make recipe selection and buffers of smelter and reprocessing plant behave like other buildings, except that a recipe may be chosen automatically

src/lib/sim/BuildingSystem.h

@@ -188,6 +188,13 @@ private:
     // (on construction completion, or when un-queuing a deconstruction). No-op for
     // non-belt-subsystem types. Splitter filters are (re)applied after placement.
 
+    // Selects a recipe for an auto-recipe building that has none, from a material being
+    // offered to it at one of its input ports (REQ-BLD-AUTO-RECIPE). No-op for every
+    // other building, for one that already holds a recipe, and for a material none of
+    // its recipes consumes. Called from both intake paths -- the belt pull and the
+    // direct coupling -- since either can be where the first material arrives.
+    void                 selectAutoRecipeIfUnset(Building& building,
+                                                 const ItemType& offered);
     // 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).