wip(assembler): round L13 -- one density field for every route (multiplayer determinism fix)

Region pages fell back to the legacy GetDensityAt evaluator while the base shape used the Core
manifest field, so a tile's density (and sometimes mesh) depended on streaming history. Pages
are now bound to their world's base FStandaloneShapeWorld evaluator before publication; density,
lattice, detail, classification and solid queries all delegate to it. WorldAssemblyEvaluatorVersion
5 -> 6. Route-parity audit: fails on L12 (5/5); after the fix 0 mismatches over 87 tile pairs
(base/page, base/native-only, edited, two histories), 56 exact-query pairs, 2.3M page samples,
4 seeds/recipes. Page-tile proof audit: 1,274 blocks, 0 violations. The spawn and island worlds
are unchanged; crossing output changed as intended. Reviewer interleaved spawn: +1.1% (noise).

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

ARCHITECTURE.md

@@ -1823,6 +1823,23 @@ column metrics. All W1/W12 L1 hashes, exact queries, and the seed-0 FloatingIsla
 the pre-L7 binary with Clang FP contraction off and GCC defaults. See
 [`Standalone/Research/WorldAssemblerM3/Linux7/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux7/REPORT.md).
 
+### 8.36 Route-invariant Core density — World Assembler M3 L13
+
+For an unedited Core world, tile density, mesh, payload, and topology are a function of the world
+manifest/recipe, seed, and tile key. The reviewed manifest field is authoritative: SurfaceWorld uses
+its `Heightfield2D`, while FloatingIslands uses its `FloatingIslandFieldV1`. `World::densityAt` and
+tile generation read the same `FStandaloneShapeWorld` instance. A compiled analytic region page
+retains bounded spatial bins for page ownership and routing, but `SetSharedDensitySource` binds it to
+that base shape before publication; density, lattice, detail, classification, and solid queries
+delegate to the shared evaluator. This keeps exact queries, collision occupancy signs, page tiles,
+and base tiles on one field. Player edits remain explicit versioned overlays on that world state.
+
+The route-binding change increments `WorldAssemblyEvaluatorVersion` from 5 to 6. Do not restore a
+page-local legacy evaluator: it disagrees with the reviewed field. Uniform-block proof audits must
+fill and check page tiles against the evaluator they actually sample. This is the shared Core path;
+the Unreal adapter and its asynchronous MPSC/Epoch flow are unchanged. See
+[`Standalone/Research/WorldAssemblerM3/Linux13/REPORT.md`](Standalone/Research/WorldAssemblerM3/Linux13/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