wip(assembler): round S10 -- LOD8 horizon sampled at MC spacing: LOD8 worker time 18.8 s -> 4.3 s

Planar far horizon samples the LOD8 interior at the MC cell spacing, keeping
128-voxel boundary strips; far recipe v3. LOD8 p95 59.8 -> 13.9 ms, spawn
worker-seconds ~41 -> 26.9, full set 7.8 -> 7.1 s, ring 0.49 s, LOD0 1.43 s,
40 m/s ring 75/75. S3/S4 2 cm agreement, 100% cap coverage, W1/W8/W12 and
W1/W8/W16 determinism pass. Report: Standalone/Research/WorldAssemblerM3/Round14.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Core/src/WorldAssemblerInternal.h

@@ -1487,6 +1487,17 @@ namespace world_assembly_detail
         HeightfieldColumnStats.columnComputeMilliseconds+=std::chrono::duration<double,std::milli>(
             std::chrono::steady_clock::now()-start).count();
         ++HeightfieldColumnStats.columnMisses;
+        if(HeightfieldColumnStats.captureCoordinates&&HeightfieldColumnStats.coordinateCaptureComplete)
+        {
+            try
+            {
+                HeightfieldColumnStats.evaluatedCoordinates.push_back({x,y});
+            }
+            catch(...)
+            {
+                HeightfieldColumnStats.coordinateCaptureComplete=false;
+            }
+        }
         entry={&recipe,&plan,recipe.contentHash,plan.contentHash,x,y,column};
         return column;
     }
@@ -1954,10 +1965,19 @@ HeightfieldPointSample Heightfield2D::point(std::int64_t x, std::int64_t y,
     return out;
 }
 
-void Heightfield2D::resetThreadColumnCacheStats() noexcept
-{ world_assembly_detail::HeightfieldColumnStats={}; }
+void Heightfield2D::resetThreadColumnCacheStats(bool captureCoordinates) noexcept
+{
+    auto& Stats=world_assembly_detail::HeightfieldColumnStats;
+    Stats.pointCalls=0;
+    Stats.columnHits=0;
+    Stats.columnMisses=0;
+    Stats.columnComputeMilliseconds=0.0;
+    Stats.captureCoordinates=captureCoordinates;
+    Stats.coordinateCaptureComplete=true;
+    Stats.evaluatedCoordinates.clear();
+}
 
-HeightfieldColumnCacheStats Heightfield2D::threadColumnCacheStats() noexcept
+const HeightfieldColumnCacheStats& Heightfield2D::threadColumnCacheStats() noexcept
 { return world_assembly_detail::HeightfieldColumnStats; }
 
 HeightfieldBoxClass Heightfield2D::classifyLatticeBox(std::int64_t minimumX,