Persist circuit protection updates

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

@@ -742,7 +742,9 @@ Acceptance:
 Status: In progress. The complete tree read model E1, pure structural
 projection E2a, grid rendering E2b and mutable component editing E3a are
 complete. Basic group management E3b1 is also complete. Circuit-protection
-editing and structural drag/renumber/delete workflows remain pending.
+editing now has its persistent E3b2a command boundary; insertion defaults and
+the editor modal as well as structural drag/renumber/delete workflows remain
+pending.
 
 - render fixed header components
 - render group components and circuit blocks
@@ -777,6 +779,10 @@ Implemented in E1/E2a/E2b/E3a:
   child BMKs remain stable
 - an exactly empty group can be removed through the persistent group command;
   populated deletion stays disabled until the dedicated warning UI is present
+- `circuit-protection.update` inserts or updates one validated 1:1 protection
+  snapshot, rejects stale state and preserves exact persistent Undo/Redo
+- user commands cannot remove circuit protection; a nullable target exists
+  only as the inverse of adding protection to a retained circuit without it
 
 Acceptance: