render: extract WMO scene instance factory

Work-Package: M03-RND-WMO-SCENE-INSTANCE-FACTORY-001
Agent: sindo-main-codex
Tests: 65/66 headless verifiers; proprietary ADT probe unavailable; checkpoint dry-run 7/7; docs and coordination passed
Fidelity: valid cached/live naming, placement, validation and Resource identity preserved; invalid-root leak fixed

docs/modules/wmo-placement-resolver.md

@@ -7,7 +7,7 @@
 | Status | Implemented |
 | Target/work package | M03 / `M03-RND-WMO-PLACEMENT-RESOLVER-001` |
 | Owners | Pure WMO cache-key, placement-identity and world-transform rules |
-| Last verified | Worktree `work/sindo-main-codex/m03-wmo-placement-resolver`, 2026-07-17 |
+| Last verified | Worktree `work/sindo-main-codex/m03-wmo-scene-instance-factory`, 2026-08-01 |
 | Profiles/capabilities | Existing ADT/WDT WMO placement paths |
 
 ## Purpose
@@ -31,14 +31,17 @@ live-prototype instance paths.
 flowchart LR
     Parsed[ADT/WDT WMO placement] --> Loader[StreamingWorldLoader adapter]
     Loader --> Resolver[WmoPlacementResolver]
+    Loader --> Factory[WmoSceneInstanceFactory]
+    Factory --> Resolver
     Resolver --> CacheKey[Normalized cache key]
     Resolver --> Identity[Registry unique key]
     Resolver --> Transform[World Transform3D]
     CacheKey --> Cache[Loader WMO caches/requests]
     Identity --> Registry[WmoPlacementRegistry]
     Transform --> RenderRoot[Lightweight render root]
-    Transform --> Scene[Cached scene instance]
-    Transform --> Live[Live prototype instance]
+    Transform --> Factory
+    Factory --> Scene[Cached scene instance]
+    Factory --> Live[Live prototype instance]
 ```
 
 Allowed dependencies are Dictionary/String values and Godot `Vector3`, `Basis`
@@ -62,7 +65,7 @@ WorkerThreadPool, mutexes, files, gameplay, network and editor UI are forbidden.
 | Input | Tile key and placement index | Loader build job | Synthetic identity fallback | Copied scalar/String | Registry entry lifetime |
 | Output | Normalized relative path | Resolver | Render/scene cache and load-request maps | New String value | Request/cache lookup |
 | Output | `uid:*` or `tile:*:*` key | Resolver | `WmoPlacementRegistry` and loader ref arrays | New String value | Until unregister/reset |
-| Output | World `Transform3D` | Resolver | Three WMO instance adapters | Value copy | Instance lifetime after assignment |
+| Output | World `Transform3D` | Resolver | Lightweight render-root adapter and cached/live instance factory | Value copy | Instance lifetime after assignment |
 
 The resolver retains no source Dictionary, output or engine resource.
 
@@ -91,6 +94,7 @@ and shutdown require no resolver operation.
 ```mermaid
 sequenceDiagram
     participant Loader as StreamingWorldLoader
+    participant Factory as WmoSceneInstanceFactory
     participant Resolver as WmoPlacementResolver
     participant Registry as WmoPlacementRegistry
     participant Instance as Render/cached/live instance
@@ -98,9 +102,15 @@ sequenceDiagram
     Resolver-->>Loader: cache key
     Loader->>Resolver: resolve_unique_key(placement, tile, index)
     Resolver-->>Registry: identity adopted by loader
-    Loader->>Resolver: resolve_world_transform(placement)
-    Resolver-->>Loader: value Transform3D
-    Loader->>Instance: assign transform and attach/build
+    alt lightweight render root
+        Loader->>Resolver: resolve_world_transform(placement)
+        Resolver-->>Loader: value Transform3D
+    else cached/live instance
+        Loader->>Factory: create with placement
+        Factory->>Resolver: resolve_world_transform(placement)
+        Resolver-->>Factory: value Transform3D
+    end
+    Loader->>Instance: attach/build prepared instance
 ```
 
 ## Ownership, threading and resources
@@ -109,7 +119,9 @@ sequenceDiagram
 - `WmoPlacementRegistry` owns placement-key reference sets. The loader owns its
   key-to-Node map, cache/load-request state, jobs/queues, resource fallback and
   cancellation.
-- The loader and builders own every Node/Mesh/MultiMesh/material/RID lifecycle.
+- `WmoSceneInstanceFactory` owns detached cached/live candidate roots until
+  rejection or transfer; the loader/builders own attachment and remaining
+  Node/Mesh/MultiMesh/material/RID lifecycle.
 - Pure calls are thread-safe; current consumers execute on the main thread.
 
 ## Errors, cancellation and recovery