Document deferred retained scaling polish

docs/window-animations-plan.md

@@ -20,6 +20,9 @@ be handled deliberately.
   working and testable.
 - Content freezing will use retained per-surface texture references, not a full
   offscreen snapshot as the default design.
+- Retained records should keep using the existing renderer behavior for now,
+  including clipping and edge stretch/clamp behavior for undersized contents. A
+  dedicated retained-tree scaling path is deferred to a later polish phase.
 - The multiphase animation concept is original to Wry. Hy3 is relevant only as
   partial inspiration for tiling style and titlebar/grouping behavior.
 - Mono mode should mostly avoid animations. Exceptions are windows entering or
@@ -107,6 +110,8 @@ Initial retained-record implementation status:
 - Retained records hold both `GfxTexture` and `SurfaceBuffer` references so the
   existing buffer release/sync path remains authoritative.
 - Single-pixel buffers can be retained as color records.
+- Retained records render through the same texture and stretch/clamp paths used
+  by live surfaces. This is the expected Phase 2 behavior.
 - Async SHM textures are not retained yet because Wry's per-surface SHM
   front/back textures can be reused by later commits while an animation is still
   running. Those surfaces fall back to live rendering until an explicit offscreen
@@ -121,13 +126,16 @@ Implementation shape:
 - Extend event/sync handling so retained buffers remain valid until the animation
   is complete.
 
-Open design work:
+Deferred/future polish:
 
-- Exact lifetime model for retained `SurfaceBuffer` / `GfxTexture` references.
 - Whether retained records participate in frame callbacks or presentation
   feedback. Default assumption: no, because they are compositor animation frames,
   not client commits.
 - How to fall back when a buffer cannot be safely retained.
+- A distinct retained-tree scaling render path for true spawn-in/spawn-out
+  content scaling. If added, start with retained GPU-backed records only, keep
+  the animated frame as the clip boundary, and avoid live SHM scaling until there
+  is an explicit snapshot/copy fallback.
 
 ## Phase 3: Multiphase No-Overlap Animations