measure(step2b): per-brick setup rebuilds the chunk caches -- 10x slower; live cost attributed

Editor-only brick API (<= 8^3 points per call, TunnelNetwork/Underwater op-stack routes, 1.16%
scalar fallback). Exact: 0 Q16/sign disagreements on the full 259^3 ring and the five-seed probe
set, same hash on 1 and 6 workers, reach shrink still caught (18,107 Q16 / 735 sign).
Speed: 69.19 s wall, 17.6 us/sample vs live 7.04 s, 1.65 us/sample. Stack sampler (inclusive):
BuildChunkCache 93.5%, PropagateSdfOverBox 92.5%, BuildActiveOpList 92.6% -- each brick rebuilds
the cache windows and active-op lists; EvalBlock itself is 3.6%.
Live path attribution (inclusive, 68,934 stacks): op-stack RoomGraph EvalBlock 54.4%, SDF and
spatial candidate scans ~28%, tunnel core 18.4%, passage floor segment 15.0%, structural posts
14.6%, noise octaves 2.6%, disturbances 0.6%, diff layer 0.3%.

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

Tools/VoxelForgeTest.ps1

@@ -4,6 +4,13 @@ param(
     [string]$Scenario = 'canonical',
     [switch]$Build,
     [switch]$EnableRender,
+    [switch]$SampleDensityStacks,
+    [ValidateRange(1, 1000000)]
+    [int]$StackSampleIntervalUs = 1000,
+    [switch]$RegionHashProbe,
+    [ValidateRange(1, 32)]
+    [int]$RegionWorkers = 6,
+    [string]$RegionReferenceHash = '',
     [ValidateSet('owner', 'default')]
     [string]$Assets = 'owner',
     [hashtable]$Cvars = @{},
@@ -1430,6 +1437,17 @@ try {
             $args = New-CommonArguments 'commandlet' $regionLog (Merge-Cvars $baseCvars)
             $args += New-CommandletArguments $commandletOut 'walk,export' ($Assets -eq 'owner') $false 128
             $args += @('-regioneval', '-regionsamples=262144')
+            if ($SampleDensityStacks) { $args += "-samplestacks=$StackSampleIntervalUs" }
+            if ($RegionHashProbe) {
+                if ([string]::IsNullOrWhiteSpace($RegionReferenceHash)) {
+                    throw '-RegionHashProbe requires -RegionReferenceHash from a reference full-ring run.'
+                }
+                $args += @(
+                    '-regionhashprobe',
+                    "-regionworkers=$RegionWorkers",
+                    "-regionreferencehash=$RegionReferenceHash"
+                )
+            }
             $commandletLedger = Invoke-UnrealLaunch 'region-eval-commandlet' $args `
                 $regionLog (Join-Path $RunRoot 'Logs\region-eval.stdout.log') `
                 (Join-Path $RunRoot 'Logs\region-eval.stderr.log')