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/Research/WorldAssemblerM3/Linux2/WindowsReplay.ps1

@@ -0,0 +1,46 @@
+$ErrorActionPreference = 'Stop'
+$Root = [IO.Path]::GetFullPath((Join-Path $PSScriptRoot '..\..\..\..'))
+$Viewer = Join-Path $Root 'Standalone\bin\VoxelForgeCoreStandalone.exe'
+$Data = Join-Path $Root 'Standalone\data\owner_world.json'
+$SeedFile = Join-Path $PSScriptRoot 'seeds.txt'
+$LogDir = Join-Path $Root 'Saved\Linux'
+[IO.Directory]::CreateDirectory($LogDir) | Out-Null
+
+$Recipes = @(
+    @{ Name = 'surface-world'; Camera = '0,-35,-487.94,0,-22' },
+    @{ Name = 'floating-islands'; Camera = '0,0,-32,0,-22' }
+)
+$Seeds = @(Get-Content -LiteralPath $SeedFile | ForEach-Object { [int]$_.Trim() })
+if ($Seeds.Count -ne 48) { throw "Expected 48 seeds in $SeedFile" }
+if (-not (Test-Path -LiteralPath $Viewer -PathType Leaf)) { throw "Viewer not found: $Viewer" }
+
+foreach ($Recipe in $Recipes) {
+    foreach ($Seed in $Seeds) {
+        foreach ($Workers in @(1, 12)) {
+            $Arguments = @(
+                $Data,
+                "--seed=$Seed",
+                "--recipe=$($Recipe.Name)",
+                '--render-distance-chunks=0',
+                "--workers=$Workers",
+                '--world-assembler-prototype',
+                '--stream-benchmark',
+                '--stream-pipeline',
+                '--stream-hash',
+                '--force-generate',
+                '--clip-radius=1',
+                '--max-clip-level=0',
+                "--camera=$($Recipe.Camera)",
+                '--far-horizon-lod8-step=0',
+                '--process-affinity=4095',
+                '--process-priority=Normal',
+                '--frame-limit=60'
+            )
+            $Stem = "windows2-seed-$Seed-$($Recipe.Name)-w$Workers"
+            $Log = Join-Path $LogDir "$Stem.log"
+            Write-Host "& `"$Viewer`" $($Arguments -join ' ')"
+            & $Viewer @Arguments *> $Log
+            if ($LASTEXITCODE -ne 0) { throw "Viewer failed ($LASTEXITCODE); see $Log" }
+        }
+    }
+}