wip(assembler): round S3 -- far ground from the native heightfield; LOD7/8 tiles 36-66% cheaper

Far-shell repair (81-96% of S2's LOD7/8 tile time) is skipped for certified
SurfaceWorld tiles; ground and cap come from the shared planar heightfield.
Near LOD0-3 hashes equal S2; far recipe version 1 salts LOD5+ identities.
Cold first view 6.6 -> 3.4 s (aim 1.57 s). Not a visual sign-off: distant cap
shows floating pieces, sprint streaming arrives late.

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

ARCHITECTURE.md

@@ -1364,6 +1364,37 @@ Validation compares complete placement transforms and canonical anchor residuals
 clears an isolated populated HISM fixture under BuildHost null RHI. These CPU costs do not measure
 rendering or GPU upload. See the Round 6 report for results and limits.
 
+### 8.24 Shared native far horizon — World Assembler M3 Round 7
+
+The shared Core tile generator reads each family declaration from the immutable assembly snapshot.
+`WorldAssemblyPlanV1::strates` declares SurfaceWorld ground and cap profiles through `Heightfield2D`;
+`floatingIslands` declares bounded 3D features and has no planar ground/cap datum. This keeps the
+horizon rule in the shared worker path while allowing each family to provide the shape it can prove.
+
+At LOD5 and above, an unedited SurfaceWorld tile builds its ground from the native heightfield on
+a globally aligned 128-voxel grid, using the tile step below 128. The cap remains on the 128-voxel
+grid so adjacent far levels share samples. Ground and cap are clipped to the tile-Z bounds and to
+`cap >= ground`; shared ground vertices replace nearby upward-facing coarse MC ground triangles,
+while existing ceiling seam skirts remain. At LOD7/8, a tile that intersects a native SurfaceWorld
+profile but intersects no island plan skips the derived stratum/connector repair
+shells: the exact native ground and cap already provide its exterior closure. Player-edited tiles
+keep the real edited field and repair path at every visible LOD. Islands-only and mixed island tiles
+keep the shared 3D field and far-shell path.
+
+For the 3D connector repair path, LOD7/8 use the same 256-voxel axial station/ring spacing. LOD6 and
+nearer far-shell work retain 128-voxel stations. This reduces source-field probes while keeping a
+continuous repair mesh at the resolution used by the far tile. It does not alter canonical density
+arithmetic, feature order, water datum, `Epoch`, `ModsLock`, task ownership, collision policy, or the
+Core-off legacy route. All horizon work runs on the resolved immutable worker snapshot.
+
+`TileGenerationStats` exposes classification, XY column, MC meshing, shell and horizon times, repair
+field calls, skipped repairs and replaced ground triangles. `farHorizonVersion` is part of the tile
+generation recipe and salts far mesh, payload and topology hashes at LOD5+; it does not salt density
+or LOD0–LOD3 identities. Increase it when changing far geometry again. Round 7's staged owner checks
+measure eight warmed keys per LOD and compare the shared LOD7/8 surface lattice against exact near-field
+density roots, including a 100 cm datum-offset negative control. See
+`Standalone/Research/WorldAssemblerM3/Round7/REPORT.md` for results and the visual evidence limits.
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a