Persist populated group deletion

docs/spec/08-current-product-backlog.md

@@ -30,7 +30,7 @@ requirements and intended sequencing, not proof of implementation.
 - [x] Phase D2a: deterministic same-category circuit-move plan.
 - [x] Phase D2b: persistent same-category circuit-move command.
 - [x] Phase D3a: complete validated group-subtree snapshot and warning summary.
-- [ ] Phase D3b: persistent populated-group delete/restore command.
+- [x] Phase D3b: persistent populated-group delete/restore command.
 - [ ] Phase E: editor projection and editing.
 - [ ] Phase F: documentation and full GUI verification.
 - [ ] Keep full electrical sizing and cable-dimensioning rules separate until

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

@@ -662,9 +662,7 @@ Acceptance:
 
 ### D. Group Numbering and Circuit Moves
 
-Status: In progress. Group renumbering D1 and deterministic circuit-move
-planning and persistent moves D2 plus the deletion snapshot D3a are complete;
-persistent populated deletion D3b remains pending.
+Status: Complete.
 
 - implement nested identifier generation
 - support same-category cross-group circuit moves
@@ -721,6 +719,16 @@ Implemented in D3a:
 - the snapshot derives the confirmation summary for upstream protection, RCD,
   circuit count and device-row count
 
+Implemented in D3b:
+
+- `circuit-group.delete-subtree` requires the exact previously confirmed
+  snapshot and re-captures the full current subtree before deletion
+- `circuit-group.restore-subtree` restores stable UUIDs in foreign-key-safe
+  order, including both protection layers and row link/override metadata
+- deletion and restoration are exact persistent inverses for Undo/Redo
+- stale confirmation state and late history failures leave no partial delete
+  or restore
+
 Acceptance:
 
 - target identifiers use highest suffix plus one