refactor(M03): extract M2 mesh resource traversal

Work-Package: M03-RND-M2-MESH-RESOURCE-EXTRACTOR-001
Agent: sindo-main-codex
Tests: 36 headless renderer/coordinate contracts pass; checkpoint dry-run 7/7; documentation and coordination gates pass
Fidelity: preserves first-Mesh preorder and temporary PackedScene cleanup; no visual parity claim

docs/modules/world-renderer.md

@@ -7,7 +7,7 @@
 | Status | Partial |
 | Target/work package | M00 baseline; `M01-RND-STREAMING-FOCUS-001`; `M01-QAR-SERVER-SPAWN-RENDERER-001`; M03 facade/planner/scheduler/internal-access/ground/environment/entity packages; M03 terrain packages; M03 M2 packages; M03 WMO placement package |
 | Owners | Renderer workstream / milestone integrator |
-| Last verified | Worktree `work/sindo-main-codex/m03-m2-mesh-resource-cache`, 2026-07-17 |
+| Last verified | Worktree `work/sindo-main-codex/m03-m2-mesh-resource-extractor`, 2026-07-17 |
 | Profiles/capabilities | `Performance`, `Balanced`, `High`, `Custom`; Blizzlike fidelity incomplete |
 
 ## Purpose
@@ -135,6 +135,7 @@ from externally reading/writing loader-private queue, task, cache and tile-state
 | `M2RuntimeMeshRebuildClassifier` | Internal memoized M2 service | Detects billboard/UV-rotation metadata requiring stale cached-mesh rebuild | Renderer main thread; cached until reset | Invalid variants/indices skipped; first path decision wins |
 | `M2MeshLoadPipelineState` | Internal M2 async-state service | Owns static Mesh pending request records and terminal finalize FIFO | Renderer main thread; map/session | Empty/duplicate/unknown transitions rejected |
 | `M2MeshResourceCacheState` | Internal M2 Resource cache | Owns prepared static Mesh references by normalized path | Renderer main thread; final shutdown | Empty path/null Mesh rejected; same path replaces |
+| `M2MeshResourceExtractor` | Internal M2 scene/resource service | Selects first Mesh from direct Resource, PackedScene or Node subtree | Renderer main thread; stateless except temporary instance | Invalid/no Mesh returns null; temporary PackedScene root freed |
 | `WmoPlacementResolver.normalize_relative_path/resolve_unique_key/resolve_world_transform` | Internal pure WMO service | Resolves cache key, registry identity and world transform | Main/any thread; stateless | Missing UID uses tile/index fallback; transform fields use historical defaults |
 | `WmoPlacementRegistry.add_reference/release_reference/contains/active_count/diagnostic_snapshot/clear` | Internal WMO service | Owns placement-key to tile/global reference sets | Renderer main thread; map session | Empty/unknown/non-owner input is rejected without mutation |
 | `WmoRenderBuildStepPlanner.plan_step` | Internal pure WMO service | Selects one mesh-first lightweight render-group operation and next cursors | Main/any thread; stateless | Raw integer comparisons are preserved without clamping |
@@ -375,8 +376,11 @@ sequenceDiagram
   terminal statuses and completion-order finalize FIFO. The loader retains cache
   path selection, ResourceLoader calls, permits, shared missing state and adoption.
 - `M2MeshResourceCacheState` owns prepared static Mesh references and releases
-  them at the existing final-shutdown site. The loader retains extraction,
-  material refresh/rebuild, missing/prototype state and materialization.
+  them at the existing final-shutdown site. The loader retains material
+  refresh/rebuild, missing/prototype state and materialization.
+- `M2MeshResourceExtractor` owns depth-first first-Mesh selection and temporary
+  PackedScene instance destruction. The loader retains ResourceLoader I/O,
+  runtime preparation, cache/missing adoption and materialization.
 - Rendered-ground query results and diagnostic snapshots are caller-owned values;
   the facade never returns Mesh, Node, tile-state or queue references.
 - Loaded-mesh ground sampling is renderer diagnostics, not authoritative gameplay
@@ -580,6 +584,7 @@ Exact exported settings and cache versions remain documented in [`../../RENDER.m
 | `src/render/m2/m2_runtime_mesh_rebuild_classifier.gd` | Billboard/UV-rotation stale cached-mesh rebuild decision and memoization |
 | `src/render/m2/m2_mesh_load_pipeline_state.gd` | Static M2 pending Resource paths, terminal statuses and finalize FIFO |
 | `src/render/m2/m2_mesh_resource_cache_state.gd` | Prepared static M2 Mesh references and final-shutdown release |
+| `src/render/m2/m2_mesh_resource_extractor.gd` | First-Mesh selection and temporary PackedScene instance lifetime |
 | `src/render/streaming/streaming_target_planner.gd` | Scene-free wanted/retained ADT target calculation |
 | `src/render/streaming/streaming_target_policy.gd` | Immutable renderer radius/prefetch policy |
 | `src/render/streaming/streaming_target_plan.gd` | Immutable planner result with read-only tile-key sets |
@@ -597,6 +602,7 @@ Exact exported settings and cache versions remain documented in [`../../RENDER.m
 | `src/tools/verify_m2_runtime_mesh_rebuild_classifier.gd` | M2 rebuild predicate/cache/boundary/timing regression |
 | `src/tools/verify_m2_mesh_load_pipeline_state.gd` | Static M2 request/terminal/FIFO/boundary/timing regression |
 | `src/tools/verify_m2_mesh_resource_cache_state.gd` | Static M2 Mesh cache ownership/lifetime/boundary/timing regression |
+| `src/tools/verify_m2_mesh_resource_extractor.gd` | M2 direct/PackedScene/subtree order/lifetime/boundary/timing regression |
 | `src/tools/verify_streaming_target_planner.gd` | Planner behavior, dependency and bounded timing regression |
 | `src/tools/verify_render_budget_scheduler.gd` | Scheduler bounds, shared-lane priority, cancellation and timing regression |
 | `src/tools/verify_renderer_internal_access.gd` | Gameplay/EditorPlugin/registered renderer-tool boundary gate derived from private streamer fields |