render: extract M2 Mesh resource finalizer

docs/modules/m2-mesh-load-pipeline-state.md

@@ -78,7 +78,7 @@ Side effects are limited to collection mutation and retaining String/integer val
 flowchart TD
     Start[Successful ResourceLoader request] --> Remember[remember request]
     Remember --> Snapshot[request records snapshot]
-    Snapshot --> Poll[Loader polls status]
+    Snapshot --> Poll[Mesh resource finalizer polls status]
     Poll --> Active{In progress?}
     Active -->|yes| Snapshot
     Active -->|no| Complete[complete request with terminal status]
@@ -86,7 +86,7 @@ flowchart TD
     FIFO --> Permit{Loader permit available?}
     Permit -->|no| FIFO
     Permit -->|yes| Pop[Pop oldest terminal record]
-    Pop --> Finalize[Loader gets Resource and delegates first-Mesh extraction]
+    Pop --> Finalize[Mesh resource finalizer gets Resource and extracts first Mesh]
     Finalize --> Prepare[M2RuntimeMeshFinalizer prepares Mesh]
     Prepare --> Adopt[Loader adopts Mesh or marks prototype outcome state]
 ```
@@ -113,6 +113,7 @@ again only if loader cache/missing rules permit it.
 ```mermaid
 sequenceDiagram
     participant Loader as StreamingWorldLoader
+    participant Finalizer as M2MeshResourceFinalizer
     participant Resource as ResourceLoader
     participant State as M2MeshLoadPipelineState
     participant Budget as RenderBudgetScheduler
@@ -120,14 +121,16 @@ sequenceDiagram
     Resource-->>Loader: OK or ERR_BUSY
     Loader->>State: remember_request(normalized, cache path)
     loop frames
-        Loader->>State: request_records_snapshot()
-        Loader->>Resource: load_threaded_get_status(path)
+        Loader->>Finalizer: poll_terminal_requests(state, prototype cache)
+        Finalizer->>State: request_records_snapshot()
+        Finalizer->>Resource: load_threaded_get_status(path)
     end
-    Loader->>State: complete_request(normalized, terminal status)
+    Finalizer->>State: complete_request(normalized, terminal status)
     Loader->>Budget: try_consume_permit(M2_MESH_FINALIZE)
-    Loader->>State: pop_finalize_record()
-    Loader->>Resource: load_threaded_get(path)
-    Loader->>Loader: extract/refresh/adopt Mesh or mark missing
+    Loader->>Finalizer: finalize_next_resource(state, caches, directory)
+    Finalizer->>State: pop_finalize_record()
+    Finalizer->>Resource: load_threaded_get(path)
+    Finalizer->>Finalizer: extract/refresh/adopt Mesh or mark missing
 ```
 
 ## Dependency diagram
@@ -135,7 +138,9 @@ sequenceDiagram
 ```mermaid
 flowchart TB
     Loader[StreamingWorldLoader] --> State[M2MeshLoadPipelineState]
-    Loader --> Resource[ResourceLoader]
+    Loader --> MeshFinalizer[M2MeshResourceFinalizer]
+    MeshFinalizer --> State
+    MeshFinalizer --> Resource[ResourceLoader]
     Loader --> Budget[RenderBudgetScheduler]
     Loader --> MeshCache[M2 Mesh resource and prototype outcome cache states]
     Loader --> Finalizer[M2RuntimeMeshFinalizer]
@@ -148,7 +153,9 @@ flowchart TB
 
 - Main thread serializes all state mutation and snapshots.
 - State owns only request/finalize Dictionaries containing Strings and status integers.
-- Loader owns ResourceLoader request lifetime and drains active paths before shutdown clear.
+- `M2MeshResourceFinalizer` owns terminal status polling, terminal Resource
+  retrieval, first-Mesh extraction, runtime preparation and cache/missing adoption.
+- Loader owns request admission, scheduler permits and shutdown drain ordering.
 - `M2MeshResourceCacheState` owns prepared static Mesh references and
   `M2RuntimeMeshFinalizer` owns refresh/rebuild/fallback. The loader owns shared
   adoption decisions, raw I/O and remaining engine resources; the prototype
@@ -161,9 +168,9 @@ flowchart TB
 |---|---|---|---|---|
 | Empty/duplicate request | State guard | Reject unchanged | Contract verifier | Correct caller/request later |
 | Request start failure | Loader return code | No state insert; mark missing | Existing loader behavior | Cache/source correction |
-| Non-terminal status | Loader poll | Keep pending | Existing queue metric | Poll next frame |
-| Terminal load failure | Status in popped record | Loader marks missing | Existing missing behavior | World/cache reload |
-| Empty defensive path | Loader before poll | Discard and mark missing | Source regression | Correct request producer |
+| Non-terminal status | Finalizer poll | Keep pending | Existing queue metric | Poll next frame |
+| Terminal load failure | Status in popped record | Finalizer marks missing | Existing missing behavior | World/cache reload |
+| Empty defensive path | Finalizer before poll | Discard and mark missing | Source regression | Correct request producer |
 | Shutdown | Loader drains pending Resource paths | Clear state | Shutdown verifier | New loader starts empty |
 
 ## Configuration and capabilities
@@ -207,7 +214,7 @@ rebuild policy are unchanged; no migration or rebake is required.
 |---|---|---|---|
 | Static M2 request/finalize state | Implemented extraction | Contract/source/timing verifier | Asset-backed long traversal pending |
 | Static request admission I/O | Implemented in observer | Observer/shutdown regressions | Asset-backed traversal pending |
-| Static request polling/finalize I/O | Existing loader-owned | Shutdown/material regressions | Finalize extraction optional |
+| Static request polling/finalize I/O | Implemented extraction | Finalizer contract/source/timing verifier | Asset-backed traversal pending |
 | Mesh cache | Implemented extraction | Mesh resource cache state verifier | Asset-backed memory/leak run pending |
 | First-Mesh extraction | Implemented extraction | Resource/order/lifetime verifier | Asset-backed corrupt-scene fixture pending |
 | Mesh preparation | Implemented extraction | Runtime finalizer transition/rebuild verifier | Asset-backed material comparison pending |
@@ -225,11 +232,12 @@ rebuild policy are unchanged; no migration or rebake is required.
 | Path | Responsibility |
 |---|---|
 | `src/render/m2/m2_mesh_load_pipeline_state.gd` | Pending records, terminal FIFO and metrics |
+| `src/render/m2/m2_mesh_resource_finalizer.gd` | Terminal polling, Resource extraction, preparation and adoption |
 | `src/render/m2/m2_mesh_resource_cache_state.gd` | Prepared static Mesh references and final clear |
 | `src/render/m2/m2_mesh_resource_extractor.gd` | First-Mesh selection and temporary PackedScene lifetime |
 | `src/render/m2/m2_runtime_mesh_finalizer.gd` | Refresh/rebuild/fallback preparation |
 | `src/render/m2/m2_prototype_cache_state.gd` | Missing-model outcome retention |
-| `src/scenes/streaming/streaming_world_loader.gd` | Cache path choice, I/O polling, permits and adoption decisions |
+| `src/scenes/streaming/streaming_world_loader.gd` | Cache path choice, request admission, permits and composition |
 | `src/render/m2/m2_runtime_mesh_rebuild_classifier.gd` | Downstream stale Mesh rebuild decision |
 | `src/tools/verify_m2_mesh_load_pipeline_state.gd` | Lifecycle/boundary/timing regression |