wip(assembler): round S14 -- 4-way column cache + memoized MC gradients (output unchanged)

Worker-local XY column cache uses deterministic 4-way sets at LOD3-8: LOD4
misses 8,224 -> 1,437, conflicts 7,407 -> 0 (direct-map control: 6.62 s /
43.5 worker-s vs 4.24 s / 21.7). Exact LOD0 lattice gradients memoized per
tile: MC-exclusive 242 -> 201 ns/sample, two-pass loop unchanged. Hashes
identical, no recipe bump. Primary cold trace 4.24 s full set, ring 0.45 s,
75/75 at 40 m/s; a repeat ran uniformly ~40% slower on every LOD (machine
contention suspected); tick p95 to re-check on an idle machine. CVars
voxel.CoreColumnCacheDirectMapped / voxel.CoreMCGradientMemoization.
Report: Standalone/Research/WorldAssemblerM3/Round18.

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

Tools/TestVoxelForgeCoreWorldHost.ps1

@@ -15,6 +15,8 @@ param(
     [ValidateRange(0, 4096)][int]$StreamingResultBacklogCap = 256,
     [ValidateRange(0, 10)][int]$StreamingReadyQueueDepth = 8,
     [ValidateRange(0, 1)][int]$StreamingBackgroundWorkerCap = 1,
+    [ValidateRange(0, 1)][int]$CoreColumnCacheDirectMapped = 0,
+    [ValidateRange(0, 1)][int]$CoreMCGradientMemoization = 1,
     [ValidateRange(0, 900)][int]$Step1MaxMeshApplies = 0,
     [ValidateRange(0, 900)][int]$TestTeleportAfterSeconds = 0,
     [ValidateRange(0, 1000000)][int]$TestTeleportDistanceCm = 0,
@@ -29,6 +31,7 @@ param(
     [switch]$CoreOffTest,
     [switch]$CorePlanOnly,
     [switch]$SharedFeatureAuditOnly,
+    [switch]$CoreMCStageAudit,
     [int]$CoreTestSeed = [int]::MinValue
 )
 
@@ -105,6 +108,10 @@ if (-not $StreamingTraceOnly -and ($TestMoveSpeedCmPerSecond -ne 600 -or
     $TestTeleportDistanceCm -ne 0)) {
     throw 'Streaming, backlog, apply and teleport controls require -StreamingTraceOnly.'
 }
+if (-not $StreamingTraceOnly -and -not $SharedFeatureAuditOnly -and
+    ($CoreColumnCacheDirectMapped -ne 0 -or $CoreMCGradientMemoization -ne 1)) {
+    throw 'Column-cache and gradient-memoization controls require a streaming or shared-feature audit.'
+}
 if (($TestTeleportAfterSeconds -eq 0) -ne ($TestTeleportDistanceCm -eq 0)) {
     throw 'Set both -TestTeleportAfterSeconds and -TestTeleportDistanceCm for the teleport probe.'
 }
@@ -180,7 +187,13 @@ if ($SharedFeatureAuditOnly) {
     if ($SelectedModeCount -ne 0) { throw '-SharedFeatureAuditOnly uses the SurfaceWorld owner route.' }
     $RunName = 'shared_feature_audit'
 }
+if ($CoreMCStageAudit -and -not $SharedFeatureAuditOnly) {
+    throw '-CoreMCStageAudit requires -SharedFeatureAuditOnly.'
+}
+if ($CoreMCStageAudit) { $RunName += '_mc_stages' }
 $RunName += if ($StreamingOrder -eq 'Legacy') { '_legacy_order' } else { '_coarse_first' }
+$RunName += if ($CoreColumnCacheDirectMapped -eq 1) { '_colcache_direct' } else { '_colcache_4way' }
+$RunName += if ($CoreMCGradientMemoization -eq 1) { '_gradientmemo_on' } else { '_gradientmemo_off' }
 $RunName += switch ($NearReserveMode) {
     'Legacy' { '_nearreserve_legacy' }
     'Dynamic' { '_nearreserve_dynamic' }
@@ -328,6 +341,8 @@ $BaseArguments += "-voxel.CoreRegionConcurrentAdmission=$CoreRegionConcurrentAdm
 $BaseArguments += "-voxel.StreamingResultBacklogCap=$StreamingResultBacklogCap"
 $BaseArguments += "-voxel.StreamingReadyQueueDepth=$StreamingReadyQueueDepth"
 $BaseArguments += "-voxel.StreamingBackgroundWorkerCap=$StreamingBackgroundWorkerCap"
+$BaseArguments += "-voxel.CoreColumnCacheDirectMapped=$CoreColumnCacheDirectMapped"
+$BaseArguments += "-voxel.CoreMCGradientMemoization=$CoreMCGradientMemoization"
 if ($Step1MaxMeshApplies -gt 0) {
     $BaseArguments += "-voxel.Step1MaxMeshApplies=$Step1MaxMeshApplies"
 }
@@ -350,6 +365,7 @@ if ($StartupTrace -or $StreamingTraceOnly) {
     $BaseArguments += '-voxel.StartupTraceMaxTiles=16384'
 }
 if ($SharedFeatureAuditOnly) { $BaseArguments += '-corefeatureauditonly' }
+if ($CoreMCStageAudit) { $BaseArguments += '-coremcstageaudit' }
 if ($HasManifestOverride) {
     $BaseArguments += ('-coreworldassembly="{0}"' -f $StagedWorldAssembly)
 }