wip(assembler): M3 round 4 -- plans built inside Unreal from the owner's strates; no import needed

SurfaceWorld and FloatingIslands plans generate at startup from the resolved seed,
strate types and heights (hashed, cached). Imported JSON is an opt-in override (off by
default); an invalid override shows an on-screen notice and falls back to legacy.
BuildHost on staged owner assets: SurfaceWorld cross-system checks, islands at owner
height (route, collision, anchors, BP edits), seed 137501, W1/W8/W16, Core-off legacy.
XY-column cache verified (hashes kept); island LOD0 p95 91 ms vs 133 ms sprint deadline.
Not exercised: season-seed path (no Season in staged settings), rendered notice pixels.

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

Tools/BuildVoxelForgeCoreHost.ps1

@@ -1,6 +1,6 @@
 [CmdletBinding()]
 param(
-    [ValidateRange(1, 16)][int]$MaxParallelActions = 16,
+    [ValidateRange(1, 4)][int]$MaxParallelActions = 4,
     [ValidateRange(60, 900)][int]$TimeoutSeconds = 900
 )
 
@@ -33,6 +33,42 @@ function Assert-UnderPath([string]$Candidate, [string]$Root) {
     }
 }
 
+if (-not ('VoxelForgeRound4BuildMemoryProbe' -as [type])) {
+    Add-Type -TypeDefinition @'
+using System;
+using System.Runtime.InteropServices;
+public static class VoxelForgeRound4BuildMemoryProbe {
+    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
+    private struct MEMORYSTATUSEX {
+        public uint dwLength;
+        public uint dwMemoryLoad;
+        public ulong ullTotalPhys;
+        public ulong ullAvailPhys;
+        public ulong ullTotalPageFile;
+        public ulong ullAvailPageFile;
+        public ulong ullTotalVirtual;
+        public ulong ullAvailVirtual;
+        public ulong ullAvailExtendedVirtual;
+    }
+    [DllImport("kernel32.dll", SetLastError = true)]
+    private static extern bool GlobalMemoryStatusEx(ref MEMORYSTATUSEX lpBuffer);
+    public static ulong AvailablePhysicalBytes() {
+        var status = new MEMORYSTATUSEX();
+        status.dwLength = (uint)Marshal.SizeOf(typeof(MEMORYSTATUSEX));
+        if (!GlobalMemoryStatusEx(ref status)) throw new InvalidOperationException("GlobalMemoryStatusEx failed.");
+        return status.ullAvailPhys;
+    }
+}
+'@
+}
+
+function Wait-ForLaunchMemory {
+    while ([VoxelForgeRound4BuildMemoryProbe]::AvailablePhysicalBytes() -lt 4GB) {
+        Write-Warning 'BuildHost UBT launch is waiting for at least 4 GiB of free physical memory.'
+        Start-Sleep -Seconds 20
+    }
+}
+
 function Copy-DirectoryContents([string]$Source, [string]$Destination) {
     if (-not (Test-Path -LiteralPath $Source -PathType Container)) {
         throw "Canonical Core source directory is missing: $Source"
@@ -92,11 +128,11 @@ Copy-Item -LiteralPath (Join-Path $PluginRoot 'VoxelForge.uplugin') `
 # never resolve, open, copy, or compare against the owner's project Content directory.
 $hostAssetRoot = Join-Path $HostRoot 'Content\VoxelForge'
 $expectedAssetHashes = @{
-    'DA_Settings' = '5D2977F57E75A63B6B73499CD6E0AA7FBBF3718CE7F70318107BF922F0819AB7'
-    'DA_Strate1' = 'CDA1F985E589F28CA6E93A068FECC3CA92487E4AD5700F2C301C4B563E40E5F9'
+    'DA_Settings' = '8ABE8243104980260FECA0A6F4CF4927768E8E568221A6F6A2C2694F6D15D454'
+    'DA_Strate1' = '76063D691D5CE26D2014B587E1972A6724787BE1204E4652CA863BB8D5001BD0'
     'DA_Strate2' = '02F56A18CED991BAF93DFB2F69438152275E8353B5E279C1CB7DD6E079E352E2'
     'DA_Strate3' = 'F47437F8D156C608AA06E40C5B76716ED4A19FA0F057688E7FECC04DC976428C'
-    'DA_Strate4' = '279570AE3CBA7B3507269C8209A7C931EEB7A15CC3241CE07B50120996B1C656'
+    'DA_Strate4' = '7C0DE7D06876035AC7BC4F117B9166AFD77402021843BA4900B470F4B0D0185B'
 }
 foreach ($assetName in $expectedAssetHashes.Keys) {
     $stagedAsset = Join-Path $hostAssetRoot "$assetName.uasset"
@@ -105,7 +141,7 @@ foreach ($assetName in $expectedAssetHashes.Keys) {
     }
     $stagedHash = (Get-FileHash -LiteralPath $stagedAsset -Algorithm SHA256).Hash
     if ($stagedHash -ne $expectedAssetHashes[$assetName]) {
-        throw "BuildHost asset copy differs from the recorded round-2 hash: $assetName"
+        throw "BuildHost owner asset copy differs from the recorded round-4 hash: $assetName"
     }
 }
 
@@ -131,6 +167,13 @@ for ($attempt = 1; $attempt -le 2 -and -not $buildSucceeded; ++$attempt) {
     $attemptStdout = if ($attempt -eq 1) { $BuildStdout } else { Join-Path $LogRoot 'UBT-CoreIntegration.retry.stdout.log' }
     $attemptStderr = if ($attempt -eq 1) { $BuildStderr } else { Join-Path $LogRoot 'UBT-CoreIntegration.retry.stderr.log' }
     Write-Host "BuildHost UBT attempt $attempt of 2; max parallel actions=$MaxParallelActions; BelowNormal priority."
+    Wait-ForLaunchMemory
+    $foreignEditors = @(Get-Process -ErrorAction SilentlyContinue |
+        Where-Object { $_.ProcessName -like 'UnrealEditor*' })
+    if ($foreignEditors.Count -gt 0) {
+        $ids = ($foreignEditors | ForEach-Object { "$($_.ProcessName):$($_.Id)" }) -join ', '
+        throw "UnrealEditor is already running; leaving it untouched: $ids"
+    }
     $process = Start-Process -FilePath $dotnet -ArgumentList $argumentList -WorkingDirectory $PluginRoot `
         -RedirectStandardOutput $attemptStdout -RedirectStandardError $attemptStderr `
         -WindowStyle Hidden -PassThru