standalone: 64 m full-detail override, detailed round tunnels, optional mesh cache -- generation itself NOT faster

ClipRadius override 3 (64 m at 25 cm). Uncached full detail 20.3 s on 8 workers (512 tiles at
~51 ms serial each should be ~3-4 s: the in-stream inefficiency is unsolved); full clipmap 170.6 s.
The 1 s / 5 s targets were met only from an on-disk mesh cache (.vfmesh, not committed) of
already-generated tiles: a revisit speed-up, not generation speed. Round tunnels gained
deterministic multi-scale wall relief and lost the larger mouth wedges (1.54% of lattice signs
changed, mean 0.20 m). Hashes stable across runs and 1 vs 6 workers.

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

Standalone/Research/VoxelSpeedRound/final/round_compare_16.stdout.log

@@ -0,0 +1 @@
+[RoundTunnelCompare] tiles=16 lattice_samples=686000 changed_signs=10539 changed_share=1.536297% legacy_density_hash=0x5e366a455ea4ddb6 detailed_density_hash=0x85c8615a10bb5787 old_vertices=19506 new_vertices=18585 symmetric_vertex_mean_m=0.1955 symmetric_vertex_max_m=2.0457 unmatched_vertices=0