move the placement rules and the config-dependent queries off BuildingSystem

isPlacementValid, findRotateInPlaceTarget and the bodyCellsWithinWorldBounds
helper become PlacementRules.h — where a building may go and what already sits
on those tiles, answered from the factory state and the config. getInputPorts
and getSiteSplitterInfo join FactoryQueries.h, whose header comment now says
plainly that the last two also take the config because answering them means
reading a building definition.

computeInputPorts goes to PortGeometry.h alongside outputBodyTile/inputBodyTile:
it needs only Port and QPoint, so it belongs in core rather than in sim.

BuildingSystem is left with no query that reads the factory — its remaining const
methods are the emerging/incoming item walks, the checksum fold, and the buffer
initialisers. It changes the factory now; it no longer describes it.

Verified with a golden-checksum capture before and after — all four sample ticks
identical.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG

src/lib/sim/FactoryQueries.cpp

@@ -2,6 +2,9 @@
 
 #include <limits>
 
+#include "PortGeometry.h"
+#include "SurfaceMask.h"
+
 #include "Item.h"
 #include "ItemType.h"
 
@@ -126,3 +129,53 @@ bool deliverScrapToSalvageBay(FactoryState& state, BuildingId bayId)
     bay->outputBuffer.items.push_back(Item{ItemType{"scrap"}});
     return true;
 }
+
+std::vector<Port> getInputPorts(const FactoryState& state, const GameConfig& config,
+                                BuildingId id)
+{
+    if (const Building* building = findBuilding(state, id))
+    {
+        return building->inputPorts;
+    }
+    if (const ConstructionSite* site = findSite(state, id))
+    {
+        // A site stores no ports; derive its output ports from the mask (absolute)
+        // and run the same input-edge scan (REQ-BLD-BELT-DRAG, REQ-MAT-INPUT-PORTS).
+        const BuildingDef* def = config.buildings.findBuildingDef(site->type);
+        if (def == nullptr) { return {}; }
+        const ParsedSurfaceMask mask = parseSurfaceMask(def->surfaceMask, site->rotation);
+        std::vector<Port> outputPortsAbsolute;
+        outputPortsAbsolute.reserve(mask.outputPorts.size());
+        for (const Port& port : mask.outputPorts)
+        {
+            outputPortsAbsolute.push_back(Port{ site->anchor + port.tile, port.direction });
+        }
+        return computeInputPorts(site->bodyCells, outputPortsAbsolute);
+    }
+    return {};
+}
+
+
+std::optional<BeltSystem::SplitterInfo>
+getSiteSplitterInfo(const FactoryState& state, const GameConfig& config, BuildingId id)
+{
+    for (const ConstructionSite& site : state.constructionQueue)
+    {
+        if (site.id != id) { continue; }
+        if (site.type != BuildingType::Splitter) { return std::nullopt; }
+
+        const BuildingDef* def = config.buildings.findBuildingDef(site.type);
+        const ParsedSurfaceMask mask = parseSurfaceMask(
+            def ? def->surfaceMask : std::vector<std::string>{}, site.rotation);
+        if (mask.outputPorts.size() < 2) { return std::nullopt; }
+
+        BeltSystem::SplitterInfo info;
+        info.outputA = mask.outputPorts[0].direction;
+        info.outputB = mask.outputPorts[1].direction;
+        info.filterA = site.splitterFilterA;
+        info.filterB = site.splitterFilterB;
+        return info;
+    }
+    return std::nullopt;
+}
+