wip(assembler): round L29 -- strate transitions honoured at the bedrock/ceiling interface

EVoxelStrateTransition from the upper strate shapes the bedrock(N)/ceiling(N+1) interface in the
shared composition layer: Hard flat; Gradient = smooth 2D hash surface (16 m owner width, about 4 m
measured undulation); Interleaved = 3D domain-warped fingered overlap within the width. Each band
keeps >= 2 Core voxels solid; faces return to the seam near passage mouths. Interface audit over
512 m: 0 hole columns for all modes; wider-than-declared and too-thin controls rejected. All passage,
route, proof and validator audits pass; deterministic Clang = GCC. Evaluator 15. Cost +4% SW,
+1.3% FI vs L28. Open: ring-like artifact on the FI floor capture; transition look unverified.

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

Standalone/Source/StreamBenchmarkHeadless.cpp

@@ -69,6 +69,9 @@ namespace
         bool AuditResolvedLayoutBoundaries=false;
         bool AuditResolvedLayoutPassages=false;
         bool AuditSurfaceClearance=false;
+        bool AuditStrateTransitions=false;
+        int TransitionModeOverride=-1;
+        int TransitionWidthChunksOverride=-1;
     };
 
     bool ParseInteger(std::string_view text,int& output)
@@ -103,6 +106,38 @@ namespace
         return true;
     }
 
+    bool OverrideTransitions(VFJson::Value& root,int mode,int widthChunks,std::string& error)
+    {
+        auto* object=std::get_if<VFJson::Value::Object>(&root.Data);
+        if(!object){error="transition fixture override requires an owner JSON object";return false;}
+        const auto stratesIt=object->find("strates");
+        if(stratesIt==object->end())
+        {error="transition fixture override cannot find the resolved strate array";return false;}
+        auto* strates=std::get_if<VFJson::Value::Array>(&stratesIt->second.Data);
+        if(!strates||strates->empty())
+        {error="transition fixture override found an empty or invalid strate array";return false;}
+        for(auto& strate:*strates)
+        {
+            auto* strateObject=std::get_if<VFJson::Value::Object>(&strate.Data);
+            if(!strateObject){error="transition fixture contains a malformed strate";return false;}
+            const auto assetIt=strateObject->find("asset");
+            if(assetIt==strateObject->end())continue;
+            auto* asset=std::get_if<VFJson::Value::Object>(&assetIt->second.Data);
+            if(!asset)continue;
+            if(mode>=0)
+            {
+                VFJson::Value value;value.Data=static_cast<double>(mode);
+                (*asset)["TransitionType"]=std::move(value);
+            }
+            if(widthChunks>=0)
+            {
+                VFJson::Value value;value.Data=static_cast<double>(widthChunks);
+                (*asset)["TransitionBlendChunks"]=std::move(value);
+            }
+        }
+        return true;
+    }
+
     bool ParseOptions(int argc,char** argv,FOptions& options)
     {
         const std::filesystem::path executable=std::filesystem::absolute(argv[0]);
@@ -126,6 +161,8 @@ namespace
                     "  --resolved-layout-output=FILE (canonical plan-time layout snapshot)\n"
                     "  --resolved-layout-only (exit after plan and snapshot validation)\n"
                     "  --audit-resolved-layout-boundaries (query Core at each recorded endpoint)\n"
+                    "  --audit-strate-transitions (measure interface crossing, band thickness and holes)\n"
+                    "  --transition-mode=hard|gradient|interleaved --transition-width-chunks=N (fixture override)\n"
                     "  --audit-resolved-layout-passages (capsule, support, route-binding and blocked-control audit)\n"
                     "  --audit-surface-clearance (sample biome terrain/caps against the resolved ceiling)\n"
                     "  --auto-surface-camera (place the 27-tile cube on this seed's surface)\n"
@@ -149,6 +186,21 @@ namespace
             else if(arg=="--audit-resolved-layout-boundaries")options.AuditResolvedLayoutBoundaries=true;
             else if(arg=="--audit-resolved-layout-passages")options.AuditResolvedLayoutPassages=true;
             else if(arg=="--audit-surface-clearance")options.AuditSurfaceClearance=true;
+            else if(arg=="--audit-strate-transitions")options.AuditStrateTransitions=true;
+            else if(arg.starts_with("--transition-mode="))
+            {
+                const std::string_view mode=arg.substr(std::string_view("--transition-mode=").size());
+                if(mode=="gradient")options.TransitionModeOverride=0;
+                else if(mode=="hard")options.TransitionModeOverride=1;
+                else if(mode=="interleaved")options.TransitionModeOverride=2;
+                else {std::fprintf(stderr,"Invalid transition mode: %.*s\n",static_cast<int>(mode.size()),mode.data());return false;}
+            }
+            else if(arg.starts_with("--transition-width-chunks="))
+            {
+                if(!readInt("--transition-width-chunks=",options.TransitionWidthChunksOverride)
+                    ||options.TransitionWidthChunksOverride<0||options.TransitionWidthChunksOverride>64)
+                {std::fprintf(stderr,"transition width chunks must be in 0..64\n");return false;}
+            }
             else if(arg=="--stream-benchmark")options.StreamBenchmark=true;
             else if(arg=="--stream-pipeline")options.StreamPipeline=true;
             else if(arg=="--stream-hash")options.StreamHash=true;
@@ -303,6 +355,10 @@ int main(int argc,char** argv)
     if(options.FloatingIslandsRecipe
         &&!StandaloneWorldAssemblyPrototype::SelectTopStrateAsFloatingIslands(ownerJsonRoot,error))
     {std::fprintf(stderr,"Floating-island recipe selection failed: %s\n",error.c_str());return 2;}
+    if((options.TransitionModeOverride>=0||options.TransitionWidthChunksOverride>=0)
+        &&!OverrideTransitions(ownerJsonRoot,options.TransitionModeOverride,
+            options.TransitionWidthChunksOverride,error))
+    {std::fprintf(stderr,"Transition fixture override failed: %s\n",error.c_str());return 2;}
     if(!StandaloneOwnerLoader::Resolve(ownerJsonRoot,*ownerWorld,error))
     {std::fprintf(stderr,"Owner data load failed: %s\n",error.c_str());return 2;}
     std::printf("[ColdTimeline] stage=owner_data_load end_ms=%.3f\n",
@@ -551,6 +607,6 @@ int main(int argc,char** argv)
         options.RegionCrossing,options.AuditTileShapeReadiness,
         options.DiagnosticSlowShapeCompileMs,options.AuditBasePageEquivalence,
         options.AuditRouteParity,options.AuditResolvedLayoutBoundaries,
-        options.AuditResolvedLayoutPassages,
+        options.AuditResolvedLayoutPassages,options.AuditStrateTransitions,
         &resolvedLayout);
 }