Add deconstruction queue

src/lib/sim/Simulation.h

@@ -139,9 +139,14 @@ private:
     // Returns the new entity id, or nullopt if blocks are insufficient.
     std::optional<BuildingId> tryPlaceBuilding(BuildingType type, QPoint anchor, Rotation rotation);
 
-    // Demolishes the building with the given id and refunds building blocks.
+    // Marks the building with the given id for demolition: a construction site is
+    // removed instantly (full refund), a built building is queued for timed
+    // deconstruction (REQ-BLD-DECON-QUEUE), refunded on completion.
     void demolish(BuildingId id);
 
+    // Takes a queued building back out of the deconstruction queue (REQ-BLD-DECON-QUEUE).
+    void cancelDeconstruction(BuildingId id);
+
     // Applies the player's chosen schematic from the pending choices.
     // choiceIndex must be in [0, pendingChoices.size()).
     // Clears the pending choices after application.