(secondsToTicks(30.0)), tick);
+
+    const Building* smelter = bs.findBuilding(smelterId);
+    REQUIRE(smelter != nullptr);
+    // iron_ore reached the smelter over the direct coupling and was smelted.
+    bool hasIronIngot = false;
+    for (const Item& produced : outputSideItems(*smelter))
+    {
+        if (produced.type.id == "iron_ingot") { hasIronIngot = true; }
+    }
+    REQUIRE(hasIronIngot);
+}
+
+// A producer coupled to a building that cannot accept its item delivers nothing; the
+// item stays stuck at the producer's output port (REQ-MAT-DIRECT-COUPLE acceptance).
+TEST_CASE("BuildingSystem: direct coupling to a non-consumer leaves the item stuck",
+          "[building]")
+{
+    const GameConfig cfg = loadConfig();
+    BeltSystem belts(cfg.world.beltSpeed_tps);
+    int stock = 0;
+    std::mt19937 rng(0);
+    BuildingId nextBuildingId = 1;
+    BuildingSystem bs(cfg, belts,
+                      [&nextBuildingId]() { return nextBuildingId++; },
+                      [&stock](int n) { stock += n; },
+                      [](const std::string&, QVector2D, const std::optional<ShipLayoutConfig>&) {},
+                      [](const std::string&) -> bool { return true; },
+                      rng);
+
+    // Producing miner at (0,0), output port (1,1) East.
+    const BuildingId minerId = bs.place(BuildingType::Miner, QPoint(0, 0), Rotation::East, 0);
+    bs.setRecipe(minerId, "mine_iron_ore");
+    // A second, idle miner anchored at (1,1) occupies the output-port tile but takes
+    // no inputs, so it cannot accept the iron_ore.
+    const BuildingId sinkId = bs.place(BuildingType::Miner, QPoint(1, 1), Rotation::East, 0);
+
+    Tick tick = 0;
+    // Both miners build sequentially (10s each), then the producer runs and jams.
+    runTicks(bs, belts, static_cast<int>(secondsToTicks(25.0)), tick);
+
+    const Building* miner = bs.findBuilding(minerId);
+    const Building* sink  = bs.findBuilding(sinkId);
+    REQUIRE(miner != nullptr);
+    REQUIRE(sink != nullptr);
+    // Nothing was delivered, and the producer's output side has backed up to its cap.
+    REQUIRE(sink->pendingInputCount(ItemType{"iron_ore"}) == 0);
+    REQUIRE(miner->outputItemCount() == miner->outputBuffer.capacity);
+}
+
 // ---------------------------------------------------------------------------
 // setRecipe clears buffers
 // ---------------------------------------------------------------------------