refactor(M03): extract M2 runtime mesh finalizer

Work-Package: M03-RND-M2-RUNTIME-MESH-FINALIZER-001
Agent: sindo-main-codex
Tests: 37 headless renderer/coordinate contracts pass; checkpoint dry-run 7/7; documentation and coordination gates pass
Fidelity: preserves refresh version 2, classifier, rebuild and fallback transitions; no visual parity claim

docs/modules/m2-runtime-mesh-rebuild-classifier.md

@@ -29,13 +29,13 @@ runtime-cache lifetime.
 
 ```mermaid
 flowchart LR
-    Cache[Stale cached M2 Mesh] --> Loader[StreamingWorldLoader]
-    Loader --> Raw[M2Loader raw Dictionary]
+    Cache[Stale cached M2 Mesh] --> Finalizer[M2RuntimeMeshFinalizer]
+    Loader[StreamingWorldLoader] --> Raw[M2Loader raw Dictionary]
     Raw --> Classifier[M2RuntimeMeshRebuildClassifier]
     Classifier --> Decision[Memoized rebuild boolean]
-    Decision --> Loader
-    Loader -->|true| Builder[M2Builder rebuild]
-    Loader -->|false| Refresh[Mark material refresh version]
+    Decision --> Finalizer
+    Finalizer -->|true| Builder[M2Builder rebuild]
+    Finalizer -->|false| Refresh[Mark material refresh version]
 ```
 
 Allowed dependencies are Dictionary/Array, `PackedInt32Array`, `Vector4` and
@@ -57,7 +57,7 @@ WorkerThreadPool, Mesh/Node/RID ownership and other layers are forbidden.
 |---|---|---|---|---|---|
 | Input | Normalized M2 relative path | Loader cache lookup | Classifier cache key | String value copied | Until clear |
 | Input | Raw M2 batches/transforms/combos Dictionary | Native `M2Loader` adapter | Classifier | Borrowed; not mutated | First classification call per path |
-| Output | Rebuild-required boolean | Classifier | Loader material-refresh adapter | Scalar | Memoized until clear |
+| Output | Rebuild-required boolean | Classifier | Runtime Mesh finalizer | Scalar | Memoized until clear |
 | Output | Detached decision Dictionary | Classifier | Verifier/future diagnostics | Caller-owned copy | Snapshot lifetime |
 
 Side effects are limited to inserting and clearing boolean memoization entries.
@@ -103,16 +103,18 @@ stateDiagram-v2
 sequenceDiagram
     participant Loader as StreamingWorldLoader
     participant Native as M2Loader
+    participant Finalizer as M2RuntimeMeshFinalizer
     participant Classifier as M2RuntimeMeshRebuildClassifier
     participant Builder as M2Builder
     Loader->>Native: load_m2(normalized path)
     Native-->>Loader: raw Dictionary
-    Loader->>Classifier: needs_runtime_mesh_rebuild(path, data)
-    Classifier-->>Loader: memoized boolean
+    Loader->>Finalizer: finalize_mesh(path, mesh, data, dir)
+    Finalizer->>Classifier: needs_runtime_mesh_rebuild(path, data)
+    Classifier-->>Finalizer: memoized boolean
     alt rebuild required
-        Loader->>Builder: rebuild mesh from raw data
+        Finalizer->>Builder: rebuild mesh from raw data
     else no rebuild required
-        Loader->>Loader: stamp material refresh version
+        Finalizer->>Finalizer: stamp material refresh version
     end
 ```
 
@@ -120,7 +122,8 @@ sequenceDiagram
 
 ```mermaid
 flowchart TB
-    Loader[StreamingWorldLoader] --> Classifier[M2RuntimeMeshRebuildClassifier]
+    Loader[StreamingWorldLoader] --> Finalizer[M2RuntimeMeshFinalizer]
+    Finalizer --> Classifier[M2RuntimeMeshRebuildClassifier]
     Loader --> Native[M2Loader]
     Loader --> Builder[M2Builder]
     Loader --> Cache[M2 Mesh/Scene caches]
@@ -132,8 +135,8 @@ flowchart TB
 ## Ownership, threading and resources
 
 - The classifier owns only normalized-path boolean entries.
-- The loader owns raw loading, cache/resource selection, Mesh replacement and
-  material refresh metadata.
+- The finalizer owns classifier lifetime, rebuild decisions and refresh metadata.
+- The loader owns raw loading, cache/resource selection and Mesh adoption.
 - Raw Dictionaries are borrowed and never retained; only the computed boolean is cached.
 - Current calls and clears are serialized on the renderer main thread.
 - No Node, Resource, Mesh, material or RID reference crosses into the classifier.
@@ -154,7 +157,7 @@ flowchart TB
 |---|---|---|---|---|
 | Maximum texture stages inspected | `4` | Existing M2 material path | No | Preserves historical four-stage shader boundary |
 | UV rotation-speed epsilon | `0.000001` exclusive | Existing M2 material path | No | Larger absolute speed requires rebuild |
-| `M2_MATERIAL_REFRESH_VERSION` | Loader constant `2` | All | Code version | Gates whether classifier is called |
+| `MATERIAL_REFRESH_VERSION` | Finalizer constant `2` | All | Code version | Gates whether classifier is called |
 
 ## Persistence, cache and migration
 
@@ -193,7 +196,7 @@ reset/shutdown sites. No persisted cache version or rebuild instruction changes.
 | Billboard rebuild classification | Implemented extraction | Flag/count fixtures | Asset-backed cache refresh timing pending |
 | UV-rotation rebuild classification | Implemented extraction | Combo/stage/threshold fixtures | More build-12340 material fixtures pending |
 | Runtime memoization lifetime | Implemented extraction | First-decision/clear/source fixtures | Byte/count runtime metric not exposed |
-| M2 mesh loading/finalization | Existing loader-owned | Material/shutdown regressions | Separate state extraction pending |
+| Runtime Mesh finalization | Implemented extraction | Finalizer transition/rebuild fixtures | Asset-backed material comparison pending |
 
 ## Known gaps and risks