Use `modifyClass("model:post", ...)` as an alternative to `addPostTransformCallback`

assets/javascripts/discourse/initializers/extend-for-assigns.js

@@ -392,7 +392,6 @@ function initialize(api) {
   api.addPostSmallActionIcon("unassigned_group", "group-times");
   api.addPostSmallActionIcon("unassigned_from_post", "user-xmark");
   api.addPostSmallActionIcon("unassigned_group_from_post", "group-times");
-  api.includePostAttributes("assigned_to_user", "assigned_to_group");
   api.addPostSmallActionIcon("reassigned", "user-plus");
   api.addPostSmallActionIcon("reassigned_group", "group-plus");
 
@@ -712,6 +711,30 @@ function initialize(api) {
 }
 
 function customizePost(api) {
+  api.addTrackedPostProperties("assigned_to_user", "assigned_to_group");
+
+  api.modifyClass(
+    "model:post",
+    (Superclass) =>
+      class extends Superclass {
+        get can_edit() {
+          return isAssignSmallAction(this.action_code) ? true : super.can_edit;
+        }
+
+        // overriding tracked properties requires overriding both the getter and the setter.
+        // otherwise the superclass will throw an error when the application sets the field value
+        set can_edit(value) {
+          super.can_edit = value;
+        }
+
+        get isSmallAction() {
+          return isAssignSmallAction(this.action_code)
+            ? true
+            : super.isSmallAction;
+        }
+      }
+  );
+
   api.renderAfterWrapperOutlet(
     "post-content-cooked-html",
     PostAssignmentsDisplay
@@ -872,12 +895,18 @@ function customizeWidgetPost(api) {
     },
   });
 
-  // This won't have a direct translation in the Glimmer API as it uses can_edit from the model
+  // `addPostTransformCallback` doesn't have a direct translation in the new Glimmer API.
-  // TODO (glimmer-post-stream): check the post small action component and introduce a transformer to override the
+  // We need to use a modify class in the post model instead
-  //   canEdit behavior there
   api.addPostTransformCallback((transformed) => {
-    if (
+    if (isAssignSmallAction(transformed.actionCode)) {
-      [
+      transformed.isSmallAction = true;
+      transformed.canEdit = true;
+    }
+  });
+}
+
+function isAssignSmallAction(actionCode) {
+  return [
     "assigned",
     "unassigned",
     "reassigned",
@@ -891,12 +920,7 @@ function customizeWidgetPost(api) {
     "details_change",
     "note_change",
     "status_change",
-      ].includes(transformed.actionCode)
+  ].includes(actionCode);
-    ) {
-      transformed.isSmallAction = true;
-      transformed.canEdit = true;
-    }
-  });
 }
 
 function customizePostMenu(api) {