wip(L17, side branch): FloatingIslands seal-cap fix + owner/Core chunk-scale change (breaks SurfaceWorld)

Not for assembler/world: the 8 m -> 4 m strate chunk change moves every stratum, so the SurfaceWorld
spawn camera floats in a void and the L1 mesh export shrank 58.7 -> 31.7 MB. Kept for its
diagnostics, the boundarySeal finding and the readable capture shading. See Linux17/REPORT.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Research/WorldAssemblerM3/Linux17/boundary-before.txt

@@ -0,0 +1,35 @@
+camera_m=(-22.0, -19.0, -22.799999237060547) yaw=0.0 pitch=-4.0 boundary_band_m=-80.0..-45.0
+lod tiles_with_boundary_faces faces z_m_p05/median/p95 tile_span_m_p50/p95/max
+1 65 144957 -60.4936/-60.4872/-59.5000 0.0059/0.9906/2.2272
+2 75 29057 -76.1525/-61.3304/-60.7788 0.8725/2.9863/8.5642
+3 87 26484 -73.0968/-63.0185/-62.4964 1.3211/11.6236/14.1057
+4 48 25679 -72.6651/-62.8690/-62.2182 3.2371/15.9700/17.0106
+5 48 26381 -67.4390/-62.7489/-61.8320 4.2721/11.9903/14.5467
+6 14 390 -73.7183/-67.0059/-62.3980 4.0318/11.7718/12.7473
+7 18 483 -74.7834/-71.1169/-67.5754 4.0317/7.3030/8.1412
+8 22 176 -75.3669/-69.9656/-63.4334 3.5327/3.5370/13.7478
+nearest_xy_boundary_tiles_by_lod:
+lod=1 key=(-2, -2, -4, 1) xy_distance_m=5.39 boundary_median_z=-60.4712 within_tile_p05_p95_m=0.0177 faces=2048
+lod=1 key=(-2, -1, -4, 1) xy_distance_m=11.18 boundary_median_z=-60.4718 within_tile_p05_p95_m=0.0158 faces=2048
+lod=1 key=(-1, -2, -4, 1) xy_distance_m=14.87 boundary_median_z=-60.4550 within_tile_p05_p95_m=0.0212 faces=2048
+lod=2 key=(-1, 1, -2, 2) xy_distance_m=67.27 boundary_median_z=-60.7421 within_tile_p05_p95_m=0.2955 faces=496
+lod=2 key=(1, -1, -3, 2) xy_distance_m=70.06 boundary_median_z=-74.2743 within_tile_p05_p95_m=2.9398 faces=97
+lod=2 key=(1, -1, -2, 2) xy_distance_m=70.06 boundary_median_z=-60.7387 within_tile_p05_p95_m=1.2725 faces=496
+lod=3 key=(-3, -1, -1, 3) xy_distance_m=138.61 boundary_median_z=-62.5408 within_tile_p05_p95_m=0.3465 faces=512
+lod=3 key=(-1, -3, -1, 3) xy_distance_m=141.35 boundary_median_z=-62.5378 within_tile_p05_p95_m=1.6699 faces=512
+lod=3 key=(-3, 0, -1, 3) xy_distance_m=147.12 boundary_median_z=-62.5837 within_tile_p05_p95_m=0.3165 faces=512
+lod=4 key=(-3, -1, -1, 4) xy_distance_m=301.38 boundary_median_z=-62.3784 within_tile_p05_p95_m=4.5901 faces=546
+lod=4 key=(-1, -3, -1, 4) xy_distance_m=303.92 boundary_median_z=-62.3534 within_tile_p05_p95_m=10.4664 faces=596
+lod=4 key=(-3, 0, -1, 4) xy_distance_m=309.34 boundary_median_z=-62.3696 within_tile_p05_p95_m=6.1327 faces=544
+lod=5 key=(-3, -1, -1, 5) xy_distance_m=627.54 boundary_median_z=-62.0651 within_tile_p05_p95_m=9.5826 faces=523
+lod=5 key=(-1, -3, -1, 5) xy_distance_m=629.98 boundary_median_z=-61.9414 within_tile_p05_p95_m=2.3891 faces=526
+lod=5 key=(-3, 0, -1, 5) xy_distance_m=635.24 boundary_median_z=-62.0996 within_tile_p05_p95_m=9.3777 faces=567
+lod=6 key=(-3, 0, -1, 6) xy_distance_m=1287.71 boundary_median_z=-69.5358 within_tile_p05_p95_m=4.1243 faces=26
+lod=6 key=(0, -3, -1, 6) xy_distance_m=1291.28 boundary_median_z=-70.4254 within_tile_p05_p95_m=12.7473 faces=41
+lod=6 key=(0, 2, -1, 6) xy_distance_m=1328.41 boundary_median_z=-63.9805 within_tile_p05_p95_m=0.0000 faces=1
+lod=7 key=(0, -3, -1, 7) xy_distance_m=2596.50 boundary_median_z=-70.2015 within_tile_p05_p95_m=4.1663 faces=36
+lod=7 key=(2, -1, -1, 7) xy_distance_m=2628.64 boundary_median_z=-70.1072 within_tile_p05_p95_m=3.5366 faces=8
+lod=7 key=(-3, 1, -1, 7) xy_distance_m=2976.49 boundary_median_z=-70.9568 within_tile_p05_p95_m=4.8223 faces=24
+lod=8 key=(-1, 2, -1, 8) xy_distance_m=5235.77 boundary_median_z=-65.8628 within_tile_p05_p95_m=3.5343 faces=8
+lod=8 key=(-1, -4, -1, 8) xy_distance_m=7218.88 boundary_median_z=-71.4663 within_tile_p05_p95_m=3.5332 faces=8
+lod=8 key=(-4, 0, -1, 8) xy_distance_m=7221.71 boundary_median_z=-70.6999 within_tile_p05_p95_m=3.5335 faces=8