wip(assembler): round S8 -- region rebuilds no longer stall admission; result backlog capped

voxel.CoreRegionConcurrentAdmission (default on): tiles independent of the
entering region keep submitting while a region page compiles; pages are
immutable shared_ptr owners so running readers survive eviction. 6 m/s: 11
whole-pass skips -> 0, walkable ring ready at every centre change.
voxel.StreamingResultBacklogCap=256 bounds finished results (slow-apply worst
case 125 -> 76 MB). Spawn unchanged at ~7.7 s: LOD8 is 46% of worker time.
At 60 m/s + teleport the collision ring is outrun (102/113 centres).

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

Source/VoxelForgeEditor/Private/VoxelForgeExploreCommandlet.cpp

@@ -17487,6 +17487,9 @@ bool RunCoreWorldActorIntegrationTest(const FExploreArguments& Arguments, FStrin
         const double ActorBeginSeconds = FPlatformTime::Seconds();
         constexpr double WalkStartSeconds = 30.0;
         constexpr double RunDurationSeconds = 45.0;
+        float WalkSpeedCmPerSecond = 600.0f;
+        FParse::Value(FCommandLine::Get(), TEXT("voxel.TestMoveSpeedCmPerSecond="),
+                      WalkSpeedCmPerSecond);
         TArray<double> SpawnTickMilliseconds;
         TArray<double> WalkTickMilliseconds;
         TArray<TPair<double, double>> TickSamples;
@@ -17566,11 +17569,11 @@ bool RunCoreWorldActorIntegrationTest(const FExploreArguments& Arguments, FStrin
             return false;
         }
         UE_LOG(LogTemp, Display,
-            TEXT("[VoxelForgeCoreWorldStreamTrace] pass complete=1 recipe=%s voxel_cm=%.3f walk_speed_cm_s=600 walk_direction=+Y"),
+            TEXT("[VoxelForgeCoreWorldStreamTrace] pass complete=1 recipe=%s voxel_cm=%.3f walk_speed_cm_s=%.0f walk_direction=+Y"),
             Arguments.CoreHybridMesherVersion == 2 ? TEXT("WorldAssemblerHybridV2")
                 : (Arguments.CoreHybridMesherVersion == 1 ? TEXT("WorldAssemblerHybridV1")
                     : TEXT("MarchingCubesV1")),
-            Arguments.CoreVoxelSizeCm);
+            Arguments.CoreVoxelSizeCm, WalkSpeedCmPerSecond);
         return true;
     }