wip(assembler): round S2 (Sol) -- shared per-tile feature queries for every Core family; island placement 30x faster

Island-only worker context replaced by a shared worker-local candidate domain
(WorldAssemblyFeatureTileListV1 / ScopedWorldAssemblyFeatureQueriesV1) serving
SurfaceWorld, FloatingIslands and far-shell queries; a per-domain cost hint keeps the
full scan on small plans. Content placement prepares the same queries and skips proven
air: owner island cell p95 7.07 -> 0.24 ms; populated fixture 572 exact placements,
3.27 s -> 29 ms. Full/candidate hashes equal with dropped-feature controls on both
families; S1 default W1/W8/W16 hashes reproduced; Core-off and M2 fixtures pass.
Default contract for future families in ARCHITECTURE 8.23. Run on gpt-6.1-sol medium.

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

ARCHITECTURE.md

@@ -1326,6 +1326,44 @@ figures measure anchor-search work and steady update overhead, not spawn/asset-i
 See Standalone/Research/WorldAssemblerM3/Round5/REPORT.md for the test matrix, owner-plan hash proof,
 and content-placement measurements.
 
+### 8.23 Shared assembler query domains — World Assembler S2 / M3 Round 6
+
+Meshing, far-shell field queries and placement share `ScopedWorldAssemblyFeatureQueriesV1`.
+Each family prepares conservative candidates for an inclusive domain, including normal halos.
+Scopes borrow immutable recipe/plan pointers from the owning world/snapshot, live on the worker,
+restore the previous scope when nested, and fall back to full evaluation outside their domain.
+Queues, generation epochs, edit locks, streaming policy and canonical field arithmetic are unchanged.
+`candidateEvaluationUseful` is a cost hint resolved once per domain: the measured one-feature
+SurfaceWorld and four-island plans prefer the full evaluator. Larger plans use candidates. Validation
+can force candidates to prove the bounds even for a small plan; this never changes recipe identity.
+
+The default family contract for caves, shafts, pits, passages and rivers is:
+
+1. Declare conservative inclusive influence bounds, including blend, displacement and warp.
+   Unknown influence retains the feature. Keep canonical operation order.
+2. If remote features can determine exact positive density, provide sound value-side certificates
+   or evaluate them. Geometric AABBs alone cannot preserve arbitrary density values; island root
+   ellipsoids retain S1's slope and smooth-min certificate. Optional union-group data belongs to the
+   family proof, not to the engine's notion of Euclidean distance.
+3. Families with a proven air base may declare conservative solid-support bounds. The shared column
+   union skips only proven air; solid-base caves and unknown support retain their ordinary march.
+   Preserve the original sampling phase, crossing count, bisection and final interpolation.
+4. Audit full-scan versus candidates, halos and outside-domain fallback with equal hashes and a
+   deliberately removed needed feature before enabling a new proof.
+
+SurfaceWorld's biome-site search remains its bounded local lattice. Cached XY column evaluation
+uses finite feature candidates; types 1/3 affect every Z, while types 2/4 are neutral outside their
+validated boxes. Shelf source-column queries outside the scope use the full column evaluator.
+Core meshing prepares both native families, including cross-strate tiles. FarShells remains derived
+repair geometry with its existing connector/stratum filtering; its canonical field calls benefit
+from the same scope wherever their samples lie inside the domain.
+
+Content snapshots declare support bounds once. Decoration cells and landmark columns prepare the
+shared domain with a gradient halo, and retain exact crossings. Core-off retains its legacy march.
+Validation compares complete placement transforms and canonical anchor residuals, and applies then
+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.
+
 ## 9. Multiplayer model (listen-server first, dedicated-friendly)
 
 > **Status: transport is DESIGN ONLY — nothing is networked in-tree yet** (no `Replicated`/`HasAuthority`/RPCs; a