Add circuit group reordering

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

@@ -593,9 +593,7 @@ Acceptance:
 
 ### C. Persistent Commands and Board Defaults
 
-Status: In progress. New-board defaults C1, component management C2a and
-empty-group CRUD C2b1 are complete. Complete group reordering C2b2 remains
-pending.
+Status: Complete.
 
 - extend `distribution-board.insert` with fixed components and three groups
 - implement component and group CRUD commands
@@ -647,6 +645,15 @@ Implemented in C2b1:
 - project/list ownership, stale state, Undo/Redo and late rollback are covered
   at the shared transaction boundary
 
+Implemented in C2b2:
+
+- `circuit-group.reorder` requires every group in the circuit list with its
+  exact expected and target `sortOrder`
+- sorting changes no group number, prefix or circuit equipment identifier
+- incomplete or stale assignments are rejected before history is recorded
+- the complete reorder is one project revision and one persistent Undo/Redo
+  step; late failures roll back every position
+
 Acceptance:
 
 - new boards contain the agreed fixed structure