research(step2d): a simpler field is fast (81 ns/sample) -- but it is not the owner's world; NOT a pass

Editor-only, default off (voxel.ResearchRedefinedDensityField). The redefined field is a seeded,
periodic cross-corridor pattern per strate plus the authored passages, landings and a shaft tree,
with four value-noise detail bands at every near-surface 25 cm sample and sound 8^3 brick proofs.
259^3 ring, six workers: 308 ms median (467 ms without skips) vs 8.9 s for the live field.
Detail, boundary-artefact, determinism (1 vs 6 workers, two runs) and bound-audit checks pass.

Why it is not a pass: the slices show a mostly-solid field with a few straight corridors, where the
owner's world is mostly open space; rooms, the tunnel network, composer recipes and archetypes are
gone. Much of the speed comes from 60% of bricks being proven solid in that simpler world.
What it does show: detail at full resolution plus brick skipping costs ~80-130 ns/sample; the
cost of the live field is how rooms/tunnels/passages are represented, not the detail or the lattice.

The two walkability tests were redirected to the research field in the working tree; that change
is NOT committed (saved as scratchpad step2d-test-redirect.patch) so they keep testing the live world.

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

Tools/VoxelForgeTest.ps1

@@ -1,6 +1,6 @@
 [CmdletBinding()]
 param(
-    [ValidateSet('canonical', 'owner', 'probe', 'perf', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'parity', 'horizon', 'horizon-render', 'determinism', 'symbolize-stacks', 'region-eval')]
+    [ValidateSet('canonical', 'owner', 'probe', 'perf', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'parity', 'horizon', 'horizon-render', 'determinism', 'symbolize-stacks', 'region-eval', 'step2d')]
     [string]$Scenario = 'canonical',
     [switch]$Build,
     [switch]$EnableRender,
@@ -575,7 +575,7 @@ function Sync-OwnerAssets {
         $null = Copy-Item -LiteralPath $source -Destination $target -Force -PassThru
         [void]$rows.Add([ordered]@{
             name = $assetName
-            used_by_scenario = $Scenario -in @('owner', 'probe', 'parity', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'horizon', 'horizon-render', 'determinism', 'region-eval')
+            used_by_scenario = $Scenario -in @('owner', 'probe', 'parity', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'horizon', 'horizon-render', 'determinism', 'region-eval', 'step2d')
             source_path = $source
             source_sha256 = Get-Sha256 $source
             staged_path = $target
@@ -623,7 +623,7 @@ function Get-AssetEvidence {
         $target = Join-Path $HostRoot "Content\VoxelForge\$assetName.uasset"
         [void]$rows.Add([ordered]@{
             name = $assetName
-            used_by_scenario = $Scenario -in @('owner', 'probe', 'parity', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'horizon', 'horizon-render', 'determinism', 'region-eval')
+            used_by_scenario = $Scenario -in @('owner', 'probe', 'parity', 'tests', 'surface-fall', 'crossing', 'gate-stress', 'visual-edit', 'visual-lod', 'visual-gap-walk', 'visual-gap-inject', 'dig-motion', 'horizon', 'horizon-render', 'determinism', 'region-eval', 'step2d')
             source_path = $source
             source_sha256 = Get-Sha256 $source
             staged_path = $target
@@ -1473,6 +1473,32 @@ try {
                 }
             }
         }
+        'step2d' {
+            $step2dLog = Join-Path $RunRoot 'Logs\step2d.log'
+            $args = New-CommonArguments 'commandlet' $step2dLog (Merge-Cvars $baseCvars)
+            $args += New-CommandletArguments $commandletOut 'walk,export' ($Assets -eq 'owner') $false 128
+            $researchOut = Join-Path $PluginRoot "Saved\Research\step2d\$Label"
+            $args += @('-step2d', '-regionworkers=6', ('-researchout="{0}"' -f $researchOut))
+            $commandletLedger = Invoke-UnrealLaunch 'step2d-commandlet' $args `
+                $step2dLog (Join-Path $RunRoot 'Logs\step2d.stdout.log') `
+                (Join-Path $RunRoot 'Logs\step2d.stderr.log')
+            $step2dReportPath = Join-Path $researchOut 'step2d_report.json'
+            $step2dReport = Read-JsonFile $step2dReportPath
+            if ($null -eq $step2dReport) {
+                $CommandletMetrics = [ordered]@{ status = 'missing'; output = $researchOut; report = $step2dReportPath }
+                Add-Failure "step2d did not produce $step2dReportPath"
+            } else {
+                $CommandletMetrics = [ordered]@{
+                    status = if ((Get-JsonValue $step2dReport 'pass' $false) -and $commandletLedger.status -eq 'passed') { 'passed' } else { 'failed' }
+                    output = $researchOut
+                    report = $step2dReportPath
+                    result = $step2dReport
+                }
+                if (-not (Get-JsonValue $step2dReport 'pass' $false)) {
+                    Add-Failure 'step2d speed, detail, boundary, or determinism gate failed'
+                }
+            }
+        }
         'symbolize-stacks' {
             if (([string]::IsNullOrWhiteSpace($StackSamplesPath)) -or -not (Test-Path -LiteralPath $StackSamplesPath -PathType Leaf)) {
                 throw "-StackSamplesPath must name an existing raw sampler CSV."