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/VoxelForgeTest.ps1

@@ -488,10 +488,10 @@ function Invoke-UnrealLaunch([string]$Kind, [string[]]$Arguments, [string]$LogPa
         $process = Start-Process -FilePath $EditorExe -ArgumentList $Arguments -WorkingDirectory $HostRoot `
             -RedirectStandardOutput $StdoutPath -RedirectStandardError $StderrPath -WindowStyle $windowStyle `
             -PassThru
-        try { $process.PriorityClass = [Diagnostics.ProcessPriorityClass]::BelowNormal }
+        try { $process.PriorityClass = [Diagnostics.ProcessPriorityClass]::Normal }
         catch {
             try { Stop-Process -Id ([int]$process.Id) -Force -ErrorAction Stop } catch { }
-            throw "Could not lower owned Unreal PID $($process.Id) to BelowNormal: $($_.Exception.Message)"
+            throw "Could not set owned Unreal PID $($process.Id) to Normal priority: $($_.Exception.Message)"
         }
         $ledger.pid = [int]$process.Id
         $wait = Wait-OwnedProcess $process $LaunchTimeoutSeconds -EnforceMemoryLimit
@@ -547,10 +547,10 @@ function Invoke-BuildProcess([string[]]$Arguments, [string]$LogPath, [string]$Er
         $process = Start-Process -FilePath $dotnet -ArgumentList $Arguments -WorkingDirectory $PluginRoot `
             -RedirectStandardOutput $StdoutPath -RedirectStandardError $ErrorPath -WindowStyle Hidden `
             -PassThru
-        try { $process.PriorityClass = [Diagnostics.ProcessPriorityClass]::BelowNormal }
+        try { $process.PriorityClass = [Diagnostics.ProcessPriorityClass]::Normal }
         catch {
             try { Stop-Process -Id ([int]$process.Id) -Force -ErrorAction Stop } catch { }
-            throw "Could not lower owned build PID $($process.Id) to BelowNormal: $($_.Exception.Message)"
+            throw "Could not set owned build PID $($process.Id) to Normal priority: $($_.Exception.Message)"
         }
         $wait = Wait-OwnedProcess $process $LaunchTimeoutSeconds -EnforceMemoryLimit
     } finally {