wip(assembler): round S6 -- in-game cold view counted; workers mostly idle, apply cap not the floor

Direct per-tile trace on the BuildHost actor (owner plan, 2,578 keys): full set
17.4 s legacy; gated coarse-first (after the 9-tile walkable ring) 11.7 s with
the ring still at 0.63 s, but full LOD0 slips 2.3 -> 10.2 s. Startup apply
boost changed nothing (0.4%). 37.6 worker-s over 17.4 s on 10 slots = ~3.3
busy: the floor is admission/work supply. S5's 251 ms staircase was the trace
sampler. Fixed CVar parsing in headless BeginPlay and the 60 m/s crossing
instrument. All three knobs stay opt-in.

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

Source/VoxelForge/Public/VoxelWorld.h

@@ -132,6 +132,11 @@ struct FChunkResult
     // opt-in profile. It is carried through the worker queue so the report can separate scheduler
     // wait from generation time.
     uint64 RequestStartCycles = 0;
+    // Full background-task boundaries include stream conversion and result packaging around the
+    // generator call; they let the trace reconcile per-tile worker-seconds with worker occupancy.
+    // Les bornes de tâche incluent la conversion et la préparation du résultat autour du générateur.
+    uint64 WorkerTaskStartCycles = 0;
+    uint64 WorkerTaskEndCycles = 0;
     // Worker timing boundaries for separating scheduler wait from generation and result/apply wait.
     // These are captured with low overhead for the clean streaming-latency summary; expensive
     // per-tile profiling remains opt-in.
@@ -1118,6 +1123,9 @@ public:
 
     // Number of async tasks currently running — EndPlay waits for this to reach 0
     std::atomic<int32> ActiveTaskCount{0};
+    // Active workers are counted inside the launched tile task, distinct from tasks queued by UE.
+    // Les travailleurs actifs sont comptes dans la tache de tuile, distincts des taches en attente UE.
+    std::atomic<int32> ActiveGenerationWorkerCount{0};
 
     FORCEINLINE bool ShouldAbortWork(const std::atomic<bool>* ObsoleteFlag = nullptr) const
     {
@@ -1175,6 +1183,10 @@ public:
     bool bAllChunksLoaded = false;
     bool bStartupTraceDesiredRecorded = false;
     bool bSampleStacksStarted = false;
+    bool bStartupApplyBoostStarted = false;
+    bool bStartupApplyBoostEnded = false;
+    uint64 LastApplyFrameCycles = 0;
+    float StartupTraceSpeedCmPerSecond = 0.0f;
     TArray<FVoxelTileKey> DesiredSorted;   // critical floor prefix, then true-pawn distance-first
     TArray<FVoxelTileKey> CriticalDesiredTiles; // occupied/support tile, then heading tile
     // Ancestor -> desired descendants, rebuilt with DesiredSorted. Reconciliation uses this