diff --git a/apps/pwa/src/components/MemberEditorSheet.tsx b/apps/pwa/src/components/MemberEditorSheet.tsx
index f770391..7e1624b 100644
--- a/apps/pwa/src/components/MemberEditorSheet.tsx
+++ b/apps/pwa/src/components/MemberEditorSheet.tsx
@@ -207,10 +207,11 @@ export function MemberEditorSheet({
 
   // ── handleClose ──────────────────────────────────────────────────────────
 
+  // WR-04: only reset ephemeral fields (password inputs, error states, create-mode
+  // fields). Member-derived fields (displayName, isAdmin) are owned by the useEffect
+  // below and will re-sync from the live member prop when the sheet re-opens or when
+  // membersQuery refetches — no stale closure problem.
   const handleClose = useCallback(() => {
-    // Reset all form state
-    setDisplayName(member?.displayName ?? '');
-    setIsAdmin(member?.isAdmin ?? false);
     setProfileError(null);
     setNewPassword('');
     setConfirmPassword('');
@@ -228,7 +229,7 @@ export function MemberEditorSheet({
     if (triggerRef?.current) {
       triggerRef.current.focus();
     }
-  }, [onClose, triggerRef, member?.displayName, member?.isAdmin]);
+  }, [onClose, triggerRef]);
 
   // Sync profile state when member changes (different row opened)
   useEffect(() => {
@@ -259,10 +260,19 @@ export function MemberEditorSheet({
   const profileMutation = useMutation({
     mutationFn: async () => {
       if (!member) throw new Error('no-member');
-      await updateMemberProfile(member.id, {
-        displayName: displayName.trim(),
-        isAdmin,
-      });
+      // WR-01: send only the fields that actually changed to avoid re-writing
+      // displayName on an admin-toggle-only save (and to prevent 400s when a member
+      // has a null displayName and the admin only wants to toggle the admin flag).
+      const payload: { displayName?: string; isAdmin?: boolean } = {};
+      const trimmed = displayName.trim();
+      if (trimmed !== (member.displayName ?? '')) {
+        if (trimmed.length === 0) throw new Error('name-required');
+        payload.displayName = trimmed;
+      }
+      if (isAdmin !== member.isAdmin) payload.isAdmin = isAdmin;
+      // No-op guard — nothing changed, skip the network call
+      if (Object.keys(payload).length === 0) return;
+      await updateMemberProfile(member.id, payload);
     },
     onSuccess: () => {
       void queryClient.invalidateQueries({ queryKey: ['admin', 'members'] });
@@ -272,9 +282,15 @@ export function MemberEditorSheet({
     onError: (err) => {
       const msg = err instanceof Error ? err.message : 'server';
       if (msg === 'last-admin') {
-        // D-03 guard: revert toggle to previous value (member.isAdmin was true)
-        setIsAdmin(member?.isAdmin ?? true);
+        // D-03 guard: revert toggle to the actual prior value on the member object.
+        // WR-02: use member!.isAdmin explicitly rather than `?? true` — the `?? true`
+        // was accidentally correct only because the guard fires when demoting an admin,
+        // but it would incorrectly set isAdmin=true for any future error path where
+        // member is non-null but isAdmin is false.
+        setIsAdmin(member!.isAdmin);
         setProfileError('Cannot remove admin — at least one admin must remain.');
+      } else if (msg === 'name-required') {
+        setProfileError('A display name is required before saving.');
       } else {
         setProfileError('Something went wrong. Please try again.');
       }