Plan circuit group moves

docs/spec/09-distribution-board-components-and-protection-groups.md

@@ -662,8 +662,9 @@ Acceptance:
 
 ### D. Group Numbering and Circuit Moves
 
-Status: In progress. Deterministic planning D1a and persistent execution D1b
-are complete; cross-group moves D2 and populated deletion D3 remain pending.
+Status: In progress. Group renumbering D1 and deterministic circuit-move
+planning D2a are complete; persistent moves D2b and populated deletion D3
+remain pending.
 
 - implement nested identifier generation
 - support same-category cross-group circuit moves
@@ -690,6 +691,15 @@ Implemented in D1b:
 - Undo/Redo uses the exact inverse plan; late revision/history failures roll
   back every group, prefix and BMK
 
+Implemented in D2a:
+
+- a pure planner permits moves only between distinct groups of the same
+  category
+- it validates the source BMK and stores source/target group and sort position
+- the target BMK uses the highest existing target-group circuit suffix plus one
+  and never fills gaps
+- the computed target BMK is part of the plan and is not recalculated for Redo
+
 Acceptance:
 
 - target identifiers use highest suffix plus one