render: extract cached M2 animation resource observer

docs/modules/m2-build-resource-snapshot.md

@@ -28,7 +28,9 @@ static Mesh and terminal missing-model state. The snapshot never owns engine lif
 
 ```mermaid
 flowchart LR
-    Loader[StreamingWorldLoader observations] --> Snapshot[M2BuildResourceSnapshot]
+    Native[StreamingWorldLoader native observation] --> Snapshot[M2BuildResourceSnapshot]
+    Cached[M2CachedAnimationResourceObserver] --> Snapshot
+    Static[M2StaticBuildResourceObserver] --> Snapshot
     Snapshot --> Dispatch[M2BuildDispatchPlanner]
     Snapshot --> Loader
     Loader --> Animated[M2AnimatedInstanceMaterializer]
@@ -60,8 +62,8 @@ are forbidden.
 | Direction | Contract/data | Producer | Consumer | Ownership | Thread/lifetime |
 |---|---|---|---|---|---|
 | Input | Normalized relative path | Loader path adapter | Snapshot/diagnostics | Copied String | Snapshot lifetime |
-| Input | Optional animated prototype | Prototype/native animation path | Snapshot/materializer adapter | Borrowed exact Node3D reference | One build operation |
-| Input | Animation request pending | Animation pipeline state | Snapshot/dispatch planner | Boolean copy | One build operation |
+| Input | Optional animated prototype | Native/cached animation observer | Snapshot/materializer adapter | Borrowed exact Node3D reference | One build operation |
+| Input | Animation request pending | Cached animation observer | Snapshot/dispatch planner | Boolean copy | One build operation |
 | Input | Optional prepared static Mesh | Mesh cache/request path | Snapshot/materializer adapter | Borrowed exact Mesh reference | One build operation |
 | Input | Static model terminally missing | Prototype cache state | Snapshot/dispatch planner | Boolean copy | One build operation |
 | Output | Availability/pending/missing values | Snapshot | Dispatch planner | Scalar reads | One dispatch plan |
@@ -110,8 +112,12 @@ sequenceDiagram
     participant B as M2BuildBatchPlanner
     participant D as M2BuildDispatchPlanner
     participant M as M2 materializer
-    L->>L: resolve/request animated prototype
-    L->>S: construct(path, prototype, pending)
+    L->>L: resolve native animated prototype
+    L->>S: construct native result
+    opt no native prototype
+        L->>L: delegate cached animation observer
+        L->>S: receive cached/pending snapshot
+    end
     alt animation not pending
         L->>B: plan batch using snapshot availability
         opt positive static batch
@@ -143,7 +149,8 @@ flowchart TB
 ## Ownership, threading and resources
 
 - Snapshot owns only copied scalar state and temporary references.
-- Prototype/cache services retain resource state; loader owns observation order.
+- Prototype/cache services retain resource state; loader owns native-first
+  observation order while cached/static observers own their phases.
 - Scene roots remain loader/tile-owned; Mesh lifetime follows cache/resource refs.
 - Dispatch planner reads only snapshot accessors and never mutates the snapshot.
 - Current construction/adoption occurs on renderer main thread.
@@ -187,9 +194,10 @@ queue/hitch metrics remain unchanged.
 
 ## Extension points
 
-`M2StaticBuildResourceObserver` now produces the static phase. A later animated
-observer may produce the first phase. The value contract remains independent of
-both producers and of generic callback frameworks.
+`M2CachedAnimationResourceObserver` produces the cached animated phase and
+`M2StaticBuildResourceObserver` produces the static phase. Native animation
+observation remains loader-owned. The value contract stays independent of all
+producers and of generic callback frameworks.
 
 ## Capability status
 
@@ -198,14 +206,15 @@ both producers and of generic callback frameworks.
 | Typed per-step M2 resource observation | Implemented extraction | Identity/adoption/lifetime/source/timing verifier | Asset-backed traversal pending |
 | Dispatch decision | Implemented separately | Dispatch planner verifier | Asset-backed traversal pending |
 | Static lookup/request execution | Implemented separately | Static observer verifier | Asset-backed traversal pending |
-| Animated lookup/request execution | Loader-owned | Animation regressions | Service extraction pending |
+| Cached animated lookup/request execution | Implemented separately | Cached observer verifier | Asset-backed traversal pending |
+| Native animated lookup/build execution | Loader-owned | Native renderer regression | Service extraction pending |
 | Engine lifetime/materialization | Loader/materializer-owned | Lifetime/materializer regressions | GPU/p95/p99 evidence pending |
 
 ## Known gaps and risks
 
 - Static observation is mutable during its short two-phase construction.
 - Raw Node3D/Mesh references remain necessary for current materializer APIs.
-- Loader still owns synchronous/native prototype attempts and ResourceLoader requests.
+- Loader still owns synchronous native prototype attempts and terminal polling.
 - Synthetic timing does not measure resource, Node or GPU work.
 
 ## Source map
@@ -215,7 +224,8 @@ both producers and of generic callback frameworks.
 | `src/render/m2/m2_build_resource_snapshot.gd` | Typed per-step resource observations and diagnostics |
 | `src/render/m2/m2_build_dispatch_planner.gd` | Snapshot-to-action planning |
 | `src/render/m2/m2_static_build_resource_observer.gd` | Static snapshot production and requests |
-| `src/scenes/streaming/streaming_world_loader.gd` | Animated observation/request execution and materializer borrowing |
+| `src/render/m2/m2_cached_animation_resource_observer.gd` | Cached animated snapshot production and requests |
+| `src/scenes/streaming/streaming_world_loader.gd` | Native animation observation and materializer borrowing |
 | `src/tools/verify_m2_build_resource_snapshot.gd` | Identity/adoption/lifetime/boundary/timing regression |
 
 ## Related decisions and references