wip: Tunnel Network cave planner on Core caves (L134, route support still failing)

Seed + 21/47 legacy fields -> 30 compound rooms (72 primitives), 3 branches, destination chamber; mouths fixed;
8.67 deg max grade. Passage composer no longer skips native cave layers (incoming passage 21,425/21,425 open).
Open: route-support audit has 380 unsupported samples near the arrival mouth. Not for merge.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Research/WorldAssemblerM3/Linux134/layout-seed0-walk-gate.json

@@ -0,0 +1 @@
+{"schema_version":3,"world_identity":"owner-world/seed/0","owner_voxel_size_um":125000,"core_voxel_size_um":250000,"strate_layout_chunk_size_um":8000000,"strate_layout_chunk_width_subvoxels":8192,"strates":[{"stable_id":"owner-world/seed/0/strate/0/generator/SurfaceWorld","order":0,"strate_index":0,"generator_kind":"SurfaceWorld","recipe_id":"SurfaceWorld.Heightfield2D","recipe_version":2,"interior_bottom_um":-504000000,"interior_top_um":8000000,"voxel_size_um":250000,"lattice_origin_um":[0,0,0],"ceiling":{"kind":"ceiling","bottom_um":7500000,"top_um":8000000,"present":true,"diggable":true,"protected":false,"solid_density_q16":524288,"behaviour":"solid ceiling from strate BoundarySealThickness; breakable by default","density_side":"interior-facing lower surface","cap_path":"shared resolved-layout density band"},"content":{"kind":"content","bottom_um":-503500000,"top_um":7500000,"present":true,"diggable":true,"protected":false,"solid_density_q16":65536,"behaviour":"resolved generator interior","density_side":"none","cap_path":"none"},"bedrock":{"kind":"bedrock","bottom_um":-504000000,"top_um":-503500000,"present":true,"diggable":true,"protected":false,"solid_density_q16":524288,"behaviour":"solid bedrock floor from strate BoundarySealThickness; breakable by default","density_side":"interior-facing upper surface","cap_path":"shared resolved-layout density band"},"transition_mode":"Gradient","transition_blend_chunks":1,"transition_width_um":8000000,"transition_warp_amplitude_um":0,"transition_interpenetration_um":2000000,"transition_honoured_in_core":true,"transition_falls_back_to_hard":false,"transition_dispatch_path":"shared composition moves both band faces together with the smooth declared-width transition field","bound_dispatch_path":"BuildSurfaceStratumPlan uses resolved layout chunk width from ResolvedLayoutSnapshotV3","query_dispatch_path":"NativeSurfaceDensityAt selects floor(CoreZ / resolved layout chunk width) from ResolvedLayoutSnapshotV3","manager_lookup":"UVoxelStrateManager::GetGeneratorTypeForChunk; transition is controlled by upper strate","manager_chunk_width_um":8000000,"dispatch_chunk_width_um":8000000,"anchors":[{"kind":"cap_profile","stable_id":"biome/4097","units":"1/256 Core voxel","values":[-18022,0,64000,1536,0]},{"kind":"route_point","stable_id":"route/0","units":"1/256 Core voxel","values":[8192,24576,-381223,1024]},{"kind":"route_point","stable_id":"route/1","units":"1/256 Core voxel","values":[8192,24320,-381254,1024]},{"kind":"route_point","stable_id":"route/2","units":"1/256 Core voxel","values":[8192,24064,-381284,1024]},{"kind":"route_point","stable_id":"route/3","units":"1/256 Core voxel","values":[8192,23808,-381302,1024]},{"kind":"route_point","stable_id":"route/4","units":"1/256 Core voxel","values":[8192,23552,-381304,1024]},{"kind":"route_point","stable_id":"route/5","units":"1/256 Core voxel","values":[8192,23296,-381291,1024]},{"kind":"route_point","stable_id":"route/6","units":"1/256 Core voxel","values":[8192,23040,-381270,1024]},{"kind":"route_point","stable_id":"route/7","units":"1/256 Core voxel","values":[8192,22784,-381242,1024]},{"kind":"route_point","stable_id":"route/8","units":"1/256 Core voxel","values":[8192,22528,-381218,1024]},{"kind":"route_point","stable_id":"route/9","units":"1/256 Core voxel","values":[8192,22272,-381192,1024]},{"kind":"route_point","stable_id":"route/10","units":"1/256 Core voxel","values":[8192,22016,-381161,1024]},{"kind":"route_point","stable_id":"route/11","units":"1/256 Core voxel","values":[8192,21760,-381118,1024]},{"kind":"route_point","stable_id":"route/12","units":"1/256 Core voxel","values":[8192,21504,-381122,1024]},{"kind":"route_point","stable_id":"route/13","units":"1/256 Core voxel","values":[8192,21248,-381155,1024]},{"kind":"route_point","stable_id":"route/14","units":"1/256 Core voxel","values":[8192,20992,-381183,1024]},{"kind":"route_point","stable_id":"route/15","units":"1/256 Core voxel","values":[8192,20736,-381207,1024]},{"kind":"route_point","stable_id":"route/16","units":"1/256 Core voxel","values":[8192,20480,-381219,1024]},{"kind":"route_point","stable_id":"route/17","units":"1/256 Core voxel","values":[8192,20224,-381220,1024]},{"kind":"route_point","stable_id":"route/18","units":"1/256 Core voxel","values":[8192,19968,-381202,1024]},{"kind":"route_point","stable_id":"route/19","units":"1/256 Core voxel","values":[8192,19712,-381167,1024]},{"kind":"route_point","stable_id":"route/20","units":"1/256 Core voxel","values":[8192,19456,-381130,1024]},{"kind":"route_point","stable_id":"route/21","units":"1/256 Core voxel","values":[8192,19200,-381101,1024]},{"kind":"route_point","stable_id":"route/22","units":"1/256 Core voxel","values":[8192,18944,-381072,1024]},{"kind":"route_point","stable_id":"route/23","units":"1/256 Core voxel","values":[8192,18688,-381092,1024]},{"kind":"route_point","stable_id":"route/24","units":"1/256 Core voxel","values":[8192,18432,-381149,1024]},{"kind":"route_point","stable_id"Line truncated