Document geometry state over CultMesh

src/GameCult.Geometry/README.md

@@ -14,3 +14,51 @@ The package is deliberately substrate-shaped:
   the xeno boundary, but the live machine eats and emits typed CultCache
   documents.
 
+## Runtime Path
+
+`vg-csg` emits domain documents, selected-cut manifests, and chunk artifacts as
+MessagePack CultCache documents. A Unity runtime, local worker, or remote
+geometry process should receive the same records through CultMesh/CultNet and
+read them back as `CultGeometry*` types.
+
+```csharp
+using GameCult.Caching;
+using GameCult.Geometry;
+using GameCult.Mesh;
+using GameCult.Networking;
+
+var geometryDocuments = new CultNetDocumentRegistry(CultDocumentRegistry.Shared)
+    .Register(CultNetDocumentBinding.ForDocument<CultGeometryDomainDocument>())
+    .Register(CultNetDocumentBinding.ForDocument<CultGeometryBuildRequest>())
+    .Register(CultNetDocumentBinding.ForDocument<CultGeometrySelectedCutManifest>())
+    .Register(CultNetDocumentBinding.ForDocument<CultGeometryChunkArtifact>());
+
+using var node = await CultMesh.CreateNodeAsync("ragnarok-geometry.ccmp", new CultMeshNodeOptions
+{
+    DatabaseOptions = new CultNetDatabaseOptions
+    {
+        RuntimeId = "unity-runtime",
+        DocumentRegistry = geometryDocuments
+    }
+});
+
+using var chunks = node.Database
+    .Watch<CultGeometryChunkArtifact>()
+    .Subscribe(change => ApplyChunk(change.Document));
+```
+
+The record key is part of the contract. Rust and C# must compute the same key
+for the same geometry record, so stable fingerprints use the Rust canonical
+field order and invariant float text. If this drifts, the same chunk becomes two
+different chunks depending on which runtime touched it first. That is not a
+cache miss; that is split-brain geometry.
+
+## Documents
+
+- `CultGeometryDomainDocument`: one hierarchical domain tree, suitable for
+  Ragnarok/Fensalir-style feature DSL output.
+- `CultGeometryBuildRequest`: one LOD/frustum/budget request for workers.
+- `CultGeometrySelectedCutManifest`: the selected domain cut, deferred children,
+  fallback rows, and diagnostic contribution rows.
+- `CultGeometryChunkArtifact`: render mesh, optional collider mesh, source
+  domain/claim identities, build counters, and transition clipping seed.