two concurrent saves could land out of order

main.js

@@ -97,11 +97,20 @@ module.exports = class RibbonClasp extends Plugin {
     this.mergeNewItems(ribbon);
   }
 
+  // a drag saves, and the dom change it makes wakes the observer up, which can
+  // save again before the first one has finished writing. queue them instead.
+  save() {
+    this.writing = Promise.resolve(this.writing)
+      .catch(() => {})
+      .then(() => this.saveData(this.settings));
+    return this.writing;
+  }
+
   recordOrder(ribbon) {
     const ids = ribbon.items.map((item) => item.id);
     if (this.sameOrder(ids, this.settings.order)) return;
     this.settings.order = ids;
-    this.saveData(this.settings);
+    this.save();
   }
 
   // only append icons we haven't seen before instead of overwriting the
@@ -113,7 +122,7 @@ module.exports = class RibbonClasp extends Plugin {
     const newIds = ribbon.items.map((item) => item.id).filter((id) => !known.has(id));
     if (newIds.length === 0) return;
     this.settings.order = [...this.settings.order, ...newIds];
-    this.saveData(this.settings);
+    this.save();
   }
 
   sameOrder(a, b) {