wip(assembler): M1 round 5 -- native SurfaceWorld manifest delivered into the Unreal Core route

Manifest imported into UVoxelSettings (hash 8933693d9560ba9f), folded into the season
content hash only when Core is on. BuildHost: W1/W8/W16 stable, 2553 surface tiles match
standalone, 432 LOD transitions, collision on all 36 expected tiles. Matched timing
96.8 s native vs 197.3 s bridge (2.04x). Collision support tiles wait for Core region admission.

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

Standalone/UNREAL_INTEGRATION_REPORT.md

@@ -428,3 +428,57 @@ legacy route. After the owner rebuild, recheck the SurfaceWorld shoreline, hills
 at the matched camera after fine tiles settle; also recheck the opening-room floor. The captures show
 the exact-density bridge improves the surface field, but water/presentation and the other missing
 archetypes are still open work.
+
+### Round-5 native SurfaceWorld delivery
+
+Round 4 above is historical. The native manifest route now supersedes the temporary legacy density
+bridge for a reviewed `SurfaceWorld` when `AVoxelWorld::bUseVoxelForgeCore` is enabled. Existing Core
+cave generation remains supported when there is no world-assembly manifest. With the switch off,
+legacy generation and the existing season identity hash remain on the old path.
+
+The editor `UVoxelSettings` asset now has a `SourceWorldAssemblyManifestJson` picker and
+`ImportWorldAssemblyManifestJson` button. Import stores canonical JSON plus the verified Core content
+hash in the settings asset. `GetCurrentSeasonContentHash()` combines that hash only while Core is
+active. Core adapter initialization checks the manifest seed against the resolved layout and
+requires exact, unique `SurfaceWorld` slot index/top/bottom matches. The test passes the reviewed
+JSON to BuildHost through `-coreworldassembly`; it does not edit an asset. Manifest, recipe and plan
+hashes were `8933693d9560ba9f`, `c37de78b759c0a4c` and `1ca84619c8600ee5`.
+
+The final BuildHost commandlet passed the W1/W8/W16 matrix, cave initial streaming, anchor movement,
+carving, lower-surface travel and native SurfaceWorld travel. At `(37,165,-2011)` Core voxels, all
+2,553 expected visual tile hashes matched standalone Core. Coverage checked 573 local tiles, 3,438
+neighbour faces and 432 LOD transitions across two regions. The collision gate checked 125 expected
+near tiles: 36 non-empty tiles had cooked bodies; 89 expected-empty tiles correctly had none. Native
+SurfaceWorld hashes were density `56ccc76575aa5f5f`, mesh `f3aeb31de1f967c1`, payload
+`95cb4781a1be4b73`, topology `26ac366d430599bd`. The BuildHost path uses Unreal mesh upload and
+Chaos collision cooking; standalone checks field and mesh output only.
+
+The narrow switch-off check is source-level, not a second runtime actor session: Core remains
+default-off; the legacy `UpdateChunksAroundPosition` branch is retained; Core-only manifest
+initialization and collision admission are guarded by the switch; and the legacy hash returns before
+reading optional manifest data when disabled. This does not claim a full flag-off runtime replay.
+
+In the same BuildHost session, 2,553 identical keys were generated with hashes on. Native
+`Heightfield2D` vs the legacy bridge took 0.015903 vs 0.012752 s for region compilation and
+96.800984 vs 197.333401 s for summed tile generation; compile plus tiles was 96.816887 vs 197.346153
+s (2.038× speedup). This is serial headless tile generation, not rendered frame time. The ~1.57 s
+full-view aim remains unmet: the last full 529-tile LOD8 stream measured 4.446 s, 2.83× the aim.
+No full-view viewer benchmark ran in round 5.
+
+The existing downscaled native/owner cliff overlook pair was inspected. The sharp ridge peaks remain
+attached to the highland surface with no detached shard trail, so the field/mesh was not altered;
+their appearance is left for the owner to judge in-game. Handoff instructions and actor-local camera
+targets for the surface, coast, cliff, route and cap are in
+[`ASSEMBLER_M1_REPORT.md`](ASSEMBLER_M1_REPORT.md). Likely project compile touchpoints are
+`VoxelSettings.h/.cpp`, `VoxelForgeCoreAdapter.cpp`, `VoxelWorld.cpp` and
+`VoxelForgeExploreCommandlet.cpp`.
+
+Round-5 BuildHost run ledger: the first UBT compile failed to link non-exported settings methods;
+exporting them made the retry pass. Actor attempt 1 found a surface support-tile hash mismatch;
+attempt 2 reproduced it and exposed collision work starting before region admission. Actor attempt 3
+failed the legacy biome-query assertion because the native surface does not provide that legacy
+decorator query; it was replaced with direct native heightfield sampling. After the collision-admission
+fix, the actor test passed. The final rerun after gating the manifest hash on the Core switch also
+passed in 9m20s with 3,880,357,888 bytes peak sampled private memory (3.61 GiB). No `0xC0000142`
+retry or new UECC folder occurred. The owner's project was not opened or built and no `.uasset` was
+edited.