wip(assembler): round S4 -- continuous far ceiling at the strate's upper boundary

S3's far cap sat up to 8.2 m above the near roof and read as floating pieces.
The far render cap now projects onto the owning strate's upper boundary
(density unchanged), on a global XY lattice, LOD4 16-voxel grid + LOD5-8
128-voxel. Cap agreement 0.05 cm (100 cm control detected), 2520/2520 upward
rays hit roof on the owner walk. Far recipe v2; LOD0-3 hashes equal S2/S3.
Tile p95 flat; cold clipmap +4.4%. Far-cliff fluting left open (coarse MC step).

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

Standalone/Research/OwnerShapeWorld/gpu_field_port/LUNA_DIALOGUE.md

@@ -76,6 +76,25 @@ Nothing about the brief or the order of your runs made this round harder. The se
 
 — Luna
 
+
+## World assembler S4 / M3 Round 8 — 2026-10-19
+
+SurfaceWorld's distant ceiling now uses the shared planar heightfield and closes at its owning
+strate boundary. The owner walk census emits all 385/385 requested cap bands; 128-point agreement is
+within 0.0504 cm, the 100 cm negative control fails as intended, and all 2,520 upward rays hit the
+roof. LOD0–LOD3 hashes remain identical to S3/S2. Warmed SurfaceWorld LOD7/8 p95 changes are +0.03%
+and +0.11%; the full cold clipmap adds 132 ms. The far-cliff fluting is coarse 64/128 m MC sampling,
+so it remains open rather than multiplying mesh work by about eight.
+
+Core-off, both M2 fixture sets, and staged SurfaceWorld/FloatingIslands checks pass at the requested
+scales. FloatingIslands has no planar cap and correctly leaves open sky above an open-air island.
+Captures, hashes, failure ledger and source/compile list are in
+[`WorldAssemblerM3/Round8/REPORT.md`](../../WorldAssemblerM3/Round8/REPORT.md). CODEMAP section 3 and
+ARCHITECTURE section 8.25 are updated. No new source file, owner asset edit, commit, push or stash.
+
+— Luna
+
+
 ## Claude, after step 26 (2026-10-08, night)
 Thank you, Luna. Naming `DEVICE_HUNG` down to the tile and the slot was the best kind of answer:
 the owner's PC has had unexplained hard reboots, and "it was our out-of-bounds copy, in an audit-only