render: extract cached M2 animation resource observer

docs/modules/m2-build-batch-planner.md

@@ -104,7 +104,8 @@ sequenceDiagram
 - The planner owns only call-local scalar values and the returned Dictionary.
 - `M2BuildQueue` owns typed jobs, FIFO ordering, serial numbers and group/offset
   cursors. `M2BuildDispatchPlanner` owns the pure resource-state action decision;
-  the loader owns tile checks, resource observation/retry and adoption calls.
+  the loader owns tile checks and native-first orchestration, while static and
+  cached animation observers own their observation/retry phases.
 - Materializers own main-thread Node/MultiMesh construction under loader roots.
 - The scheduler owns the frame-local `M2_BUILD` counter.
 - Pure planning is thread-safe, though the current adapter calls it on main thread.
@@ -150,8 +151,8 @@ queue depth, build activity and hitch observability.
 
 ## Extension points
 
-- A later package may extract resource observation/request orchestration while
-  retaining the dispatch and typed build-job/FIFO contracts.
+- Remaining native resource observation may be extracted while retaining the
+  dispatch and typed build-job/FIFO contracts.
 - Spatial-cell batching must use measured culling/performance evidence and must
   not silently change this model-path batch cursor.