Fallback layout animations by motion group

docs/window-animations-plan.md

@@ -221,6 +221,9 @@ Current pure planner status:
   orientations: peer/container space scales first, the extracted child moves
   only after space exists, and orthogonal growth happens in the final phase.
 - Every produced plan is sampled for overlap at each phase before it is accepted.
+- Live layout batches are partitioned by overlapping motion bounds, so unrelated
+  groups can still use multiphase animation when another group falls back to
+  linear motion.
 
 Tests: