wip(assembler): round L2 -- the cross-platform hash check can fail; FP contraction changes the world

Clang -ffp-contract=on/fast and GCC's default (fast) all change the density hash on the L1 view;
contraction off reproduces L1 (= Windows S13) at W1/W12. Seed sweep: 48 FloatingIslands seeds and
14 effective SurfaceWorld seeds (34 of 48 fell on a seed-independent cube) match across Clang/GCC
and W1/W12. Standalone gains --seed/--recipe/--render-distance-chunks (viewer + headless) and a
Windows replay script. Linux standalone workers get 32 MiB pthread stacks (TLS is 17.3 MiB/thread),
so no external stack limit is needed. No Core or world-output change; MSVC compile unverified.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Standalone/Source/StreamBenchmarkHeadless.cpp

@@ -2,6 +2,7 @@
 #include "StandaloneCoreScheduler.h"
 #include "StreamBenchmarkPipeline.h"
 #include "WorldAssemblyPrototype.h"
+#include "StandaloneTlsProbe.h"
 #include "../Core/src/StandaloneSnapshotAdapter.h"
 
 #include <algorithm>
@@ -32,6 +33,13 @@ namespace
         bool StreamHash=false;
         bool ProfileColumnOverlap=false;
         bool ForceGenerate=false;
+        bool HasSeedOverride=false;
+        int SeedOverride=0;
+        bool HasRenderDistanceOverride=false;
+        int RenderDistanceOverride=0;
+        bool FloatingIslandsRecipe=false;
+        bool TlsProbeRequested=false;
+        int TlsProbeWorkers=0;
         bool HasCamera=false;
         FVector CameraMeters=FVector::ZeroVector;
     };
@@ -72,6 +80,9 @@ namespace
                     "  --workers=N --clip-radius=N --max-clip-level=N --max-level=N\n"
                     "  --camera=X,Y,Z,YAW,PITCH (position in metres) --stream-hash\n"
                     "  --profile-column-overlap --far-horizon-lod8-step=N --force-generate\n"
+                    "  --seed=N --recipe=surface-world|floating-islands\n"
+                    "  --render-distance-chunks=N (0 disables the extra far ring)\n"
+                    "  --tls-probe=N (Linux worker TLS/stack measurement; N=0..12)\n"
                     "  --process-affinity=MASK --process-priority=Normal --frame-limit=FPS (viewer compatibility only)\n",
                     argv[0]);
                 return false;
@@ -82,6 +93,28 @@ namespace
             else if(arg=="--stream-hash")options.StreamHash=true;
             else if(arg=="--profile-column-overlap")options.ProfileColumnOverlap=true;
             else if(arg=="--force-generate")options.ForceGenerate=true;
+            else if(arg.starts_with("--recipe="))
+            {
+                const std::string_view recipe=arg.substr(std::string_view("--recipe=").size());
+                if(recipe=="surface-world")options.FloatingIslandsRecipe=false;
+                else if(recipe=="floating-islands")options.FloatingIslandsRecipe=true;
+                else {std::fprintf(stderr,"Invalid --recipe value: %.*s\n",static_cast<int>(recipe.size()),recipe.data());return false;}
+            }
+            else if(arg.starts_with("--seed="))
+            {if(!readInt("--seed=",options.SeedOverride))return false;options.HasSeedOverride=true;}
+            else if(arg.starts_with("--render-distance-chunks="))
+            {
+                if(!readInt("--render-distance-chunks=",options.RenderDistanceOverride))return false;
+                options.RenderDistanceOverride=std::max(0,options.RenderDistanceOverride);
+                options.HasRenderDistanceOverride=true;
+            }
+            else if(arg.starts_with("--tls-probe="))
+            {
+                if(!readInt("--tls-probe=",options.TlsProbeWorkers))return false;
+                if(options.TlsProbeWorkers<0||options.TlsProbeWorkers>12)
+                {std::fprintf(stderr,"--tls-probe must be in 0..12\n");return false;}
+                options.TlsProbeRequested=true;
+            }
             else if(arg.starts_with("--camera="))
             {
                 if(!ParseCamera(arg.substr(9),options.CameraMeters))
@@ -112,6 +145,7 @@ namespace
         options.ClipRadius=std::clamp(options.ClipRadius,1,64);
         options.MaxClipLevel=std::clamp(options.MaxClipLevel,0,8);
         options.FarHorizonLOD8InteriorStepVoxels=std::max(0,options.FarHorizonLOD8InteriorStepVoxels);
+        if(options.TlsProbeRequested)return true;
         if(!options.WorldAssemblerPrototype||!options.StreamBenchmark||!options.StreamPipeline)
         {
             std::fprintf(stderr,"This headless target runs the world-assembler streaming pipeline; pass --world-assembler-prototype --stream-benchmark --stream-pipeline.\n");
@@ -127,10 +161,12 @@ int main(int argc,char** argv)
     const auto coldStart=Clock::now();
     FOptions options;
     if(!ParseOptions(argc,argv,options))return 2;
-    std::printf("[HeadlessConfig] data=%s workers=%d clip_radius=%d max_clip_level=%d max_level=%d hash=%s column_overlap=%s force_generate=%s\n",
+    if(options.TlsProbeRequested)return StandaloneTlsProbe::Run(options.TlsProbeWorkers);
+    std::printf("[HeadlessConfig] data=%s workers=%d clip_radius=%d max_clip_level=%d max_level=%d hash=%s column_overlap=%s force_generate=%s recipe=%s seed_override=%s render_distance_override=%s\n",
         options.DataPath.string().c_str(),options.WorkerCount,options.ClipRadius,options.MaxClipLevel,
         options.MaxLevel,options.StreamHash?"on":"off",options.ProfileColumnOverlap?"on":"off",
-        options.ForceGenerate?"on":"off");
+        options.ForceGenerate?"on":"off",options.FloatingIslandsRecipe?"floating-islands":"surface-world",
+        options.HasSeedOverride?"yes":"no",options.HasRenderDistanceOverride?"yes":"no");
     std::printf("[ColdTimeline] stage=owner_data_load begin_ms=%.3f\n",
         std::chrono::duration<double,std::milli>(Clock::now()-coldStart).count());
 
@@ -147,6 +183,16 @@ int main(int argc,char** argv)
         if(!VFJson::Parser(std::move(ownerJsonText)).Parse(ownerJsonRoot,error))
         {std::fprintf(stderr,"Owner data load failed: %s\n",error.c_str());return 2;}
     }
+    if(options.HasSeedOverride
+        &&!StandaloneWorldAssemblyPrototype::OverrideStandaloneSeed(ownerJsonRoot,options.SeedOverride,error))
+    {std::fprintf(stderr,"Seed override failed: %s\n",error.c_str());return 2;}
+    if(options.HasRenderDistanceOverride
+        &&!StandaloneWorldAssemblyPrototype::OverrideStandaloneRenderDistance(
+            ownerJsonRoot,options.RenderDistanceOverride,error))
+    {std::fprintf(stderr,"Render-distance override failed: %s\n",error.c_str());return 2;}
+    if(options.FloatingIslandsRecipe
+        &&!StandaloneWorldAssemblyPrototype::SelectTopStrateAsFloatingIslands(ownerJsonRoot,error))
+    {std::fprintf(stderr,"Floating-island recipe selection 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",
@@ -167,9 +213,14 @@ int main(int argc,char** argv)
         cameraVoxels=FVector(options.CameraMeters.X*4.0f,options.CameraMeters.Y*4.0f,options.CameraMeters.Z*4.0f);
 
     const auto planStart=Clock::now();
+    VoxelForgeCore::WorldAssemblyManifest worldAssembly;
     if(!StandaloneWorldAssemblyPrototype::AttachRound1WorldAssemblyPrototype(
-        *ownerWorld,ownerJsonRoot,error,{}))
+        *ownerWorld,ownerJsonRoot,error,{},&worldAssembly))
     {std::fprintf(stderr,"World assembler prototype setup failed: %s\n",error.c_str());return 2;}
+    if(options.FloatingIslandsRecipe
+        &&!StandaloneWorldAssemblyPrototype::AttachFloatingIslandWorldAssembly(
+            *ownerWorld,ownerJsonRoot,worldAssembly,error))
+    {std::fprintf(stderr,"Floating-island assembly setup failed: %s\n",error.c_str());return 2;}
     std::printf("[WorldAssemblerPlanTiming] total_ms=%.3f status=PASS\n",
         std::chrono::duration<double,std::milli>(Clock::now()-planStart).count());