Mirror stack extraction multiphase planning

docs/window-animations-plan.md

@@ -214,6 +214,14 @@ Preferred approach:
 - If a legal no-overlap sequence cannot be found for a group, fall back to the
   linear animator for that group only. Float windows are outside this invariant.
 
+Current pure planner status:
+
+- Two-window same-axis swaps use shrink lanes, move, then grow.
+- Stack extraction/return patterns are covered in both horizontal and vertical
+  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.
+
 Tests:
 
 - horizontal swaps shrink, move, then grow without overlap