wip(assembler): round L30 -- FI floor ring defect fixed; transition cost recovered

The Gradient interface left native solid density in the air-side gap and snapped the face to
voxel levels (concentric ring steps on the FI floor). The owner Gradient path now writes signed
distance both sides; match error RMS 0.36 -> 0.11 m. Band and fade-tile culling cut transition
cost: whole view vs L24 SW +2.7%, FI +0.2%. Evaluator 16. Deterministic across compilers and
workers; interface and passage audits pass. Found: on the real FloatingIslands recipe, the
rock-column connected-ends audit fails (all styles); earlier matrices ran SurfaceWorld twice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Research/WorldAssemblerM3/Linux30/ProbeTransitionNoise.cpp

@@ -0,0 +1,28 @@
+#include "CoreNamespacePreamble.h"
+#include "ResolvedLayoutInternal.h"
+
+int main()
+{
+    VoxelForgeCore::ResolvedLayoutStratumV2 upper, lower;
+    upper.strateIndex=0;upper.order=0;upper.transitionMode="Gradient";
+    upper.transitionWidthMicrometres=16000000;
+    upper.bedrock.bottomMicrometres=-120000000;
+    upper.bedrock.topMicrometres=-119500000;
+    upper.bedrock.presentInCurrentField=true;
+    lower.strateIndex=1;lower.order=1;
+    lower.ceiling.bottomMicrometres=-126250000;
+    lower.ceiling.topMicrometres=-120000000;
+    lower.ceiling.presentInCurrentField=true;
+    for(const auto& point:std::array<std::array<std::int64_t,2>,5>{
+        std::array<std::int64_t,2>{64000000,-32000000},
+        {65000000,-32000000},{64000000,-31000000},{70000000,-32000000},
+        {80000000,-35000000}})
+    {
+        const auto bands=VoxelForgeCore::EvaluateResolvedLayoutTransitionBandsV1(
+            upper,lower,0,8000000,point[0],point[1]);
+        std::printf("x_m=%.3f y_m=%.3f top_m=%.6f bottom_m=%.6f\n",
+            point[0]/1000000.0,point[1]/1000000.0,
+            bands.upperBedrockTopMicrometres/1000000.0,
+            bands.upperBedrockBottomMicrometres/1000000.0);
+    }
+}