wip(standalone): GPU step 27 -- slot-overflow fallback, -SkipCpuDetailBand (slower), -AffinityMask; full machine cached 0.93 s

Luna: normal completion path reads the raw vertex count before residency; an
over-cap count or failed readback falls back to CPU meshing. Max seen 18,153 of
19,456 vertices at (2,-9,-4,lod1) -- 1,303 headroom for this seed only.
Consumer map: 320 GPU near, 640 CPU near (skirted), 1,114 GPU far, 152 CPU far.
Exceptions are exported separately from roughness. Opt-in -SkipCpuDetailBand skips
CPU roughness for GPU-owned near visuals (lazy exact reconstruction on query).
Runner gains -AffinityMask (default 0xFF00) and -NormalPriority.

My runs outside the sandbox (Step27.exe, marker removed first):
  half machine (0xFF00, BelowNormal), interleaved:
    CPU 1.374 / 1.285 / 1.296 s
    GPU miss 1.330 s; cached 1.151 / 1.143 / 1.129 s (1,434 GPU tiles)
    GPU cached + -SkipCpuDetailBand 1.316 / 1.303 / 1.307 s -- SLOWER: detail apply
      331 -> 297 ms, but intervals+signs 112 -> 286 ms (the plan), shape 557 -> 692 ms
  full machine (0xFFFF, Normal), interleaved:
    CPU 1.004 / 1.015 / 0.974 s
    GPU cached 0.931 / 0.930 / 0.925 s -- first sub-second launches
Audits (Luna): hashes w1/w8, walk 5,642/5,642, near (skip) / far 0 sign/topology
diffs vs CPU and WARP, auto + cold survival pass, ten captures pass.

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

Standalone/Research/OwnerShapeWorld/gpu_first_port/VoxelForgeGpuMesher.hlsl

@@ -1283,6 +1283,10 @@ void ScanGroupsCS(uint3 dispatchId : SV_DispatchThreadID)
     DrawArgs.Store(OutputArgsByteOffset + 32, 0);
     DrawArgs.Store(OutputArgsByteOffset + 36, 0);
     DrawArgs.Store(OutputArgsByteOffset + 40, 0);
+    // Keep the unbounded scan total beside the indirect arguments. The draw uses
+    // the capacity-clamped count above; the viewer reads this word after the
+    // completion event and sends an overflowing tile through the CPU fallback.
+    DrawArgs.Store(OutputArgsByteOffset + 44, offset);
 }
 
 StructuredBuffer<float> Density : register(t2);