wip(assembler): round L22 -- one 8 m layout chunk for every strate; real ceiling -> content -> bedrock

StrateLayoutChunkSizeMeters (world setting, default 8 m; owner decision) is resolved once in
the director/adapter and standalone loader; every generator reads the resolved width (no
CHUNK_SIZE / Core-tile inference). Every strate gets solid ceiling and bedrock bands from its
BoundarySealThickness in the shared composition path (diggable by default); faces come from the
shared boundary path. Owner world: FloatingIslands +8..-120 m (128 m, now with a bedrock floor),
SurfaceWorld -120..-632 m (unchanged; full-detail and exact-query hashes equal L21); the 60 m gap is
gone. The strict layout validator passes on the real world, with 0 endpoint dispatch
disagreements. Spawn/benchmark camera derived from route.front. Ledges under the islands gone
(reviewer capture). Evaluator 7, recipe schema 2, layout snapshot 2, FI geometry 4.
Open: SW cap profiles exceed the ceiling band (owner call); transitions still Hard; Unreal
setting/manager/adapter edits uncompiled here.

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

ARCHITECTURE.md

@@ -1869,7 +1869,7 @@ 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
+### 8.39 Resolved layout snapshots and nominal strate bands — World Assembler L21 (historical)
 
 `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,
@@ -1899,6 +1899,31 @@ parameter blend at either recipe boundary. The FI v3 upper seal remains a ceilin
 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).
 
+### 8.40 Fixed-metre strate layout units and shared boundary volumes — World Assembler L22
+
+`StrateLayoutChunkSizeMeters` is one world-level setting, defaulting to **8 m**, independent of the
+legacy 32-voxel chunk and Core's 32³ storage tile. The director resolves the setting once to physical
+micrometres and Core subvoxels; every generator plan and dispatch reads that snapshot. At a 25 cm Core
+voxel, an 8 m layout chunk is 32 Core voxels (8192 1/256-voxel units); at 20 cm it is 40 Core voxels
+(10240 units). The Core tile remains 32³ voxels and is not a layout chunk.
+
+The owner's FI/SW intervals are contiguous: FloatingIslands occupies [−120,+8) m and SurfaceWorld
+occupies [−632,−120) m. Each strate is ceiling → content → bedrock. Both solid, diggable boundary
+bands use its generator's existing `BoundarySealThickness` and `BaseDensity`; `InterStrateGapChunks`
+controls only spacing, and `EdgeSealThickness` remains horizontal. No new thickness parameter or hidden
+band height was added. The shared composition layer emits both volumes for every generator and the
+shared mesh path closes their visible ceiling and floor faces.
+
+The snapshot is schema V2 and is consumed by bounds planning, native and legacy dispatch, solid-band
+composition, and validation. Strict validation accepts the real owner layouts, and the boundary probe
+audit agrees at all 27 sampled endpoints in both recipe modes. The owner authored Gradient transition
+is recorded as an explicit Hard fallback with zero interpenetration; Gradient and Interleaved mixing
+remain unimplemented and must not be inferred from the declared blend width. Seven validator negative
+controls continue to reject malformed bands.
+
+Evidence and owner caveats are in
+[`Standalone/Research/WorldAssemblerM3/Linux22/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux22/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