wip(assembler): round S5 -- streaming gates + trace; coarse-first order kept opt-in (no win)

Walkable/enclosed/refined gates defined; JSONL trace joins request, worker start,
build/apply and discards. Coarse-first + dynamic near reserve behind
voxel.StreamingCoarseFirst / voxel.StreamingDynamicNearReserve (default 0 =
S4 order): matched runs showed no walkability or full-view win and slower
LOD0/1 refinement. Instruments settled: 3.1 s standalone reproduced (16.7 s was
another generation route); black early captures were clear-only frames.
Hashes equal S4; Core-off, M2, SurfaceWorld/FloatingIslands BuildHost pass.

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

Tools/TestVoxelForgeCoreWorldHost.ps1

@@ -2,6 +2,9 @@
 param(
     [ValidateRange(60, 900)][int]$TimeoutSeconds = 900,
     [ValidateRange(12.5, 25.0)][double]$CoreVoxelSizeCm = 25.0,
+    [ValidateSet('CoarseFirst', 'Legacy')][string]$StreamingOrder = 'CoarseFirst',
+    [switch]$EnforceCollisionGate,
+    [switch]$StartupTrace,
     [string]$WorldAssemblyManifestPath = '',
     [ValidateSet('MarchingCubesV1', 'WorldAssemblerHybridV1', 'WorldAssemblerHybridV2')][string]$CoreMesherRecipe = 'MarchingCubesV1',
     [switch]$EnableHybridFixturePlacement,
@@ -133,6 +136,9 @@ if ($SharedFeatureAuditOnly) {
     if ($SelectedModeCount -ne 0) { throw '-SharedFeatureAuditOnly uses the SurfaceWorld owner route.' }
     $RunName = 'shared_feature_audit'
 }
+$RunName += if ($StreamingOrder -eq 'Legacy') { '_legacy_order' } else { '_coarse_first' }
+if ($EnforceCollisionGate) { $RunName += '_collision_gate' }
+if ($StartupTrace) { $RunName += '_trace' }
 
 $foreignEditors = @(Get-Process -ErrorAction SilentlyContinue |
     Where-Object { $_.ProcessName -like 'UnrealEditor*' })
@@ -247,6 +253,15 @@ $BaseArguments = @(
     ("-corehybridfixturesonly=$HybridFixturesOnlyFlag"),
     ('-out="{0}"' -f $OutputDirectory)
 )
+$CoarseFirstValue = if ($StreamingOrder -eq 'CoarseFirst') { 1 } else { 0 }
+$DynamicReserveValue = if ($StreamingOrder -eq 'CoarseFirst') { 1 } else { 0 }
+$BaseArguments += "-voxel.StreamingCoarseFirst=$CoarseFirstValue"
+$BaseArguments += "-voxel.StreamingDynamicNearReserve=$DynamicReserveValue"
+if ($StartupTrace) {
+    $TracePath = Join-Path $LogDirectory "CoreWorldValidation-$RunName.trace.jsonl"
+    $BaseArguments += ('-voxel.StartupTraceFile="{0}"' -f $TracePath)
+    $BaseArguments += '-voxel.StartupTraceUntilEndPlay=1'
+}
 if ($SharedFeatureAuditOnly) { $BaseArguments += '-corefeatureauditonly' }
 if ($HasManifestOverride) {
     $BaseArguments += ('-coreworldassembly="{0}"' -f $StagedWorldAssembly)
@@ -254,7 +269,8 @@ if ($HasManifestOverride) {
 if ($CoreTestSeed -ne [int]::MinValue) {
     $BaseArguments += "-coretestseed=$CoreTestSeed"
 }
-if ($FloatingIslandsOnly -or (-not $CoreFallbackTest -and -not $CoreOffTest -and -not $CorePlanOnly)) {
+if (-not $EnforceCollisionGate -and
+    ($FloatingIslandsOnly -or (-not $CoreFallbackTest -and -not $CoreOffTest -and -not $CorePlanOnly))) {
     # This commandlet keeps the travel pawn stationary; surface's initial collision cooks are still audited,
     # and FloatingIslandsOnly separately probes cooked island/span capsule contacts.
     # Le pawn de voyage du commandlet reste immobile ; les collisions de surface initiales sont auditees,