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

src/lib/sim/BuildingSystem.h

@@ -181,6 +181,25 @@ public:
     void appendChecksum(Hasher& hasher) const;
 
 private:
+    Building*            findBuildingMutable(BuildingId id);
+    // True if the consumer would accept `type` at the given input port right now:
+    // it is a required input (or a building block for the HQ), the reservation-aware
+    // buffer has room, and the input belt entry is free (REQ-MAT-INPUT-INTAKE).
+    bool                 canAcceptInput(const Building& consumer,
+                                        std::size_t inputPortIndex,
+                                        const ItemType& type) const;
+    // Places an accepted item onto the consumer's input belt at progress 0.0,
+    // reserving a per-material buffer slot (REQ-MAT-INPUT-INTAKE).
+    void                 depositToInputBelt(Building& consumer,
+                                            std::size_t inputPortIndex,
+                                            const Item& item);
+    // Attempts to hand an emerging output item straight into a directly adjacent
+    // building whose input edge meets the producer's output port (REQ-MAT-DIRECT-COUPLE).
+    // Returns true if the item was accepted onto the consumer's input belt.
+    bool                 tryDirectCoupleDeposit(BuildingId producerId,
+                                                const Port& outputPort,
+                                                const Item& item);
+
     const BuildingDef*  findBuildingDef(BuildingType type) const;
     const RecipeDef*    findRecipe(const std::string& id, BuildingType type) const;
     const ShipDef*      findShipDef(const std::string& id) const;