wip(unreal): round 3 -- owner's in-game defects classified; opening room fixed; Core biome query

Luna, integration round 3, from the owner's four in-game screenshots:
- Capsule rings at the opening and the shaft continuing through the cave room were Core
  world defects: the synthetic bore is removed and the opening gets a finite origin room
  and floor (solid below). New world version, W1/W8/W16 identical: density
  a8bcb72d41092503, mesh 90f29ba15e24579f, payload 82c6b489e7bb7fd7, topology
  7b99448a1f844f2c.
- B-side landing and surface: headless coverage found no missing tiles or LOD-transition
  gaps (960 / 640 fine tiles compiled after travel); best explained by Core's missing
  SurfaceWorld representation. Null-RHI cannot rule out a presentation-only issue.
- Core mode GetBiomeAtWorldLocation now answers (e.g. Biome_Surface_Plain); biome
  terrain itself is not generated yet (proposal: native Core SurfaceWorld evaluator).
Owner checked the Step29 viewer himself: the surface strate type is absent there too.

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

ARCHITECTURE.md

@@ -1099,6 +1099,36 @@ and physical play check remains the hand-off step. See
 [`Standalone/UNREAL_INTEGRATION_REPORT.md`](Standalone/UNREAL_INTEGRATION_REPORT.md) for evidence,
 known limits, and instructions.
 
+### 8.18 Core world correction and biome gap — integration round 3
+**Status (2026-10-08):** the owner confirmed that Core runs in his game. His first visual review found
+two shape-world defects and two suspected streaming/feature defects. The finite origin room and its
+floor now follow the owner layout; the synthetic 256-voxel entry bore was removed, and invalid
+passage descriptors no longer create micro-landings. This is an intentional Core world-version
+change. The standalone viewer's old hashes are not compatible with this corrected field; the new
+BuildHost initial clipmap hashes match at W1/W8/W16:
+`density=a8bcb72d41092503`, `mesh=90f29ba15e24579f`, `payload=82c6b489e7bb7fd7`,
+`topology=7b99448a1f844f2c`.
+
+The BuildHost actor proof now travels to the B-side landing and the surface strate. At each position,
+the desired visual tile-key set is complete, tile payload hashes match standalone Core, and adjacent
+same-LOD and transition faces have full coverage. Fine tiles compiled around the travelled player
+(960 at B and 640 at the surface position). The surface actor phase had extra stale/support keys in
+its loaded collection, so the check filters collision-only support and asserts the exact 2,553-key
+visual set; it does not claim every collision-support compile had quiesced. Null rendering still
+means this is streaming/payload evidence, not an Unreal screenshot.
+
+`GetBiomeAtWorldLocation` now queries the copied owner biome evaluator in Core mode at the legacy
+12.5 cm query scale expected by that evaluator. It returns biome identity/data for the surface sample
+(`Biome_Surface_Plain`, index 2); this query does not add biome-driven terrain or decorations to the
+Core shape field. A full biome surface remains a separate feature. Recommended next design: make
+strate evaluation explicit in the resolved Core snapshot, with a deterministic `SurfaceWorld` path
+that consumes resolved biome/height parameters and uses fixed-order noise plus per-column caching.
+This is a medium-to-large port with controllable per-voxel cost and straightforward worker
+determinism. Routing SurfaceWorld through the copied legacy evaluator is a smaller fidelity bridge,
+but it duplicates the field boundary, costs roughly the legacy evaluation per sample, and inherits
+more float/platform constraints; keep it as a temporary compatibility route only if exact behavior
+is required before the port. See the round-3 table in the integration report for per-defect evidence.
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a