wip(assembler): round L21 -- resolved strate layout snapshot + validator (no world change)

Core ResolvedLayoutSnapshotV1 (canonical JSON, stable identity): per strate stable ID, generator,
recipe, interior bounds in metres, ceiling/bedrock bands as Core really applies them, transition
mode/width, dispatch provenance. Validator: compat mode reports today's deviations; strict mode
enforces ceiling -> content -> bedrock -> next ceiling (owner rule), two separate bands, nominal
contiguity, interpenetration only within the declared EVoxelStrateTransition width; 7 negative
controls rejected. Findings: SW built at -120..-632 m although the params say -60 m; a 60 m unowned
gap filled by analytic FI fallback; no active bedrock bands; transitions ignored by Core.
All L19 hashes unchanged (28 + 14 crossing runs). The Unreal adapter exports resolved_layout
(uncompiled here).

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

ARCHITECTURE.md

@@ -1869,6 +1869,36 @@ query, stratum position, scale, or asynchronous route changes. The strict LOD0
 audit and the matched before/after captures are in
 [`Standalone/Research/WorldAssemblerM3/Linux19/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux19/REPORT.md).
 
+### 8.39 Resolved layout snapshots and nominal strate bands — World Assembler L21
+
+`ResolvedLayoutSnapshotV1` is a separate Core-owned record built from the resolved manager slots and
+the native SurfaceWorld/FloatingIslands plans. It has a canonical JSON representation, schema version,
+and stable FNV-1a identity. Its physical intervals use half-open micrometre coordinates; recipe anchors
+retain their serialized fixed-point units. The Unreal adapter exports it beside `world_assembly`, so the
+layout digest never salts a recipe, manifest, density, or mesh hash. The standalone exporter follows
+the same builder after plan resolution. It runs once per plan request and is not read from density or
+tile-worker loops.
+
+Each record separates the nominal ceiling, content, and bedrock bands. A strict layout requires that
+sequence for every strate and requires bedrock(N) to touch the next strate's ceiling(N+1). The two
+bands remain separately owned. Gradient and Interleaved interfaces may declare interpenetration only
+inside their explicit transition zone; Hard has zero effective width. The manager's `TransitionBlendChunks`
+is expressed in owner-chunk metres. Interleaved's existing two-chunk domain warp extends its possible
+fingers beyond the blend width and is recorded separately. Compatibility validation reports current
+gaps, overlaps, ambiguities, inactive/missing bands, and unhonoured transitions while accepting them;
+strict validation rejects them. Core dispatches per-strate recipe fields without applying that
+parameter blend, even though the legacy manager helper implements it. Both band types default diggable,
+with protection represented explicitly.
+
+Compatibility facts from L21: native SurfaceWorld plan/query bounds use 32 Core voxels (8 m) per
+dispatch chunk, while FloatingIslands converts the 32-voxel owner chunk through its 12.5/25 cm scale
+(16 Core voxels, 4 m). In the prototype where the top slot is FloatingIslands, this leaves a nominal
+60 m interval between the FI bottom (−60 m) and SurfaceWorld top (−120 m); the Core selectors fall
+through to the compiled analytic FloatingIslands fallback there. Core does not apply the manager's
+parameter blend at either recipe boundary. The FI v3 upper seal remains a ceiling inside its current
+content range, and its missing lower bedrock is recorded without changing evaluation. See
+[`Standalone/Research/WorldAssemblerM3/Linux21/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux21/REPORT.md).
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a