wip(assembler): round S12 -- short ready queue keeps workers fed between ticks: full set 6.0 s -> 4.9 s

voxel.StreamingReadyQueueDepth=8 admits one extra worker-set of prioritized
tasks; voxel.StreamingBackgroundWorkerCap=1 sizes slots to the 8 TaskGraph
background workers actually running tile tasks. Full set 5.96 -> 4.91 s,
LOD0 1.40 -> 1.09 s, ring 0.49 -> 0.51 s, 40 m/s ring 75/75. Tick p95
+0.6 ms spawn / +0.26 ms walk, max flat. No geometry change.
Report: Standalone/Research/WorldAssemblerM3/Round16.

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

Source/VoxelForge/Private/VoxelStartupTrace.cpp

@@ -284,9 +284,17 @@ void RecordTile(const FTileSample& Sample)
 
     GState->Samples.Add(Sample);
     ++GState->TileRecordsWritten;
+    const double TraceNowSeconds = FPlatformTime::Seconds() - GState->StartSeconds;
+    const double SubmittedAtSeconds = Sample.RequestStartCycles != 0
+        ? TraceNowSeconds - Sample.RequestToApplySeconds : -1.0;
+    const double WorkerStartedAtSeconds = Sample.WorkerTaskStartCycles != 0
+        ? SubmittedAtSeconds + Sample.WorkerQueueSeconds : -1.0;
+    const double WorkerEndedAtSeconds = Sample.WorkerTaskEndCycles != 0
+        ? WorkerStartedAtSeconds + Sample.WorkerTaskSeconds : -1.0;
     WriteEventLocked(*GState, TEXT("tile"), FString::Printf(
         TEXT("\"tile\":[%d,%d,%d],\"level\":%d,\"priority\":%d,"
              "\"request_ordinal\":%llu,\"generation_ordinal\":%llu,\"resident_at_request\":%d,"
+             "\"submitted_t_s\":%s,\"worker_start_t_s\":%s,\"worker_end_t_s\":%s,\"worker_thread_id\":%u,"
              "\"verdict\":%d,\"proof\":%d,\"empty\":%d,\"vertices\":%d,\"triangles\":%d,\"geometry_bytes\":%llu,"
              "\"request_to_apply_s\":%s,\"queue_wait_s\":%s,\"worker_queue_s\":%s,\"result_queue_s\":%s,\"worker_task_s\":%s,"
              "\"generation_s\":%s,\"classify_s\":%s,\"mesh_s\":%s,\"stream_s\":%s,\"apply_s\":%s"),
@@ -295,6 +303,10 @@ void RecordTile(const FTileSample& Sample)
         static_cast<unsigned long long>(Sample.RequestOrdinal),
         static_cast<unsigned long long>(Sample.GenerationOrdinal),
         Sample.bResidentAtRequest ? 1 : 0,
+        *Number(SubmittedAtSeconds),
+        *Number(WorkerStartedAtSeconds),
+        *Number(WorkerEndedAtSeconds),
+        Sample.WorkerThreadId,
         Sample.Verdict, Sample.bSealedSolidProof ? 1 : 0,
         Sample.bEmpty ? 1 : 0, Sample.Vertices, Sample.Triangles,
         static_cast<unsigned long long>(Sample.GeometryBytes),